parallel fuse wire

lets say im building a 13s4p battery. I don't think I need the parallel connections to carry more than 1 amp so basically what im saying is the battery is built with 4- 13s1p strings that are paralleled together with 1amp fuse wire to make the 4p group and it will allow for balancing the pack. so if 1 cell goes bad it will blow the fuse wire without taking out the p group and your battery keeps working. you will know something is wrong with the pack because you will be short the ah of 1 series string

anyone try this?

Personally, I think parallel fuses would be a pain in the neck to install, and a pain in the neck to replace if they ever blew. Depends on how you build it. You can't shrink wrap it if you have to get back inside.

How is the cell connected in series? In your scenario, if it goes bad and the parallel fuse wire blows, isn't it still connected in series? So it is still effectively in the circuit.

Can you draw a diagram?

serious_sam said:

How is the cell connected in series? In your scenario, if it goes bad and the parallel fuse wire blows, isn't it still connected in series? So it is still effectively in the circuit.

Can you draw a diagram?

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the blue wires can be fused at 10 or 20 amps depending on what your setup is the red wire would be the fuse wire and for bms/balancing.



im just watching my charger with a watt meter. its a 4p pack charging at 5 amps. the last volt from 69v to 70v the amps slowly taper off. im at 69.9v charger is 0.42a /26.3watts. no bms on pack.

I could use 8 amp fuse wire

You need to decide why you want fuse wire: what fault it is providing protection from? Then calculate current flows (a circuit diagram helps) during that fault condition.

From the incomplete wiring in the photo, I'm still not seeing how parallel and series fuse wires provide protection. Each cell terminal is connected by 2or3 wires (1 series and 1or2 parallel?) so in any "fault" event, you need all 3 wires to blow to fully disconnect the cell. That makes no logic.

If you want to fuse the cells, do it like it's been previously done. Fuse each cell individually to a main "bus". Then only one fuse wire needs to blow to fully disconnect the cell, and it has minimal effect on the rest of the pack.

Also as has been mentioned by docw009, it means you need access to the cell and fuse wire to perform any repair. PITA. And you need some way to indicate if/when/where a fault has occurred.

serious_sam said:

You need to decide why you want fuse wire: what fault it is providing protection from? Then calculate current flows (a circuit diagram helps) during that fault condition.

From the incomplete wiring in the photo, I'm still not seeing how parallel and series fuse wires provide protection. Each cell terminal is connected by 2or3 wires (1 series and 1or2 parallel?) so in any "fault" event, you need all 3 wires to blow to fully disconnect the cell. That makes no logic.

If you want to fuse the cells, do it like it's been previously done. Fuse each cell individually to a main "bus". Then only one fuse wire needs to blow to fully disconnect the cell, and it has minimal effect on the rest of the pack.

Also as has been mentioned by docw009, it means you need access to the cell and fuse wire to perform any repair. PITA. And you need some way to indicate if/when/where a fault has occurred.

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im really not worrying about series fuses im just looking at parallel

I understand accessing a blown fuse wire is a PITA.
walking a bike home because 1 cell took out an entire parallel group is a pain in a few things and I still have to open the pack whether it is fused or not.

once I had 1 dead cell it was 0 volts, my bike still ran and operated but the volt sag was very noticeable and I lost 2.5ah. so I opened my pack, it was a PITA

another time I had an entire p group go dead, it was the backpack battery I use when I need more range. so 20 km from home I had to pedal, that was a double PITA

I really don't understand fusing batteries. no experience at it, so if im fusing the series connections to a bus where all the amps are flowing I cant help myself but to think that im creating a lot of unnecessary heat. 15 amps through a series fuse wire


from those 2 experiences, im probably wrong. I started thinking how many amps flow sideways (p groups) there really shouldn't be any except when balance charging or when it starts shorting it can pull upto 60 amps from the 3 other cells in the p group

when charging, how many amps go sideways to the bms. if you put in 5 amps on a 13s4p pack, as the bms starts burning off energy its not burning off 5amps on 1p, the other 12p are still taking amps and eventually the 13p will absorb the 5amps split between them half amp max but the last bit of charging the charger starts dropping the amps being supplied.

my charger dropped to half an amp by the time it was done. so half an amp split 13 times is nothing.

as far as I can tell the parallel connections are just for keeping a pack balanced, no real amps flow

my thinking is by just parallel fusing, I can lose 1 cell and still get home but if I lose 1 cell and it takes out the entire p group my battery is dead and im pedalling home. no matter what, its a pain in the ass lol

If your cell is still in series (i.e. not fused in the series connection), then there's absolutely zero point in fusing the parallel connections. The cell will still be in the circuit causing issues.

