Alternator Voltage Fluctuation

dhubz · Samba Member Joined: July 02, 2003 Posts: 61

I recent "upgraded" to a new style alternator. I have a USB charger installed that gives a voltage reading. When running the old generator with a regulator, I was getting about 13v at idle and 13.9 at driving speed 2-3k RPM. The new one is only giving 12.1 at idle and maybe 12.6-12.8 at higher RPM. I disconnected the regulator and made the connections as per some other posts/diagrams on here. What is the normal range for a newer style alternator? The new belt is nice and tight, I don't think there is any slippage.

21golden007

Doesn't sound like enough. I recently went through this. From rob and daves aircooled-

"As the engine speeds up, the voltage should increase to about 14.2-14.5 volts. If it does, then the generator/alterator is working properly and charging the battery as it should. At idle the voltage across the battery terminals should be somewhere between the 12 and 14 volts."

Is your alt/gen light staying on?

jsturtlebuggy

Reading your post I am trying to understand did you have a alternator or generator before you changed it out to new style alternator?
All new alternators being sold now have internal regulator. They use only two wires on them. The post that has a nut on it goes to battery. The terminal for slip on connector goes to idiot light on dash. This light circuit is what excites alternator to charge.
Do you have a picture of your setup?
_________________
Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960

jspbtown · Samba Member Joined: January 27, 2004 Posts: 5156

My guess is that its not wired correctly. You have a charging lamp thats not LED?

Dale M.

About 14 volts is optimal but could be about 0.2 volts either way....

If its wired correctly... B+ directly to battery and D+ to working ALT/GEN lamp then the alternator its self is not functioning as it should and probably is bad unit right off the shelf....

Check output voltage at B+ terminal on alternator with known good voltmeter.... Have little faith in cheap electronics may in China...
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

dhubz · Samba Member Joined: July 02, 2003 Posts: 61

This is how I removed the regulator and wired it. I will have to check the output with a multimeter. The indicator light is LED, but it worked fine before, and seems to be ok now, when the voltage is at 12v the light is on, but flickers out when the RPM increase. I am going to change the wiring so the B+ ties onto the battery directly, or to the starter cable.
I'm not sure I understand the function of the D+ wire from the indicator light, is it providing signal to the generator to charge? I will have to do some reading. Why would the system work ok with the generator and voltage regulator, but not with the new style alternator with the regulator bypassed?

Image may have been reduced in size. Click image to view fullscreen.

jsturtlebuggy

A LED light does not allow enough voltage through it to tickle alternator to start charging.
My setup is the same way with LED in dash, I had to install a regular indicator light inline for alternator to charge.
You can also use a resistor inline too instead of the extra light.
_________________
Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960

dhubz · Samba Member Joined: July 02, 2003 Posts: 61

Dale M. · Last edited by Dale M. on Wed Aug 18, 2021 6:52 am; edited 1 time in total

This circuit has been recommended by several when using a LED as charge indicator...

_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

jspbtown · Samba Member Joined: January 27, 2004 Posts: 5156

You can also throw on a incandescent light anywhere you want. Under the dash where it is hidden? Near the alternator in the engine area?

That way you can keep your LED as well.

dhubz · Samba Member Joined: July 02, 2003 Posts: 61

I figured out the problem. It turns out I'm an idiot, figured out it really helps if you tighten the cable that's attached to the B+. I'm currently charging at 14v, the LED's indicators I bought must have resistance built in, it seems to function OK. Thanks for the help.

slalombuggy

I have LED warning lamps and no resistors. Everything works just as it should in both cars

Dale M.

A typical LED only require 1.5 to 3 volt to illuminate, a LED pilot lamp rated for 12 volts probably has a internal resistor built in....

Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...


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