DC to AC Inverters

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I just picked up a DC to AC inverter at Radio Shack. It allows you to run small appliances, lights, tools, pumps, radios, tv from a 12 volt car battery. Cost $40 to $150 depending on output capacity. A must have, even without Y2k.

-- fatanddumb (fatdumb@nd.happy), December 09, 1999


I got a 300 watt dc to ac inverter at Costco for $34 this week. That is the best deal I've seen anywhere. Here is a link with the description of the exact product (with a much higher price3 tag):


-- nobody (nobody@nowhere.com), December 09, 1999.

A couple of months ago, I set up a solar array, 2 deep cycle batteries, and a switching system. The primary reason I did this was to run ham radio equipment directly from the 12v solar-charged batteries.

As an afterthought, I picked up a DC-AC inverter at Pep Boys ($59 I think) and I agree that it is a neat gadget to have, with our without Y2K. I even tried running things like lights off of a fairly small gel cell battery, and it worked fine. Also worked great in the car.

I agree, it's a "must have."

-- No Polly (nopolly@hotmail.com), December 09, 1999.

You can do a lot with those. Here's a thought, most ideas stolen from other places...

NOTE: 120 VAC wiring discussion. Proceed at your own risk. Use caution, if you don't know what I'm talking about, don't do it. Don't even think about it. You don't want this to be DIE-2K!

Use standard connectors wherever possible. Standard receptacles, plugs, wire-nutted/soldered connections. Use minimum 10 ga. wire for DC side. Use minimum 16 ga. wire for AC side. Lost already? Hit your browser's "BACK" button and read another post.

I've got a generator but it makes noise/uses fuel/pain to run just for lights. OK, get two inverters and some 12 volt batteries. Another thread talked about getting used, "dead" batteries for near free from a repair shop. Say, two dead batteries.

Hook the batteries in parallel (plus to plus, minus to minus) and connect that to the two inverters, also in parallel. Now, take the two AC outs on the inverters and connect ONE AC leg from one inverter to the same AC leg on the other inverter. This leaves each inverter with one independent output wire, and one "shared" wire. PLEASE do this with standard receptacles and well made jumpers. As a standard, hook the left prong of each inverter's output plug together (left when facing the outlet, with the ground lug down). No ground lug? Just use the "same" lug on one iverter to the "same" lug on the other.

What you now have is two independent 120 VAC supplies sharing a common return wire. You do NOT NOT NOT NOT have a 240/120 VAC supply! NO NO NO! Don't think for a moment you do. You DO have two 120 VAC supplies.

You can connect these to the same house wiring points you would use for a generator. This should be a transfer switch. Some people rely on connecting to a dryer or range outlet and shutting the main panel breaker off, but this is not to code. Got it?

Connect each of the inverter's independent AC wires to the transfer switch's HOT input wires. Connect the inverter's shared wire to the transfer switch's neutral wire. This can also go to ground (it will do that, anyway, in most of main panels).

Anyone completely lost now? Hit the BACK button and read about something else. Forget all about this.

OK, now you can charge your two DC batteries with a standard charger whenever you run your generator, or from your car. You should be able to get hours of low AC power from a fairly short charge. Use a 20 Amp charger for the batteries.

Now, once the house is powered up, kill all the 240 volt (two pole) breakers. Kill all the breakers for your refrigerator, furnace, and any other dedicated load. All you want to energize are wall outlets and overhead lights.

Use 15 - 25 watt compact fluorescents in your lamps. You should be able to run ten of these at once, but you'll get better battery life if you shut off as many as possible.

Having *real* light can be a safety and morale booster.

OK, if you're still with me you'll probably want to flame me. This setup can be deadly and messing with AC, panel boards and wiring is NOT for the inexperienced. Please don't tell me that people could get hurt. I know and I think I've made that clear. Any other comments?

-- Gary S. (garys_2k@yahoo.com), December 09, 1999.

Good observation - I checked quite a few sources, and ended up "building my own system" from the parts and pieces, wires, connectors, and ammeters. Have a 400 watt invertor, battery charger (to recharge when power is up), a solar controller (for when/if it isn't), and 4 200 ec deep cycle batteries. (Am getting a 1500 invertor to carry the furnace fan, other household loads later to try to reduce summer time power bills.)

Am not using a power panel cross connect (yet) - but will add it after things settle down later this summer. (Good Lord willing and the creek don't rise....) THings just plug into the invertor, and you have readily available, silent, immediately accessible power.

Sure, batteries (no matter how big) are best for limited loads for limited time frames, but why start a 2500 watt generator to run an electric razor for 5 minutes, or run a NiCd battery recharger for six hours? Too much waste, noise, chance of it getting stolen, etc.

Straightforward to make your own, but you do have to be careful. Be absolutely sure you get everything correct, since the energy you are "playing" with is enough to weld things and kill people if misused. There is a LOT energy in the batteries, and it is easy to touch the wrong leads at the "right" time.


I did find a "plug-in-play" charger/battery/invertor/(optional solar hookup) system at a place near me that was professionally assembled, and is in a good looking, transportable case. Nice rig, good features, though slightly more expensive than hand-building everything. (The case, for example, has all the connections already mounted and wired that I had to but and put together. It shelters the batteries better too. Keeps little fingers out of trouble, and big fingers from touching leads or battery acid at the wrong time.)

Pre-assembled sizes range from 300 watt to 2500 watts ac, battery capacity depends on how much you want to add (read pay for): some users have as much as 15,000 watt-hours. Most go for shorter (less expensive) amounts, all the way down to 800 watt-hours or less.

