Electronics > Repair
What part number is this transformer?
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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.
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