Alternator not charging at idle

K

Kevin88RRC

Well-known member
Hey...
As the title says brand new alternator is not charging at idle. I get a reading around 11.5v at idle and will climb to 14.4v by 1500rpm. Before I pull it and bring it to be bench tested, is there anything else to check? Would a grounding issue cause this? Belt is tight. Alternator is the 140amp model from BP Utah.
Thanks!


Edit.... one other note with the ignition on & engine off the speakers have a very noticeable whine. Seems to go away with engine running or at leasts gets drowned out.
 
RDavisinVA

RDavisinVA

Technical Excellence Contributor
Disconnect the field and connect a non-led light bulb to the alternator field connection at one end and the other end to the ignition.
Let the field wire hang loose and remain disconnected, but not grounded.
Key on, light bulb should glow, engine running light should go out.
Measure idle voltage and voltage at 2,500 RPM.
Report back.
 
K

Kevin88RRC

Well-known member
RRC 3.5 V belt

Field wire is the charge light right? Charge light works... on with ignition off when running.
 
K

Kevin88RRC

Well-known member
Belt is new & tight. Steering pump belt could be a tiny bit loose though... looks a little jumpy, but I did not have an issue with the old alternator before it died. Light came on, made it home and it was not putting out much power so I ordered this new one.

Can I use my meter in place of test light? White wires are ignition right? If so, my meter does not zero out when engine is running. If not the correct wire, where is a good place to tap into the ignition?

Another observation, ignition on the alternator hums with field wire attached and goes away when unhooked.
 
K

Kevin88RRC

Well-known member
Ignition off.... battery & alt 11.5
Ignition on.... alt 11.4
Idle 700rpm.... alt 11.25
2000+rpm... alt 14.2
Return to idle.... gradually decreases to 11.0 over a couple minutes & looked like it would continue to drop.
 
Napalm00

Napalm00

Technical Excellence Contributor
rocky said:
My new one does the same no charge until revved. Weird. Not from same source
Click to expand...


It's normal for an internally excited alternator to not charge at idle. But only initially once it's revved up past the charging point it should charge at idle no problem.

If you aren't charging at idle at all but could be another issue. Or possibly as simple as too large of a pulley
 
RDavisinVA

RDavisinVA

Technical Excellence Contributor
Kevin88RRC said:
Ignition off.... battery & alt 11.5
Ignition on.... alt 11.4
Idle 700rpm.... alt 11.25
2000+rpm... alt 14.2
Return to idle.... gradually decreases to 11.0 over a couple minutes & looked like it would continue to drop.
Click to expand...

What's the non-LED light doing?
 
RDavisinVA

RDavisinVA

Technical Excellence Contributor
Kevin88RRC said:
It's in the process of being crafted but first it wants me to get a 6 pack. ;)

What wire is best to tie into the ignition?
Click to expand...

Temporary bulb has 2 wires: 1 to the ignition (white circuit) easy to find on the engine harness firewall plug.
2. to the Field on the alternator after you remove and isolate the brown with yellow wire.

Purpose is to rule out the ignition warning light circuit has a break that is not allowing proper connection at idle.

Alcohol and electrical wiring just go together like vanilla ice cream and chocolate syrup.
 
K

Kevin88RRC

Well-known member
RDavisinVA said:
Temporary bulb has 2 wires: 1 to the ignition (white circuit) easy to find on the engine harness firewall plug.
2. to the Field on the alternator after you remove and isolate the brown with yellow wire.

Purpose is to rule out the ignition warning light circuit has a break that is not allowing proper connection at idle.

Alcohol and electrical wiring just go together like vanilla ice cream and chocolate syrup.
Click to expand...

Thanks to a delayed project of adding second bonnet light, I had easy materials to make my test light.

Results:
Ignition on... light on
Engine on... light off

Tested on ignition side of coil & also on a random white wire not hooked to anything. Voltage readings were similar as before.


Napalm00 said:
It's normal for an internally excited alternator to not charge at idle. But only initially once it's revved up past the charging point it should charge at idle no problem.

If you aren't charging at idle at all but could be another issue. Or possibly as simple as too large of a pulley
Click to expand...

Pulley is substantially larger but the alternator is designed for Rovers. Even tried an old OEM belt but it sits even higher in the pulley.

So what's next?
 

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RDavisinVA

RDavisinVA

Technical Excellence Contributor
Kevin88RRC said:
Results:
Ignition on... light on
Engine on... light off

Tested on ignition side of coil & also on a random white wire not hooked to anything. Voltage readings were similar as before.

Pulley is substantially larger but the alternator is designed for Rovers. Even tried an old OEM belt but it sits even higher in the pulley.

So what's next?
Click to expand...

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?
 
rocky

rocky

NAS-ROW Addict
Napalm00 said:
It's normal for an internally excited alternator to not charge at idle. But only initially once it's revved up past the charging point it should charge at idle no problem.

If you aren't charging at idle at all but could be another issue. Or possibly as simple as too large of a pulley
Click to expand...

Just the initial idle is no charge. As you say once revved up, all is good. I'm not sweating it. Lets face it, getting replacements if they fail doesn't take long these days and is much cheaper than it was 15 or so years ago.
 
Napalm00

Napalm00

Technical Excellence Contributor
rocky said:
Just the initial idle is no charge. As you say once revved up, all is good. I'm not sweating it. Lets face it, getting replacements if they fail doesn't take long these days and is much cheaper than it was 15 or so years ago.
Click to expand...

Yup , then you are operating as normal
 
L

LR Max

Well-known member
Kevin88RRC said:
Ignition off.... battery & alt 11.5
Ignition on.... alt 11.4
Idle 700rpm.... alt 11.25
2000+rpm... alt 14.2
Return to idle.... gradually decreases to 11.0 over a couple minutes & looked like it would continue to drop.
Click to expand...

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.
 
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