Dialing in MidNite Kid LifePO4 settings

[ChrisCarr]

Hey Guys,
So currently setting up a "new to us" motor home for some adventuring this summer.
Current setup..
2X200 watt panels, Midnite Kid with whizbang jr, KISAE 2000 watt pure sine inverter & 280 AH DIY LifePO4 with JBD BMS
Battery is pretty much brand new and other then some light testing has not really been cycled.

Now my question

My charge controller absorb settings.....I have it at 14.2 volts for 15 min. Pretty much everyday it goes to float and says the battery is at 100%, the BMS how ever says about 40%.
So, wondering if I should increase absorb time?
Is posible they will ballance out after getting some "real" use?

 

[sunshine_eggo]

DID YOU TOP BALANCE YOUR CELLS? IF YOU DIDN'T, YOU MAY NOT BE ABLE TO FULLY CHARGE.

You're likely not triggering the sync requirements of the BMS. It won't show until it's been charged to true 100% at high 3.5V+.

Do you see the 14.2V on the battery BMS or just the MPPT?

If there's a voltage drop between the KID and the battery, you're falling short.

Recommend:
Confirm presence or lack of voltage drop by measuring voltage at the KID output terminals and the battery terminals.
Fully charge to 14.6V for two hours or until the BMS syncs to 100%.
Once synched adjust absorption down to 14.2V and tailor absorption period as needed to cut off when current drops to < 10A.

 

[ChrisCarr]

DID YOU TOP BALANCE YOUR CELLS? IF YOU DIDN'T, YOU MAY NOT BE ABLE TO FULLY CHARGE.

You're likely not triggering the sync requirements of the BMS. It won't show until it's been charged to true 100% at high 3.5V+.

Do you see the 14.2V on the battery BMS or just the MPPT?

If there's a voltage drop between the KID and the battery, you're falling short.

Recommend:
Confirm presence or lack of voltage drop by measuring voltage at the KID output terminals and the battery terminals.
Fully charge to 14.6V for two hours or until the BMS syncs to 100%.
Once synched adjust absorption down to 14.2V and tailor absorption period as needed to cut off when current drops to < 10A.

Thank you for the info.

Yes, cells were top balanced to within .002 of a volt.
As for voltage drop between the kid and battery....I've never been around to observe the absorb stage. However the BMS and Kid have show the same voltage at all other times.

As soon as I get a sunny day (damn crappy weather this spring) I'll give your recommendation a go.

Then afterwards wile the RV is not in use, I know litium doesn't like to be stored at full charge. Do most people disable charging until needed?

Thanx Again

 

[sunshine_eggo]

Thank you for the info.

Yes, cells were top balanced to within .002 of a volt.

This is confusing. Are you saying you charge all cells to voltages between 3.648 - 3.650?

As for voltage drop between the kid and battery....I've never been around to observe the absorb stage. However the BMS and Kid have show the same voltage at all other times.

Is the KID fed by some other voltage sense like a shunt or other sensor? If that's the case, then it doesn't matter if you have voltage drop. In most cases, I would expect the KID to show a little higher when under max current in bulk mode.

As soon as I get a sunny day (damn crappy weather this spring) I'll give your recommendation a go.

Good luck!

Then afterwards wile the RV is not in use, I know litium doesn't like to be stored at full charge. Do most people disable charging until needed?

Thanx Again

Depends on temp too. Cold/cooler temps don't matter much. Warm temps can accelerate degradation when stored at full charge.

One option is to drop absorp/float to 13.15 and discharge it to about 70%. That should allow the battery to discharge ot the 40-70% range and hold it there.

Worth noting that it's very common for DIY LFP batteries to lose their top balance even after short periods (1-2 weeks) of storage.

 

[ChrisCarr]

This is confusing. Are you saying you charge all cells to voltages between 3.648 - 3.650?

Oops sorry, I meant they were top ballanced and since then the cells usually sit within .002 of a volt of each other

Is the KID fed by some other voltage sense like a shunt or other sensor? If that's the case, then it doesn't matter if you have voltage drop. In most cases, I would expect the KID to show a little higher when under max current in bulk mode.

The kid has the "Whizbang Jr" added, which is connected to a shunt.

Thanx

 

[sunshine_eggo]

Oops sorry, I meant they were top ballanced and since then the cells usually sit within .002 of a volt of each other

Top balancing is pushing all cells simultaneously to or near 3.65V. Sitting there with voltages within .002V of each other tells you nothing about balance. Balance is about state of charge, not voltage. You KNOW 100% SoC is 3.65V. You KNOW 0% SoC is 2.5V. Those are the only two places you can accurately balance cells.

You are likely to find that you're unable to hit 14.6V due to one or more cells being "runaway" where they hit the protection voltage while the others are less then 3.40V.

The kid has the "Whizbang Jr" added, which is connected to a shunt.

Okay, so that eliminates any voltage drop concerns.

 

[ChrisCarr]

Top balancing is pushing all cells simultaneously to or near 3.65V. Sitting there with voltages within .002V of each other tells you nothing about balance. Balance is about state of charge, not voltage. You KNOW 100% SoC is 3.65V. You KNOW 0% SoC is 2.5V. Those are the only two places you can accurately balance cells.

You are likely to find that you're unable to hit 14.6V due to one or more cells being "runaway" where they hit the protection voltage while the others are less then 3.40V.



Okay, so that eliminates any voltage drop concerns.

I have a question about voltage drop....I have calibrated my charge controller (MidNite Kid) to the same voltage that my BMS reads wile floating. But have noticed it will always read higher wile in bulk/absorb mode (sometimes a few 10ths of a volt) causeing it to jump to float prematurely. Should I calibrate for bulk voltage instead? or just bump up my absorb voltage by .1 or .2 volts instead?

Also... I'm currently having an odd behavor....ocasionaly the charge controller will not start a new bulk stage for a new day. It just starts the day in float and stays there unless I re-boot it. Not sure if this is from my messing with the caliberation or not....but thought it was worth a mention.