Micro 12v Generator Project

[mattnj]

Thought some people may be interested in my micro generator project....

Plan is for a tiny, light 12v generator capable of a decent output 20amps min, hopefully 40amps+, super quiet....light and small, with a simple diode mod on the regulator to boost the output voltage.

Starting point is a Honda WX10 water pump based on a GX25 Honda petrol 4 stroke, which is 25cc and 1hp ish, they use about 250ml of fuel per hour.

Will be directly coupled to a Denso Lightweight Motorsport Alternator (55amp max)

The standard engine is air cooled, the first version will stay air cooled, but i have fabriated a raw water cooled exhaust manifold with a 12v pump so the exhaust can be run via a longer output pipe over the side of the boat and things should be much quieter and take most of the heat away, the 12v pump runs when the alternator is producing charge, and is a small submersible unit that you chuck over the side. The idea is to make the whole thing water cooled later on, so it can go in a box, for now, it will need to stay ourside and exposed for cooling.

The whole unit is under 8kg at the moment and very small...

First pictures to give an idea, mounting the alternator today, will update as i go.

 

[Heckler]

Thought some people may be interested in my micro generator project....

Plan is for a tiny, light 12v generator capable of a decent output 20amps min, hopefully 40amps+, super quiet....light and small, with a simple diode mod on the regulator to boost the output voltage.

Starting point is a Honda WX10 water pump based on a GX25 Honda petrol 4 stroke, which is 25cc and 1hp ish, they use about 250ml of fuel per hour.

Will be directly coupled to a Denso Lightweight Motorsport Alternator (55amp max)

The standard engine is air cooled, the first version will stay air cooled, but i have fabriated a raw water cooled exhaust manifold with a 12v pump so the exhaust can be run via a longer output pipe over the side of the boat and things should be much quieter and take most of the heat away, the 12v pump runs when the alternator is producing charge, and is a small submersible unit that you chuck over the side. The idea is to make the whole thing water cooled later on, so it can go in a box, for now, it will need to stay ourside and exposed for cooling.

The whole unit is under 8kg at the moment and very small...

First pictures to give an idea, mounting the alternator today, will update as i go.

Wow, neat and tidy BUT sorry to throw a dampener on the proceedings, number 1 is that car alternators run approx 3 times as fast as the engine, so the direct coupling idea wont spin it fast enough, Number 2 simple electric math, 55 amps times 13.8v = 759 watts (lets forget about inefficiencies at the mo) Thats 1 hp, so the engine will have to run flat out to give its peak output,
Sorry!
Stu

 

[mattnj]

Wow, neat and tidy BUT sorry to throw a dampener on the proceedings, number 1 is that car alternators run approx 3 times as fast as the engine, so the direct coupling idea wont spin it fast enough, Number 2 simple electric math, 55 amps times 13.8v = 759 watts (lets forget about inefficiencies at the mo) Thats 1 hp, so the engine will have to run flat out to give its peak output,
Sorry!
Stu

yeah, yeah, thats why i said 20amps upwards....i never mentioned an output of 55amps? and am fully capable of simple electric maths thanks, it will be doing 20amps upwards, dont worry your self about that.....im sure i have though about it more than you have....

anyway, even based on your calculations....

car engine at say very fast idle 1400rpm x 3 = 4200 rpm alternator speed
honda engine, operating range 5000-7000rpm, sounds perfect to me no?

honda at say 6000rpm does 0.62kw = 620watts/14v = 45amps ish? minus all the losses, lets say they are 50% worst case = 22.5amps ish?

Think i have it spot on????

miserable git, just too many people on here poo pooing everything, throwing some maths about when they dont really have a clue!

 

[Heckler]

yeah, yeah, thats why i said 20amps upwards....i never mentioned an output of 55amps? and am fully capable of simple electric maths thanks, it will be doing 20amps upwards, dont worry your self about that.....im sure i have though about it more than you have....

anyway, even based on your calculations....

car engine at say very fast idle 1400rpm x 3 = 4200 rpm alternator speed
honda engine, operating range 5000-7000rpm, sounds perfect to me no?

honda at say 6000rpm does 0.62kw = 620watts/14v = 45amps ish? minus all the losses, lets say they are 50% worst case = 22.5amps ish?

Think i have it spot on????

miserable git, just too many people on here poo pooing everything, throwing some maths about when they dont really have a clue!

Wow again, miserable git eh? dont have a clue?
hmm
Stu

 

[mattnj]

ok, maybe that was a bit harsh, sorry, but you were wrong, right?

guess i was just saying too many people jump in with negatives on this forum, put people off and are often incorrect themselves.

