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Old 05-25-2009, 07:47 PM   #1
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how low is too low AC voltage?

I'm preparing for a weekend trip to a relative's driveway. I know that the standard 30 amp hookup will not be available. So, I'm planning on using the standard converter to 15 amp household current. Yes, this is fine for everything but air cond. and in a nice August summer in Indiana, the A/C will be necessary. I have my trailer plugged in to 15 amp AC via an extension cord to my garage when I am at home. So, the other day, I turned it on just to see if a breaker would blow or something would die. When I kicked on the A/C compressor, the AC voltage (via a std. RV plug-in gauge) dropped to about 100V and then stabilized at 105V. I have a newer Carrier A/C unit so the whole argument of "older units are sensitive" does not apply. So my question is: how low of AC voltage is too low? My plug-in gauge shows that the 105V lies in the "red zone", but is this conservative? If it only dips that low when the A/C is on is it really a concern? I anticipate that the A/C will only be on at night when we're trying to sleep, so shouldn't be much else running to draw current.
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Old 05-25-2009, 08:20 PM   #2
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It sounds to me like you have made up your mind.
I would not run AC below 105VAC and I would not run AC thru a 30amp to 15amp plug, you will melt the plug, I have two of them from the PO the tried that. The amp draw is too much, while you AC unit may survive, there is too much of a risk of fire at the plug. My own opinion, somebody else may refute.
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Old 05-25-2009, 08:32 PM   #3
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mind's not made up... just whether or not I feel confident in running the AC at 105V or if the family sleeps w/ windows open and hope that the temp. outside drops low enough that it makes it bearable to sleep.
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Old 05-25-2009, 08:56 PM   #4
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Hey Jason,

I'd be hesitant to pull the AC through a 15amp plug. If the cirucit is dedicated you may get away with pulling a light load. If it were me I'd opt for for a shady parking space (if possible) and a couple of fans. Do you have access to a generator?

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Old 05-25-2009, 09:26 PM   #5
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mind's not made up... just whether or not I feel confident in running the AC at 105V or if the family sleeps w/ windows open and hope that the temp. outside drops low enough that it makes it bearable to sleep.
Running an AC at 105 volts, will put you in the market for another AC, sooner than you think.

When an AC runs on low voltage, it's current draw actually increases. That in turn, is making the compressor work even harder, until it decides "enough" and then burns up.

The answer is easy. When the AC voltage will be low, "DON'T".

Andy
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Old 05-25-2009, 09:30 PM   #6
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The A/C compressor (read: high-buck$ piece of equipment) has been documented here at AIR as requiring 22-23 amps for unstrained startup. I've understood that a standard 3-prong 15 amp outlet could eventually get it up and running. Without adequate amperage, startup will take something longer and add significant strain to the unit. How many times do you want to do this? 3 times? 5 times?

I spent a trip to near Chicago to look at a really cool Overlander. The owner had burned out his 2nd A/C and still had it hooked up to a low-gauge 15A extension cord and was clueless about his part in wrecking the previous units. I passed it up for unrelated reasons but definitely factored the dead A/C into the equation.

How long do you want to own this unit? Ripoff place or not, Camping World lists something approaching $1000 for smaller units. Installation extra? Add it up.

I've had an electrician out recently and his estimates for installing a 30A circuit at our home was short of that. A significant cost -- but short of me ruining the A/C and having to replace it.
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Old 05-25-2009, 09:47 PM   #7
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Recently there was a 2007 CCD at our shop for some repairs, the person had just purchased the trailer. Among the things that needed work was the nearly new air conditioner. The compressor was DOA. I found the "smoking gun" in the bumper compartment: A melted and burned to a crisp 30 amp to 15 amp power adapter.
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Old 05-25-2009, 10:07 PM   #8
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Ok I think we all agree that if you are running a Ac you should never run it on a 15 amp circuit ONLY A 20 amp circuit...PERIOD..... Sounds good to me I trust the experts.
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Old 05-26-2009, 07:34 PM   #9
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OK. So we've definitively established this as a bad idea. For the record, though, my A/C unit got up to steady operation and was blowing cold air, thus why I wondered if 105V really was too low. A 30 amp outlet at my house might be a future installation, but I'm going to be at a relative's house for a weekend so I don't think he's going to have a 30A 110V outlet installed just for me for 2 days. I guess I jsut hope for a cool night with a light breeze.

