Making my own portable AC power supply

[dcphoto]

I think that for just a little more money you could buy a portable gas generator. I did a quick search and was able to find a 1100 watt generator for $300. I am certain I've seen a smaller generator for less, I just can't think of who made it or where I saw it. Plus, the generator could come in handy the next time the power goes out.

[flb_78]

You'll be fine. I had 3 semi batteries and an 1100 inverter in a big green tub to haul to a camp site.

To be honest, a generator would be easier.

Walmart and Harbor freight also carry Solar powered 12 volt chargers now as well.

[ninemm]

You're on the right track. It's all about amp-hours. You can parallel as many as you want but the cost and weight will get prohibitive. Also, because you'll be taking them from full charge to no (or very low) charge, a deep cycle battery designed for such an application would be best.

[flb_78]

Cig lighter inverter will be fine. Just make sure the load you're pulling through isn't too high for the inverter.

[caldvn]

If you do get a generator, don't put it in the tent with ya!

Given the amount of sunlight and heat Texas has been getting, that solar panel idea would work!

I've been Lake Somersville (probably misspelled) a long time ago, and I believe they had camping sites with electricity available. Which would make bringing a portal A/C unit in a good size tent handy!

[quidni]

So..... I have been mulling over making my own portable AC power supply, by building a box that holds three 12V car batteries, all wired in parallel into a DC to AC inverter.

I've got something similar to provide power in the field to a mobile ham radio, that another ham (K5CW) helped put together for me. I picked up a Shuriken brand battery (gel cell), designed to power megablaster stereos in vehicles, and hooked it up parallel with a switching power supply from Radio Shack. They're wired into a Saratoga Powerpanel, and from there to the radio. I can switch between the battery and power supply as needed, and the whole thing fits into an audiophile's "luggage case" designed to carry and protect 33-1/3 LPs. (anybody remember those? lol) I've also got a trickle charger to recharge the Shuriken off wall current when it's low. The Shuriken will power the radio for 6-8 hours in the field depending on how much transmitting vs. receiving I do, and it's no bigger than a motorcycle battery.

I went with the Shuriken gel cell instead of a regular auto battery because it can be mounted sideways or even upside down without danger, and it allowed me to mount it sideways in The Box to save space. Regular lead-acid batteries shouldn't be tipped. A lead-acid would have been cheaper but no guarantees that my setup wouldn't get tipped or flung around a bit in a field situation,

I don't know how much/long you'll be able to effectively draw off several batteries before they needed recharging, but as far as my limited knowledge goes, I don't see why you couldn't come up with something that would work. Whether it would be cost effective is another thing!

Good luck & let us know how it works out!

[jimlongley]

Shades of my youth!

Every telephone central office in existance uses a backup battery system such as you describe to power the office in the event of commercial power failure. That's oversimplifying it, but it will do.

My father worked for the phone company when I was a child and he bought the batteries that the phone company was discarding. The phone company had rules about what the service life of a lead/acid cell was, and once they reached the cutoff, they were replaced, usually a whole bank at a time since they were placed in service simultaneously. The result was that a 48~52 volt set of lead acid cells capable of powering a telephone central office for ~48 hours would be "surplused" and my father being one of the engineers involved in seeing to the timely replacement would bid for the batteries, and usually win. Talk about insider trading.

So we had a huge bank of batteries in our basement, that I learned to "routine" as a lad, checking specific gravity and replenishing the distilled water or Sulfuric acid as needed, wearing a very oversized rubber apron, safety googles, and rubber gloves thsat went to my elbows. I only had to do this when my father was out of town, but that was frequent because he was in the process of designing and implementing one of the early microwave networks.

When the power went off in our rural neighborhood, if my father was out of town, my other job was to go down in the basement and throw the "Bulldog Switch" which was a handle about the size of a little league baseball bat, and our lights would, like magic, come back on.

Back in the fifties, there were no "inverters" but there were "motor/generators" which used DC to run a motor that turned a generator to produce AC to run the house. The DC juice ran out to the barn on a relatively huge cable, and the AC came back on the same cable (different wires, of course) and the motor/generator could be heard whining away for hundreds of yards.

I have two large 12 phone company batteries in the garage, which can be hooked up in parallel to provide a pretty good amp/hour level through a 2000 watt inverter that I have, but I have never actually used them.

A bunch of years ago I used to power my ham radios off a similar setup, twelve volt batteries providing the power and on a constant trickle charge. My radios always worked.

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What others have said about weight is important to consider. To get a truly practical power supply, it has to be impractically heavy. A cigarette lighter inverter must draw less current than the lighter socket is fused for, which limits them, the one I have for emergencies clips to the battery terminals directly.

[dicion]

Cig lighter inverter will be fine. Just make sure the load you're pulling through isn't too high for the inverter.

Ok. I'll interject here. Quick Quals: Military Trained Electronics & Electrical Systems expert. Do Generator and Solar power systems for TxDot, HCTRA, and Houston Metro on almost a daily basis (If you've seen solar trailers, or RF sites out there anywhere in Houston, chances are I was involved with it in one way or another). So I deal with Solar, AC-DC Rectification, and DC-AC Inversion on a daily basis :) Anyways, lets get started.

