Adding a DPDT switch to the sense lines ?

[EagleOne]

Hello again. I'm still new to this whole solar thing, but I now have my panels up and running on my 'RV'. I am curious if I could put a switch into the battery voltage sense lines for the MS-MPPT60 controller? I would like to take advantage of the sun even when my batteries are full by using the 'system' as a charger for other batteries - such as a friend's or some extra batteries I have that are not connected to my 'house' bank. (All of them AGM)

I have already wired a switch after the 60A DC breaker on the battery + output of the charge controller, so I could switch the output of the controller to feed a second 'load'. I would like to either 'turn off' the existing, and/or 'turn on' a different, sense line if I wanted to use the system to charge other batteries after mine are full. I spent a few bucks (OK, a whole lotta bucks) on the system and I might as well spend a few more to get more use out of it. I have buss/posts to provide 'temporary' bolt-on connections to the charging system.

My usage is spotty, so I have a whole lot of time between uses that the solar isn't really being used. I just wanted to the ability to have it when I needed it.

Is this a do-able scenario? I know I would still have the remote temp sensor on my house bank, but I figure if the batteries are sitting right next to each other during charging I should be pretty close on the temps (as long as I let the temps stabilize a little on the 'other' batteries).

Other than a DPDT switch 'reversing' the lines (I think this is how they work normally), does anybody have any advice about me missing something?

Thanks for any input,
- Chris J.

[Cariboocoot]

Yes it can be done.

In fact, in one sense it must be done for if you leave the sense lines connected to your charged battery it's going to tell the controller that the battery is charged and it won't send much current to a different battery now connected to the output lines.

At the very least you need a SPST on the (+) of the sense lines to disconnect them from your regular battery. The controller will still function, relying on feedback from the charge leads to give it Voltage info on the battery. The sense lines are more accurate in that they don't carry the charge current so the V is the same at both ends, as it were.

You could use a DPDT switch to change both the (+) and (-) from the 'main' battery to the 'accessory' battery and get an accurate reading on it. Just remember you have to switch both the sense lines and the charge lines. This could be built up to a level of complexity that would switch both simultaneously, but that's somewhat unnecessary.

Be sure the 'temporary' connections to other batteries are as solid as 'permanent' ones or else you won't get good charging.

[EagleOne]

Thanks for the reply Cariboocoot. You are very helpful for us new folks.

- Chris J.