Question:
I had reported almost having a battery fire a while back when one set of batteries shorted out and tried to consume the rest. Those were pulled out of service and all seemed well. I had to remove another set last night as performance had dropped rapidly and when checking water levels found that the plates were almost exposed in them. The others were fine. Again, hot to the touch and boiling without much input from the panels. After removal performance shot up! They are 9 years old and all will be replace next week. Just a lesson to keep your eye on things especially when they are getting near end of life. Kirk "Moe, Larry, the cheese!", Curly www.sandpoint.net/captkirk www.stormyacres.com
Response:
>I had reported almost having a battery fire a while back when one set >of batteries shorted out and tried to consume the rest.
I had one cell in a series string of two golf cart batteries fail: http://compusmiths.com/~w_smith/DailyBatteryVoltage.htm but the voltage, when it dropped, took almost 11 hours to drop from 12.5 to 10.5 volts, and even the ‘quick’ drop at http://compusmiths.com/~w_smith/CellShortCloseup.htm took 45 minutes (though Excel doesn’t seem to want to show the chart that way…). Maybe having cells in parallel allows more current to dump into a short, or maybe I had a different failure mode… — William Smith ComputerSmiths Consulting, Inc. www.compusmiths.com
Response:
> I had one cell in a series string of two golf cart batteries fail: > http://compusmiths.com/~w_smith/DailyBatteryVoltage.htm but the > voltage, when it dropped, took almost 11 hours to drop from 12.5 to > 10.5 volts, and even the ‘quick’ drop at > http://compusmiths.com/~w_smith/CellShortCloseup.htm took 45 minutes > (though Excel doesn’t seem to want to show the chart that way…). > Maybe having cells in parallel allows more current to dump into a > short, or maybe I had a different failure mode…
Failure mode of a 12v battery system. I will give an idea of the events that would accrue in the failure of a series 12V (6 cells) system, And a series parallel 12V system consisting of 10 batteries (of 6 cells each) in parallel.. Series system. Stage one. One cell shorts, The total energy capacity of that cell will be turned to heat in that cell. Other cells will not be affected, besides moderate heating of adjacent cells for a short period of time. Total battery voltage under load is 8.3V to 10V When the charger brings it up to 13V float voltage, You will be giving the working cells a good EQ charge. Operator may not notice, but may think the system is running low all the time. Automatic low state of charge cut outs may shut down the system at night. Most systems that don’t use low state of charge protection will operate close to normal. Constant EQ charge levels may reduce life of working cells, and promote shorting of cells. Stage two. Second cell shorts. Any automatic low state of charge cut outs would render the system unusable at night. The remaining cells would receive a heavy EQ charge each day the sun shines. On systems that don’t use a low SOC cutout, only voltage variance tolerant electronic equipment will remain functioning, Incandescent lights will be noticeably dimmer. The charging equipment will work hard to get it up to 13V, if possible. The battery size is considerable compared to available charging current, so there is not enough charge current to promote thermal runaway. Life of remaining cells will be short from the heavy charging during the day. Stage three. Half of the cells are shorted. Charging system will not be able to bring voltage to regulation levels. Only the most tolerant electronic equipment will work at night. Incandescent will be dim. If there is an operator present, he should have found the problem by then. Most smart charging systems will know there is a problem and go into an error state. Stage four. Two cells left. If the site has any contact with the outside world, they should know there is a problem. Remote radio sites will be obvious from the system not working. Stage five. One cell working. Only small things like 12V clocks that can work down to 2V or so, will remain working. Stage six. Complete short. Panels will be dumping into a short, nothing works. For a series parallel system. Stage one. One cell on a battery in the system shorts. The problem battery will be in a quasi float charge in comparison to the rest of the system. During the day, it will get a good EQ charge. During the night, it will deliver no useable capacity. It will be a leach on the system. Only the most picky and finicky operator will notice. He will have to take a SG check on the shorted cell to know there is a problem. Most people with sealed batteries will be completely un aware of any fault condition. They will just think that the battery bank it getting old, and loosing capacity. Some may find out by pulling strings and doing voltage checks during normal maintenance. Some may find out by the problem battery gassing abnormally during EQ charges on the system. Some may find out by doing a simple "temperature by hand", check after an EQ charge. Some may notice by the abnormal water consumption of the problem battery. Constant overcharging will promote shorting in the other cells of the affected aging battery. Stage two. The second cell shorts in the problem battery. The battery will become a moderate load on the system. If it is a system of 10 or more batteries, and the dally system usage is high, many operators will not notice. The battery will be noticeably hotter than the rest of the units all the time. The battery will probably not go into thermal runaway unless the ambient temp is high. Gassing will be noticeable during most of the normal system cycle. Thermal runaway may be triggered by an EQ charge. Life of the existing cells will be short. If it stays in that condition, and no more cells short, the battery will safely boil dry. Shorting of other cells is highly possible by the sediments being stirred up in the battery by charging. Stage three. Half the cells are shorted. You have just started down the one way track to Chernobyl. Power consumption off the rest of the battery bank, will be large Thermal runaway is guarantied. Battery case may soften from the heat generated. Boiling will obvious. Remaining cells will either boil dry, or short, or boil dry and short, in quick order. Most interbank fuses will blow at this time. Stage four, Two cells left. Any Interbank fuse or fuseable links will melt at this time. You will have gas venting out the top of the battery like a steam pot. Case of the battery will start melting which will cause the last two cells to short. The already shorted cells will boil any remaining fluid off, and the hot plates will start melting through the plastic case. Stage five. One cell left, and it won’t last long. Stage six. A complete short. If there is any sizable charge left in the rest of the bank. Plastic of the problem battery will probably ignite from the molten lead. The insulation on the battery interconnects will melt off, and any remaining insulation will ignite. Cables will arc cut through any metal enclosure like a blow torch through hot butter. Any plastic conduit will burst into flame on contact with red hot conductors. Any wood will ignite on contact with conductors. Flames will encompass most of the area until, all consumable materials inside or outside a solid metal enclosure is consumed, or the enclosure burns down (the owners house), or the fire department puts out the fire.
