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Author Topic: [hypothetical] Solar to charge batteries without charge controller.  (Read 1103 times)
fourfootfarm
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« on: January 23, 2017, 08:50:25 PM »

After stumbling across thread.

http://www.navitron.org.uk/forum/index.php/topic,16462.15.html

A bit of a wheeze occurred to me. I've seen panels available which are 27.3 volts Vmp which is just under float.

If directly connected to a 24v battery would they charge up to 27.3 (minus line losses) and then taper off?

Would those panels actually be suitable for use with a charge controller, my head says know if wired all in parallel as the voltage would to too low.

This is hypothetical as I have a pile of TS-45s I've yet to use. But it would be interesting to know in any case!

Thanks
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Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

Turkish Turnip
rogeriko
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« Reply #1 on: January 23, 2017, 09:46:20 PM »

Indeed and I have had many an argument/discussion about this. A panel of say 26v MPP will give maximum amps up to that voltage. As the voltage climbs to say 30v OCV the amps will drop to zero. if you want to charge your batteries to 29v and float them at that voltage you need panels that will give you just enough amps at that voltage to maintain that voltage. Dont forget a panel of say 8 amps will give 8 amps at any voltage below the MPP voltage, therefore a 12v battery will only take 8x12 =96w out of a panel that could produce 24x8 = 192w so you have to match the panels carefully for full efficiency. Done properly you can beat any expensive MPPT charger by a mile.
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bautsche
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« Reply #2 on: January 23, 2017, 09:49:55 PM »

I'm not sure what you are asking in detail, but I've got a string of panels direct attached to my battery bank.
I've got a Sunny Island and a Trace inverter connected to that bank and between them they make sure that the batteries don't get overcharged.

Not sure that helps answer your question?

Eric

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fourfootfarm
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« Reply #3 on: January 24, 2017, 09:41:00 AM »

I'm not 100% sure what my point was now. Didn't have much sleep.

If you have a say 30v Vmp panel then its going to try to charge up to 30v?

Would it be possible to use the 27.3v panels with a charge controller or is the voltage too low taking into account voltage drop in the system?


PS: Thanks for info Roger and Bautsche
« Last Edit: January 24, 2017, 05:21:21 PM by fourfootfarm » Logged

Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

Turkish Turnip
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