That was a close call!

See. I wish it was still obvious, but I’m still learning all this, including what it means to break a circuit. Im guessing i attach it on one of the two wires inside the board coming from the charger, so that it “blows” when an issue arises so the battery circuit is no longer connected?

1 Like

Burned down house - great way to see in the new year

1 Like

It goes in line on the positive wire. Never hurts to do more research. Often hurts to not do enough research!


I would fuse only the charge, not the discharge; see


Why not the discharge ?


@b264 Thx for the detailed recommendation on the fuse. This really helps.

1 Like

I’m not electronic savy… but are you sure putting your charging port over the metal mounting plate has nothing to do with it? Shit looks like an arc conducting-tesla coil-hut burning-transformer circuit !!



Meh… If you are having the fuse blow then there is something already much worse happening. The times I’ve had fuses blow in my power systems, the BMS or ESC is already on fire and malfunctioning. The fuse only prevents a short through your system to reach the battery and make more things catch on fire (The fire on your ESC/BMS might still propagate to the battery but it’ll be much slower).

If you are at speed and a discharge fuse rated appropriately for the board blows. Your ESC should already be a piece of flaming toast and you should have already bailed, if not, may the force be with you…

Failure order should be ESC/Switch/Charger BMS Fuse Battery

This means that your BMS should be able to handle more current than your ESC. Your fuse should be able to handle more current than your BMS and your battery should handle more current than your fuse (maximum for an 18650 30Q cell is about 80A, I’ve tested this).

1 Like

Panel mounted ports in metal are not:

A. Dangerous B. New

I shorted the charging pins on one of my builds once but because I have my Bestech bms wired for discharge, the bms sensed the short and cut power instantly. It was just a quick arc and off. No damage to batteries or electronics.


Just checking my groups after one full charge cycle.

My lowest group is 4.17 highest is 4.21. This seems a bit off for a bestech. maybe I didn’t leave it at float for long enough?


Let it balance down and then charge it full again. Repeat until the pack is fully charged and balanced.


My port sparks a little when I plug my charger in, would a fuse mitigate this? Or is there some thing I’m doing wrong like plugging my port in before plugging in the charger to the wall outlet ?

Sounds more like it’s related to your specific charger. Have you tried a different style charger? A fuse would not mitigate that. Which specific charger are you using?

Are you sure you’ve used all 5.5mm x 2.1mm barrely plugs and that none are 5.5mm x 2.5mm by mistake?

1 Like

Typically you do want the charger hooked up to the wall but not in charging mode yet when connecting the battery after you connect the battery you should select the charge option… basically sparks like this happen because of capacitors in the device you’re plugging the battery into getting filled with the charge from the battery (high inrush current causing the spark, usually happens when hooking batteries to the VESC though not to a charger). I have seen some small sparks on my own charger though too I don’t think it’s something to be really to concerned about but if it is unnerving you can always use a “antispark” connector that includes a resistor inline when you first plug the antispark plug in the current is slowed by the resistor so there isn’t a high current/energy spark.

1 Like

I bought the 11s3p battery and assigned charger from build kit boards, paired together by Jared. So it has a charge only bms I’m sure, but past that I know little. The barrel plugs seem to be the right size

@wafflejock hmm I didn’t see my charger have a “charge” option switch, I’ll check it out when I get home. It’s definitely a small spark, but no spark is best I thought so I needed to ask. Is the xt90 the best for this situation? I don’t know of anything else I could use. Or should I buy a certsin resistor and solder it in line?

Which specific charger are you using?

1 Like

I’m using a 42v 2A charge from jlabs and I also get Sparks most of time but now I just plug it in to the board first and the plug it in to the wall. No Sparks if I do that.

1 Like