Tractor PTO Powered Battery Charger

Thank you for your help, Tobugrynbak. I think I will remove one v belt if I only have two batteries to charge. The PTO turns at 540rpm at 1500rpm tractor engine, so I would have to step it up at least 5 times, which is not a problem at there is plenty of power delivery from the PTO.

I certainly will build a cage around everything to prevent those wandering fingers.

What amperage alternator should I go for. Most of my batteries are more than 130Ah capacity.

What do you think about one very high amp alternator to charge the 4 batteries connected in parallel?

If you have access to a scrapyard and there are some VW diesels there, some of them used a 120 amp alternator, it looks like any other, but you need to read the plate. The regulator is built in.

But probably anything over 60amps will work just fine in such a system.

Do take the warning about the gas, it is highly dangerous, a ventilator on the shaft to blow any gases away from the motor, or long charging leads......

Don't let your batteries get fully discharged, some battery types will get damaged if held below 12.6 volts for long, sulfation happens.

Leisure batteries handle it better than car batteries.....

GA, you covered the subject well.

What is a "dash globe"? Some sort of 12 volt filament bulb?

I would look for a higher-amp alternator capable of handling the number of batteries.

How big, Tornado? (welcome)

There's probably a good reason not to use one of these, but I figured I'd throw it out there. I know it won't do it in a 1/2 hour.

http://www.northerntool.com/shop/tools/product_200328565_200328565

I am assuming that you are building this from "scrap" that you have available from wrecking yards or dumps.

I would be looking for bosch 12v 55A to 85A alternators with internal regulators

you'll find those on 140/160,240/260,340,440,740/760 series Volvos some Mercedes Benzes early BMW's

If you are buying new parts then Ingram's do a range of universal mount alternators up to 160Amp

http://www.ashdowningram.com.au/CA2571B7001604B3/Lookup/NovTechpoint/$file/July%2007%20Techpoint.pdf

You would have an agent in SA for them

Is it not more simple to use a 1-3 ph motor as a generator, or a generator if you can get one and make 110/220 v and use simple tranceformer to step it down to the 12 v. I like what Tobugrynbak did say. Then you only have to connect one unit to the shaft, and everything is much more simple. And you can use the power for much more than just charging a batteries.

Just a thought

a generator will give you AC. we are talking about 12v DC for charging 12v batteries.

I know that, you only have to use a Bridge rectifier to convert AC to DC.And the charger convert the AC to DC.
http://www.kpsec.freeuk.com/powersup.htm#rectifier
http://www.google.is/search?q=Bridge+rectifier&hl=is&sa=G&biw=1280&bih=899&prmd=ivns&tbm=isch&tbo=u&source=univ&ei=iXvqTZucDpGBhQfW1Nm6Bg&ved=0CDQQsAQ
http://en.wikipedia.org/wiki/Diode_bridge

Mains AC requires a fixed frequency, either 50 or 60 Hz depending upon your country.

This requires that the alternator (for AC, a generator is really for DC only, but many mix them up!) is turned very accurately at a set speed, otherwise the frequency will be very inaccurate..... I would guess that getting that setup would be quite complicated as well as being possibly dangerous.

The nominal 12 volt idea of the OP does not waste power through transformers, nor is it complicated to achieve......and if anyone wants mains voltage, there are electronic 12 volt to mains AC converters that could be bought for very little money nowadays....

Making AC from a motor is possible, but it sure is not easy......its far easier to make from a properly designed alternator.....

DC is far easier, but DC motors are generally low on efficiency as a DC generator.....

Alternators from cars (they make AC which is internally rectified to DC by the way) are cheap and freely available from scrap yards for very little money..........

I beleive the OP is trying to utilise what he has readily available to him to achieve a desired result . He is most likely in a "rural" situation hence the tractor.

So this "solution" seemes appropriate if not a little "Heath Robinson"..

Well put.

If my double pulley on the PTO was 590mm diam and the PTO turned at 540 rpm, what would the alternator spin at if I used the standard pully it has fitted to it (approx. 80mm diam) Could someone help me with the math?

It would be a speedup of 7.375 times. This equates to 3,982 RPM at the alternator, a good usable value for Car type alternators.....

I believe this to be correct, though open to a correction if needed.....

Hmm, 580mm diameter = 1822mm circumference / 80mm = 251mm circumference

1822/251= 7.25:1

540rpm x 7.25 = 3915rpm

I think that's right, but I'm only a busted arse radio mechanic not a maths professor

So if you run the tractor at half speed (i.e. 270 PTO rpm) should give you close to 2000 Alternator RPM give or take.

But I may be wrong, though I'm likely to be close...