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Old 08-11-2021, 03:21 PM   #1
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Exclamation Charging Chassis Battery from Solar

I've confirmed the solar panels only charge the house batteries I'd like to charge the chassis battery as well. It seems (if there is a common ground) that all one would need to do is run a wire from the positive of the house batteries to the positive of the chassis battery. Use say a 10 A fuse at both ends to protect both batteries and done.

I'd only use this for off season storage, so the issues of the engine running, engine compartment heat, etc. wouldn't be an issue. I do have a concern that the chassis battery is a flooded type and the house batteries are SLA if that make a difference.

Where am I missing something?

Thanks,

John C
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Old 08-11-2021, 03:52 PM   #2
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technically they should all be the same type. Worst case the flooded battery may use a little more water, assuming that the setting on your charge controller is for SLA, but the current involved is so low that I wouldn't really worry about it.
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Old 08-12-2021, 06:51 AM   #3
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hen in theory my idea should work?

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Old 08-12-2021, 07:06 AM   #4
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hen in theory my idea should work?

John C
Yes...
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Old 08-12-2021, 08:01 AM   #5
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Great. I'll work on this once I get home about Labor Day.

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Old 08-12-2021, 08:35 AM   #6
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Great. I'll work on this once I get home about Labor Day.

John C
You could put a 10 amp auto reset breaker in the line between the battery banks instead of the fuses. It will prevent you worrying about forgetting to remove it when starting (and blowing the fuses).

https://www.amazon.com/ZOOKOTO-Unive...s%2C243&sr=8-8
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Old 08-12-2021, 08:51 AM   #7
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Use a Trik-L-Start. That's what it's for. It even has a Winnebago part number on it.

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Old 08-12-2021, 09:13 AM   #8
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Why go through the trouble and expense when you can already tap into the results of solar battery charging by using the emergency start feature as described in the owners manual???
"NOTICE
The house battery can also provide emergency power to start the engine if the chassis battery is discharged. House batteries are automatically charged by the chassis alternator while the engine is running."
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Old 08-12-2021, 09:47 AM   #9
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Why go through the trouble and expense when you can already tap into the results of solar battery charging by using the emergency start feature as described in the owners manual???
"NOTICE
The house battery can also provide emergency power to start the engine if the chassis battery is discharged. House batteries are automatically charged by the chassis alternator while the engine is running."
Th OP wanted a long term storage solution with solar, not a boost start. You can't use the boost start circuit since the solenoid draws significant current when energized and leaving it energized only backed up by solar would deplete the batteries.
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Old 08-12-2021, 10:26 AM   #10
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Th OP wanted a long term storage solution with solar, not a boost start. You can't use the boost start circuit since the solenoid draws significant current when energized and leaving it energized only backed up by solar would deplete the batteries.

Why would you leave the boost start energized? If the OP wants to use solar for storage....it's already hooked up to the domestic batteries. When the time comes, if needed, he can then use the boost start....only energize when needed.
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Old 08-12-2021, 10:39 AM   #11
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Why would you leave the boost start energized? If the OP wants to use solar for storage....it's already hooked up to the domestic batteries. When the time comes, if needed, he can then use the boost start....only energize when needed.
Because he doesn't want the chassis battery to go dead during extended storage. Solar panel charges the house...but not the chassis, hence a wire between the two during storage. Not a good idea to have the chassis go completely dead, even though you can still start with the boost switch.
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Old 08-12-2021, 11:29 AM   #12
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On many units there is a relay that will charge the chassis batteries after the house batteries are charged and it will charge the house batteries after the chassis batteries are charged when the engine is running. On the Dynamax units they are a Bird or Bim. Most motorhome style units have one. You may check and see you may have one and it will keep both charged. Mine will. Good luck.
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Old 08-12-2021, 12:12 PM   #13
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I think the resetable relay would defeat the purpose of the fuses. I wouldn't want a short of the wire to get into a reset-short continuum. My thought was an online fuse holder adjacent to the battery posts which would double as my disconnect points.

