I have a 600 amp hour 12 volt battery which I made from 6 Golf Cart batteries purchased from Sam's Club at a cost of about $300. For those unfamiliar with the golf cart batteries, they are 6 volts each. I have paired them in series to make three 12 volt batteries. These 3 pairs are then connected in parallel to make one large 12 volt battery.

The 12 volt direct current power has to be changed to 120 volt alternating current before standard household appliances designed for 120v power can be powered from the batteries. This is accomplished by an "inverter" which electronically processes the power and makes the change.

I have a cheap ($70) inverter which puts out 300watts of 120v ac power. It supposedly will put out 600 watts for short periods of time to handle surge loads.

Today I tested my computer system on the inverted power. I have a fairly standard setup; 266 Pentium in a mid-size tower, 15 inch monitor, HP Laserjet 3100 printer/scanner/fax.

When I ran the test, I did not hook everything up at once, because I believe the box, the monitor and the printer each draw about 150 watts, so I was scared of any overload that might bring real smoke into this "smoke test."

I did run the box and the monitor together. The computer and drives seemed to work fine. The monitor had a very choppy picture with horizontal lines scrolling down the screen at a rapid rate, but funtionally it appeared to work fine.

Then I plugged the monitor and computer back into their regular commercial APC power supply. I then plugged the HP Laserjet into the inverter.

The HP Laserjet did not function in on the inverter supply. It would turn on for about one second or less, and then cut off. Then it would try to turn on again.

I called HP support to invetigate. Their knowledge base did have an entry saying that the fuser in the Laserjet could operate only on sinewave power. Naturally, my inexpensive inverter only has "modified sinewave" output which is a squarewave that has been slightly modified to give it a stairstep appearance if you were to examine it on a scope.

I hope the above helps any other laymen out there who have contemplated such a backup system.

I have some questions of the forum:

1. My monitor shows those choppy lines when on modified sinewave inverted power -Am I doing any damage to the monitor when I run it on that inverter?

2. I have an inkjet printer which I did not test. The inkjet has its own "wall wart" power supply. It is my assumption that the inkjet will run fine on inverted power, since the wall wart is going to transform it all to dc anyway. Am I right on that?

3. Are there any other pitfalls to running a computer safely on inverted power?

All comments appreciated.

-- Puddintame (achillesg@hotmail.com), October 28, 1999

Answers

1) Smart money bets "Probably" and doesn't use the cheap inverter again for the monitor.

2) MAYBE, as the wall wart MAY pass a lot of ripple from the inverter..... Why not just plug the cord from the inkjet into a cig plug power supply set to the proper voltage??

3) If you use one of the prohibitively expensive inverters ($Trace$ comes to mind) you should have no problems.

C

-- Chuck, a night driver (rienzoo@en.com), October 28, 1999.

Computers are badly sensitive to harmonic noise/RFI from funky power sources. Most cheap inverters kick out a 60 Hz square wave or approximated sine wave in the form of a stepped square wave (like yours), and this generates a fierce amount of interference that a computer, printer, monitor, etc. will pick up and react to in some manner. And then there's the issue of the swithcing transients, the spikes caused by the transistors or MOSFETs switching the DC into the transformer that does the actual inversion. Cheaper inverters rarely include any real filtration to stop or lessen these, which get worse as the load increases. AC adaptors are only good against this if the output is sufficiently filtered against the noise, which is a "try it and see" situation at best.

Unfortunately if you plan to run sensitive electronics gear (a computer and any peripheral for it will fit in this category) you'll need to get an inverter that approximates a typical sinewave home AC source accurately enough to keep switching transients and harmonics and all that to a minimum. True-sine inverters are NOT cheap, though. But at least you won't risk frying the equipment.

-- OddOne (mocklamer_1999@yahoo.com), October 28, 1999.

Puddintame,

If you have a surge suppressor between the inverter and your monitor, you might try without it. Some surge suppressors are said to get confused by non true sine wave power.

Some inverters use peak to peak volt-amps to describe their capacity. This is not the same as RMS watts. RMS watts would be about 71 per cent of peak to peak volt-amps.

The laser printer has a heating element that may draw as much as 1000 watts.

Be sure to keep those batteries well ventilated.

Good luck!

Jerry

-- Jerry B (skeptic76@erols.com), October 28, 1999.

Another option may be to get a small UPS. Supply the UPS power from the inverter and let the UPS supply the components. My guess would be that this should work OK. Startup surges, etc. would be handled by the UPS battery and not the inverter. The inverter would simply supply the charge for the UPS.

