caiman
Well-Known Member
So all we need now is a source for the 'adjustable regulator'.
Cheers
Cheers
Micro 12v Generator Project
- Thread starter mattnj
- Start date
nedmin
Well-Known Member
I hate to put my oar into a really interesting topic but dont forget about saturation.You can only get so much out,regardless of what you put in.
pvb
Well-Known Member
I've never fully subscribed to the belief that the PBO forum largely consists of people who don't know which way is up, but posts like yours do make me wonder if I need to review my position. Have you ever seen an alternator output curve? There's one in post #218 of this thread. Have a look at it, and then consider whether the "power output is proportional to the square of the rotational speed".
electrosys
Well-Known Member
Jeez - this thread is like watching a blind man trying to cross a motorway.
The output of an alternator is proportional to both rotational speed (of which there is an effective minimum in practice - somewhere around 2,000 rpm), and the magnetic force exerted by the rotor windings, which in turn is proportional to the voltage applied to it via the regulator.
BTW, if your battery ever becomes flat, you're screwed: no battery voltage = no voltage to the rotor = no magnetic field = no alternator output. One fix for this is to cannibalise a modern hard drive and recover the head actuator magnets - they're rare-earth and very powerful. They're also thin enough to slip under the 'horns' of the rotor. Use 3 to keep the rotor balanced, make sure you have their polarity right, and glue in place with Araldite Rapid (or similar). These will then always ensure that there is enough magnetic field present to give an output, even with a flat battery. The downside is that there will always be a residual output from the alternator, i.e. it will never switch fully off, as before.
Using a PIC to regulate an alternator is total overkill ...
Search the web, there are lots of simple regulator circuits already in use.
Oh yes, and if you want to drive a vehicle alternator, start off with a 3.5HP engine - a far more realistic proposition.
Or simply graft a vehicle alternator onto an outboard engine (one with a clutch), that way you've got the best of both worlds.
The output of an alternator is proportional to both rotational speed (of which there is an effective minimum in practice - somewhere around 2,000 rpm), and the magnetic force exerted by the rotor windings, which in turn is proportional to the voltage applied to it via the regulator.
BTW, if your battery ever becomes flat, you're screwed: no battery voltage = no voltage to the rotor = no magnetic field = no alternator output. One fix for this is to cannibalise a modern hard drive and recover the head actuator magnets - they're rare-earth and very powerful. They're also thin enough to slip under the 'horns' of the rotor. Use 3 to keep the rotor balanced, make sure you have their polarity right, and glue in place with Araldite Rapid (or similar). These will then always ensure that there is enough magnetic field present to give an output, even with a flat battery. The downside is that there will always be a residual output from the alternator, i.e. it will never switch fully off, as before.
Using a PIC to regulate an alternator is total overkill ...
Search the web, there are lots of simple regulator circuits already in use.
Oh yes, and if you want to drive a vehicle alternator, start off with a 3.5HP engine - a far more realistic proposition.
Or simply graft a vehicle alternator onto an outboard engine (one with a clutch), that way you've got the best of both worlds.
mikefleetwood
Well-Known Member
I'm not quite sure why you are making such an issue of this.
The graph you refer to shows output current, not power. You will also notice a fairly linear relationship between RPM and current, until the internal resistance becomes a limiting factor <2500 RPM. It also does not state under what conditions. I was talking about the general principle - voltage is proportional to RPM, current (assuming a resistive load - which a battery isn't) proportional to voltage and power voltage x current, so proportional to RPM squared.
The sole reason for my explanation was to answer the question of "where does the extra current come from?" quite a few posts ago. The "RPM squared" was just a throw-away to counter your statement that "power output was proportional to RPM, which is wrong, although current output might be to some extent.
