More on inverters

[HeyBub]

From a blog post:

[harry]

Tch. What drivel. Automotive alternators are not continuously rated. You only get the full output at fairly high engine revs anyway. Why is 20-40 amps needed to run the car?

Trying to use cars for a significant power sources is a waste of time. A few lights and a radio and that's it. Oh, wait you don't need an inverter to run those.

[trader4]

Oh, no. Now you've done it. That EA imbecile from the other thread is probably gonna buy a fire truck now...

[HeyBub]

Can you work a pencil?

Depends on what you mean by "full output." Car alternators are connected to voltage regulators which hold the output voltage (almost) constant, irrespective of RPM.

A 2000-watt amplifier will use (at least) 170 amps. Add headlights, a/c fan, cigarette lighter, and, of course, the engine, and you'll be above 200 amps.

[Art Todesco]

Yeah, to get constant high power from a car alternator, you need a bigger alternator. Auragen makes such an animal. It works well, but isn't cheap. And, for the higher outputs, it does take over the engine throttle so you have to be stationary. But for use as a backup, that's not a problem. The one I am familiar with is a 5KW unit. It, along with its box of electronics, puts out a clean 120 volt true sine wave. The company installs it in your vehicle. I had one in a video production truck in my former life.

[clare]

A 2000 watt amplifier will draw PEAKS of 170 at full volume - average current well less than 100 amps - and 2000 watts is INSANE.

Big thing is a few amps to run the alternator field, another 10-ish for ignition at full bore, and another 17-25 for EFI including fuel pump - then add cooling fan, heater fan, and air conditioning clutch.

60 amps will barely keep up.

[Jon Danniken]

Or you could just install an additional alternator or two on the same engine, assuming they could be connected in parallel at some point to get the desired output current.

Jon

[gfretwell]

You will quickly run into the limits of the belt unless you add some pulleys to the crank shaft.

[Vic Smith]

Too much messing around. You can get a 200 amp alt for many cars, including my '97 Lumina. Even with the stock 100 amp alt and a good inverter setup it can start and run a fridge, power some house lighting, etc. All without breaking a sweat. Nothing wrong with that as a low watt emergency power source. You just expect only what it can give. There's a lot of confusion and false trails about this, but it gets down to simple math and amp draw. Here's one list of car component amp draw.

car idles in the driveway. You don't have the headlights on, or the A/C on, or the stereo cranked up, or the courtesy and dome lights on. Because that makes no sense for running your fridge. Figure ignition and fuel pump use about 5-7 amps. Figure your cooling fan(s) will kick in for whatever length of time and duration they do for your car and pulling what amps they pull. Whatever is left from the alt output goes to the inverter. I don't want to recalc it, but I think I came up with about 500 available continuous 120v watts at idle for the house. That was with inverter loss of 15% I think. My 100 amp alt car. If that's not enough, too bad. Go get more juice somewhere else. I already decided to stick my head in the sand until the outage hits, then decide what I'm gonna do. Leaving town is my favorite option.

[clare]

Just make sure you make the decision to leave town BEFORE you burn out your 100 amp alternator by running it at over 50% for more than half an hour.

[Jon Danniken]

[snip]

Well there 'ya go!

Jon

[Jon Danniken]

Indeed; my original thought was to use an increasingly longer belt to drive additional alternators, but your idea of utilizing a "distribution" pulley (like a pillow block) would only necessitate the additional belt length for driving one extra pulley (and would, as a result, be a lot more feasible). Eventually the point would be reached where the belt was physically unable to handle the additional load, whereupon it would slip, with the generational capacity of the system resting upon that limitation.

Jon

[Vic Smith]

Need more numbers. Figure winter time driving A/C defrost on, heater fan on high, headlights on, parking and sidelights on, rear window defroster on, radio cranked up, fuel pump and ignition running. Pretty sure that's more than 50 amps, or close. I do it every winter for hours at a time. For years on the same alt. Of course I would have to measure actual amp draw on my car. Anyway, I low-balled the 120v output at 500 watts, and figuring inverter loss into it that's still less than 50 amps from the alt. I've read that a typical alt puts out 60% of rated amps at idle. If I ever set up an inverter I'd measure draws. You can burn up your alt if you want to. But you don't have to, and I don't fall for scare tactics without numbers backing them up.

[clare]

You will generally run at about 50 amps average - you are not cranking windows up and down, adjusting power seats, etc constantly while driving - and the rear defogger cycles after about 3 minutes or so. The difference between 50 and 70 amps is significant - and between 70 and 100 a whole lot more significant - and add to that the fact that while drivivng down the road there is a LOT more airflow through the engine compartment than sitting running the inverter - helping remove excessive heat.

[harry]

What 2000 watt amplifier is this? A car needs less than an amp for the ignition circuit. If you have a diesel car,not even that. You won't need anything else whilst you're trying to use your car as a power source.

You are very uneducated. Best to keep silent.

[harry]

All that is nonsense. Except for lighting, 10 amps will cover everything. The alternator is larger to recharge the battery which takes a few minutes only. Which is why they have no need to be continuously rated.

[harry]

Exactly so.

[harry]

If you ever set up an engine on a "rolling road" an external fan has to be set up to keep the engine cool as there is no "slipstream".

[HeyBub]

Yep. But I have an insane person drive down my street every 30 minutes or so. (Not the SAME insane person.)

[HeyBub]

I guess you DON'T know how to work a pencil or, for that matter, Google "automotive+audio+amplifier" which will return many results at or exceeding

2000 watts.