Power Inverter

[jwax]

Anybody ever test one of these 12 VDC in, 120 VAC output inverters for rated capacity?
I see Harbor Freight has one on sale ($129.99) rated: 2000 watt continuous, 4000 watts peak.
What? That's 12 VDC input at 167 amps! And where does the 333 amps come from to invert 4000 peak watts? That's a hefty battery!
Wonder if anybody has ran one of these to capacity, or is it another marketing ploy like the 2000 watt sound system? (RMS/Peak/pulse, etc.)

[sghioto]

Deep cycle marine batteries for solar power.
12 volt 400amp hour batteries are typical and expensive.

Steve G

[dacflyer]

when i was working with battery back up solar, i had a 2kw 3.5kw surge for a min or so.
pure sine wave inverter made by XANTREX
i had the Pro-Sine wave model, 24V it required a 250 amp fuse i believe..
and it would preform every bit that it claimed it could do.
it could actually start a small compressor with no problem, but you could see the battery juice getting sucked down fast, even with the 100amp alternator i had connected to the battery / inverter you could hear the alternator really whining and engine bogging down a little.

i just sent in a 5Kw audio amp in to a repair enter for repairs ( only because i could not get the parts i needed )
but it required a 500 amp fuse, and it had dual 1Ga battery inputs. how the foil on the board handled that power i do not know. the board itself weighed 18# alone.

but basically ya.. low voltage to high voltage inverting will eat up some very high amps..

[Powerguy]

let's see 500 amp fuse 1ga wire... i think 4 0000 is rated at 350 amps....small wire big fuse

[gerty]

I have one of those 2,000 watt inverters. I sincerely doubt it'll do what they claim, mine is from Homier. Homier is the traveling tool company that used to come around our town about every year or so. They would rent the civic center or the National Guard armory for the weekend. Last I heard they were being sued, their extension cords were labeled 16 gauge and were much smaller wire. Seems there were several fires, we haven't seen them since.
As far as the inverter, I plugged a 7" side grinder into it, 12amps I think, and ran it for a few minutes without problems.
I also used it for an electric drill a few times, never really stressing it. So far , no problems. Oh yeah, the price marked on it was $39.95, I asked if it was correct, and the reply was pay as marked so I took a gamble.
The input cables are like a set of cheap jumper cables, with the large clamps and approx # 4 wire.

[haklesup]

Given the very spotty record HF has for quality, I wouldn't bet the life support equipment on it.

Peak ratings are no doubt for a very brief time, possibly less than 1second (which even a smaller battery may be capable of). Finally their are plenty of places in the design for inefficeincies (think IR drop across insufficinet connectors or conductors) but the primary failure mode would probably be electrolytic cap failure or any on a number of overheating related faulures (assuming no quality or assumbly defects). I would expect this to meet spec in cool ambient well ventilated conditions but if you use it in a car for instance where it may already be quite warm in the mounting area, it's a gamble. The true test is if it can do that for years or do it after being stored for years. Thats where a quality design with well selected components and properly scaled heatsink stands out.

Its not hard to scale up the inverter design, all you need are more FETs in parallel (or a better FET with lower Rdson) and more heatsink area and a few misc. circuit changes to get more gate drive. Its also not hard to screw that up.

Does anybody have a sense of how output power correlates to waste heat power in the heatsink?. in other words, while producing 2000W at the output, how many watts are wasted as heat or how much extra DC Power do you need to make that output. The HF efficeincy probably is not as good as other brands. This is really important in solar, not so much if you are using a truck as a generator.

On the brighter side. Oversupply in the solar sector is probably pushing the price of these units down

[MrAl]

Hello,


I used to design and do testing of inverters for a living. That was a long time ago however, and that was the pure sine wave type with very clean outputs that could sustain sub cycle loading and still put out a clean sine wave, by pure design. They were expensive.

But before i came along there was a saying and i adopted it too because of the older design units. Instead of calling it "Full Load" we could call it "Fool Load". It was a play on words of course but also a play on foreign accents trying to pronounce the English word, "full".

It was funny every time someone mentioned that.

But now we are in the future 30 or more years later, where technology got a little better mostly because of the onset of MOSFETs instead of bipolar designs. The key difference was that the MOSFET could switch faster, and that gave the industry a boost because that meant a faster switching frequency could be used which boiled down to smaller and cheaper support components.

But also the non sine wave type (ie switching with rectangular waves and no filtering) are a different type of inverter. From what i see there are several ways to do it, and some of them are not that bad either. As long as you can put up with a 'square' wave you're good to go. I have one too, a lower power unit, which i bought mostly because it was so cheap and could power my big soldering gun out at the car when i have to do some heavy soldering. Efficiency comes in around 90 percent, but that's not surprising at all because the only things between the battery and the load are relatively low resistance components. The MOSFETs are low resistance and any inductive parts are too i would presume. That makes the difference, plus no power eating filter components. So efficiency isnt too bad.
I would bet that the efficiency of most of these new square wave inverters (rectangular wave really) is pretty good but you can always feel the case to see how hot it gets. If it gets too hot then the efficiency cant be that good. Of course a current measurement on the input cant hurt either and since it is DC it isnt too hard to do.

As far as batteries putting out tremendous current levels, that's old hat i think. Even regular car batteries can often do 400 cold cranking amps. But of course dont expect your T1 terminal 12 volt 7 Ampere hour battery to handle that much. Look for a battery with a min of T3 terminals for higher amps, like in the 300 ish region. They bolt on to the leads. Better yet the big bolt hole terminals. You can often get 300 amps for some 10 seconds perhaps. Recall that going too high in current could ruin the battery if it's not rated for it.
I tested several of my 12v smaller batteries and they do 45 amps, rated for 50 amps max. Depending on age, the voltage loads down lower as the age gets higher. A new one easily supports 11.2 volts, while an older one is down to 10 volts at that current.