Feel free to argue against laws of physics if you wish, but I think we have gone way beyond the purpose of my original clarification, and I will call it a day here until something else catches my interest.
mattnj
Well-Known Member
I thought I had posted a link to the circuit on here already, but maybe on the other thread, will find it and re-post
mattnj
Well-Known Member
if you say so.
the reason for the PIC is so the alternator output can be matched exactly to the engine power graph, so its essential not overkill. please do post a link to a regulator circuit that will do what I need.
finally a 3.5HP engine isn't going to weigh 2.3kg so its wouldn't be s "micro" generator.
mattnj
Well-Known Member
all good fun!
highest number of views for any thread?....keep it up....
we should all be getting together with our science/engineering minds to help solve some of the issues, not just shouting on at each other.
no-one is going to stop me finishing it off, almost done, and it does exactly what I wanted, 20-30amps, shouting about physics is pointless.
Thanks to all those who have actually helped so far by making sensible suggestIons/comments.
highest number of views for any thread?....keep it up....
we should all be getting together with our science/engineering minds to help solve some of the issues, not just shouting on at each other.
no-one is going to stop me finishing it off, almost done, and it does exactly what I wanted, 20-30amps, shouting about physics is pointless.
Thanks to all those who have actually helped so far by making sensible suggestIons/comments.
Trundlebug
Well-Known Member
Have you made the box for it yet Matt?
That'll be the next challenge, and no doubt another source of controversy about the best material, construction method, and everything else!
Not meaning to hurry you along, you understand, just keen to see what's next and how it turns out!
That'll be the next challenge, and no doubt another source of controversy about the best material, construction method, and everything else!
Not meaning to hurry you along, you understand, just keen to see what's next and how it turns out!
Leonidas
Well-Known Member
electrosys
Well-Known Member
At the risk of making an assumption - I take it that you started the project with the engine already in your possession ?
So - anyone wanting to make a clone will have to source an engine ? I'm wondering how much that will cost ?
The reason I suggested a 3.5HP, is not only the increased horsepower which will allow the engine to run at a lower throttle setting, but such engines are commonly available ex-lawnmower for around £20. An alternator ex-scrappy for a fiver, and there you go .....
No - it wouldn't be a 'micro' (650 watt suitcase gennies can commonly be bought for around £60) - but it would be very cheap to make and within most people's skill-range.
I take it you've not done much work with op-amps ...
All-in-all I favour the outboard-alternator set-up - could be a very nice project.
2Tizwoz
Well-Known Member
For the case
Will it fit into a tool box such as this and further reduce noise? It will need an air inlet of course and a fuel tank. Water and exhaust could pass through bulkhead fittings. The whole thing could mount to a piece of ply which fits the box,making removal simple for servicing. Electronics and electrical connections could live on the outside.
From here http://www.toolbox.co.uk/irwin-pro-structural-foam-4668-79676?CAWELAID=268737104
Will it fit into a tool box such as this and further reduce noise? It will need an air inlet of course and a fuel tank. Water and exhaust could pass through bulkhead fittings. The whole thing could mount to a piece of ply which fits the box,making removal simple for servicing. Electronics and electrical connections could live on the outside.
From here http://www.toolbox.co.uk/irwin-pro-structural-foam-4668-79676?CAWELAID=268737104
mikefleetwood
Well-Known Member
I wondered why he didn't take a more "analogue" approach. But then, if you have the tools to hand, it's a lot easier to change parameters or add sections to software than it is to fiddle around soldering/de-soldering extra components.
mattnj
Well-Known Member
hi,
been away for a while but back on the case now.
The genny is coming on well, i have re-done the coupling as the one i bought originally broke when the grub screw came loose, that is all finished now, but have a couple of minor issues to work on at the moment, firstly the charging circuit doesnt go over 14.1v so i need a tweak there, and also it charges the battery so quickly that i cant keep it running long enough under heavy load to de-bug the software...
So, what can i use to put say a 10/20/30 amp load on my batteries? (without spending money?) ideas please.
will update with some pictures and videos later on
Matthew
been away for a while but back on the case now.