Never built any serious packs. I did solder two 3S-3P booster packs. I have like six commercial ebike packs and six cheapo shrink wrapped packs and never had a cell fail, so it's not an outcome I consider to be likely. So I guess you have to take precautions against what you've seen in the past.

If you were using mismatched cells, I think there could be cases where your parallel connections would see unusually high flow. Let's say one of the next cell suddenty developed a higher internal resistance, or the spot weld lifted. The current will have to flow sideways to follow the path of least resistance and blow the parallel fuse. I guess that's OK, if the parallel fuse blows. The idea is to isolate the bad cells and prevent a fire, not to allow a battery to keep working if a cell fails.

serious_sam said:

If your cell is still in series (i.e. not fused in the series connection), then there's absolutely zero point in fusing the parallel connections. The cell will still be in the circuit causing issues.

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yes it will cause issues but if my pack doesn't go up in flames I can still get home. if I lose 1 out of my 4 series strings I will still have 3 strings to limp home on.

if im running 20amp cells in 4p groups, fused at 1amp parallel and each of the series strings are fused at 20 amps, so 4-20 amp fuses on the leads leaving the pack. if anything happens to 1 cell that series will get disconnected from the other 3 series strings and the damaged cell wouldn't be getting hit with 60 amps from the other 3p. again I don't know fusing but I don't understand your zero point of fusing parallel. the point is im not dead on the side of the road

not dead dead, my battery wont be dead. I really should proof read before clicking submit.

doc, I was playing with batteries that went to 0 volts and I brought them back. 20amp 25rs in a 4p running at about 45amp bursts. so after 2 pack failures, no smoke, no flames cell wrappers weren't damaged. I could've still rode home if it was paralleled fused.

maybe I just need to look into a 20 amp fast fuse wire to fuse individual cells to bus bars that wont set a fire when they blow and don't run hot at 15 amps continuous

draw it out and you'll see it.

imagine a ladder, laying on it's side. thsi represents one set of parallel cells. each rung (now vertical) represents a cell. each ladder side represents the connection bus or strip that connects all teh cells together to the next set of parallel cells within the series of cells.

stack a bunch of these ladders together, where all the sides of the ladders are touching, thse are the series connections.

so...even if you remove (blow the fuse on) the positive connection (side rail) of the far left end cell to the to the rest of the cells, it's still connected to the same rail that's on the negative end of hte next row of cells.

taht means that the fuse blowing (which it wouldn't do because of the other cnnection) would not be ablet o disconnect the cell from the other paralleled cells in it's set, since it's still connected to them via the next cell set's paralel connection.

the only way to do what you want, to disconnect a single cell from the entire pack, is to fuse from one end of that cell to whatever connects both serially and parallel, at the same time.

either that means effectively a minimum of three fuses (for end of row cells) or four fuses (for non-end of row cells), or using a busbar of some type and fusing from the cell to the busbar. (even if the busbar is just a nickel strip--the strip cannot be connected directly to any cells, it has to be separated from them by the fuses).

goatman said:

yes it will cause issues but if my pack doesn't go up in flames I can still get home. if I lose 1 out of my 4 series strings I will still have 3 strings to limp home on.

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You're missing the point. If all of the cells are connected in parallel, and all the cells are also connected in series, then blowing the parallel fuse still leaves the cell connected in series, and that series string is still connected at all the other parallel connection points.