-- BH (silentvoice@pobox.com), October 28, 1999.

The UPS that I got when I purchased my current PC was an APC Back-UPS Office. It puts out a square wave! Not even a "modified sine" wave. The PC and monitor work fine on it. Small battery though. I've since acquired a more serious UPS with more serious batteries. Got real sine waves as a fringe benefit. :-)

Jerry

-- Jerry B (skeptic76@erols.com), October 28, 1999.

Don't print. Hopefully, this problem (loss of household AC power) will be a short-time affair. Perhaps as little as 12-72 hours (I said maybe...) or perhaps 1-2 weeks.

Regardless, your little battery/invertor setup is a good, perfectly capable (and very quiet! and relatively inexpensive! and continuously availble! ) backup power supply. If you have one, your generator can produce large amounts of power ONLY when it is running.

So, your choice becomes: run the generator all the time. Waste fuel on light loads, make noise, annoy the neighbors, keep running outside to re-fuel, adjust etc. Or - run the generator only for 2-3 hours a day to recharge the batteries at a high rate for a short time, and use the battery+inverot to run small continuous loads the rest of the time.

It's exactly what the US, UK, JPN, and German submarines used to do in WWII in their war patrols. Works real good.

---

Use your current system that way - don't waste your precious voltage powering a printer.

Use it for truly vital loads: like your furnace fan.

A NiCD charger for the other batteries you'll need.

A few (4-5 2 amp) 12v lights, or the LED assemblies (to save even more wattage.)

Don't even bother trying to run a refrigerator or freezer. (If you wish, run these while the generator is running - that will lower temp's for the rest of the day - if you keep the door closed.)

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), October 28, 1999.

Regarding the suggestion to plug a UPS into the inverter: that may fry the UPS. I only tried it once, but an APC Smart UPS 1000XL, plugged into an APC Smart UPS 2200XL, fried the 1000XL in less than 2 minutes after I unplugged the 2200XL input, thereby requiring it to run on battery.

Jerry

-- Jerry B (skeptic76@erols.com), October 28, 1999.

Hi Puddintame,

I would do two things differently (akshully, I did two things differently :) ).

First, if you want to rely on backup power, don't use a laser printer during power outages, use an inkjet (takes about 20 watts as opposed to 1000+ watts for the laser). Your 300 watt inverter couldn't possibly handle the laser.

Second, you might want to think about using your batteries to feed the APC UPS. They use either one or two 12-volt gel-cells (depending on size, the bigger ones put them in series for 24 volts) and you should be able to tie two wires from your golf-cart batteries to the battery wires in the UPS (remove the original battery). The UPS puts out much cleaner power than a cheap inverter.

BTW, using a laser with the UPS isn't a good idea, either. You'd could overload even that (I have several APC, UPS's with the biggest being a 1400 VA, and have never considered powering the laser with them).

-- Dean -- from (almost) Duh Moines (dtmiller@midiowa.net), October 28, 1999.

Oops.

Missed the wall-wart question.

Cheap inverters and most wall-warts don't mix.

The wall-warts will overheat and could burn up (assuming a standard, non-regulated wall-wart). The square-wave outputs of cheap inverters can play havoc with power transformers and associated components, because the produce both high-voltage spikes (destroying semiconductors) and lower average peak voltages (overheating transformers).

-- Dean -- from (almost) Duh Moines (dtmiller@midiowa.net), October 28, 1999.

If, by wal-mart, you mean a little indepepndent ac/dc transformer to produce some dc voltage for a generic appliance, then get a dc/dc convertor.

I've got one at home from a CA group - don't have address immediately availble, but it has a "cigarette-lighter" plug input (to the 12 vdc "cigarette lighter female sockets attached to my master 12 vdc "bus" from the batteries) and a selectable output of 3 vdc, 4.6 vdc, 6 vdc, etc. (You might need to get an adapter to fit your inkjet - if you chose to print at all - to mate with your inkjet.)

I don't use the "cigarette lighter plugs" very often - since they add a little resistance to the setup, but they are avialble for whatever misc. dc needs I might come across. (And in any case, although power interuptions are more frequently lately, they rarely occur while we are home.)

Radio Shack has 1, 2, 3, and 4 set female plug adapters. Cost around 8-12.00 per set.

Rest of my 120vac loads come from my invertor.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), October 28, 1999.

Puddin, I have an ONEAC 2.5KVA power conditioner I bought from a local sales rep See ONEAC Homepage Essentially, it cleans up trashy generator/inverter power to a very reasonable sine wave.

Query: what would you give for one?

-- ken (ken.mcwilliams@dalsemi.com), October 28, 1999.