Response:
Presuming that your senario is correct, or nearly correct, what design provisions could be made to avoid the most catastrophic failure mode in an unattended system? You seem to suggest that observation and immediate repair is necessary for preventing a cascading mode of failure. But, surely there must be some automatic means to prevent a bank from digressing into a catrosrophic house fire. My system will run attended for 5 months of the year. While I’m willing to assume some risk of a bank self distructing, I would invest in automatic systems to prevent my house from burning down. What comes to mind is using a fireproof battery enclosure for the bank. Maybe concrete block, with a fire rated ceiling. That expence would seem to be a good investment if it could prevent a bank fire from spreading to the rest of the structure. What is the purpose of the interbank fusing if not to prevent a fire? Where are fuses required in series parallel arrangement? How do you calculate their rating? Would there be any safety advantage to reducing the number of charging panels to a minimum just to keep the batteries from freezing over the winter? Over the winter months, my loads are almost nil, so the PV would be used just to keep the bank from self discharging and eventually freezing. -50f is not uncommon over the winter. Design for safety ideas?
Response:
Soooo, in your opinion what’s the odds of a ‘meltdown’ occurring ? Just starting to build up a ‘power set-up’ (inverter, batts (all at once soon $$) charger). Should I also figure in an outdoor enclosure for the batts? Live in Canada so winter would sap avail power, but burning down the house would make the emergency power set-up a moot point….Rob. – Hide quoted text — Show quoted text ->I had reported almost having a battery fire a while back when one set >of batteries shorted out and tried to consume the rest. > I had one cell in a series string of two golf cart batteries fail: > http://compusmiths.com/~w_smith/DailyBatteryVoltage.htm but the > voltage, when it dropped, took almost 11 hours to drop from 12.5 to > 10.5 volts, and even the ‘quick’ drop at > http://compusmiths.com/~w_smith/CellShortCloseup.htm took 45 minutes > (though Excel doesn’t seem to want to show the chart that way…). > Maybe having cells in parallel allows more current to dump into a > short, or maybe I had a different failure mode… > — > William Smith > ComputerSmiths Consulting, Inc. www.compusmiths.com
Response:
– Hide quoted text — Show quoted text -> I had one cell in a series string of two golf cart batteries fail: > http://compusmiths.com/~w_smith/DailyBatteryVoltage.htm but the > voltage, when it dropped, took almost 11 hours to drop from 12.5 to > 10.5 volts, and even the ‘quick’ drop at > http://compusmiths.com/~w_smith/CellShortCloseup.htm took 45 minutes > (though Excel doesn’t seem to want to show the chart that way…). > Maybe having cells in parallel allows more current to dump into a > short, or maybe I had a different failure mode… >Failure mode of a 12v battery system. >I will give an idea of the events that would >accrue in the failure of a series 12V (6 cells) system, >And a series parallel 12V system consisting of >10 batteries (of 6 cells each) in parallel.. >Series system. >Stage one. >One cell shorts, >The total energy capacity of that cell will be turned to heat in that cell. >Other cells will not be affected, besides moderate heating of adjacent cells >for a short period of time. >Total battery voltage under load is 8.3V to 10V >When the charger brings it up to 13V float voltage, >You will be giving the working cells a good EQ charge. >Operator may not notice, but may think the system is running low all the >time. >Automatic low state of charge cut outs may shut down the system at night. >Most systems that don’t use low state of charge protection will operate >close to normal. >Constant EQ charge levels may reduce life of working cells, >and promote shorting of cells.
This is a very good description of what I saw in my system. Kirk "Moe, Larry, the cheese!", Curly www.sandpoint.net/captkirk www.stormyacres.com
Response:
>Soooo, in your opinion what’s the odds of a ‘meltdown’ occurring ?
