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Old 10-12-2021, 07:38 AM   #1
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Electrical question

I knew when we started on this journey electrical issues were going to be my biggest challenge and that has been the case to this point. This is our first extended trip in our coach and it appears when not hooked up to shore power I can only go 2-3 hours before drawing my battery bank down to 12.4 to 12.3 volts. This is overnight with just the residential refrigerator, outside Dometic refrigerator, one fan and 2-3 phones/I-pads plugged in. Going in I assumed I would be able to make it through a night (8-10 hours) without having to run the generator before the batteries drained but that has not been the case. Is this normal for a all electric coach? I was told the battery bank was new when we purchased 6 months ago but do not see any type of date sticker on the 8 “Discover” batteries. any hep is appreciated.
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Old 10-12-2021, 07:50 AM   #2
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when not hooked up to shore power I can only go 2-3 hours before drawing my battery bank down to 12.4 to 12.3 volts.
Why do you consider the batteries 'drained' at that voltage? What other source of power usage do you have. e.g. any battery monitor of some kind?

Mark B.
Albuquerque, NM
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Old 10-12-2021, 07:58 AM   #3
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Mark,
The microwave clock had to be reset and I thought I read that you should not let a 12 volt battery go below 12.3 to 12.5. Our screen shows the house batteries at 13.4 when plugged in or when running the generator. Thanks
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Old 10-12-2021, 08:00 AM   #4
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It is VERY common for dealers, shippers, etc to let batteries go completely dead….this causes damage to the plates even after they are recharged. Sounds like the batteries have lost some capacity due to this.

Check to be sure you don’t have other phantom loads you are not aware of……. Basement lights left on? Engine block heater on? Kerig coffee maker keeping water hot 24/7

You also seem to have lots of capacity left if you are reading 12.3 - 12.4 volts….. you can draw down to 12.0 volts and still be at 50% charge.


What is the battery reading after 8 hours ?
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Old 10-12-2021, 08:13 AM   #5
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The microwave clock had to be reset
That's an AC appliance, which implies power to it was interrupted.

Quote:
you should not let a 12 volt battery go below 12.3 to 12.5.
That's not true. The operating range of a lead acid battery under load is from 12.7V to 10.5V. There are logistical reasons to choose a particular cutoff point (maintaining some degree of reserve) but there's no hard number to never cross except 10.5V under load. It would be useful to know the exact kind of battery you have so you can know what kind of performance you can expect from them.

Quote:
Our screen shows the house batteries at 13.4 when plugged in or when running the generator.
That's a typical "absorb" voltage you'll see when batteries are between 80-100% charged. Perfectly normal.

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Old 10-12-2021, 08:16 AM   #6
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Assuming lead acid batteries due to the coach you have listed in the sig line. Here is a chart to help with your cut-out setting in your power management system. There are lots of charts out there in the cyberworld, I just happened to choose this one. Your battery manufacturer should have a chart on their web site for your particular batteries.






My coach will run on inverter well over a day to a day-1/2 powering the residential fridge, lights and other low current stuff on my factory lead-acid batteries. I think I have mine set to auto-start the generator at 11.9 or 12.0 volts, don't remember. I will be changing to AGM batteries in the future (not ready for lithium yet) which will change the settings a little.


Just remember, do not let the batteries get too low or extremely low, individual cells or units can actually reverse polarity and cause issues. Then the bank is pretty much shot.


In summary, 12.3 V cut-out seems a bit conservative to me.
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Old 10-12-2021, 08:43 AM   #7
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do not let the batteries get too low or extremely low, individual cells or units can actually reverse polarity and cause issues. Then the bank is pretty much shot.
That's what can happen if you go below 10.5V, so that's why it's the "hard" number to not cross. Anything above that is a "cushion" one may want to have for that reason, and as an operational reserve. Making sure batteries get a 100% charge helps keep the cells balanced. Charging whenever possible is a good idea but one shouldn't be afraid to use the battery capacity they have, and paid for. Just takes an awareness of what the batteries are capable of and suitable monitoring.

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Old 10-12-2021, 08:51 AM   #8
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Mark,
The microwave clock had to be reset and I thought I read that you should not let a 12 volt battery go below 12.3 to 12.5. Our screen shows the house batteries at 13.4 when plugged in or when running the generator. Thanks
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Old 10-12-2021, 08:57 AM   #9
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Thanks for the replies the batteries are “Discover”. I have to read up on my AGS to see what it is set at. We are going full time in April and trying to get a better understanding of our systems. I appreciate the guidance.
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Old 10-12-2021, 09:08 AM   #10
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Be sure not to confuse:


Voltage with batteries at rest


WITH


Voltage of batteries under heavy load.


Voltage under load is OK to be well below that of batteries at rest.




Voltage tables showing SOC (State OF Charge) vs voltage are for batteries at rest, not batteries under heavy load.
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Old 10-12-2021, 09:14 AM   #11
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Thanks for the replies the batteries are “Discover”.
There are different kinds of "Discover" batteries. There's got to be a label or other visible clue that will lead to figuring out which ones you have.

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Old 10-12-2021, 09:16 AM   #12
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Your voltages aren't bad but, with 8 batteries, I don't think they should be that low. You should add up your total amp hour capacity and compare it to your total amp hour usage.

You might want to get one of these to determine how much your residential refrigerator consumes:

https://www.amazon.com/P3-P4400-Elec.../dp/B00009MDBU

Just remember that the amps it consumes on 12V via an inverter is a little more than ten times that consumed at 120V AC shore power. For example, if you consume 5 amp hours at 120V AC, that's 50 amp hours at 12V DC, plus a little more to account for inverter inefficiency.

Watts = Amps x Voltage, so an appliance that consumes 100W continuously will consume 100/120 = 0.83 amps per hour on 120V AC shore power and 100/12 = 8.3 amps per hour on 12V DC via an inverter (not allowing for inverter inefficiency).

One of these is also a good idea:

https://www.amazon.com/AiLi-Voltmete...56&sr=8-4&th=1

You can't go by the rating on your refrigerators since they don't run continuously.

My other recommendation is to find a good, old school battery shop and have them test your batteries.
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Old 10-12-2021, 09:18 AM   #13
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Quote:
Originally Posted by wolfe10 View Post
Be sure not to confuse:


Voltage with batteries at rest


WITH


Voltage of batteries under heavy load.


Voltage under load is OK to be well below that of batteries at rest.




Voltage tables showing SOC (State OF Charge) vs voltage are for batteries at rest, not batteries under heavy load.
Exactly. The factory information center is just a volt meter and the reading is pretty useless if the batteries are either in use or being charged. The only way to get an accurate SOC for batteries in use or charging is to install a shunt based battery monitor. Anything else is pretty much a guess, unless you let the batteries rest with no load and no charge for several hours before checking. You may not have a problem at all.
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Old 10-12-2021, 09:25 AM   #14
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Originally Posted by Cmftblynumb View Post
................ I assumed I would be able to make it through a night (8-10 hours) without having to run the generator before the batteries drained but that has not been the case. Is this normal for a all electric coach? .......
In general, yes it is. For an all elec unit, once the batts are drained, even new, they 'd need an all night shore power or gen to fully restore them for further use over night.

IF you have the gel batts, preferably you might want to have them recharged starting at 12.2. The all elec units can drain the 12.2 rapidly.

The all elecs are not very suitable for dry camping. You can consider solar panels. if sunny, they can help charge and maintain the batts during the day, which 'could' help to survive the over night batt use.
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