What should high vs low idle voltage be?

[Raider L]

as written above, "...ten times since 1981 when I bought the truck the field coil was worn out..."
I meant to say, "...bought the truck (,) the field coil was worn out..."
I meant that I had rebuilt the alt. a bunch of times but had never replaced the field coil, it was original. I had just been replacing the rectifier bridge, diode trio, and regulator, even the brushes one time or two, or one or the other brush if one looked kinda chewed up.

I took my old alt. and bought a new coil for it and all new parts so I can have a spare alt. just in case. I did notice a difference in the coil shaft lengths though. The new coil didn't have that step on it that is right after the windings big finger looking things. That step measures 3/8ths of an inch out from those finger things. What I found it does is sets the distance the coil rides between the bearings and the housing halves. If that step isn't there the coil will move back and forth inside the housing halves after it's together. That step holds the coil away in the rear bearing so that it is held at the right position in the housings.

Actually it's not a step. It appears that it's somekind of serration section inside the windings area and the end of the serrations is sticking out 3/8ths of an inch that has a function of keeping the housings and the coil firmly between the bearings when the halves are brought together.

 

[SirRobyn0]

so new alt is on, well, new-to-square, and the voltage when running at high idle is Pretty darn consistent at 14.7 even with load applied, it just dips and goes back. at regular idle, it seemingly dips into low 12s and goes into 13s, but perhaps the idle is set too low? I guess I just dont know what the "proper" idle voltage is. This is checked with digital volt meter at the battery, the gauge reflects this about .5 to 1 volt lower than meter but it could be the needle being bent in the gauge lol.

If the idle voltage is good or nornal i wont worry too much

I did not read though all the posts but state of battery charge will affect voltage. 14.7 is fine at high idle. Possibly a little high but we are talking .2 volts high, nothing to worry about. mid- 13's even low 13's is fine at low idle. Possibly into the high 12's with all the electrics turned on, but not any lower. The main thing at low idle is you need to voltage to be high enough not to discharge the battery if for example you get stuck in traffic at night in the winter.

 

[AuroraGirl]

Too much generalization here.

There are a lot of factors that affect the output of the alternator, the biggest is the capacity of the alternator in the first place.

If you're comparing a 150Amp alternator to a 68Amp alternator, then idle output on the smaller one is going to take you to low voltage at idle.... but this is what the battery's there for.

The battery stabilizes the voltage and at an idle, and maybe at a long traffic light - and the lights are on, the brake lights are too, the blower motor is running either for the AC or the heater, the wipers are running, a stereo is on - [although a stereo isn't too much of a drag] ... you will more than likely see the headlights "flare" when you hit the throttle.

Then there's the temperature of the alternator and the battery 'cause those variables affect the output too.

I'd say again that if you are experiencing "flaring" of your headlights when you step on the gas after waiting for along traffic light, a long train at the crossing --- then the battery's maybe a little long in the tooth or just not up to the job too.

If you're not getting below 12.8 Volts output at idle and everything's warmed up and you aren't running a lot of accessories, then you're pretty much OK.

In the end it boils down to this: if you can start your engine, the battery and charging system are in a more-normal-than-not condition.

SOME flaring on older systems is a given, and shouldn't be something to worry about.

Idle speeds are kinda hard to state over the internet - 'cause you may have a manual transmission verses an automatic transmission - the stall of the convertor matters here too.

See? There's a lot of factors to consider --- but if you can reliably start the vehicle in the morning - or when it's hot - or after sitting a week - then I'd say you're in the ballpark of a balanced system.

you seem knowledgeable. do you know how to wire a ad237 and mount it? it shares the same case as 2000+ cs130 i think... maybe...

 

[77 K20]

In my '77 truck it came stock with the 10si alternator. At idle and in gear at night, with the headlights on, heater and fan on, and the wipers on in the rain was pretty much too much for the alternator.

Instead of buying some expensive aftermarket alternator I installed a 12si alternator and put a smaller pulley on in. That way the alternator spins faster at idle. This makes more current.

And my engine redlines at 5,000 so I'm not worried about ever over spinning it.

