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Old 05-27-2009, 07:36 PM   #29
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Voltage Drop can be calculated several ways:

Using Ohms Law

Voltage Drop = Current In Amps x Resistance in Ohms

Or you can use this following typically formula:


Voltage Drop = K x 2 x Wire Length in Feet x Current in Amps
Wire Area in Circular Mils

K = Specific resistivity in ohm – circular mils / foot
K = 11 for copper in circuit loaded less than 50% of capacity
K = 12 for copper wire loaded aluminum wire in circuit loaded to 50 to 100% of capacity
K = 18 for aluminum wire

Another interesting tidbit. If the line voltage doubles (say 120 to 240) the voltage drop decreases by a factor of 4.
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Old 05-27-2009, 07:41 PM   #30
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The forumal is supposed to be K x 2.... over Wire Area in Mils... but it won't align as formatted for some reason...
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Old 05-27-2009, 08:22 PM   #31
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Just get the largest gauge cord you can find #10 would be great,plug it into a kitchen or laundry outlet [20 amp] with your adaptor,run it for 30 mins, then feel ithe cord and plug see if its warm or hot.If its hot-----you better not---My old 75 ac runs fine on a 50' 12 gauge cord.You never told us what gauge cord you were using.A larger size can make a HUGE differance. Try it you will be happy

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Old 05-27-2009, 09:35 PM   #32
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whew! a guy goes to work for the day, spends some time working around the house, then time w/ family and then reads the threads before bed; and whoa!

My welder outlet (remember, I'm electrically dumb) is a 3 prong. Not sure what that means with relation to making a 120v 30a conversion, but that's what I got and the welder works just fine w/ it.

Yes, I do have a generator, but it wouldn't be suitable for travel, much less the noise it makes. I've got a 6500W generator that is a my backup for the whole house when the power goes out (yeah, that's a common occurrence here, especially in winter, and I don't like $^%#@* freezing up nor my deep freeze thawing out). The thing is on a cart...not exactly portable to a campsite nor is it quiet. Funny story though...it is a 220v generator (needed that for my well pump). It has a 4 prong 220v on it and when I'm using it, I back-feed its power to the house via my welder outlet in the garage. Being electrically stupid, I didn't know what I was doing but I wired it up anyway. Funny, some lights in the house were REALLY bright. Later, I corrected that. Now it works like a charm. But back to topic...

So when I tested my AC in the AS, I was juicing the AS with (yeah, I know a lot of you will cringe) a std. orange 100' ext. cord...yeah, the 14AWG variety. But, I knew I wasn't going to run the AC long. It was just a test. So the breaker for the outlets in the garage is 15A at the box in the basement; if I flicked on the AC in the AS drawing through a 15A circuit and didn't blow the breaker and still maintained 105V in the trailer through a 100' 14AWG cord...isn't this a good sign? As in: if I were connected to a 15A outlet via, say, a 12AWG cord that was only like 25' long that I might be in good shape? Or better yet I get close enough that my umbilical is long enough and then I use a thick-gauge 15/20A to 30A conversion dogbone? Seems good enough in my hillbilly logic.

Regardless, I think that a 15/20A plug at my relatives' house is going to be my only option. I'm banking on a nice breeze, but still bleeding dumb electrical ideas just in case.
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Old 05-27-2009, 10:59 PM   #33
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Jason,

I hope you have a nice cool breeze, because frankly some of your ideas scare me to death. I recommend you hire a good electrician before you try anything on your own.

Really, experimenting with backfeeding 240 through a welding outlet? No neutral?

I wouldn't post anymore of your ideas in case your insurance underwriter is reading this.
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Old 05-28-2009, 06:39 AM   #34
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There's no experimenting. It's set up and it gets used regularly. If I'm doing wrong by that then you better start a crusade through rural central Ohio because I am not the only one. As a matter of fact, when the power is out for long periods of time, you can step outside and hear the hum of generators all over the place. When you are without power for 3-4 days sometimes; you can't just go away and come back when the power is back on. People that have big farms, especially with livestock, can't go more than a few hours without electricity without starting to lose major $. The way I set things up is how most people who already have a large-amp outlet somewhere at their house do their connection to a generator.

Granted, a lot of what I post is just food for thought. I post to see what the reactions of people are. A lot of people have one idea of the way things MUST be. That's not me. We must remember that many of the discoveries in this world have been via chance experimentation or accident. If we don't try and wonder, then we don't learn.

