Trying to identify ferrite core transformer

[Western]

Hi,

I am trying to identify a small ferrite core transformer with a centre tapped primary of 4 ohms total (approx .3mH inductance) and a single secondry of 1.2 ohm (approx 4.6mH).

From what I've been able to find out, I believe it has an 'RM Core' ... and is approx 15mm across by 10mm high.

I require 3 of them to repair some pcb's which are approx $700 each.

I've attempted to dismantle one, but it had been potted in some sort of rubbery material and there is no way it is going to come apart well enough to identify the way it's been wound.

If anyone could suggest where else these things may be used so I can see if I can find something suitable, I would really appreciate it.

There are a couple of photos of the device at the bottom of the attached pdf.

Thanks, Wes

 

[ronsimpson]

Wes,

Transformers are custom made and hard to reproduce. This is probably not going to work.
I can get RM cores. There are several common core materials. We don't have to get the exact same type but we need to get close. In this type of core there may be a "gap" or a 'center leg gap'. That is important. We may be able to determine that. If you brake the core is there any indication the center leg has been ground short and does not touch?
Is the primary and secondary wire size the same
It looks to me you have a 4:1 turn ratio. (square root of inductance ratio)
The 4 ohm 0.3mH winding (c.t.) has high resistance and low turns the wire size must be small.
The 1.2 ohm 4.6mH winding has larger wire and 4 times more turns.
Do you see any markings in the core?
The milking machines I have used have isolation, primary to secondary, that is tightly controlled. I don't know there this pcb is used but even uA of current can light up a cow!
I need to know if there is special insulation on the wires.

 

[ronsimpson]

Do you have a schematic? I have empty core and bobbins of a different type but about the same size.
Where are you?

 

[Western]

Thanks Ron,

I’m in South Australia, so couldn’t be much further away.

I don’t have a circuit either, rarely have the luxury. Have to draw out my own if I need it badly enough, so it’s a lot of work.

In this case, will have to chisel off more of the potting mix to be able to see more.!!!

Thanks for your insight regarding turns ratios, inductance and wire size … that helps a lot.

I don’t have anything to lose so I may have a go at pulling one apart and see what I can learn.

The board is a Westfalia ACR2 used in an ACR3 case. They have been around for a while but are still used all over the world, so I think the isolation part has been designed ok. What wire I can see is so fine and the device is so tiny, there’s no room for any fancy insulation over and above the normal enameled wire.

Any way, I guess I was hoping someone would say … I’ve seen transformers like that used in an “xyzabc” … and I could look up the specs, choose one, fit it, and live happily ever after …

Thanks again for your help ... I'll let you know how I get on.

Wes

 

[Western]

Well ... I got one of them apart although I broke the ferrite in the process.

There’s certainly nothing special about the windings but I haven’t tried unwinding them yet to count the turns.

Just by eye so far, both windings appear to use the same size wire.

The ferrite has “N30" printed on the top ... and one of the units had V4 with 2004 on the line below it. It looked like there may have been something before the V4, but it was shaved off.

One unit in the small plastic cube has the number 0202 on the top.

The height of the coil inside the bobbin is only 4.5mm and there are about 17 - 18 turns per layer, so that would make the wire approx .25mm diameter.

I've attached a photo of the coil alongside a rule.

 

[Western]

I’ve finally found what the original former is … it’s an EPCOS device …

B65805J0000R030 Core
B65806P1006D001 Coil Former
B65806B2203X000 Clamp

Trouble is the coil former has been withdrawn in April last year.

X-ON (Perth, Aust) which is tied up with Mouser, lists the core in their catalogue, but no stock !!! .. plus with no former to wind the coil .. will make it hard.

 

[Nigel Goodwin]

Any way, I guess I was hoping someone would say … I’ve seen transformers like that used in an “xyzabc” … and I could look up the specs, choose one, fit it, and live happily ever after …

Unfortunately it's almost certainly a customer transformer, made specifically for that manufacturer, and possibly just for that model?.

It's a pretty specialised application, not something any manufacturer is likely to make as a stock item - as are most ferrite cored transformers.

What goes wrong with them?, they are VERY reliable devices.

 

[MrAl]

I’ve finally found what the original former is … it’s an EPCOS device …

B65805J0000R030 Core
B65806P1006D001 Coil Former
B65806B2203X000 Clamp

Trouble is the coil former has been withdrawn in April last year.

X-ON (Perth, Aust) which is tied up with Mouser, lists the core in their catalogue, but no stock !!! .. plus with no former to wind the coil .. will make it hard.

Hi,

Can you salvage the old coil forms or do they break?

You have to be careful because there could be some safety issues that go with the isolation requirement. Probably not in this application, but could be.

 

[ronsimpson]

Why do you think the transformer is bad? They art strong and in your application there is very little power involved.
I looked for a pulse transformer with 1ct:4 turn ratio and the right inductance. They all looked small and very different core & bobbin.

 

[Western]

Ah .. good ... some easy questions.

The coil former on the one I got apart could be reused ... so if I can get the others apart without breaking it, plus get some new cores, I may solve my problem.

They are definitely faulty ... the secondry's are o/cct.

Why ... the tech who was installing them plugged the 24volt supply into the milk sensor socket ... 24volt across 1.2 ohm = faulty!!!

Just lucky it didn't do any more damage to the board ... or to more of the 20 he was fitting.

Of course the wisdom of the board designers in allowing the possibility is suspect too.

Thanks for your input,

Wes