Alternator not charging at idle

[Kevin88RRC]

With the engine idling and the light is out, the alternator is producing > 12V.
Where and how are you specifically taking the voltage readings?

This is puzzling.
How much larger than OEM is the alternator pulley diameter?
It may be a smaller pulley will up the alternator RPM and solve your problem unless there is a discharge somewhere that is draining down the system.
Your battery should be under 14V, but above 13V.
With the negative battery terminal disconnected, attach a light between the negative battery post and the disconnected negative battery terminal at the end of the cable.
Does the light filament glow with all electrical devices switched off?

Alt readings are at the battery post on back of alt and ground strap to block.
Test light glows on initial contact but then immediately goes out.

Battery is your problem. Throw a charger on it. Just sitting there, a healthy battery should be at like, 12.4-12.8v. Assuming you don't have a slow drain. If you have a lead acid battery, check the wells, make sure you've got water in there.

Also some batteries don't start making a legit charge until 1200 rpm or so. So keep that in mind.

Do a cranking test. What is your voltage when cranking? If it drops to like, 4-5v, then yes your battery is crap.

Put the charger on the battery for a few hours & it went back up to 12.25.
Ran tests again with results slightly higher but still under 12v at idle. Alt reading is about .1v lower then battery.
Battery is a Napa Legend and seems sealed rather well.
Crank test dips 10v and catches quickly.
Will pull both battery & alt to have checked at Napa.

To make it even more interesting she runs rough between 2000-2500rpm.

 

[RDavisinVA]

How much larger than OEM is the alternator pulley diameter?

 

[Kevin88RRC]

How much larger than OEM is the alternator pulley diameter?

Original is 2 3/8"
New is 2 5/8"

The pulley should be irrelevant since the alternator is designed for this vehicle. I could put an original pulley on but I do not want to mess up returning it if that what it comes down too.

Battery tested fine but Napa's alt tester was down. Local shop on the way home did a makeshift test and thinks the diode is no good. Will find another place that can bench test it tomorrow.

 

[RDavisinVA]

Original is 2 3/8"
New is 2 5/8"

The pulley should be irrelevant since the alternator is designed for this vehicle. I could put an original pulley on but I do not want to mess up returning it if that what it comes down too.

Battery tested fine but Napa's alt tester was down. Local shop on the way home did a makeshift test and thinks the diode is no good. Will find another place that can bench test it tomorrow.

The 1/4" larger pulley could make a difference.
What engine is it mounted on again?
V8 was it?

 

[rocky]

The 1/4" larger pulley could make a difference.
What engine is it mounted on again?
V8 was it?

Hopefully the tensioner has enough movement to accommodate the change.

 

[RDavisinVA]

The change will not require a different belt.
The concern is the lower RPM caused by the larger 1/4" pulley, which could be an issue with alternator output at idle.

 

[Kevin88RRC]

The 1/4" larger pulley could make a difference.
What engine is it mounted on again?
V8 was it?

3.5 V8
I would agree that a larger pulley would make a difference if the alt was designed for a different engine but this one is designed for a Rover V8 w v-belts.

Here is the alt... http://www.britishpartsofutah.com/Range-Rover-Classic-Alternator-STC1753-p/stc1753a.htm

Will get it bench tested today & report back. Should have done this in the first place but wanted to rule out operator error.

 

[RDavisinVA]

3.5 V8
I would agree that a larger pulley would make a difference if the alt was designed for a different engine but this one is designed for a Rover V8 w v-belts.

Here is the alt... http://www.britishpartsofutah.com/Range-Rover-Classic-Alternator-STC1753-p/stc1753a.htm

Will get it bench tested today & report back. Should have done this in the first place but wanted to rule out operator error.

I hope your meter is not working properly because under 12V at idle is a real issue.
If your battery is good it doesn't make sense to me.

 

[Kevin88RRC]

I hope your meter is not working properly because under 12V at idle is a real issue.
If your battery is good it doesn't make sense to me.

So when Napa tested the battery it checked out as good but recharge. Charged it overnight out of rover. Voltage was 12.8 in the morning & held after being disconnected for a few hours. Battery appears fine..... now.

According to the interweb test the diode is good.

Reinstalled battery & alt. Much better readings. Alt is over 12v at idle and gains quickly with rpms.

I will retest tomorrow but my conclusion is the alt wants over 12v on the exiter to start making juice.

Side note.... shops could not test is since it is aftermarket with no known part number. But my local Orielles tried so hard.


Side question ...... is an over amp'ed alt a bad thing for a rover that currently does not have the power demand?

