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Old 03-24-2020, 03:08 PM   #1
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House Battery Discharge Question

Hi All...

Just picked up my Newmar from the winter storage facility. I turned off most of the breakers and plugged into a standard 110V 15amp plug. It looked like it was maintaining a float charge for all batteries.

I was wrong. The facility put a trickle charger on the chassis battery so that was fine. The house batteries were at 4.5V when I went to pick it up.

Started the engine and within 10 mins the house came to life. Drove it home (2 hrs) and plugged it into shore power (50A). Been on shore power for a week and all looks normal.

Turned off shore power to exercise the GEN. When I was done, I stopped GEN and looked at power monitors. Frig is on, I have a portable electric heater in basement (to keep it warm as the temp still dips under 32).

I watched the meter go from 12.7V to 11.9V in 5 mins from the house batteries. Chassis battery stayed at 12.7V, as it should.

So, here is the question... Do I have to be concerned the house batteries are damaged or is 11.9V in 5 mins normal? Was the drain to 4.5V fatal?

Any opinion would be helpful.

Thanks
Mike
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Old 03-24-2020, 03:20 PM   #2
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You have a bad battery.
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Old 03-24-2020, 03:24 PM   #3
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When talking about flooded lead acid or AGM anything under 12 is damaging. Anything under 10 can be fatal. I'd bet that at this point your house batteries are just so much boat anchor.

The guidelines I was given is that you never discharge a lead-acid to under 50%,
and If you can manage to keep them to 75% or higher then your batteries will last a LOT longer. An acquaintance worked at the local telephone central office until 9 years ago, and told me about their battery plant... it's a 48 volt system, their batteries are maintained at 100% state of charge (SOC) by very expensive battery chargers/maintainers... the batteries are individual 2 volt cells, in 3/8 thick glass containers, 24 cells in series, multiple strings in parallel... lead-calcium chemistry, were installed in the 1930s, and professionally rebuilt in the 1960s and 1990s... they are still in service.


Look at the two charts below. One is for flooded, the other is for AGM, and the gentleman that sent them to me didn't identify which was which.

The upper table shows two voltages - example: 12.7 / 6.35. The 6.35 is for each of two 6 volt batteries wired in series for 12 volts.

I suggest you find out why your house batteries were not being charged, fix that, and then go out and buy a new set of batteries...

Undoubtedly others will chime in on what you should do next....

Mike
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Old 03-24-2020, 03:28 PM   #4
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Even with the elecric heater in the basement if running off inverter, that's a quick voltage dive.

Likely the batteries were down for awhile before you picked it up.

I'd ensure fully charged to float. Remove the loads. Check specific gravity. Equalize. Recheck specific gravity. This will likely provide insight to each batteries health.
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Old 03-25-2020, 06:10 AM   #5
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OK, let's get real here. He is running a space heater off the batteries, most likely 1500 watts. Well that will kill any battery in quick time.
Now lets talk about the batteries, are they AGM or wet cell? If normal cheap batteries, when was the last time you performed maintenance on them, ie put water in them?
Check the water level in them and charge them up. You will be amazed at how resilient they are. I forgot to perform annual maintenance and I thought they were toast. I took a chance, put water in them and them exercise them. I also have a 165watt solar system hooked up to them to help maintain charge during the winter months. So far they have maintained there charge even though last year due to lack of maintenance they would not even hold a charge for 3 days.
If you just open circuit the chassis batteries after they have been properly charged they should last for awhile due to not having any load on them.
I recommend spending the money and having a Solar panel system installed, even if it's a small one like mine. I don't dry camp so I don't need 500 watts of power or more to go off grid camping.
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Old 03-25-2020, 06:30 AM   #6
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...what superGrewl said....while having let the bats drop to 4.5 volts is not good news, the OPS's test using a space heat is invalid....don't know the number of bats, but in fact, running a space heater for 5 mins sounds pretty good]...bat voltage is measured "at rest" [see note on chart in post #3][no draws for 5-30 mins, some say 3 hrs], but not during a heavy draw event...I would check and clean all the cables [both ends] as a precaution and see how the bats perform over time...older bats, left at 4.5v for a period, they could be damaged....
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Old 03-25-2020, 09:48 AM   #7
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Guys.. thanks for all your replies..

Flooded bats.
Clean and maintained 4 times a year.
Topped off, distilled, when I got home. Took 1 qt. on all 8 bats.
All plates were submerged before adding.

