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ajpaero · 07-23-2017, 11:40 AM

It's been posted before that the mystery switch near the microwave is the electric water heater switch. While that is true, I ran into an interesting problem while boondocking this week.
After only 2 days & nites of boondocking, all 4 of my house batteries were at abt 11.5 Volts. We had been running the generator for air conditioning and battery charging during the day We run my wifes CPAP on batteries at nite.
I took the less than 1 year old batteries to the local Interstate Battery distributor to exchange under warranty. They tested very repeated with possible bad cells. He said that this situation is very unusual.
He gave me 4 loaner batteries to use while he charged and tested my batteries. He suggested that perhaps the converter was not providing wnoug charging current/voltage and to test it using the loaner batteries.
We also have 150 watts of solar panels charging the batteries.
Everything went well for 2 nites, but battery voltage was down to 11.5 Volts this morning. I checked charging voltage with the generator running and it was about 11.5 Volts. While pondering the cause of the drop, the generator RPM increased and charging voltage jumped to 12.3 Volts. After a few minutes the generator RPM and charging voltage dropped. There was no apparent load on the system.
Then I noticed that the mystery switch was on. I turned it off and generator RPM and charging voltage increased and stayed at normal levels.
CONCLUSIONS:
Mystery switch on may activate heating element in water heater when on battery power. Causing excessive drain on battery.
When running generator, for A/C, microwave, etc, it provides no charging current to house batteries.
It may be that whomever installed the switch in my MH messed up.
MORAL OF THE STORY. Make sure Mystery Switch is OFF WHEN BOONDOCKING.

Hangfive · 07-23-2017, 03:52 PM

Couldn't help noting that you may have an electrical issue. While on a land line or generator your house batteries should be charged by the integrated battery charger that is usually located below the house circuit breaker panel that has AC and DC circuit breakers. This charger converts 110v into @ 12.8vdc square wave to charge your batteries. If it hasn't been upgraded to the new electronic controlled style, your batteries are being cooked, as it isn't smart enough to know when they are fully charged. Progressive Dynamics makes several replacement chargers that are easy to wire in in place of the old style. I upgraded to the 80W unit when I replaced my cooked batteries.

4x4van · 07-23-2017, 04:00 PM

I wonder if your electric water heater element has been wired through an inverter?

Hangfive · 07-24-2017, 01:35 PM

Yeah, my water heater element is 110vAC

MontyL · 11-25-2017, 07:21 PM

4x4van may be on to something...

Is the CPAP AC powered, plugged into a 110 outlet? If so, it seems you have an inverter (12DC > 110AC) built into the rig, and it's wired in such a way as to be able to power the water heater.

Our mystery switch is tucked under the right side of the sink.

MartinP · 11-28-2017, 12:12 PM

I believe the heater element is rated at about 1500 watts and should only come on when plugged in to shore power or when the generator is online. If your system is similar to ours, the switch should be labeled Water Heater and have a red light. The generator should not have a voltage or rpm drop when under load unless it is pulling an excessive load. The power control center should monitor the voltage also. Do check the out put of the invertor/battery charger. If it is the original it may be starting to fail. I did replace ours due to a bad diode that was allowing stray AC to leak through to the DC side. There are several kits on the market which are a simple installation and have 3 stage battery charging algorithm.

Old-Biscuit · 11-28-2017, 12:35 PM

First off........

Charging voltage when gen was running at 11.5V and then jumping to 12.3V is way too low even if EVERY DC appliance was in service.
Charging voltage should be at minimum 13.2V be from a converter/charger or an inverter/charger system

YOU have a 'charger' that is failing.

Secondly........
A water heater element wired thru an inverter would definitely drain a battery bank quickly.
1500W at 12V is 125AMPS (1500W at 120V is 12.5A)

Resistive loads (element coils) are NOT something one would wire thru an inverter.

You need to ID where the water heater element is getting power from
And IF it was wired thru the inverter.......change it to 120V AC from Main AC Panel CB

AND look into that 'low charging voltage' issue......