Bulk, absorption and float — why are my battery (almost) always full with standard settings for 48v LiFePo4 Off Grid? (Victron)

[Messier11]

I finished my Off Grid build based around a Multiplus II 48/5000, Victron MPPT, 16p 280AH Eve battery and a JK BMS.

It’s working great. But one thing is unexpected to me — my battery is always full!? I expected it to get to 100%, then drop down to like 40% floating before it started another bulk session to 100% again, absorption for like a hour, before floating to 40%. Are my settings wrong?

I use the standard settings, I think!?





This is some data from the VRM:

 

[Messier11]

A picture of my system:

 

[upnorthandpersonal]

Why would it go down to 40%? Your float voltage is at 3.375V per cell, which is still pretty much full full after you reach 100% state of charge. Your solar controller is probably keeping your loads going for much of the time (isn't summer in the north nice ) and recharging once you hit that 3.375V per cell (which really is reached as soon as you have a somewhat decent load on the pack).

 

[upnorthandpersonal]

Personally I think your absorb voltage is a bit high - you can definitely drop that in summer time since you have the time to absorb at e.g. 3.45V per cell even.

 

[Messier11]

Why would it go down to 40%? Your float voltage is at 3.375V per cell, which is still pretty much full full after you reach 100% state of charge. Your solar controller is probably keeping your loads going for much of the time (isn't summer in the north nice ) and recharging once you hit that 3.375V per cell (which really is reached as soon as you have a somewhat decent load on the pack).

I am looking for a combined refrigerator and freezer and a few other appliances. This doesn’t work, we consume far too little electricity! But the summer light is amazing right now, get good production from 8 to 18, and it never get darker than this (snapped 00.15):


OTOH, I was looking at my sun tracker app, and darn, already in late September it starts to get darn dark here and the sun is so low, will get shadowing on the roof from pretty short trees…

Hope everything is well on your side of the border!

 

[LittleLebowski]

Very cool window into another part of the world, thanks for sharing.

 

[upnorthandpersonal]

Hope everything is well on your side of the border!

Pretty good; not as hot as it was a week or two ago, so I can actually get stuff done.

already in late September it starts to get darn dark here and the sun is so low, will get shadowing on the roof from pretty short trees

I'm surrounded by trees on three sides of the property, so yeah, I know the feeling...

 

[Bluedog225]

Nice set up.

 

[Rocknemo]

Can you explain what type breakers and size cable you have going with your setup, trying to decide what I need to use.

 

[Bluedog225]

Can you explain what type breakers and size cable you have going with your setup, trying to decide what I need to use.

Seconded.

 

[Bud Martin]

I am also curious about those 4 breakers wiring on the top right with wires looping through on the top side.

 

[Rocketman]

Nice job wiring - looks good.
What is all the little boxes and circuit boards for? You have several items that I don’t recognize and I like to learn what others do..

Thanks!

 

[Wet1]

With the sun up around the clock, it's no surprise your batteries are always full!

I think I would probably raise the balance voltage to 3.4 (or even a little higher) to keep out of the flatter part of the curve as well.

As others have said, nice looking setup!

 

[Messier11]

Thanks guys, this is the rough design, albeit not 100% updated, I will post the actual breakers I wound up getting later. I must however caution that I am not an electrician nor that knowledgeable. Known faults: the 35mm2 cables are too small for the fuse, albeit good margin to how much I can use. The MCB between the MPPT and inverter can never trip, it’s at best a breaker. Never trusts it alone anyway. And yeah, I don’t have the 48v to 12v function yet, but I got a one panel two hobby 12v system in place since before and runs the RPIs and small appliances on that instead. I actually considering just hooking up a Ctek or another charger to the AC out 2 to keep that running.

 

[Messier11]

The T fuse situation for us in Europe isn’t workable. I ended up paying 200 USD for my fuse and a holder, and it took like 6 weeks to get it. There are cheap alternatives that are very similar, but much cheaper.

Like this, that can be had for like 20-30 bucks:

https://www.distrelec.de/en/knife-blade-fuse-200a-400v-din1-schurter-1301-0226/p/30087888

 

[JayEmmEll]

Does anyone else find it odd that the MPPT isn't turning off at night? Am I looking at this wrong or is there no nighttime where you live?

 

[upnorthandpersonal]

Does anyone else find it odd that the MPPT isn't turning off at night? Am I looking at this wrong or is there no nighttime where you live?

He doesn't really have darkness this time of year. It's like where I am - it's light 24/7. My charge controller makes a few Watts even though it's the middle of the night and the sun is on the horizon in the north.

 

[Messier11]

Does anyone else find it odd that the MPPT isn't turning off at night? Am I looking at this wrong or is there no nighttime where you live?

Yeah, I was unsure of that myself, but I recon DC out on the inverter also can pull DC power.

 

[DJSmiley]

For Europe, the bs88 fuses are a lot cheaper and easier to get.
Example eg the Eaton/Bussmann TKF250 or ED250