Victron MultiPlus & MPPT 24V Charger Settings - What are they? Not an exact science!

[HaloThere]

How do you pick the right MultiPlus/Quattro and MPPT Charge Controller settings?

I used the chart below to come up with the corresponding Voltage-SOC settings, based on what I learned in a YouTube video that impressed me, but I don't know if this is correct or if I am doing the best thing with regards to charging my new lithium batteries?

...Or all these settings based on personal preferences, whatever that means?

For starters, I think you want to set your MPPT Charge Voltage equal to your MultiPlus-Charger Absorption Voltage. Is this correct?

The Victron distributor support reps says to follow your battery manufacture recommendations, but this documentation often does not include everything you need to know.

So, maybe this explains why there is a range of voltages printed for each type of system. For example I came across this for lithium batteries:

12V==> 13.8-14.1V
24V==> 27.6-28.7V
48V==> 55.2-56.4V

=== WHAT I CHOSE TO DO ===

This is how I picked the right value for my 24V Lithium charge parameters, and I would like to know if you took a different approach and why?

I also assumed the MPPT "Charge Current" setting to mean the same setting as I used for the MultiPlus Absorption Voltage, which I set to 28.2V. Why?

...I used 28.2V, because my 24V Lithium battery mfg said not to exceed 29.2V charging volts ever, and according to the chart below, 28.2V is still above the 100% SOC mark on the chart below (at rest) which is 27.2V.

I also set the Float Voltage to 26.8V because this is 90% SOC according the the chart.

And, then I set the Smart Shunt device 100% mark (using the Victron Connect App on my cell phone) to "synchronize" 100% SOC with 26.8V, which I verified my battery came to rest at after sitting uncharged for 8 hours.

=== WHY DO IT THIS WAY? ===

My reasoning is based on this logic I gleaned off a YouTube video on this subject:

My 24V Lithium Batteries have 8 cells, and each cell reaches its full charge at 3.65V/Cell. So the max charge setting (Absorption Charge) should not be more than 8 cells x 3.65v/cell= 29.2V

Okay, so did I chose to set the Absorption Voltage to 1V less? ...Well, I think the only difference between 29.2V and 28.2V is the time it takes to fully recharge your batteries, and I typically have plenty of time to cuarge my lithium when I connect to shore power. So, why push it?

And according to the chart below, Float Voltage is also a fully charged battery and that occurs when each of my 8 cells rests at 3.35V. So, I set the Float Voltage to be 8 x 3.35V/cell=26.8V.

What do you set your Absorption Voltage and Float Voltage to?

Note: In theory, a 12V lithium battery setting can be doubled for a 24V lithium battery setting, and 4x for a 48V lithium battery setting.

Would you agree these are good MultiPlus Charger and MPPT Charger settings?

The last picture shows what what one Victron Distributor recommended for a 12V Lithium charger profile, and in red are the settings I chose to use for my 24V lithium batteries. If you see a problem with these settings, or would like to make a recommendation, please let me/us know. Thank you!

[SafariBen]

That all makes sense to me, except this: "24V==> 27.6-28.7V" should be 28.2V as you use everywhere else.



There could be some personal preferences involved. Like you might want the solar or shore power to charge at a slower rate because you figure you'll be plugged in all night, or solar will be charging most of the day (solar should be sized to charge much lower than the Li charge rate usually) but you might want the vehicle alternator to charge at a higher current because you won't be driving all day. In theory if you know you're not using the full battery capacity, you could hold them around 50%, or cycle 80-20 or even 60-40. Probably not worthwhile for an RV, but EV drivers will do that for max battery life (lifetime)

[HaloThere]

The MP + MK3 setup has an "Advanced" option to limit the charge to lower voltage (and corresponding SOC). I have not played with it, but I gather that is what you meant by programming the system to 80/20 or 60/40; thereby letting the free solar power recharge the batteries instead of the shore power to save money.

I'm also guessing an RVer is not the concerned with lowering the charge voltage, because these LiFeP04 batteries claim they have a life of 5000+ cycles, and I personally don't like hooking up the MK3 just to change the MP charge parameters.

As an RVer I don't see the need to lower the charge voltage that much if at all.
And I have 1600W of solar on my roof that keeps me at full charge when I'm driving. And 90% of my travels and boondocking are during sunny days. (So far.)

I will say this: If the Victron MP operated as a "Hybrid" inverter-charger, so I could utilize the free solar when I also have shore power, then that would be a nice feature, but again not a requirement for a traveling RVer.

For grins: If I did want the Victron charger to stop charging at 40% SOC (26.0V) how would I do that? ...Would I just program the MP with the MK3 to set the absorption voltage to 26.0V? ...Or would it be better to use the MP "Advanced" settings to limit the charge to 26.0V and leave the absorption voltage at 28.2V?