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Fusing the balance/monitoring wires?

Martijn

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Searched, but couldn't find an answer.

Would it be wise to fuse the balance/monitoring wires that go to the BMS? Or is there internal over-current protection in the BMS for these wires?

I see additional connections (for the fuses) and some resistance.

Yay or naye?

With regards,

Martijn
 
Last edited:
For balance/sense wires i use 22AWG silicone insulated cable. It self fuses without burning at 15A. This way minimises the potential for bad connections at fuses.
 
If they're silicone insulated, not the 60/80 degree ones, right?
the "fuse" part is the metal NOT the insulation....

silicone wires are nice and flexible, great at resisting solder iron temps , and have a higher insulation failure point than say pvc, however...
copper wire melting point is much higher than silicone failure so the wire insulation will "fail" (not actually melt but it will break down).
whether you use pvc or silicone, the internal 24awg metal wire is going to just "pop"...like a fuse if anything shorts...
If you have a high resistance connection (partial short?) where the copper wire turns into a large hot resistive load, the silicone wire will survive much longer than the typical pvc jacket (pvc will "melt" rather than turn brittle).

usually balance wire is only 24awg, it will fail with more than say 10amp load, so a short will blow it open fast. A balance lead short is a definite worry and the wire itself will quickly solve that. the fault scenario of a low current constant load over the balance wire of say less than 10amp continuous is very different and while certainly possible, much less likely; in the end itwill probably result in an eventual short that will disconnect the lead.

fyi, using pvc wire means that if a problem occurs you will most liklely "smell" the problem, not so with silicone wires...just something to think about.
 
the "fuse" part is the metal NOT the insulation....

silicone wires are nice and flexible, great at resisting solder iron temps , and have a higher insulation failure point than say pvc, however...
copper wire melting point is much higher than silicone failure so the wire insulation will "fail" (not actually melt but it will break down).
whether you use pvc or silicone, the internal 24awg metal wire is going to just "pop"...like a fuse if anything shorts...
If you have a high resistance connection (partial short?) where the copper wire turns into a large hot resistive load, the silicone wire will survive much longer than the typical pvc jacket (pvc will "melt" rather than turn brittle).

usually balance wire is only 24awg, it will fail with more than say 10amp load, so a short will blow it open fast. A balance lead short is a definite worry and the wire itself will quickly solve that. the fault scenario of a low current constant load over the balance wire of say less than 10amp continuous is very different and while certainly possible, much less likely; in the end itwill probably result in an eventual short that will disconnect the lead.

fyi, using pvc wire means that if a problem occurs you will most liklely "smell" the problem, not so with silicone wires...just something to think about.
OK, thank you for the explanation. My worry was that PVC would burn/smolder easier, but from reading above, it seems that's no problem with such thin wires.

All in all: no fuse in the balancing/monitoring wires, cause they're so thin, once a higher current starts running, they'll melt anyway before it can do any real damage.

Thanks again.
 
this seems a bit dangerous
if the wire "fuses" that is a failure with some high temperature (copper melting) and not a lot of control / predictability on where exactly it is happening.
will some nearby plastic catch fire ?
will something else happen?
call me a control freak, but I want to be sure this happens inside a glass or ceramic tube where it is meant to happen and can't cause any collateral damage.
just my 2 (engineering) cents.
 
this seems a bit dangerous
if the wire "fuses" that is a failure with some high temperature (copper melting) and not a lot of control / predictability on where exactly it is happening.
will some nearby plastic catch fire ?
will something else happen?
call me a control freak, but I want to be sure this happens inside a glass or ceramic tube where it is meant to happen and can't cause any collateral damage.
just my 2 (engineering) cents.
You need to get hold of some 24AWG silicon sheathed wire and short circuit it so you can relax a little bit.

It’s not as spectacular as you would imagine.
 
You need to get hold of some 24AWG silicon sheathed wire and short circuit it so you can relax a little bit.

It’s not as spectacular as you would imagine.
what voltage to supply? 1~N cells worth of 2.5-3.6V?
 
so 0.5V is ok? some variable voltage power supplies will not provide enough amps to fuse at that voltage.

agree that one fuse per balance lead is a significant increase number of failure points, ignoring adding two points of variable resistance in the path (fuse contacts), which may or may not matter. more failure points = undesirable

another important aspect to me is: how does one automatically sense when a balance lead fuse is blown? look for a cell measurement to be 0 Volt?

a fuse blowing on a balance lead will prevent balance current from flowing

it will also prevent the proper sensing of cell level voltage, which would presumably result in cell level voltage disconnect functionality failing to operate (cannot sense a cell being overvoltage condition)

thank you?
 
You need to get hold of some 24AWG silicon sheathed wire and short circuit it so you can relax a little bit.

It’s not as spectacular as you would imagine.
This is true I've not seen this happen.
In my defense, the "silicone" wire I got from amazon has the insulation melting during my clumsy soldering.
The wires that came w. JK BMS do seem to hold up better during soldering (while I was attaching those inline fuses yesterday :D ).
While you are probably correct, it seems cheaper to me to fuse this whole thing than buy and test good quality wires.
150 fuses assortment + 10 inline holders were $12 on amazon. So 2 of those + 2 episodes of some show worth of soldering.
And I have 17 sense leads from the BMS fused.

Absolutely agree on additional failure points.
This whole project is a new hobby for me, not something I'm comfortable with at all. So I put "belts on suspenders" wherever I can and pay some extra time and money to be sure I will not burn down the house :) .
For example, I'm adding a contactor in series with the BMS and a DS18b20 temp sensor on every negative terminal with ESP8266 to make sure everything will switch off if the temperature rises on any individual cell.

I am not arguing here at all, just explaining why I did install fuses.
1671374281137.png
Peace
 
This is true I've not seen this happen.
In my defense, the "silicone" wire I got from amazon has the insulation melting during my clumsy soldering.
The wires that came w. JK BMS do seem to hold up better during soldering (while I was attaching those inline fuses yesterday :D ).
While you are probably correct, it seems cheaper to me to fuse this whole thing than buy and test good quality wires.
150 fuses assortment + 10 inline holders were $12 on amazon. So 2 of those + 2 episodes of some show worth of soldering.
And I have 17 sense leads from the BMS fused.

Absolutely agree on additional failure points.
This whole project is a new hobby for me, not something I'm comfortable with at all. So I put "belts on suspenders" wherever I can and pay some extra time and money to be sure I will not burn down the house :) .
For example, I'm adding a contactor in series with the BMS and a DS18b20 temp sensor on every negative terminal with ESP8266 to make sure everything will switch off if the temperature rises on any individual cell.

I am not arguing here at all, just explaining why I did install fuses.
View attachment 125188
Peace
love the temperature sensor on each negative and shutoff if a single cell heats up! great idea ???️
 
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