Running tests. Started at 13.7v. 0amps shown.
After 15 mins shows 12.7. Turned on stereo. Draw 11A shows. Frig and heater also on from beginning. Showing 12.4 after 30 mins. (15 mins after draw of 11a)
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Old 03-25-2020, 01:46 PM   #8
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….actually, those readings sound pretty good while under draw.....again, a fully charged 12v bat [or two 6-volts in series]--while at rest, is 12.7 volts...not measurable while being charged and not during the draw, and not immediately following the draw....only while at rest....
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Old 03-25-2020, 04:35 PM   #9
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when the storage company put a charger on your house batteries, it told your inverter/ charger that the batteries were fully charged, so it did not charge the house batteries. you would need to jump the "big boy" solenoid so the charger the storage company put on would charge both sets of batteries. Stan
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Old 03-25-2020, 10:55 PM   #10
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What is the amp hour rating of the batteries?
If battery bank is eight 6v batteries in series/parallel then the total amp hour rating will be the sum of all of the amp hours divided by two.

Once you know the amp hour rating of the battery bank, then you can do a proper test with the correct amperage draw

Fully charge first:
Be sure to do a full charge with a long absorption phase, then an equalization cycle.
After that let the batteries rest for 12 hours, then test and record the voltage of each battery and the specific gravity of each cell to get a baseline and see if you have any bad cells.

Rundown test:
Then perform a run down test by applying a draw equal to the total amp hours of the battery bank divided by 20.
Measure the voltage on a regular basis to see how long it takes for the voltage to drop to 10.5 volts. No lower than 10.5 volts.
Ideally with new batteries you could get twenty hours, but as batteries age that will drop.
I ran this test a few months ago on my two year old battery bank and got around 17 hours telling me the batteries have aged but are still in decent shape.
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Old 03-26-2020, 01:07 PM   #11
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Quote:
when the storage company put a charger on your house batteries, it told your inverter/ charger that the batteries were fully charged, so it did not charge the house batteries.

I don't think that is what happened, Stan. If the inverter/charger was seeing the voltage from that other charger, then the trickle was charging the house as well as chassis batteries and they both would be ok. But with the engine ignition off, the crossover "Big Boy" solenoid was not engaged the inverter/charger sees only house battery voltage. If it had 120v power available, it would have charged the house battery when & if needed. That didn't happen.
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Old 03-26-2020, 01:23 PM   #12
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Quote:
Originally Posted by 36PFT View Post
when the storage company put a charger on your house batteries, it told your inverter/ charger that the batteries were fully charged, so it did not charge the house batteries. you would need to jump the "big boy" solenoid so the charger the storage company put on would charge both sets of batteries. Stan
I read in the OPs first post that the storage company put the charger on the chassis battery, and it was a trickle charger.

A trickle charger will maintain the chassis battery but not output enough voltage to signal the " big boy " isolation solenoid to close and charge the house batteries.

Most isolation systems need 13.4 volts to interconnect the 2 battery banks.

As far as connecting multiple chargers, most 3 stage models, including inverter/chargers, charge based on voltage.

Its only after the battery voltage reaches over 14 volts that they cut back to a lower voltage. Once a battery reaches 14+ volts, its about 80% charged.
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Old 03-26-2020, 01:34 PM   #13
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Quote:
Originally Posted by stutch View Post
Hi All...

Just picked up my Newmar from the winter storage facility. I turned off most of the breakers and plugged into a standard 110V 15amp plug. It looked like it was maintaining a float charge for all batteries.

I was wrong.

Thanks
Mike
I think you turned off one too many breakers.
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Old 04-05-2020, 10:07 PM   #14
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Guys thanks for the informative threads. I have a similar problem with my 2011 Itasca 40 u. I have a residential refrigerator and a bank of 6 house (interstate,wet). My storage unit turns on the 110v power for 3 hours per night. On my 2nd set of batteries in less than 3 years. I do the main and also have a watering system on the batteries and check it every other month. Picked up my RV and put it on my 50 home plug for 2 days. Went out boondocking last weekend and with only the refrigerator running, I couldn’t get more than 5 hours before having to start the generator. I’d run the gen until 10 pm and by 7 am, it was down to 11.7, which I know is critical levels. I’ve researched about 20 hours of information and still have questions. First, I’ve asked numerous mechanics and Winnebago...when in storage, and on 110v, do I leave the battery switch off button engaged? Could this be my problem? I ran the generator so long that it actually dropped rpm (2x) and lost Electric power. I’m now concerned that it may also be a problem. Open to any ideas, thoughts. Thanks.
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