Beats me, somewhere between 2 (my experience) and 9(?) years (Kirk’s) would certainly cover all the bases, even if it’s not a very useful answer. I think I’d build a setup that could withstand a battery fire (or leak, or explosion, or other catastrophic failure) just to be safe. [What that means in each case is probably different, but a fireproof battery box {vented to the} outside shouldn't be rocket science.] I’d also rather have one set of large cells in series than having a number of parallel batteries, to reduce the fault current in the event of a short. — William Smith ComputerSmiths Consulting, Inc. www.compusmiths.com
Response:
>For a series parallel system. >Stage one. >One cell on a battery in the system shorts. >The problem battery will be in a quasi float charge in comparison to the >rest of the system. >During the day, it will get a good EQ charge. >During the night, it will deliver no useable capacity. >It will be a leach on the system.
It’s worse than that, isn’t it? The battery with the shorted cell will discharge the parallel battery, overheating the shorted one and ruining the parallel one, yes? — William Smith ComputerSmiths Consulting, Inc. www.compusmiths.com
Response:
> My system will run attended for 5 months of the year. While I’m willing to > assume some risk of a bank self distructing, I would invest in automatic > systems to prevent my house from burning down. > What comes to mind is using a fireproof battery enclosure for the bank. > Maybe concrete block, with a fire rated ceiling. That expence would seem to > be a good investment if it could prevent a bank fire from spreading to the > rest of the structure.
Those are good ideas. You want something that is non conductive, and won’t burn. Concrete is a good idea. Something like A concrete pit, with a fiberglass, or asbestos cover And nothing flammable around the pit, that a flying spark could ignite. The batteries will burn themselves out without the fire spreading. > What is the purpose of the interbank fusing if not to prevent a fire?
That is what they are there for. I was just making a note of where they would most likely blow. When they blow, the digression of the condition stops. > Where are fuses required in series parallel arrangement? > How do you calculate their rating?
It would depend upon the amount of reliability you want out of the system. > Would there be any safety advantage to reducing the number of charging > panels to a minimum just to keep the batteries from freezing over the > winter? Over the winter months, my loads are almost nil, so the PV would be > used just to keep the bank from self discharging and eventually > freezing. -50f is not uncommon over the winter. > Design for safety ideas?
Design the system to fail in a safe mode. Put fuseable links, or fuses in all parallel setups. Keep the batteries out of the main house when possible. If they are in the house, make sure that they won’t destroy something if they do melt down. The safety measures will depend upon the installation. Design for the worst case scenario, hope for the best.
Response:
>>Soooo, in your opinion what’s the odds of a ‘meltdown’ occurring ? >Beats me, somewhere between 2 (my experience) and 9(?) years (Kirk’s) >would certainly cover all the bases, even if it’s not a very useful >answer. I think I’d build a setup that could withstand a battery fire >(or leak, or explosion, or other catastrophic failure) just to be >safe. [What that means in each case is probably different, but a >fireproof battery box {vented to the} outside shouldn't be rocket >science.] >I’d also rather have one set of large cells in series than having a >number of parallel batteries, to reduce the fault current in the event >of a short.
For me, unfortunately, I must keep the batteries in the house in the utility room. ( N. Idaho winter is detrimental to battery capacity.) Wooden house, wooden floor, wooden battery box. I am going to look into fusing the parallel hookups now but since I am obsessive concerning safety I will have to rely on eyeball monitoring for the near future. I DO have the batteries in plastic tubs to catch any acid but it won’t do much good for hot lead. The box is vented to the outside with forced ventilation when the batteries get to 14.5 V. This is handled using the programmable relays in my SW2512. Realistically I don’t think the chances for me of a true meltdown are a great concern. But then I am here year round. If it was a vacation cabin things might be different. Kirk "Moe, Larry, the cheese!", Curly www.sandpoint.net/captkirk www.stormyacres.com
Response:
Aside from fusing parallel batteries, one thing a person could do, particularly if the battery bank is inside a house, would be to provide a tank (say a plastic barrel) filled with baking soda solution, and mount this tank several feet above the battery bank. Run a line from this tank to a fire sprinkler head mounted over the batteries. If something really nasty ahppens, and it gets hot in there, the sprinkler head will function and drizzle the area with soda solution, which would tend to quench a fire,a nd also neutralize any spilled acid. Just a thought, and it would be pretty cheap insurance. Gordon Richmond
Response:
> Aside from fusing parallel batteries, one thing a person could do, > particularly if the battery bank is inside a house, would be to > provide a tank (say a plastic barrel) filled with baking soda > solution, and mount this tank several feet above the battery bank. Run > a line from this tank to a fire sprinkler head mounted over the > batteries. If something really nasty ahppens, and it gets hot in > there, the sprinkler head will function and drizzle the area with soda > solution, which would tend to quench a fire,a nd also neutralize any > spilled acid.
Good idea but I don’t think it would work. I don’t think the baking soda would "drizzle" out, you’d have to have a pressurized system. If you are really worried and need something like this I’d look for a restaurant supply house and check out the fire ex designed for deep fat fryers. IIRC, they use baking soda, nontoxic, and having seen one of them in action I can tell you it would put out more than enough soda to handle quite a few batteries.