First Issue - Starting Current.

Depending on the size of the AC, you might not find an inverter large enough. An AC Compressor can pull up to 10x it's running current during startup. That is why home AC units usually have their own 30 or 40 amp breaker.

If you're bringing a wall unit, or portable AC unit, be prepared to have to supply 10-15 amps @120VAC for startup, then it will settle down to a nicer 2-3A running.

10 Amps at 120VAC, with an inverter running at 85% efficiency (which is a high estimate btw) will require 1411 Watts just to start the thing.

So, you'll need a 1500W inverter, minimum. More then likely, you will actually need a 2000W.

Second Issue - AC Motor

Since the compressor is an actual AC Motor, you WILL need a true Sine Wave Inverter. AC Motors WILL NOT run on the Square Waves generated by your typical inverter. It will cause nothing but problems. True Sine Wave inverters are $$$ compared to your cheap-o square wave ones. I'm not going to dive down into the electrical theory of a single phase AC motor vs 3 phase vs DC vs etc etc. But Trust me on this. Your Cheap Home Depot Brand 1500W inverter will just destroy the compressor of an AC unit, if it starts at all.

EDIT: Here's the cheapest 2000W True Sine Wave inverter I could find:
http://www.invertersrus.com/sk2000-112.html" onclick="window.open(this.href);return false;

The BETTER option is to find a 12VDC Air Conditioner. They exist, mostly in a roof-mount setup, for RV's and such, but I have seen them in standalone. These use a DC motor, and will not require any inversion, and therefore, no efficiency loss!!

EDIT #2: I'm an idiot. He wasn't talking about air conditioning! Doh! Well, I'll leave this here in case anyone ever searches about Building Mobile Air Conditioning! LOL

[Reloader]

Go to http://www.arrl.org" onclick="window.open(this.href);return false;. You will find many articles to accomplish your mission. Hams have been doing this type of thing for YEARS..KE5LDO.

[caldvn]

Ok, you guys are mixing up Air Conditioner and Alternating Current.


I'm talking about my own portable alternating current system. Not air conditioner. I just want to run cell phone chargers, laptops, and a small box fan.

It's not camping if you have an air conditioner in your tent!

I know, it's just that I was thinking, hmm...if I can get some power while camping to power an air conditioning unit...I'd go out camping and fishing more!

[WarHawk-AVG]

Gasoline generators that generate AC voltage are HORRIBLY inefficient..I would almost bet that 60-80% of the fuel run thru it is wasted *unless* you are running a full time AC appliance such as an air conditioner

The reason being is its ALWAYS running but tied to a freezer or some other off/on/off appliance the current generated is shut off when not being used yet the gasoline motor is still running, even at idle its using fuel.

The only other thing I can think of other than the new hybrid cars that use a generator and batteries is the old WWII submarines...the Germans had a solid driveshaft and in between the props and the diesel engine was a generator/motor (capable of being both a generator and a motor) with clutches separating them so they could run the engines and uncouple the props while running the motor in generator to charge HUGE batteries, when fully charged they just uncoupled the diesels and could run on battery power under water..the Americans had generators only w/ no solid driveshaft and could run the diesels to charge the batteries, they could run all the diesels very hard providing direct power to the motors to push the boats up to 20 knots on the surface.

The trick to efficiency is that they run the engines to charge the batteries then shut the engines off and run on batteries saving fuel.

It also depends on what you plan on running off that battery system.

I would recommend deep cycle batteries as car batteries if you drain them too far too often it will sulfate the plates destroying thier efficiency, and either thru equalization or using a pulsating charger the batteries rapidly quit working, deep cycle allow the batteries to be discharged almost completely w/o problems because the plates are much thicker.

This would be a more efficient setup if you had 4-6 large deep cycle batteries for emergency home use (running a fridge and lights) than any AC generator

http://theepicenter.com/tow02077.html" onclick="window.open(this.href);return false;

For a home type setup a 100+ watt solar panel is best, otherwise it won't be able to keep up with the current draw of appliances, the cool thing is it will reduce the amount of time needed to use the gasoline engine in which you will save fuel, the only thing is solar panels ARE NOT CHEAP!!

Something like this with a few deep cycle batteries would be good..but very expensive
http://www.siliconsolar.com/sunlinq-fol ... 16365.html" onclick="window.open(this.href);return false;

The biggest thing is the storage capacity of the batteries, the current output of the charging units, and the power draw of the appliances
It takes a PHD in gizmos to figure it out but here are some calculators to help..gotta figure out the amp hours

http://www.xantrex.com/support/howlong.asp" onclick="window.open(this.href);return false;
http://www.lifelinebatteries.com/marinesizing.php" onclick="window.open(this.href);return false;
http://www.bigfrogmountain.com/powerconsumption.html" onclick="window.open(this.href);return false;