Charging Secondary Lithium (remove in winter)

[ekkonomix]

I have an existing AGM battery bank (2x100AH) in my Sprinter/RV that I want to leave permanently. I replaced the combiner solenoid under the passenger seat with a CTEK Smartpass 120s and was also planning to add the CTEK D250SE. The Smartpass currently charges the AGM bank.

Now I am thinking about adding a secondary lithium bank given I can work remotely more and need a bit more power. But I want to have the option to remove it in the winter as my van is cold. I would just use this lithium bank for an inverter and the existing AGM batteries would take care of existing stuff (fridge, DC distribution, etc)

Could I just a run another DC to DC charger from the AGM battery bank in the back to the new Lithium bank? I realize I would have to run another alternator signal cable, but that's a lot easier than placing another DC to DC charger under the passenger seat and running new battery cables all the way back. It would also let me run solar to this DC to DC charger down the line. My concerns /questions:

1. Is it a bad idea to charge from AGM to Lithium? Having it only run with alternator signal cable help at all?
2. Is this bad on the alternator/existing CTEK Smartpass to add another DC to DC down the line?
3. Is there a better way I should be thinking about this?

Thanks-

 

[Supervstech]

This sounds like a bad plan to me, unless the lithium is isolated from the agm, it will have the potential to seriously overcharge, one or the other batteries due to low internal resistance...

 

[ekkonomix]

Ok I'm confused. I thought the DC to DC charger running form the AGM to Lithium does provide isolation?

 

[hour]

Ok I'm confused. I thought the DC to DC charger running form the AGM to Lithium does provide isolation?

You could do a Victron Orion-TR Smart from the AGM bank to the lithium. It has engine running detection so you wouldn't have to run another signal wire, it'd just know to operate based on the AGM bank voltage. I've done this with a TR-Smart from my truck's house battery (lifepo4, but that doesn't matter) to charge smaller lifepo4 portable packs. The solar going in to the house battery and settings on the victron make it see things as a running vehicle.

I don't think this would be bad in any way. It's just another load on your house AGM bank like any other and it's not like it'd be siphoning off your AGM all the time, only when it's being charged.

If you did the CTEK D250 to your AGM and starter battery and added solar you could be charging all three batteries automagically

BTW ammo cans are great for portable DIY lifepo4 setups. I built mine for remote work too, anderson powerpole panel mount round jacks and a USB-C panel mount 60w charger for my macbook.

 

[ekkonomix]

If you did the CTEK D250 to your AGM and starter battery and added solar you could be charging all three batteries automagically

Ok very interesting. I didn't realize this option existed with the Orion-TR. So if I did something like the Orion TR-Smart 12/12-18, which produces more than my solar system (230 watt total and my Zamp usually shows 11amps max), how would the batteries charge? Sorry if this is a basic question, but trying to learn. i.e. Will the Orion send 18 amps to the Lithium bank (from AGM) while 11 amps are coming back into the AGM from the sun? Would I risk draining the AGM since the Lithium bank is bigger? Should I reverse my plan and charge from Lithium to AGM with the Orion instead?

i.e. CTEK 250SE/Smartpass 120s from alternator to Lithium bank and then Orion-TR Smart from Lithium bank to AGM? (meanwhile ditch the Zamp solar controller and run panels direct to CTEK 250)

BTW ammo cans are great for portable DIY lifepo4 setups. I built mine for remote work too, anderson powerpole panel mount round jacks and a USB-C panel mount 60w charger for my macbook.

Ammo cans are something totally new to me. Off to research! Thanks for the ideas.

 

[hour]

Ok very interesting. I didn't realize this option existed with the Orion-TR. So if I did something like the Orion TR-Smart 12/12-18, which produces more than my solar system (230 watt total and my Zamp usually shows 11amps max), how would the batteries charge? Sorry if this is a basic question, but trying to learn. i.e. Will the Orion send 18 amps to the Lithium bank (from AGM) while 11 amps are coming back into the AGM from the sun? Would I risk draining the AGM since the Lithium bank is bigger? Should I reverse my plan and charge from Lithium to AGM with the Orion instead?

i.e. CTEK 250SE/Smartpass 120s from alternator to Lithium bank and then Orion-TR Smart from Lithium bank to AGM? (meanwhile ditch the Zamp solar controller and run panels direct to CTEK 250)



Ammo cans are something totally new to me. Off to research! Thanks for the ideas.

I'd keep the AGM hooked up to the SmartPass and hook the D250 up to that + vehicle battery, too. Just running the Orion as an accessory off the AGM that just so happens to be an (intelligent) charger for another battery. I don't think you'd have any trouble doing that while the engine is on.

While the engine is off though and you're only charging via solar @ 11 amps but discharging at 18 amps through the Orion, yes you would be favoring the lithium being charged over the AGM. Eventually the voltage would drop to your set point on the Orion and it would think the engine is off, and stop charging the lithium (or the lithium would be full and it'd stop charging). You can adjust the charge current via bluetooth app too on the fly, so if you're in peak sunlight and know you'll be getting your 11 amps for a while, maybe drop the Orion down to 7 amps to prioritize topping off your AGM. You can also disable the Orion all together via app at will, to prioritize topping off the AGM from solar or vehicle.

 

[ekkonomix]

While the engine is off though and you're only charging via solar @ 11 amps but discharging at 18 amps through the Orion, yes you would be favoring the lithium being charged over the AGM. Eventually the voltage would drop to your set point on the Orion and it would think the engine is off, and stop charging the lithium (or the lithium would be full and it'd stop charging).

Ahh...this totally makes sense now. I acknowledged the ability to start charging at a specific voltage, but neglected it can also stop at that voltage.

Thank you for the guidance

 

[bodiepetro]

I have a similar situation I am dealing with, large lead acid battery bank and about to add lithium and debating whether to keep as a separate battery bank or combine as you have described. Let us know how you proceed with your setup, good luck!

 

[hour]

FWIW I've been sitting in a field for the last several days with a depleted lead acid camper battery (oops, for the third time) that I've been keeping alive. Truck bed aux lithium battery -> inverter -> battery charger/maintainer -> camper battery. 24 hours a day. It's something I wish I had grasped from the beginning. Everyone bellyaches over efficiency but I've just prevented myself from freezing to death running the camper furnace on a knuckle dragger setup. Replace my lead acid charger with a lithium charger, and source bank from lithium to AGM, and that's you. Just another load when you put something somewhat smart between one battery and another

 

[grizzzman]

I have been running a hybrid LFP-FLA system since last summer. The banks are combined during camping The LFP keeps the FLA bank trickle charged at all times and the FLA load shares during hi amp draws. Works great.