Response:
– Hide quoted text — Show quoted text -> Presuming that your senario is correct, or nearly correct, what design > provisions could be made to avoid the most catastrophic failure mode in an > unattended system? > You seem to suggest that observation and immediate repair is necessary for > preventing a cascading mode of failure. But, surely there must be some > automatic means to prevent a bank from digressing into a catrosrophic house > fire. > My system will run attended for 5 months of the year. While I’m willing to > assume some risk of a bank self distructing, I would invest in automatic > systems to prevent my house from burning down. > What comes to mind is using a fireproof battery enclosure for the bank. > Maybe concrete block, with a fire rated ceiling. That expence would seem to > be a good investment if it could prevent a bank fire from spreading to the > rest of the structure.
Sounds smart. Passive venting is also smart, to prevent gas buildup. Fusing each battery makes good sense. Lighting & attendant switching for this enclosure should be rated for explosive conditions, also. (enclosed bulbs, switches, etc). > What is the purpose of the interbank fusing if not to prevent a fire?
Fire prevention is one goal. Prevention of damage to other components is the other reason. > Where are fuses required in series parallel arrangement?
_I_ would break each positive connection to the nest point with a big ole fuse. > How do you calculate their rating?
Good question.. Here’s where my ignorance shows. Somebody help me here please. My guess: calculate biggest current load, add what …..? ….40%? and that’s the size. > Would there be any safety advantage to reducing the number of charging > panels to a minimum just to keep the batteries from freezing over the > winter? Over the winter months, my loads are almost nil, so the PV would be > used just to keep the bank from self discharging and eventually > freezing. -50f is not uncommon over the winter.
Add a heater plate under the battery bank. Thermo switch to kick it on when it’s COLD. This will give some exercise to the batteries, too. > Design for safety ideas?
That’s it for now. All opinions supplied out of ignorance and "common sense" Mark (If I’m wrong, an expert can correct me) Dunning
Response:
>> Would there be any safety advantage to reducing the number of charging > panels to a minimum just to keep the batteries from freezing over the > winter? Over the winter months, my loads are almost nil, so the PV would > be used just to keep the bank from self discharging and eventually > freezing. -50f is not uncommon over the winter.
That’s good, for battery lifetime. Cold batteries last longer, and their self-discharge rate is lower. But they have less available capacity. This capacity returns as they are warmed… >Add a heater plate under the battery bank. >Thermo switch to kick it on when it’s COLD.
I’d do this only as needed to discharge them. A watt-hour of heat energy can "release" more than a watt-hour of capacity. Nick
Response:
> Aside from fusing parallel batteries, one thing a person could do, > particularly if the battery bank is inside a house, would be to > provide a tank (say a plastic barrel) filled with baking soda > solution, and mount this tank several feet above the battery bank. Run > a line from this tank to a fire sprinkler head mounted over the > batteries. If something really nasty ahppens, and it gets hot in > there, the sprinkler head will function and drizzle the area with soda > solution, which would tend to quench a fire,a nd also neutralize any > spilled acid. > Good idea but I don’t think it would work. I don’t think the baking soda > would "drizzle" out, you’d have to have a pressurized system.
I think he was thinking of baking soda dissolved in a water solution, not dry powder. Although I *have* seen dry powder fire systems, they use CO2 or N2 to blow the powder out. Perhaps a bit too complicated for this. But a drum suspended up high with a water-soda solution might be practical. Of course, putting water of any kind on an electrical fire is a bad idea.
> If you are > really worried and need something like this I’d look for a restaurant supply > house and check out the fire ex designed for deep fat fryers. IIRC, they > use baking soda, nontoxic, and having seen one of them in action I can tell > you it would put out more than enough soda to handle quite a few
batteries. Yep. That’s the kind I’ve seen. A pressurization canister (CO2 I think) helps to put out the fire as well. But what a *mess* to clean up afterwards. daestrom
Response:
> Yep. That’s the kind I’ve seen. A pressurization canister (CO2 I think) > helps to put out the fire as well. But what a *mess* to clean up > afterwards.
Keep it in perspective – a few hours or days cleaning up a mess of powder goes a _lot_ faster than cleaning up the charred remains of the building. The last restaurant fire in this town took the restaurant (business) out for over a year, and they moved up the street when they reopened – the building has taken over 3 years to get fixed (the landlord let it sit boarded up for quite a while, I assume due to the insurance dawdling/ligitgating over the settlement). Makes a powdery mess look quite attractive. — Cats, Coffee, Chocolate…vices to live by
Response:
> > How do you calculate their rating? > Good question.. Here’s where my ignorance shows. Somebody help me here > please. > My guess: calculate biggest current load, add what …..? ….40%? and > that’s the size.
Sizing a fuse for this still has me scratching my head. For house wiring, you select a fuse based on the ampacity of the wire thet the fuse is intended to protect. But, used in between series runs of a series-parallel bank, you have batteries in the circuit that you want to protect. It is not clear to me that the rating has much to do with the banks load, because with a failure such as shorted battery plates, the shorted plates become the load. A DC disconnect fuse or breaker is required by NEC to protect the load. So, I’m speculating that the rating of an interbank fuse would have more to do with the ampacity rating of the series string of batteries, or perhaps a single battery in that string. I’d also guess that it has something to do with the implicit charge rate numbers associated with lead acid batteries. I’d love to see how to do the calculation based on a simple example. I currently have four 6 volt 220 amp-hour golf cart batteries in a bank wired series-parallel. It seems to me that calcuating the correct size is crtical. Too small and it’s going to constantly be blowing expensive DC fuses. Too large and it’s usless.
