Another AGM to Lithium conversion question

[nuwarrior]

Current state:
I currently have some 12V AGM batteries in my FWD Fleet that are 9+ years old that I would like to replace. I already installed a 200W solar panel with a Bouge RV controller with lithium charging capability.
I currently have the Blue Sea ACR and the Atwood plug going to the truck battery.
The truck has an aftermarket alarm that has a parasitic draw that will kill the truck battery if it sits a few days w/o using. But the solar panel keeps the house batteries charged and provides a back up to the truck battery so everything is hunky dory in current state and I can leave the truck parked for days w/o worrying whether it will start or not. It fires right up.

Future state:
I purchased a 100 AH lithium battery to do the upgrade but not sure how to set up the connections.

I really only want the new lithium battery to provide backup power to the truck. I do not need the alternator to charge the house battery as the solar panel does just fine on its own.

I've read where you should not mix lithium batteries with agm which is what the truck has so not sure if I need to use a dc to dc charger between the lithium to truck battery and if I need to bypass the relay etc.

The FWC Lithium Manifesto says I can just "chuck one in there" which is what I'd really love to do but want to make sure I am not missing anything that would kill my new lithium battery.

I'd appreciate some guidance as I don't want to remove the alarm system in my truck as it has remote start and lock/unlock capabilties that come in handy.

TIA

 

[K7MDL]

You can put the Li battery in and set the solar charger preset for the Li type battery. I would force off, or disconnect the ACR, or just do not connect your camper to the truck since you are fully on solar charging.

The Li batteries run at 14.4V or so and in time may overcharge your starter battery if left connected. The Li should eventually float at 13.6 and the cable drop may help prevent starter battery overcharge so in practice so you might get away with mixing them. Another consideration with leaving the start and camper batteries connected is your alternator max available output. The Li battery can draw a lot of charge current, limited somewhat by your cable loss.

Seems like in your case not connecting your camper will be the norm, but you could likely plug the camper into the truck for the odd time you need a truck charging boost.

 

[rando]

I think it is fine to mix them. I am in the same situation you are and have been doing this for the past 7 years with no issue still on original truck AGM and lithium camper batteries.

 

[CPT Davenport]

I just "chucked one in there" I did disconnect the lithium house battery to alternator wire to avoid damage to my smart alternator. My lithium stays topped off with solar but I have charged it off of shore power, and it only charges to 90 something % that way. Set the charge controller to lithium and away ya go.

206ah SOK lithium with 175w solar.

 

[Vic Harder]

The voltage level difference is actually NICE if you are wanting to charge your truck from the camper. In the winter when the rig is mostly parked and covered, I keep it plugged into shore power, camper power systems off, but the victron gear is set to "float" at 13.3V, which is a nice trickle charge for the truck batteries.

 

[nuwarrior]

So it sounds like I'll be chucking the lithium battery in there this weekend. If others have done it then I feel better than my odds are good as well.
If I start having problems, then I'll follow K7MDL lead and put a battery disconnect on the cable to the truck and only connect it when I need a boost.
Thanks for all the replies and advice.
Appreciate it!

 

[GflGdog]

Im also considering this conversion. From what I read on the threads here, running 6 awg wire from battery to bed plug, and from bed plug to battery, installing a victron dc2dc controller, removing/disabling the Blue Sea ACR, anything I am missing here besides the battery upgrade? Looking at the powerus 200ah BT self heated battery.

 

[Vic Harder]

breaker at the truck end of the wire, 6-12" from the battery/alternator. Shunt. Potentially +ve and -ve busses.

 

[nuwarrior]

I just want to give a quick update. Everything is working as before with no changes other than the battery swap. I simply replaced the AGM batteries with the Lithium and I was good to go.
As an added bonus, I reduced the weight of the camper by ~80 lbs. Each AGM was 50 lbs x 2 =100 lbs vs Lithium is 19 lbs.
I also recouped a bunch of space in my battery compartment and was able to mount the solar controller to the cabinet wall and still had room for other things like my portable power station and I still have a little bit of room left.
I don't have a before pic but the 2 AGMs took up most of the compartment space. Attached is the new look with lithium battery toward back of compartment.
Thanks again for all the feedback and hope this helps someone else.

 

[pawleyk]

I think it is fine to mix them. I am in the same situation you are and have been doing this for the past 7 years with no issue still on original truck AGM and lithium camper batteries.

How are they connected?

 

[Openroad]

breaker at the truck end of the wire, 6-12" from the battery/alternator. Shunt. Potentially +ve and -ve busses.

Why 6-12"? I have my Blue Sea breaker at about 4". Is there a safety issue here? I always thought the closer the better.

 

[Vic Harder]

oh gee... 4" is even better

 

[K7MDL]

The distance is a calculated risk of cable damage that may occur resulting in an unprotected short circuit scenario. The longer the cable between the protection device and the battery, the higher the risk. If the cable is protected (sheathed or in a conduit) then longer lengths are allowed. The distances are set by experts and experience in various standards in marine, RV and vehicle regulators and manufacturers.

These standards were primarily created for batteries before LI with built-in BMS protection so some upading is likely needed. Regardless, if the battery can put out more current then the BMS will limit than your cable size can handle under short circuit condition, then you need a breaker or fuse. Fuses should be selected to protect the wire 1st, the load 2nd. Ideally loads have their own fusing.

 

[Openroad]

The distance is a calculated risk of cable damage that may occur resulting in an unprotected short circuit scenario. The longer the cable between the protection device and the battery, the higher the risk. If the cable is protected (sheathed or in a conduit) then longer lengths are allowed. The distances are set by experts and experience in various standards in marine, RV and vehicle regulators and manufacturers.

These standards were primarily created for batteries before LI with built-in BMS protection so some upading is likely needed. Regardless, if the battery can put out more current then the BMS will limit than your cable size can handle under short circuit condition, then you need a breaker or fuse. Fuses should be selected to protect the wire 1st, the load 2nd. Ideally loads have their own fusing.

Thanks to you, Vic and many others. If it weren't for all you guys with the expertise, guidance and help I would have never been able to do my upgrade from AGM to Lithium (with all the associated components). Tip of the hat !!!