Of Alternators, Inverters, and such..... - PeachParts Mercedes-Benz Forum

deerefanatic · #1 10-27-2005, 10:47 PM

Hi, I just bought an 800 Watt Continuous (1600 Surge) inverter on eBay. I want to be able to run my studio recording system on a mobile scale and my client's pc's here at my shop when power is out.

My question is this, how much amperage does a stock alternator put out at idle, (800 rpms)? How bout 1000? 1500?

Thanks!

1985 300SD Sady · #2 10-28-2005, 01:31 AM

you have a 65 amp alternator.

if that really is 800 watts continuous then the inverter alone is going to pull 60 amps, and thats at 13.5 volts, the lower the voltage, the higher the amperage.

Thats a simple power formula, I = P/E

You will probably want to upgrade the alternator, search on "115 amp bosch alternator in a W123 and it works!"

Search alternator upgrade, lots of good info.

deerefanatic · #3 10-28-2005, 08:22 AM

I really don't plan on using all 800 of those watts. I only bought it cause it wasn't much more than the smaller ones for sale elswhere. Maybe 500 continuous (for more than 5 mins) max.

1985 300SD Sady · #4 10-29-2005, 07:38 PM

you should be ok.

Especially for only 5 minutes.

Also, because the engine does not rely on electricity to run once the 5 minutes are up, the alternator will just build the battery back up again, I would think.

#5 10-29-2005, 07:42 PM

Quote:

Originally Posted by 1985 300SD Sady

Also, because the engine does not rely on electricity to run once the 5 minutes are up, the alternator will just build the battery back up again, I would think.

If you have all your goodies like lights/AC/heater/etc. off

I 2nd the "it should be okay". Just don't run it too long and make sure you hook it somewhere close to the battery. The Vehicle's wiring cannot support much over 10-15amps out of a lighter socket without ruining a wire.

I would recommend running a set of neg/pos directly from the battery (fused of course)

deerefanatic · #6 10-30-2005, 06:35 PM

Ya, I figured on running heavy gauge wire through the passenger side firewall to the inside, with 3 30 amp relays in parralell. Have these relays switched by the cig lighter socket. that way, the inverter is switched, but hooke direct to the battery.

I plan on using the inverter on the passenger side front floor (It is long and skinny so it should run cross-wise right along the front of the passenger seat.) I will basically be using it to charge cell phones, run my mobile DJ outfit, (uses about 250 watts a MAX volume, closer to 125 at reasonable volumes) and maybe a pc & monitor when the power is out and I need to fullfil a commitment to a client.

So ya, 500 watt continuous for long periods is a safe hi-end guess.

500 watt load @ 85% efficiency = 588.2 watts consumed = 42.6 amps @ 13.8 volts.

How fast should I run my engine to be able to sustain this? 2500?

#7 10-30-2005, 07:18 PM

Quote:

Originally Posted by deerefanatic

500 watt load @ 85% efficiency = 588.2 watts consumed = 42.6 amps @ 13.8 volts.

How fast should I run my engine to be able to sustain this? 2500?

Probably run it at about 1000-1200RPM or so. WHen you see the headlights get brigther you will know you are there.

redly1 · #8 10-30-2005, 09:31 PM

make sure to let the car run a while after you use the inverter. In fact, take it for a good drive afterwards with no shut offs in between. Colder temps require longer charging periods, as the battery doesn't accept a charge as efficiently when colder.

I'd recommend the 115A alternator, but if you have a good battery and will be using the inverter for short periods in a warm environment (40F plus), you should be fine as is as.

Wire it directly to the battery, and make sure to install a fuse close to the battery.

According to this guide ( http://www.powerstream.com/Wire_Size.htm ), 8AWG will be adequate for 800W (67A) operation, 10AWG will be adequate for 500W (42A) operation.

enjoy!

deerefanatic · #9 10-31-2005, 07:57 AM

Thanks for the info guys! I will try and post pics when I get it installed. For those interested, it is a Pyle PINV5 inverter www.pyleaudio.com

Thanks!