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:D 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.

[mcirco]

My bus has a system supplied by Auragen. It consists of a device similar to an alternator (actually a multiphase generator) connected to an ECU (electronic control unit) The generator is belt driven off the Detroit Diesel and the ECU delivers 8KW of 240/120 Volts AC at 60 Hertz to power my Air Conditoners, Barney's heating pad, Wash clothes or waterever you want while you are going down the road. God forbid if my Powertech Generator fails while I am dry camping, I can always fire up the Bus Engine and use the Auragen to generate AC Voltage to recharge the house batteries, cook and cool.


Miles and Laura Circo
2004 Country Coach 45' XLII D/S

[Jeff Bayley]

Jon-

I agree about overloading the alternator since I've replaced several of them on both of my coaches and that was just from normal use. Having bad house batteries will burn them up to I'm pretty sure. I finally got tired of the stock 170 amp or so alternators and put a $1,300 Leece-Neville Alternator on the coach I have now. It puts out 270 amps. No modifications were required on my coach. I bolted it right in place where the old one had been. I think this gives a better chance of the overload problem. Yes ?

What WAS happening however was the in line fuse between the battery bank and the inverters kept burning out. The fuses are the large round ones that mount on two heavy posts. One for each inverter and are called "Class T" non arching fuses. They're about $50-$60 each time they burn out. I spoke to my converter and they told me they were now using a larger fuse there and it was safe to bump it up from 350amp to 400amp. It gave me a longer run time but they were still burning from time to time and it was costly. I installed the new style fuse and holders that I got from Burenstein's Distributing in Elkhart IN. in case anyone else wants to do this I can provide info and part numbers and my salesmans name who was very knowledgable and came out to the coach to see what I was trying to accomplish. The new holders are $4.00 each and the fuses are $10.00 each. During the testing phase (still testing as a matter of fact), it's a lot cheaper. Plus the old,original location of the fuse holders required you to be a contortionist to get to so I relocated them. They don't make a 450amp fuse in that style yet but they will in the fall Burnstein's informs me.

Jon- I know fuses and they're rating exist for a reason and I don't want to tempt fate, but do you think it's ok to bump it up another notch to the 450amp ? Besides burning the bus down, what other risks are there ? I presume the answer may be in overloading or burning up an inverter. Currentley, using the 400amp, I try not to leave the air on for extended periods of time. BUT, I did in fact have one of the new style holders have a melt down on me so maybe there's my answer right there.

How do the latest converstions configure the roof airs to work when going down the road ? One post here said he had a generator on his conversion going through a regulator or something. But don't some of them set it up to work through the inverters like my modification does ? I have a toggle switch to move the A/C's between the shore power panel breaker and the house side panel where I had two empty slots for the house side and installed two breakers there. The roof A/C's don't do well when at idle. Only at cruise speed since the alternator is spinning faster.

[Jon Wehrenberg]

Jeff,

You are now in scary land. The only help I can offer is to put your bus back the way it was before you make an ash of yourself.

If you want AC while going down the road run the generator.

Alternator power is not free. As the alternators get higher output it takes more HP to turn them and thus more fuel is used. AC is not free. The power to run it can come from your generator which will use some fuel or your big alternators which make your engine use more fuel, just like OTR air makes the engine use more fuel.

[Jeff Bayley]

Jon-

Noted.



PS- The shortest reply I have ever posted. I start for redeming myself for too getting too wordy ?

[truk4u]

I think Jeff has Genaphopea! He is always trying not to run the good ole safe and sound diesel generator!:D

[Jeff Bayley]

Yes, I'm a something holic. When I was a kid, I was alwasy in trouble for playing with matches. Now I have this fixation with electricity. What happened was the turbo burned up on the generator one time and diesel was leaking all over the generator and it I happened to walk outside at 10pm at night and noticed the smoke. It didn't flash up to a fire but was one step away. Ever since then, I've had this fear of running the generator, most noteably while sleeping at night. So....Guilty as charged. I NEVER used to go to RV parks and always dry camped. But I can't sleep sound at night with the generator running. Hense, more RV parks now OR the 3,500 watt pony generator I keep in the bay and use to run one A/C at night. Runs for 10 hours on one tank of gas.

[Coloradobus]

Jeff,

Marathon uses 2 Trace 4000 watt inverters to run 2 a/c units down the road. The older Marathons with 2 2500W Heart Inverters , are unable to run a/c units down the road without the use of the generator.