Automobile Inverters

[markp]

I live in an area with an occasional power outage, usually less than four hours. I have a small (3500 watts) gasoline generator that I can use to power the water pump and refrigerator if needed. I was wondering about using an automobile inverter for the short periods I need. I can get a 2000 watt ( 4000 watt peak ) inverter from Harbor Freight for $150. Can an automobile alternator supply the necessary currect? <p>2Kw at 12 volts, 100% efficient, would be 167 Amps!
At 65% efficiency that goes to 256 Amps! <p>I know very little about automobile engines, but the wireing doesn't look like it would handle anywhere near that current. If not, why are these inverters sold? For big trucks?

[josmith]

I have a 4000w inverter for that purpose. It won't run my water pump and it causes problems with home electronics. YOu already have a generator that works ok,stick with it.<p>Where I work we bought a sine wave inverter to back up the phone system. Somthing like that would work better in the home as well but it was around $800 with 15 minutes of backup built in. Extra capacity is very expensive.

[Robert Reed]

Mark
Its like something you trip on daily until the day you want it and it isn't there. I have seen an add many times for deriving 120VAC direct from an auto alternator. Never had an interest, never investigated further. I will search thru some old subscriptions and see if I can find it for you. In the meantime you may try Googling around and see if you come up with something. All I can tell you is it's out there somewhere. The largest passenger car alernator that I know of is 80 amps-(1000+ watts?). Commrecial and marine go larger but so does cost. Like you I never could figure out how to use those large wattage inverters to their max. capacity.

[jwax]

Correct Mark. Your car won't supply OR handle the current for 2 KW. (Maybe the starter motor for 10 seconds!)
I have a 600 W (1200W Peak) inverter that will not operate plugged into the cig lighter in the car because there is way too much voltage drop in the wire and connections. The specs on those are poorly represented. Maybe under ideal conditions they could approach the advertised output, but I'd trust that gas driven generator first!

[rstofer]

Large inverters such as you propose are used on sailboats all the time. But, then, they use very large storage batteries and maybe run for an hour. Oh, and huge, but very short, wire.<p>The average auto alternator might put out 30 amps or about 360 watts. Maybe there are a few on luxury cars that are larger.<p>Go to www.westmarine.com and look around. This kind of thing is EXPENSIVE!

[Dean Huster]

Robert, those old 110v-from-an-auto-alternator ads were more for non-caring items like universal-motor drills and soldering irons. Getting and maintaining a 60Hz frequency at 120v is another issue altogether and very necessary for a lot of our home electronics.<p>Dean

[Chris Smith]

You can decouple [the diode block] a pair of alternators to produce the 120 volts AC [about 75 volts each] or above, and two delco’s would produce 100 amps each. [in theory]<p>However, at the RPMS needed, it would not be 60 Hz. [more like 3600hz]<p>Then You could try two 100 amp delco alternators normally at a loss, using any invertor, but to produce 200 amps at 14.7 volts, including a loss, you would probably need three 100 amp alternators. <p>So, If you have room under the hood, and all the belts, plus three delco 100 amp alternators, plus a invertor, you can do the job?<p> Practical? NO<p>All my Toyota could handle under the hood was two 55 amp alternators, and two batteries, for camping. <p>That was realistic and gas was cheap in the 80s.

[markp]

Thanks. I didn't think it really was possible. When you consider the current involved, the alternator leads would have to be a lot bigger than jumper cables. Even jumper cables get warm when in use, and that's only a few seconds.

[jollyrgr]

If you want to power sensitive electronic devices you might consider converting an old UPS into service as an inverter.<p>Most can be cold started, if you figure out the secret handshake. Usually it is pushing and holding the power button for about ten seconds. These things power sensitive electronics like computers and will power TVs, VCRs, etc. just fine. Don't expect to power a well or sump pump or even your refrigerator with one though. You can get away powering a fan or other easy to start motor.<p>Convert the UPS by connecting external batteries. Most of the higher power units use batteries in series for either 24V to 48V DC power supplies. Remove the original batteries and add heavy guage power wires to the UPS. Use something like the highly flexible jumper cables. These can handle higher currents in most cases.<p>Cut or mod the case with numerous drill holes and add an extra cooling fan (i.e. a muffin fan from a computer) to help cool the heatsinks. Most UPS designs are for a maximum load for only a short time (several minutes) until the UPS batteries are dead. Without extra cooling, the devices will soon overheat. <p>You could use the car alternator idea to power several smaller 12V input UPS devices. The UPS will provide a relatively clean (more so than the automobile inverter) power.

[dacflyer]

i have here a old UPS that uses 4 deep cycle batterys. 80AH..and it will handle 1200 watts easily. so if you look around,,they are out there.

[zotdoc]

I have a 3600 watt inverter that hooks directly to the battery of my truck. I use it on my farm to run a 1/2 inch drill or skill saw when I am working on projects in remote areas, and it works well for this purpose. It will not run a small pancake air compressor and I doubt if it would run a water pump. As an aside for our forum, once I momentarily reversed the polarity at the battery by misteak and the whole thing went dead. When I took it apart, there was a row of automotive type fuses that had all blown, and after they were replaced it worked well again.

[Robert Reed]

Dean
thanks for the tip. I will discontinue my search, and I kind of figired there would be strings attached.
I really believe these large inverters were not meant for automotive use at all, but rather in a statonary situation with large battery banks. Probably a last ditch situation for obtaining 120VAC.
Zotdoc--- you probably arent using a 1000 watts with your hand held tools, but still an acceptable amount of power at that.