Hi, I have only thought about it slightly so far, but can I direct current from the PV panels to an element once the batteries are charged with one SSR? It seems with only one relay the input to the classic will still be connected to the panels. Is this ok: Do I need two relays?
Thanks,
Midnite has in the past advised against pv side diversion. When this has been discussed previously, as i recall you need two things:
- a diode to prevent backfeed to the classic.
- leave some current for the classic to manage mpp.
Dgd is the one to ask, he does it this way.
Quote from: zoneblue on October 09, 2014, 05:34:40 PM
Midnite has in the past advised against pv side diversion. When this has been discussed previously, as i recall you need two things:
- a diode to prevent backfeed to the classic.
- leave some current for the classic to manage mpp.
Dgd is the one to ask, he does it this way.
Ok thanks, I see this:
A simple water heating solution is to simply divert some of your PVs to a heating element when the Classic is in Float. This way the power for water heating is not going through your Classic and you get to retain your doorstop.
All you need is an SSR and diode
Dgd
So that sounds pretty hopeful. My element will take a maximum of 12 amps at 24 volts ( 6 ohms) . The panels will put out a maximum of 26 amps at 72 volts. What value diode would I use?
Also, I have attached a diagram bottom example) from a site to set up a Waterspout generator. Is this circuit the one that's no advisable?
I would love to do the top system and that way the voltage is a steady 24 volts but not sure how successful it will be.
Remember the water turbine is a PV array in my case.
Thanks,
Quote from: asdex on October 09, 2014, 09:29:37 PM
So that sounds pretty hopeful. My element will take a maximum of 12 amps at 24 volts ( 6 ohms) . The panels will put out a maximum of 26 amps at 72 volts. What value diode would I use?
Your element is likely 2 ohms (not 6), remember resistance is voltage divided by current with wattage of near 300w.
If you connect your PVs to this with an MVP of 72v then the max current through a 2 ohm element could be near 36amps.
Since your array can make 26amps then that would be 72 *26 = over 1800 watts. It's doubtful your 300watt rated element could cope with this and would probably just burn up.
You probably need to work backwards using a 120volt rated element so for example a 2kw/120volt element will take about 17.5 amps and be about 7 ohms.
With input of 72volts that will take 10 amps giving you 720 watts power.
That will work well with your array, you could even design it so that only 720 watts or just above this was switched by the SSR to your element.
The diode is placed between the classic +ve input and the +ve from the PVs being switched by the SSR. Best to use a bridge rectifier connecting PVs to both Ac inputs wired together and output from +vo on bridge to +vo on Classic
A 100volt 40amp type is good. I use a 3 phase rectifier.
Also look at the Crydom spec sheet and you will need a diode, Schottky type, to suppress switching spikes across the SSR..
I also used a 15,000uF 150volt power capacitor before rectifier to make things a tad smooooother.
Dgd
Thank, I have just looked at the element and it has three elements which are 2 ohms each. So I connect them in different ways. It says 24 volts and 900 watts. This is about 12 amps if I connect them in series I think. What I might give a try is to connect it dirrectly via the SSR to the 24 volt battery bank so I don't need so much extra electronics and have the Midenite switch on the SSR when the batteries are full. !2 amps should be two much of a draw on the batteries and will only be running the element when the sun is out. I'll run it off Aux 1.
Cheers,