Response:
- Hide quoted text — Show quoted text -> > How do you calculate their rating? > Good question.. Here’s where my ignorance shows. Somebody help me here > please. > My guess: calculate biggest current load, add what …..? ….40%? and > that’s the size. >Sizing a fuse for this still has me scratching my head. For house wiring, >you select a fuse based on the ampacity of the wire thet the fuse is >intended to protect. But, used in between series runs of a series-parallel >bank, you have batteries in the circuit that you want to protect. >It is not clear to me that the rating has much to do with the banks load, >because with a failure such as shorted battery plates, the shorted plates >become the load. A DC disconnect fuse or breaker is required by NEC to >protect the load. >So, I’m speculating that the rating of an interbank fuse would have more to >do with the ampacity rating of the series string of batteries, or perhaps a >single battery in that string. I’d also guess that it has something to do >with the implicit charge rate numbers associated with lead acid batteries. >I’d love to see how to do the calculation based on a simple example. I >currently have four 6 volt 220 amp-hour golf cart batteries in a bank wired >series-parallel. >It seems to me that calcuating the correct size is crtical. Too small and >it’s going to constantly be blowing expensive DC fuses. Too large and it’s >usless.
One thing I’m confused about, relative to the sizing of the fuses, is the total draw from the bank. I have my positive lead at one end of bank and the negative at the other. This puts the total load eventually going through 1 fuse. Or am I missing something? Irregardless of the configuration it seems to me that each fuse would be seeing a different current load. Kirk "Moe, Larry, the cheese!", Curly www.sandpoint.net/captkirk www.stormyacres.com
Response:
– Hide quoted text — Show quoted text ->> > How do you calculate their rating? >> Good question.. Here’s where my ignorance shows. Somebody help me here >> please. >> My guess: calculate biggest current load, add what …..? ….40%? and >> that’s the size. >Sizing a fuse for this still has me scratching my head. For house wiring, >you select a fuse based on the ampacity of the wire thet the fuse is >intended to protect. But, used in between series runs of a series-parallel >bank, you have batteries in the circuit that you want to protect. >It is not clear to me that the rating has much to do with the banks load, >because with a failure such as shorted battery plates, the shorted plates >become the load. A DC disconnect fuse or breaker is required by NEC to >protect the load. >So, I’m speculating that the rating of an interbank fuse would have more to >do with the ampacity rating of the series string of batteries, or perhaps a >single battery in that string. I’d also guess that it has something to do >with the implicit charge rate numbers associated with lead acid batteries. >I’d love to see how to do the calculation based on a simple example. I >currently have four 6 volt 220 amp-hour golf cart batteries in a bank wired >series-parallel. >It seems to me that calcuating the correct size is crtical. Too small and >it’s going to constantly be blowing expensive DC fuses. Too large and it’s >usless. > One thing I’m confused about, relative to the sizing of the fuses, is > the total draw from the bank. I have my positive lead at one end of > bank and the negative at the other. This puts the total load > eventually going through 1 fuse. Or am I missing something? > Irregardless of the configuration it seems to me that each fuse would > be seeing a different current load.
Lets work from a simple example.. Two 6v batteries in series, paralleled with another two in series. Hope this text drawing is ledgable.. (if not try fixed font) | | | | 6v (battery A) 6v (battery C) 220 amp hr 220 amp hr battery battery | | | | (-) (-) | series string A | series string B | | LOAD (12v) (+) (+) | | | | 6v (battery B) 6v (battery D) 220 amp hr 220 amp hr battery battery | | | | It seems to me that fuse 1 would only need to handle 1/2 the current supplied to the load. The current from battery D and C do not flow through Fuse 1. If you added another string (and fuse), then it would need to handle 2/3 of the current (I’m still speculating) If battery A shorts a two plates, it then produces 10V. Series String B will still be at 12v and try and backdrive string a with 2v. But what will the current be? It would seem to be dependent upon the internal resistance of string A. I don’t know how you determine the internal resistance of a battery. I suspect there is some rule of thumb based on chemistry. I’ve never seen it mentioned in the limited specs provided by manufacturers, so maybe it is implicit. Bug – Hide quoted text — Show quoted text -> Kirk > "Moe, Larry, the cheese!", Curly > www.sandpoint.net/captkirk > www.stormyacres.com
Response:
- Hide quoted text — Show quoted text -> >> > How do you calculate their rating? > >> Good question.. Here’s where my ignorance shows. Somebody help me >here > >> please. > >> My guess: calculate biggest current load, add what …..? ….40%? and > >> that’s the size. > >Sizing a fuse for this still has me scratching my head. For house wiring, > >you select a fuse based on the ampacity of the wire thet the fuse is > >intended to protect. But, used in between series runs of a >series-parallel > >bank, you have batteries in the circuit that you want to protect. > >It is not clear to me that the rating has much to do with the banks load, > >because with a failure such as shorted battery plates, the shorted plates > >become the load. A DC disconnect fuse or breaker is required by NEC to > >protect the load. > >So, I’m speculating that the rating of an interbank fuse would have more >to > >do with the ampacity rating of the series string of batteries, or perhaps >a > >single