DC Output Swith Options

mjp24coho

All-
I’m trying to find a way to wire in DC output switching ability for my PV/battery system.* I currently have 450 Watts of panels feeding a charge controller that charges by 400 AH battery bank (12V).* I also have a separate PV array that powers a Grundfos deep well pump. However, that pump isn’t need in the winter, so I’m looking at a way to utilize the well pump PV array to charge my battery bank via a separate charge controller in the winter (rather than having all that PV wattage go unused).* To do that, I’ve looked into getting some kind of a transfer switch (which is wired to both the well pump controller and solar charge controller), where the well pump array wiring would come into the switch, and you could switch it to go either to the well pump controller or charge controller.* The benefit of that system is that it would always be wired, and I could easily switch it back and forth.* However, I could find any kind of a switch that could do this (especially given the ~140V DC coming from the pump panel array.* So I thought I’d reach out to the group to see if anyone is aware of any switch that could meet these needs.
*
One alternative I considered would be to modify a Midnite PV Combiner to do this, where the input from the pump array panels went to the combiner.* Within the combiner, the DC- would go to the DC- busbar, with the positive going to the DC+ out bus bar, which would then feed the input to (2) separate 300V DC breakers (on the input side).* The DC+ output from one of the breakers would go to well pump controller, and the DC+ output from the other breaker would go to the solar charge controller. This way, the breakers could be used as switches – turn the pump controller breaker off (and the solar charge controller on), to send power only to the solar charge controller, and vice versa.* Would this work (safely)?* Anything I’m missing here?* Any other ideas would be appreciated.* Thanks.
*
Mike

mjp24coho

Re: DC Output Swith Options

Attachment not found.I wanted to bring this previous question back to life. I have a wiring diagram with the proposed wiring above (see attached). Can you guys take a look at the proposed wiring and challenge it, to see if it will safely accomplish my purpose? Thanks.

H2SO4_guy

Re: DC Output Swith Options

I do something similar to switch where the panels go. The panel wire comes into a Midnite breaker and the output of the breaker is split between however many choices I want to be able to send it. Example: String one comes into a breaker, the output of the breaker goes to 3 breakers so it can be switched between charge controller 1, 2, or 4. It does take more breakers, but works just fine. Just make sure that you don't have more than one of the output breakers on at the same time. I can take the strings of panels and send them to different charge controllers so as to not have dedicated panels per charge controller, but I do have dedicated charge controllers per battery pack with temp. sensors. It does work for me and I was trying to do things on the cheap and still be safe.

Your drawing would do the same thing, just make sure that you don't have both breakers on at the same time.

Good luck and let us know how it works!

mduck

Re: DC Output Swith Options

Hey Mike,
Thanks for your post. I have also been looking for a DC transfer switch for sometime now. But ran into the same high voltage problem as you did.
Have you had a chance to build your well pump combiner box switch yet? I also have a Grundfos deep well too, that I want to divert solar power when its not pumping.
I have drawn up a design for my solar well ... Attachment not found. both current design and proposed Configuration . The Well has been operational for about eight months now and will provide water to my retirement home which is under construction. Note that I took the liberty of putting your Combiner Switch in the design. Again thanks and let me know how it worked out for you. Thanks Mike Duck

inetdog

Re: DC Output Swith Options

mjp24coho wrote: »

This way, the breakers could be used as switches – turn the pump controller breaker off (and the solar charge controller on), to send power only to the solar charge controller, and vice versa.* Would this work (safely)?* Anything I’m missing here?* Any other ideas would be appreciated.* Thanks.
*
Mike

The biggest factor in the cost of a DC switch or breaker the need to safely interrupt a high current high voltage DC load in the course of switching or transferring.
One way to reduce the cost would be to set up one or more DC switches that can handle the necessary current when closed and voltage when open, but using one single DC beaker or switch upsstream of them to interrupt the panel output current before you change the position of the cheaper switches and then turn the breaker back on again.
Ideally you would want to interlock access to the switches to prevent somebody inadvertently switching the selector switches while the breaker was still closed.

WNY Dave

Re: DC Output Swith Options

inetdog wrote: »

The biggest factor in the cost of a DC switch or breaker the need to safely interrupt a high current high voltage DC load in the course of switching or transferring.
One way to reduce the cost would be to set up one or more DC switches that can handle the necessary current when closed and voltage when open, but using one single DC beaker or switch upsstream of them to interrupt the panel output current before you change the position of the cheaper switches and then turn the breaker back on again.
Ideally you would want to interlock access to the switches to prevent somebody inadvertently switching the selector switches while the breaker was still closed.

In one of the build threads on someones breaker box, I saw opposing breakers with a bar attached to them, so when one breaker was pushed off, the other one came on and visa versa, so neither would be one at the same time. it was screwed or mounted to the tabs of the breaker.