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Using a Victron DC-DC charger as a 'battery maintainer/tender'

mkeys

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My setup is in a 2020 Sprinter van with a large (700ah) lithium bank of batteries used as the 'house' battery for all of my loads. This is used as a camper van and a common use case would be to park somewhere fun and not start the engine for days.

All the coming/going from the van through the day triggers the van dash computers to come on and it puts a beating on the starter battery. It isn't uncommon to get a low voltage warning after a few days of not driving in this scenario.

I want to setup a battery maintainer that I can just set and forget. All of the devices I have seen for this use case run on AC power, but I do not run an inverter 24/7 so my solution will need to be DC.

I bought a Victron Smart Orion-TR 12/12-18 charger for this purpose. It is wired to charge the starter battery from the house and only gets activated when the van engine is OFF. However I have read conflicting information online about if it is healthy for the battery to leave this on 24/7. So I currently manually flip this charge on/off using breakers when I think it is appropriate.

What I am hoping to gain here is confidence/knowledge on two questions:
  1. Is it healthy to keep an AGM battery ( Specifically this battery ) on float all the time. Basically anytime the van is off the charger would activate, and in most scenarios I would expect it to very shortly end up in the 'float' stage of its charging profile as the vans own charging system would have just finished charging the battery.
  2. If it is healthy to keep a battery on float, are there any tweaks I would want to make to the float voltage in the Victron profile.
Thanks,

Matt Keys
 
Is it healthy to keep an AGM battery ( Specifically this battery ) on float all the time. Basically anytime the van is off the charger would activate, and in most scenarios I would expect it to very shortly end up in the 'float' stage of its charging profile as the vans own charging system would have just finished charging the battery.
All lead acid batteries need to be kept at 100% SOC as much as possible. Since the battery you linked to is not a deep-discharge battery. It is even more important to keep it at 100% SOC. Given what you have described as the use case, it should work well while you are out camping.

What will you do when the van is parked? For long-term storage, there are conflicting needs. The LiFePO should be stored at ~50% - 60% SOC and the AGM should be stored at 100% SOC. Consequently, it is best to separate charging the starter battery from the house battery when stored for long periods. You can leave the LiFePO 4 completely disconnected for a few months, but need some kind of trickle charge on the starter.

If it is healthy to keep a battery on float, are there any tweaks I would want to make to the float voltage in the Victron profile.
In the Victron Connect app. Go into settings (The little Gear icon) -> Battery Settings. At the top, there is a pull-down menu with 'factory default' selected by default. Choose 'Select Preset'. In the pop-up choose AGM Spiral Cell.

This will give you the best default and should work reasonably well.

Note: All lead acid batteries have slightly different chemistries so the charge and float values are also slightly different. If you want to hone it in to the absolute best settings, you would need to get detailed values from DieHard for the various settings and then create a user-defined charge profile for the charge controller. The last time I tried to get detailed info for a Diehard LA battery, I was unsuccessful. This was several years ago and maybe they have changed, but I would not hold my breath.
 
Thanks for your response @FilterGuy.

It sounds like from what you are saying, not only would it not hurt the battery to use this DC-DC charger full time, it could only be considered a benefit to that starter battery.

What will you do when the van is parked? For long-term storage, there are conflicting needs. The LiFePO should be stored at ~50% - 60% SOC and the AGM should be stored at 100% SOC. Consequently, it is best to separate charging the starter battery from the house battery when stored for long periods. You can leave the LiFePO 4 completely disconnected for a few months, but need some kind of trickle charge on the starter

This van has yet to really go into long term storage, it tends to get used periodically throughout the month even if we aren't on a big trip. There are a number of parasitic draws on the house battery so the SOC is often around 85-95%. Not the 50-60% you recommend but better than 100% anyways. Using the house full time as a battery tender for the starter battery would be one more draw on the house keeping it a bit lower, maybe for the best.
 
not only would it not hurt the battery to use this DC-DC charger full time, it could only be considered a benefit to that starter battery.
This ?

This van has yet to really go into long term storage, it tends to get used periodically throughout the month even if we aren't on a big trip. There are a number of parasitic draws on the house battery so the SOC is often around 85-95%. Not the 50-60% you recommend but better than 100% anyways. Using the house full time as a battery tender for the starter battery would be one more draw on the house keeping it a bit lower, maybe for the best.

I’m always wary of parasitic draws. Everything is always alright till it’s not.

Thinking it through, if set up correctly the charger will only charge when the battery it’s charging needs it. It sounds like the primary problem is the constant activation of the vehicle systems due to activity like doors opening etc. If there is no activity it should mean minimal system activation power use so minimal charge draw
 
I’m always wary of parasitic draws. Everything is always alright till it’s not.
Yeah I keep an eye on the SOC with a shunt and display that is fairly visible. I also use a Victron Battery Protect which will disconnect power to all loads if the SOC of the house bank gets too low.

Thinking it through, if set up correctly the charger will only charge when the battery it’s charging needs it. It sounds like the primary problem is the constant activation of the vehicle systems due to activity like doors opening etc. If there is no activity it should mean minimal system activation power use
Yeah with no coming/going activating the van dashboard it should have very minimal draw to keep that AGM floated.

I am going to enable it and keep a close eye on it over the coming days and make sure everything looks good.
 
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