208V to 480V Transformer

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Little Bill

Little Bill

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Tennessee NEC:2017
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I was asked to give an estimate for connecting two chargers for stand-up lifts. I looked at the chargers and the name plate says:
AC input
Voltage: 480V, Three Phase, 50/60Hz
Max current: 10.8A
No. of Modules 3
DC Output
Voltage: 36V
Max Current: 176A

I then checked the building voltage and it is only 208/120V 3ph.
My question(s) are would it be better to have one transformer large enough for both loads?
Or, would it be better to have a transformer for each load?

I was thinking of a single transformer to power a small panel and feeding each charger from the panel.
Also, in either case, would I need primary and secondary protection?

Disclaimer: I'm almost transformer illiterate!:(
 
drcampbell said:
Have you considered getting 208-volt chargers?
Click to expand...
That would be preference one.

At 10a and change, I'd say a single transformer feeding a little panel would be better and cheaper than two transformers.

The best way to visualize a job is to draw it on paper, with everything involved shown and labeled; then ask us questions.

Added: Interesting that the output power exceeds the input power using simple multiplication.
 
I'm with Larry, one transformer feeding a small panel, or if it's more cost-effective/available, one transformer with two sets of secondary conductors each feeding a safety switch. Might go with a15 kva depending on the nature if the loads.
 
One transformer is a better way to go than two, but I also agree that no transformer is an even better option.

They want to pay for a transformer, disconnect, secondary grounding electrode, 480V panel (which ain't gonna be cheep), and run up twenty four hour a day transformer losses just so the charger can be powered up by a 15A, 480V circuit instead of 30A, 208V circuit?
 
ActionDave said:
One transformer is a better way to go than two, but I also agree that no transformer is an even better option.

They want to pay for a transformer, disconnect, secondary grounding electrode, 480V panel (which ain't gonna be cheep), and run up twenty four hour a day transformer losses just so the charger can be powered up by a 15A, 480V circuit instead of 30A, 208V circuit?
Click to expand...

Believe it or not, I actually told them they would be better off to get different chargers that are 208V. The guy I talked with was not in charge (totally anyway). His boss is on vacation and he's going to give him all the info when he gets back.

The way I understand it, the corporate just sent down new lifts w/chargers and didn't get nor ask for any voltages that were present. My best guess is they use the same equipment in their mfg plant and just sent these assuming everything was the same. The building where I'm at is just warehousing & shipping. They have plants all over the States.

I'm just gathering info about the transformer in case they are determined to go that route.
 
LarryFine said:
That would be preference one.

At 10a and change, I'd say a single transformer feeding a little panel would be better and cheaper than two transformers.

The best way to visualize a job is to draw it on paper, with everything involved shown and labeled; then ask us questions.

Added: Interesting that the output power exceeds the input power using simple multiplication.
Click to expand...
don't forget to multiply input by 1.732, it says it is three phase input and DC output.
 
It’s not uncommon for companies to do this sort of thing, they will negotiate a price for equipment based on nationwide use, and those buyers don’t know an amp from a volt. It even happens internationally sometimes, which is an even bigger PITA for a local electrician...

Yes, you likely need primary and secondary protection which will skew the value proposition toward one larger transformer. Just make sure your 480V secondary is 4 wire 480Y277 even though you don’t need the 277. Id the secondary is Delta, it gets more complicated because you either need to add Ground Fault Monitoring or you need to corner ground it, but more importantly most power electronic systems do not like Delta sources.

So on the 208V side, even if it is a Wye configuration you would NOT connect the neutral to ground, but on the secondary side you WOULD ground the neutral, even though you don’t actually run a neutral conductor to anything.
 
If you're in the business of doing electrical installations to make money then give them what they want. :cool:

I agree use a step up transformer and a panel to distribute the 480 volts.
 
All good suggestions. However:
Maybe consider calling one's supplier and checking on the price.

Application is 8.8kva x 1.25 = 11kva.
2 each 15kva,
or
1 each 30 kva

Make a guess at the installation costs, one xfm vs two xfm

Shouldn't be a tough choice.

My guess (no better that the average shoe clerk):
Does matter much. Go for the ease of installation.
 
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