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Alternator voltage fluctuation

anwat

anwat

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Had a drive belt misalignment issue which morphed into an attempt to clean up the 13 different ring terminals attached to the positive side of my battery terminal. In doing so, I added a junction block and fuse block, and tried to design the system like MAD electrical outlines. Everything works, but now my volt gauge is showing one of two voltages: either 14.5, or just under 12. I've got a CS144 alternator with the "s" wire hooked to the junction block. I've run pretty much everything off that junction block. I only have a 10 ga 8 ft. wire to charge the battery, and only the starter and ECM are connected directly to the batteries. (Batteries are Odyssey Extreme AGMs both about 6 mo old). I thought everything was good, but now I'm not sure. Seems this system should be running at more than 12 volts most of the time. Batteries started at 12.3v, now both are 12.1. The engine fans are really about the only large draw item I have, so I think I'm slowly running the batteries down, doesn't seem they are being charged.

Here's the issue: When I start up, the gauge will read about 14.5v, and the multimeter will show about 14.3v.After about 30 seconds, the output will drop to 12v. It will stay there, but does have random spikes into the 14.5 range, lasting a few seconds, then dropping back to 12. This is not occuring in conjunction with accessories being turned on or off. When the two 225 watt fans turn on, the voltage dips momentarily, then returns to 12 with occasional spikes up to 14-14.5v.

Here's the part I really can't figure out: So, trying to see if I mixed up something, this morning i went out and took the "S" wire off the junction block, and ran it back to the output stud, so the alt is sensing it's own output votage. Dash and multimeter now read an output of 14.3v, nice and steady, no fluctuations. Accessories on, no fluctuations.

Is this normal for this setup??? It seems the voltmeter should be reading higher than 12 v when attached to the distribution block, especially since the batteries aren't fully charged. And it seems it should definitely be running higher at the junction block where all the draw is. I'll attach a sketch of he way it's hooked up in case it would help to see what I've attempted to do.

electrical.jpg
 
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In a perfect world all wires/fuses/connections have zero resistance. Theory and practice sometimes don’t behave nicely together. I can see a condition where the fusible links have a resistance building in them. They are designed to break when they heat up and melt the wire inside. This heat they generate acts like a resistor, the more heat (current) the more resistance. So the spikes you see could be when they cool down and the resistance lowers. This is strictly a far fetched hypothesis.

Best thing to do is look for a voltage drop somewhere using the same ground reference for all your readings and probing all your connections. Even check all your ground connections.

I’ll study your diagram again later tonight to see if there’s anything else that catches my eye.
 
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Where's the resistor?

AFAIK GM ran all those alternators with resistance on one of the wires (the charge bulb) which has something to do with telling the alternator to charge.

The adapter harnesses to go from the 10/12 series to CS has a resistor built in. Doesn't seem like everyone that DOESN'T use a resistor has a problem, but perhaps that is what is going on here?
 
Older square bodies used a shunt if it had an ammeter instead of a #194 bulb for the "ALT" dash indicator for the resistance needed in the #1 wire on the plug..
I'm not familiar with the newer trucks setup though..my experience ends when ECMs began..
 
I was thinking that the resistor on the L wire may have been the problem. However, I kind of went away from that theory when I connected the S wire back to the alternator and it went back to a steady 14 volts. I traced the L wire as far as I can without ripping out the dash, which I'm trying to avoid. There may be a resistor in the adapter plug, but there isn't anything inline from what I can tell.

This has been pretty much rewired from scratch by the P.O.. It's set up very simply, and from what I can tell was correct with the exception of the sense circuit looped back to the output. Which isn't necessarily wrong, from what I understand, it just doesn't allow the alternator to function as efficiently as it can. I added the junction block and then rewired some of the components that were connected to the battery to the junction block as well as running the S wire to the block.

Is it possible that the alternator is putting out 12v because there isn't enough electrical draw to cause it to put out any more? Seems that even one fan coming on would cause it to increase output since the fan is connected directly to the junction block for power.

All that said, I guess it wouldn't be too hard to add a resistor in the L wire and see what happens. I'll just have to figure out where I can get a resistor on Sunday now that Radio Shack is gone...

