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Electrical Problem


TJones

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We have a Travel Supreme TSO40. We have a 2000 watt inverter with solar system that is eight years old.

 

The problem: When the AC cycles on there is a momentary loss of power to the other parts of the electrical. This does not happen every time however frequently enough to be a Pita. The power shuts down for about a half second, just enough that the microwave will lose power to hold settings. The directv box and TV shut off and reboot.

 

Any ideas what could be causing the momentary interruption. I am guessing a power drop when the AC kicks in.

 

Ideas on how to diagnose.

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First, assuming you are hooked to shore power, the inverter and solar have nothing to do with the problem.

 

It does sound like a power drop when the AC kicks in.

 

Something in the power string from inside the RV to the shore power or the shore power itself is not working correctly.

 

It could be low voltage coming from the shore power and nothing to do with your RV.

 

Or it could be something wrong with your power cord going to the shore power.

 

Do you have the knowledge and experience to start trouble shooting with a meter?

 

Any chance this happens when one AC is in cooling cycle, the water heater is heating and the 2nd AC starts its cooling cycle?

 

Intermittent problems are some the hardest to figure out.

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When your AC cycles on, there is enough of a voltage drop to cause the voltage sensitive items to lose memory. The only way to solve this, is to provide a better source of power that can handle all the loads without that much voltage drop. This is not a total drop of power, just a quick and momentary lowering of voltage that causes your problem. You will need a much larger supply of power and cabling to overcome the voltage dip.

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Tony, if this is occurring at more than one campground, then good chance there's a weak termination or connection somewhere in the 5er or the cabling to the power pedestal. If only one campground, likely it's a problem on their side.

 

In either case, what's occurring is the high starting current for the AC is causing the voltage drop as Al and 57 explained. If the problem is in the 5er, I'd first go around and see if you can find any obvious sources which might show up as a warm/hot cable plug or circuit breaker. It could be nothing more than a loosened screw in your breaker panel or frayed connection between the cable and plug. Be careful and pull power at the pedestal before you go anywhere near energized connections.

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Are you on Shore Power or generator?

 

SCClockDr is on the right track. Too little information for folks to be very helpful. You're solar setup is "out of the loop" though so shouldn't be an issue.

 

Aside from what SCClockDr asked.. is your rig 30 or 50 amp? Size, number and brand of AC/'s? If on genset.. what type and output rating (watts)?

 

You mentioned your inverter... I'm going to assume you're actually on shore or genset power, but if there is a chance you're actually trying to power your AC unplugged off your inverter then 'that' would be you're problem right there. The startup "pull" from an AC would most certainly cause a "brownout" throughout your rig. If that is the case then it's no fault of your power system.. solar and a 2000watt inverter just aren't up to the task of running even a moderately sized AC unit. No getting around that one.. ;)

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Tony and Pamela, I'm thinking your guess "I am guessing a power drop when the AC kicks in" IS CORRECT

 

When the AC's compressor engages there can be a short term current draw of maybe 5 or 6 times its normal run current, which drops voltage across resistive wire runs or contactors or connections in the power supply anywhere from the pedestal throughout the RV to the AC. Extreme low voltage (brown out) can cause electronic devices to loose their mind and re set.

 

HOWEVER what you describe above isnt typical, so if its NOT the RV parks problem???????? but your RV problem (check RV pedestal voltage, does it do it at different parks or only one????) I suspect 1) A loose burned resistive connection (panel or breaker or AC input junction box) or 2) A faulty power cord especially one of its connections/terminals or the plug 3) A compressor or capacitor (if it is a capacitor start) problem.

 

Like Clock man asked is there an EMS that may be sensing the low voltage???

 

If the parks pedestal isn't exhibiting extreme voltage drop when the compressor engages and causing the problem (IE voltage drop is in the RV system), Id look in your panel and check and tighten if needed all the connections especially the breaker that feeds the AC and the AC circuits Neutral connection,,,,,,,,,,Then open the junction box where the circuit connects to the AC and check all that,,,,,,,,,,,,,,If its NOT any RV pedestal or power cord or circuit or connection problem, the AC compressor (or capacitor if it has one???) or the relay/contactor comes to mind.