The genny is coming on well, i have re-done the coupling as the one i bought originally broke when the grub screw came loose, that is all finished now, but have a couple of minor issues to work on at the moment, firstly the charging circuit doesnt go over 14.1v so i need a tweak there, and also it charges the battery so quickly that i cant keep it running long enough under heavy load to de-bug the software...
So, what can i use to put say a 10/20/30 amp load on my batteries? (without spending money?) ideas please.
will update with some pictures and videos later on
Matthew
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mattnj
Well-Known Member
i think you have missed the point of the project, its a micro genny, water cooled in a box, electric start, what you are suggesting is something very different to this project.
As for analogue and op amps, well there is just no point, PIC does everything that an op amp will do, cost is irrelavent (about a £1 for a PIC) and does thousands of other things too, and is way easier to adjust all the parameters in software via the laptop.
PIC is cheaper, easier, more control, more functions. (oh and by the way it does have a 741 op amp too in the curcuit, so yes, i do know about them)
Digital is the way forward my friend, every time....
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Monique
Well-Known Member
http://www.mfgsupply.com/m/c/GHI0002.html
Have you considered a starter/generator???
Just a thought.
Have you considered a starter/generator???
Just a thought.
mikefleetwood
Well-Known Member
What about a big lightbulb - spare spotlight or headlamp? Probably not quite as big as you're looking for, but maybe use a couple in parallel?
I'm assuming you don't have any high-power, low-Ohm resistors knocking about.
How about a starter motor with some kind of "brake" on it? Could be an adjustable load then.
mattnj
Well-Known Member
yes, I have 2 options for electric start:-
1) using the electric start motor that fits on the back where the pull start is. (have it, havent fitted it yet and you loose the pull start.
2) run the alternator as a motor, just needs a model brushless motor speed controller, this is my preferred option. will work on this when all is finished and it runs ok with hand starter, if i cant get it working will go for option 1
Monique
Well-Known Member
Good luck with your project; I could use such a small generator. Though my boat is well equipped electrically it is quite frugal.
....But I HATE to run the engine to top off the bats just because I need the refrigerator.
....But I HATE to run the engine to top off the bats just because I need the refrigerator.
2Tizwoz
Well-Known Member
No cost electrical load
Some scrap car headlights from a helpful yard. They aren't much use commercially once the reflective coating has gone.
Chainsaws have suitable petrol pipe and filters which are both available on ebay. Plastic petrol tanks are available of course as they're used for outboards but they don't seem to come with a return line connection off the shelf so would need to be modified.
The Honda inverter generators have an electronic servo throttle which may be available as a spare. It mounts on the carburetor making a linkage unnecessary. Only problem could be price and availability.
Dave Tidwell used an IRF3205 power mosfet which costs around a £1 . http://www.youtube.com/watch?v=Cqf4ICwFBIU. He gives all the detail of his alternator to stepper motor conversion which retains the original rectifier diodes which presumably means the alternator remains functional, only requiring your field control circuitry to balance engine power to demand or vice versa.
With the operation of the finished article being so simple it may be too easy to run out of oil or overheating to go unnoticed but those problems could be overcome with oil level and temperature sensors which you are familiar with.
Some scrap car headlights from a helpful yard. They aren't much use commercially once the reflective coating has gone.
Chainsaws have suitable petrol pipe and filters which are both available on ebay. Plastic petrol tanks are available of course as they're used for outboards but they don't seem to come with a return line connection off the shelf so would need to be modified.
The Honda inverter generators have an electronic servo throttle which may be available as a spare. It mounts on the carburetor making a linkage unnecessary. Only problem could be price and availability.
Dave Tidwell used an IRF3205 power mosfet which costs around a £1 . http://www.youtube.com/watch?v=Cqf4ICwFBIU. He gives all the detail of his alternator to stepper motor conversion which retains the original rectifier diodes which presumably means the alternator remains functional, only requiring your field control circuitry to balance engine power to demand or vice versa.
With the operation of the finished article being so simple it may be too easy to run out of oil or overheating to go unnoticed but those problems could be overcome with oil level and temperature sensors which you are familiar with.
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