Voltage switching circuit

[kenl]

 I'm looking for a circuit that will turn on a definite purpose contactor when my batteries are fully charged. Currently I just heat water when this happens through my controllers dump load circuit. What I'm trying to do is run my fridge during the day when I'm producing excess power and then have it return back to mains power when the sun goes down and the batteries start to discharge. Any direction from the board would be great. kenny

seemed like a good idea at the time

[Hilltopgrange]

Hi Kenny

        You could a voltage alarm type meter

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190044523993&fromMakeTrack=true&ssP
ageName=VIP:watchlink:middle:uk

I use these to control my dump loads etc, the internal relays can be configured to trip on and off at any level you choose. I would not depend on the internal relays to carry much load. I use mine to switch solid state relays for ac loads.

Only snag is they need a min of 20v, so not much use if your on a 12v set up. I am all 48v so its not a problem.

Hope this helps!

Russell

 

[ghurd]

Guessing the definite purpose is not a constant load?  Maybe a `fridge, etc?

A non-constant load or a load under the peak power input will still need the dump controller and load.

Kind of sounds like you are looking for the antique `bang-bang' controller, maybe set a bit lower for the high trigger point.  When the battery reaches the high trigger point, the relay would send power to the definite purpose device until the batteries are down to the low trigger point.

The load specifics need to be known to get much good information.

G-

[kenl]

 ghurd, I think I sorta kinda see where your going with this. The dump load would still be used on the charge controller because the fridge load would not be enough to consume all the excess current from the pv's due to not being a constant load. I guess what I was looking for was some type of electronic circuit that could be hooked to the battery and read the voltage, when the voltage hit around 28.6v, flip a dry contact to energise a dpdt contactor and switch the fridge to the inverter power. It would need a low point setting also so when the batteries hit say 26.5 volts the fridge load would be put back on mains power.

  Hilltopgrange linked to something that could do the job, but would like to see what other members are using for this type of control. Thanks for your input. kenny

seemed like a good idea at the time

[ghurd]

Will the inverter run the fridge?

When the batteries first hit say 28.6V, and the fridge kicks on, how far do the batteries drop at that instant under the start-up surge?

I have a couple ideas.

G-

[kenl]

Ghurd, The inverter will run the fridge no problem. Te fridge doesn't like it if I switch to inverter power when it's running though. Been reading the posts lately haveing to do with that issue. The inverter is 24v 3000w without a charger. I'm only running 400 ah of bateries right now at 24v but they don't get draged down too much when the fridge comes on and the sun is shining, maybe 27-26.7v max and the dump starts switching a minute or two after its running. The PV's are 6 @ 110w and 2 @ 120w wired in pairs in series for 24v. Have 4 more 94w panels but don't have enough load to use the extra current. I'd be interested to hear what you have in mind.Would really like to use the excess power the system generates for something besides heating a bucket of water. kenny

seemed like a good idea at the time

[ghurd]

I'll try to send you an email in ~14 hours. G-