So to tie everything together in this thread...again back to the original topic: how low is too low AC voltage? This question has not been definitely answered because there's no real right or wrong answer, but I was looking for experience of someone who broke / blew up something on their own that knew what their voltage was at the time. Some people have responded that they go lower than 100V with seemingly no problems. Some have said they use extension cords without issue. Some have taken the hard line of "give me 115V or give me nothing". And that's fine. But like everything there's a tolerance band. For example, your tires: typical load range E tires have a max pressure of 80psi. So like to run 50, some 60, some 70, some 80. Some vary thier pressure based on load. Some don't even thing about the pressure unless they see something visually wrong with the tire. I can go through numerous other examples but the point is that each person has a comfort zone. Based on where I live and what I must be prepared to deal with, my tolerance band is generally pretty wide on lots of things. You can't take the hard line against mother nature.

And for the record, I know my insurance agent personally and he's very happy that I have a generator. The first time there was a major outage and he had to pay me a lot of money...he was happy to hear that I got a generator after that.
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Old 05-28-2009, 07:01 AM   #35
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Jason,

I don't mind that you use a generator. I don't even mind that you backfeed through a large amp outlet. I really mind that you do it right. If you feed split phase power through a three prong outlet, you're using your ground wiring for neutral. Please put in a four prong outlet.

While I'm sure your insurance agent is happy, I doubt that the underwriters would feel the same way.
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Old 05-28-2009, 05:46 PM   #36
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the information on the spec sheets for your air cond. unit. do you have a model number of the unit?
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Old 05-28-2009, 07:33 PM   #37
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Ricky...thanks for reminding me. I looked that up. It's a Carrier AirV (the standard model, w/ heat strip). When running the AC it's drawing max 12.8A. Ironically, but it makes sense I guess, when running it on heat mode it draws 13.8A. So, if I do the math that I think I understand from being told on the forums before anytime I've asked electrical questions: 115V x 12.8A = 1472W. Therefore, at 105V, I'm drawing 14.0A (max) which in turn would not trip the breaker. As for the 100' cord, yeah, bad idea for sure. But, it was for testing purposes, not long term use.

So, I'll go to my relatives' house prepared for boondocking and hope that I can get close enough to an outlet that perhaps I can draw enough current (safely) to run the A/C at least to put a chill in the AS as we're all trying to drift off to sleep.
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Old 05-28-2009, 08:50 PM   #38
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i think you're blending can with should in respect to survival of the equipment. while even if you had the amp capacity, if the voltage drops too low, you still operate the unit beyond its designed limits.

you understand about cords now, so you know that wiring, connectors and cords can all become unwilling fuses that 'blow' in an unsafe manner.

one other thought is one of those portable air conditioners. i think they draw less than the roof unit but you would still need to maintain voltage at a safe level.
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Old 05-28-2009, 08:56 PM   #39
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the best answer will come from the manufacturer :-)

Carrier Transport Air Conditioning
715 Willow Springs Lane
York, PA 17402
Ph: 1-800-673-2431
Fax: 1-717-764-0401

http://www.penndda.com/carrier/pdf/c...V_Brochure.pdf
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Old 05-28-2009, 10:56 PM   #40
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Jason, where do you get 115 v.? Taking an average of 110 and 120? Does it makes it closer to 105? I think you're bending the numbers to talk yourself into something. I hate sleeping in the heat—I don't sleep well and if I were in a trailer I'd sure want to run the A/C. Sometimes you can't, or you can get away with it for a while, but you are straining the unit and will shorten it's life. You won't know why it lasted several months or a year less than the average A/C, but it could be because of pushing the limits.

The A/C is designed to operate at 120 v, but will operate at more or less because power companies do not provides exactly 120 v., so there's some range of voltage that's ok, but then you get into a grey area and efficiency drops faster and faster. My power company used to provide a little more than 117 v., but they've improved the distribution system and they are now closer to 120. The further you get from 120 v., the less efficient appliances and electronics become.

That 12.8 amps is probably the normal amps once the unit has started. It will draw considerably more when the compressor is starting. Anyway, optimal is 120 x 12.8 = 1,536 watts. And not tripping the breaker does not mean you aren't damaging the A/C .

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Old 05-29-2009, 06:37 AM   #41
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115v came from Carrier's documentation...the rated input by Carrier is 115V @ 60 Hz. Carrier even does the math for you to tell you that it needs 1472W. According to the documentation, the 12.8A is a "Full-Load Amps" rating. The locked motor draw is 60A, but if the motor's locked then I've got other issues beside the electricity going to it.

So, no, I'm not talking myself into anything, just reading what the manufacturer has provided to the world.
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Old 05-29-2009, 05:06 PM   #42
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You shouldn't connect a generator to your house through a backfeed arrangement. You must use a transfer switch, otherwise you are pumping electricity back through the grid... and could zap a lineman who believes he is working on a cold wire.

I wonder if the 12.8 full load amps is the normal operating draw or the starting amperage? Worth checking with an ammeter. I would want to ensure that things are okay at startup, when the load is highest. The startup condition will occur every time the unit cycles, which is often enough to cause a problem with low voltages.
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