Basic Question About AC Power Wiring

[HadEnough]

How are RVs usually wired up?

I have a standard arctic fox RV and I’m having trouble with the AC portion of the wiring.

Symptoms:

*After running an air conditioner for 4-5 hours, off an external generator connected to the shore power cable, I get a brownout” situation and the microwave turns on and off every second or two repeatedly during this brownout.

*Its getting worse. Sometimes I get the same thing on startup. Other times it randomly works great for hours and hours.

*when I use the onboard generator, it will either work great or it will have the same type of problem as the external. HOWEVER, when the external generator would have the brownout or cycling, the onboard generator is smarter and just shuts down.

*there seemed to be a VERY long delay tonight using the onboard generator before the power came on.


So far I’ve looked at the transfer switch. I opened it. Hard to see the contacts, but they didn’t really seem to do anything actually probably because I was on the shore power generator. And it was working fine.

So my question is related to diagnosis.

What components are involved?

What components are common to the shore power and the onboard generator such that they can cause brownouts, cycling on/off of power and the onboard generator to decide to shut down?

I’m looking hard at the automatic transfer switch but I don’t see any problem.

It seemed to get better a bit when I exercised the main breaker on the panel, but it’s intermittent and that may not even be it.

What components are there to check?

[Timmo_]

Could it be the generator is not providing sufficient power? I believe most RV AC's require around 16 amps (1920 watts or so)

A simple test would be to directly plug into 120v service and see if the problem persists.

[enblethen]

Sounds like a bad connection.
That is why it is necessary to check the connections through out the system.

[cavie]

Sounds like a transfer switch problem. Open the TS and check with a voltmeter while you are having the problem. Get to the wire connections. Also check all connections in the 120-volt breaker box.

[HadEnough]

cavie wrote:

enblethen wrote:
I am guessing you have the truck camper with 30 amp shore power and no genset.
I would start by checking the connections in the 120 volt AC power distribution panel.
Pay close attention to the neutrals (white wires) in the back of the panel. I would suggest getting some electrical de-ox grease. Disconnect each wire, one at a time, check for brittle or melted insulation. If there is enough slack cut this portion off. Apply a good coat of de-ox grease, and re-terminate.
Check connections on the circuit breakers in the same manner.
Check the shore power connection in the small junction box. Make sure those are clean and tight. Coat connections in de-ox grease. Your cord may go straight to the 120 volt AC panel.
Careful about using the AC and microwave at the same time.
Check the cord body on the shore power cord for any signs of melting or black blades.

OP stated that he has a transfer switch so not likely a truck camper

Actually. It is a truck camper, but that’s not relevant to the discussion of an electrical system so I didn’t bother with it.

[HadEnough]

Just remembered one other thing.

It did the brownout type behavior with the microwave actually running once too.

Mid microwaving of a baked potato, the microwave bulb dimmed, the fan and magnetron slowed down and I quickly jumped to stop it for fear of damage.

[cavie]

enblethen wrote:
I am guessing you have the truck camper with 30 amp shore power and no genset.
I would start by checking the connections in the 120 volt AC power distribution panel.
Pay close attention to the neutrals (white wires) in the back of the panel. I would suggest getting some electrical de-ox grease. Disconnect each wire, one at a time, check for brittle or melted insulation. If there is enough slack cut this portion off. Apply a good coat of de-ox grease, and re-terminate.
Check connections on the circuit breakers in the same manner.
Check the shore power connection in the small junction box. Make sure those are clean and tight. Coat connections in de-ox grease. Your cord may go straight to the 120 volt AC panel.
Careful about using the AC and microwave at the same time.
Check the cord body on the shore power cord for any signs of melting or black blades.

OP stated that he has a transfer switch so not likely a truck camper

[HadEnough]

wa8yxm wrote:
You may have a problem with the A/C. Go topside (up on the roof) and if it's a Coleman (they suck, a good thing) take a good look at the condenser. Is it "Crudded up"? (Yes Remove the outer cover and peal the crud off) 4 screws on top.

most other models. (They blow, more efficient but read one)
Remove the outer cover (Generally around 10 or more screws along the bottom of the cowel) (See note) then remove the inner cover over the condenser (may be a few screws or a major job involving cuttng metal tape and bending tabs) and inspect if needed clean. and re-assemble

NOTE: you may be able to inspect using a mirror without removing the inner cover over the condenser.

Why: If the condender is "Crudded up" it can not shed heat as fast as it is deisgned to, as the heat builds in the A/C's system the pressures rise. the compressor has to work harder and harder, Draws more and more current and ..> Well. Bad things happen. On my 50 amp rig the click of darkness (Tripped breaker) perhaps you are just overloading the generator.

