480/277 3ph Generator Battery Charger Circuit

[BackCountry]

For a 3ph 480/277 Generac generator, I’m seeing that T1/T2 are supposed to be 120v phase to neutral for the built in battery charger. Am I reading that right?

I don’t see a T1/T2 in their 200a rated transfer switch, so there must not be a step down transformer in the ATS.

I’m no where near a step down transformer with this installation, am I going to have to tap the load side of the ATS, install a fused disconnect and provide a 480x120/240 step down transformer to supply the battery charger circuit?

Generator number is RD05034, ATS is RTSW200K3

 

[don_resqcapt19]

Yes, you typically have to provide an external power source for the charger and heater circuits.
I have done exactly what you suggested a number of times where there was no close by circuit to supply power to the generator auxiliary equipment.
If the generator does not include an electric fuel transfer pump as part of the auxiliary load, you can tap either the line or load side of the ATS.

 

[BackCountry]

Yes, you typically have to provide an external power source for the charger and heater circuits.
I have done exactly what you suggested a number of times where there was no close by circuit to supply power to the generator auxiliary equipment.
If the generator does not include an electric fuel transfer pump as part of the auxiliary load, you can tap either the line or load side of the ATS.

I finally was able to find a line diagram.

It does have two step down transformers in the ATS, but they’re 480x240, no neutral.

The battery charger is 120 to neutral.

Looks like a tap is in my future, and a step down, and we’ll provide a receptacle as well. Dang. Wish that was built in!

 

[infinity]

What's wrong with using another power source? We usually use a circuit from an EM panel backed up by the generator.

 

[BackCountry]

What's wrong with using another power source? We usually use a circuit from an EM panel backed up by the generator.

I wish I could. Nearest backup panel is 500’ away.

Generator is being placed halfway between the service disconnect and three step down transformers. 500 feet to the step downs, and 500 feet to the service entrance (1000’ run).

 

[GeorgeB]

It does have two step down transformers in the ATS, but they’re 480x240, no neutral.

In my experience, most transformers of that type/size have 2 240V windings for the primary, and 2 120V windings for the secondary. If so, you would connect the primary in series and the secondary in parallel. The diagram is usually on the label.

 

[BackCountry]

In my experience, most transformers of that type/size have 2 240V windings for the primary, and 2 120V windings for the secondary. If so, you would connect the primary in series and the secondary in parallel. The diagram is usually on the label.

They’re built in to the ATS — I don’t see any way around doing a tap into a small dry transformer, unless I’m misreading something

 

[don_resqcapt19]

Those are control power and voltage monitoring transformers and not sized to supply any real loads.

 

[BackCountry]

Those are control power and voltage monitoring transformers and not sized to supply any real loads.

I wasn’t sure — I’ve seen some that have guidance to grab the ATS step downs for the charger (since its load is small).

Tap and transformer it is, that’s ok.

 

[infinity]

They’re built in to the ATS — I don’t see any way around doing a tap into a small dry transformer, unless I’m misreading something

How is this powered when the generator is not running?

 

[BackCountry]

It’ll be on the line side only. The generator has an alternator to charge the battery when the line side is opened.

 

[GeorgeB]

They’re built in to the ATS — I don’t see any way around doing a tap into a small dry transformer, unless I’m misreading something

I agree. I guess that's the way the cookie crumbles. Add a transformer.