Maybe Hedges will chime in also. I put up 200 amp class T fuse on each of my 48 V packs. And I have 16 packs. But the others above addressed it also. In case the BMS fails. Etc.
65kw panels+ ~600kwh storage DIY build
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Hedges
I See Electromagnetic Fields!
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It is common for FETs to fail shorted, higher resistance than when actually turned on. I've seen that in a small board when inrush occurred as the FET was being turned on (not yet low resistance so high I^2R energy deposited in FET.)
I think I have a BMS that is now leaky, can't turn off completely, due to having turned on looking into inverter capacitors.
Failed BMS can mean over-discharge if inverter doesn't cut out at low voltage, also over-charge and possible fire even with inverter/charger working correctly if there is cell imbalance.
Fuses can protect wires in the event output of battery sees a dead short. May or may not protect FETs, might if "semiconductor" fuse which means very fast metal element.
Fuses won't help if FETs go bad. Charging current will never be enough to blow a fuse, and over/under voltage of battery and cells won't either.
Failed FETs and dead short on battery could cause fire in BMS and wires. Fuse would blow in that case due to high current.
So I'm not sure that fuses per battery will help if a battery goes bad. One guy had a fire in 16s7p battery where BMS had only one disconnect after 7 strings in parallel. It appears one 16s string went bad, others dumped current into it causing outgassing, an inadequate fuse did blow, providing the spark that started the fire. Just my guess. So a fuse that can't interrupt current without arc sometimes might be worse than no fuse. Properly rated ceramic fuses should open without causing ignition.
Maybe contactor based BMS with precharge circuit would be best. I'm using FET based, battery to go in "ammo dump" away from the house.
I think I have a BMS that is now leaky, can't turn off completely, due to having turned on looking into inverter capacitors.
Failed BMS can mean over-discharge if inverter doesn't cut out at low voltage, also over-charge and possible fire even with inverter/charger working correctly if there is cell imbalance.
Fuses can protect wires in the event output of battery sees a dead short. May or may not protect FETs, might if "semiconductor" fuse which means very fast metal element.
Fuses won't help if FETs go bad. Charging current will never be enough to blow a fuse, and over/under voltage of battery and cells won't either.
Failed FETs and dead short on battery could cause fire in BMS and wires. Fuse would blow in that case due to high current.
So I'm not sure that fuses per battery will help if a battery goes bad. One guy had a fire in 16s7p battery where BMS had only one disconnect after 7 strings in parallel. It appears one 16s string went bad, others dumped current into it causing outgassing, an inadequate fuse did blow, providing the spark that started the fire. Just my guess. So a fuse that can't interrupt current without arc sometimes might be worse than no fuse. Properly rated ceramic fuses should open without causing ignition.
Maybe contactor based BMS with precharge circuit would be best. I'm using FET based, battery to go in "ammo dump" away from the house.
so kinda fucked either way?
my batteries are about 20 ft away from the house in a separate little shed, so if they go up in smoke, house itself should be fine.
what would be the recommended ceramic fuse?
SMD Ceramic ANL Fuses - 200A
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we talking something like this?
I’m sure Hedges will reply, but I’m pretty sure no. This is what I got below. Someone will correct me if I’m wrong, but I think that’s the style that fails with a spark. The class t is enclosed, and no sparks can come to the outside.
https://www.donrowe.com/TFB1-200-200A-Class-T-Fuse-Kit-p/tfb1-200.htm these are $60 each.
There are some class t available on Amazon for like $13 each, but I’m not exactly sure on how good of a quality those are.
https://www.donrowe.com/TFB1-200-200A-Class-T-Fuse-Kit-p/tfb1-200.htm these are $60 each.
There are some class t available on Amazon for like $13 each, but I’m not exactly sure on how good of a quality those are.
thanks!
robbob2112
Doing more research, mosty harmless
Notes on the flat breakers - they are two pieces of metal with sintered tungsten contacts-- once they heat up the top part unkinks and opens the contact --- this is supposed to be at a particular point but it generally isn't terribly accurate -- And because of hose they are made they have a higher contact resistance that only gets worse when they are opened with current passing through it - so they run hot and tend to fail when the lever breaks off or weld the contacts
If you are dealing with 48v batteries I would put a class T per battery rated for 125% of the BMS continuous output. Should only blow if there is a current high enough to cause a problem.... JLLN curve will let it run at 2x current for 10minutes, but will blow in a fraction of a second for a dead short or 6x current. Wires should also be sized for 125% of continuous current output of the BMS.
There are ANL ceramic fuses like you mentioned but the generally have a higher internal resistance than a class T so they run hotter and waste energy as heat. But they AIC rating on ANL is far lower than that of a class T. AIC = Amps Interrupt Current - as in how large an arc can it break. The ANL just burns open and contains the arc,, but won't interrupt beyond 2500amps depending on style... the class T has 20,000amps at 48v.
LFP batteries can put out a short circuit current in the thousands of amps limited by the internal resistance and the connection/wire resistance... This depends on cell size and type... a 12v battery made from 314ah EVE cells can put out 8000amps if the BMS is shorted and there is an external short next to the battery, say a dropped wrench across the terminals.... It should shutdown but as Hedges mentioned the FETs tend to fail shorted first.... then they burn open with sufficient current..... Now 8000amps it the theoretical max with good connections you won't reach that but you could do a significant amount of that.
Design note - if you have a bunch of parallel batteries connecting to a bus bar with long wires ... long is greater than 6~12" then it is better to put the fuse close to the bus bar verse right at the battery.
example - 7 batteries connected to bus bar and they are using 3ft of wire. Say 100amp BMS each. So the fuse and the wire is rated for 125amps.
