Pulley size and engine rpm advice

[lashfay]

Hi all. I'm looking for some advice on engine rpm and pulley diameters.

I have a Listeroid 16/1 1000RPM direct injection engine.
It will be coupled to a Stamford (copy) 12kva brushless head.

when working out the pulley size it got me thinking about the engine RPM. I was thinking is it advisable to run it a little slower say 850/900rpm so when the alternator loads up it has breathing space? I know it will make a little less HP by running it slower but can't really think of any other consequence apart from that.
 
I was going to run a 8pk serpentine belt, so it will use the existing flywheel.

My flywheel diameter is 590mm. If the engine is running at say 900RPM and I need my alternator to turn at 1500RPM I would require a pulley diameter of 354mm.
 
The only problem is I cannot find a supplier for one.

Maybe I'm going about this the wrong way and I should install a separate pulley on the Listeroid and forget about using the flywheel.

Any suggestions?

Dave.
 

[38ac]

I have a 1000 RPM Listeroid twin and in the absence of any hard facts or evidence I'd bet some pocket change on a drastically shortened lifespan at rated RPM vs anything slower.  If you don't need the HP that 1000 RPM produces Id slow it down to 800 or so but be mindfull that you may need to back down the injection timing a bit. When I built my 6/1 gen set I found a sweet spot for balance which was between 600 and 650 and machined a pulley for that RPM driven by the rim of the flywheel. Without the capability to machine parts your stuck with stock items and the engine RPMs that result.  In my (slightly ) opinionated opinion waaay too much is made about getting the engine RPMs exactly right and jumping through hoops with the belt drives to get it there. Im talking about 10% shifts in RPMs.  If the set up is for stand by power you can go with a V-belt drive and get a lot closer to the ratio  you wish and the increase in fuel usage due to losses is more fun to talk about than real dollars. Off grid and long hours would be differant.

 Here is a link to the Dodge PT wizard, a cool tool for what you are trying to find out. You have to register but its no biggie. Figure your drive ratio say 1500 RPM driven (gen head) / 1000 RPM driver (engine)  or 1.5 to 1. go to the tables for the belt section you wish to use A -B 5l etc, find the ratio and it will list the stock sheaves to get there and better yet go to the right and find the center distance between them and your belt size is there too, no guess work and right parts first go.

http://www.ptwizard.com/validateIpAddress.do

[lashfay]

Thanks for the tips. I do have a lathe in the workshop and I could machine something up but wanted to try and use an off the shelf part. It will be running upto 8 hours a day when put into service, serp belt.

I'll get my optical tacho out over the weekend and adjust the gov down and see if I cant find that sweet spot for balance, with no load and check out the timing while im there.

Thanks for the link, i'm heading over there now

Dave.

[SHIPCHIEF]

I have an Ashwamegh 25/2, rated at 1000 RPM. So I originally installed an alternator pulley to match. What a mistake. The enigne isn't really ballanced to run at 1000 RPM, it was quite twitchy. It broke mount bolts and shuddered during slight overspeeds when load was reduced. I added and moved weights all around the flywheels to try to find a sweet spot, but the choices were up and down hopping with rocking side to side, or back and forth swaying with rocking side to side. Singles like your's wont have the rocking.
I got a smaller Alternator pulley, and started the engine, then turned down the governor until the engine was running at it's smoothest spot. (I should have tried that before I bought a new pulley!!) about 940 RPM was the best, really smooth. but I was still above frequency, so I continued to slow it down, ending about 735 RPM @ 60 Hz. Still nice and smooth, but 940 was better. However, it's nice to have some safety factor RPM in reserve.
I run a 12 Kw ST alternator. Now I can get only about 10 Kw out of it; the belt squeeks and the engine exhaust is smoking a bit. Still, it runs my house with power to spare, as long as I limit the load to only one major appliance at a time. So I can have all the regular lights on, heating furnace, coffee pot etc, and run the clothes drier, or the electric stove, or the electric water heater, or the air compressor. Like that.