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transformer tap switches (relay or fets)

Hi,

I am using a transformer with tap switches to accomodate a wide input voltage range, initially I was going to use fets for the tap switches (two in series for each tap switch with sources and gates connected), but since the tap switch frequency is very low (lower than once per minutes average) I think relays may be better to use for this, also there is no power transfer during switching so the relays should last long.

The transformer is driven by an Hbridge with 500VDC, and the max pulsed current is around 15amps.

Any suggestion on good relays to use for these tap switches?

I was thinking this one might work:

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?name=RM507024-ND

Hard to get at digikey (min 100 quantity). Anyone have another source for high voltage relays rated to at least 5000VA, and with the UL approval.

Heres a picture of the transformer with the tap switches:

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cheers, Jamie

Reply to
Jamie Morken
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Interesting. When you drive the 62 volt tap, the rest of the primary acts like an autotransformer, and you could get huge voltages/spikes out of the 500 volt tap. That could be hard on fets.

How about using some DPDT relays and switching some windings from series to parallel? That would improve transformer efficiency dramatically, by using most of the copper most of the time.

Is the primary current 15 amps peak when driving the 62 volt tap?

John

Reply to
John Larkin

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Yes I think I will need some RC snubbers for this at the least, or else maybe this is another reason to go to high voltage rated relays, especially on the 500V tap.

I think I would have to have more leads to separate the primary coils for that, also except for the 62V and 125V coils the turns counts wouldn't match up.

Yes, the power drops as the lower voltage taps are selected, at the

62Volt coil I think the peak current will be under 10amps.

cheers, Jamie

Reply to
Jamie Morken

urce

Big switching transformers usually have split/sandwich windings, your tap changing might not be as simple as you think.

Reply to
cbarn24050

work:

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?name=RM50...

switches:

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I don't understand, do you mean because the coupling between the primary and secondary will be reduced if using only the part of the primary that is selected from the tap switch?

cheers, Jamie

Reply to
Jamie Morken

source

If you only change one half of a split primary you will increase the leakage inductance of the transformer.

Reply to
cbarn24050

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