30 amp variac instead of an autoformer?

Tuna, forgive me as I briefly give my broken record another spin:

Anyone with a decent inverter and batteries has 90% of what they need to cure any power issue short of a complete loss. Buy an Iota DLS charger and use an aux hookup instead of your shore power. Then charge with the Iota while inverting for your AC.

The Iota will chug along happily anywhere from 80 volts to 130 volts. I said EIGHTY volts. All that an Autoformer can do is take moderately good voltage (104v+) and turn it into perfect voltage. Below 104v it's just going to shut your power off. Your AC isn't going to have any issue with 104v, it's 90 v that it needs help with!

Would not inefficiency rear it's ugly head as BTU or Gauss in a transformer?

Don,
It looks like both of the devices you are asking about, the 30 amp variac and the 3000W voltage regulator are questionable in quality. The variac has a 25 amp fuse, for instance. the regulator has reviews with the totally substandard construction pictured. I wouldn't buy either.

What I would do is visit my local electronics surplus distributors and shop for an isolation transformer. You will pay more, probably, than these other solutions but have a more reliable and functionable device.

wa8yxm wrote:
Actually I would not use a Variac. they do a fair job of regulating voltage.. not as good as some other devices but a fairly good job, but they do it by wasting a whole lot of energy.. This means you may plug into a 30 amp park outlet but if you get 25 out of the Variac before you trip the breaker you are doing good (or you don't need it) You might notice the case is well vented and on that size most likely fan forced as well.

That said I do have a small one (Two small ones actually) I use in electronic testing.. but These are for the "Test Bench" normally not plugged in.

Since a variac is basically an auto transformer, I would expect it to be fairly low loss assuming a large heavy transformer with associated low I^2 R and magnetic loss. Not having ever used or considered one, can you quantify specified efficiency of some available variac examples rather than speaking in general terms?

Dick

Actually I would not use a Variac. they do a fair job of regulating voltage.. not as good as some other devices but a fairly good job, but they do it by wasting a whole lot of energy.. This means you may plug into a 30 amp park outlet but if you get 25 out of the Variac before you trip the breaker you are doing good (or you don't need it) You might notice the case is well vented and on that size most likely fan forced as well.

That said I do have a small one (Two small ones actually) I use in electronic testing.. but These are for the "Test Bench" normally not plugged in.

Hi Fred,

Do you happen to know the model number for the 40 amp coils at 12 volts each from Grainger?

pianotuna wrote:
Hi all,

Just to make life more interesting they also make a 5000 watt model.

Simran AR5000

Yes that would do it. I did not read the specs, but am guessing that the output voltage is automatic? But restricted to only 110 volts, while I prefer 120 volts for my motors.

I plugged in my refrigerator to the power post directly, as the refrigerator will work fine on anything from 90 - 119 volts, but hates boosted voltage that will increase amperage through the electric heat element, and thus possibly overheat the heating element and can lead to cracked tubing on the very expensive refrigerator. .

But my air conditioner likes 120+ voltage. While I will run it at 105 volts, I know how to replace that compressor without buying a whole new unit. At 110 volts, I will get out my 12 volt voltage booster. I bought a 40 amp rated 12 volt coil buck/boost transformer from Grainger.com and wired it to boost the incoming voltage by 12 volts.

So 120 in = 132 volts output. Fine in my case, as the TV really did not care, and when I turned on the A/C compressor, then the voltage dipped to 118 volts due to the 300 foot distance from the ranch house I was parked near for 4 years!

No you do not need to monitor the variac, just check the output voltage every hour or so. If it gets to 128 - 135 volts while the compressor cycles off on a cool day, that is OK for my application. (I ran 132 volts into my RV for all summer months for 4 years, and the TV never complained.) I did not run my inverter / charger at all during summer, I have solar charger 415 watts.

If the output from the variac is over say 125 volts, and you wish to reduce it a bit, most say to shut off the load, then move the control knob, and then turn on the load. I suppose if there is a 50 watt light bulb, and 0.5 amp load, then you can turn the dial under load, but I would not! If under 110 volts while under load, stop it, turn the dial, leave the compressor off for at least 5 minutes, and then turn it back on.

