500va Transformer

wreck-it-steve · 9 Apr 2014

Hi,

I have a 500VA control panel transformer (55-0-55) that I want to use in a project, what is the max rated current of a 500VA transformer?

I tried to calculate it and got about 4 amps??

Also on the primary side it has terminals for: 10v-0v-220v-240v

what is the 10v for?

Thanks

PrenticeBoyofDerry · 9 Apr 2014

Deleted as Rubbish!

winston1 · 9 Apr 2014

stevo66 said:
Also on the primary side it has terminals for: 10v-0v-220v-240v

what is the 10v for?

Thanks

Connect 0v and 220v for 220V supplies (Europe).
Connect 10v and 220v for 230v supplies (NI).
Connect 0v and 240v for 240V supplies (UK).
Connect 10v and 240V for 250V supplies (Nowhere as far as I know).

winston1 · 9 Apr 2014

PrenticeBoyofDerry said:
The 10V is the voltage given on the secondary output.

Rubbish. The 10v is a primary tap. The secondary output is 55-0-55V.

JohnW2 · 9 Apr 2014

PrenticeBoyofDerry said:
The 10V is the voltage given on the secondary output.

No, that's wrong. Arrangements like "10v-0v-220v-240v" are a standard way of arranging primary tappings to give versatility of input voltage (the '10V' is 'on the other side' of 0v, phase-wise, from the 220v and 240v taps):
With a 220V supply, connect it to 0v and 220v
With a 230V supply, connect it to 10v and 220v
With a 240V supply, connect it to 0v and 240v
With a 250V supply, connect it to 10V and 240v

Kind Regards, John
Edi: whoops - winston1 typed faster than me - but at least our replies were almost identical

ericmark · 9 Apr 2014

JohnW2 is spot on no need to say any more about that.

As to power 500VA = 9A at 55 volt and 4.5A at 110 volt so yes I would fuse at 5A being the closest fuse to 4.5A I could find.

Control panel transformers are normally 110 volt not 55-0-55 as only one fuse is required with 110 volt. Do check if really 55-0-55.

wreck-it-steve · 9 Apr 2014

Thanks for all your replies. There are terminals for 55v 0v 55v

PrenticeBoyofDerry · 10 Apr 2014

winston1 said:
Rubbish. The 10v is a primary tap. The secondary output is 55-0-55V.

Sorry of course you are correct, brain not functioning correctly.

Jackrae · 10 Apr 2014

The concept of 55-0-55 is for the 0 point to be grounded (earthed) such that neither output terminal of the 110 volt secondary exceeds 55 volts with respect to earth. All UK 110 volt utility tool transformers (the yellow ones) are wired like this (or at least they should be)

As to the secondary current rating the maximum current is 500/110 = 4.5amps

You cannot connect both secondary 55 volt outputs together to produce a 0-55 volt output at 9 amps. Doing so places a direct short circuit across the secondary

wreck-it-steve · 10 Apr 2014

Jackrae said:
The concept of 55-0-55 is for the 0 point to be grounded (earthed) such that neither output terminal of the 110 volt secondary exceeds 55 volts with respect to earth. All UK 110 volt utility tool transformers (the yellow ones) are wired like this (or at least they should be)

As to the secondary current rating the maximum current is 500/110 = 4.5amps

You cannot connect both secondary 55 volt outputs together to produce a 0-55 volt output at 9 amps. Doing so places a direct short circuit across the secondary

Thanks for your reply. So when wiring it all up I should connect the 2x 55v terminals to my equipment (to produce 110v) and the 0v terminal to earth?

JohnW2 · 10 Apr 2014

stevo66 said:
So when wiring it all up I should connect the 2x 55v terminals to my equipment (to produce 110v) and the 0v terminal to earth?

If your equipment wants 110V, you will certainly have to connect it to the two 55V terminals. However, the question of what (if anything) you should connect to earth is a much more complicated question, and depends on factors such as the nature of the equipment and the arrangement of protective devices you will have.

KInd REgards, John

wreck-it-steve · 10 Apr 2014

JohnW2 said:
stevo66 said:

So when wiring it all up I should connect the 2x 55v terminals to my equipment (to produce 110v) and the 0v terminal to earth?

Click to expand...

If your equipment wants 110V, you will certainly have to connect it to the two 55V terminals. However, the question of what (if anything) you should connect to earth is a much more complicated question, and depends on factors such as the nature of the equipment and the arrangement of protective devices you will have.

KInd REgards, John

I was going by what Jackrae wrote: "The concept of 55-0-55 is for the 0 point to be grounded (earthed) such that neither output terminal of the 110 volt secondary exceeds 55 volts with respect to earth. All UK 110 volt utility tool transformers (the yellow ones) are wired like this (or at least they should be)"

JohnW2 · 10 Apr 2014

stevo66 said:
I was going by what Jackrae wrote: "The concept of 55-0-55 is for the 0 point to be grounded (earthed) such that neither output terminal of the 110 volt secondary exceeds 55 volts with respect to earth. All UK 110 volt utility tool transformers (the yellow ones) are wired like this (or at least they should be)"

Yes, what Jackrae wrote is true of site tools in the UK (e.g. as used on construction sites), but we have no idea of what sort of equipment you plan to power from this transformer, or how you plan to deal with protective measures.

Kind Regards, John

wreck-it-steve · 10 Apr 2014

JohnW2 said:
stevo66 said:

I was going by what Jackrae wrote: "The concept of 55-0-55 is for the 0 point to be grounded (earthed) such that neither output terminal of the 110 volt secondary exceeds 55 volts with respect to earth. All UK 110 volt utility tool transformers (the yellow ones) are wired like this (or at least they should be)"

Click to expand...

Yes, what Jackrae wrote is true of site tools in the UK (e.g. as used on construction sites), but we have no idea of what sort of equipment you plan to power from this transformer, or how you plan to deal with protective measures.

Kind Regards, John

The transformer will provide a control circuit in a control panel (contactors, relays, lamps etc) the primary side will be protected by a MCB and the secondary either single pole MCB, double pole MCB or quick blow fuses

Not yet sure on the correct protection for the secondary side.

JohnW2 · 10 Apr 2014

stevo66 said:
The transformer will provide a control circuit in a control panel (contactors, relays, lamps etc) the primary side will be protected by a MCB and the secondary either single pole MCB, double pole MCB or quick blow fuses ... Not yet sure on the correct protection for the secondary side.

This outside my sphere of experience, so I'll leave others to comment. However, for such an application (as opposed to site tools) I can see no obvious reason why you would want to earth the centre point of the secondary (i.e. the 0v terminal of the 55-0-55). That would leave the choice between leaving the secondary 'floating' or connecting one side of it (one of the 55V terminals to earth), and there are all sorts of issues to consider there.

Protection-wise, if you wanted/needed RCD protection on the secondary side, you would have to have one end of secondary connected to earth and install an RCD on the secondary side, since any RCD on the primary side would offer no protection on the secondary side.

... now over to the experts!

Kind Regards, John

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500va Transformer

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