Wiring Solar cells to a UPS system for charging

[TheEquineFencer]

He's what I was asked by a friend to ask. He has a UPS system for a computer system, salvage stuff I guess, He wants to take out the dead UPS batteries and replace them with ful size deep cycle barries. It has the small low Ah batteries about the size of your hand in it now. It has ( 12V batties in series. H wants to charge them with solar power from some VW OEM solar cells. The cells are rated 18.8VDC 3.2W .170 ma. He does not want to use the 120V charging system from the UPS to charge the batteries but does want to use it for the 120VAC output when he looses power. Can this work, or am I in for a real treat trying to make it work for him. Can I series the cells to charge the entire rack as a unit, or will it need to be one cell for each battery? He has about 40-60 of these solar cells. I'm not sure if the VW solar cells are self regulating or not. They are made to plug in through the diagnostic port for the ECM.

[dnix71]

If the UPS is 24v nominal (2 12v in series), then you need a charge controller that can handle a 24v bank. The solar panels would be set in series to raise the input to the charge controller to 36v at least so you get some charging in partial sun.

[mettleramiel]

One problem you may have is turning it on. UPSs are designed to run on mains power and then switch to battery when the power goes out. Some will not turn on without having mains power first. There may be a way to bypass this, such as holding the power button for x amount of seconds to enter test mode. Also, you will likely hear a constant beeping sound telling you that you are running on battery power. You may be able to just disconnect the speaker, but some systems will not function properly if it detects a faulty or missing speaker.

Charging the batteries is easy. Just get a solar charge controller and forget about the built-in charger in the UPS.

A final word of warning. Some big, expensive UPS units are great because they may put out a pure sine wave, but even some of the best built ones are not designed to be running all the time. You may have to deal with using much less power than rated. The unit may be rated for 1000watts but was designed with the expectation that it would only run that large a load for a few hours. Still, your friend may have got lucky. I myself have a few 3000w pure sine wave UPS units that run great for extended periods and I got them completly for free because the batteries were dead. I even sold the batteries for scrap so I actually made money!

[TheEquineFencer]

To be honest, I really did not give much thought to the actual theory of operation the way he might use it. I may bring it over here and check to see if I can get it running like it is now and see what the wave form look like. I have a scope. I wonder if I install some small lawn mower batteries in place of the UPS batterries, just for testing because they are cheap for testing and see what it does. Then try leaving it powered off, unplugged, and then connect the batterries if it will work. If that does work, then I'm guessing he could use it I guess like  amanually operated "generator" and switch it manually to battery power. My guess is this would work. Now onto the use of his VW solar cells. I know the cells he has are OEM designed to be cannected to a 12V car battery through the diagnostic compter port to charge the car battery when the car is shipped. Can I wire these in series to charge the whole bank of batterries? I'm wondering if I can take let's say 40 of his panels, Run (5) strings of ( cells in series and tie all (5) strings in parralel to the ( batteries. What I do not know is if these solar pannels he has have a regulator already built into them. If they do, I'm guessing the control is at the plug end. Let's assume it is, will they work in series? If not then I'd have to seperate that out so I have ust a plain 18.8VDC solar cell. Then I guess I'll need a way to run them in series and control the charging to the batterries right? To turn the system on I could power a relay or contactor from the Normal power source so when power failed it would drop out the contactor and switch the load to the UPS. At the same time I can have a signal wire go to a second contactor and drop that out and conect the batteries back to the UPS. Do you think that would work?

[TheEquineFencer]

Here's what some of his cells looks like. Some are the cigerette plug type some are the ODBII type.
http://www.beneteau235.com/vw_solar_panel_f235.htm

[tecker]

Model number of the ups is?