Multiple charging sources?

hayton55 · Sep 30, 2020

I'm new to all of this battery info; just bought a Class A RV and am trying to get the power setup so I can boondock for a few days and then travel on without worrying about the power system of the RV (minus the Air Conditioner). Trying to understand some basic assumptions so I can make the right decisions about what pieces of equipment I should buy that will all work in harmony? Right now I have 2 105 Ah batts with a smart converter/charger @55 amps; I want to add a DC2DC charger (40 amps?) to charge from the alternator (130amps) to use while driving. I plan on adding solar and adding 2 more 105 Ah batteries, 420 Ah total; the confusion is what do I need to buy to keep these batteries charged with the minimal amount of time required. From everything I read too much info is provided confusing the basic questions. For solar I was looking at 2 panels that are 320 watts each (640 watts parallel) with a 150/60 MPPT controller and at some point adding a 3000 watt inverter to manage all AC requirements while boon docking (minus AC); so with all sources connected to the batteries providing power I do not understand what will be the interaction between all of these devices providing a charge. On some threads it appears they will just act independently, on others they say one will take control, on others they suggest it could destroy the batteries with overcharging...I don't work with this stuff everyday and its overwhelming...just looking for some help

snoobler · Sep 30, 2020

While flooded and AGM/SLA batteries list different charge parameters, most alternators and chargers for either charge to something lower - 14.0-14.4V. At this level you may not be fully charged, but you'll be close enough to insure you have 90%+ charge, and there is no risk of damage to the batteries due to low SoC (70% or lower).

The built-in system for joining the coach and chassis batteries is likely more than adequate for alternator charging. The only harm is the AGM won't get to true 100%, but they'll be close enough.

If you have 420Ah, you need to target 42-61A (10-15% of capacity) charging. That would mean 42*12 = 500W or 61*12 = 732W - or anything in between. Those 2X 320W panels sound very nice at this point.

Concerning the interactions, they're rarely an issue. All charge sources will react to the battery voltage. It's common for a charging source that is stronger than another, or slightly higher voltage to "take over" because the weaker source sees the higher voltage and tapers its current to nothing. Alternator, solar, shore, generator - they should all coexist well. The only time it's an issue is if your batteries are really low, and all sources can charge at their maximum - which might be too high for health, BUT the batteries will rapidly hit their absorption voltage, and the chargers will all start tapering.

In those cases, it's easy to address by disconnecting one of the charge sources or just electing to not start one.

Personally, I wouldn't worry about it.

hayton55 · Sep 30, 2020

Wow! Awesome! Okay, that's all I was really looking for...so the different amp charging sources I listed will just co-exist based on the voltages seen by all...do you think I can buy the batteries now or wait until I have all pieces assembled to ensure compatibility?

snoobler · Sep 30, 2020

Yep. The chargers just see the battery voltage, and the voltage responds to current from all sources, and the sources adjust accordingly. If you find something that isn't optimal, one way to address multiple devices is to change the bulk/absorption voltage where you can. If you set the solar absorption voltage to above that of the alternator, the alternator would stop pushing current as voltage rises above its absorption voltage, and you're on pure solar then.

I'd lay it out. Measure, re-measure. Create a bill of materials list, etc. Make sure you have everything planned out as best as possible.

AGM retain charge for longer periods of time than flooded, so if you expect to have it online within the next 30 days or so, getting batteries now wouldn't be a bad idea.

hayton55 · Oct 1, 2020

snoobler said:
While flooded and AGM/SLA batteries list different charge parameters, most alternators and chargers for either charge to something lower - 14.0-14.4V. At this level you may not be fully charged, but you'll be close enough to insure you have 90%+ charge, and there is no risk of damage to the batteries due to low SoC (70% or lower).

The built-in system for joining the coach and chassis batteries is likely more than adequate for alternator charging. The only harm is the AGM won't get to true 100%, but they'll be close enough.

If you have 420Ah, you need to target 42-61A (10-15% of capacity) charging. That would mean 42*12 = 500W or 61*12 = 732W - or anything in between. Those 2X 320W panels sound very nice at this point.

Concerning the interactions, they're rarely an issue. All charge sources will react to the battery voltage. It's common for a charging source that is stronger than another, or slightly higher voltage to "take over" because the weaker source sees the higher voltage and tapers its current to nothing. Alternator, solar, shore, generator - they should all coexist well. The only time it's an issue is if your batteries are really low, and all sources can charge at their maximum - which might be too high for health, BUT the batteries will rapidly hit their absorption voltage, and the chargers will all start tapering.

In those cases, it's easy to address by disconnecting one of the charge sources or just electing to not start one.

Personally, I wouldn't worry about it.

That's great! Really appreciate the info......

Multiple charging sources?

hayton55

New Member

snoobler

Solar Honey Badger

hayton55

New Member

snoobler

Solar Honey Badger

hayton55

New Member

Similar threads