battery in that string. I’d also guess that it has something to do > >with the implicit charge rate numbers associated with lead acid >batteries. > >I’d love to see how to do the calculation based on a simple example. I > >currently have four 6 volt 220 amp-hour golf cart batteries in a bank >wired > >series-parallel. > >It seems to me that calcuating the correct size is crtical. Too small and > >it’s going to constantly be blowing expensive DC fuses. Too large and >it’s > >usless. > One thing I’m confused about, relative to the sizing of the fuses, is > the total draw from the bank. I have my positive lead at one end of > bank and the negative at the other. This puts the total load > eventually going through 1 fuse. Or am I missing something? > Irregardless of the configuration it seems to me that each fuse would > be seeing a different current load. >Lets work from a simple example.. Two 6v batteries in series, paralleled >with another >two in series. Hope this text drawing is ledgable.. (if not try fixed font) >| | >| | >6v (battery A) 6v (battery C) >220 amp hr 220 amp hr >battery battery >| | >| | >(-) (-) >| series string A | series string B >| | >LOAD (12v) >(+) (+) >| | >| | >6v (battery B) 6v (battery D) >220 amp hr 220 amp hr >battery battery >| | >| | >It seems to me that fuse 1 would only need to handle 1/2 the current >supplied to the load. The current from battery D and C do not flow through >Fuse 1. If you added another string (and fuse), then it would need to handle >2/3 of the current (I’m still speculating) >If battery A shorts a two plates, it then produces 10V. Series String B will >still be at 12v >and try and backdrive string a with 2v. But what will the current be? It >would seem >to be dependent upon the internal resistance of string A. I don’t know how >you determine >the internal resistance of a battery. I suspect there is some rule of thumb >based on >chemistry. I’ve never seen it mentioned in the limited specs provided by >manufacturers, so >maybe it is implicit. >Bug
I was thinking a bit differently but I see the point here. Fusing between the series pairs would drop those batteries out if the fuse popped. Is this correct? If so this is the simplest method. But again what value fuse to use? But if the battery, in the series pair, before the fuse was to short will the fuse still pop? Isn’t the current being converted to heat in that battery instead of passing through the fuse? Been too long since I’ve had to use any electronics theory. My thought was fusing the parallel connections. In this case the fuses would see different current loads but would still leave the series pair vulnerable. I’m running 8 L16’s in series parallel so the current through the fuse closet to the load connection could be quite a lot. I’ve already got a 400 amp T fuse for the total load but that doesn’t protect the batteries in a situation like mine. Kirk "Moe, Larry, the cheese!", Curly www.sandpoint.net/captkirk www.stormyacres.com
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> It seems to me that fuse 1 would only need to handle 1/2 the current > supplied to the load. The current from battery D and C do not flow through > Fuse 1. If you added another string (and fuse), then it would need to handle > 2/3 of the current (I’m still speculating)
Depends on how you connect it. The way I’d connect it, each would only need to carry 1/3 of the 3-parallel battery bank. A smaller diagram: +out + + + B1 B2 B3 – - – -out But that would allow B2 to get fried by B1 and B3 acting together (ie, B1 or B 3 shorting would be limited to F amps, but B2 shorting could get 2F amps), so the following would be better, and scales to as many parallel strings as you have: +out F F F + + + B1 B2 B3 – - – -out In actual point of fact, some sort of thermal cutout which sensed battery temprature might be a good plan, as well as the current limiting of the fuses, but it can get quite complicated/expensive and could also be inefficient. Temperature monitoring of the batteries and high temperature alarms are probably well worthwhile, especially given cheap temperature sensing devices. It argues in favor of fewer parallel strings of larger batteries. — Cats, Coffee, Chocolate…vices to live by
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– Hide quoted text — Show quoted text ->> >> > How do you calculate their rating? >> >> Good question.. Here’s where my ignorance shows. Somebody help me >here >> >> please. >> >> My guess: calculate biggest current load, add what …..? ….40%? and >> >> that’s the size. >> >Sizing a fuse for this still has me scratching my head. For house wiring, >> >you select a fuse based on the ampacity of the wire thet the fuse is >> >intended to protect. But, used in between series runs of a >series-parallel >> >bank, you have batteries in the circuit that you want to protect. >> >It is not clear to me that the rating has much to do with the banks load, >> >because with a failure such as shorted battery plates, the shorted plates >> >become the load. A DC disconnect fuse or breaker is required by NEC to >> >protect the load. >> >So, I’m speculating that the rating of an interbank fuse would have more >to >> >do with the ampacity rating of the series string of batteries, or perhaps >a >> >single battery in that string. I’d also guess that it has something to do >> >with the implicit charge rate numbers associated with lead acid >batteries. >> >I’d love to see how to do the calculation based on a simple example. I >> >currently have four 6 volt 220 amp-hour golf cart batteries in a bank >wired >> >series-parallel. >> >It seems to me that calcuating the correct size is crtical. Too small and >> >it’s going to constantly be blowing expensive DC fuses. Too large and >it’s >> >usless. >> One thing I’m confused about, relative to the sizing of the fuses, is >> the total draw from the bank. I have my positive