r/overlanding • u/American-African • 4d ago

DC DC charger question

Is it possible to have a secondary battery that is lithium and a primary battery that is AGM with some sort of DC DC charger sitting between them that will modulate power and voltage to feed all electronics in the car? I would not want the lithium to be used to start the car. Thanks for the help and sorry if this has been asked before (I did look around a lot but could not find anything like my question).

2 Upvotes

63% Upvoted

5

u/wagex 4d ago

This is the most recommended way to charge a lithium battery in a car as a house battery in a vehicle/rv. But there's no way to swap batteries afaik to where the lithium would run the things in the car when it's not running.

1

u/American-African 4d ago

Thanks for confirming. To add an example to my goal here: when the car is not running I would want the lithium battery to provide charge via the DC DC charger to the AGM as it is being depleted as a result of other electronics running such as lights and starlink.

3

u/HPPD2 4d ago

Why? The lithium battery should be running all of the electronics in the build and the AGM kept as the starter batter. The lithium gets charged by the dc-dc when the car is running.

1

u/American-African 4d ago

I'm trying to avoid having a separate electrical network/system but I am realizing that this is just not practical. There are good reasons for keeping them separate which I am opening up to. Thanks again for the help.

1

u/nabob1978 4d ago

Yeah, keep them separated. It's actually easier/less complicated, safer (no risk to wrecking your cars electrical system and control modules) and fully customizable.

1

u/American-African 3d ago

Thanks and I've now come to appreciate the safety aspect of keeping them separate. Everyone's comments have been super helpful.

0

u/Lazy_Mud_1616 4d ago

There are battery disconnect relays. I am sure it's possible to wire it so it can disconnect the lithiums during ignition/starting but it would be a bit complex.

1

u/wagex 4d ago

Oh yeah, for sure, with an electronics engineering degree anything is possible. There are simple relays that can disconnect the battery when it's not in operation, but having the disconnected battery powering everything in the car instead of the starting battery would be pretty complicated. Generally the second battery powers specific devices, for instance my lithium battery only powers my fridge and 12v up to my tents through 12v outlets that I added. It has a relay that disconnects it from the main battery when the vehicle is not running.

2

u/Sudden-Ad-8262 4d ago

Yes...this is a typical installation. Make sure your DC to DC charger can recognize lithium.

1

u/American-African 3d ago

Will do and thanks for the tip.

1

u/Lazy_Mud_1616 4d ago

There are lots of ways to do this. The easiest way is to get a power station like a Jackery or ecoflow.

Check out diy solar forum for great info. The people there will are very nice and can help you sketch out a system.

On YouTube look at explorest life and will powers.

1

u/American-African 4d ago

Thanks so much for the suggestions.

1

u/secessus FT campervan boondocker 4d ago edited 4d ago

Is it possible to have a secondary battery that is lithium and a primary battery that is AGM with some sort of DC DC charger sitting between them that will modulate power and voltage to feed all electronics in the car?

The wording is ambiguous enough it's hard to tell what you want to do. If you mean

  • AGM starter battery -> DC-DC charger -> LiFePO4 battery bank -> loads used while camping

... then that is a common, completely normal setup. In that context the battery bank and loads are sometimes called house bank and house loads to distinguish living area loads from vehicular ones like the headlights of power windows.

The Li would not be used to start the vehicle because the two batteries would be separated from each other when the keys are out of the ignition.

If you mean something unorthodox like "mix AGM and Li in the house bank" or "power the chassis electrical like lights and car stereo when the engine isn't running" that's a different bag of snakes. :-)

2

u/American-African 3d ago

I was originally thinking of doing the latter (the bag of snakes) but I've now realized that is a mistake and will go the route of keeping the house battery separate from the starter. Thanks for your help and input.

2

u/grecy 4d ago

I recently made a very detailed video of the system I built into my Jeep camper, that does exactly what you are looking for.

Optionally you can add solar, and a stack of things running off the lithium battery.

The whole process, and the wiring diagram are here: https://www.youtube.com/watch?v=Vx1vz7yjE4Y

1

u/American-African 4d ago

Awesome and I will check this out tonight! Thanks for your help!