As far as the heat in the fusible link wire hypothesis, it's possible, but the fact that it starts right away as soon as I start up the truck makes me doubt it. Plus, the cycling between 12 and 14 doesn't seem to be long enough to allow the wire to cool sufficiently. It also seems that that would cause the frequency to increase as the truck ran, and the wire never cooled down all the way between fluctuations, and it doesn't happen that way, it seems to be completely random in fluctuation. I'm going to try turning on all the lights and fans and see if I can figure out if this is related to draw or not this morning. I had picked a wire that wasn't hot with the ignition on to turn on the solenoid to the added fuse block, so now that I have that fixed, I can turn on all that stuff and try to pull the draw up a little more.
 
A #194 bulb would provide the right amount of resistance if you cant find a resistor..

Like I said any newer trucks I haven't messed with much,but doesn't the ECM also regulate the alternator field to control the amount of amps & volts it puts out on computerized trucks ?...on the older trucks the idiot lamp or ammeter shunt provided the resistance,but newer ones with computers may be wired a lot differently..

The alternator needs a voltage reference that is less than its output at the "sensing" wire in order for the regulator to kick in on the older trucks..looping the #1 wire to the #2 wire "works" but it may result in the alternator putting out maximum all the time..

I have had issues with "half fried" fusible links on several square bodies in the past..they can cause all sorts of weird issues and intermittently..
 
That actually helps a ton. I take it that reference voltage is going to be the "L" wire in the connector? Or are you saying the S wire has to be less that the alternator output? I think it's got to have something to do with moving that S wire, because when I move it back, it works like it did before, no fluctuation. It seems to be doing what it's supposed to and changing the output, but shouldn't it always be above 12? I thought these systems were supposed to run at around 13.2v?

I'm sure I have a bulb and socket somewhere, I'll put that in and see what happens....I know I saw a diagram on here somewhere of how to wire it in when I was trying to figure this out....

This is wired like an older truck...The ECM I'm referencing is the FiTech unit, which has nothing to do with anything except the fuel system, so you can disregard any input from that angle. My other Blazer is a 90, and even that didn't have any input from the ECM as far as alternator regulation, but I"m sure it's there in the obd2 systems.

I went through and checked all the fusible links...they are all solid, conduct well under movement, and the solder joints are sound. I replaced all of them when I rewired, so they're new. I also ran it for a while, and they aren't hot to the touch.. Still won't rule that out, though, I've had similar odd issues with them, but for now they look good.
 
My info is on the older 10SI alternators that only had the 2 wire plug and the stud on the rear for wiring..

I know squat about the later alternator wiring that have multiple terminals (3 or 4 I think)..but I'm sure google has the pin out on them,and it is probably similar to the older units,one terminal needs a constant hot feed and another needs a switched 12V source with a resistance..

GM or an aftermarket source had a conversion plug available I think,to adapt a later alternator to an older truck,I remember seeing posts here about them..if I remember right they had a resistor or diode built into the plug..
I looked them up!-- check out # W1201 and # W1204,if you had a 10SI originally and put a CS144 in its place ,these two adapters allow it to be a plug in swap...note the one for vehicles with no idiot light HAS a resistor,and the one with an idiot light does not...(the bulb itself provides the resistance)..Wiring Harness Accessories for CS144 Alternators
 
I think the first thing I need to do is check the plug I have on there and see if there's resistance there. I know it adapts the four prongs on the CS 144 to just two wires, the larger red sense wire and the brown L wire.

The sense wire would have a constant hot, since it's attached to the junction block, which is attached to the battery. So all I need to do is make sure there's some resistance on that brown wire, and then it would seem to be wired correctly.

Assuming a fully charged battery and no draw whatsoever, what should my alternator be putting out in terms of volts?
 
Yes, two in parallel, no isolator or anything else.

Both purchased at the same time and have about the same use to them (they've been in the truck since I bought them).

I've got the 10 ga. charging wire from the junction block going to one of the batteries, and a 0 ga cable between the two batteries. The only things connected directly to the battery are the FiTech and the starter. 2 ga between the alternator and the junction block.
 
anwat said:
Yes, two in parallel, no isolator or anything else.

