Preventing overcharge of lithiums

[Mark_S]

I know that lithium batteries do not like to be kept at 100% SOC for a long period of time, but I can’t figure out how to prevent an RV converter/charger from charging lithiums past a lower threshold. Seems they are all designed to pump the batteries up to 100% SOC ASAP and then maintain them there.

I have the same question regarding the Jayco-provided gopower solar charger.

Ideally I would like to set a lower maximum SOC threshold (for example 80% or 90%) and not allow either charger (shore or solar) to exceed that SOC unless I am boondocking in which case I will then manually set the SOC threshold to 100%.

Basically I’m looking to treat the RV lithiums exactly the same way as electric cars do... stop charging them at a lower threshold unless you need a “range mode” charge.

Can you recommend a converter/charger that can be configured to stop charging the lithium bank at a lower threshold? What do you do to prevent the solar charger from going to 100% SOC as well?

[Bookemdanno]

I know that the Battle Borns have a built in BMS, as well as most brands. I don't think that you'll have a problem, as long as your batteries have the BMS.

[craigav]

There really isn't a great way to do this, however one way to do this is to use a Powermax PM3-60LK power supply (they make these in other amps as well such as the PM3-100LK) which has adjustable voltage and set the voltage to a lower value (~14v) when you don't want the Lifepo4 batteries to become fully charged and then to the higher value (~14.5v) when you want them charged 100%. I have two powermax pm3's one set at each voltage because adjusting the voltage is not convenient to do all the time. Another option (in addition to the adjustable voltage charge) is to use a battery monitor that measures Ah (amp hours) and then calibrate it for the amp hours you have (lets say 100ah for this example) and then when the battery is fully charged drain ~20 amps back out of it prior to long term storage or when you don't need 100% charge. The one linked here once calibrated will measure what goes in and out of the battery and give you a good idea of the percent charge you have. Even with this, you still have to have a way to stop charging once you hit the percentage charge you prefer, which back to the powermax, if you control the charge voltage to a constant voltage charge of say 13.8~14v, your battery will never reach full charge and the battery monitor will give you an idea (pretty close) to the charge level.

I have quite a few Lifepo4 batteries that I use for standby power here at my house, but I haven't setup my RV just yet. I have a good idea with my plans though when time allows I will likely install ~350ah of lifepo4 in my RV and use two powermax converters, one set at ~14 and the other at 14.5 along with the item linked here to accomplish what you are asking about. Not all Powermax converters allow for adjusting the voltage so be sure it has the two holes on the side, first hole you turn off the 3-stage charging and that sets it for CV (constant voltage) charge and the second hole has the voltage adjustment.

As I write this and think about it, I have a 138ah lifepo4 in my RV now but the converter in the RV never charges it up fully, I think the current RV converter runs close to 14v (need to check again). So what I may do is simply add one of the powermax converters set at 14.5~14.6v and never turn it on until the times when I want 100% battery capacity and leave the existing converter as it is for all the other times.

https://www.ebay.com/itm/DC-120V-500...cAAOSwOIlb1Wva

~CA

[craigav]

Regarding solar, you need a solar charge controller with adjustable voltage similar to what I was saying with the converter. Or at minimum if it has setting for different battery types, you can set it for regular batteries (lead acid) when you don't want a full charge and to lifepo4 when you do want 100% charge, having an adjustable charge voltage though would be best and just set the voltage lower when desired. ~CA

[01tundra]

I just charge mine to around 90% SOC and then turn the disconnect switch off if I'm not going to be using them for a while.

I turn the batteries on after unhooking from shore power before pulling out for a trip, if we are camping with hookups I simply turn the battery switch back off while camping and connected to shore power.

It's a pretty simple process.

The batteries have internal BMS to prevent overcharging, but I prefer to just manually control our batteries.

I've seen some people use the Victron BMV-712 with a relay to cut charge at a certain point. The BMV App has a relay control option. Set the relay to disconnect the batteries at whatever SOC you desire. Toggle the relay control off in the App if you want to go to 100% SOC.