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Author Topic: Air Conditioner amperage draw at low voltages  (Read 2183 times)

Art Welter

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Re: Air Conditioner amperage draw at low voltages
« Reply #20 on: September 29, 2018, 03:08:41 pm »

Note there is indeed a 2 amp or so increase in the compressor motor current when the voltage is reduced from 115 to 105 volts. But the shaded-pole fan motor has a decrease in current when the voltage is reduced from 115 to 105. So the effect is real and substantial.
The roughly 10% increase in amperage with a 10% reduction in voltage Dometic noted seems to correspond  well with what " Desmostylus" wrote 4/26/2005:
"Reduce voltage by 1%, slip increases by 2%, reducing impedance by 2%, current increases by 1%."

Between the increased amperage from the air conditioner and refrigerator compressor motors, sunlight directly heating connectors, and increased electrical resistance on worn connections, not surprising to see connectors burn/melt at low voltage in the campground.

Art
« Last Edit: September 29, 2018, 03:18:36 pm by Art Welter »
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Mike Sokol

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Re: Air Conditioner amperage draw at low voltages
« Reply #21 on: September 29, 2018, 09:01:48 pm »

The roughly 10% increase in amperage with a 10% reduction in voltage Dometic noted seems to correspond  well with what " Desmostylus" wrote 4/26/2005:
"Reduce voltage by 1%, slip increases by 2%, reducing impedance by 2%, current increases by 1%."

It will be interesting to see what happens to the amperage as the voltage drops down to 93 volts, which is the lowest reported campground voltage so far. It obviously can't be linear, with a 50% reduction in voltage causing a 50% increase in amperage. But it's possible that dropping the voltage down into the mid 90's could increase the amperage by 20% or so, and that will probably lead to a lot of internal heat buildup in the compressor.
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Mike Sokol
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Mike Sokol

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Re: Air Conditioner amperage draw at low voltages
« Reply #22 on: September 29, 2018, 09:05:28 pm »

Between the increased amperage from the air conditioner and refrigerator compressor motors, sunlight directly heating connectors, and increased electrical resistance on worn connections, not surprising to see connectors burn/melt at low voltage in the campground.

While there's an increase in the amperage draw, but since the wiring is protected by the upstream circuit breaker, I'm not sure it would cause the connector to overheat. But that's EXACTLY when my readership suggests...
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Tom Bourke

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Re: Air Conditioner amperage draw at low voltages
« Reply #23 on: September 30, 2018, 06:44:32 pm »

While there's an increase in the amperage draw, but since the wiring is protected by the upstream circuit breaker, I'm not sure it would cause the connector to overheat. But that's EXACTLY when my readership suggests...
That breaker is going to have a trip curve.  The cycling of the compressor is probably just enough to keep the breaker from tripping.  However the connectors and wire are still being over heated each cycle.  I think your seeing cumulative damage.
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Tim McCulloch

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Re: Air Conditioner amperage draw at low voltages
« Reply #24 on: September 30, 2018, 09:55:25 pm »

While there's an increase in the amperage draw, but since the wiring is protected by the upstream circuit breaker, I'm not sure it would cause the connector to overheat. But that's EXACTLY when my readership suggests...

They're talking about the shore cord 14-50 at the pedestal or related CS series connector at the coach?  Or something else?

I've read a number of electrical threads at the "Miss Manners" RV forums and some of the crap people think is real simply astounds me... Then there are a couple of retired electricians who set some of them right...
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Mike Sokol

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Re: Air Conditioner amperage draw at low voltages
« Reply #25 on: October 01, 2018, 07:56:27 pm »

They're talking about the shore cord 14-50 at the pedestal or related CS series connector at the coach?  Or something else?en there are a couple of retired electricians who set some of them right...

Yes, but it's usually a 30-amp TT-30 (Travel Trailer) receptacle and cordset that overheats.
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Art Welter

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Re: Air Conditioner amperage draw increases at low voltages
« Reply #26 on: October 01, 2018, 10:10:41 pm »

Yes, but it's usually a 30-amp TT-30 (Travel Trailer) receptacle and cordset that overheats.
Because most every receptacle in the campground has been serially abused by people plugging in with their AC and refrigerator on, arcing and pitting them out, covering the connections with carbon deposits..
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Tim McCulloch

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Re: Air Conditioner amperage draw increases at low voltages
« Reply #27 on: October 01, 2018, 10:56:41 pm »

Because most every receptacle in the campground has been serially abused by people plugging in with their AC and refrigerator on, arcing and pitting them out, covering the connections with carbon deposits..

Yepper.

De-energize the outlet, connect, re-energize.  Turn on AC or water heater, charge house battery(ies).

NO hot connections - why is it a difficult concept.
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Tim McCulloch

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Re: Air Conditioner amperage draw at low voltages
« Reply #28 on: October 01, 2018, 10:58:17 pm »

Yes, but it's usually a 30-amp TT-30 (Travel Trailer) receptacle and cordset that overheats.

I'm with Art, I was just trying to figure out *which* connections were doing the Joan of Arcing...

Also my mind is in Class A 50 amp land (my next RV, sometime, maybe) so a hard-wired TT30 cord set didn't immediately present itself as the connector under suspicion.  :-[
« Last Edit: October 01, 2018, 11:02:45 pm by Tim McCulloch »
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Jonathan Johnson

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Re: Air Conditioner amperage draw increases at low voltages
« Reply #29 on: October 02, 2018, 12:20:51 pm »

Yepper.

De-energize the outlet, connect, re-energize.  Turn on AC or water heater, charge house battery(ies).

NO hot connections - why is it a difficult concept.

Why hasn't anyone designed an interlocking switch/receptacle panel where the RV plug can't be connected or disconnected with the switch on?

It could be as simple as a switch handle that covers the receptacle and plug when on. I think every RV I've ever seen has a right-angle plug, so it shouldn't be too difficult.
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Stop confusing the issue with facts and logic!
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