Inverters -- diy?

My guess is that in the end you will spend $2,000 in time plus money, to replicate a $310 inverter. Additionally, it will not work well.

i

Not particularly uncommon in yachts. Usually to power an AC fridge. It works. Measure the actual amperage used by the fridge connected to AC and then amp and volts required by the inverter powering only the fridge and you get a good idea of the efficiency of the inverter. As for sizing the inverter most people use a factor of 2, you need 1KW buy a 2 KW inverter.

Insulated generator enclosure and efficient exhaust system.

Of you look around..you should be able to find a nice quiet natural gas powered genset someplace for very little money.

You will absolutely need a running power source for an inverter. Ive got a 6000 watt Hart inverter that came out of a brand new but wrecked greyhound bus sized RV...and I dont have anything big enough to feed it the 12 volts required to output 6000 watts of 120 volts AC

Ive got a Xantrex 3000 watt inverter in my big van. It has dual batteries and a second set of paired deep cycle batts mounted inside the cargo compartment. Works very very well for about an hour or so when Im running close to 3000 watts of power tools and lights. So I had to install an oversized alternator to keep the batteries charged when the inverter is running.

Now if you can stack up forklift batteries in a big enough pile..with a big enough charger ..you might be able to run the important stuff in your house for day or so..at most.

etc etc

Building a small noise canceling cover for it...like a small shed is not a big deal

Gunner

Or a couple/three smaller ones.

Then you'll find out why they're going for cheap. I've heard the cost to run them is simply -outrageous-. From the Generac website:

--snip--

7) How much does it cost a month to run the generator when it runs for 15 minutes a week?

Depending on the price of natural gas, it shouldn?t cost more than $4 or $5 per month to run the unit in test mode. During a power outage, under 50% load expect to pay less than $30/day for gas usage. A lot cheaper than a hotel room or spoiled food!

--snip--

That's up to $900/mo ($10,800/yr) for gas at half power! IF The pipeline remains pressurized. (yes, worst case scenario)

That's a whole lotta inverter!

How often do you use it for more than an hour? And what tools are hooked up to it? Will it handle a good sized welder?

...but it's a necessary thing. Engine noise really grates on nerves. Especially non-tool-user nerves.

Indeed. But as you indicated..worst case secenario. If one is trapped somewhere for more than a couple months with generated power...its cheap enough.

It sure is. Want to buy it? Works great! The bus had a pull out drawer on electrically operated slides that had batteries so big it looked like a landing field when we managed to get the drawer open.

On idle...with a deep cycle marine battery about 800 cca...it took 3 hours to go into low battery alarm simply sitting there idling. When I plugged a tig welder (110vt Weldpak 100) it sucked the battery down in about 20 minutes of just 20/80 welding time. Probably 5 minutes of actual welding.

Its very capable! It just needs a crap load of batteries to provide much power.

Ive used it extensively with a Weldpac 100 and a Thunderbolt AC/DC stick welder (with a big! step up transformer) and its enough to get the job done if Im quick about it. I dont like to push any inverter that costs as much as those do.

True indeed. However..if done properly...one simply overlooks that very very muted "rrrrrrrrrrrrr" in the background...even from the neighbors.

Gunner

Well, they kinda are rated in "Sears HP" because nobody ever allows for start surges on motorized items - like your Refrigerator and Freezer. The inverter might have enough power to /run/ both at once along with a few lights and things, BUT it'll take pretty much the entire inverter output to get either one *started* - the start surge on an induction motor is usually around 10X the running current, if not more.

Look up the Locked Rotor Amps if it's listed on the nameplate, that's the Start Current for the first quarter-second when the motor is at a dead stop, then the current ramps down as the motor spins up.

For one, running a 5KW inverter to backup the house will require a large battery bank to feed it with a low enough impedance to toss a

500A surge toward the inverter. You can use an ultra-low-impedance battery like a Gates Cyclon or Optima Spiracell, but while the design can supply huge surges it doesn't have the Amp-Hours of capacity to back it up for long.

