|not done it yet||16/09/2019 22:17:49|
|3946 forum posts|
And the hydraulic pressure? Always some risk of something going wrong sometime!. I’ve been doused in oil when a hydraulic pipe has failed. Worse might be a pin-hole leak at high pressure. Certainly will withstand getting wet (with water), though.
|5138 forum posts|
I'm not impressed by single-phase electric motors for this application. Compared with other types they have too many limitations: for traction their low torque (turning power) and difficult speed control are killers, on top of that they run bumpy with relatively poor efficiency. A DC Motor, Brushless or 3-phase motor will be much more satisfactory. As these and suitable controllers are all readily available I don't see any advantage in single-phase, only pitfalls.
Andy's problem is how best to match the output of an off-the-shelf 240VAC generator to a motor. Now that VFDs are affordable, I'd be inclined towards a 3-phase motor - reasonable torque, efficient and VFDs do a good job of speed control. However, even though it will easily out-perform a single phase motor my main concern would be a 3-phase motor's ability to shift a heavy load from a standing start. This is why IC engines need a flywheel, clutch and gearbox.
Indirect electric drive, for example when a generator charges a battery, which in turn powers a DC motor is a good compromise. The battery provides a high-current source which is good at satisfying peak demand during starting and acceleration.
These peak demands don't last long. Once an indirect drive vehicle is moving, the generator tops up the battery and then powers the wheels via the battery. Having a storage system deal with peaks means the generator can be sized to meet average demand, which is considerably less than the start-up demand. Get the sums right and the battery can also be quite small because it only works hard during starting. An interesting development in Hybrid Vehicles is the use of super-capacitors rather than batteries. Although a super-capacitor holds less energy than a chemical battery, it charges and discharges much faster at almost 100% efficiency. This makes super-capacitors attractive for stop-start operation and regenerative braking.
|Andy Cameron||17/09/2019 12:41:14|
|9 forum posts|
I do like the idea of a generator constantly charging a small capacity battery system or super capacitors, I guess could also use a small 4 stroke to alternator to provide the charging input ( just like a car ) I guess the battery/s used would need to capable of fairly high charge rates I am only really familiar with Lipo battery packs and 1C charge rates i.e. a 4500Mah battery charging at 4.5Amps max not sure about car battery max charge rates.
|Andy Cameron||17/09/2019 13:01:05|
|9 forum posts|
I had a look at super capacitors as an example a 3000F 2.7V capacitor can be as cheap as 20quid x6 in series with upto a million charge/discharge cycles it looks like it could be a good project not sure what rating of capacitor would be needed but the peak current potential on what I have looked at is extremely high. I would imagine one of those battery start boosters would even be possible if they allow an input charger while outputting a load ?
|Jon Freeman 2||18/09/2019 18:07:25|
10 forum posts
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 Cameron||18/09/2019 19:53:02|
|9 forum posts|
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
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.