Petrol Gen for 7 1/4 locomotive

[Jon Freeman 2Participant @jonfreeman2]

Hi Andy,

As Neil suggests, take a look at the series currently running in M.E. (I’m the author). You’ve had some good guidance above, but a few quick points :

Super capacitors – really ain’t that ‘super’ once you look a little deeper. Take a look at time specs. They don’t like being charged/discharged too quickly. If you spend £120 to buy 6 pcs 3000F 2.7V super-caps, once wired in series the capacitance is 3000F/6 = 500F. If charged to, say, 12V, how much useful energy have you stored?

Energy E = ½ C V^2 = 500 * 12 * 12 / 2 joule = 36kJ, or 0.01kWh. Not going to get you far! Spend the money instead, maybe, on a 12V 100AH traction battery, storing 1.2kWh, a safely usable 0.6kWh.

As for power sources, a standard mains voltage gen feeding a VFD driving small three phase induction motors ought to work well but I’d be a little wary of the voltages involved. For safer, lower voltage systems, a 4 stroke petrol engine driving a permanent magnet generator or vehicle alternator are good starting points. I use a large brushless motor as a 3-phase permanent magnet generator, but with this type the output voltage varies with engine revs (not a problem with the electronics I use). Using small 4 stroke engines to drive vehicle alternators – seems like a simple idea that ought to work well, but many a model engineer has fallen into a bit of a hole here by not appreciating that for any given output, alternator input torque rises as revs fall. So easy to design a system good mainly for stalling engines! There are ways around this, some better than others, and this is a project I’m currently working on.

A good place to start is to decide how much output power you want – what load do you hope to pull up what gradient at what speed, what acceleration, and with what losses, then do the arithmetic. Choose a 4 stroke capable of delivering twice this. Then if you want any further advice, contact me ‘jon at jons-workshop dot com’.

[Andy CameronParticipant @andycameron27025]

yes excellent input from everyone thank you all. I found your website Jon so will have a good look and will get hold of the article in ME you have written…….look out for some emails

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