Kinda back to the "original" question though...how low is too low AC voltage? 110? 105? is 105 OK if the A/C isn't running? are there other conditions that effect things and low limit of the range? Or do I just blindly trust the red/green area on my volt meter and forget about the science / theory behind it?

One last thought...would it be possible to convert a 50A 220V line (i.e. welder outlet) to 30A 110V? I'm kinda an electrical dummy so would it just be as simple as taking the two "hot" poles of the 220 line and joining them into one line of larger gauge wire. There's 3x more wattage there than what 30A x 110V could draw so I assume it would have no issue supplying the juice.
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Old 05-26-2009, 08:14 PM   #10
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One last thought...would it be possible to convert a 50A 220V line (i.e. welder outlet) to 30A 110V? I'm kinda an electrical dummy so would it just be as simple as taking the two "hot" poles of the 220 line and joining them into one line of larger gauge wire. There's 3x more wattage there than what 30A x 110V could draw so I assume it would have no issue supplying the juice.
Your question would be answered as soon as you joined the 2 wires together. You would have an explosive ark blow the fuses and maybe start a fire.

However you can use "one leg" of the 220 circuit fused for 30 amps and create a 30 amp receptacle. Let the other leg float at the box or remove it altogether from the fuse box. Removal is the safest approach.

I would use 110 as a rule of thumb for the low limit for operating the AC.
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Old 05-26-2009, 08:28 PM   #11
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220 is just two 110 hots and a ground. Usually coded as 110-Red, 110-Black, and a Ground-Green. You can drop the red or black to go to a 110 circuit. A 50amp/220 should have the wire size to carry your service loads, however the issue of capacity is determined by wire gauge and circuit length. Voltage drop is your primary concern at that point.
PM me if you need a copy of the voltage drop formula.

Most of the know world uses 220/240 in everyday applications. It's much more efficient. But then again, we still love our inches, feet and yards too.
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Old 05-26-2009, 08:55 PM   #12
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When I was a kid, the standard house voltage was 110 and for the really big bad stuff (stoves primarily), 220. Somewhere along the line it became 120 and 240 v. Back in the ancient times, 50 amp service for a house was pretty normal, now it's 200 or more.

I still think 110 and 220, but I try to remember it's 120 and 240. The point of this is there's a lot more difference between 105 v and 120 v than 105 v and 110 v and, therefore, 105 v. is just not enough. If we continue to think in the former standards, we easily deceive ourselves to what's ok. The AC will cool just fine for a while, but when it dies, well, you know the answer.

So, if you want to have a 30 amp. receptacle for shore power, and you are an electrical dummy, hire an electrician. You can get a book on how to do residential wiring and buy a multimeter to check what you are doing, and it's great to know how to do electrical work. But when I installed a 30 amp receptacle, I got it all screwed up even though I have rewired several houses. Yeh, I fixed it before I did any damage, because I was smart enough to test and retest with the multimeter, but you have to know what you're testing for.

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Old 05-26-2009, 09:10 PM   #13
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Well, I think I'm just screwed all-around and once again when faced with the topic of AC electricity...I am going to run and hide. I'm not about to "disassemble" my welder outlet or anyone else's in order to obtain weekend power for my trailer. I was thinking that one could make an "adapter" of sort that could convert the 220 (240, sorry) to 120 w/ increased amps but it seems that the best I could hope for is 120 w/ 1/2 the amps of the 240 so like 25 amps. Baaahhhh...kinda makes me wonder how the heck RV parks get 30 or 50 amps to each site. Then again it helps explain why some can't!
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Old 05-26-2009, 10:46 PM   #14
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Well don't give up yet!

You actually have 50 amps of 120 v for each leg. You can indeed make an adapter with a 50a welding plug on one end and a 30a receptacle on the other end. It will give you a full 30a at 125V.

In fact, Camping world will sell you one ready made.
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