# DIY DC Generator? (Help)



## Atarijedi (Apr 1, 2009)

I am wondering if anyone here has made their own DC Generator from a Gas/Diesel/Propane/NG motor and PMDC motors?

I am planning to build a series hybrid (Reverse Trike design) which will use a Generator (bought or built) to power the traction motor (AC Induction), and be augmented with batteries, or vice versa, maybe run off batteries until the generator is needed.

Anyways, I can buy a store bought generator, I found a somewhat small portable one that puts out 17.5kW continuous and 26kW surge. But I don't know exactly what would be involved in modding it. I am guessing it outputs at 240VAC then steps down for the 120VAC sockets, and the easiest way for me to modify it would be to either step that down again to 60VAC, which would involve a rather large transformer, then fully rectify for 84VDC, or fully rectify the 240VAC and DC/DC convert down to something between 48VDC and 96VDC for the AC controller.

Or I thought about building my own generator using 3 E-Tek like PMDC Motors in parallel and a 40HP Kohler Gasoline Motor, modded for bifuel (Gas/Propane). The problem with this is I don't know if they can be safely run in parallel. If they aren't matched, there might be problems if one or more is underproducing, reverse currents and all that. I would prefer this, simply because the E-Teks would put out [email protected] each, and the Kohler is tuned to run optimally at around 3840RPM. So I am assuming with them in parallel, I would have a combined [email protected] on-tap if needed.

Does anyone have any info they can provide on running multiple DC Generators in parallel, will there need to be any sort of balancing circuitry involved, they are all powered from the same motor, so I don't think there will be, but I don't know much about it. 

Any help would be appreciated!


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## rillip3 (Jun 19, 2009)

I know nothing of the design issues you're raising, but you may wish to consider going with a prebuilt engine from an auto if it's going to power an auto. Most generators are made to be stationary, and may not react well to the bumps and vibrations. Even if that's not an issue, there's rarely any sort of ducting or exhaust system on a stationary generator. I see it in the news all the time here where the power goes out after a Hurricane and someone dies or nearly dies of carbon monoxide poisoning when they have their generator in the house, or near an air duct, or not far enough away from the windows, etc.

It may be easier to modify a motorcyle or small engine to turn a dynamo than it would be to manufacture an exhaust system for a stationary generator. Just my $.02.


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## todayican (Jul 31, 2008)

A few questions:

What is the size / weight of the trike you are wanting to build? 40kw seems like it mat be a bit much for what your trying to do.

I for example am building a lightweight trike, good aero. it will be flexible in its power ranging from 200cc i.c.e. only, to 85v electric only, to both series and parallel hybrid.

in the parallel version, I figure 7 to 10kw should be enough to drive the vehicle via the electric motor on gen output only.

(series about 1kw less due to less losses in the gen)

do an ebay search on "permanent magnet" windmill

there are a lot of dc gen options for sale to the windmill crowd id bet would work if your power needs are small enough.
Tom


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## Atarijedi (Apr 1, 2009)

It might be a 24kW generator, not 40kW, the Gasoline/Propane engine might need to be a 40hp.

As for the size and weight of the trike, it is roughly going to be the same size, maybe a bit bigger, than the Campagna T-Rex, and I am assuming it will probably weigh around 1400lbs minimum to 1800lbs maximum. (Based on what the XR3 weighs). The XR3 weighs 1480lbs, it has a 158lbs (20HP) Diesel powering the 2 front wheels and a 550lbs Electric System powering the rear (That is motor, controller and batteries)

All I need to know is whether 2 or 3 DC Permenant Magnet motors, all being turned from the same Motor, be put in Parallel without any supporting electronics for load balancing etc... I believe I should be able to just stick high power diodes in there and that should be sufficient.

I have calculated that the 24kW Generator will weigh around 210lbs and the 16kW Generator will weigh around 150lbs. That is just the ICE Engines (Dry Weight) and the PMDC Motors, no sprockets, chains, gears, belts or mounting plates.


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## Gavin1977 (Sep 2, 2008)

You would need some way of isolating the generators from the battery pack to ensure you dont drain the battery when the generators are not running. So you would need a diode/mosfet/something else anyway. So you might as well put a power diode on each output, then it would be fine to parrallel them up after the the diodes. Though under load it would be fine to tie the outputs together directly anyway.


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## Nomad (May 8, 2009)

Isn't that size of generator expensive?

Are you needing it for long trips? Lithium might be a better bang for your buck depending.

But, Since you asked I wasn't going to let this cat out yet, I'm currently designing a range booster with a local small motor shop. Currently off the self designs are only 11% eff. Which sucks lol. Your talking about getting worse gas mileage than an ICE.


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