 

[LR Max]

Over amperage will cause a problem but the internal regulator should take care of that.

I would say a loose connection would be an issue. Do a voltage drop test (voltmeter) at all of your connections. If you see anything with more than .2v drop, then there is your problem. .08-.12v is pretty common voltage drop for a connection.

We use voltage drop vs ohm test as it is more accurate in finding a bad connection.

Actually do all of that for your exciter wire. We just had that problem, no exciter wires and not allowing charge at lower end. Alternators, at higher RPM will self-excite (I usually hear 1800 rpm but 1500 sounds plausible as well).

Do that and then we can look up alternator specs. What is the alternator model? What is the crank pulley diameter? You said the alternator pulley diameter is 2 5/8"?

 

[Kevin88RRC]

I followed this info for testing. Both positive & negative passed with flying colors... .016 & .005

The exciter wire is a different story and I'm not sure I did it correctly. Just to confirm the exciter wire is the charge light wire right?

Ignition on power side is 10.9 and ground side 1.28
Running power side .145 and ground 11.8

If I did that correctly then that looks like the issue. If I'm understanding it all the alt wants to see 12v+ to start charging.

Sooo confusing. This should have been plug & play. Link to the alt is above but not much info there regarding specs.

 

[vintagepatina]

Do you have photos of the wiring youve done?

I believe you are mistaking the excite wire for the charge lamp wire. this is not the case. the excite wire just gets looped back over to the positive post on the alternator.

I've installed several of these GM CS130 alternators on Rover V8s, 200Tdis, 2.25s in place of the Lucas. Nothing special about the BP Utah one aside from they have rotated the front case to fit.

 

[Red90]

The BP alternator only has two leads according to their site. One for the charge light (L) and one for a tach (P). The one for the charge light is what is being referred to as the excite wire, as that is what it does.

http://www.britishpartsofutah.com/Range-Rover-Classic-Alternator-STC1753-p/stc1753a.htm

A wire that would go to the positive terminal would be a "sense" wire (S). These are used for sensing the voltage and the idea is to account for voltage loss between the alternator and the battery.

 

[O2batsea]

Just reading thru this now.. You have a dead battery. I say that based on the fact that you say you charged it for several hours and it came up to 12.8. Believe it or not that is effectively dead. You should be seeing 13.5 v at rest and 14.4 with engine on./
Get the voltage over 13 then you can start troubleshooting the alt.

 

[1of40]

Buy ur next battery from Costco and anytime it drops below 13 again within 48 months they replace it no questions asked. I honestly can’t remember the last time I bought a new battery for any of the 4 vehicles in my family.

 

[Kevin88RRC]

Just reading thru this now.. You have a dead battery. I say that based on the fact that you say you charged it for several hours and it came up to 12.8. Believe it or not that is effectively dead. You should be seeing 13.5 v at rest and 14.4 with engine on./
Get the voltage over 13 then you can start troubleshooting the alt.

Battery tested fine at Napa but bought a new battery... same results. Both batteries at rest engine off 12.5v. By 'rest' do me idle? I have the charger on the new battery for shits & giggles and will try again. Running above idle both get to 14.4.

To me it seems like the exciter wire is not providing enough volts to get the alt to produce power at idle. I tried a wire direct from battery + to exciter wire but did not help. Will try again with new battery.... why not.

Going to try to get a model number for alt from BpUtah so I can get it benched tested.

 

[vintagepatina]

it is a GM CS130 alternator for a 1990s saturn SL1 that is clocked 90* and has a v belt pulley on it.

it needs to be wired like this:

omit the ECU wire.

 

[Kevin88RRC]

it is a GM CS130 alternator for a 1990s saturn SL1 that is clocked 90* and has a v belt pulley on it.

it needs to be wired like this:

omit the ECU wire.

Awesome! Sure looks like it. Maybe now I can get it bench tested.

My wiring only has two... D+ and tach
What does the battery sense wire do and could that be the issue? If so it's strange they would send it out with that omitted.

 

[vintagepatina]

the battery sense wire monitors electrical system voltage so that the internal regulator can make adjustments. it may be the problem in your system. every CS130 wiring diagram on the web includes the sense wire. i also have no idea why bputah deems it unnecessary.

 

[Kevin88RRC]

Did a rough test with a T pin jab into where the S wire should be.
New battery off 12.5v
Battery idle drops to 12.25v but appears to hold there
Alt idle 12.15v power climbs with rpm but did not have my tach

Still going to bench test and if it passes will source a new plug & wire Sense in. Research suggests to connect to + on starter. Correct me if there is a better place.

Thanks everyone for your help so far.