Water Pump Causes Lights To Dim

[Ustamiata]

2007 Adventurer: When I use the water pump, the house lights dim.
We are hooked up to electricity only, Camp Hosting in Nebraska. Just filled the water tank, and noticed each time we use the water pump, the lights dim. The refrigerator has shut off several times with the Low DC message on the readout. The panel meter reads 12.8 volts after no other electrical use all night, but after a little bit of water pump use this morning, it reads 10.4. The florescent overhead lights do not fully light up. Switched the refrigerator to LP, tries to light, but does not, panel on door reads lo dc. Gauge on propane tank is just under 1/2, propane water heater lights and burns fine.
Tried so far: House batteries are full of water, terminals removed and wire brushed. Voltage across each battery with cables disconnected reads 12v. Wife reports an occasional grunt from the water pump, unrelated to the ice maker.
I'm thinking either the water pump is going bad or the converter is not properly charging the batteries. I suppose it could be a refrigerator problem, too. I did unplug the water pump and replug, thinking maybe the terminals were dirty.
Of course, being July 4, no service facility will be open until Tuesday. I will appreciate any suggestions from the forum members!

["007"]

How are your battery grounds connected to frame of your coach clean, no corrosion and tight to frame.
You have some high resistance connection some where.

[TandW]

Whenever you check the battery connections because you suspect a problem don't forget to check the connection to ground. In fact if you never have you should unbolt that black battery cable from the chassis and scrape or brush away any rust or paint you see that is preventing good metal to metal contact with the cable end. Reassemble it with chassis grease or petrolatum to inhibit further rusting. Good luck!!

[DancinCampers]

Have someone hold you battery boost switch & see if the pump works ok. If so, I would think your house batteries are not being charged properly. My house batteries read 13.6 on shore power.

Check your breaker panel, also I believe there are fuses on the converter.

If you have an inverter/converter, then it becomes more complicated, I think. I have just the converter.

[bigskymt]

Measure both load and no load voltages at the batteries and at the converter output (like a light or fuse). If there is little to no difference then you have either a battery or charging problem.
If there is significant difference between the two you will have to go back toward the source to find the fault.
It could be a ground or a faulty disconnect solenoid on the + side.
The 'grunt' in the water pump indicates a loss of pressure causing the pump to start and retain pressure. Could be a slight leak.

[skigramp]

How old are your house batteries?

My guess is that your house batteries are not up to par ... according to a table included in a post several years ago a house battery that reads 12.0 volts is 50% discharged ...

If you start your engine and let the alternator charge your batteries for a a couple of hours ... and you measure the voltage when the engine is running ... and again a couple of hours later (with no load on the battery) ... my guess if there is a big difference (more than 0.5 to 0.75 volts) your batteries have come to the end of their life ...

I bought new house batteries about 2 years ago ... they were defective and failed within a month ... they were replaced under warranty ... the replacements are still doing fine after 2 years ...

Table (courtesy of Dave from MN)

Voltage State of Charge
12.6+ ........100%
12.5 ...........90%
12.42 .........80%
12.32 .........70%
12.20 ..........60%
12.06 ..........50%
11.9 .............40%
11.75 ...........30%
11.58 ...........20%
11.31 ...........10%
10.5 ...............0%

Avoid discharging the
battery below the 40%
level whenever possible!

[Ustamiata]

Thanks for all of the advice! I removed the black cable from the chassis ground, wire brushed it and the ground area good, and reassembled. That seems to have done the trick! (Fingers crossed) I've read of the need for good grounds before, but the connection looked clean and I thought the coach was too new for that problem. Lesson learned!! Proves again the value of this forum!!

["007"]

When you have some free time place a star washer under the nut holding wire on frame use di-electric grease and you should be go to go for some time.

[AFChap]

Sounnds like good advice so far -- that said, our 12v incandescent lights always dim a bit when the 5.7gpm water pump kicks on, and return to normal when it kicks off. That alone would not send me looking for a problem. But the other symptoms described do indicate there is a 12v problem somewhere.