Doug/Vamonos
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Location: Bahia de los Angeles
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Solar - 24 volt array to 12 volt battery bank?
Hi. At Bahia now installing my new solar system. I have 8 100 watt 12volt panels going to an outback FM 80 flexmax controller and charging 6 105 amp
12 volt batteries. Everything is wired for twelve volts. Also a xantrex prosine 2000 pure sine inverter. Can I configure the panels for 24 volts to
the controller but still keep the battery bank at 12? Or would I need to wire the batteries for 24 and get a 24 volt inverter? My distances are not
critical so I can keep it at 12 with the wire I have. Just curious about the 24 volt configuration and if that would be beneficial. As it stands I
will max my controller with two more panels if I stay at 12 volts whereas 24 volts has a lot of potential growth.
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BigWooo
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Yes, with the FM80 charge controller you must wire the panels at a higher voltage than the battery bank for it to work properly With 12 volt
batteries, the minimum voltage for the panels is 24 volts. Here's a link to the instructions for the FM80 charge controller. Read them very
carefully. There's breaker and wire size minimums that must be adhered to. Read up on wiring, breakers, and maximum panel watts that can be hooked
up to the controller.
FM 80 manual
Not @ edit. FM80 at 12 volts (battery bank) can have a maximum of 1250 watts worth of solar panels. You might want to even consider wiring the solar
panels at 48 volts as there is less loss between the panels and the charge controller.
[Edited on 10-10-2016 by BigWooo]
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Bob and Susan
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i agree...bring the voltage down from the panels at 48v
let the controller change the voltage to your batteries...
you can always change your batteries later to 24v if you need a new inverter
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larryC
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Definitely wire your panels to atleast 24v. My panels are wired to 90v in so I can use a smaller wire gauge. To take advantage of the growth potential
of a 24v system you would have to change your battery bank and your inverter to 24v or even 48v to maximize the potential of your FM80 charge
controller.
[Edited on 10-11-2016 by larryC]
Off grid, 12-190 watt evergreen solar panels on solar trackers, 2-3648 stacked Outback inverters, 610ah LiFePo4 48v battery bank, FM 60 and MX60
Outback charge controllers, X-240 Outback transformer for 240v from inverters, 6500 watt Kubota diesel generator.
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wessongroup
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Thanks ... always good info from folks off the grid
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ncampion
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Agree with Larry. The FM80 can take a max of 150 volts input (be careful, that is the Voc voltage not the Vmax) The higher the voltage the better.
Living Large in Loreto. Off-grid and happy.
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larryC
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If Voc of those panels is 17 then 8 in series would be 136v going into the charge controller. Awfully close to the 150v that Outback says will burn up
the charge controller. I would probably wire them in 2 strings of four panels to give an input voltage of around 88v. Doug will have to look at the
back of the panels and see what the Voc is for those panels. The panels I have have a Voc of 35v.
Larry
Off grid, 12-190 watt evergreen solar panels on solar trackers, 2-3648 stacked Outback inverters, 610ah LiFePo4 48v battery bank, FM 60 and MX60
Outback charge controllers, X-240 Outback transformer for 240v from inverters, 6500 watt Kubota diesel generator.
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del mar
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northern arizona wind and sun is your friend 
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willardguy
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bingo! 
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ncampion
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Quote: Originally posted by larryC  | If Voc of those panels is 17 then 8 in series would be 136v going into the charge controller. Awfully close to the 150v that Outback says will burn up
the charge controller. I would probably wire them in 2 strings of four panels to give an input voltage of around 88v. Doug will have to look at the
back of the panels and see what the Voc is for those panels. The panels I have have a Voc of 35v.
Larry |
Again, agree with Larry. Most "12v" panels have a Vmax around 17v but the Voc is usually 20 - 21v . This would exceed the input rating of the FM80.
Fortunately the cc will just shut down with no damage. Use two strings.
[Edited on 10-12-2016 by ncampion]
Living Large in Loreto. Off-grid and happy.
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Doug/Vamonos
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Thanks everyone. I was hesitant because I didn't see anything in the manual specifically addressing "down converting". It does say it can do it but
didn't expand on that. Time to go fishing. Yesterday toros were crashing the sardines on the beach right in front of geckos. Too much fun! Play with
solar later.
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Doug/Vamonos
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I set up two strings of 48 volts each and it seems to be working fine. Thanks.
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larryC
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Good for you, as long as none of the wires get hot and the magic smoke stays in the controller then you did good.
Off grid, 12-190 watt evergreen solar panels on solar trackers, 2-3648 stacked Outback inverters, 610ah LiFePo4 48v battery bank, FM 60 and MX60
Outback charge controllers, X-240 Outback transformer for 240v from inverters, 6500 watt Kubota diesel generator.
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Doug/Vamonos
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Registered: 6-19-2006
Location: Bahia de los Angeles
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I set up two strings of 48 volts each and it seems to be working fine. Thanks.
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