What is the RPM of our alternators ?

[Jeff Bayley]

Does anyone know what the average RPM is of our alternators (12 Volt House and/or 24 volt chassis) at cruising speed which I think is around 4,500-5,000 RPM's if I recall. I don't know what that translates into on the alernators. I'm certain it could changed (with a bigger pulley). I've got something extra I'm considering adding there and I hate to admit it's a generator head. Between 5kw and 10kw. Their just about the same size, maybe a tad larger than the 24 volt Delco on my bus. It's rated to turn at 1,800 RPM's. I think it's going to over rev beyond that but no certain. I presume it will burn up bearings or break in some fashinon if over reved. It may only be useful on the Hwy but that's ok. I belive some of the new converstions have something like this as an option. Here's a photo of one that I ran across for $300. I have to check and see it's 220 4 pole but I'm pretty sure I'll find out it is.

I haven't looked at it yet but it migh be possible to add it to the belt of the transfer box that runs the fan belt for the radiator if that is a lower RPM like I think it is but know neight RPM's on either point. The alternators that run off the main engine pulley must be 4,500 or more since they have pulley's on them.

Also, still trying to find out how to reset or trouble shoot the fire alarm sensor on my H3 shell. I have a post titled "H4-45 A/C head unit not powering on" that's only a day old.

[jack14r]

You can do a calculation of the ratio of the pulleys and multiply it times the engine RPM and that is the alternator RPM.

[Jeff Bayley]

I found out that I was WAY off from my memory of the engine turning at what I thought was 4,500 RPM's at curising speed. It's more like......well......just about 1,800 RPM's which is what the generator head calls for. But....I guess your right about calculating in the diameter of the pulley. I'm pretty good with math in my head but I never mastered the Texas Instruments scientific calculator to compute the acutal RPM's based on the pulley diameter vs. the RPM of the engine. In fact, now that I give pause to consideration on the matter, it occurs to me that the given (smaller) diamgeter of the generator head I propose would in fact turn at a slower RPM than the engine. The large drive wheel off the engine is 3 or 4 times the diameter of the wheel of this generator. So, I'm acutally loosing RPM's, not overspinning and gaining unwanted RPM's as I had presumed prior. Is that correct ? Anyone ?

[merle&louise]

Jeff,

You need some help from someone with a degree in quantum physics or celestial mechanics Or, maybe someone who has a Millenium with the 8.5 KW auxillary generator: Bob or Loc perhaps could help.

[sawdust_128]

We can all be quantum physicists. It's called "The Ratio Computer"

http://www.markanddebbie.net/overdriv.htm

[jack14r]

If the drive pulley is larger than the alternator pulley then the alternator will be spinning faster than the engine.For example if the drive is 10 inches and the alternator is 5 inches and the engine is turning 1800 RPM then the alternator is turning 3600 RPM.most 60 HZ generators are either 1800 or 3600 RPM units,you need to get the correct RPM to have the right frequency which determines the RPM of the electric motors that you are trying to power.

[Jon Wehrenberg]

Don't mix AC and DC Jack. I think an alternator on a bus engine has to be for DC output because of the varying engine speeds.

The critical question is not how fast it will spin, but directed to the alternator manufacturer should be the question "what is its operating RPM range?"

Once that is known, then the pulley, either the drive or driven pulley should be changed to provide that RPM range since we already know our engine operates within a range of about 600 to 2150 RPM.

What I want to know is how Jeff intends to hook that up and regulate the voltage.

[Jeff Bayley]

Thanks to all. John, I got to thinking about it just about the time you posed your very good question decided not to bother sticking myself with more needless needles. I got to thinking that IF I did want to make it work, it would require running a heavy gauge 3 or 4 wire shore power type line from the generaor up to the automatic transfer switch and I presume it would require a manual switch in line to transfer it from the bay gen to the engine gen. It isn't worth it after all. On top of that, I have to find a place for the generator head to pull power off a belt and it's probabley just asking for trouble in the long run. I saw that unit and it looked like a tasty idea.

I've already successfully modified the electrical system to allow two roof airs to run off the inverters when I'm running down the road in case (for example) someone wants A/C in the bedroom while driving so I don't have to run the gen to make that work. The 270 amp house alternator is enough to put a charge back into the batteries fast enough to keep with the draw the A/C's are taking out of the batteries through the inverters. So, having already accomplished that, the only other thing I'd be able to do is what ??? Laundry ? Run the electric stove ? The A/C's working are already enough.

[Jon Wehrenberg]

Jeff, I do believe you are settling down. That's good. The short version regarding your quest to use that device to generate electric is that if in fact it puts out AC power, the cycles will vary all over the place because your engine RPM varies. It needs to be driven from a constant speed power source.

The use of the big alternator to charge house batteries so the AC can be run is a solution a lot of converters have used. The only caution is that as you load an alternator to its capacity it is really being worked hard.

Why doesn't anybody just accept the fact that a coach with bus OTR air eliminates these problems.

[jack14r]

Jon,I think that jeffs question is related to a AC generator that would run off the DD to supply AC electricity for the various needs while traveling,some other converters do this and they regulate it to operate 2 AC units while the coach is underway.I agree bus air solves this problem.