Saturday, June 10, 2023


RVelectricity – Hughes Autoformer testing – Part 3

By Mike Sokol

Disclaimer: Hughes has not offered to pay me for this test, and I neither asked for nor received any compensation. But Hughes did send me a 30-amp version of the Autoformer for testing with the understanding that I have 100% control over all tests and publication of my data. I have offered to share my results with them after the testing is done. So you can be assured that whatever data I gather and conclusions I come to are unbiased. In short, I don’t have a horse in this race. It’s just an interesting engineering question to answer.

Hughes Autoformer measurements

I’ve just gathered the next set of voltage and current measurements showing how the Hughes Autoformer works with a 15 kBTU Dometic Penguin II air conditioner, this time using the stock starting capacitor.

Just the facts, ma’am…

It’s now operating with the voltage/current boost ratios that all my textbooks predict should happen. By itself, none of this data is conclusive one way or another in terms of reversing the NEC decision to ban all booster transformers from campgrounds as of the 2020 code cycle.

Yes, as soon as any local authority authorizes use of the 2020 National Electrical Code, then any type of voltage booster transformer is a violation. That doesn’t mean that the code police will be looking for transformers on your RV. But it does mean that any campground in that jurisdiction can deny supplying your RV with electricity unless you remove it. Hey, don’t complain to me. I’m just the messenger.

It’s all in the pictures

In all of the pictures below, the top two meters are the pedestal voltage (left) and amperage (right) after my own Variac transformer. So this is just like a campground with a sagging voltage prior to going through the Hughes Autoformer.

The bottom two meters are what’s coming out of the Hughes Autoformer, again with the air conditioner voltage (left) and current (right). I don’t have four matched/calibrated meters yet, but I’m planning on acquiring matched units for the next test, so don’t get excited.

Running the numbers

As you can see, I’m starting around 120 volts at 14.2 amperes, and taking it down a few volts at a time, finally ending up with the pedestal supplying 15.2 amps to the air conditioner when campground voltage dips down to 100.2 volts. However, note that the Autoformer is working as intended by keeping the voltage being supplied to the air conditioner up at 107.5 volts.

Even more experiments

So now I have to do several sets of experiments with and without the Hughes Autoformer in-circuit to determine if it creates too much extra current draw in a campground, or if it actually can reduce current draw from an air conditioner that’s operating on extremely low campground voltage. Or is it a break-even that may help air conditioner efficiency without drawing excess campground amperage?

Stay tuned next month to this same bat-channel to find out.

In case you missed them, here are Hughes Autoformer Testing – Part 1, and Hughes Autoformer Testing – Part 2.

Okay, everyone. Electricity is a powerful friend, unless you don’t respect it. Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.



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1 year ago

Do you have an estimate on when part 4 will be out?

Daniel Pankiewicz
2 years ago

I can’t find part 4 as mentioned above. Can you give an update? Is this the end of your fantastic research on this device?

RV Staff
2 years ago

Thanks for asking, Daniel. I asked Mike and he says he’s working on it in his bat cave. 😆 So you’ll read about it as soon as he’s done. Take care. 😀 —Diane at

2 years ago

From my understanding the NEC rules are for park installed buck boost autoformers not plug in end use user devices. This is an important distinction. The reason for the rule change was to prevent parks from using them to avoid changing out undersized and or inadequate wiring. A park could in theory boost the voltage to avoid upgrading the wires.

2 years ago

Looking forward to your continued testing.

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