lead at one end of >> bank and the negative at the other. This puts the total load >> eventually going through 1 fuse. Or am I missing something? >> Irregardless of the configuration it seems to me that each fuse would >> be seeing a different current load. >Lets work from a simple example.. Two 6v batteries in series, paralleled >with another >two in series. Hope this text drawing is ledgable.. (if not try fixed font) >| | >| | >6v (battery A) 6v (battery C) >220 amp hr 220 amp hr >battery battery >| | >| | >(-) (-) >| series string A | series string B >| | LOAD (12v) >(+) (+) >| | >| | >6v (battery B) 6v (battery D) >220 amp hr 220 amp hr >battery battery >| | >| | >It seems to me that fuse 1 would only need to handle 1/2 the current >supplied to the load. The current from battery D and C do not flow through >Fuse 1. If you added another string (and fuse), then it would need to handle >2/3 of the current (I’m still speculating) >If battery A shorts a two plates, it then produces 10V. Series String B will >still be at 12v >and try and backdrive string a with 2v. But what will the current be? It >would seem >to be dependent upon the internal resistance of string A. I don’t know how >you determine >the internal resistance of a battery. I suspect there is some rule of thumb >based on >chemistry. I’ve never seen it mentioned in the limited specs provided by >manufacturers, so >maybe it is implicit. >Bug > I was thinking a bit differently but I see the point here. Fusing > between the series pairs would drop those batteries out if the fuse > popped. Is this correct?
Yes, if fuse 1 popped, String A would be disconnected from String B and the load. String B would still be supplying 12v to the load, same current, but at half storage capacity. Current flow would also stop in string A, even with a internal battery short in that string. > If so this is the simplest method. But > again what value fuse to use? But if the battery, in the series pair, > before the fuse was to short will the fuse still pop? Isn’t the > current being converted to heat in that battery instead of passing > through the fuse? Been too long since I’ve had to use any electronics > theory.
There still has to be a complete circuit for current to flow in any series string. The fuse is in series with that circuit, so it would see any increased current flow and pop as long as it was of the correct rating. > My thought was fusing the parallel connections. In this case the > fuses would see different current loads but would still leave the > series pair vulnerable.
I thought that my diagram WAS fusing the parallel connection between series strings. Parallel goes from left to right, and series goes from bottom to top in my drawing. I can’t see how it matters whether it’s in a series of a parallel leg, but most discussion talks about putting it in the parallel leg, which I believe I have done in my drawing. > I’m running 8 L16’s in series parallel so the current through the fuse > closet to the load connection could be quite a lot. I’ve already got > a 400 amp T fuse for the total load but that doesn’t protect the > batteries in a situation like mine.
That fuse would be to protect the wiring between the load and the battery and the battery bank as a whole. But, it does nothing to protect individual strings. I have to admit to being a bit rusty on theory myself. There has to be some trick in understanding this, and I think that is an understanding of internal battery resistance. Somebody out there has to have done this before. I’m hoping they will pop in and set us straight. – Hide quoted text — Show quoted text -> Kirk > "Moe, Larry, the cheese!", Curly > www.sandpoint.net/captkirk > www.stormyacres.com
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– Hide quoted text — Show quoted text -> It seems to me that fuse 1 would only need to handle 1/2 the current > supplied to the load. The current from battery D and C do not flow through > Fuse 1. If you added another string (and fuse), then it would need to handle > 2/3 of the current (I’m still speculating) > Depends on how you connect it. The way I’d connect it, each would only > need to carry 1/3 of the 3-parallel battery bank. > A smaller diagram: > +out > + + + > B1 B2 B3 > – - – > -out > But that would allow B2 to get fried by B1 and B3 acting together (ie, > B1 or B 3 shorting would be limited to F amps, but B2 shorting could get > 2F amps), so the following would be better, and scales to as many > parallel strings as you have: > +out > F F F > + + + > B1 B2 B3 > – - – > -out
I think I grok that. You have more fuses, but they can be at a lower rating in the second diagram. If you go with dirgram 1, you need to increase the current rating of the fuse as you add additional series strings. Diagram 2 would also seem to simplfy the calculating the ampacity of the fuse. Since you are fusing each series string, you want to select a fuse to protect the weakest link in that series circuit, which would be a battery, a cell, or the smallest conductor in that string. It would not matter how many batteries were in series, because that only increases voltage and not current. So, I agree, diagram 2 simplifies the problem considerably. Now, all that is needed is some form of battery specification, internal resistance, or charge rate that allows you to determine how much input current it can take before it catches fire or otherwise endangers the rest of the bank. > In actual point of fact, some sort of thermal cutout which sensed > battery temprature might be a good plan, as well as the current limiting > of the fuses, but it can get quite complicated/expensive and could also > be inefficient. Temperature monitoring of the batteries and high > temperature alarms are probably well worthwhile, especially given cheap > temperature sensing devices. It argues in favor of fewer parallel > strings of larger batteries.