 

[pampas]

LRA100 run from strimmer engine, direct coupled by Norton coupling worked ok but couldnt stand the noise so scrapped it. Think your will perform better than you anticipate. best of luck. Keep up the pionering spirit

 

[mattnj]

LRA100 run from strimmer engine, direct coupled by Norton coupling worked ok but couldnt stand the noise so scrapped it.

The GX25 is quiet out of the box, amazing little 4 stroke for the money.....with my new water cooled extended exhaust system it will be very quiet (hopefully) just need to hope the copper exhaust manifold doesnt melt/deform!

 

[VicS]

Interesting project... seems to have evolved a bit from the original idea although I cant remember what that was

The alternator should give you 40 amps at something in the region of 2500 rpm but to develop the power you'll need the engine running at about 5500 rpm

20 amps though looks easy to achieve The alternator should give you that at a speed as low as 1650 rpm although the engine will have to be turning at about 4000rpm to develop the power.

Flat out you should just about manage a max of 50amps, limited by the engine power rather than by the alternator.

All based on the manufacturers data of course but but it looks like the idea is a goer!

Keep us informed. Look forward to knowing if the theory stacks up in practice.

 

[mattnj]

Interesting project... seems to have evolved a bit from the original idea although I cant remember what that was

The alternator should give you 40 amps at something in the region of 2500 rpm but to develop the power you'll need the engine running at about 5500 rpm

20 amps though looks easy to achieve The alternator should give you that at a speed as low as 1650 rpm although the engine will have to be turning at about 4000rpm to develop the power.

Flat out you should just about manage a max of 50amps, limited by the engine power rather than by the alternator.

All based on the manufacturers data of course but but it looks like the idea is a goer!

Keep us informed. Look forward to knowing if the theory stacks up in practice.

Where are you getting that data from please? and what does "seems to have evolved a bit from the original idea although I cant remember what that was " mean?

Main criteria for me is the water cooling part and silencing, then can go in a box, with sounds proofing and the output is less important as the run time can go up and up, as you wont be able to hear it!

 

[Heckler]

ok, maybe that was a bit harsh, sorry, but you were wrong, right?

guess i was just saying too many people jump in with negatives on this forum, put people off and are often incorrect themselves.

No not wrong, just pointing out the pitfalls, by the way talking about peeps that dont know what they are talking about, my practical knowledge tells me that a copper exhaust wont melt or deform, UNLESS you solder it! you arent that daft are you?
I bought an SDMO genny, just under a kilowatt, built for the job, quiet, does what it says on the tin, £239. Ok i like messing around but by the time you have fiddled and messed around you will end up with noisy thumblethumbs project that looks like a home made effort, that is as noisy as hell (when you hear that outboard coming across the moorings with its distinctive beat you know its going to be an aircooled Honda outboard) and sits there revving its little 25cc guts out!
Stu

 

[mattnj]

No not wrong, just pointing out the pitfalls, by the way talking about peeps that dont know what they are talking about, my practical knowledge tells me that a copper exhaust wont melt or deform, UNLESS you solder it! you arent that daft are you?
Stu

Well, if trying something makes me daft then yes, again please less of the negativity, i am not saying that it will work i am trying some things out here, and just sharing my experiance, maybe i just wont bother sharing....thats the point of the project, yes its soldered, but it is getting 10l/min of cold water through the whole assumbly that butts right up to the head, so god knows how hot it will actually run at the soldered joint, one way to find out!

No doubt there is some maths to some about latent heat of water, melting point of solder blah blah blah, but ive made it now, so think i will just pull the chord and see what happens thanks if it melts, blows up and makes 1amp, i will still be happy, had fun making it with my son thanks....

 

[capeholm]

Cooling

Ineresting project, I had thought about it but was too lazy to start. Just remember, when you put the unit in the box, you will require quite some cooling air for the generator. The best way would be forced ventilation straight on the air intake of the generator.
Good luck
Horst

 

[VicS]

Where are you getting that data from please?

I did a Google for Honda GX25 and found this page for the engine performance
http://www.honda-engines.com/engines/gx25.htm

Googled for the Denso alternator and eventually found http://www.brise.co.uk/alternators.html and looked at the info for the Denso 5021 .. hopefully that's the right one!

and what does "seems to have evolved a bit from the original idea although I cant remember what that was " mean?

Probably muddling you up with someone else !