Puddin',

Not to be priggish about this but WHY would you want to run your 'puter in the dark? If the power is out for any length of time then your phones will go out also (battery back up for phones only lasts about 24-48 hrs after their gennie fuel runs dry. Internet would probably be a fouled up as well. I'm just wondering why you would care to have your computer up (?).

-- ..- (dit@dot.dash), October 28, 1999.

--(Double Dash?}

I'm not trying to be coy, I just don't want to publicize my occupation on the web, but to somewhat answer your question, my occupation requires me to produce printed documents. I do most of my grunt work from home, and my home power is not quite as reliable as the average class A office tower, so I'm interested in boosting the reliability so I have no more downtime than my counterparts in the office tower.

If things go full Thunderdome, regardless of the reason, then my computer will be a boat anchor. But if I'm affected by one of Kosky's lesser "local disruptions", then I'm not going to have any excuses if I miss a deadline.

For everyone who has responded, thanks for the great input!

-- Puddintame (achillesg@hotmail.com), October 28, 1999.

Puddintame,

For the intended use that you describe in your subsequent post, I would encourage you to bite the bullet ($) and get a real UPS.

Of course, it's easy for me to suggest that you spend your money on something, but if you are concerned about dirty/unreliable power occurring repeatedly and unpredictably over possibly many weeks, the extra cost of a real UPS may be viewed as a trade off for the ulcers you may get trying to cope with repeated uses of the setup you described in your opening post.

With a real UPS, your equipment is plugged into it all of the time. As long as the line voltage is clean, the UPS just passes it through. But, if the line voltage gets out of spec, the UPS switches to battery before your PC notices, and then back again when the line voltage cleans up. Meanwhile, you would have constant surge protection, constant brownout (low voltage) protection, the batteries would be maintained at full charge, and without having to worry about ventilating the hydrogen gas generated by the golf cart batteries. And, depending on make/model specifics, you could also check the condition of your line power and your batteries at any time you got curious, i.e. some UPSs come with software that enables your PC, via a serial port cable connection, to interrogate UPS status indicators as well as alter various UPS settings.

This is not a sales pitch, so I won't go into specific make and model data for running a UPS with/without the laser printer.

In any case, may the juice be with you. :-)

Jerry

-- Jerry B (skeptic76@erols.com), October 28, 1999.

The square-wave outputs of cheap inverters can play havoc with power transformers and associated components, because the produce both high-voltage spikes (destroying semiconductors) and lower average peak voltages (overheating transformers).

Use a surge protector between your "dirty sine wave and the computer, thats what they are there for, to clean up any spikes coming from your power source. Once the "AC" gets to your computer it goes through a transformer to change the voltage and change it back into DC anyway, there isn't anything in your computer that uses AC. Your computer isn't an appliance like your refrigerator. Do you know what those transformers that you plug into your AC power does? It changes the AC back to DC. The sine wave is rectified into a DC voltage.

You have to rectify your DC into a sine wave to increase your voltage, and then rectify it back into a DC voltage. In other words Get a Laptop with a battery.

problem with the monitor is that the rasters are out of sync.

But hey what do I know? It's only basic electronics and computer electronics.Just something I have worked on for over 30 years which in no way makes me knowledgable about the subject, right?

-- Cherri (sams@brigadoon.com), October 29, 1999.

We at Home Power have been running computers and all sorts of equipment on inverters for over 10 years.

You didn't mention if the HP printer still works...."modified sine wave" (really modified square wave) power often frys the electronics in the laser printer (HP). I fried one on a Powerstar 1300 (wanted to see if the stories were true-the HP was given to me since they knocked it off a desk and cracked the case). It can also fry things like computerized Pfaff sewing machines, some washing machine electronics, DeWalt cordless tool and some Makita tool chargers. Personally I wouldn't give a "modified sine-wave" inverter to my dog let alone actually plug anything into one these days. Gave away my last one a couple weeks ago; now have 2 Exeltech pure sine-wave (1% THD) units.

The wall wart may or may not smoke. My HP 660 inkjet got along with funky power just fine though and drew 15 watts.

The monitor and computer lifespan will be shortened on funky power. We tested a monitor and the hot air exhaust out of an operating computer power supply. Both ran noticeably hotter (no suprise to you techies) which indicates to me shorter lifespan. The computer may run for quite some time though...it may also get a bit "flakey".

Good Luck

DCK, Home Power Magazine, "The Hands-On Journal of Home-Made Power" http://www.homepower.com

-- Don Kulha (dkulha@vom.com), October 29, 1999.