Now assume one battery has a fault that drops the voltage by 3.2v (shorted cell)... 6 batteries will be dumping current into the faulted one and using that wire only good to 125 amps and now it is seeing 600amps. This is close to the 6 x current so it should blow pretty quick at only a few seconds. But if you have 4 batteries and one faults the same way the wire will see 300amps and the fuse will take minutes to blow.
Put the fuse near the bus bar and the wire is safe and the fuse blows.
If you are dealing with 48v batteries I would put a class T per battery rated for 125% of the BMS continuous output. Should only blow if there is a current high enough to cause a problem.... JLLN curve will let it run at 2x current for 10minutes, but will blow in a fraction of a second for a dead short or 6x current. Wires should also be sized for 125% of continuous current output of the BMS.
There are ANL ceramic fuses like you mentioned but the generally have a higher internal resistance than a class T so they run hotter and waste energy as heat. But they AIC rating on ANL is far lower than that of a class T. AIC = Amps Interrupt Current - as in how large an arc can it break. The ANL just burns open and contains the arc,, but won't interrupt beyond 2500amps depending on style... the class T has 20,000amps at 48v.
LFP batteries can put out a short circuit current in the thousands of amps limited by the internal resistance and the connection/wire resistance... This depends on cell size and type... a 12v battery made from 314ah EVE cells can put out 8000amps if the BMS is shorted and there is an external short next to the battery, say a dropped wrench across the terminals.... It should shutdown but as Hedges mentioned the FETs tend to fail shorted first.... then they burn open with sufficient current..... Now 8000amps it the theoretical max with good connections you won't reach that but you could do a significant amount of that.
Design note - if you have a bunch of parallel batteries connecting to a bus bar with long wires ... long is greater than 6~12" then it is better to put the fuse close to the bus bar verse right at the battery.
example - 7 batteries connected to bus bar and they are using 3ft of wire. Say 100amp BMS each. So the fuse and the wire is rated for 125amps.
Now assume one battery has a fault that drops the voltage by 3.2v (shorted cell)... 6 batteries will be dumping current into the faulted one and using that wire only good to 125 amps and now it is seeing 600amps. This is close to the 6 x current so it should blow pretty quick at only a few seconds. But if you have 4 batteries and one faults the same way the wire will see 300amps and the fuse will take minutes to blow.
Put the fuse near the bus bar and the wire is safe and the fuse blows.
would this work?
robbob2112
Doing more research, mosty harmless
That style can be fine, but you need to be able to find a datasheet on it -- the AIC rating has to do with distance the arc has to travel... The standard class T is filled with silica so when the fuse element burns away it fills the space and it absorbs a lot of energy before it can melt.
With the smaller bodies like that one it is usually just vacuum or nitrogen filled and has a much smaller AIC
The lack of a datasheet is the main reason to stick with Littlefuse, bussmann and eaton for brands.... the cheap no-name stuff can be ok, or it can fail.
The kit @Calvin98 mentioned is a good one .... I haven't seen any kits for less than $55 that I would use myself. The have JLLN series in them.
much appreciated!
42OhmsPA
Who likes Electrical Gremlins?
Just ordered 2 from them, free shipping for 2.
I've been using the BlueSea relabels.
You will like them. Very sturdily built. Very heavy duty.
Yep, I think I spent over $1000 on these. I did it in two goes so less painful. Think of it as cheap insurance though. You don’t want anything burning down.i need 14 for all my packs, thats a decent hit to the wallet
If you do the calculations for each of your 16S packs, you might be able to use K5 fuses. They can be had in 250VDC and 20kAIC. And are much cheaper then class T
One class K5 at each pack and a class T after the busbar
I don't know what size fuse you will want for each pack, but basically the total current draw divided by the number of packs plus some overhead
Here is an Amazon example of a class K5. I found mine for about $4 each on eBay
One class K5 at each pack and a class T after the busbar
https://www.littelfuse.com/products/fuses-overcurrent-protection/fuses/ul-class-fuses/class-k5-fuses
I don't know what size fuse you will want for each pack, but basically the total current draw divided by the number of packs plus some overhead
Here is an Amazon example of a class K5. I found mine for about $4 each on eBay
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fancy a link to said fuse pretty please?
Edit abovefancy a link to said fuse pretty please?
robbob2112
Doing more research, mosty harmless
Link to buy the fuses and mounts?
To OP
The other options cost more --- and a fire would be devastating to the wallet and time invested..
I would buy a couple of extra fuses to have hanging around .... but - they would be the very last thing installed so you should not accidently blow one---just keep them in a box until you are ready.
The good thing is a fuse never blows unless you have something bad go wrong.
Do you have a means of disconnect per battery?
yes, if you look at pictures i posted on the previous page i think, i have 100 amp 'disconnect' breakers that i can isolate each group with
robbob2112
Doing more research, mosty harmless
If you mean the flat breakers on the wall I detailed the problems with those above --- I wouldn't use them at all personally and if I did somehow get where I would the brand would be Bussman or Blue Sea --- but there are so many cheap fakes of those I just wouldn't trust any from random sources...
robbob2112
Doing more research, mosty harmless
Link where they can be purchased? pictures are great but can't see any useful details
Remember, this is what I am using for my pack. You might want or need a different amp rating then mine
Bussmann NON-60 60A Type Non Cartridge Fuse (2PK of 2) | eBay
UL Listed - 250Vac: Class H (65-600A), Std. About this item. General Purpose.
www.ebay.com
Marathon 60 AMP 3 Pole Fuse Holder RH30B 5 | eBay
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even as a disconnect?
The problem is, if they do actually trip then they might not extinguish the arc. Hopefully the current to sustain the arc will be enough to blow the fuses your putting on each pack and it will keep the whole thing from burning down. You are definitely safer with fuses added to the mix. But some of those "breakers" won't trip when supposed to and instead just start to smoke and burn
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