Steps To Check If Alternator Is Working?

James V · Jun 14, 2017

Just bought the 130amp alternator upgrade kit from lmr. Finished the whole install and finally turned on the car to check if the alternator was working. I have a voltage meter plugged in and it says my battery is still at 11 amps like it was before. What are some steps I can take to find the exact problem of why the alternator isn't working? Please and thank you!

Boostedpimp · Jun 14, 2017

How are you testing the amp out put?

Does it supply the 13+ volt at idle to the battery?

Mustang5L5 · Jun 14, 2017

Rev the engine up a bit. Do you hit 13.5-14.7 volts?

Did you leave the big pulley on the alt, or swap it out for the original smaller pulley?

jrichker · Jun 14, 2017

Electricity flows like water:
Voltage is like pressure,
Current in amps is like volume,
Resistance is like the kink you put in a garden hose to decrease the pressure or volume.
Power is pressure multiplied by volume or voltage multiplied by current (amps)

Go re-read the instructions that came with your meter - if you measured amps and not volts you have a problem.

Automotive circuits are mostly simple stuff: a power source, a connection path, a control device, a load, and a ground.
The battery/alternator is the positive power source.
The wire and fuses are the connection path.
Control devices are switches, relays and sensors.
A load is a light, motor, solenoid, relay coil or heater element.
In automotive circuits, grounds are the return path so the electrical power can flow from the load to the negative side of the power source.

James V · Jun 14, 2017

Mustang5L5 said:
Rev the engine up a bit. Do you hit 13.5-14.7 volts?

Did you leave the big pulley on the alt, or swap it out for the original smaller pulley?

Even after reving it, no change in volts. The reason I got the new alternator upgrade was because the previous alternator wasn't charging the battery either. I left the bigger pulley on the new alt

James V · Jun 14, 2017

Boostedpimp said:
How are you testing the amp out put?

Does it supply the 13+ volt at idle to the battery?

I have a voltage reader. At idle the battery is at 11.5, like it was before I put the alternator in.

Mustang5L5 · Jun 14, 2017

You're probably just reading battery voltage then.

How did you wire the alt up?

James V · Jun 14, 2017

Mustang5L5 said:
You're probably just reading battery voltage then.

How did you wire the alt up?

Yep that's what I meant, I'm reading the battery voltage. What else can I check to see if the new alt is working?

I wired it up exactly how it showed in the lmr instruction video.

Boostedpimp · Jun 14, 2017

Ok so voltage not amps got it

Is there no increase in volts when you raise rpm? You will have to swap the stock pulley over to the 3g, if not you'll have issues charging your battery at idle

Mustang5L5 · Jun 14, 2017

James V said:
Yep that's what I meant, I'm reading the battery voltage. What else can I check to see if the new alt is working?

I wired it up exactly how it showed in the lmr instruction video.

I didn't watch the video.

Did you remove the two 10gu wires from the starter solenoid end of the wiring harness as well? The voltage regulator feeds off these two wires. Usually they say to disconnect them from the alt side and run the larger gauge wire to the chanrging post, but I've seen guys remove the two 10gu wires completely, which causes a similar problem

mikestang63 · Jun 14, 2017

did you reattach the two power wires to the post on the 3g alternator? Take those off and tape them off. Only run the 4 gauge power wire from the 3g positive post to the starter solenoid with a 150 amp inline fuse

Also- did you reattach the stator wire from the original 2g connector to the male stator fitting on the 3G.

Finally what alternator pulley are you using. The 3g is larger than the 2g.

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