Synchronizing Car Alternators

[(unknown)]

Hello,

I would like to know if anyone on the list has hands on experience running two

or more car alternators in parallel.

This project will consist of two or three identical GM alternators and will be used

as a welding power supply.

Would it be better to hook up the AC output from both alternators and rectify

afterword ? How do you promote load sharing between the two alternators ?

I have plenty of experience with electronics over the past 20 years, just nothing

to do with alternators, and though I would ask a few people before jumping into a

bunch of complicated conclusions.

It's a little off topic, but this site has the correct type of people to work

on this problem !

Thanks,

Scott

[bob g]

syncing them on the ac side is going to be a difficult project requiring chain or cog belt drive to keep them locked together in my opinion.

how many amps are you after?

bob g

[nick1234]

personally i would do on the DC side after the bridge rectifier that way no back circuit and as long as voltage same current will add in dc like  using batteries  

nick

[dnix71]

Three 12v batteries in series is enough to weld with. A golf cart can be used as a portable welder. If you full field a car alternator you might get a voltage high enough to recharge a 36 v array. It's easier to full field with the old style floating reed switch regulators. Just pop the cover and jam a twig to force the relay to stay closed.

[spinningmagnets]

There are a dozen 4WD sites with info and pics telling how to make and install a voltage regulator bypass switch so the alternator armature recieves the full field voltage.

With the trans in neutral and the engine revved to 3K RPM's, the output can make welding repairs in remote locations. I have no idea how to synch two alternators, best of luck.

[sk windpirate]

type in www.alternator secrets Everything you ever wanted to know about automotive alternators, and more.

[bob g]

if you are going to gang a set of alternators, they will need to be controlled with either one reostat or one regulator, and

you should use fail safe diodes on the output of each alternator, one diode on each output

that way if one alternator shorts out a rectifier bridge you don't have the other two backfeeding and trying to cook the failed unit and in the process flaming the good ones out in the process.

you might want to start with some heavier alternators to start with, maybe that way you only need two?

maybe a pair of 160amp truck alternators? that would get you upwards of 240amps continous,

also you will likely benefit from a large inductor or as they are called in welders

"reactor" this will stabilize the arc and take some of the surge off the alternators when you strike an arc.

figure on at least 2hp for every kwatt output, maybe 3 would be better for this application, and make sure to get the rpm up on the alternators so the cooling fans can do an adequate job keeping thing cooled down.

if i were to do this project i would start with two 110-555 prestolite/leece neville alternators, they have a piggy back regulator that is easy to bypass (delco's do not, so don't use them), i would drive them with an 8 groove serp belt and pulleys, and i would turn the alternators upwards of their rated rpm limit of 8krpm so they cool well. i would use two 300amp 200piv diodes (stud mounted on good heat sinks) and field control reostat, a reactor from surplus center (they still have a few left, and i doubt they will be getting more) and drive the alternators with a 20hp engine minimum, using quality drive pulley's and oem truck alternator pulley's. also i would put two (2)amp meters on the alternator outputs to determine for sure they are pulling equal loading or near so.

should make one heck of a welder if done right

bob g

[hiker]

here you go....

http://www.google.com/search?hl=en&q=car%20alt%20welder&gbv=2&ie=UTF-8&sa=N&tab=
iw

[Flux]

As others have said to synchronise them you would need a positive drive such as a timing belt, chain or gears.

You will have to use them rectified to dc as the single phase output would be lousy so there is no need at all to synchronise. Without some electronic control on the field to give current limiting the control will not be good. To some extent the reactance limit current is controlled by the field current so a single field rheo feeding both fields in series from a 24v battery may be good enough. If you want better low current control then you may have to use a tapped low resistance.

You will need a good speed to get a decent voltage to strike the arc especially if you use low field current for low amps. You may have to use a combination of engine speed and field current to get better control.

The overall efficiency will be very low so it will take a big engine.I have a commercial device that seems to be a specially wound big vehicle alternator and that gives about 130A from a 6hp Honda engine, I would imagine you may need 10hp for a pair of car alternators. My commercial thing was usable but not nice in its original form, fortunately it came cheap. I fitted an electronic regulator with current feed back and now it is a useful tool. With voltage feedback on the thing as well it becomes a wonderful current limited constant voltage battery charger/jump starter.

