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Old 07-27-2015, 11:39 PM   #1
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Battery longevity with mild cycling (24/7 Fridge + solar)

I know this topic has been tossed around before, but didn't find anything too recent.

This question is primarily aimed at those that are running solar arrays such that they can leave their fridge running 24/7. I assume that any cycling is worse for battery life than just leaving it in a sustained float state until it is used. Certain charts suggest that an AGM bATTERY is good for about 3000 cycles at a 10% DOD.

So, what are your thoughts? I've really enjoyed being able to just leave the fridge on and be charged up by the end of the day before the night cycle. How much of my battery life am I sacrificing by this convenience?

Setup:
Battery bank - AGM's with about 280-300 AH total (I think of 120 as my conservative limit)
Fridge Draw - TF130, this summer has been using 18-22AH overnight
Solar - 100W Renogy flexible panel and Chinese MPPT controller

As stated above, as long as there is adequate sun I have been charging my batteries back to 100% by the end of the day with the single 100w panel (which I'VE actually been quite impressed with). My depth of discharge for just the fridge is never more than 10% of my capacity.

I know LenS has recently posted some great analytical bits on his solar setup. Anyone have some long term experience with constant battery cycling at minimal depth of discharge rates?

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Old 07-28-2015, 01:38 AM   #2
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

This probably isn't terribly useful data: I got lax about leaving our ARB cooler running on solar last year. As of this spring the 90Ah AGM no longer made it through the night, but dropped to where the fridge would shut off around 5am. Solar would get things going again not long after sun-rise. Since the AGM was of unknown age (though at least 4 years old), I replaced it recently (with a 100Ah unit).
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Old 07-28-2015, 07:43 AM   #3
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Below is a chart showing cycles to discharge rates. So I would not think a 10% depth of discharge would not be huge impact and perfectly acceptable.


I think the key is managing that as our prime solar weather goes away.

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Old 07-28-2015, 11:36 AM   #4
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Greg's chart looks like the same one from Northern Arizona Wind & Sun

http://www.solar-electric.com/deep-cycl ... -faq.html/

It's well worth reading. They talk about short cycling and is one reason I keep plugged in (with the charger off) if the fridge is on and the van is sitting at home. My fridge kicks to AC whenever it detects shore power. Being as my AGM's can hold a full charge with no load for over a month I figure the solar will keep things topped off. I don't see a reason to cycle the batteries every night if there is shore power handy and the fridge is running. My Norcold pulls 5+ amps and when it's 100+* outside my van gets very warm inside. I really don't know how much it pulls off the battery system at night but I doubt it's a drop in the bucket. JMO
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Old 07-28-2015, 12:26 PM   #5
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Thanks guys. Ever since discovering that the solar takes care of the fridge (at least for now with the longer non-cloudy days) I have been pretty lax about it. I think I will start flipping it off for long periods of non-use though, especially when fall and winter rolls around and it spends more time in the garage.

The flip side of me though says that even if I lost a year of battery life (say from 6yrs to 5 yrs), at least I was USING the van for its intent.

I appreciate the graphs and charts - that is the kind of data I was looking for.
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Old 07-30-2015, 03:55 AM   #6
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Not necessarily related to the topic at hand but during long times of inactivity it might be a good idea having the fridge run 5-10 minutes each day. Internal seals etc require some circulating lubrication to remain viable, in theory increasing the life of the fridge.

Others might have a different perspective or experience about this, I'm going from commercial refrigeration and home appliance POV.
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Old 07-30-2015, 10:44 AM   #7
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

JWA - that is definitely the other part of the equation. If I am leaving my fridge on 24/7, am I effectively using up its life? Hopefully these little units are as robust as a home fridge. Based on everyone else's experiences I have no reason to believe that I shouldn't get 10+ years out of it (knock on wood).

Great tip on the non-use. I think that tip pretty much goes across the board on all RV parts. People that use their rigs quite a bit often seem to get more life out of them than the garage queens.
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Old 07-30-2015, 08:01 PM   #8
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Quote:
Originally Posted by JWA
Not necessarily related to the topic at hand but during long times of inactivity it might be a good idea having the fridge run 5-10 minutes each day. Internal seals etc require some circulating lubrication to remain viable, in theory increasing the life of the fridge.

Others might have a different perspective or experience about this, I'm going from commercial refrigeration and home appliance POV.
Damn, I never really put that in mind. Being I've always kept the Norcold on since 2005, I guess I never really put the numbers together as to why my fridge stalled when it went into the shop and was off after several months. I'd heard about the freon not circulating causing issues.

Thanks, I think I'll kick the new one back on. It probably doesn't need to be set at 4 while not in use do you think? I'm planning to keep it set to 1-2 and just keep plugged into shore power.

I hate to say it but after SMB installed the new unit, they called to tell me the old one was working fine Guess the moving it did the trick but being I wasn't sure I just let them do what they wanted with it.
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Old 07-30-2015, 10:12 PM   #9
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Related to the fridge running -

Keep in mind that your fridge at home is plugged in and operational all the time and they last for years and years. Our van fridges are the same basic design only smaller. Should not not be a problem leaving them running. I have mine set to the 1/2 setting.
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Old 07-30-2015, 10:58 PM   #10
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Re: Battery longevity with mild cycling (24/7 Fridge + solar

Our Isotherm fridge has been running continuously for 2.5 years off the solar and battery system. Everything seems to still be in great shape......
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