FM-60 Diversion Load switching using cheap MOSFET

AntronX

There is a way to use solid state relay with FM-60 to make solar diversion load. I got inspired to try from information posted here: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865&sid=85f7fefa4ca13f5bd7e0582a353954e9&start=25 But SSRs are a bit expensive, around $60 - $80. There is a way to use N-channel MOSFET that costs $2 plus few passive parts. I used 55V 53A TO-220 MOSFET and few resistors to attenuate gate voltage and to act as fuses too. FM-60's Aux output is not ground isolated, so I had to switch negative battery wire to avoid creating short circuit from Aux negative to battery positive (learned hard way). Here is video of it in action: http://www.youtube.com/watch?v=0RklbVgzHtI

Parts List:

R1, R2 = 550 ohm
R3 = 3.3 Kohm
R4 = 220 ohm
C1 - something big like 10,000 uF. I used 440uF because that's what I had. It was not enough, I still had 500 mV of voltage ripple on battery bus (I am switching 15A at 333 times per second).
For MOSFET, I used IRFZ46N, but any other will do. I would choose one rated for at least double operating voltage and current. Heatsink will be needed, but it will dissipate very little. Mine dissipates about 5W while passing 400W to the load. MOSFETS are very efficient devices.
R(load) - I used 8 x 50W Vishay 1 ohm resistors, 4S2P to get me 2 ohms at 400W. Heatsink salvaged from 1KW audio amplifier. In my case, I just waste diverted power in order to increase my solar harvest numbers. But great use of this excess energy would be to heat water. I want to charge secondary 12V battery using this diverted energy. Building stand alone switch mode diversion charger would be my next project soon.

blackswan555

Re: FM-60 Diversion Load switching using cheap MOSFET

Random ebay link with no recommendation implied, Would something like the below be any use to you ?
http://cgi.ebay.co.uk/24-Volt-WATER-HEATER-IMMERSION-ELEMENT-Solar-Wind-24V-V_W0QQitemZ180269338808QQcmdZViewItemQQptZUK_Home_Garden_Hearing_Cooling_Air?hash=item29f8e3d0b8

Have a good one
Tim

System2

Re: FM-60 Diversion Load switching using cheap MOSFET

This is what I've been using to dump about 650 to 1000 watts at 48VDC (nominal) for the last few years using the diversion relay output of a Outback MX60.

Don't have time to answer questions on it right now, but if the schematic makes sense to you, use it, otherwise be careful, possibility for much expensive smoke.

regards

Rob

AntronX

Re: FM-60 Diversion Load switching using cheap MOSFET

Hey Rob, welcome to the forum! The circuit make pefrect sense to me. I was going to do exact same thing with opto isolator. But I did not have any at the time and figured it would work without one given that I be careful and pay attention.

System2

Re: FM-60 Diversion Load switching using cheap MOSFET

Thank you AntronX,

Missing in the diagram is simultaneous connection to a 500W 48V homemade baseboard heater (4 - 225 watt wirewound resistors). A subsequent redesign of the water generator put out more power than the hot water heater could handle at 48-55VDC (a 2KW/120V hot water coil).

I do recommend a small (90MM) temp-activated computer-type fan if the unit is intended to divert 500W or more continously. That heatsink can get quite warm.

Regards

Rob

crewzer

Re: FM-60 Diversion Load switching using cheap MOSFET

AntronX wrote: »

There is a way to use solid state relay with FM-60 to make solar diversion load. I got inspired to try from information posted here: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865&sid=85f7fefa4ca13f5bd7e0582a353954e9&start=25 ...

Here is video of it in action: http://www.youtube.com/watch?v=0RklbVgzHtI

8) Nice job, AntronX!

Regards,
Jim / crewzer

AntronX

Re: FM-60 Diversion Load switching using cheap MOSFET

Thanks C

Hey, did you have issues with current oscillation, or other words having PWM start going smoothly from 0% to 100% and back to 0% repeating every 1 second? This seems to happen when diverting more than 8A out of 15A maximum. This happens when batteries have absorbed for few hours and cooled off panels get blasted by full sun after long passing cloud.

crewzer

Re: FM-60 Diversion Load switching using cheap MOSFET

Antron,

I did indeed have a little problem with current oscillation when I began my project. OutBack worked with me and tweaked the software a bit, and the problem went away after I played with the delay/volt settings a bit.

I can see where this would be a problem when the controller is in absorb and there's little or no regular load, as the (nearly) full-battery voltage "elasticity" could be a challenge.

Regards,
Jim / crewzer