Flux

[tanner0441]

Hi

Most of the engine driven welders I have used have been 400Hz AC with an optional DC unit (a big rectifyer or diode block, depending on age).  You will get tremendous voltage sagging as you strike the ark with a vehicle alternator, also to get a reasonable degree of penetration you realy need 45 to 90 V OC.

If you have a lot of welding to do I would look at buying a second hand welder, if it is only for the occasional job then I would look at hiring. If you just want to try it for fun then go for it and see what happens..

Brian

[(unknown)]

Hi Folks, Im brand spanking new and reading tons of your great site here.

 From what Ive been reading, an alternator welder is certainly a nice fun DIY. In part due to the 6 phase, high frequency output. Just a simple rectifying circuit still gives you a wiggle in your DC. This is a curious question to me using more than one alternator. Will that in effect increase the phases and frequency on DC output?

Thanks for the fun reading.

Cornbread

[bob g]

there is a lot to be said for looking for a used portable welder

they are out there and sometimes go very reasonably in my opinion

one i would recommend is a miller 1E,

it has not been in production for probably 30-35 years,

it is powered by a kohler castiron engine, produces 160amps AC welding at 100% duty

cycle at 3600rpm, and best thing is

it produces 3.5 kwatt of 120 vac power at 60 hz at 1800engine rpm!

so that means the welding current is 120hz, which it is and makes for easier and cleaner welds in my opinion.

the kohler engine is very simple to work on, and the block is hard as heck so it doesn't wear much at all.

i have redone several of these using only a new conrod, piston, rings and gksts

and it can be done in place without removing the engine.

you should be able to find a good runner for 400 bucks or so, and if it smokes and burns oil, but otherwise run's for less than 200bucks.

thats one example, there are others, i just like the 1E for its dual rpm operation

its hard to imagine building up a portable welder for less money than you should be able to find used if you look around.

bob g

[Flux]

The frequency is irrelevant as the thing has to be used dc. The car alternators are just not capable of being used single phase. Once rectified the dc is almost smooth and the 5% or so ripple has no effect. It doesn't make any difference whether it is 3 phase or 6 phase and unless you use a synchronous drive the thing will be changing from 3 phase ripple to 6phase with belt slip and you won't see any difference.

For ac welders the frequency does make a difference and high frequencies have some advantage if you don't mind a noisy arc. DC has many advantages especially with special alloys but has the problems associated with arc blow so you can't really win.

Flux

[(unknown)]

Thanks for all your input.

I think that it would be better to pick up a 130 to 180 amp

alternator than try to parallel two cheaper ones. The cost

of mounting, belts and pulleys would outweigh the cost of a

single large alternator.

I did find an IC that drives the field current (with external

transistor). It will regulate the voltage at the sense terminal

to within 1 percent. I can use a voltage divider to extend the

voltage range from the nominal 12 volt to the high 50 volt range,

and the IC will still regulate the voltage.

Best of all I think I can drive the terminal with the output

of a current amplifier for constant current control.

I'll post something when my 'economy' picks up.

I would like to ask has anyone used this kind of welder to

stick weld a large project, like the wedge on a log splitter ?

Thanks to all,

Scott

P.S.

My luck with batteries is poor at best. This would be fairly

cheep, but I would kill them in a year. I did think about

using my trucks built in alternator, but I need my truck

more than a new welder, so an externally driven alternator

would be best for me.

[bob g]

what IC are you thinking of using?

i am always interested in regulator IC's

bob g

[spinningmagnets]

Hi scotta, here's some links that may be useful.

From my "homemade welder" file (PS I haven't made one yet, best of luck)

http://www.qsl.net/ns8o/Induction_Generator.html

http://www.pirate4x4.com/tech/on-boardwelder/

http://classicbroncos.com/homemade-welder.shtml http://members.cox.net/cglabe1/Air/Air.html http://www.motherearthnews.com/library/1980_November_December/Build_a_20_Portable_DC_Arc_Welder

http://www.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm

http://theepicenter.com/tow102899.htmlv

[(unknown)]

Bob,

Its a freescale part:

http://www.freescale.com/files/analog/doc/data_sheet/MC33092A.pdf

Looks good, but I'm not sure if anyone stocks it.