Draw a full diagram. Remove one of the parallel links. Notice how the cell is still connected in the pack.

goatman said:

doc, I was playing with batteries that went to 0 volts and I brought them back. 20amp 25rs in a 4p running at about 45amp bursts. so after 2 pack failures, no smoke, no flames cell wrappers weren't damaged. I could've still rode home if it was paralleled fused.

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OK. I see why we have different expectations.

docw009 said:

goatman said:

doc, I was playing with batteries that went to 0 volts and I brought them back. 20amp 25rs in a 4p running at about 45amp bursts. so after 2 pack failures, no smoke, no flames cell wrappers weren't damaged. I could've still rode home if it was paralleled fused.

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OK. I see why we have different expectations.

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I wanted to know why I should throw cells out once they've been damaged, that's how I learn.

I scribbled this out

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im just trying to isolate the series string

I have a battery where I can try out a 1 amp fuse wire on 1 p group to see what happens under throttle and charging.

just to show even more ignorance, a different thread someone replied to me about using xt60 spark arrestors but I couldn't find them. what about using a resistor for parallel connections?

AveRage Joe on youtube was testing an 8 ohm resistor as a fuse wire that blows at 8 amps. he didn't test the resistor he only tested the wire. the wire is fuse wire.

wouldn't a small resistor do the same thing as a fuse? it would limit the amps flowing to the damaged cell and if high amps tried to pass through the resistor the resistor wire would be an 8 amp fuse

Look at the attached image. Say the "X" cell fails as short circuit. In your scenario, the parallel fuse wires blow (shown in red). Look at the circuit paths between point A and B. Compare pink and green.

See how the pink path has 1 good cell and one bad cell. So that's 4.2v.

The green paths all have 2 good cells. So that's 8.4v.

But both strings connect at A and B. 4.2v fighting against 8.4v. Current will still flow out of the good cells, into the bad cell. Your bad cell is still in the circuit (via the series links), and still causing problems.

if im using 1 amp parallel fuses and my 18650 is 20 amp, maybe this is where im going wrong, in a 4p group that would be 80 amps

in your drawing the cell is mid pack, would 20 amps@4.2v flow sideways into the damaged cell from 1 direction and 40 amps from the other 2 cells@4.2v. if no say im wrong and ill clue in.



if the amps do flow that way, I would have 1 damaged string and 3 good strings trying to pump 20 or 40 amps into the damaged string blowing all the 1 amp fuses and isolating the damaged string from the pack. in my brain im thinking the 1 amp fuses would all start blowing one by one along the entire string. with your drawing it shows 7s4p, so 14-1 amp fuses would blow

Sure. All the parallel fuses would probably blow along that series chain (until the cells' series resistance increases enough to reduce the current to a level below the fuse current rating). But the bad cell and it's series chain will STILL be in the circuit doing harm, flowing current at just below the next parallel fuse rating. AND you still have to rebuild the whole pack because of one bad cell...

I guess ill just try the fuse wire and see what happens but resistors are pretty cheap.

1amp at 4.2v= 4.2 watts

1 amp@4.2v=4.2 ohms

a 4w 4ohm resistor haven't found on a quick search and prices climb with the watts but I really don't need watts or amps, when balancing the bms wire takes the watts/amps

a pack of 200- 1w4.3 ohm resistors is $8 on amazon. I think that means the resistor is rated for 4.3v and 0.25 amps, I really don't know this stuff im just using converters from the internet.

Ill see what the electronic store says to me.

serious_sam said:

goatman said:

yes it will cause issues but if my pack doesn't go up in flames I can still get home. if I lose 1 out of my 4 series strings I will still have 3 strings to limp home on.

Click to expand...

You're missing the point. If all of the cells are connected in parallel, and all the cells are also connected in series, then blowing the parallel fuse still leaves the cell connected in series, and that series string is still connected at all the other parallel connection points.

Draw a full diagram. Remove one of the parallel links. Notice how the cell is still connected in the pack.

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I WAS missing the point, I have to rebuild the WHOLE battery.

I was stuck on stupid,just individually fuse the cell, thanks

Usually when doing this a single fusible link wire is the only connection between each cell and the buss it is wired to.

So if it blows, it is electrically removed from the pack.