DIY 12V DC 70A Petrol Generator

[gooseknack]

Good idea, more efficient than an ac generator and battery charger. Alternator speed versus power output is an interesting one, and I've seen these work quite efficiently with only a 4 inch pulley on the motor and the standard pulley on the alternator. Most alternators are capable of producing close to max amps at between 2500 and 3500 rpm(depends on the car). the trade off with the bigger pulley is lower engine revs, quieter running and less fuel usage, but lower amps.

[ohyrag]

A car alternator is not very efficient as it needs to excite the field, if you get a permanent magnet alternator it saves having to generate power for the field. I am building a similar setup using a Fisher Paykel washing machine motor. You can find the same type of motor in direct drive LG washers also. I also intend to use a regulator to control the engine throttle with a soleniod so as the batteries reach charge the engine will slow down.

[videokfm]

@ohyrag thanks for your info.I will start looking out for a washer motor like that.

[gooseknack]

@ohyrag actually, a car alternator is fine for this application, as the staionary motor has enough speed to run an alternator(usually 2 to 3000 rpm at the alternator is fine), it's only the initial start up that's the problem, as you mentioned, it needs to exite the field, once that happens and the alternators turning, it keeps itself going. A pm alternator would be advantages, they can generate a high output at much lower rpm's, not to mention, they need no power to start generating!

[stdavross666]

Hey mate nice video. I have a suggestion to modify your setup with a simple to program micro controller such as a PICAXE etc that would take engine RPM OR throttle position and alternator load as an input to operate a small servo that could automatically adjust engine RPM to the load? Hi from Perth Western Australia. OK back to the beers.

[VisioninScience]

very nice project.

[theevilovenmit]

You could install an ultra capacitor bank to act as a buffer for momentary high loads, though it would need to be charged before hand otherwise it would act like a shorted circuit.

You could use a couple deep cycle lead acid batteries as the buffer.

You could also install a large flywheel as the buffer..

And lastly you might be able to install a second gas engine, however it would be quite complicated to synchronize them if not unfeasible.

[oregonmeds]

It's not that the engine is too small it's that your pulley ratio is way wrong. Too many alternator rpms per engine rpm's change the ratio.

[jib1000]

They sell gas generators at the hardware store already guy...

[videokfm]

@jib1000

Here where I live I have only ever seen AC generators not DC generators.

[jib1000]

@videokfm They don't have batteries where you live? Transformers?

[videokfm]

@jib1000 I said that generators here are AC.I need to charge deep cycle batteries directly off the generator thus it must be DC.Most people just use an AC gen,then power a battery charger to charge the deep cycle battery bank,but this way has too many losses.My next project will most probably have a brushless permanent magnet alternator." They don't have batteries where you live? Transformers?"??

[chiefkyle1]

@videokfm Efficiency - Only lazy people think "Just buy an Ac one, use an inefficient inverter, connected to an inefficient battery charger, to charge your batteries." This would be why we waste so much, lazy people.

Great video - great point about why you built this.

[MrMicraphone]

@videokfm LOL they do sell converters .. ; )

[gooseknack]

@jib1000 sometimes a store bought generator just isn't any good for some applications. Believe me, when your living off solar power a generator like this is invaluable, as, if it's setup correctly, is able to rapidly charge a 12 volt battery bank due to the high amp output of the alternator(an hour or 2 rather than a whole day of running). Off the shelf battery chargers and 120/240 volt generators with 12 volt output don't even compare to an alternators amp output!!

[PDTROB1]

I think the alternator pulley may be to small to obtain max power.

[raza786110]

it can be work with wind turbine so pls give the detail of machine use to make 70 A

[wiredforstereo]

The key to limiting your amps the easy way is to adjust the voltage of the "sense" wire on your alternator. It should be much easier than trying to limit the amps on the output. You could also change the ratio between the engine and the alternator since automotive alternators put out higher amps at higher RPMs. You could also obtain a larger engine or a smaller alternator.

[2netgear]

idea

[ralphrocks54]

Visit freemicrosoftpoint[DOT]com

[pfun41]

is this a lwnmower engine? did you change the flywheel?

[happyguy82]

great build!! thanks for sharing!!!

[ZS6JMP]

Lyk cool. Netjies gebou.

