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I believe an autotransformer will correct maximum 10% for low voltage. Your 150 ft cable already eats up 8%. Not much margin left over.

What's taking all this juice? Heaters? You usually want good ac regulation for motors & compressors.

pianotuna wrote:

Voltage drop is in the range of 8% (pretty high) for #10 wire. That takes it down to 110 from 120.

My install

Cord (park to RV)
"line" RV inlet to added 50 amp outlet
Autoformer
Added 50 amp "Pigtail" from Autoformer to ATS.

And that's how you shoudl do it.

Logic:
Device is at the RV end of things so line loss in the shore cord is included in what it looks at when deciding if boost is needed,, Also it's out of sight so passing sticky fingers do not stick to it.. Likewise it's always there so I can not forget it cause I'm only here for the one night.

And some parks,, Have a "No Autoformers" rule. so they too won't see it,, I just plug in direct via my surge guard.

And that's all.

Hi Salvo,

I would be using #10 cord (a 120 foot and a 30 foot) and plugging into a 50 amp shore power service while drawing up to 30 amps on one leg.

Voltage drop is in the range of 8% (pretty high) for #10 wire. That takes it down to 110 from 120.

The other leg will be 20 amps X 2 and I'd be using #12 cord (x 2). That leg will not be going through the autoformer. Each 20 amp would be doing no more than 13 amps into resistive loads. These would exhibit 6% drop to 112 volts.

My inclination was to put the autoformer at the RV.

Salvo wrote:
Do you have a 150 ft extension cord? What size conductors? That could be a huge voltage drop. Will an autotransformer correct a 20V drop?

Agree, it goes at/in the RV. You don't care about voltage at the other end of the extension, only voltage at the RV.

From an efficiency point of view, having it before the cord is fractionally better, but probably not sufficiently so to worry about too much. Just be aware that you're trading current for voltage, so for a given power consumption the current carried by your cord and the campground outlet is higher with the autotransformer than the current going through the RV. Don't skimp on the cord.

From a keeping ownership of the autotransformer point of view, having it next to your RV is probably better, especially if you can have it inside the RV or chained securely to it.

I used a 6/3 130' cord and was only able to pull 11 amps out of it before voltage drooped into the DO NOT USE A/C range. So I connected a multi-tap 2Kw transformer at both ends and blew out a 20-amp receptacle. This was back in the 70's. Long distances are murder on volt drop. Remember a 150' is really 300' forth and back. I recommend studying some tables - worst case loading, then figure out if arriving voltage exceeds the boost percentage capacity of your new gizmo. And be kind to the sending receptacle. I figured out it was wired with 10-gauge so on went a 30-amp twist lock. Gizmos are like solar panels they grow legs with running shoes. It goes on the load end of the circuit - your rig.

Do you have a 150 ft extension cord? What size conductors? That could be a huge voltage drop. Will an autotransformer correct a 20V drop?

I would want the autoformer to be at the RV end of the cord so it's seeing the maximum voltage drop, and correcting as needed.

If the autoformer is inside the RV it is not nearly as likely to be stolen, even if that is not the better location (I have no idea which end of the shore cord is better for efficiency)