12v charging problem.. What am I missing?

Brad Gyde · Dec 4, 2012

Hey all.. Been a while since I've posted now, but tonight I seem to have found a problem I can't seem to figure out..

I finally got my long term project running this evening, but for some reason it don't want to charge properly..

I have a 3-wire 10si Delco alternator installed.. "Batt" post connected to Ammeter, "white" (small wire on plug) connected to the ignition switch with a light in the line (as I have done many times before) and the larger wire looped back and connected to the "batt" post..

I've done it this way a few times after reading it here long ago, and have had great success.. until tonight. When the key is turned on, the light will come on (as it should) but the alternator will not excite like it should. If I use a jumper and touch the excite terminal, it will kick in and charge like it should.

I can't figure out what I am missing.. I have it wired as I have done a few times.. Used the same light as I have always used.. I know it's hard to diagnose just by reading, but does anyone have a idea as to what I am overlooking? I looked, tried, and tried again to figure this out for a couple hours tonight, and I am stumped.

Thanks in advance

Brad

BCnT · Dec 4, 2012

have you tried kicking engine up to about 3/4 throttle? sometimes the pulley ratio runs the alternator too slow to excite.

gene bender · Dec 5, 2012

Like other post says maybe not enough rpms at idle to start it charging. I sold a C with an alt on it and it had the lite and didnt charge untill more rpms on the engine with throttle.

LJD · Dec 5, 2012

I assume the light is hooked to the #1 terminal? I also assume #1 is what you are calling the "excite terminal."

The colors of your wires don't help. When you are facing the alternator from the back - the two spade connectors on top are #1 (excite) to the left and #2 (sensing wire) on right.

If I read you correctly, you say your light goes on when hooked to #1 but no charge. You then jump 12 volts positive to #1 and it charges? If so, obviously you're not getting enough power through the light wire to excite.

Since it charges when you jump, RPM cannot be the issue. But do keep in mind that the 10SI or 12SI needs to spin 1600 RPM to charge. If the engine idles at 800 RPM, the pulley ratio must be at least 2 to 1.

Brad Gyde · Dec 5, 2012

Your assumptions are correct, and you read it correctly.. #1 is the terminal I am using to excite (I opted to leave that out last night). The light will come on and stay on, unless I jump the excite terminal to 12v positive, then it will charge (and when it charges, it will do so even at a idle)

So, I will go with not enough power to excite.. I Know (as of last night) I had about 12.3 volts at the batt terminal on the back of said alternator, but I never did check voltage of excite wire, but I will today.. But for the sake of assuming, what would you recommend if I do have low voltage? Could my bulb have too much/little resistance? I quickly tried to find a picture of the light I am using on the NAPA website, but without the part number handy that could take all day, but it is a small "sealed" light, about 1/2" in diameter.. I have seen similar used in semi trucks and the like for indicator lamps.

I would like to add that ALL wiring, gauges, battery, etc is new, and as I also said, I wired it just the same as I have many times before, using the same components as I always have, which is what has me stumped..

Thanks

Brad

showcrop · Dec 5, 2012

What has been keeping you busy Brad? If I recall correctly you do a lot of manure spreading, so you have probably just been through a very busy time.

oldtanker · Dec 5, 2012

Brad, have you bench tested the alt to make sure it's good? I work for a time as a mechanic. I've seen starters and alternators bad out of the box as new rebuilds.

Rick

JMOR · Dec 5, 2012

(quoted from post at 09:42:42 12/05/12) Your assumptions are correct, and you read it correctly.. #1 is the terminal I am using to excite (I opted to leave that out last night). The light will come on and stay on, unless I jump the excite terminal to 12v positive, then it will charge (and when it charges, it will do so even at a idle)

So, I will go with not enough power to excite.. I Know (as of last night) I had about 12.3 volts at the batt terminal on the back of said alternator, but I never did check voltage of excite wire, but I will today.. But for the sake of assuming, what would you recommend if I do have low voltage? Could my bulb have too much/little resistance? I quickly tried to find a picture of the light I am using on the NAPA website, but without the part number handy that could take all day, but it is a small "sealed" light, about 1/2" in diameter.. I have seen similar used in semi trucks and the like for indicator lamps.

