What part number is this transformer?

[kff]

A tiny transformer on the BMS board for an EGO 56V 4AH battery has an open on one of the three coils. I would like to replace it but cannot figure out the part number.

The transformer looks very similar to the Vishay MTBAUGDT line:



https://www.vishay.com/docs/34567/mtbaugdt.pdf

Same ~6x6 mm size, metal can, and 1.854 mm spacing between the 6 pins. However, the transformer on the EGO board has 5-6 ohm resistance on its coils and 60-120 uH of inductance. I believe it is an air core design. I was able to unwind two coils, and they both had close to 100 turns of 40AWG wire. The topology is as indicated on the PCB below:



The transformer appears to be part of a step-down voltage converter used with a TL3843 PWM controller and a FQT4N20L MOSFET. There are unfortunately no markings anywhere on the transformer.

If anyone knows what part number this might be or what company manufactures such transformers, could you please let me know?

Thanks!

[james_s]

It's probably a custom part designed specifically for that device, most transformers of this sort are.

[floobydust]

The open-circuit is usually where the magnet wire is (poorly) soldered to the pin, I would look there. Scrape enamel off with an Exact-O knife with and resolder.
Coilcraft also have transformers like that, you really need to know Vin and Vout, or the IC # driving it.

[kff]

A custom part would explain why there are no markings on the metal can. I didn't realize making custom transformers was economical (vs. using an off-the-shelf one), but I suppose the machines that wind these transformers can be programmed pretty easily for a custom design.

I did check that the magnet wire made good contact with the pins. The open was definitely somewhere inside the transformer. The magnet wire is only 0.07 mm in diameter and very fragile.

Thank you for pointing me to Coilcraft. I found some parts in an identical package, but sadly nothing to match the topology. Same for Pulse Electronics transformers. The unusual part is the 1-2 / 3-4 / 5-6 coil pin connections. They usually go 1-6 / 2-5 / 3-4.

The IC driving the transformer is TL3843. I believe the conversion is between 30V and 8V or so, although I don't have a working board to verify this. I don't fully understanding why the transformer needs 3 coils for voltage conversion.

[james_s]

Custom transformers have been used in the vast majority of mass produced goods for a very long time, almost all switchmode power supplies and even a lot of iron transformers. When you're making a bunch of units the cost to order a transformer that produces exactly the voltages you need is not much.

[wasedadoc]

3 windings is fairly common. The one on the right is the output feeding the diode D11 just below it and then into the electrolytic. The winding at the bottom is probably the input side and connected to the Q10 transistor/FET. The winding at the top would be feedback to make it oscillate.

[kff]

Update: I ended up using Coilcraft DA2320 in place of the blown transformer. The pinout of that transformer is very different, so I made a tiny adapter PCB that sits between the BMS board and the transformer.

Another possibility is P0926NL from Pulse Electronics, although I haven't tried it.

DA2320 is not a perfect (or even a close) match, and one of the rails now reads 11.5V instead of the 8V indicated on the silkscreen. That doesn't seem to matter, as there is a voltage regulator to generate the needed 3.3V, and current consumption is pretty low to worry about efficiency.

I've charged / discharged the battery a few times after replacing the transformer and so far all is good.

Hope someone will find this info helpful.

[Te]

Hi,

I have replicated your transformer repair on one of my Gen3 EGO battery BMS boards, however instead of using the DA2320, I used the DA2317 (with a 2:1:1 ratio) as I though the transformer may have been a 2:1 instead of 1:1 based on resistance measurements.  However, I still see the same 11V output on one of the rails like your repair.  Was a tricky soldering job given the different topology of the pinout. I also searched for a few hours for a transformer with the matching topology.

Is your battery still functioning?  Mine charged correctly after the repair.

Thanks!

[raymond008]

I have the exact same issue with my 7.5ah battery packs. Both failed for this transformer on the exact winding.
How does the DA2320 or DA2317 works out? Also, please provide the pin mapping if you could. Greatly appreciated.

[raymond008]

I ended up fixing the transformer instead of replacing it.
The top winding turns out to be the outside winding of the transformer. I use hot air gun to disassemble the ferrite core and rewind
the outside winding and properly soldered the broken wire back. The breakage usually either at the beginning or at the end.
You may ended up just loosing 1 round of wire. I think it will match the original spec better a replacement transformer.
For those who may need to rewind it from scratch if the wire break in the middle, the outside winding is of 0.1mm diameter (38 AWG) and 24 inches long.
My repair was a success and the BMS works again.