Anyway - The system idea works real well - as long as you recognize it won't help big loads like a refrigerator, freezer, or oven. The invertor can be used later, (post-2000 disruptions) from your car battery for field use for drills, saws, or other power tools if you are a long ways from the power. (I've rebuilt band equipment in the middle of a practice field using the pieces from my home system, since my little 400 watt invertor is mounted on a board to be semi-portable. Times like that I've wished I had the package to roll around: it saves all the disconnect/move/re-connect/use/dis-connect/move/re-connect hassle.)

Enough, your time is valuable. Anyway - the guys who assemble these units are also in Kennesaw, phone number is -800-805-9289.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), December 09, 1999.

FYI gang...Just so you know. Those cheapie square wave inverters generally don't last very long so don't be suprised if they die early next year. They were designed for campers to use for short periods during vacations, camping trips, etc.

In our "Home Power" type world, where folks have been off-grid for years and inverters are routinely counted on to run 24/7 for years on end feedback on the Whistler, Power-to-Go, Cherokee, etc. cheapie inverters is not good...they were built to meet a "price point" for infrequent users, not supply reliable or even decent quality power. In general you do "get what you pay for".

I'd rather go totally with DC power as opposed to relying on some cheap inverter. I run Exeltech inverters and use 500w and 1100w sinewave units...the 1100's run about $750 per and have a MTBF of over 20 years. The cheapie inverters are made for the same folks who would buy marine "deep cycle" batteries, or worse, car batteries for their "security". If you must buy a cheap "modified square wave" inverter spend a few bucks more and buy at very least one of the cheaper Statpowers and get golf cart batteries.

-- Don Kulha (dkulha@vom.com), December 09, 1999.

The cheap inverters, so called modified sine wave(!? its own mother wouldn't recognize it) is basically a two step square wave. A lot of equipment doesn't recognize this as being useful. Specifically there are some brand of flourescent lights that don't work at all with certian cheap inverters, no matter what the power rating. Running them anywhere near ther rated power will cause them to get quite hot. IF used in a limited fashion in certian application they'll do just fine. Just realize their limits.

P.S. while they will run small audio equipment, with some the buzz and noise will drive you buggy.

-- Ken Seger (kenseger@earthlink.net), December 09, 1999.


-- DOUG (DKIRKLAND7@AOL.COM), December 11, 1999.



-- n (d@hm.m), December 11, 1999.

I'll bite,

<< If you must buy a cheap "modified square wave" inverter spend a few bucks more and buy at very least one of the cheaper Statpowers and get golf cart batteries.

-- Don Kulha (dkulha@vom.com), December 09, 1999. >>

Don: you mentioned this in the quote above, but didn't elaborate or justify your position.

I absolute agree with avoiding auto-style batteries - the plates and design are intended for short, quick bursts of energy, not long cycles of deep discharges; but why golf cart batteries instead of marine deep cycle? (Assuming both are available. obviously, if only marine deep cycle are available, they should be used.)

Also, why not the greater value (more expense, but better energy conversion factors, less maintenance) from the newer gell-cells at 12v, rather than golf cart batteries at 6 volts?

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), December 12, 1999.

Wow - green letters. Thanks, "tester" - I think...8<)

---I'm afraid - for too many jobs - all of us will get "tested" on early January. Again, whether we like to or not.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), December 12, 1999.

green off?

-- plonk! (realaddress@hotmail.com), December 12, 1999.

Robert, I'm not as knowledgable as Don, but the plates on Marine Deep Cycle batteries are "inbetween" the thickness of "automotive" (thin) and 6v "golf cart" thick.

The thicker plates in the golf cart batteries are designed to discharged and recharged over and over again. The marine deep-cycles can do this, but not as many times and not as deep a discharge.

After reading as much as I could (and I'm still reading and learning), I went with the next step up from golf cart batteries and got an L16 style from Trojan. More discharge/recharge cycles for the buck.

I have eight of these batteries wired up in series for use on a 48vdc sine-wave inverter.

If I went with marine deep-cycles, I would have paid more for the total watts available, plus they wouldn't have lasted as long, so I'd have to replace them sooner.....

this doesn't mean Marine Deep-cycles are crap. Batteries are designed for different things. If I was on a boat, I wouldn't want these giant heavy Trojan L16 Batteries onboard.

-- plonk! (realaddress@hotmail.com), December 12, 1999.

Shock and vibration resistance are part of the equation certainly for golf carts - they are much more likely to be "banged around" than a marine battery - which would sit quietly in the bottom of a boat instead of a golf path or roads and bumps. (Use? The golf cart (on a public course) is much more likely to be cycled daily up and down rather than a trolling motor used only for summer weekends half the year.)

Result - for irregular cycles (in a basement - no shock expected) of deep use every now and then, or for regular very deep use as batteries are discharged at night, which is better?

Also - where is best place to go to get the latest word on long-term maintenance (need for and frequency of equalizing cycles, routine trickle charge rates, deep discharges (if at all?), etc.


That's the reason I'm asking - to get the most info possible when things aren't "cut-and-dried", but rather "wet, torn and mildew'd."

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), December 12, 1999.

at the moment, this is my favorite "one source" for a Battery F.A.Q.:

Battery FAQ

there are pretty good descriptions of all sorts of batteries and their lifespans in DeepCycle applications as well as what they are good at and what they are not good and what they are made of.

go there and see if any of your questions are answered in better detail.

-- plonk! (realaddress@hotmail.com), December 12, 1999.

Robert, something else to consider is to go to:


and order their 3 CD-Roms, Solar2,3 & 4.

These are all the back issues of HomePower magazine on CD, searchable and extremely informative.

Your questions go beyond just selecting a type of battery. this is a good reference set for any library of anyone interested in alternative to grid power.

now I'm going to bed.

-- plonk! (realaddress@hotmail.com), December 12, 1999.

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