Sizing a MPPT charge controller

[Sunking]

I
To address some of your questions. Yes, if the sun is bright but your battery bank is full, your CC display will read very low watts, only what is required to maintain the batteries. Once the absorb cycle is complete at 56ish V, it will immediately drop to the 52V float voltage. Where does the other 4V go? I believe it is dissipated as heat by the CC.

It does not go anywhere, it is just not being used. It is very rare for a solar system to ever generate its rated power. In fact it never happens. The batteries only take what it needs. In a battery system most of the energy the panels are capable of generating i snever used. Just lost forever because it is never produced.

[Living Large]

OK so what? All you worry about is not to exceed the max 100% limit.

That's easy for people who know the answer to bat around. But Paul realized I didn't know the answer, and explained it. He'd get a "Answered. Best Response" from me if that feature was part of the system. "so what?" would never have occurred to me, but it is an interesting alternative.

[Amy@altE]

Schneider does have their Conext Designer that allows you to figure out with their charge controllers. You should be able to do 2 strings of 8 of those 275s you like with the XWMPPT 80 600. I can run the math later, gotta run now.

[Living Large]

Schneider does have their Conext Designer that allows you to figure out with their charge controllers. You should be able to do 2 strings of 8 of those 275s you like with the XWMPPT 80 600. I can run the math later, gotta run now.

Yes, Amy. I have Conext and have run it on the 2 x 8. I like the fact it does the wiring analysis for you - very cool. It was when I saw the drops in voltage, and varied the wire lengths, that the light bulb came on that I could locate the panels far from the controller and batteries. I initially was thinking I had to go to AC before making that 60'-80' run. Then I accepted having FLA batteries in my basement, which I initially resisted, and things got better because I didn't have to worry about keeping the batteries at a temp above 50 or 55 degrees. I am told one can fashion outside air intakes and exhaust to handle the battery out gassing. Thanks.

[Amy@altE]

cold batteries

If you keep the batteries in a cold room, make sure you factor in the temperature deration. 50F means multiply the size you need by 1.19 to compensate for the capacity loss at cold temps. It may be worth it to make an insulated battery box to help keep in the heat they generate while charging. You can then vent the gasses to the outside with a ZEPHYR POWER VENT.

Amy

[russ]

If you keep the batteries in a cold room, make sure you factor in the temperature deration. 50F means multiply the size you need by 1.19 to compensate for the capacity loss at cold temps. It may be worth it to make an insulated battery box to help keep in the heat they generate while charging. You can then vent the gasses to the outside with a ZEPHYR POWER VENT.

Amy

If the room is vented then how do you keep the gases (mainly hydrogen) in the room?

A fan is not necessary. H2 is lighter than air and readily goes upward and out if possible.

[Amy@altE]

Don't vent the whole room, too much heat loss, just the battery box.

[russ]

Don't vent the whole room, too much heat loss, just the battery box.

Then run the vent from the battery box. The fan is a horrible idea - the day it quits you have the potential for an explosion.

[SunEagle]

Then run the vent from the battery box. The fan is a horrible idea - the day it quits you have the potential for an explosion.

I agree with you. A fan can be used if it is necessary for a "quick air purge" but it is always better to have natural ventilation of explosive gases.

[Mike90250]

a 2 or 3 inch pipe with a continuous uphill slope will vent without a fan. you can even put a T rain trap on it to help keep stuff out. To vent out, you also need an inlet vent too.