anyone know how to cheaply run a large dc industrial motor?

woops- i guess i did mention this is for a D.E..sorry

 

If you like the D.E. system and that's what motivates you, just do it.
It will certainly work.

Of course this indirect way to obtain and store energy is not very efficient but given the limited amounts involved it won't change the climate noticeably.

Bear in mind that these large alternators really draw power and each needs its own V-belt. I made such a generator once for a guy living in the bush without power grid. Two large alternators on the flywheel side of a 1.5 l. diesel, the diesel fixed at 1500 rpm, the alternators spinning at approx. 10.000 rpm.
The set daily operated 5 hours, started and stopped automatically and kept on doing that for several years until it died from running without oil because nobody ever looked at it. But that won't happen to you.

 

CDK- how big a diesel engine would be needed??.i have a cat d 318 its old and has huge torque runs at 1750 rpms. i could gear the alternators to accept a gearing increase say to 5000 rpms? but would that be enough -if not i could gear them even higher..

some years ago i experimented with a charging system with an alternator and a small gas go cart motor- for some reason i couldnt get the alternator to work? the voltage wasnt even reading on the multimeter- i thought maybe 1. it wasnt running high enough rpms? and/or 2. it needed to be hooked up to the batteries to have a circuit before the alternator would kick in? or possibly the alternators used and were shot...
what rpms would i need to get the alternators to run and do they need a battery to start working? i.e. a voltage input to the alts?

 

In the case I wrote about it was an old VW Golf 1.5 l. engine with approx 1:6 belt pulleys. For the alternators to deliver full output, you need 10.000 rpm or more with the diesel running at high idle. Calculate 3 hp for each alternator.
Because the guy had his batteries in a room and the diesel was standing quite far away, I used a separate sense wire to keep the alternators at their jobs until the battery voltage was 14 V. Without that the charging current drops to early and you are wasting fuel.
Any alternator can be modified in this way: just cut a wire from the regulator that normally is connected to the output and extend that to the location of the batteries.

 

CDK--whats sad is-- the engine i have would great for the tugboat but too big for the DE system i do have an option of going with a smaller engine by trading the one i have --the engine in question is an older petter air colled engine- 18 hp. not sure of the rpms but comes with a clutch but no reduction and fwrd only.

 

You will increase range more by just idling the main engine for 15 minutes out of every hour.

The additional expense of the electrics, the additional weight, the huge additional maintenance, and the fuel burned for charging will never be cost or effort effective.