# Transfer switch



## frank (Dec 16, 2008)

Hey All,
I'm picking up 8 130W panels(12V), an outback fm80 charge controller, and a vfx 3524 inverter. I plan on wiring the panels in series to get a 24 V system. 6V golf cart batteries in pairs of 4 (24v).

I saw a system where a guy had a nice transfer switch to select grid or solar power. Does anyone have any info or links for this transfer system??? As I remember, he took individual wire runs out of the main box and put them in another box, which was fed by the transfer switch. 

Basically I'm building an off grid system that can switch back to grid power safely. Thanks!

Frank


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## greg273 (Aug 5, 2003)

Frank, the 'Northern Arizona Wind and Sun' store has a great solar forum. Check them out, there is some great discussion and advice there.


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## ace admirer (Oct 5, 2005)

so there are about 4 ways of transfer. retrofit a wholehouse transfer switch before your existing panel (northern ) the 150 amp switch is not too expensive. the 200 amp was around $400 few months ago. the new panel which has built in transfer switch also northern around 600. the emergency circuit retro fit. which is what you saw....you can only choose a few circuits to feed from solar. its intended to be a emergency generator feed only. lowes and probably other home builder suppliers has them for around 300 i think.....someone with some knowledge could take a few heavyduty three way switches and make an emergency circuit box....it might void insurance policy.....


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## TnAndy (Sep 15, 2005)

Here's a 6 circuit ( 4 @ 15amp, 2 @ 20 ) manual switch meant for wiring in a generator, but will work fine with your solar. 120v only. $280

Sportsman's Guide

Here's a 10 circuit 120/240 from WW Grainger.....has a watt meter too. $550

Both of these have the advantage that the transfer switch and breakers are built into the same box.

But you could go the route I did. I bought a 100amp manual transfer switch, and wired in a separate 100amp sub panel at the same time I was replacing the 200amp main panel, moving the circuits I wanted to run off my solar backup into that subpanel . The feed from the main panel runs unbroken thru the sub panel to the transfer switch on the right, and then back from the TS to the lugs of the sub panel. The solar feed in from the bottom.....the feed from the transfer is UP = grid, DOWN = solar/battery/generator

Mine is an Eaton brand I bought at a local electrical supply house for about $300.












By the way, you can wire the 130w solar panels in series sets of 4 if you want.....the FM80 will handle up to 140v in with no problem....that will keep your wire sizes down and voltage loss low......also, if you're using a combiner box near the panels, you could get by with something like a Midnite 3 instead of having to go to a 6 circuit box....save you a little, and still have room for another set of 4 if you decided later to expand.....using the FM80 charge controller, you have some expansion room there as well....good move.


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## frank (Dec 16, 2008)

Thanks guys!

Andy, Thats what I was looking for with the manual SW.
I'm thinking about wiring 4 sets of two in series to get 24v/28a. Junction boxes (4) on roof to get 4 runs of 24v/7a into a 100 amp subpanel "combiner" with 4 15a breakers that feed to the main out to the Charge controller. That way I can isolate each set of two and still get power from others. 12 ga wire from panels to combiner.(about 15 feet) Would you combine 4 panels to get 48v, and then run from the roof? or go series with 'em all (96v). I'm not sure what the fm80 can put to the inverter. Can it vary voltages out as well as in? I was looking at the 3524 inv so batterie can go in sets of 4... Thanks again!!!


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## TnAndy (Sep 15, 2005)

You setup is somewhat similar to mine. I have 18 "24v" panels in pairs of two on pole tracker mounts. Pair of Outback charge controllers ( one MX60, one FM60 ), 12 2v batteries in series to make a 24v bank, pair of Outback GTFX2524 inverters ( which gives me true poly phase 120/240 ) and 5000 watts output.


On the FM80:

When you do the initial setup, you have to set it for the output voltage you want....12,24,36,48v. The input voltage doesn't matter UP TO the limit ( which if I remember, is 140v ). You can watch the screen on the FM and see the input volts/amps and the output volts/amps.....the FM does drop the input voltage down to whatever you set it for your batteries/inverter, and gives you the extra as amperage.

You also have to set your float and absorb points for the batteries.....see your battery manufacturer for those, and set the FM to those recommendations.


On wiring panels in series: Remember to use the Vmp, which for a "12v" panel is usually around 17-18v, not the nominal voltage ( 12v ) when running panels in series......2 panels would be 34-36v, (not 24 ) three panels 51-54v,(not 36 ) and so on....and then stay 25% or so below that as you approach a maximum to allow for the MAX the panel could ever produce in an open circuit or such condition. The number you suggest of 2 is fine.....I just wanted to make you aware you COULD connect more if that would save wire, breakers, etc. There IS one downside to connecting in series you need to be aware of.....if you get shading on a portion of a set of panels in series, it pretty much KILLS the power output of that whole set.....soooo, the more you have in series, the more shading becomes a potential problem.....watch your trees if that's an issue where you mount.

On the combiner subpanel:

I take it you plan to run 4pair of 12ga wires down from the roof to the sub panel located near the FM80 ? What you have to be aware of is the voltage drop in that run. Combiner boxes are "normally" mounted AS NEAR to the panels as possible, so you have short runs of smaller wire to the combiner, then a LARGE pos/neg pair from the combiner to the charge controller......a distance of 30-40' can wreck your power input to the charge controller if you run low voltage ( like that 24v ) and a small wire. Look up a wire voltage loss calculator online, enter 24v and the distance, and shoot for a 2-3% MAX drop, and you'll likely find the wire size needs to be quite a bit larger than 12ga......which you can do with ONE pair of wire putting the combiner box AT the panels. My own run is about 35' from the panels to the charge controller, and I used #2 wire ( which was overkill, but I had a bunch, so that's what I used ).....I think the bare minimum was #6 if I recall. The FM80 will accept up to #2 wire size on the terminals. ( I have a pair of Outback CCs )

The combiner:

You didn't say what brand 100 amp subpanel you are using for a combiner box...make sure it's something like a Square D QO series that is RATED for DC volts....and even the Square D's are only rated up to ( but not including ) 48v.....which means you CAN'T combine the panels in more than 2 in series, or you would be over the rating of the breakers for DC. You really don't need a "main" on the combiner. Midnite and Outback both make combiners ( I like the Midnite a little better ) and both are NEMA 3 ( weatherproof ) rated so you can mount them outside. You can size the breakers down closer to your panel amp rating....a 10amp or 12amp for a 7a panel output, for example.
All you need is a SMALL combiner box ( Midnite makes a nice 6 circuit one ) up near the panels.

Also, don't forget a lightning arrestor like a Delta IN THE COMBINER box, and ground your panels to the ground lug in the combiner box, and run a heavy ground ( #6 or 4 ) to a ground rod....and the negative terminal DOES NOT BOND to the box like a neutral often does in AC systems....the grounding of the box/panels is totally separated.

http://store.solar-electric.com/deliar.html











A "Flow chart" of components would look like this: ( if I could draw one online...ahahaaa )

Panels to combiner box ( located close to panels ) to a DC disconnect right beside the charge controller ( fused/breaker box like you see on an outside AC unit is fine ) to charge controller to another disconnect on the output side between the batteries and CC ( you need to be able to isolate the CC on BOTH sides ) ( THIS is a good place to put a small sub panel like the Square D QO series with a single pole 50- 80amp breaker from the CC to the batteries, AND you can tap at this point for small DC circuits if you want to use DC for anything ) to a LARGE breaker/disconnect ( like a 250 amp... See This One ) between the batteries and the inverter. ( bet you didn't know you had so much stuff to buy, huh ? )


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