Both purchased at the same time and have about the same use to them (they've been in the truck since I bought them).

I've got the 10 ga. charging wire from the junction block going to one of the batteries, and a 0 ga cable between the two batteries. The only things connected directly to the battery are the FiTech and the starter. 2 ga between the alternator and the junction block.
Click to expand...

would be good way to check if it’s related to battery differences by disconnecting one battery and seeing if it changes.
 
Most vehicles I've checked the charging voltage on,reads between 14 and 14.5V if everything is up to snuff..

Higher than that will tend to boil the batteries ,lower they might not get a good charge..you need a 2V increase over system voltage to charge a battery ..
 
Update: So, I was checking the brown wire for resistance with the ignition on, and i dropped the plug and somehow it landed on the alternator in such a way that the metal pin inside was able to short to the body of the alternator. Just a quick spark as it hit and fell off.
So, I plug it back in, start it up and the voltage is at 14.7v. I turn everything on, both fans all the lights, radio, compressor, all of it, and it inches up to just about 15v. I measure it at the junction block, 15v. I measure it at the batteries, 14.3v. Turn all the accessories off, junction is at 14.5, batteries at 13.7. Did it a couple of times, and the same results. So it looks like I either shorted my way to fixing it, or maybe the plug wasn't pushed all the way in, but whatever the case, it appears to be working as designed now. I'm sure tomorrow it will be at 12 again, but for now, I'm happy jack and I'm going to consider it fixed. Whatever it was. Thanks for the input and help...we can start up here next time it acts up...or maybe I'll just go buy a AD244 and be done with it. Right after I win the lottery.
 
My CS130 runs at 14.4 no matter what the load is. No idea what happened, it wasn't always like that, but while it might be hard on the battery, I'm not messing with it lol.
 
I'm thinking I may have fried the regulator when it shorted. Like you, I've got bigger things to worry about, I'll just keep an eye on the batteries and maybe go to a smaller gauge charging wire and add some length to it.
 
Here's some information I gathered when I was putting CS alternators in my rig:

  • Alternator will have either an “F” terminal or an “I” terminal, but not both.
  • If the alternator has an “F” terminal (i.e. no "I" terminal):
    • It must be excited by the L terminal.
    • When exciting via the L terminal, there must be some resistance in the circuit (bulb and/or resistor) or a short circuit will be created.
    • If no alternator warning lamp is desired, a 50 Ohm resistor is used.
    • If an alternator warning lamp is used, a resistor should still be used, in parallel with the lamp. This is so that the bulb burning out does not prevent current flow and therefore alternator excitation. The resistor should be equivalent to a 3-4 watt bulb. Using Ohms law, we can use the Electrical Wheel of Doom from Part 1 to calculate the required value of the resistor as R = V^2 / Watts. In this case R = (14v*14v) / 4W = 49 Ohms. So a 50 Ohm resistor will do.
  • If the alternator has an “I” terminal:
    • You can use this I terminal to excite the alternator, whether or not you are using an alternator warning lamp (i.e. whether or not anything is connected to terminal L).
    • Terminal “I” has a built-in internal resistor to prevent a short circuit when connected to the excitor wire. Therefore, you can connect the ignition switch to terminal “I” using an excitor wire with or without a resistor in series.
    • If you do not have or do not wish to install an alternator warning lamp, you can excite the alternator by connecting the ignition switch to terminal “I” using an excitor wire with or without a resistor in series.
    • If you do have an alternator warning lamp connected to terminal “L”, you can still connect the the ignition switch to terminal “I” using an excitor wire with or without a resistor in series as a backup method of exciting the alternator. This is good practice as this type of redundancy enhances reliability.
Wiring PLFS-type

Mandatory connections:

1) Connect the alternator output terminal (B or Bat) to the electrical system's main distribution point (bus bar, junction, etc.) Less optimal alternatives that will work include connecting it to the battery + terminal or a terminal on the starter motor that also connects to the battery + terminal.