I forgot my calculations on pulley sizes... I *think* I remember the alternator spins 3 times faster than the crankshaft. So at idle in gear you might be 600 RPM. That means the alternator is spinning around 1,800 RPM. My original alternator was a 63A version so at that engine RPM the alternator is making around 21 amps. The 12si alternator I installed (94 amp version) with the same size pulley puts out 40 amps. I wanted a bit more, so bought a slightly undersized pulley. This pulley makes 50 amps or so at idle.

I did try the undersized pulley on the stock alternator. It worked better- but with my non-stock addons it still couldn't keep up.

You must be registered for see images attach

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Both images above the 10si is the one on the left.

 

[AuroraGirl]

In my '77 truck it came stock with the 10si alternator. At idle and in gear at night, with the headlights on, heater and fan on, and the wipers on in the rain was pretty much too much for the alternator.

Instead of buying some expensive aftermarket alternator I installed a 12si alternator and put a smaller pulley on in. That way the alternator spins faster at idle. This makes more current.

And my engine redlines at 5,000 so I'm not worried about ever over spinning it.

I forgot my calculations on pulley sizes... I *think* I remember the alternator spins 3 times faster than the crankshaft. So at idle in gear you might be 600 RPM. That means the alternator is spinning around 1,800 RPM. My original alternator was a 63A version so at that engine RPM the alternator is making around 21 amps. The 12si alternator I installed (94 amp version) with the same size pulley puts out 40 amps. I wanted a bit more, so bought a slightly undersized pulley. This pulley makes 50 amps or so at idle.

I did try the undersized pulley on the stock alternator. It worked better- but with my non-stock addons it still couldn't keep up.

You must be registered for see images attach

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Both images above the 10si is the one on the left.

I have about 12 10si, 2 cs130, and 1 ad237 alts. and i would like to rebuild the ad237 and put it on the square if i can figure out how because its a 130amp stock

 

[SirRobyn0]

In my '77 truck it came stock with the 10si alternator. At idle and in gear at night, with the headlights on, heater and fan on, and the wipers on in the rain was pretty much too much for the alternator.

Instead of buying some expensive aftermarket alternator I installed a 12si alternator and put a smaller pulley on in. That way the alternator spins faster at idle. This makes more current.

And my engine redlines at 5,000 so I'm not worried about ever over spinning it.

I forgot my calculations on pulley sizes... I *think* I remember the alternator spins 3 times faster than the crankshaft. So at idle in gear you might be 600 RPM. That means the alternator is spinning around 1,800 RPM. My original alternator was a 63A version so at that engine RPM the alternator is making around 21 amps. The 12si alternator I installed (94 amp version) with the same size pulley puts out 40 amps. I wanted a bit more, so bought a slightly undersized pulley. This pulley makes 50 amps or so at idle.

I did try the undersized pulley on the stock alternator. It worked better- but with my non-stock addons it still couldn't keep up.

You must be registered for see images attach

You must be registered for see images attach

Both images above the 10si is the one on the left.

Just a side note since you mentioned it. some of you may already know this but a lot of modern cars have a clutch of sorts on the alternator. That way they can run a small pulley on it so it'll spin faster at idle, and when it reaches a certain pully RPM it can slip some to keep from over spinning the alternator.

 

[AuroraGirl]

Just a side note since you mentioned it. some of you may already know this but a lot of modern cars have a clutch of sorts on the alternator. That way they can run a small pulley on it so it'll spin faster at idle, and when it reaches a certain pully RPM it can slip some to keep from over spinning the alternator.

all alternators have that i think for slowdown of engine RPM if i recall correctly.. but maybe the added functionality for undersized pulleys later on? just a theory.

but that would likely necesitate a serp swap, which is probably being used in such a scenario

 

[SirRobyn0]

all alternators have that i think for slowdown of engine RPM if i recall correctly.. but maybe the added functionality for undersized pulleys later on? just a theory.

but that would likely necesitate a serp swap, which is probably being used in such a scenario

Basically you have that right but older alternators like on our squares are direct drive off the belt and have no way of reducing alternator speed at high RPM.

Going to an alternator with a slip clutch would require a serp belt swap, and given the relatively low RPM ranges our engines operate you'd gain very little in my opinion.