Compact 24V generator

[Roog]

I am struggling to find practical advice on how to build a compact ic powered generator with 24V and approx 400W output. The unit needs to fit inside my next project, a diesel electric RC railway locomotive to run on just 3.5” gauge track.

My initial thoughts are to use an OS 91 4 stroke aero engine and link it up to a brushless DC motor of the type used in electric scooters working as an alternator and rectify the 3ph output to unregulated 24V DC ish. I have looked at repurposing a ‘small petrol suitcase’ portable generator but they are just too wide. I recon I have just 6.5” width to play with, but may be 14” length. The response from most seems to be choose a wider gauge ,but that would make the same loco type 5.8ft long, or bigger!

I know it’s a long shot but I thought id ask just in case someone has a need for recharging in remote locations?

 

[CertifiedMike]

I am struggling to find practical advice on how to build a compact ic powered generator with 24V and approx 400W output. The unit needs to fit inside my next project, a diesel electric RC railway locomotive to run on just 3.5” gauge track.

My initial thoughts are to use an OS 91 4 stroke aero engine and link it up to a brushless DC motor of the type used in electric scooters working as an alternator and rectify the 3ph output to unregulated 24V DC ish. I have looked at repurposing a ‘small petrol suitcase’ portable generator but they are just too wide. I recon I have just 6.5” width to play with, but may be 14” length. The response from most seems to be choose a wider gauge ,but that would make the same loco type 5.8ft long, or bigger!

I know it’s a long shot but I thought id ask just in case someone has a need for recharging in remote locations?

Lol!!! You're not one to shy away from the tough projects, eh?
I am not aware of anything like this but I never looked either!.

My initial thought was a truck alternator but might be too heavy or large for your build. Have you looked into any of those options?

This will be another fun build to watch I bet!!!

 

[WickedFog]

My uncles were diesel mechanics. I remember one of their projects on a D7 Caterpillar dozer was they needed a generator, so they made one out of a starter motor.

In racing, there are mini starters. Lightweight starter motors with much smaller cans than your typical car starter. Could you make one of those work?

 

[aklindeman]

Modern starter motors have a little gear reduction transmission. My old Triumph came with an old school generator and a direct-drive starter. They've both been swapped with modern units. An alternator and a gear-reduction starter. That starter made a HUGE difference. It's just able to spin the motor with a lot more ease. The alternator/generator swap really only means my headlights don't dim at a stoplight. Well, that and a little less parasitic power loss.

 

[CertifiedMike]

Modern starter motors have a little gear reduction transmission. My old Triumph came with an old school generator and a direct-drive starter. They've both been swapped with modern units. An alternator and a gear-reduction starter. That starter made a HUGE difference. It's just able to spin the motor with a lot more ease. The alternator/generator swap really only means my headlights don't dim at a stoplight. Well, that and a little less parasitic power loss.

Gear reduction starters are why old mopars sound different than chevy or ford when they are turning over.
I bet the alternator made a huge difference!!!

 

[tudordewolf]

I am struggling to find practical advice on how to build a compact ic powered generator with 24V and approx 400W output. The unit needs to fit inside my next project, a diesel electric RC railway locomotive to run on just 3.5” gauge track.

My initial thoughts are to use an OS 91 4 stroke aero engine and link it up to a brushless DC motor of the type used in electric scooters working as an alternator and rectify the 3ph output to unregulated 24V DC ish. I have looked at repurposing a ‘small petrol suitcase’ portable generator but they are just too wide. I recon I have just 6.5” width to play with, but may be 14” length. The response from most seems to be choose a wider gauge ,but that would make the same loco type 5.8ft long, or bigger!

I know it’s a long shot but I thought id ask just in case someone has a need for recharging in remote locations?

I love this kind of project. People have attempted them a variety of ways, even down to a .049-powered project.

One of the first issue's you'll run into is that glow fuel doesn't pack much energy density, so you'll be burning a lot of fuel to make a little electricity, relatively speaking. Gasoline will be a must for any practical power generation.

I've considered a Saito FG-11C or 14C for a portable mini-generator.
You could rectify the output from a brushless motor, then feed it through a DC-DC converter to stabilize it. This way you could also have an Arduino throttle the engine based on load and keep a constant voltage output. At 24V you'll want about 15-20A to do 400W, so something like this could work. You'd need an output of 9-40V from your genset, which is entirely feasible, with a 3000-9000RPM range from the engine, you'll need a ~360kv motor, so this one would be a good choice.

You could have an Arduino throttle it several ways, maybe having an RPM sensor, current sensor, and a lookup table of target RPM values for different loads, or just a "throttle curve" where if it detects the RPM's dropping below the target for the current throttle setting, it increases the throttle until they stabilize.

There was a kickstarter for a mini generator that claimed to have solved all the above problems, the Kower P1. It claimed to have a 3cc 4-stroke that could produce 150W from a butane canister.

They haven't posted any updates in over a year and followers are clamoring for refunds.

The question always becomes, would a battery pack of the same size offer better performance and practicality? For anything smaller than 1hp, that seems to be the case.