 

Looking in the panel and AC junction box and plug connection (if not molded) for loose or burned connections isn't that difficult, give it a shot. NOTE while voltage readings are of course relevant and needed, its the voltage and V = I x R voltage DROP WHEN THE COMPRESSOR ENGAGES that's the problem, and that wont show up taking readings when current isn't being drawn.

 

Obviously I'm talkin about shore power which your solar and inverter has nothing to do with.

 

John T

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A transfer switch issue is another possibility. If setup giving the inverter priority then when the voltage sags it shifts to Shore/Gen causing the interrupt. Also if the contactor coil is a bit weak and/or the contacts pitted it could be losing contact during the start-up surge.

 

The reason I asked about AC coil cleaning is the added stress on the compressor leading to hard starts and excessive current draw while running. (Went through this very scenario this summer in our new to us, Unit Two. Previous owner ran the AC 24/7/365 for 2 years straight parked under a metal RV port in FL W/O any maintenance. The compressor began drawing 20+amps running and more to start. Our Honda 3000si refused to start it unless ECO was off and even that failed near the end.)

 

Was any recent electrical work done?

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I would check ALL the AC connections for tightness. Inside the main panel also.Disconnect AC power, get a screwdriver and go at it. I had a loose connection in my transfer box which finally burned up the transfer box and left me without any AC. Why it did not burn up the coach is a good question.That was a high resustance connection for a while.

After more thought do the DC stuff also, Engine quit going down the road. Only error light that worked was the ABS. Saturday 100 miles from Albuquerque. Good Sam towed my 40 ft motor home to the shop. Service tech was there. Loose connection on a 50 amp 12v connection, he said.

Picked up coach on Monday. LUCKY

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There is also a distinct possibility that the start capacitor in the air conditioner has failed or is failing. Replacements only cost $10 or so and can make a huge difference. Some of the replacement capacitors available are even an improvement over the original. The start capacitor stores up and releases power during the start cycle so as to reduce the maximum amount of current needed to start the unit. I recently noticed that my unit was starting slowly and making a "groaning" noise. Replacing the start capacitor fixed it.

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Rif and others, to your post "The start capacitor stores up and releases power during the start cycle so as to reduce the maximum amount of current needed to start the unit." Looks like we both agree a bad starting capacitor (if his unit has one) is one of the many possibilities that might cause his problem.

 

Let me explain in more detail how start capacitors actually function for those who may not be aware. This is ONLY a brief very basic guide and not intended to be all inclusive nor 100% accurate.

 

Actually, when the motor starts there's no available stored up power in the capacitor "assuming" ???? its typical a split phase capacitor start motor. When the motor shuts down the start winding centrifugal switch closes, so any energy previously stored in the capacitor discharges through the windings.

 

HERES THE DEAL: While its true a charged up capacitor stores energy, its only a matter of time before its depleted subject to resistance and insulation and discharge current paths (like windings) plus other factors that eventually bleed it off. A single phase motor, unlike a three phase, is NOT self starting so the out of phase start winding is necessary to get the shaft initially rotating in one direction. The PRIMARY reason a start capacitor is used in the start winding is to increase the phase shift between the start winding and the run winding (which has no capacitor) and it does so in part because voltage lags the current when power is applied. This also increases the starting torque. Some motors also have a "run" capacitor in the run winding but that serves a different purpose.

 

Best wishes n God Bless, fun sparky chattin with yall

 

John T It was nearly fifty years ago I was an engineer with Century Electric Motor Company and my memory is getting weak lol so no warranty but believe this is still accurate.

 

PS I just found this website, it explains how and why the capacitor provides added phase angle between the start (Is) and run (I'm) windings for starting and shows a circuit diagram of the energy discharge path when the motor stops and the centrifugal switch is closed. Hope it helps.

 

http://www.brighthubengineering.com/diy-electronics-devices/44951-learn-about-capacitor-start-induction-run-motors/

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