DIY panels to charge a 36v battery bank

[naymx5]

hi there.
so, im new to the idea solar power and struggling to get my head round a few things.

my initial idea is to run my computer and two 42" tvs off of a UPS, using extra batteries for extended runtime. to charge the batteries i was planning to make my own panels.

i stumbled upon someone selling poly cells that claim they are 2.4v @500ma does this sound right for a 66mm x 66mm sized cell?

so, i figured 6 cells in series would give me 14.4v @500ma if i were to charge a 12v battery

i also checked out a commercial 12v "trickle charger" panel and that appears to give out 20v

would this mean that i would need to match the voltage (20v) with my cells setup to charge a 12v battery?

[SunEagle]

Depending on the AH rating of your UPS battery you will need about 1/10th the Ah to charge it. I doubt 6 cells will generate what you want.

First off building your own solar panel may be a fun (or not) project but no matter how low the cost for the cells you end up not getting a reliable panel. Most fail due to moisture getting in and shorting the circuit or breakage of the cells. They also may not produce the voltage you expect regardless of what they are rated based on resistance in the circuit wiring.

A 12volt battery requires at least 16 volts or more to charge. A "12 volt" commercial solar panel is usually rated about 17 to 18vDC which is a good match with a charge controller. Without a charge controller you may either over or under charge a battery.

For your small system a low cost PWM type CC will work. But I would recommend sizing your panel wattage based on the battery Ah rating.

[Logan5]

Many store brand UPS you can not add batteries or even use different amp hour rating. as Most store type UPS are made so the user can safely save documents and shut down your computer. Some won't even allow you to boot your computer up after a power failure. They are not designed for continuous use and these are some of the safe guards to prevent misuse.

[naymx5]

the UPS i have is an older type, so its not very intelligent so i don't think it would cut itself off after a certain time. its rated at 1050w but my load will be 760-780w. it is a 36v UPS so it would draw 30 amps roughly to run at 1000w. if i use 3 100ah car batteries in series i should get around 3hrs of use? i will have no doubt missed something in working it out. i expect that id also have to wire up an isolator switch to switch from series to parallel for charging. as for the panels, i know id need a considerable amount 250+ i expect to get the amperage to charge 300ah of batteries. as im at work all day and would only be using it at night i thought it may stand a chance of charging up.

would it be more advantageous to buy panels to do what i want to do? would i still have to split the battery bank up to charge it or would the panels pump out 36v+ to charge in series?

[jflorey2]

the UPS i have is an older type, so its not very intelligent so i don't think it would cut itself off after a certain time. its rated at 1050w but my load will be 760-780w. it is a 36v UPS so it would draw 30 amps roughly to run at 1000w. if i use 3 100ah car batteries in series i should get around 3hrs of use?

No. "Car batteries" are for starting, and do not work for long-discharge applications.

However if you used 3 100ah deep cycle batteries it might work out.

would it be more advantageous to buy panels to do what i want to do?

It would be far more advantageous to buy panels and get a grid-tied inverter.

would i still have to split the battery bank up to charge it or would the panels pump out 36v+ to charge in series?

Plenty of charge controllers (like the Midnite Kid) will allow you to program output voltages. To get 36 volts (really around 42-45 volts for charge) you will need panels that will put about 100 cells in series.

[Mell23]

In case you have 3100 ah deep cycle batteries it can work, I'm sure. Hope you manage to make it right.
Mell