Hobby airplane engines are optimized for their specific role, and some of the trade-offs will be a constant battle to make up for. They have total-loss oil systems (a funny way of saying no oil system) and depend on lots of airflow and a rich tune for their cooling. Compare the 38cc NGH 4-stroke and a 35cc Honda 4-stroke - they both turn around 4k-8k RPM, but the Honda weighs more than twice as much and only produces 1hp to the NGH's 3hp. However, it has a separate oil system, and will run happily in a hot environment for hour after hour with no more than its integrated cooling.

For that matter, a Honda GX35 might be a better choice for your train, Roog, than a plane engine.

Edit - better yet, check this out, for a steal on Amazon. 31cc, 4" across at the narrowest dimension.

 

[Roog]

I love this kind of project. People have attempted them a variety of ways, even down to a .049-powered project.

One of the first issue's you'll run into is that glow fuel doesn't pack much energy density, so you'll be burning a lot of fuel to make a little electricity, relatively speaking. Gasoline will be a must for any practical power generation.

I've considered a Saito FG-11C or 14C for a portable mini-generator.
You could rectify the output from a brushless motor, then feed it through a DC-DC converter to stabilize it. This way you could also have an Arduino throttle the engine based on load and keep a constant voltage output. At 24V you'll want about 15-20A to do 400W, so something like this could work. You'd need an output of 9-40V from your genset, which is entirely feasible, with a 3000-9000RPM range from the engine, you'll need a ~360kv motor, so this one would be a good choice.

You could have an Arduino throttle it several ways, maybe having an RPM sensor, current sensor, and a lookup table of target RPM values for different loads, or just a "throttle curve" where if it detects the RPM's dropping below the target for the current throttle setting, it increases the throttle until they stabilize.

There was a kickstarter for a mini generator that claimed to have solved all the above problems, the Kower P1. It claimed to have a 3cc 4-stroke that could produce 150W from a butane canister.

They haven't posted any updates in over a year and followers are clamoring for refunds.

The question always becomes, would a battery pack of the same size offer better performance and practicality? For anything smaller than 1hp, that seems to be the case.

Hobby airplane engines are optimized for their specific role, and some of the trade-offs will be a constant battle to make up for. They have total-loss oil systems (a funny way of saying no oil system) and depend on lots of airflow and a rich tune for their cooling. Compare the 38cc NGH 4-stroke and a 35cc Honda 4-stroke - they both turn around 4k-8k RPM, but the Honda weighs more than twice as much and only produces 1hp to the NGH's 3hp. However, it has a separate oil system, and will run happily in a hot environment for hour after hour with no more than its integrated cooling.

For that matter, a Honda GX35 might be a better choice for your train, Roog, than a plane engine.

Edit - better yet, check this out, for a steal on Amazon. 31cc, 4" across at the narrowest dimension.

Thanks everyone, yes as ever I seem to have picked a challenging model to build, everyone else at the club who run 'diesel' locos nearly always go for battery electric and because weight is not a big issue, in fact to a point it is required for traction, they use mobility scooter sealed lead acid batteries!

My inspiration for this project is a UK television programme form circa 1984/85 the model in question was designed by Bob Symes (interesting chap) to run on track gauge half the width than I propose, 1 7/8" I believe and yet he achieved it, scroll forward to 3:26 in the following video.

I agree gearing down of the engine speed is a must and yes it isn't going to sound very realistic, RC engines or strimmer engines are likely to give the most reliable performance, although I have been told that those people using petrol engines with purely mechanical drive have experienced fuel evaporation issues dues to the confines of the loco bodywork resulting in big fans which sap engine power.

Another idea is to fit a large battery which can provide the initial motor start current and build a hybrid with the engine driven generator topping up the battery, might require a specific battery technology?

Here's an interesting diversion, a WW2 steam generator fueled by what ever you can get your hands on in the field, the bonus with using steam is it is quiet running not to give your position away!

 

[Roog]

I wondered if an old helicopter engine might be the thing? they have to operate at high power whilst enclosed in a housing, they seem to incorporate a well engineered compact fan too. I guess they don't need to run too long though. Also not too sure if a centrifugal clutch would be a good idea, nice for 'hi idle' then power up for run.

One other option, and a realistic solution for some British locos from the 60's and 70's, (US too I expect) is diesel hydraulic. The real things used a hydrostatic torque converter with cardan shafts to drive each of the bogeys at each end, very much like a 4x4 crawler. I wonder whether a crawler running gear can be adapted for this purpose? Because of the articulation of the bogeys (lets assume 7 deg turn max.) the cardan shafts have to be freely extendable and UJs 'fixed'. I quite like this solution because it fees up a lot of space, no alternator required, in the body of the loco and the cramped location of the drive motors in the bogeys.

Examples of Diesel Hydralics in the UK from the 60's

British Rail Class 52 'Western' used to run on my local line here in the West!

and the cute little Class 35 'Hymek', I've never knowingly seen one in person.

I would be interested to see photos of US locos that fit the description of interesting or easy to to make the superstructure! BTW, in the scheme of things 8 wheels is better that 12 in the world of manual machining.

