Alternator current/voltage control

[zmoz]

UPS man brought me a 100 amp GM alternator today...I think it's a 17si. I plan on hooking two of them up to a Briggs engine for battery charging and welding.

First of all, to control the current output from the alternator I need to control the current into the field of the alternator, correct? Will this let me vary the current from 0-100 amps, leaving the regulator to do it's job when the batteries get full?

What about controlling the voltage? Say I want to charge a 24v battery bank. Can I hook a rheostat up to the voltage sensing pin of the alternator, and basically trick it into putting out higher voltages?

[bob g]

if i am not mistaken the delco is an internally regulated alternator.

so gaining control over the field (rotor) will not be as easy as with an externally regulated type.

the sense pin is what is commonly conected to the idiot light, in that the light gets its power from the ignition switch when on, and the light grounds thru the pin to trigger the regulator into operation at idle, when the regulator is triggered on the pin goes positive and the light goes out.

hooking a reostat to this terminal will not accomplish what you are trying to do.

is this a new alternator? or a rebuilt? or a used one?

reason being, if it is new, perhaps you can return it for an alternator that is externally regulated, and easier to work with or?

if it is used and you don't have much into it, or can't return it then,

you can dismantle it and modify or bypass the regulator, and make it externally controlled with a reostat.

it may also be possible to install a bypass, in that you can get external control and also retain the voltage regulator for charge control.

tell us more about what you have and what you feel comfortable doing

bob g

[sh123469]

Here's a site that should answer some of your questions about regulation and voltage.

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

[zmoz]

Yes, this is an internally regulated alternator, although I'm 99% sure that controlling the current is relatively easy. This page shows controlling the current in the way I mentioned above:

http://www.webpal.org/webpal/b_recovery/3_alternate_energy/electricity/lawnmower/generator/thrpag.ht
ml

The main thing I'm wondering about is controlling the voltage. The voltage sensing terminal is what the alternator uses to see what voltage the battery is at, and decide whether or not it should stop charging.

[bob g]

i might also add a couple of points

if you are intent on useing the delco units:

you should be able to bypass the regulator interally and bring out the one or possibly two wires that deliver power to the rotor, and use an external regulator for charging and via a switch use the reostat for welding.

a purpose built regulator or marine charge controller would be the much preferred means of battery charging control as either example would allow for much higher and faster charge rates to your battery bank.

there are a couple of manufactures of charge controllers that can handle two alternator fields (rotors) that have multistep charging regimes, ie. bulk, absorption, float, and equalizing set points, along with temp sensors for the battery to allow for temp compensation. these controllers are specifically designed to charge deep cycle battery banks in the fastest and most economical manner, (lower engine run time).

the delco regulator does not have that capability, and while able to deliver 100 amps will taper back drastically very quickly, far before the batteries require. this means much longer run times. these regulators are basically designed for charging starting batteries which deliver short bursts at high amperage, and charge a bit differently than deep cycles.

do a search on marine charge controllers, those folks lead the pack on alternator controllers for deep cycle charging.

also why do you want two 100 amps? is it for charging capacity or welding?

100 amps can do quite a bit of welding if you keep the rod diameter small, like 3/32"

such as 6013 for out of position and 7018 for down hill and flat work.

and finally if you are not locked into the use of the delco units, then take a look at the prestolite/leece neville  units, of 140 amps.

these are externally piggyback regulated units, larger in diameter, heavier built units, that run about 150 bucks US new , without any core charge.

also they can be had sometimes for nothing from truck shops as there is no core charge, usually all they need is new brushes and a set of brgs to put them back into operation.

they will charge at 90 amps at engine idle of around 1300 rpm at the alternator, and jump up to full rated power at around 3000 rpm.

if you like i will see if i can find my link to these units and post it.

bob g

[bob g]

the sense terminal does not tell the regulator what voltage the battery is at, only is used to trigger the unit on after start up

what are you trying to control the voltage for, charging or welding?

the regulator controls the charge voltage, and the amps as a byproduct of this control, so as when the battery voltage climbs to nearer the full point the amperage is reduced.

bob g

[zmoz]

I'm using the Delco alternators because they are the cheapest and most plentiful alternators available. Parts and replacements can be found anywhere...and I only paid $12 for this whole alternator. I'm trying to keep this whole project cheap and simple. I'm almost positive bypassing the regulator is not necessary, of the dozens of web pages I've read about lawnmower powered generators/welders, the vast majority of them use internally regulated GM alternators. I'm sure some kind of external marine regulator would be nice, but it's definately not necessary. By the time I'm done finding external regulators and truck alternators I could just go out and buy a brand new welder/generator. The field terminal on this alternator is expecting 12v for full output. If I connect a rheostat to it and give it less than 12v, it should put out less current, right?

[zmoz]

Yes, the voltage sense terminal is for the regulator to determine how much to charge. If there's a .5v drop in the alternator cable, and the voltage regulator is trying to maintain 14.5v, then only 14v is going to get to the battery. The voltage sense terminal senses the voltage at a remote location, after the voltage drop. This allows the alternator to put out 15v, so by the time it gets to the battery it is 14.5v. If I was to put a resistor in this wire, the alternator could be putting out say, 28v, but only see 14.5v at the sense terminal. As I said above, I want to be able to control the voltage so that I can charge 24v systems.