2) Connect the L terminal to a source of switched ignition power through an indicator lamp wired in series. Also connect a 50 Ohm resistor in parallel with the indicator lamp so that if the bulb burns out, the alternator will still be excited. It generally should be between 35 and 350 ohm resistance (typically the light itself). If below 35 ohm, the CS units will fail.

3) Ensure there is a good ground connection between the bare alternator case, the mounting bracketry and the engine block/heads and/or install a dedicated ground wire from the engine block to the alternator's ground terminal (if it has one).

Crucial connections:

4) Strictly speaking, the alternator will work with only the three wiring connections listed above, but I consider it crucial for good performance that you also wire up the remote voltage sensing terminal. To do this, connect the S terminal to the vehicle electrical system's main power distribution point (bus bar, main switch, fuse panel, etc.). If the S remote voltage sensing terminal is not connected, the voltage regulator will revert to internal sensing of the alternator output terminal voltage - with all the limitations that brings. You will see some alternators wired with a short jumper wire from the S terminal directly to the battery connection at the back of the alternators, but this is neither the proper method for remote voltage sensing nor necessary for internal sensing - do it properly or leave it out.

Optional connections:

5) If you have an external device such as a tachometer, hourmeter, or other device, it may be connected to terminal P. Connect the device in the manner specified by the manufacturer of the device.

This is a diagram of such a CS-series, PLFS alternator wired using terminals L, S, and BAT.


Wiring PLIS-type

Mandatory connections:

1) Connect the alternator output terminal (B or Bat) to the electrical system's main distribution point (bus bar, junction, etc.) Less optimal alternatives that will work include connecting it to the battery + terminal or a terminal on the starter motor that also connects to the battery + terminal.

2) Connect the L terminal to a source of switched ignition power through an indicator lamp wired in series. Also connect a 50 Ohm resistor in parallel with the indicator lamp so that if the bulb burns out, the alternator will still be excited.

3) Connect the I terminal to a source of switched ignition power through a 50 Ohm resistor wired in series.

3) Ensure there is a good ground connection between the bare alternator case, the mounting bracketry and the engine block/heads and/or install a dedicated ground wire from the engine block to the alternator's ground terminal (if it has one).

Crucial connections:

4) Strictly speaking, the alternator will work with only the three wiring connections listed above, but I consider it crucial for good performance that you also wire up the remote voltage sensing terminal. To do this, connect the S terminal to the vehicle electrical system's main power distribution point (bus bar, main switch, fuse panel, etc.). If the S remote voltage sensing terminal is not connected, the voltage regulator will revert to internal sensing of the alternator output terminal voltage - with all the limitations that brings. You will see some alternators wired with a short jumper wire from the S terminal directly to the battery connection at the back of the alternators, but this is neither the proper method for remote voltage sensing nor necessary for internal sensing - do it properly or leave it out.

Optional connections:

5) If you have an external device such as a tachometer, hourmeter, or other device, it may be connected to terminal P. Connect the device in the manner specified by the manufacturer of the device.

PLFS version.jpg

SFLP version.jpg

PLFIS table.png
 
Outstanding....that's the most complete outline I've ever seen, covers just about everything, all in one place so you're not having to keep referring to different pages. Thank you...that's going in my electrical folder here at home, I'm sure I will need that at least a few times more in my life.

I noticed a discrepancy, though, that maybe you can clear up. In the guide to wiring PLIS it says to wire the I to the ignition through a 50 ohm resistor. In the table at the bottom, it says the I can be wired with or without the resistor. I've got no resistor in my I circuit, and I have no resistor in my L circuit, which doesn't go to a lamp, it goes to a gauge. That may be the issue, right there.

If I'm understanding this, it's saying if you have the lamp with the resistor, you don't need the I wire, but it's a backup way to excite the alternator. If you don't have the lamp with the resistor, you must have the I wire hooked up to have the alternator start to work. Is that correct?

Thanks again for the info!
 
I think "yes"...the resistor is used with a bulb in case the bulb burned out and then the resistor takes the place of the bulb so the field excitation wont be lost..as explained in the "PLIS" list at #2...and in the chart at the bottom of the page ..
 
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