I would like to add that ALL wiring, gauges, battery, etc is new, and as I also said, I wired it just the same as I have many times before, using the same components as I always have, which is what has me stumped..

Thanks

Brad

s LJD said, probably not enough excite current. Yes, it has worked in the past, but every alternator isn't absolutely identical & when it did work in the past, it was marginal (but works counts). Yes, hundreds have gotten by with those little bulbs in the past....most likely because the bulb's cold resistance is low enough to shock/jolt the alternator field, because those little marker/clearance/dash bulbs such as 194, 1895, 1815, 53, 57, only draw about 1/10 to 3/10 th of an amp AND the field begins to kick in at about 3/10 th amp (right on the edge/marginal). GM placed a 10 Ohm/6.25 Watt resistor in parallel with that little idiot light so as to provide nearly a full ampere of excite current.
You could parallel more little bulbs, use larger bulb, or do as GM did and parallel with a resistor, or just use a diode.

Royse · Dec 5, 2012

Sounds like not enough excite current to me as well.
Possibly just a bad connection to the light or alternator.

Brad Gyde · Dec 5, 2012

Well, the spreading has kept us very busy since the 2nd of July.. Wheat came off early here in Michigan (at least in my area) and we haven't had hardly enough rain to speak of, so we've been right after it.

On top of that, I've been busy working on this tractor in the shop A LOT (and I'm trying awfully hard to hold out on pictures until it's completed LOL).. But, I might have to drive it out of the shop this afternoon and snap a picture or 2..

Oh, and I've been trying to buy my own place, which we should be closing on in the next week to 10 days.. The novelty of renting from the parents has worn off LOL.. I can't say much more about the purchase until it's over.. It's been rough to get the deal done, and I'm gonna leave it at that until it's all over.. But I'll post some pictures (and some of the story) of my house when it's mine.

I guess all in all, I've been pretty busy.. But when I look at what I accomplished, it don't look like I did a whole lot.. LOL

Brad

Brad Gyde · Dec 5, 2012

So, to be in parallel, I would have to connect a 2nd wire to my power source (in this case, the ignition switch) and add the resistor/2nd light/diode, then tie the light and the 2nd wire together "downstream" of the original light? (hopefully that makes sense.. kinda confusing, I know..)

The "original" light has to stay.. I drilled a hole in the panel for it, and I don't want to stare at the hole..

Thanks,

Brad

John B. · Dec 5, 2012

The light should act as the resistor and it needs to be of the correct resistance for it to excite the alternator.

rabbit-1 · Dec 5, 2012

I use a little "peanut" bulb like most cars use in their side marker lights, and license plate lights. Sockets are available from NAPA.

John B. · Dec 5, 2012

If you have an amp meter you don't need a light also. The light acts as a resistor and excites the alternator. If it's not the right resistance bulb it will not excite the alternator. A bulb of too little resistance will excite the alternator but will allow the current back to your ignition switch and continue to feed the ignition system after your key is turned off and the engine will continue to run. What we use to do 30 years ago on equipment with amp meters when converting the charging systems from generators to alternators we just put a diode in the place of an idiot lite. This allowed current in to excite the alternator but no back feed to the ignition switch. It worked excellent. The diode can be put any where in that wire. We put them up under the dash where they couldn't be seen. I hope this all makes sense!

JMOR · Dec 5, 2012

(quoted from post at 10:26:28 12/05/12) So, to be in parallel, I would have to connect a 2nd wire to my power source (in this case, the ignition switch) and add the resistor/2nd light/diode, then tie the light and the 2nd wire together "downstream" of the original light? (hopefully that makes sense.. kinda confusing, I know..)

The "original" light has to stay.. I drilled a hole in the panel for it, and I don't want to stare at the hole..

Thanks,

Brad

es, to the bulb or resistor connection

12v charging problem.. What am I missing?

Brad Gyde

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