Thermal lag generating electricity

Discussion on Stirling or "hot air" engines (all types)
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derwood
Posts: 113
Joined: Sat Dec 11, 2010 10:15 pm

Thermal lag generating electricity

Post by derwood » Tue Jul 08, 2014 7:11 pm

Thought I would post this for anyone who is interested.


Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Thermal lag generating electricity

Post by Ian S C » Wed Jul 09, 2014 2:42 am

derwood, that's a fine goer, what is the power cylinder? is it VW. What size is the generator. Ian S C

derwood
Posts: 113
Joined: Sat Dec 11, 2010 10:15 pm

Re: Thermal lag generating electricity

Post by derwood » Wed Jul 09, 2014 1:08 pm

Thanks! Yes it's a vw beetle cylinder. 87mm. The generator is a 5.5 amp 12vdc motor. It's too big for this engine. the dc motor has quite a bit of resistance with out a load. I need to get my hands on 2 amp 12 volt motor. I am also trying to figure out an easy way to pressurize the engine.

vamoose
Posts: 275
Joined: Tue Jul 03, 2012 12:16 am
Location: Australia

Re: Thermal lag generating electricity

Post by vamoose » Wed Jul 09, 2014 11:53 pm

Hey derwood,

I'm a bug fan (former vw campervan owner and restorer), so kudos for your adaptation..
Not sure if this can help you with your pressurized engine but I've been messing around with chopping up and adapting gas struts and also shock absorbers for my seals and shafts, they make an awesome seal. If you use older/worn out units then the seal is still there but without as much seal friction (plus using low viscosity oil helps). Also i made a runny paste out of fine buffing compound and oil to run through the shaft and seal for a period of time which really helped increase clearance slightly and reduce friction.

vamoose

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Thermal lag generating electricity

Post by Ian S C » Thu Jul 10, 2014 3:32 am

derwood, I don't know if one of these motors can be pressurized, but we'll say it can.The atmospheric side of the piston will need to be enclosed, this would involve enclosing the crankshaft, if you get the design right, the only seal required on a moving shaft would be on the flywheel side, you would take the drive from there, the little amount of oil might best be synthetic, it lasts longer, and less liable to igniting, although ordinary oil should be OK to 200 psi (Philips motor).
I'v just got hold of some old motors, I'v yet to try them . Doesn't matter the size (within reason), you only get out what you put in minus an allowance for friction, and efficiency, at this size, about half crankshaft power. Ian S C

derwood
Posts: 113
Joined: Sat Dec 11, 2010 10:15 pm

Re: Thermal lag generating electricity

Post by derwood » Thu Jul 10, 2014 2:05 pm

I tried a smaller motor and it did not work well. The motor I am using seems to be a good match after all. I also am unsure about pressurizing this type of engine. One concern I have is an increase in pressure when the piston moves outward. This occurrence does not happen under normal atmosphere. Perhaps a large reservoir would work. Maybe a regulator, but that would require a compressor to constantly top of the pressure. Any ideas would be appreciated.

Ian S C
Posts: 2221
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Thermal lag generating electricity

Post by Ian S C » Fri Jul 11, 2014 2:16 am

derwood, I don't know what effect the pressurization would have on the(can't think what to call it), the heated end, whether it might be bigger or smaller.
As far as motors go, I look for ones that run as slow as possible, then to get the rated voltage out you run it at, or just above the rated rpm, it's just a case of trying different ratios/size of pulleys.
I find that most of my motors have a fairly constant power over a wide range of speeds, if you gear up the motor runs slower under load, or gear it down, motor runs fast, both cases the out put of the generator is about the same, so split the difference, the motor is more happy, on my motors around 650rpm.
Some of the best motors I'v got came from HP Ink Jet Printers, they are the DC 12v brush type ones, there is a stepper motor to, but I have not tried that yet. Ian S C

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