Help me identify this BMS component

[braxton]

Hi
I have 4 ego 56v power tool batteries where the BMS battery management board is dead. I believe I have narrowed down the problem on all 4 to a transformer coil on the board. There are no markings whatsoever on this coil. How would I go about trying to identify it? Thanks.

I'm attaching a couple of photos for starters. The first shows the entire board with the component in question (silver square 6pin device next to caps).
The second photo shows the board with the transformer coil removed.

Any help is greatly appreciated.

[sam_sam_sam]

Re: Help me identify this BMS component

What do the two connectors connect to I amuse that one hooks to the battery cells but where do the other one hooks up to ( unless the other connector has some battery cells on that one as well and also has temperature sensors on this connector as well )

Please show us a picture of the battery pack cells as well with the connector

[braxton]

Re: Help me identify this BMS component

The two top connectors attach to the 14 cell packs (individual cell monitoring) plus wiring for two thermistors.
The bottom connector attaches to the battery contacts (negative and positive leads plus T terminal plus D terminal.
The coil in question is involved in the circuitry that drops 56v to lower voltages to drive the BMS (12v, 3.3V etc).
I can also attach another image of an older version of this BMS, which has more labels on the board.

[braxton]

Re: Help me identify this BMS component

Here is an image of an older version of the BMS board with more labels:

[braxton]

Re: Help me identify this BMS component

I took a chance and ordered this coil from digikey:
https://www.digikey.ca/en/products/d...0926NL/2265652

It looked similar and dimensions were correct. It had a slightly different pin out, but long story short, it did not work in this application.

[R_J]

Re: Help me identify this BMS component

What was wrong with the original transformer? it is unlikely it was bad unless it was physically damaged.

[braxton]

Re: Help me identify this BMS component

What was wrong with the original transformer? it is unlikely it was bad unless it was physically damaged.

For some reason this coil component is a common failure, especially in the newest ego batteries with the fuel gauge. One of the 3 coils tends to short or open up.
In my case, the 3 coils do not appear to be shorted or open, but resistance values differ slightly from working coils.

If I install a coil removed from a working BMS, it restores functionality.

[R_J]

Re: Help me identify this BMS component

For some reason this coil component is a common failure, especially in the newest ego batteries with the fuel gauge. One of the 3 coils tends to short or open up.
In my case, the 3 coils do not appear to be shorted or open, but resistance values differ slightly from working coils.

If I install a coil removed from a working BMS, it restores functionality.

Ok good to know, If it is a common problem maybe some one has a source for them.

[petehall347]

Re: Help me identify this BMS component

bms transformer by the looks of it .
see if you can match it .. https://www.digikey.bg/en/product-hi...t-transformers

[braxton]

Re: Help me identify this BMS component

Ok good to know, If it is a common problem maybe some one has a source for them.

Lots seem to be looking but I can't find any sites that mention that someone has found anything yet. It might be a proprietary part made just for EGO bms??

[braxton]

Re: Help me identify this BMS component

bms transformer by the looks of it .
see if you can match it .. https://www.digikey.bg/en/product-hi...t-transformers

Thanks. I'm not enough of an expert to know what to look for.
Based on my second photo in the 1st post, I can see that pin 1 (bottom left) has a coil connecting to pin 2 next to it. Pin 3 has a coil connecting to pin 4 across from it. Pin 5 has a coil connecting to pin 6 (top left and middle pins).

I'm not sure how to interpret coil schematics in the datasheets to find a similar profile.Closest I could find was the pulse electronics device i linked to above, but it didn't work...

[petehall347]

Re: Help me identify this BMS component

measure the inductances of a good one . a schematic would help but i know with these things its not going to be available .
makes me wonder why they are failing .

[R_J]

Re: Help me identify this BMS component

I took a chance and ordered this coil from digikey:
https://www.digikey.ca/en/products/d...0926NL/2265652

It looked similar and dimensions were correct. It had a slightly different pin out, but long story short, it did not work in this application.

How did you try this replacement transformer? did you add wires to its pins so you could connect it correctly to the board or just soldered it in place.

[braxton]

Re: Help me identify this BMS component

How did you try this replacement transformer? did you add wires to its pins so you could connect it correctly to the board or just soldered it in place.

I added wires to its pins so that it would connect properly to the pads on the boards, as its pinout was different. Pins 3-4 were correct but the others needed to be criss-crossed.

[braxton]

Re: Help me identify this BMS component

measure the inductances of a good one . a schematic would help but i know with these things its not going to be available .
makes me wonder why they are failing .

I unfortunately don't have any equipment to measure inductance

[petehall347]

Re: Help me identify this BMS component

I unfortunately don't have any equipment to measure inductance

my multimeter has it .am sure these days there are affordable things that can do this , on another note all i found with similar bms was bad thermistors . i dont see one on your board . must be connected through the plugs .

[braxton]

Re: Help me identify this BMS component

Using my 9V generic electrical component tester, the 3 coils test as resistors (in circuit and bms powered down; in a working bms). Pins 1 and 2 are 8.2 ohms, pins 3 and 4 are 6.8 ohms and pins 5-6 are 5.4 ohms. I did not do any further testing at this time as these batteries are very expensive and i don't want to risk breaking a working BMS.
Do they need to be tested out of circuit?

My tool can measure inductance as I tried other choke coils and the transformer coil part i ordered from digikey and they tested as inductors (with an ohm reading and mH reading; out of circuit).

[braxton]

Re: Help me identify this BMS component

I noticed that, on the BMS board, the 3 coil symbols each has a (-) designation at one end, which would seem to indicate a polarity. How does this factor into identifying a suitable replacement part and installing that part?

[braxton]

Re: Help me identify this BMS component

I guess a more general question is:
What is this transformer exactly doing in this configuration? What is it’s purpose in this BMS?

In a working BMS, the low voltage circuit turns on when the battery gauge button is pressed, or when the battery is used in a tool or charged on the charger. When this circuit is activated, pin 1 of the transformer (bottom left in first photo) reads approx 55v, pin 2 reads approx 54v, pin 5 reads approx 3-5v and pin 6 approximately 3-5v. Pins 3-4 measure in the mVs.