Inexpensive power inverter/charger

[Xavy]

My computer went on the blink and had to have it repaired. While I was at the shop the repairman and I were talking about solar energy and converting power from DC to AC. As I paid for my computer repairs he said, wait a second, maybe you could use these old UPS's (Uninterruptible Power Supply} in your system. These UPS's are commonly used in offices to allow you to complete computer tasks when the power goes off. He gave me a couple of these for free. Maybe a good yard sale find could get you started also.

I took them home smiling and tried them out and found both had dead batteries and wouldn't take a charge. One worked perfectly for charging, output with 6 AC outlets at 5amp 120 VAC with a load up to 240 watts enough power to operate computer system or TV, satellite with VCR.

The small lead acid batteries that came in the unit were 12VDC with 7.0ah. With the small battery it would only operate for a few minutes. However, I had a brand new 12VDC trolling motor battery with 115ah capacity. By connecting large auto size battery to the unit I could plug the unit into a wall outlet and operate my computer while the unit charges the battery when it becomes low. The best part of the deal is I have my PV panels connected to the battery keeping it at full charge throughout the day so my computer is now safe against power outages and operates for free.

I'm thinking to do the same for my family room entertainment system along with the kids TV's, VCR's and games.

These same UPS's could be installed in the trunk of the car to provide AC power in your car. The output is strong enough to operate light electric tools on a job site as long as you keep the car running so you don't discharge the car battery. The possibility of outfitting a small TV and VCR and or CD player for the kids for long trips comes to mind also.

[(unknown)]

Watch out!

Most of those AC/DC inverters in UPSs have no cooling of any kind.  They can work fine for the short amount of time that the 7 Ah batt puts on them, but using them constantly might make you a helluva furnace, and a lack of reliability!  At least hook up a fan or some heatsinks (depending on how it's already set up) to help it maintain an acceptable temp.  Or I guess you don't have to, but why risk it?

-Jeff

[Xavy]

Hey thanks!

Actually I have an inverter I routinely use and use the UPS for charging.  I never considered the absense of the fan?  With the small battery removed air circulation is allowed but you have a point!  Unplugged the unit also emits a beep warning of upcoming shutdown which is annoying.

My plan for the UPS was to use it for a backup of AC timer I use on a system I use.  It seems the UPS is a sine wave inverter since it will operate a computer printer where an ordinary inverter will not.

[JB]

There is a large computer bone yard down the road. They told me I could have this pallett of 6 UPS 2400 watts each for 150.00 They are big probably 100 pounds with 15 amp circuits with large fans. I got to go back and check the dc voltage but if they  make a lot of noise when unpluged I would probably pass on them. Are most UPS inverters pure sign wave not that it is neccessary  just a wonderin. Wish I new more about electronics but still learning. JB

[laskey]

If it were me, I'd just cut the wire to the beeper... Speaker or buzzer or whatever.  The problem I have with UPS's is that they don't turn on if the power is already off.

Cya,

Chris

[RobD]

Hey they are free! if they blow up so what, chances are they won't damage your stuff. The only thing I would watch is an UPS designed to keep a 7AH battery charged may not have the power to charge your big guy. If you use your PV to keep it going you should be fine.

RobD

[BT Humble]

There is a large computer bone yard down the road. They told me I could have this pallett of 6 UPS 2400 watts each for 150.00 They are big probably 100 pounds with 15 amp circuits with large fans. I got to go back and check the dc voltage but if they  make a lot of noise when unpluged I would probably pass on them. Are most UPS inverters pure sign wave not that it is neccessary  just a wonderin. Wish I new more about electronics but still learning. JB

I picked up one from a pile at my local scrapyard (a good way to get a dozen 7ah SLA's for free!)  Unfortunately I couldn't use it as an inverter because it was 400V (?) 3-phase.  Lots of useful parts inside it though. ;-)

BTH

[edy252]

i dont know if what i've heard from a friend is true or not....he said that UPS systems don't use the battery while connected to power supply and only uses the battery when the power is off.....so, according to this, if u connect a ups to a power supply, then it will directly use the power from this supply and not the battery......

anyone knows if this's true???

thx in advance

[Xavy]

According to the information on the box the guy gave me it operates the computer from service electricity, a battery charge is automatically maintained from the service source and the inverter is instantly activated upon loss of service power similar to emergency lighting and exit signs in public places.

[Ungrounded Lightning Rod]

Hey they are free! if they blow up so what, chances are they won't damage your stuff.

Or fill your house with toxic smoke or set it on fire.

(My wife has a story about the former when a clueless software jock plugged two workstations and a hotplate into his UPS.  B-)  Idiot wanted to hook it back up while it was still smoking, too.)

I'd go down to a trailer supply and spring a few bucks for the 12V propane refrigerator helper fan kit - the one that goes on the back of the fridge to blow air through the conderner coils, so it doesn't flake out trying to run on convection in a 4" chimney on a hot day - mainly to get the little thermostat that turns it on when things get hot.  Then if the fan with the kit is too noisy I'd substitute a quiet 12V muffin fan.

[RobD]

Yes, That's it. The battery is held in a state of charge from the UPS and goes into service only when the main power fails.

Underground, if you hook up the UPS to a high current device you deserve smoke in the house! The better ones are fused.

RobD

[(unknown)]

In reply to a couple of posts...

UPS' come in several 'Flavors'... The better, (read: more expensive) ones are 'always online', meaning that the batteries are always both supplying current and recieving it. That is, the wall plug is allowing the charging circutry to keep a charge on the battery(ies), while at the same time, the battery(ies) are supplying current to the step up circutry, with all the power factor correction and filtering that also takes place. This is how a UPS can sometimes 'magicly' clear up a buggy computer. Poor power supply, spikes, surges, droops and dropouts, all are handled well by this sort of UPS. The cheaper 'standby' kind use circutry to 'notice' the total failure of the AC, then kicks in the battery back up. Typical time lags are in the milliseconds range. These type usualy have little to NO filtering or other protections. They use a very simple circut to keep the backup batteries charged, and that's about all. They don't all offer true sine wave output either! Watch out for anything that mentions "Modified Sine Wave"... That's code for a 'stepped square wave', works, sort of, better on some kinds of things than others. (Motors, in particular, don't like anything other than a real sine waveform) The power supply on a computer operates in a 'switching mode', which is to power supplies what digital is to anything else. They can take the 'modified square wave' better.

Another thing to mention: Some UPS' won't work right if no proper ground is present... Using one in a vehicle or the like is often asking for trouble. Also, some of the better UPS' use more than one battery, but in series... So two 12 batts become one 24 volt bank. (My APC brand is like this) The note about cooling and continious duty cycle is well taken... The fulltime UPS' are better adapted for long term usage. The cheaper types usually will self destruct in short order.

I've tried using my inverter (Modified square wave output, 600 watts) in our camper, to keep my UPS charged, (and to prevent the annoying beeping:-) I didn't want to cut the wire to the beeper) to run a small TV/VCR combo running for the kids. No go. Not grounded properly, the UPS refused to work. And this is one that has "DC" startup. (That answering one question, yes, SOME UPS' CAN startup from a 'dead socket' condition) The cheaper ones won't 'startup' from a dead socket, that is, can't self start.  Check the maker's web site for your model to see what it can, and can't, do.

Junkman