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?

[valhalla360]

BFL13 wrote:
Not a clue, so ignore if wrong, but ISTR about air conditioners sometimes becoming increasingly difficult to start when cycling due to some kind of build-up. Can't remember any details.

Weird about the microwave!

The compressor pushes the freon (yeah it's nor freon anymore) to the high pressure side. As the high pressure side increases, it takes more torque to spin the compressor.

If you shut the air/con down for a few sec and then try to start it up again, the high pressure side hasn't reduced, so you have the compressor trying to overcome both the high pressure and the electric motor start up load...result it's much harder to start. (most newer electronic thermostats have a 5min delay to let the high pressure side come down).

I'm confused regarding the microwave.
- Is the microwave plugged in but off and it suddenly starts running?
- Are you trying to run the microwave while the air/con is running?

Someone beat me to it regarding the plug in voltage meter. You may see it drop into the 104-108v range before any odd operation starts but as you say, without the plug in meter, by the time you get your handheld meter out, you've passed the point of no return.

[dougrainer]

1. I would REPLACE the ATS. Why? Because you state it has worked for years. ATS boxes have Points and those points get pitted over the years and will not securely lock in place when the relay's transfer. You could attempt to file the pitted contacs but it is better to replace the complete ATS.
2. Now, you COULD open the ATS and find the GEN INPUT and the OUTPUT to the RV Main breaker box. Disconnect those 2. Using heavy duty Wire nuts, connect the Black to Black and White to White and Ground to ground and then run the system. IF you have no problems, then the ATS is the problem. Doug


PS. the actual Amps of a RV AC unit is 11.5 to 14.2 at ambient temps below 95 degrees, depending on the BTU size of the AC. Lower than 95 degrees the amps drop.

[HadEnough]

HTElectrical wrote:
You could also eliminate the transfer switch by connecting power directly to your electrical panel and see if the issue is still there. Check to make sure your Neutral connection is tight, breaker is not shorting out where it snaps onto bus bar, and also lug where your 120v line connects at bus bar is tight.

Definitely. Thank you. I’m going to work through this ASAP on a cool morning. Maybe tomorrow

[HTElectrical]

You could also eliminate the transfer switch by connecting power directly to your electrical panel and see if the issue is still there. Check to make sure your Neutral connection is tight, breaker is not shorting out where it snaps onto bus bar, and also lug where your 120v line connects at bus bar is tight.

[HadEnough]

time2roll wrote:
Consider a voltage monitor so next episode you can just glance over and observe.



https://www.amazon.com/Monitor-HOMREE-Voltmeter

Done!!!

That’s a good idea. I can never get my meter on it in time. Being able to instantly see will help a lot.

It’s arriving tomorrow

[HadEnough]

enblethen wrote:
Option genset set is a 2.5 Onan
Units come with an 8.9k AC.
Should have plenty of power for Onan or a 2000 watt genset.

Exactly. 2.7kw portable Honda generator and 2.5kw Onan LPG onboard generator.

I’ve had this rv for 4 years now and run these generators all day long all the time. Using the portable for economy and less hours in the Onan to run air conditioning 8 hours a day for weeks on end.

We are full time and off grid.

These generators have both worked fine for years and years and thousands of hours.

[time2roll]

Consider a voltage monitor so next episode you can just glance over and observe.



https://www.amazon.com/Monitor-HOMREE-Voltmeter

[Matt_Colie]

Had,

You have a lot of good answers here, but one I have not seen is one that I have experienced. I don't have much, but a lot of people that do pay me to fix things. One thing I have discovered in both the AC and DC wiring of boats and RVs is that the terminals get loose over time. I do not know if it is vibration or thermal cycling, but one of the first things I do when an owner is having trouble with a system that used to be entirely reliable is to go in an tighten every terminal and screw I can fine.

So, I suggest you get a good flashlight (because you want the power off even on the DC side) and a nice strong screwdriver and go at it. If typical, this will not be comfortable and will take way longer than you are thinking, but every time you get another 1/6 of a turn on anything, you will know that you are making progress....

This was the cheap fix. If you need more, you have to buy a monitor called a Kill-A-Watt that plugs into a receptacle to monitor voltage and a clamp on ammeter to find out what the A/C is doing.

Best of luck

Matt

[enblethen]

Option genset set is a 2.5 Onan
Units come with an 8.9k AC.
Should have plenty of power for Onan or a 2000 watt genset.

[3_tons]

ktmrfs wrote:
the question that hasn't been asked or answered

What is the watts rating on both of the generators? It could be they are marginal and when the outside temps rise, AC current rising, you are overloading the generator.

Per the OP’s previous it happens even when the air conditioner is off...This suggest that the air conditioner malady is likely a symptom and not the actual root cause... JMO

3 tons

[ktmrfs]

the question that hasn't been asked or answered

What is the watts rating on both of the generators? It could be they are marginal and when the outside temps rise, AC current rising, you are overloading the generator.

[enblethen]

Using 3 tons, list it would be number 3 to distribution panel input terminals.
OPs portable genset would not pass through transfer switch genset warm up circuit.

[3_tons]

For reference, the ATS has 3 sets of contacts as follows:

1) Shore power in
2) Generator in
3) power out to main panel

FWIW, There may be a small DIN switch on the ATS’s logic board used to defeat the genny warm-up delay...

Since the microwave is intermittent, I would initially confine my search to the incoming power supply.

3 tons

[enblethen]

Problem happens using on board or portable gensets, indicates to me that issue is between transfer switch output and the 120 volt AC distribution panel.
I would say the neutral!

[HadEnough]

SPRey wrote:
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.

Not that. Because both generators do the same thing pretty much. The only difference is the onboard generator is smart enough to turn off when there is an issue. The one connected to the shore power just keeps going and the cycling happens.

I was thinking about doing this. Plugging it directly into the 120 V and bypassing the transfer switch as a test.