Good old Tank Cells would be better for that - put up a rack in the garage and load it up with about a half-ton string of cells, and you're good to go. Get the Lead-Calcium ones, and they'll go 15 or 20 years between replacements with proper care.

You don't really need a 500A alternator to charge the battery and/or pass-through to the inverter, but it has to be large enough to both satisfy the constant loads and have enough excess to get the battery mostly recharged before the next big start surge.

But a genset is the only practical long-term alternate supply - whether it's putting out 120/240V to run the load, or large quantities of 12V or 24V or 48V DC to recharge the battery string. Even with that inverter and battery bank, you still need to recharge the batteries or your backup won't take you very far.

And it is possible to totally silence a genset if you start out with one that's intrinsically quiet to begin with - water cooled engine at a slower operating speed - 1800 RPM is a lot easier to damp than 3600 RPM, but you need to over-rate a gasoline engine running at the lower speed.

Then it's a matter of building an enclosure that keeps the noise in, and developing a labyrinth with acoustic damping to let cooling air in and out of said enclosure without letting the noise out.

The "Movie Generators" they bring out that are almost totally silent wouldn't cost that much more than a standard 60KW to 200KW unit if they were mass-produced - half the cost is they're all built custom.

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Well ... there is the confusion between Watts and VA (Volt-Amps). Watts are the real power it can deliver, while VA is the product of the voltage and the current -- which is the *same* as Watts for resistive loads (like space heaters and incandescent lamps), but inductive or capacitive loads (like motors and computer power supplies) have the current lagging or leading the voltage, so you get less power than you would expect -- and while the cooling requirements of the inverters are probably more power based, there is also a limitation on the maximum current which the transistors can pump out, so you need to know both the VA and the Watts ratings for most things.

And, I'll bet that the 5000 W rating is *instantaneous* (peak) wattage, and that it could not run that kind of output steady state.

Are these things not actually made for powering the insanely loud auto sound systems? You might get that kind of peak load every time the big pulse of bass comes out, but there are quieter periods between those.

O.K. Going to their page, I find that the 5000 Watts is the

*peak* power, and the steady state power limit is 2500 Watts.

I've downloaded the manual, and discovered that the output is not a sine wave, but rather a "modified sine wave" (synthesized from square waves), which could make some loads quite unhappy.

Also (on page 12) I find:

====================================================================== The inverter can delivery 2500 Watts for about 60 minutes. The inverter must cool for 15 minutes before it can resume operation at 2500 Watts. Note: The Wattage rating applies to resistive loads. ======================================================================

So -- you can't even get that 2500 Watts full time -- let alone the 5000 Watts.

O.K. the 5000 Watts is the "Surge rating (0.1 second)". Hardly useful. :-)

Well ... I used to have a generator which was good for at least that much current at 28 VDC. (It was used in an army Tank to power the really high power searchlights.)

Not I, at least.

Perhaps you could have the auto motor running a bank of alternators instead? And yes, you would need multiple batteries in parallel to handle the load current. To do this, you would have each alternator maintaining the charge on one battery, and you would have all the batteries connected to the inverter through diodes, so one low battery would not hog current from the others.

You also want serious sized wire. They are suggesting #4 AWG wire for runs up to four feet, and heavier for longer. They are suggesting #2 AWG which may suggest that is the largest which will fit the connectors on the back of the inverter.

Given the various limitations of this, I think that it would not be satisfactory for powering the house -- unless perhaps you had multiple ones, each run off its own set of alternators and batteries, so you could minimize the load on each inverter. And check out what you might have which would not like the output waveform.

Good Luck, DoN.

Yes, for anything over a couple hundred Watts, you really want to use a higher voltage, and put 12 V batteries in series. 48 V inverters are fairly common, also 24 V for use in aircraft. 12 V inverters are really inefficient due to the huge currents and massive wires required.

The off-grid people often use 120 V DC battery banks.

Jon

See

He uses a prius and a big inverter to run his house. The prius batteries are, I think, 220VDC. Clever idea.