Building your own generator

[jimmyhorns]

Pictures.....

Coming a little later.... unfortunately working to pay the bills is getting in the way this week....

[RafeyRJX]

Ho hum. I have done this several times in the past as I have lived on boats for a number of years. So, speaking with extreme experience and a squint eyed wisdom, be careful. It's easier to allow the ambition to exceed achievability. That little, but heavy old engine will just about spin a 35amp car alternator at 12volts. From there charge a 12volt deep cycle battery (leisure battery) you will need about a 3:1 pulley ratio to get the alternator spinning nicely and also so your not killing the engine at high revs. Yes before anyone mentions it, an alternator will charge at low revs but it won't put outax current. Use an alternator with a built on reg and you won't have any probs. you will need a charge warning light connected or it won't charge. Anyway, loads of help and advice on offer if you need. Rafeydimmock@hotmail.co.uk

[NoFixedAbode]

Re: Building your own generator

I built one a couple of years ago with a 24v alt and two batteries. The only way I got it to work was to ramp the engine to max before engage the circuit else it would stall out. I never did get it to run

I hope you have more success with venture.

[jimmyhorns]

I built one a couple of years ago with a 24v alt and two batteries. The only way I got it to work was to ramp the engine to max before engage the circuit else it would stall out. I never did get it to run

I hope you have more success with venture.

I have had it running with a single alternator, and you are right when you connect up the charge light lead the engine takes quite a hit... I think the way to do it is to 'preload' the engine and to get the carb mixture right. I did have it running nicely like that with a single alternator, so im hoping it will take two.... Unfortunately that alternator was destroyed by operator error....

[jimmyhorns]

Well thanks to discoferret lending me a tap, I now have the old pulley off and machined to have the new pulley bolt on.... Was proving a nightmare to get a multi-V pulley which would mate to the lawnmower crankshaft....

Next step is to build a sub frame to take the two alternators, and tensioner, and then fire it up to see how its looking....

[bpgoa]

Building your own generator

Thanks for sharing.

[cjcj1949]

It sounds as though you are going to have to fiddle with the load and throttle to avoid stalling and high rev problems. Batteries are a variable load depending on how charged they are. A crude way of handling flat batteries would be some resistive loads that can be used to limit the charge current, headlamp bulbs could be useful, as could a heavy flywheel. Perhaps the alternator output can be controlled, I've never played with them, apart from changing them.

[jimmyhorns]

It sounds as though you are going to have to fiddle with the load and throttle to avoid stalling and high rev problems. Batteries are a variable load depending on how charged they are. A crude way of handling flat batteries would be some resistive loads that can be used to limit the charge current, headlamp bulbs could be useful, as could a heavy flywheel. Perhaps the alternator output can be controlled, I've never played with them, apart from changing them.

Well the alternator will output a constant regulated voltage (14V), and the current will depend on whats connected. If its just the batteries, then that wont be a massive current draw.

the engine has a built in govenor, but these are not particularly sensitive, and are used to limit maximum rpm to prevent con rod destruction.

im going to do away with the in built governor as it would end up fighting with a throttle servo. Instead im going to sense RPM and control the throttle via an arduino that will hopefully by controlling all the processes involved..... after all part of the brief is that it needs to be very user friendly and as plug and play as possible....

If possible im going for this possible flow:

Open side (to vent and access control panel).

Turn switch on

Pull starter (as many times as needed to start)

Wait for charging light to come on

Start charging.

turn switch off when done.


That way everyone should be able to use it

[cjcj1949]

I was thinking a flat battery would be a massive load. Which Arduino do you have and which shields?

[jimmyhorns]

proper flat batteries take almost no current, a pretty flat battery will still not accept more than 5 to 10A with 14V across it....

[jimmyhorns]

So here is the old aluminium pulley drilled and tapped:

photo(45).JPG
image(1).jpg

[RafeyRJX]

Too much science being applied to a simple solution and task. Why two alternators? You can draw 200 amps from a fully charged battery for a short time. Leave the machine running at a reasonable speed and load, re charge said battery and go again. If you want the alternator to put put full power simply add a switch that shorts the shorts the charge light to the alternator body. But I don't know why you would want to. If you need more capacity to charge lipos just add another battery not an alternator, they are acting as a power resevoir. Draw from them and re charge at a modest rate. Just to qualify, I am an electro mechanical engineer.

[xygax]

The appliance of science is what we do best.... if we didn't we would all be flying gliders and whittleing balsa...heli pilots are guaranteed to over complicate everything....

[jimmyhorns]

Too much science being applied to a simple solution and task. Why two alternators?

Well for a start, we want 24V or more, as the PL8's and 6's are most efficient at this voltage and will also allow a faster charge. We could use a 24V alternator, with a 24V battery, but they dont come cheap, and if it doesnt have the guts to do two alternators, then I can cut back to one.

I already have the alternators, and the batteries.

I dont get the comment about charging from the batteries... you dont get to choose where the electrons come from. They will come from the source with the highest potential, which in this case will always be the alternator unless its field has broken down.

[RafeyRJX]

Damn, just re read that and it sounds snotty. Sorry it's not meant to. I design power supply and generator systems for a living. The aim would be to charge supply batteries that you can then draw high currents from for short periods whilst using fast chargers etc for flight packs. Adding a second alternator is adding mechanical load but spreading output. Your better off using medium mechanical load over a longer period and drawing all the power you want from the resevoir batteries. You will get better engine life and fuel consumption from your little engine. Honestly, a single alternator and 12v leisure or car batteries in parallel is the way to go.