Solar Float and Shore Power Float?

[BFL13]

Been a few threads on this, but I never had the "issue" until now, so I am not too clear on just what is at stake here.

On shore power Floating the batts at 13.8 (or whatever temp comp adjustment calls for) you get a steady "correct" voltage.

With solar only, no shore power, you Float the batts by letting the controller do its "profile" during the day and it quits at night. With any luck, you will average out a "correct" Float in the 24 hours for the batts to survive.

BUT as I have now discovered for myself (despite those other threads on this 😞 ), if you have both shore power and solar, then during the day, instead of being at 13.8 (say) steady, the solar puts you up into the 14s, and at night, instead of dropping right down, the shore power keeps the converter going at its 13.8 (say), so your 24 hour average is higher than it was when just on shore power.

So it looks like the answer, if you are on shore power and solar, is to disconnect the array from the controller (leaving the controller on the battery bank), and just stick with the shore power and converter's Float.

Yes?

[MEXICOWANDERER]

HTH John,

May others be blessed with your monitoring system 🙂

[full_mosey]

It will be a cold day in he77 when I disconnect my solar.

For me, shore and genny power supplement solar charging. When I see overnight low Volts decreasing over time, it is time for some bulk charging from 110VAC.

Here is a 48 hour graph of my solar while maintaining the bank 24/7.



With graphs like this, I can monitor status.

FYI, I have a Project that goes into more detail. I would appreciate anyone's comments or suggestions.

HTH;
John

[BFL13]

I am supposing it is better to stay on a steady Float voltage (the correct voltage for that at the time) 24/7 than do a Float by solar with its ups and downs.

So if the solar takes the voltage above the correct Float for part of the day when you are on converter's Float, then just shut off the solar. You could also dial down the solar's high set point, but then you have to crank that back up when you go camping next time.

Using the solar every so often to give the voltage a boost for destratification is an idea. I don't know if AGMs would benefit from that too, but for their own reasons.

[pianotuna]

Phil,

I passed along BFL's suggest of using multiple chargers to you. He is the *king* of multiple chargers at one time, whereas I'm only a solar Knave. LOL

[pnichols]

BF,

What Mex says above is right on.

Maybe what you're really asking is "can multiple RV battery charging sources be hooked up in parallel and used at the same time?".

Well .... many of us do some form of it to increase RV battery charging rates and reduce charging times:

1. Stock converter along with a portable charger.
2. Stock converter along with a permanently mounted after-market charger.
3. Stock converter or permanently mounted after-market charger along with the engine alternator.
4. Any combination of the above along with a wind generator.

In fact ... years ago either you or Pianotuna gave me the idea to use a portable charger in parallel with my stock converter. I set the portable charger to it's 50 amp engine starting mode and temporarily hook it up in parallel with the converter. This has worked like a champ for us to speed up RV battery charging ... and after years of doing this the converter, the charger, and the batteries have not been adversely affected. (But my batteries have always been AGM when doing this, so there's no water to be boiled off after the batteries become fully charged.)

[pianotuna]

I happened to check my RV which is running in storage mode but with the battery disconnect switch turned on.

Voltage during the daylight hours is about 13.2 with charging at 0.8 of an amp. Two hours after sundown voltage is 12.8.

[Sam_Spade]

BFL13 wrote:

On shore power Floating the batts at 13.8 (or whatever temp comp adjustment calls for) you get a steady "correct" voltage.

So it looks like the answer, if you are on shore power and solar, is to disconnect the array from the controller (leaving the controller on the battery bank), and just stick with the shore power and converter's Float.

You are worrying too much.

There is NO one "correct" float voltage; there is a range....and it appears that you are IN IT.

The term "float voltage" only applies when a charging source is connected.......and then only when the batteries are fully charged or very near to it.

It will not harm anything to leave the solar "ON" while the shore powered charger is also running.....but it won't accomplish much either. If it will make you more comfortable, disconnect the solar when shore power is connected.

[brulaz]

BFL13 wrote:

...
Instead of staying at 13.8 all day on just converter it gets to 14.5 or so depending on how much sun gets on it (highly variable where the RV is). It can take all of the daylight hours to get there so it is above 13.8 all day.
...

When boondocking our batts were often in the low 14s, high 13's during the day with solar charging, cause the loads never allow the absorb set point to be reached. Not too worried about it. The only way I know of to change that is to alternate between two separate battery banks: while one is charging, use the other for loads.

When on shorepower, or in storage with no shorepower, I isolate the batts from all loads and let the solar charger maintain them. So every day the batts are pulsed with 14.8V then float at 13.2V then nothing when the sun goes down. As the only load is self-discharge, it usually doesn't take long to get to 14.8V and absorb is terminated when the current drops, not time based. But on dark rainy days, it might take longer to get there.

EDIT: On sunny days in storage, my charger can record zero minutes at absorb V, with the rest of the day at float.
EDIT: And just multiply all those Vs by two for my current 24V battery bank.

Are your batteries completely isolated when on shorepower?

[centerline]

BFL13 wrote:

What 0.2 volts? Instead of staying at 13.8 all day on just converter it gets to 14.5 or so depending on how much sun gets on it (highly variable where the RV is). It can take all of the daylight hours to get there so it is above 13.8 all day.

Seems easier just to disconnect the solar at home than fiddle with the controller settings.

what solar controller do you have?

what you describe is also a symptom of a failed battery. are you absolutely certain the batteries test out ok?

[BFL13]

pianotuna wrote:
Hi BFL13,

Set the solar to the same float as the shore power. If the controller can't do that--then it is inadequate.

Honestly I don't think 0.2 volts is going to "kill" a wet cell battery. It might gas a smidgen more.

You could just float with solar only, too. I had no choice but to do that between 2009 and 2013.

What 0.2 volts? Instead of staying at 13.8 all day on just converter it gets to 14.5 or so depending on how much sun gets on it (highly variable where the RV is). It can take all of the daylight hours to get there so it is above 13.8 all day.

Seems easier just to disconnect the solar at home than fiddle with the controller settings.

[time2roll]

Pick up a book about the local area history and ignore batteries and voltage.
Play a game with the the kids.
Get a telescope.
Walk to the lake.
Ask the ranger for other interesting sights.

[Twomed]

pianotuna wrote:
Hi BFL13,

Set the solar to the same float as the shore power. If the controller can't do that--then it is inadequate.

Honestly I don't think 0.2 volts is going to "kill" a wet cell battery. It might gas a smidgen more.

You could just float with solar only, too. I had no choice but to do that between 2009 and 2013.

Agree...I like a little more push when solar only, don't notice excess water usage.

600watts/flat mount/8 T105s

[MEXICOWANDERER]

Are you saying "Never put an Armenian and a Greek in the same set of bunk beds?"

When the batteries are charged, they are floated. The batteries call the shots not the chargers. On a permanent power pedestal, boinking the batteries once a month with the solar is a good idea.

[Lwiddis]

Why if connected to shore power would you leave your solar system running? On the other side, I trust my solar system. I don’t trust shore power...RV park, my home, anywhere.