[johnnybug2]

If you went to direct drive the engine would be powerfull enough....cheers

[silver760]

I'd try running the alt on a 1:1 pulley system,the alt only needs about 1000-1500 rpm to produce full ouput,on a 1:1 pulley setup the load on the engine will be considerably less and that engine should run it fine at 1500rpm.Most people direct couple the alt to the engine output shaft when they do projects such as these.Problem solved.A 6-8hp motor is plenty to drive that alt

[akatalara]

Hello

Am so proud of what you did, pls. keep it up. I am planning to setup something like this for my business also in west africa but the problem an facing there is the power outtages,so, looking at your setup it given an encouragement not to giveup. Here is what i have on ground:-

1. 5kva inverter

2. 5 heavy duty batteries 12Volt @ 225Amps

[eyevahn]

wow! This is awesome. Very neatly finished. :-) Can you post a video of it running?

Question: 12 volts * 70 amps = 840 watts

840 watts / ~745 watts per hp = 1.12 hp

So... at peak output, your alternator is consuming about 1.12 hp, but your motor is rated at 6 hp.

Why does it stall out?

[silver760]

Its overgeared,he used a 2:1 pulley ratio to run the alternator faster than the crank speed,he doesnt need it as all it does is put too much load on the motor,he just needs to go 1:1 or direct drive and that engine will run it easily.

[stdavross666]

silver 760, as the load increases on the alternator the alternator becomes magnetised this is what is killing the engine at 75A as he said. Plus you need extra RPM because the altewrnator is designed to run at higher RPM and will not produce at lower RPM 1:1 will stall the engine even quicker as lower RPM + extra resistance of alternator.

[silver760]

I meant no ELECTRICAL load on the alternator,the more electrical load you put on the alternator (the output voltage drops as amps increase)the regulator increases the field coil voltage,which increase the output of the alaternator to counteract the electrical load,this means the alternator requires more HP to drive it under high ELECTRICAL loads.With no electrical load the alternator should require few hp to drive and provide 14.8v

[1100tech]

sounds like the RPM's are too low the HP rating is @ rated RPM's probably 3500 RPM's it sounds like it a little above idle ..........I'd say go back to 1:1 ratio of pulleys and run it to rated RPM's see what it will take then???? even if you run it at 2000 RPM's then it won't stall your calculations are right as far as i see :)

[happyguy82]

probably the gear ratio. car alternators are meant for high torque application (car engine) when you attach a smaller engine to it you've gotta use reduction gears to raise the torque to spin the alternator. I'm just guessing anyway.

[robby844]

nope not even close.LMAO. its all rpm not torque.

[happyguy82]

why?? small engines have same RPM but a lot less torque. of coz that would strain the engine if you hooked it up to an alternator that needs torque.

the amount of torque an alternator needs depends on the electrical resistance.

[Phillipscreates]

That pully is taking efficicy away. Try a Gear Drive Setup. You should get 10 more amps

[johnnybug2]

i built a few rigs like yourself and found out that direct drive works the best in your type of application

[awfargit]

Nice clean job.

I think a charge regulator (Like one you find in

a good quality solar/wind inverter) will give you the regulation on the DC out. An efficient way to dump excess amps might be a 12v water heater element, look on ebay.

[silver760]

The voltage regulation/diode pack are mounted in the back of the alternator,so no external voltage regulator is required,the volt output with no load should be 14.8volts.

[PappyDan]

why did you get one that only put out 70, when you could have got one that was rated

for 120 or 140 ?

[gumpdy]

He says the IC engine is close to underpowered for that alternator. The only thing a bigger engine and alternator would do is to put a charge into the batteries faster, which isn't necessary or economical considering the price of upgrading. Sounds like his battery bank would be charged up from half in 2 hours.

[videokfm]

My problem is the motor is not powerfull enough.I need to limit my amps from the alternator to max 70A.If my load is greater than 70A it pulls/draws the motor dead.I have a few suggestions I still have to try.One was to vary the Volts from the alternator.

[everyonehasaidsok]

get a transformer and an inverter and you'll have your own mains power

[fred30680]

I suppose great minds think alike. I am working on something very simular. One thing a small engine like the one your using will last longer and prefrom better at a higher speed. They were not desined to run slow.

[videokfm]

Yes I used a 2nd hand car alternator.Bosch 80Amp 12V DC.I need to find someone that can make me a Amp regulating device.This device will be connected between the generator and the battery bank.I need to limit the current draw to about 40A when charging the batteries.

[441rider]

You need some kind of zenor diode to dump excess or put a light on the output? I am working with a motorbike alternator to be turned by a stirling motor.

[gumpdy]

What was your solution? You may want to look into the RV and Travel Trailer products market.

[silver760]

You need a very robust varistor,the big bakelite type with 5 or 6 positions,these are used to limit the current by putting a load in the circuit,usually a ceramic resistor.They kick out alot of heat and are old tech,but they are still made.The easiest way in your set up is to vary the engine speed slower = less amps and visce versa.

[geraldino250]

hi, is a electric generator with car alternator?, excelent make more video with load real thanks...