Trace SW series inverters (and others) have battery temperature sensors to modify battery charging. I wonder if they can be used to trigger a some form of safety device. I’d have to look to see if there is a overtemperature fault. If there is it could be used to remove the load of the inverter, or perhaps to trigger a fire supression system through one of the inverters relay outputs. I agree that it seems to complex. I don’t know if I buy the fact that it argues for larger batteries. All that larger batteres buys you is fewer interconnects. You loose some modulatity and the ability to swap out a less pricy single point of failure. Good discussion. I am learning a few things, and at least exercising the brain a bit to make this all a bit more fathomable. I really want to understand this before I go out and buy a whole bunch of pricy DC fuses and fuse blocks. The item that remains illusive is how to calculate the rating of each fuse. – Hide quoted text — Show quoted text -> — > Cats, Coffee, Chocolate…vices to live by
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I have always considered his second diagram as the only logical way to do things. I go a bit on the side of reliability. If you have ten batteries in parallel, and you want to pull a maximum system load of 200 amps. You pick a size of fuse that will total to 400 amps. (ie) 40A each, and each carries 1/10 of the load. Maximum that can be pulled of the banks is 400A. That will stop things from melting down if the wires to the main inverter cutout/(over current protector) short. And the system will still operate nominally with half the batteries removed, for maintenance, by fault, or what ever. That allows you to pull maintenance on a string by just removing the fuse for that string, to isolate it from the system. If you have only two or three strings in parallel, you should probably go with 150% of the rated maximum load on the system. (ie)300A for a 200A system. 150A on each of the two strings. 100A on each of the three strings. And my opinion for batteries under 200AH is that the fuses that are widely available in stores that is rated at 10,000A ISC for about a $1.50 a piece, should be adequate. The maximum they have to handle is the current through one battery, in their intended protective mode. If the batteries are over 200AH, I would go with the bigger 20,000A ISC or larger fuses.
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Seems to me that you could get a relatively inexpensive non-contact infrared digital thermometer (point & shoot), and aim it at each battery in teh system. Record the measured tempereatures during different cycling periods (charging, standby, discharge), and see if there is great variation over time. Probably takes longer to describt than to do the measurement… I think I have seen them for sale by Exeltek for under $75USD. Just a thought… SpiderG
– Hide quoted text — Show quoted text -> > It seems to me that fuse 1 would only need to handle 1/2 the current > > supplied to the load. The current from battery D and C do not flow > through > > Fuse 1. If you added another string (and fuse), then it would need to > handle > > 2/3 of the current (I’m still speculating) > Depends on how you connect it. The way I’d connect it, each would only > need to carry 1/3 of the 3-parallel battery bank. > A smaller diagram: > +out > + + + > B1 B2 B3 > – - – > -out > But that would allow B2 to get fried by B1 and B3 acting together (ie, > B1 or B 3 shorting would be limited to F amps, but B2 shorting could get > 2F amps), so the following would be better, and scales to as many > parallel strings as you have: > +out > F F F > + + + > B1 B2 B3 > – - – > -out > I think I grok that. You have more fuses, but they can be at a lower rating > in the second diagram. If you go with dirgram 1, you need to increase the > current rating of the fuse as you add additional series strings. > Diagram 2 would also seem to simplfy the calculating the ampacity of the > fuse. Since you are fusing each series string, you want to select a fuse to > protect the weakest link in that series circuit, which would be a battery, a > cell, or the smallest conductor in that string. It would not matter how many > batteries were in series, because that only increases voltage and not > current. > So, I agree, diagram 2 simplifies the problem considerably. > Now, all that is needed is some form of battery specification, internal > resistance, or charge rate that allows you to determine how much input > current it can take before it catches fire > or otherwise endangers the rest of the bank. > In actual point of fact, some sort of thermal cutout which sensed > battery temprature might be a good plan, as well as the current limiting > of the fuses, but it can get quite complicated/expensive and could also > be inefficient. Temperature monitoring of the batteries and high > temperature alarms are probably well worthwhile, especially given cheap > temperature sensing devices. It argues in favor of fewer parallel > strings of larger batteries. > Trace SW series inverters (and others) have battery temperature sensors to > modify battery charging. I wonder if they can be used to trigger a some form > of safety device. I’d have to look to see if there is a overtemperature > fault. If there is it could be used to remove the load of the inverter, or > perhaps to trigger a fire supression system through one of the inverters > relay outputs. I agree that it seems to complex. > I don’t know if I buy the fact that it argues for larger batteries. All that > larger batteres buys you is fewer interconnects. You loose some modulatity > and the ability to swap out a less pricy single point of failure. > Good discussion. I am learning a few things, and at least exercising the > brain a bit to make this all a bit more fathomable. I really want to > understand this before I go out and buy a whole bunch of pricy DC fuses and > fuse blocks. > The item that remains illusive is how to calculate the rating of each fuse. > — > Cats, Coffee, Chocolate…vices to live by
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