Bypassing FM 80

[Tritium]

I purchased an Outback FM 80 back in November because I could not wait any longer for the Classic (yes I should have waited).

I have 2 arrays.

1 has 780 watts and is controlled by MX-60 (56vdc input).

The other 600 watt array goes to the FM-80 (120vdc input).

Here is my issue. I don't have enough storage capacity for both banks to be used efficiently (660aH at 12vdc nominal).

Since the new array is 600 watts at 120vdc I would like to bypass the controller when the bank is full (the FM 80 attached array is shut down most of the time as the system seems to favor the MX 60) and run a water heater element at 120vdc.

I can see how to divert battery charge to a dump load but I can't see a way to transfer the array from the controller input directly to a load.

Any ideas? Yes I know more battery's are the ultimate solution but cash is not available for that option at this time.

Thurmond

[ghurd]

Might call them and ask!
I'd be worried about tinkering with $omething like that.

Need to chose the heating element wattage carefully.
A 600W array at 120V will not put a whole lot of power into a 120V 1650W element.
G-

[Tritium]

I have a 120V 500watt  "Hotwatt immersion cartridge heater, Part #HS375NR.  that I was thinking of using. I will not see full output of this array till the middle of summer so it might work. Otherwise, I have a 110v 1kw water heater element that might be useful. I know I could use a double pole double throw at the controller input (or DC SSR / SSR's). I may be able to set it up to trigger at a certain battery voltage since the controller would still be wired to the battery and will still be looking at it's voltage regardless of the input condition.

Thurmond

[hydrosun]

It is possible to use the voltage control of the FM-80 to turn a double throw single throw relay to go from the input of the FM-80 to the water heating element.  The negative leg doesn't need to be switched. The trick is having a relay  that can handle 120 vdc. Most common relays don't go up to that high voltage for DC. Possibly some capacitor across the switch will suppress the arcing while switching.    Any switch needs to make sure the input to the FM-80 is never connected to the load. Reverse current can possibly damage the controller. I'm not clear how well fets or ssr would work in this situation. You might have to put some delay circuit to ensure that one shuts off completely before the other connects.
Connecting the load to the 12 volt battery is  simpler but involves 10 times the amperage so I understand why you want to go directly from the solar panels.
Chris

[Madscientist267]

Wouldnt think there'd be much in terms of arcing since it's a resistive load, so a cap probably won't do much good in terms of protecting any contacts. Might even make the situation worse.

Use a contactor - you're already looking at essentially 'wasting' the energy anyway, and even though a contactor coil will use a little more juice, who cares? The contacts can handle the stress of connecting the panels to the element.

Stay away from conventional relays with this - you're asking for trouble with things like welded contacts at the very least, on up to and including fires resulting from so much power in such a small place.

Wouldn't use 'em if it were me.

My 2 cents...

Steve

[DanG]

Relay making & breaking both legs of higher voltage DC, with proper contact swing gap, contact spring loading, barriers & spacing between them, go a long way to reducing chances of contact erosion and flashover.

[boB]

Maybe if you could just disable or turn the MF-80 off you could just
leave the input connected and then load the PVt down as you like.
i.e., don't disconnect the PV from the input of the CC.

boB

[Tritium]

Maybe if you could just disable or turn the MF-80 off you could just
leave the input connected and then load the PVt down as you like.
i.e., don't disconnect the PV from the input of the CC.

boB

Hi boB,

Interesting turn of letters and that is about how I feel about it after owning it for 3 months. You don't have a trade in program for the classic do you. I should have waited.  

Thurmond