Seriously though the issue of the torque converter is a challenge, unless you know of one in the model world or some thing that can be repurposed as one, a viscous coupling perhaps? Bit lossy I know, but the IC-electric solution is very lossy too. For passenger hawling the power transmission required is roughly 600W all in, say 1000W for margin of safety. Much less if you are happy to run a 'large train set' :0)

The fellows at the club tell me I'm on a fools errand, I feel the need to challenge this. Your ideas or even words of encouragement (yes I know, clearly needy) would be welcomed.

Missus Roog is now talking about installing a track in our back garden, weird, I'm not sure she is being serious with me, or is aware of the impact this would have, not to mention the cost, it will play havoc with the planted boarders, "mind the flowers will you"!

 

[Roog]

Seriously, adapting crawler parts might be the fast track to success here, ideas welcomed, just one slight snag, all of the lococs I have looked have use quite thick axles, even the small locos use 14mm dia shafts, typically reducing to 12mm (1/2") dia at the bearings.

 

[CertifiedMike]

I am not a crawler guy. Not really any ideas for products. The shaft idea to the boggies seems like a good solution.
I know there are also motors mounted directly to the axles. If there is enough room under this loco loco project, could something like that eliminate the joints and shafts all together?

Snow tank tracks come to mind when I think about the boggies design, not sure how I might work them onto the actual track tho.
I imagine more crawler ppl will be crawling out of bed soon too.

We are ALL on this ship of fools... but there can be only 1 captain!

 

[Roog]

I am not a crawler guy. Not really any ideas for products. The shaft idea to the boggies seems like a good solution.
I know there are also motors mounted directly to the axles. If there is enough room under this loco loco project, could something like that eliminate the joints and shafts all together?

Snow tank tracks come to mind when I think about the boggies design, not sure how I might work them onto the actual track tho.
I imagine more crawler ppl will be crawling out of bed soon too.

We are ALL on this ship of fools... but there can be only 1 captain!

Thanks for your reply @CertifiedMike i like your idea about having wheels mounted directly off the motor axles, I believe the issue is finding a motor whose torque matches the requirement to get the loco moving, relying on a push start might be a bit embarrassing. :0)

Also the internal distance between the wheel flanges is about 89mm and wheel diameter is 71mm so space is limited. I am resigned to mounting the drive motors above the bogey and use a 3:1 belt drive to the driving wheel axle.

The direct drive option is quite attractive because it should simplify the drive train.

 

[CertifiedMike]

I keep thinking about these when I think of the bogies and crawling put together.
I'm not entirely sure if somethimg like these could be modded to work on a rail track but it just keeps popping up in my head.

https://www.integy.com/st_main.html?p_catid=307


This sort of thing runnimg around my house all summer woupd be so fun!!!

 

[Roog]

Well who knew, ‘Hybrid drone generators’ are a thing!
2 stroke Petrol powered generators using VESC, and a lipo provide electric start for the engine and speed control for the connected motors, sounds perfect.

This one uses two RC engines and is designed to give 2kW+. I need about half this so I am hoping that I can get away with one engine, also I don’t mind using a nitro engine as run time and cost is not especially an issue

 

[CertifiedMike]

Well who knew, ‘Hybrid drone generators’ are a thing!
2 stroke Petrol powered generators using VESC, and a lipo provide electric start for the engine and speed control for the connected motors, sounds perfect.

This one uses two RC engines and is designed to give 2kW+. I need about half this so I am hoping that I can get away with one engine, also I don’t mind using a nitro engine as run time and cost is not especially an issue

Wow! That video was nuts!!!
I don't know if fluid dampers would react quickly enough to balance for you to try using a single motor or not.
Other than that, the harmonics of the dual motor design seemed pretty sound and possibly even necessary.
He lost me in some of the ripple explainations but I'm sure if I saw it on paper I could follow and would make good sense too.

I'll be watching to see how your designs could change and improve on this.

I am ALWAYS frightened when I see someone working on a petrol engine dressef in white!

Seems like a VERY smart and tallented individual for certain!!!

Cool vid!!!

 

[Roog]

Wow! That video was nuts!!!
I don't know if fluid dampers would react quickly enough to balance for you to try using a single motor or not.
Other than that, the harmonics of the dual motor design seemed pretty sound and possibly even necessary.
He lost me in some of the ripple explainations but I'm sure if I saw it on paper I could follow and would make good sense too.

I'll be watching to see how your designs could change and improve on this.

I am ALWAYS frightened when I see someone working on a petrol engine dressef in white!

Seems like a VERY smart and tallented individual for certain!!!

Cool vid!!!

Yeah, his presentation is a bit formal but he has certainly figured out the principles. Pity he doesn't provide a few more details, its quite tricky trying to figure out which motor makes the best generator for a specific power output.

Improve? not likely, cheaper and less powerful for sure! :0)

 

[tudordewolf]

Here's a solid example:

 

[Roog]

Here's a solid example:

Looks promising thanks for the link

 

[CertifiedMike]

I love your crazy projects!!!