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transformer tap switches (relay or fets)

J

Jamie Morken

Jan 1, 1970
0
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:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?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:
http://rocketresearch.nekrom.com/new/transformer with tap switches/transformer-tapswitches.jpg

cheers,
Jamie
 
J

John Larkin

Jan 1, 1970
0
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:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?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:
http://rocketresearch.nekrom.com/new/transformer with tap switches/transformer-tapswitches.jpg

cheers,
Jamie

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
 
J

Jamie Morken

Jan 1, 1970
0
John said:
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.

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.
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.

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

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
 
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:http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=RM50...

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:http://rocketresearch.nekrom.com/new/transformer with tap switc...

cheers,
Jamie

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

- Show quoted text -

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