question

stefans avatar image
stefans asked

MPPT 75/15 - Charging to 16,8V

I'm trying to charge a Li-Ion battery (not LFP) with a maximum voltage of 16,8V
Using a custom battery configuration, I can set all charge voltages and currents within the solar charger as needed for this battery (12V config)

But when I enable the charging the solra charger does not charge the battery (panel voltage > 20V, battery = 16,22V). It reports the battery status as OFF.

Any hints what to do to charge a Li-Ion battery?


Thx,

Stefan.


MPPT Controllers
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
Mark avatar image
Mark answered ·

The solar voltage must be at least 5v above battery voltage for the charge cycle to start in the morning.

Once charging the solar voltage only needs to be 1v above battery voltage.

It seems that your solar panel output voltage may be a little low for your application. If you have multiple panels consider rewiring them in series.

It's essential to have a decent solar voltage margin above max battery voltage with MPPT charge controllers.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

stefans avatar image stefans commented ·

This is currently only a test setup to determine wthether the MPPT solar charge is suitable to charge Li-Ion batteries. The final configuration will be with solar panels having an idle voltage of 27V and an U(mmpt) voltage of 22V.

0 Likes 0 ·
stefans avatar image
stefans answered ·

Hi Mark,

this sounds reasonable. I will start to discharge my (nearly full) Li-Ion battery to see wether this is the root cause.

Thx,

Stefan

3 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Mark avatar image Mark ♦♦ commented ·

That is one way to get it charging (as a test), but obviously not ideal.

You really need to alter the solar panel configuration or type to obtain a higher voltage output.

0 Likes 0 ·
stefans avatar image stefans commented ·

Hi Mark,

after discharging the battery to a lower level the solar charger successfully started to recharge it with solar power - good.

In the final configuration we will use a solar panel with a U(mppt) of 22V (27V idle) which should be ok for the 16,8V Vmax Li-Ion battery.


Thx again for your help,

Stefan

0 Likes 0 ·
Mark avatar image Mark ♦♦ stefans commented ·

No problem, good to hear it's working as expected.

Try to go as high as practical with the PV voltage in your final setup. It will take less sun to get it charging each morning & go a bit longer in the evening.

0 Likes 0 ·