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Old 08-12-2021, 01:21 PM   #14
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I think the resetable relay would defeat the purpose of the fuses. I wouldn't want a short of the wire to get into a reset-short continuum. My thought was an online fuse holder adjacent to the battery posts which would double as my disconnect points.

John C
Most use auto reset breakers, although if you are concerned, which I wouldn't be, they also make the same breakers as manual reset.

Now, there have been a lot of posts since yours talking about BiM and BCC circuitry in an RV that will automatically parallel both banks or bring on the downstream bank when the primary is already charged. Those are correct but if your solar panel is directly connected to the house bank, which I bet it is, Bim circuits and BCC circuits would not sense this voltage since they are looking upstream for charging voltages and not on one of their charging outputs. Hence the need for a separate circuit as you are contemplating.

As I said, if you use fuses and forget to disconnect them when starting during the off season, you stand a high probability of blowing them when the starter loads down the chassis battery and the current flows in from the house bank. No big deal and no harm done, as long as you have more fuses.
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Old 08-12-2021, 02:13 PM   #15
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The resettable breakers sound interesting. I may need to do some trial and error with a multimeter to determine a good breaker rating.

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Old 08-12-2021, 02:44 PM   #16
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The resettable breakers sound interesting. I may need to do some trial and error with a multimeter to determine a good breaker rating.

John C
Not really that complicated, all you are trying to protect is a short so 15 to 20 amps will protect for that and never pop for anything else (maybe except starting)
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Old 09-08-2021, 02:25 PM   #17
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Cool Success!

We are finally home and I got some time to perform an experiment to confirm the viability of this idea.

House batteries at 13.48V, chassis battery at 12.7. Connected positive to positive with a 10A multimeter in series and got 0.15A going to the chassis battery. Less than I expected, but in the right direction.

I hooked the two batteries together with alligator clips at both ends of the 17' of 14 gauge wire for 15 minutes or so and rechecked battery voltage. House still at 13.48 and chassis at 13.46 so I called it good.

Next step is to make up a permanent connection with breakers, etc.

John C
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Old 09-28-2021, 03:39 PM   #18
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Question

Just wondering if you made the permanent installation yet, and what fuse/breaker you chose?

Is it not possible to have this configuration installed all the time, even when using the RV? Here's why I'm asking...

We have a portable solar panel that I connect to the house batteries when we're boondocking, but we recently discovered that the chassis battery will go dead after a few days of using the dash stereo. So it would be great to have the house batteries connected to the chassis battery.

When we're ready to travel, and I disconnect the solar panel, would the added wire cause a problem when the engine is running?

Thanks,
Chris
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Old 09-28-2021, 04:26 PM   #19
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Just wondering if you made the permanent installation yet, and what fuse/breaker you chose?

Is it not possible to have this configuration installed all the time, even when using the RV? Here's why I'm asking...

We have a portable solar panel that I connect to the house batteries when we're boondocking, but we recently discovered that the chassis battery will go dead after a few days of using the dash stereo. So it would be great to have the house batteries connected to the chassis battery.

When we're ready to travel, and I disconnect the solar panel, would the added wire cause a problem when the engine is running?

Thanks,
Chris
Don't you have a radio switch on the dash?
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Old 09-28-2021, 04:34 PM   #20
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I've confirmed the solar panels only charge the house batteries I'd like to charge the chassis battery as well. It seems (if there is a common ground) that all one would need to do is run a wire from the positive of the house batteries to the positive of the chassis battery. Use say a 10 A fuse at both ends to protect both batteries and done.

I'd only use this for off season storage, so the issues of the engine running, engine compartment heat, etc. wouldn't be an issue. I do have a concern that the chassis battery is a flooded type and the house batteries are SLA if that make a difference.

Where am I missing something?

Thanks,

John C

Your idea should work fine as a maintenance charger once your batteries are fully charged. However, it is unwise to use this configuration full time: 1) because the chassis and house batteries are not the same, and 2) because the house battery load during camping will also discharge the chassis battery. Your idea could be made permanent by isolating the chassis battery from the house batteries with a DC-to-DC batter charger, such as the Renogy 20A DC to DC On-Board Battery Charger.
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