PeachParts Mercedes-Benz Forum - View Single Post

Greg in Oz · #9 07-07-2005, 04:24 AM

Quote:

Originally Posted by Jim H

I wonder if using the engine AND transmission to power the generator would work?

1800 rpm generator means 1.5:1 gearing (don't know which gear) to give 2400 rpm engine speed, right in the fat part of the torque curve.

Then, use the speed control to keep driveshaft rpm constant at varying load, and you have a crude, 3rd world-worthy generator. With the right size radiator and fan, it might work better than imagined...

What say ye all?

Best Regards,
Jim

It may appear tempting to retain the auto transmission however the numerous ratios are not required to run an alternator at constant speed (versus great variations in road speed). The transmission would also add unecessary losses and would also require the speed feedback signal be derived from the alternator. Assuming the auto transmission was retained and the speed (frequency) signal was derived from the alternator, the only possible advantage I could see with this arrangement would be that it may allow the engine speed to vary (by way of torque converter) as varying loads demanded differing amounts of torque from the engine. The speed controller would be the complex part of such a system.

Quote:

Originally Posted by rbarr8

Thanks to all who have responded to my query. I would like to learn more about the torque curve as referred to in one of the responses. If I am to consider this as a viable approach, I need to know more about the torque curve of the engine I have. If anyone can direct me to a site that has these kinds of specs, I would very much appreciate it. I have considered a lovejoy direct coupling but have read a lot about using slower speeds with large and heavy flywheels for greater torque and momentum. That is why I was looking for information relative to my engine at idle speeds. I wonder where the point of diminishing returns would be operating the engine at 1800 rpm with a direct drive coupling to the generator off the pto end and a heavy flywheel on the other. Could this be done without causing too great a load on hp while gaining momentum for demanding loads on the generator? (starting large induction motors and the like) The primary use would be for power backup during power losses from hurricanes or other long duration events. As hurricanes are in the heat of the summer, I would want to run my air conditioner as well as water pump and hot water heater.

Thanks, Roger

Being a diesel, the torque curve of that engine would be fairly flat. However, unlike diesels intended for use in generator sets, the governor in the injection pump will not attempt to maintain constant engine speed (other than providing overspeed protection). Being intended for an automotive application the governor will attempt to maintain constant torque for a given "throttle" setting. This is not ideal for use with a generator set where the result would be varying speed (and hence frequency) with varying load. You would need to obtain a different (or possibly modified) injection pump with a constant speed governor, or obtain an electronic speed control that could control your existing injection pump. With regard to the use of a flywheel, even very large ones will only compensate for very brief transients in electrical loading. The control of speed (frequency) in a generator set with greatly varying electrical loads is a difficult task. The generator set I mentioned in my previous post in which I was involved with the design (actually 15kW with peak loads to 30kW now I think of it) used the frequency of the alternator (400Hz) as a feedback signal for the electronic speed controller (governor). This was a complex PID (proportional, integral, differential) design carefully tuned to the application which had to deal with transient and regularly cycling loads varying from no load to full load. The electronic controller drove a rotary solenoid which operated the engine throttle on the petrol (gasoline) engine required for this application. Watching the very rapid response of the throttle to the varying electrical loading was amazing.