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Old 08-06-2022, 11:02 AM   #181
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
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Year: 1991
Coachwork: Carpenter
Chassis: International 3800
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ive never had a dyno to measure Horsepower of a compressor.. but looking at charts and knowing perpetual motion machines dont exist it appears 5-10 per compressor depending on system Load and size..



Amps.. ive not measured each component but a typical Large EM3 / CM3 system will pull 30-40 Amps in total.. double that for a bus that has 2 systems.



alternators in school busses typically are designed to push out close to or all of their output for extended amount of time vs car alternators which will overheat and burn up if you load them fully for more than a few minutes.



I have been charging House batteries in my DEV bus for quite some time.. its a Bosch SB200 (200 amp) school bus series alternator.. house batteries are AGM so typically they will only pull heavy amperage for the first few minutes of charging then they dont accept a whole bunch.. I run my 2 A/C systems, the stereo(500 watt amp and sub), lights.. etc and have the isolator closed to charge the batteries and I havent killed the bosch yet in 6 years..

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Old 08-06-2022, 02:45 PM   #182
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Quote:
Originally Posted by cadillackid View Post
ive never had a dyno to measure Horsepower of a compressor.. but looking at charts and knowing perpetual motion machines dont exist it appears 5-10 per compressor depending on system Load and size.. .
I thought it would be in that range. So with removing TWO large compressors I have gained 10+ HP for those long uphill climbs.
The HMMWV (Pronounced Hummer), the real one not those silly Tahoes with a squarish body passing themselves off as Hummers) had a circuit that, if you floored the throttle would shut off, or inhibit if not on, the fan clutch in order to give the FIFTEEN HP that the HMMWW's cooling fan drew. The thought being, if you're getting shot at while driving you're gonna floor it to clear the kill zone and since you're being shot at the vehicle can just deal with getting a little warmer.
Quote:
Originally Posted by cadillackid View Post
Amps.. ive not measured each component but a typical Large EM3 / CM3 system will pull 30-40 Amps in total.. double that for a bus that has 2 systems.
alternators in school busses typically are designed to push out close to or all of their output for extended amount of time vs car alternators which will overheat and burn up if you load them fully for more than a few minutes. .
Well our bus had THREE systems.

2ea EM1
1ea EM3
3ea CM3


So pulling 60 amps isn't likely to put the alternator under any more stress than running those AC units. That's 30 amps at 24 volts for the lithium batteries. Which actually isn't much since they will each take 100 amps at 24 volts. (NOTE: losses ignored for ball park calcs)

I'm just trying to decide if it's worth the expense of putting a 12 to 24 isolating battery charger on the rig. At the above output it would take 14 hours to charge the battery bank. Even if I pulled 100 amps from the alternator that's only 50 amps at 24 volts and would take 8.5 hours to recharge.
But I haven't found any known quality dc-dc converter/chargers that big. Victron's largest is like 15 amps.
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