Newbie - fried barrel socket on battery charge lead

Batteries, Chargers, and Battery Management Systems.
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Stanfr0   10 µW

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Newbie - fried barrel socket on battery charge lead

Post by Stanfr0 » Oct 14 2018 3:01pm

Hi,

I charged my 36v 20AH triangle battery pack last week. I switched off the charger at the mains and as I pulled out the 5.5mm charger plug from the inline socket on the battery charge lead there was a crackling sound and flash which lasted a couple of seconds. My hand was covered in soot and the outer part of the inline socket had vaporised. The centre pin also seems to have melted. Externally the thin charge cable seems fine and the battery remained at room temperature.

My guess is that when the charger was unplugged it shorted the centre pin of the barrel socket to the outer case and struck an ark which was in part fueled by the plastic casing of the connector ( the charger plug was sooty but otherwise undamaged).

I am now stuck. My father was a TV and I am reasonably competent around pre surface mount electronics. LiIon batteries scare me given the high currents, the available energy stored and the potential for cells to become unstable at 150 degrees. I have a fully charged battery that I am mindful not to shock in case the socket is mechanically unstable and shorts again.

I have contacted the chinese supplier who "helpfully" suggested that I replace the inline charge socket but unhelpfully have not responded with when I asked how.

Can anyone help with the following:

Assuming that I still have volts on the charge lead, will I have damaged the BMS and if so how can I tell?

How do I go about replacing the charge socket

- dismantle the battery and disconnect the BMS from the cells?

- Carefully cut through the lead with a separation of 2cm between each cut in the + & - conductors?

I am thinking about replacing the barrel socket with an XT30 female connector - is this sensible?

I would like to insert fuses into both the charge lead on the battery and the battery lead to the motor.
I am having problems locating suitable DC rated fuses (42v DC). Does anyone have any recommendations for a 5A fuse in the charge lead and 25A in the power lead I assume that the power load is inductive and charger is a resistive load?

Thanks in advance for any assistance.

Robert

Voltron   1 MW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Voltron » Oct 14 2018 5:47pm

Just replace it with something better... those barrel connectors are always a prob waiting to happen.

thorlancaster328   10 mW

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Re: Newbie - fried barrel socket on battery charge lead

Post by thorlancaster328 » Oct 14 2018 7:37pm

I'm not sure what I'd do about the fried charge plug, but if you posted photos, I'd have a better idea of what to recommend.
When in doubt, get bigger MOSFETs!

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Chalo   100 GW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Chalo » Oct 14 2018 7:42pm

Your BMS is likely to be OK. Get a multimeter and figure out where the voltage is lurking.

I use a barrel plug for my Luna/Hailong Shark pack, but I don't think it's the right plug for the job (and I have had to replace it due to spark erosion). I use XLR (microphone type) plugs on other batteries and chargers, or sometimes Anderson Powerpoles.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Stanfr0   10 µW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Stanfr0 » Oct 15 2018 11:30am

Thanks everyone for your replies.

Photos as requested

Image
Image


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Chalo   100 GW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Chalo » Oct 15 2018 4:15pm

When I replaced the socket in my battery, I found that the case insert containing the socket was easily removable upon opening the battery. I used an inline plug with leads and potted it into a lump of epoxy putty which I molded to fit the hole in the battery case. Then I soldered in a new plug on the charger cable, and I've had no more trouble with it. I now make sure to plug the charger into the wall before attaching the battery, to minimize the spark on plug-in.

The question remains, why were you able to strike such a destructive arc at the connector?
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

kdog   10 kW

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Re: Newbie - fried barrel socket on battery charge lead

Post by kdog » Oct 16 2018 5:09am

The cheap 5.5 male connectors Don't have an insulating tip on the end of the plug. If you pull them out/put them in slightly crooked they can short. But I don't know how he avoided it until now, unless it was his first time charging.
As has been suggested replace the plug with something more appropriate. Cut and isolate one lead at a time. Double check your polarity. Remember it's live!
I slipped with a dmm probe the other day whilst haphazardly checking a voltage on a 5.5mm plug... Same thing. I was a damn angry cat for a few mins. :oops:

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fechter   100 GW

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Re: Newbie - fried barrel socket on battery charge lead

Post by fechter » Oct 16 2018 9:54am

Barrel plugs are a poor choice for this application. XT30 or XT60 would be better.

