DavidR
Well-Known Member
- First Name
- David
- Joined
- Jul 22, 2019
- Threads
- 4
- Messages
- 388
- Reaction score
- 323
- Location
- Eastern CA
- Vehicle(s)
- 2019 Ranger XLT Supercab Saber FX4
- Occupation
- Engineer
- Thread starter
- #16
I just recently heard about the DC-DC chargers for vehicles like this. I'm also not 100% sure how they work, but my guess is that instead of directly connecting to the truck battery, they provide an active voltage converter that always gives the aux battery a 13.8V charging voltage regardless of the voltage on the truck battery. That would allow the aux battery to fully charge regardless of what voltage the alternator generates in response to the load it sees. It would still need to know when the engine is off so that it can stop charging.I was talking about this to the owner of Equipt outfitters the other day at off-grid expo in denver, he was suggesting a DC to DC charger for vehicles with variable alternators like the ranger. I still don't quite understand how they work, and they're a bit more expensive than typical battery isolators, but supposedly it should do the trick.
edit: Also, you don't want to have the aux battery connected straight, or just off a relay that's otherwise straight to the ranger's main battery. a battery isolator's job is to prioritize the main battery getting charged first and then supply current to the aux as available. if they're both just wired together, and not identical batteries they can get all sorts of screwed up, I'm sure the variable alternator will make that scenario even worse.
You're right about the cost. The person who told me about them said that good quality ones can cost $700-$800. To be honest, that's why I'm considering some other options even if they are a bit less optimal. I agree that by direct connecting with a relay, there may be some protections of a battery separator that would be sacrificed. Mostly, I think those would be in extreme cases, though, such as if the aux battery has shorted cells or something like that. If both the aux battery and truck battery are healthy, it should be okay to connect them in parallel as long as they are the same chemistry (lead-acid). I made some measurements today, and when the truck decides to charge the main battery, it provides a 13.6V charging voltage. That's a little less than the traditional 13.8V, but I think if the aux battery were charged with 13.6 instead of 13.8, it would be fine. If I do go this route, though, I'd need to make sure the aux battery is in good condition.
There's no doubt that the DC-DC convert is the best possible option, but I might need to wait on it due to the cost.
EDIT: Looks like they're not quite as expensive as I thought. This is the one that was recommended to me. He must have been quoting an installed price:
https://redarcelectronics.com/products/20a-in-vehicle-dc-battery-charger-ignition-control
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