 

[mattnj]

by the time you have fiddled and messed around you will end up with noisy thumblethumbs project that looks like a home made effort, that is as noisy as hell (when you hear that outboard coming across the moorings with its distinctive beat you know its going to be an aircooled Honda outboard) and sits there revving its little 25cc guts out!
Stu

i was right when i said miserable git.....it may well be that and i will put it back to the water pump it started out at....you are just making yourself look silly mate...I will be back with some updates, hopefully some others may find interesting even if it does turn out to be a pile of cr*p, you never know, it may be really good, it it can do say 15-25amps at fast idle speed and i can get it really quiet with some water cooling, it will be perfect.

 

[Lady Campanula]

I'd like to hear more, as it develops....

 

[lw395]

No not wrong, just pointing out the pitfalls, by the way talking about peeps that dont know what they are talking about, my practical knowledge tells me that a copper exhaust wont melt or deform, UNLESS you solder it! you arent that daft are you?
Stu

Soldering is fine where the water jacket is keeping the temperature to below 100degC. Melting point of solder being somewhat over 200 usually.
A simple thermal switch to kill the ignition if the exhaust goes much over 90 might be a good idea.

Are there any issues with starting? Does the alternator impose a big load on the engine when it kicks in? Some sort of soft-start regulator might help.
Is cooling the alternator an issue? I guess it's good for a pretty high ambient.

Do you have any figures for the design lifetime of the engine? At one time I was thinking about doing this with a cheapo chainsaw motor, but their life can be short. Depends what you want it for!

Good Luck and do report back.

 

[mattnj]

I did a Google for Honda GX25 and found this page for the engine performance
http://www.honda-engines.com/engines/gx25.htm

Googled for the Denso alternator and eventually found http://www.brise.co.uk/alternators.html and looked at the info for the Denso 5021 .. hopefully that's the right one!

Probably muddling you up with someone else !

Yes, not me...this is my first effort....

Thanks, slightly different alternator spec sheet to my one, why does every alternator have about 50 variants.

Soldering is fine where the water jacket is keeping the temperature to below 100degC. Melting point of solder being somewhat over 200 usually.
A simple thermal switch to kill the ignition if the exhaust goes much over 90 might be a good idea.

Are there any issues with starting? Does the alternator impose a big load on the engine when it kicks in? Some sort of soft-start regulator might help.
Is cooling the alternator an issue? I guess it's good for a pretty high ambient.

Do you have any figures for the design lifetime of the engine? At one time I was thinking about doing this with a cheapo chainsaw motor, but their life can be short. Depends what you want it for!

Good Luck and do report back.

Good points, thermal switch on the manifold and alternator should it get too hot.....wonder how long it can run before it overheats...
ideally it will need a PIC controller to monitor the temps, and adjust the charge voltage, realistically, probably wont get that far....maybe in the winter, then i could have a servo on the throttle too...

for now, i can just connect the exciter to the alternator via a switch so once it is running to give it a change to run for a few seconds and not bog down right away...

cooling the alternator could be the hardest bit inside a box, how are the big expensive 240v gensets in a box cooled, water cooled alternators?

 

[sarabande]

Matt

good luck with a very practical project worthy of the traditions of PBO.

Can I suggest that you look at the exhaust proposal, as these engines are designed very carefully with a specific back pressure in mind. If you lengthen the exhaust pipe, then back pressure might increase and adversely affect the the performance.

 

[mattnj]

Matt

good luck with a very practical project worthy of the traditions of PBO.

Can I suggest that you look at the exhaust proposal, as these engines are designed very carefully with a specific back pressure in mind. If you lengthen the exhaust pipe, then back pressure might increase and adversely affect the the performance.

i dont think the "specific back pressure" applies so much in a 4 stroke at fixed rpm, I may be wrong, it is also, more important for me, for it be be quiet (hence the longer, water cooled exhaust) than to get engine max performance.

the stock exhaust goes into what looks like a restrictive muffler, and the exit hole is about 12mm diameter from the muffler, and i am going up to 15mm dia manifold about 60mm long, with no muffler and water jacket round the outside, then a 1.5m piece of plastic 1" bore hose, and 10l/min of water going in at the head area, finger in the air guesstimate, the back pressure "feels" about the same possibly even less...

making it up now, will post a picture for you all to laugh at

 

[VicS]

Just a thought but wouldn't a more efficient dry silencer be a better bet than a water cooled exhaust.
It won't consume the power that a pump will, it's not something extra that could go wrong and you could run it way from a water supply too.

Only downside will be that it'll be hot of course.