If you can open the pack, there should be someplace you can disconnect things. On cheap ones, this will be a soldered connection. A typical BMS board will have spots labeled B+, P+, B-, P-, C- and a balance wire plug with one wire for each cell. B connections go to the actual cells. P connections (Pack), go to the load. C- is charger. All the + connections are just joined together. I recommend disconnecting the B+ connection first, then unplug the balance wires from the BMS. The B- connection can stay connected.

Once you have the BMS unplugged, you can use an ohmmeter to measure from the negative charger input to the B- connection. Reverse the meter probes and measure both ways. This should look like a diode. If it measures open circuit or short circuit both ways, then the BMS is likely toast.

After repairing the charger plug, reinsert the BMS balance plug and try to make the negative end of the connector go in first (angle slightly). Make the B+ connection last. After reconnecting the BMS, it's a good idea to measure voltage across each of the balance resistors to make sure none of them are stuck on. All should be zero volts.

If you're not sure, post pictures of your pack insides.
"One test is worth a thousand opinions"

Stanfr0   10 µW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Stanfr0 » Oct 17 2018 5:07pm

Thank you all for your help,

I still have no idea as to what caused it to short this time (second charge). Barrel sockets seem like a lethal choice as any other conductive material can easily accidentally short the centre pin to the outer case. No problem when they have a passive load but connected to the power source!!! It seems more logical to have the plug on the battery and socket on the charger.

I am going to have a go at fixing it with a female XT30 as I already have an XT60 female on the output. I have purchased a non conductive ceramic scalpel and am going to carefully shave back the insulation on either side of the cable ( 1cm apart) to see if I have any volts. If I have volts the plan is to carefully fit the XT30. If I have no volts then I will try and dismantle the battery and locate the BMS.

Can anyone see any snags with my plan?

Does anyone have a recommendation for an inline fuse holder and fuse to put in the lead as I'm finding it hard to source a 42V DC setup?

The BMS is supposed to be short circuit protected, clearly not the charge side. I'm thinking of fitting a 25-30A fuse in the output lead as a belt and braces solution (specs for the Bafang 250w mid drive are 15A peak). Is this a sensible/stupid thing to do?

Thanks again for the helpful advice which has given me some confidence.

Rob

Stanfr0   10 µW

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Re: Newbie - fried barrel socket on battery charge lead

Post by Stanfr0 » Oct 17 2018 5:17pm

fechter wrote:
Oct 16 2018 9:54am
Barrel plugs are a poor choice for this application. XT30 or XT60 would be better.

If you can open the pack, there should be someplace you can disconnect things. On cheap ones, this will be a soldered connection. A typical BMS board will have spots labeled B+, P+, B-, P-, C- and a balance wire plug with one wire for each cell. B connections go to the actual cells. P connections (Pack), go to the load. C- is charger. All the + connections are just joined together. I recommend disconnecting the B+ connection first, then unplug the balance wires from the BMS. The B- connection can stay connected.

Once you have the BMS unplugged, you can use an ohmmeter to measure from the negative charger input to the B- connection. Reverse the meter probes and measure both ways. This should look like a diode. If it measures open circuit or short circuit both ways, then the BMS is likely toast.

After repairing the charger plug, reinsert the BMS balance plug and try to make the negative end of the connector go in first (angle slightly). Make the B+ connection last. After reconnecting the BMS, it's a good idea to measure voltage across each of the balance resistors to make sure none of them are stuck on. All should be zero volts.

If you're not sure, post pictures of your pack insides.
This is really detailed and useful - thanks
I missed "If it measures open circuit or short circuit both ways, then the BMS is likely toast. " on the first reading. If there is a chance that its short circuit presumably I will have volts on the charge lead and a BMS that doesn't ballance or regulate the charge? Does this mean I should try and dismantle the battery and test the BMS first off. Is there any safe way of checking BMS operation without dismantling the battery?

Thanks again,

Robert

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fechter   100 GW

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Re: Newbie - fried barrel socket on battery charge lead

Post by fechter » Oct 17 2018 6:06pm

I can’t think of a way to check it without taking it apart.

If the plug shorted the jack, there is a definite chance the BMS was damaged.

A fuse on the charge side is a good idea. It just has to handle the charge current.
"One test is worth a thousand opinions"

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