How would that be possible when the behavior happens with the air conditioner OFF???

AGAIN, IT’S AN ELECTRICAL PROBLEM

[wa8yxm]

You may have a problem with the A/C. Go topside (up on the roof) and if it's a Coleman (they suck, a good thing) take a good look at the condenser. Is it "Crudded up"? (Yes Remove the outer cover and peal the crud off) 4 screws on top.

most other models. (They blow, more efficient but read one)
Remove the outer cover (Generally around 10 or more screws along the bottom of the cowel) (See note) then remove the inner cover over the condenser (may be a few screws or a major job involving cuttng metal tape and bending tabs) and inspect if needed clean. and re-assemble

NOTE: you may be able to inspect using a mirror without removing the inner cover over the condenser.

Why: If the condender is "Crudded up" it can not shed heat as fast as it is deisgned to, as the heat builds in the A/C's system the pressures rise. the compressor has to work harder and harder, Draws more and more current and ..> Well. Bad things happen. On my 50 amp rig the click of darkness (Tripped breaker) perhaps you are just overloading the generator.

[HadEnough]

3 tons wrote:
I’ll venture a guess or two...

Since this malady happens with either generator (with only a slight variation) I’d look elsewhere...

Since the Microwave begins to cycle off and back on, that’s a huge clue that the 120v power supply is intermittent to the RV’s main breaker panel...This also results in a intermittent power supply to the air cond, causing an overheating condition at the compressor’s passive thermal overload switch - thermal switch subsequently auto-resets...

The ATS switch has a gen-start time delay option (for gen warm-up) of about 15 to say 30 sec - this is normal...But if the power supply to the ATS Switch is intermittent, the time delay will re-occur with each power interruption...

Bottom line is that either the ATS is defective or there is a faulty connection somewhere between the power cord and (or at) the ATS...

JMO,

3 tons

Ok, you are understanding the symptoms very well.

Only slight differences are:

1) the gen startup time delay doesn’t happen when the power cycles on and off every second or two on the generator that’s attached to the shore power cable.

2) when this cycling is happening, the air conditioning unit runs like it’s experiencing a brownout. Fan slows, compressor slows. Then I get scared of damage and quickly turn off the air conditioner.

ATS was also my first thought . I opened it, looked through it, but didn’t see the problem. I’ll look much more thoroughly as a first try.

The control for the ATS is electronic, right? Like the circuit board in a refrigerator that can (and does) go bad?

I haven’t fully understood how the ATS works yet. I see a solenoid and a pair of contacts with a spring. I don’t HEAR any of the clicking sound it normally makes when it comes on and starts the power during the cycling. It just rapidly cycles on and off without making a sound.

[Dusty_R]

Maybe try an infrared temperature reader and look for a hot spot in the wiring.

[time2roll]

HadEnough wrote:

time2roll wrote:
Run a 1500w space heater full and continuous and see if you have the same issue.
How old is the air conditioner? May need a clamp-on ammeter to check the draw and compare to specs.

It’s a power issue, not an air conditioning issue

OK and low power will not hurt the space heater.

[BFL13]

That cycling on/off reminds me of the 12v low voltage shut off with the inverter. It shuts off, then the 12v recovers without the inverter load, so the inverter comes back on and then again shuts off, keeps doing that "cycling" on/off.

So you could have a 120v load that is overloading the 120v supply that comes and goes like that when it is on. Not always. Converter? Water Heater? Not always on when the MW is on or the A/C, but when they are it does that?

[3_tons]

I’ll venture a guess or two...

Since this malady happens with either generator (with only a slight variation) I’d look elsewhere...

Since the Microwave begins to cycle off and back on, that’s a huge clue that the 120v power supply is intermittent to the RV’s main breaker panel...This also results in a intermittent power supply to the air cond, causing an overheating condition at the compressor’s passive thermal overload switch - thermal switch subsequently auto-resets...

The ATS switch has a gen-start time delay option (for gen warm-up) of about 15 to say 30 sec - this is normal...But if the power supply to the ATS Switch is intermittent, the time delay will re-occur with each power interruption...

Bottom line is that either the ATS is defective or there is a faulty connection somewhere between the power cord and (or at) the ATS...

JMO,

3 tons

[HadEnough]

time2roll wrote:
Run a 1500w space heater full and continuous and see if you have the same issue.
How old is the air conditioner? May need a clamp-on ammeter to check the draw and compare to specs.

It’s a power issue, not an air conditioning issue

[HadEnough]

BFL13 wrote:
I thought a lock-up would pull a whole bunch of power and cause what you are seeing.

No, that’s disproven by the fact the microwave can cycle on/off every second or two at startup without the air conditioning unit on.