See this page for more about the voltage sensing terminal:

http://www.madelectrical.com/electricaltech/remotevoltagesensing.shtml

[bob g]

ok your points are well taken.

if you connect a reostat to the regulator field terminal and set it for less than 12 volt the regulator see's battery voltage low, and will pick up the charge rate i believe,

i guess what i am elluding to is there is no connection to the rotor outside the case, on the delco alternator. The field terminal and the sense terminal go directly into the internal regulator, and the regulator feeds the rotor thru the brush holder mounting, the regulator and the brush holder are sandwiched together with mounting screws.

i have built 100's of the delco alts, along with all the others and i guess i have really never tried to intervene between the battery and the field terminal with a reostat.  it can't hurt it to try it, the worst that can happen is it won't do what you want, but it won't burn anything out.

i guess give it a whirl and let me know if it indeed does what you want it to do.

another one of those things that make you go .... hmmmmmmm

bob g

[hiker]

what size of engine are you planning on using?

i would think of at least 7hp--2 alts are a big load!

[zmoz]

It's a 7.5hp engine, which will be putting out more like 8hp because I'm increasing compression slightly and putting on a more free flowing muffler. Given the standard 500 watts/hp, it should be just fine with well over 200 amps.

[bob g]

ok i went back and reread your questions, i guess it is late and i glossed over the obvious

it would appear that you could install the reostat and trick the alternator into higher output, but...

it likely won't be stable in output as the resistance of the reostat will fluctuate with temp and cause a swing in the sense circuit.

how much this swing will be i don't know, and further  i am not sure how much swing in the sense resistance will effect the actual charge voltage.

it may work fairly well for your intended application, i guess it is going to have to be  one of those empirical studies.

if it doesn't work as you want it to let me know and i am sure we can walk you thru a bypass to enable full reostat control of the alternator

just trying to help.. so don't kick me too hard, i am old and tired...

bob g

[zmoz]

I think you're just trying to overthink this. I think I'll end up making a constant current driver for the field.  I guess we'll see what happens if UPS ever decides to bring the rest of my parts...

While we're talking about it, I have a 60 amp ammeter that I want to hook up to this thing. Obviously the gauge would be pegged at 100 amps, but do you think it would have a problem with that much amperage running through it?

Thanks for trying to help...

[MelTx]

  Hello  I am using a 70's ford external regulated 12v alt, for charging my battery bank.Only I dont use a regulator at all.Just let the alt have full batt voltage this keeps the field on full all the time.One alt is a hand full for a 5.5 briggs.You get 18 or 20 volts 35 to 40 amps this way.To get 24 volts dont you need a alt rated for that amount?... All conections must be kept really snug at this rate, wires and guages just melt if you dont.While we are on the subject,maybe some one can tell me what might happen if I used a battery as a buffer zone, for a alt welder that I want to build.Would there be a lot of magic smoke.Or woult it just be better to hook the welding leads to the pos & neg outputs from the alt?

[BT Humble]

If, like me, you're not keen on having to be near a noisy motor while welding, you might want to consider this option:

http://www.fieldlines.com/comments/2004/11/13/22543/001/13#13

I've been told a few times now that this setup is certain to explode at any moment, but I've been using it for 18 months now and I'm not dead yet. ;-)

BTH

[zmoz]

I'm making something sort of like that, although I won't use the battery for welding. It's going to have a deep cycle battery that I can use with my power inverter, and then use the engine to charge it up every so often. I might try to make some sort of automatic start for it, so that it charges the battery on it's own whenever it needs it. Should be pretty easy since it's an electric start engine.

[Tight Yorky]

Evening zmoz,

You may be interested in some tests I carried out on a 100 amp Ford alternator some time ago. This was an internally regulated unit similar to what you describe. This unit had a 12V +ve ignition supply and a 12V +ve battery connection. The negative earth connection was through the body of the alternator. The unit was completely stripped down to the components, re-assembled with test points, placed on a variable speed lathe and driven via the chuck. The power circuit from the coils was found to be fairly simple. The rotor winding cicuit was found to be more involved due to the regulator. The rotor winding resistance was around 2.5 ohms and consumed just under 5 amp when stationary. The rotor winding was supplied by two slip rings(+ and -) on the shaft. The brushes of the slip rings were connected to the internal regulator. This regulator was a three wire Siemens unit which had a connection dedicated to zero volts (body/earth). One connection dedicated to one slip ring(-). And the last connection shared with the other slip ring(+) and the 12V +ve ignition. From the testing I found the Siemens unit was a very simple charge controller. For want of a better description, the unit simply "throttled" the current between the connection to the (-) slip ring and the connection to zero volts. This "throttling" was based upon the voltage sensed at the 12V +ve connection. When the 12V +ve connection reached 14.2V the voltage across the rotor winding was reduced steadily until the 12V +ve connection reached 14.4V. At which point the voltage across the rotor winding was zero volts (current through rotor winding equals zero). When reversing the cycle, reducing the voltage, the opposite occured but at slightly lower voltages. I assume this was to prevent the charge control becoming unstable. It should be noted that although the voltage across the rotor winding could be held constant the current consumed did vary. This depends on the load placed on the power circuit. I put this down to the back EMF (similar to what occurs in a DC motor). This does mean that the regulator can be 'frigged' by providing a false reference voltage but it needs to be from a proper voltage source that can provide a large range of current. In addition this false reference voltage needs to be related to the power output circuit if some regulation is to occur. A resistor circuit would not suffice. The rotor winding can be powered independtly of the three wire regulator unit but this does become quite complex.

My conclusion at the time was that this type of regulator was simple, cheap but not suitable for my application.

A lot of info here.

Hope it is use.

Regards.

[BT Humble]

I might try to make some sort of automatic start for it, so that it charges the battery on it's own whenever it needs it. Should be pretty easy since it's an electric start engine.

zmoz, allow me to introduce you to Old F.  Old F, zmoz.  I think you both have a lot to talk about. ;-)

BTH