Alternator Specs

[Joe Camper]

How does a manufacturer spec an alternator? How do you size it so that it is putting out enough juice at idle as well as underway.

How do you size the pullys both of them how do you know what size alt pully to run do you need the crank pully size will that pully be different if off the cam pully??

I had all these thinks asked and offered to find out?

How many amps would be acceptable for a new chassis alt if 24v system and NO OTR A/C on the bus simply just powering lights and radios?


What would be the smallest alt you would safley run for a chassis like this

[TomC]

You can go to alternator sites like Delco-Remy or Prestolite and both will have performance tables showing the output at various alternator RPM.  On a Detroit 2 stroke, the cam pulleys are running the same RPM as the engine.  If you have a set pulley diameter like the cam pulleys, then you have to size the alternator pulley to fit.  With most big alternators, you want to stay below the max RPM.  For instance, if you have a 8" pulley and the alternator max RPM is 9,000rpm, you want to figure the alternator pulley based on a max engine RPM of 2,500rpm.  So simply 9,000 alternator RPM divided by the 2,500 engine RPM gives you a ratio of 3.6 to one.  With the 8" pulley you just divide that by 3.6 and you need a 2.25" (rounded out) alternator pulley.  Course you can oversize the alternator and run it slower.

Big rigs come standard with a 160amp alternator now.  They are relatively cheap also.  It would be cheaper (and easier to get a replacement) to run two 160 amp alternators then to buy a 320amp alternator.  Good Luck, TomC

[Joe Camper]

Thank you Tom and I know 160 amps will be more than enough to run what he wants.

We find out the max rpm for whatever alt he gets and do the math to verify the correct pully diamiter we need for the engine pullys we currenty have.

I assume you did not pull 8in out of the hat but that is in fact the diamiter for the crank and cam pullies on an 8V?

Where is the correct place to measure the bottom or top of the groove?

[TomC]

You measure the top of the pulley to top of the pulley since a properly sized V belt should ride even with the top of the pulley.  If it is down in, it is to small-if it is riding higher it is to big (in width).  Good Luck, TomC

[dalej]

So do you think a 50-80 amp alternator would be good on my system with 4 chassis batteries?

[dalej]

I'm going to Delco-Remy on Monday and ask them these same questions. Here is there tech number: 1.800.372.0222

[Joe Camper]

Hey Dale your back.

O/K so we are still looking to answer what is the smallest rated alt that he could be comfortable with on a chassis without OTR A/C

Dale another thing occured to me after we talked.

CC put out conversions that I have seen configured 2 different ways in terms of charging things.

Prevost sends the chassis out with the 24volt gear driven. CC takes that alt and changes it and two different ways. First they make it 12 volt and second they use it to charge the house bank not the chassis. They also then add a belt driven 24volt to replace the change to the gear driven one.

The second way CC manages charging duties is they have no gear driven alt off the engine just the block off plate. There are 2 belt driven alternators a 12 for the house and a 24 for the chassis.

Those are the 2  configurations on CC conversios that I have seen. Your bus has all 3 alternators and I am unsure if CC did that or a previous owner did.

Enough of background for everyone to be in on the real questions.

On Dalej's prevo CC conversion HE has all 3 alternators is this original or not and why would you want this?

What is the smallest one that would do to charge the chassis without OTR A/C?.

His belt driven 24 volt puked and the one CC put in there original is a Marine unit that sells for 600+ that we are thinking is overkill and unnessessary.

[Joe Camper]

Another question I have about this goofy 3 alt setup

Obviously 2 of the 3 alts on this bus are sending charge to the same bank of batteries, the house batteries.

What other engineering comes into play when you do that, if any.

Wouldn't one of the voltage regulators get tricked by the other or some such thing?