question

7caper avatar image
7caper asked

Charging battery via solar controller load output?

Can a battery be connected to the "load" output of a MPPT 75-15? Will it damage anything?

I wish to charge a second lithium bms protected battery when the primary mppt 75-15 charge voltage gets to near full battery voltage. I would let the secondary battery bms control charging it's battery. I'm trying not to us an Orion or other dc/dc converter. I searched but didn't find a definitive answer. Thanks.

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
wkirby avatar image
wkirby answered ·

The Load Output is switched on and off to the main battery connected to the Battery terminals. This means that the Load Output will always follow the charge profile of the battery that is connected to the Battery terminals of the MPPT.
The MPPT will switch to float even if the battery at Load Output is not ready.
Also, the battery connected to Load Output will continue to charge from the main battery if its Voltage is lower than the main battery, this will continue during the night or when PV power is low.

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.

7caper avatar image 7caper commented ·

Thanks wkirby for that info! Since it looks like I will not damage anything I think I'll connect the load output to a battery and observe what happens. With the many options on the load parameters using the app I think I can get it to charge a second battery after the main battery goes to float.

0 Likes 0 ·
ripper avatar image
ripper answered ·

I have the same question. But more regarding whether the load port can take reverse current. My solar is meant for charging the trailer battery. On and off the scooter is also stored and being charged. If the fridge comes on, the scooter might supply power in reverse through the load connectors before its cut off. Is that acceptable? Cheers.

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.

wkirby avatar image wkirby ♦♦ commented ·

Yes, reverse current will flow into the Load Output terminals even when it is switched off. If there is a battery connected at Load Output whose Voltage is higher than the battery at the battery terminals then the battery at Load Output will discharge into the main battery - even when the Load Output is switched off.

This is because the Load Output is controlled by a MOSFET. MOSFETs have a parasitic diode, also called a body diode, which will allow reverse current even when it is off.

1 Like 1 ·
7caper avatar image 7caper wkirby ♦♦ commented ·

wkirby, that is excellent information! Thank you.

0 Likes 0 ·
over-and-under-victron avatar image over-and-under-victron wkirby ♦♦ commented ·
Huh. Interesting. Thank you for your post.


It shoots down my idea of using the Load output to run my van's stereo. My idea was to land the load output on the starter battery. So, when the van starts - my alternator will effectively start charging my house batteries?


Seems like the best thing to do would have the load output go to a small Orion. Then from the Orion to my start battery.

0 Likes 0 ·