Inverter

[w9kh]

Admittedly, I am trying to "step" in to solar/wind power $1 at a time.  

As far as an inverter goes, has anybody used the inverter from a ups?  What would be the downfalls to doing this?  I assume I couldn't use the charging circuit because of the variable input voltages, so I will have to do a separate charger.

I am thinking about using AGM batteries to start with.  I am going to start small (1 room -the hamshack) and try to expand it from there.

Thank You,

Kevin

[bob g]

i have had good luck useing a ups as an inverter

some work very well long term, others not so well

perhaps a bit of derating or a muffin fan?

why not?

usually  the price of an old inverter is right

read that free!

bob g

[Opera House]

Smaller UPS supplies suffer from heatsinks designed for less than 10 minutes operation.  The other problem is just getting them to turn on.  They are great for the basic parts for a PWM charge controller.  

[veewee77]

UPSs will work for inverters, but there are several caveats.

First off, some will not start without seeing 120VAC for at least a short period before they will allow UPS operation.

Second, Most UPSs are made for short periods of usage. As a result, they will not stand running them at full loads for extended durations. You might get away with running them at half of their rated capacity, but. . .

Third, they are only marginally efficient. They aren't made to run for the long term, and only on a limited battery, so they don't worry too much about efficiency when they are made.

Doug

Friendly Hint: Simple questions such as this can be answered by simply using the "Google Search the Board" link to the right.

[Tritium]

There are Standby UPS's and these fit the comments of most posters to this point. Constant use will shorten their lifetime greatly but there are also Active UPS's. These  run by charging the batteries from the line and the output always runs through the inverter (always isolated from the AC line with 0 switchover time). They will last a long time since they are made to run constantly. I have a small one I got for free when the first set of batteries went bad. It puts out 15 amps at 110vac, is 8 years old and going strong. It uses 5 batteries in a series (60V battery pack).

Thurmond

[dnix71]

One other limitation on the cheap UPS's is that they are modified sine wave, not true sine wave like the grid. Motors don't run as well on a step wave, because the steps are harmonics that change the effective frequency away from the 50 or 60 Hz it would be if plugged in the wall.

Another problem is starting loads for some appliances are much higher than the run load. If the power fails and the inverter switches quickly, it will only need to handle the run load. When you have to start up from the inverter, it may not have what it takes.

I bought an Ames true sine wave inverter for my computer setup and it has worked well so far. My DSL box has an ac adapter that puts out 10.5v AC, so a battery stepdown wouldn't have worked anyway. True sine wave inverters are 5 times the price of a cheap modified sine inverter, but worth it for long term use on expensive/sensitive equipment.

I used to have a 1300va Best Fortress that backed up an AS400 at work. It was big and heavy, but they didn't fudge the rating. It would start and run a small fridge if it had to. You might try your county's electronic recycle dropoff and see if they get old IT stuff like server UPS's. You'll have to buy a lot of batteries, but the UPS is made to run indefinitely and the output is clean.

[w9kh]

I am curious about what you consider a "server ups"?  I have an APC Smart-ups 1400 with bad batteries.  I was thinking about using that.  Are the cheap ones you are talking about the little ones you find at Best Buy and the like?

It's funny that you mention the County's electronic recycling....  There is one coming up and I happen to work for the County ;P

[dnix71]

The "Smart" series from APC are true sine wave inverters. They cost a lot more, but are preferred if you can get them. A computer server UPS is designed to run as long as necessary and has to put out very clean power because computer servers cost money to buy and money when they go off line. Servers get upgraded all the time. If you know someone who works in a server farm, maybe they have some surplus that just needs batteries.

IBM wouldn't even sell us a new AS400 until we got rid of the Best Fortress and bought something they considered acceptable. The business owner didn't even want to pay for backup (I don't even want to comment on how stupid that is). IBM said "Tough, you want the new machine, you have to buy a new UPS to go with it."

[alibro]

I am using a 1400ah APC Smart ups and it is working well. I checked the power drain from the batteries while off load and it was around 25W. This is probably a lot more than a good inverter but for me is acceptable as I only use it on load. I am not too worried about it having a short life as I have 3 of them and can probably get more. Turning them on with no mains power connected is a pain as you have to hold in the on button for 3 seconds exactly or it won't turn on.

If overloaded it will cut out but doesn't seem to do any harm, (it happens to me all the time).

I guess the biggest issue for me is that it is really only useful for powering stuff up to 500 or 600 watts long term, any more than that and it struggles. Some day I will fork out for a good Inverter but while I have free UPS's I will continue to use them.

Hope this helps

Alibro

[w9kh]

Did you just wire the batteries to it in the standard fashion, or did you do some trick wiring?  What kind of batteries are you using?  I suppose that really doesn't matter if you aren't using the ups to charge them, only to do the inversion.  How did you silence the alarm?

Thanks,

Kevin

[alibro]

Hi Kevin

 I just used the connector that came with it and wired it to bus bars (2 bits of 10mm copper pipe bashed flat and screwed to a lump of wood). I then wired all the batteries to the bus bars by drilling holes in the bars and screwing the wires to it with wood screws and washers. I have a picture of the set-up in one of my diaries. The batteries are old sla's which came out of ups's. The alarm is just a piezo sounder which I think I desoldered. It was quite a while ago so I may have just smashed it with a pair of pliers.

The UPS I am using was faulty (at least it was after I connected some very badly discharged batteries to it in an attempt to charge them off the mains), it will not work properly off the mains any longer but as I never use it that way it does not matter.

What stage are you at in the building of your turbine? I discovered that building the turbine itself is only the first part of a very big process. You then have build a tower, mount it on the tower, sort out the batteries, provide some form of dump load control and get the power into the house.

Once you have achieved all of that you then have to go back and re-do all the stuff you got wrong the first time. I guess if you take it one step at a time you will get there but make sure you read everything in the Otherpower web site, especially the tutorials which are gold dust! Maybe you can avoid some of the mistakes I made, especially by scrimping on the tower.

Cheers and good luck

Alibro