Odd electrical problem, ideas?

[wardy]

My 2007 AB 42QRP has an issue: The air conditioners will only run when I have a load on the 12 volt side i.e. turn lights on. When just the standby load(s) i.e. inverters (in float mode) I can not use the AC's. But again if I keep lights on then they will run. And if I cut the lights off they shut down immediately. I hope someone has had this issue before!

I'm leaving in an hour for Sarasota Fl so I must figure this out or I guess I'll have to leave the basement lights on for night time...

Thanks in advance for suggestions or known issue help.

[wardy]

Some addl info. My inverter/converter on float charge is only reading 13.00 volts until I add load, then it will rise to 13.1-2 volts. Since that reading is very close to the batteries then I must assume there is some voltage drop at the thermostat. Does the stat cutoff or stop working below a certain voltage? Normally the converter should be around 13.6 volts for the float charge so maybe my inverter is going...

[Pds47]

Sounds like a ground problem When you turn on the light your A/C unit is getting its ground thru the light circuit.

[wardy]

Originally Posted by Pds47

Sounds like a ground problem When you turn on the light your A/C unit is getting its ground thru the light circuit.

That's a good thought. But I'm now at the campground and the AC runs fine during the bulk-charge phase. I'm thinking maybe the thermostat drop's off the AV when it get's below a certain threshold. I guess I need to measure the voltage at the therm when it's in the float stage. I really don't know... yet.

[BFlinn181]

Clean and check all battery cables, including ground connections. Weak connections could cause low voltage to thermostat, CO detector, etc.

[94-Newmar]

Interesting problem....
There is no physical switching between anything when the Inverter/Charger travels from BULK to ABSORB to FLOAT. Thermostats will work all the way down below 10VDC

Interesting test...
If your shore power is disconnected and with the generator shut down, all lights off, is/ are your thermostat(s) "awake" and showing temp? If not, by turning on any lights, as you describe above, do/does the thermostat(s) come on/wake up?

I'll be awaiting your findings :-)

[bruceisla]

Originally Posted by 94-Newmar

Interesting problem....
There is no physical switching between anything when the Inverter/Charger travels from BULK to ABSORB to FLOAT. Thermostats will work all the way down below 10VDC

Interesting test...
If your shore power is disconnected and with the generator shut down, all lights off, is/ are your thermostat(s) "awake" and showing temp? If not, by turning on any lights, as you describe above, do/does the thermostat(s) come on/wake up?

I'll be awaiting your findings :-)

Also, is it any 12vdc load (like turning on the water pump) or just the lights?

[don-deb]

IMHO.....I dont see the problem being a ground issue. I would think that the AC and DC system would be seperate and isolated............just my $.02

[BFlinn181]

The 12 v and 120 v are tied together in that 12v controls the thermostat, water heater, refrigerator. Without 12 v to thermostat, the A/C doesn't operate. When in the A/C won't operate, is the display blank on the thermostat? Does the fridge work? the water heater?

[wardy]

94-Newmar: Thanks for the information i.e. Stat working down to 10 volts as I could not find that spec from MFG. I was (still maybe) thinking that the stat relay(s) did not have enough voltage to hold "on". When my house voltage read 13.3-4 the stat voltage is 11.97 volts so drop yes but far above 10 volts.

Also: As asked, the stat appears normal (on) when this happens. It displays all 3 zones, is responsive to temp changes etc. Yes, the fridge and all 120 VAC appliances work when this happened. I made it through last night without this issue. I've been monitoring the house 12v system and it has not dropped below 13.2 vdc since I left yesterday (best I know since it's only by visual).

NEW: Last night the lights were pulsing some. Per voltage display it would toggle between 13.2 & 13.4 (float) but I'm thinking the pulse was greater than just .2 but the monitor could not react fast enough to give the true up/down. It had a cadence of about 1 second. This lasted for about 10 minutes.

With shore power off the stat looks "on" and is responsive. The stat voltage is 11.97 and the house is 12.7 after 5 minutes no load (other than inverters). If I turn all lights on (incandescent) the voltage holds at 12.4 & the stat reads 9.51!!!

[wardy]

Ok: Still on house batts now & did a little more VOM measurements. No load (inverters only) the house DC reads 12.6 (after 15 mins on battery) & the stat 11.2. But when I start to turn on banks of lights the stat really drops off even though the house voltage only sags to 12.4, the stat drops to 9.35

[wardy]

How is the stat powered, where? Unlike a home unit where it's the air handler.

[BFlinn181]

Check the house batteries for a bad cell or two. Could be 'tricking' the converter/charger into pulsing to try to bring voltage up.

[wardy]

Originally Posted by BFlinn181

Check the house batteries for a bad cell or two. Could be 'tricking' the converter/charger into pulsing to try to bring voltage up.

Good thought, I did check and all 8 are full of electrolyte & specific gravity reads consistent. Thanks for the help!