question

deangi avatar image
deangi asked

MPPT different voltage to BMV712

Hi, I have setup a new system. 100ah lithium battery, SmartSolar MPPT, BMV712, Multiplus 12/1200 and Cerbo GX.

All settings as per the advice on here and the videos.

All seems good except the MPPT is reading a higher voltage than the BMV by .1v, so instead of charging to 14.4v/13.8v, it is charging to 14.3v/13.7v.

Here is the VRM screenshot:

untitled.png

They are very close to each other on short cables.

The battery is at 13.7v, so it is the MPPT that is reading incorrectly.

Is this normal? Should I increase the absorption and float voltages on the MPPT to get it to the correct level?

Thanks

Dean

MPPT Controllers
untitled.png (40.8 KiB)
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
Mike Dorsett avatar image
Mike Dorsett answered ·

It is not unusual for the MPPT to have a slightly higher voltage reading when charging - there is some internal voltage rise as well as the volt rise in the cables connecting the charger to the battery. If you have a venus OS device in the system with DVCC enabled, the Venus device will send the correct voltage readings to the MPPT. Raising the MPPT set points would endanger the battery - as the voltage rise is I*R where R is the resistance of the cables to the battery. This would only affect the absorption voltage at max current - the voltage difference should tail off as the battery approaches full charge.

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.

deangi avatar image deangi commented ·
Thanks Mike. I have enabled DVCC, which should bring them in line.
0 Likes 0 ·
deangi avatar image
deangi answered ·

UPDATE. I thought I would put it on mains charging to see.... It now seems to have brought the 2 in sync!

So, mains now off, and I will see what happens when the sun comes up tomorrow on the MPPT.

Also, should have stated in the original post, this is on a motorhome/RV.

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.