sv572 a tale of woe

Andrew · Post by **Andrew** » Wed Nov 14, 2012 7:06 am

At 57mA a short/duff rectifier would not seem to be the obvious culprit too little current, I would have thought. Hope your finger is OK.....

ed · Post by ed » Wed Nov 14, 2012 8:08 am

Andrew wrote:At 57mA a short/duff rectifier would not seem to be the obvious culprit too little current, I would have thought. Hope your finger is OK.....

Finger is fine, I mentioned it mainly for comic relief...but it was damned hot, but thanks for asking. The current through the ht power supply was 26ma(250v worth), making it even less a candidate for conspiracy.

keep the ideas coming guys, the longer this thread gets then the bigger fewl I will be when I find out what I've done wrong. I'll be able to qualify for Phil's prat of the day award.

simon · Post by **simon** » Wed Nov 14, 2012 12:51 pm

You're nobody in this game ed if you can't lay claim to at least one prat of the week award... We've all done it - be proud!

Mike H · Post by **Mike H** » Wed Nov 14, 2012 1:41 pm

ed wrote:the meter is one of those that you plug into a socket on the wall and then plug your appliance into the meter...it shows mains voltage, frequency, current, power...etc..so far it's proved pretty accurate...

Oh right gotcha. Didn't realise that's what it was.

ed · Post by ed » Wed Nov 14, 2012 3:12 pm

ok chaps..todays update so far...I really do hope your not losing interest cos I'm in need of help.....

so I put myself up for the prat award at the moment because I mis reported the measurements from the maplin wall meter.......it measures in amps, and 0.57 AMPS is 570 ma not 57 ma as I reported before....

so: I took out the HT power supply and screwed the transformer secondaries into an empty screw block.....no contact whatsoever...and switched on

wall meter said 0.33 as it did yesterday, thats 330ma from the wall(249v). After 30 seconds the relay clicked and the meter jumped to 0.58, thats 580ma. So the HT transformer is using 250 ma and the secondaries are not connected to anything.........the only thing eating into the 250ma is the 12v relay which uses 16ma(720R coil)......now I'm scratching my head big time.

anyway, left it on for 1 hour and the transformer is hot, not untouchable, but hot.

I had a bit of a thought(stop sniggering) and measured the voltage between the screen earth on the transformer and the chassis. The screen earth comes out of the windings with the primary so no way of knowing how it's connected..anyway there is 65 volts between screen and chassi/frame although I've no idea what this means.

ed · Post by ed » Wed Nov 14, 2012 3:16 pm

This is what is between the eart/shield wire and the frame/chassis ground. As I said really don't know what it means or if there is a voltage here normally.

andrew Ivimey · Post by **andrew Ivimey** » Wed Nov 14, 2012 5:13 pm

I'd be scared, really scared....

no, not really - only kidding! I might be cross because I'd be thinking that the transformer isn't working properly.

IslandPink · Post by **IslandPink** » Wed Nov 14, 2012 7:49 pm

Ok Ed, that's an electrostatic screen there is it, and I assume it was not grounded at that point, so floating ?
Probably acquired some voltage by proximity to the primary windings, what sort of resistance to ground pulls it down, and do you get any significant current with lower resistance values ?
Just checking for leakage.

Mike H · Post by **Mike H** » Thu Nov 15, 2012 6:45 pm

ed wrote:wall meter said 0.33 as it did yesterday, thats 330ma from the wall(249v). After 30 seconds the relay clicked and the meter jumped to 0.58, thats 580ma. So the HT transformer is using 250 ma and the secondaries are not connected to anything.........the only thing eating into the 250ma is the 12v relay which uses 16ma(720R coil)......now I'm scratching my head big time.

Fooookinell

That is a lot. Too much. It is just one single mains transformer? I've lost track....

Is it still screwed onto chassis? Next thing to try, take it out, and try in on a bit of board, no cover no screws, see what it measures then. This is to eliminate all the usual suspects for shorted turns.

If it's got a ES screen (which should be connected to mains earth) then it's concentric wound (usually what it means, all layers on top of each other).

We do have an issue sometimes ('we' meaning me & Dave @ Danbury) with split-bobbin type formers because it means poor coupling between primary & secondaries, so mains leakage or magnetisation current is more likely, also depends how good the quality of the laminations is, but 570mA is taking the pee

Les Reed · Post by **Les Reed** » Wed Nov 21, 2012 9:07 am

I may just be lucky, but for years I've only used Majestic Transformers for all my power supplies. Specify the max. VA you expect for each winding and they build them with sufficient headroom and never get too hot, or hum/vibrate. I can't remember what their exact spec. is, but they are always heavier and larger than you were expecting

ed · Post by ed » Wed Nov 21, 2012 12:49 pm

I am in danger of losing track here as I've been posting about this elsewhere....

as a recap I took both transformers out of the chassis and ran them on the bench.....with secondaries in a screw block(no load whatsoever) both transformers consume 250ma(that is each tx consumes 250ma) at the wall and both get hot after 1 hour, not excessively but stil hot.

I wont get back to the manufacturer until I've fitted some shoulder washers and retested.

This has dented my interest considerably because I thought by specifying the output requirement I would get something usable....so far I am pretty sure these are not fit for purpose and I am considerably out of pocket...

if anybody can suggest a course of action I'd welcome the input. The Tx have been painted(fewl that I am) and the wires have been cut to fit.

Mike H · Post by **Mike H** » Thu Nov 22, 2012 12:10 am

Yes it's a pickle. Looking back this is:

Hammond 372FX (300-0-300 170ma) from Philip at Bluebell and decided to use an RS 2x9v 100va frame

I'm querying this with Danbury. I would say 250mA is excessive but need to check if I'm right. I'm guessing these are split bobbins. That usually means inefficient coupling and possibly high magnetisation current. Which will be aggravated by lower quality lams. Not saying they are but batches can vary, we've been caught out like that. Also the RS one could be borderline minimum construction for the total VA it's supposed to do.

If they were Danbury's he could test them in the exact same way, on bench no metalwork no load etc. just to prove it

Trouble is different people have different ideas about what a transformer should be like

ed · Post by ed » Thu Nov 22, 2012 12:18 am

hi Mike

I may be wrong but I think you've lost the plot here. I've had 4 more transformers since the ones you highlighted.

Did you think it was the ones you've highlighted that were drawing 250ma?

Mike H · Post by **Mike H** » Thu Nov 22, 2012 12:50 am

Oh yeah I forgot.

Still 240 x 0.25 = 60W, before you start taking any power out!

So 500 x 0.113 is another 56.5W, it's now 116.5W

Post by **Nick** » Thu Nov 22, 2012 8:11 am

Still 240 x 0.25 = 60W, before you start taking any power out!

Only if I and V are in phase.

Though I agree, it does seem a high value.

audio-talk

sv572 a tale of woe

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