AS for input amperage. It is very easy to calculate and get away with 'consuming' 35 amps into the transformer and have 30 amps to the RV cord and on to the 30 amp main panel in the cool RV. Just use a 50 to 30 amp reduction adapter, and plug into the much larger 50 amp plug - more brass in the plug means less voltage loss across the terminals.

So here is a extreme example of my booster. It is actually 500 watts and has a pair of 40 amp coils at 12 volts each, isolated from the input voltage. I have a 3 way switch, so I can put 1 or both 12 volt coils inline with the output 30 amp wire.

While in Bowling Green KY, at Big Bend RV park and race track, I was in the pits, hooked up to a 15 amp receptacle, hooked up to #10 wire going to overhead #2 wires, with no fuses in site. My guess is someplace there would have been 150 amp (or 200?) fuses protecting the overhead wires. I had my 50' long #14 cord plugged into the 15 amp receptacle. Then a 25' long #12 cord, then a 15 - 30 amp adapter, and my 25' long #10 cord. Then the voltage booster, then the 25' long factory cord, and 10 more feet of #10 into the electrical panel. With the A/C running I was getting about 112 volts on 12 volt boost. AS others turned on their A/C units, the voltage dropped to only about 105, so I shut everything off, unplugged, switched to the +24 volt setting, and plugged back in. I now had 115 volts while the A/C was on. My guess was the input voltage was around 90? at the end of all those extension cords. Who knows how many amps, but only my A/C was running, and perhaps a 1 amp tv. (remember solar kept the battery full).

Also living 300+ feet from the main house would put a strain on the A/C if I did not boost it. I would see 132 volts on my wall mounted digital voltmeter all the time when the A/C is off. It does not bother me. . .

Yes I would use the 30 amp variac. Hopefully with 100 volts input it will put out a little over 113 volts, and that will be enough. This 10% boost means that input amperage will be about 11% more than the output amperage. So plan accordingly, and have a 50 to 30 amp reducer adapter handy.

No I do not worry about 130 volts going into my TV set, it never bothered it in 4 years at the ranch. The TV also works great when there was only 95 volts to it as well!

Good luck,

Fred.

Hi all,

Just to make life more interesting they also make a 5000 watt model.

Simran AR5000

I do not believe in buying products and pushing them to within an inch of their capacity, so I think this might just do the job for me. It does weigh in at 43 pounds.

Hi all,


A seller answered your question, "If the input voltage is 105 what would the output voltage be? Can it raise it to 110?" about Simran AR-3000 3000-Watt Heavy Duty Voltage....
VCT ELECTRONICS answered:
"Yes, it will automatically adjust it to 110/120V"

pianotuna wrote:
Hi Gde,

I am not looking for "over parity" devices. I'm looking for a voltage boost. I know that costs more amps.

Sure you can boost the voltage going to the A/C which would reduce the current draw of the A/C. BUT the device boosting the voltage would then in turn demand more input current..

Even worse is the boosting device will insert considerable line loss of energy in the form of heat.. That loss also means that the booster is consuming some energy in the process adding that loss to the input current of the booster.

In the end, the A/C draws some less current, the booster draws more current and add the loss in heat of the booster and the over all result is a net loss.

Putting it another way.. boost 108V at 30A, 10% increase of voltage gives you 118.8V but now the booster will add 10% MORE current to the input which would be 3A of additional current PLUS what ever loss due to the transformer losses in heat say 1A.. You are now 34A of current..

Keep in mind that you could set your fridge to propane, that would free up 275W-325W depending on the fridge.. That just may be enough to stop the tripping breaker..

Thinking outside of the box, perhaps consider a window A/C unit?

RV A/C units are terrible for efficiency, window A/Cs reuse the condensate water by splashing over the condenser coils. This effectively allows the A/C to give more cooling power per watt than a non splash A/C which is what a RV unit is.

I use two window A/Cs in my 26ft TT, a 10K BTU and a 6.5K BTU, combined I get 16.5K BTU but they use a little less wattage than the 13.5K RV A/C unit they replaced..

Having two allows me to only cool part of the trailer if I want or if limited power (20A) I can turn on the 10K BTU and allow it to run to get trailer somewhat cool then turn the 6.5K on to get it to comfy temps.. I am able to do that when I stop at my Cousins house with 100F to 110F outside temps and not pop their 20A breaker..