Three races ago we put a RPM Performance data logger on my wifes car. First thing we learned was the alternator was weak. Put a friend's spare Powermaster on it and it made a steady 14.2 volts all the way down the track.

Bought a new East Coast Auto Electric Ultra mini (same as on my car) for the following week and it put out oscillating voltage, the voltage graph looks like a sine wave from 14.3-14.8 and exactly .1 of a second from each dip to peak. Called ECAE they didn't know what to say.

Figured it was a bad alternator so had JEGs send out another. Put it on this weekend and the voltage graph looks like a sine wave still. .1 second from dip to peak, but now oscillating up to 15.2+ and down to 14.6.

Anyone ever see this before? I can't imagine I got two bad alternators but I can't see it being anything else, particularly because my friend's spare painted a nice flat graph. Graph from my car is a steady 14.5 all the way down the track. Next step is to swap alternators and see what happens.

These are data logs from time trial and first round.

Shout out to RPM for providing a great product and fast service. If you're in need of a logger check them out.

In the world of welders .....Some Lincoln’s produce DC like an old car generator but

Many engine drives are AC alternators

They produce AC voltage and are rectified to DC for the DC weld output.

They always have a large transformer type device wired in series on that DC output side and they call it a stabilizer. It dampens the voltage to get rid of a ripple just like your seeing.

A car alternator (AC) has nothing but diodes and a voltage regulator. The diodes rectify the AC output. There is still that ripple effect without a dampening device.

Your data recorder is reading the ripple normally not seen by a meter.

It’s sampling rate is fast enough to read it. If it were adjustable like a scope you could smooth it out....


That’s just my guess....

AC goes from whatever the peak voltage is to positive and then negative. So if the alternator produces 20 volts AC + down thru zero to 20 volts - The diodes rectify it and the VR cuts the voltage down by controlling the field. The ripple is still there...

I don't think it's a sampling rate issue since the time between successive mins and maxes is .1 second....that's a long time. Plus other alternators make a smooth graph. Also notice how the engine RPM graph is rough on the TT - it's never done that when it had the borrowed alternator on it.

But yes the alternator should internally change its AC to DC, so I'm thinking the problem is there, but 2 in a row??

Put a good meter on it. A Fluke, see what it reads. They move around very easily so if it reads pretty steady without bouncing around I would not know what to say. ?

Make sure your belt is tight and wire connections are tight. That’s probably a non issue though.

I have an RPM also and the oscillations on mine are very small. Also that is a huge dip at the shift.

I had it on one alternator. Changed alternators and it went away.

To OP my question is this. Prior to the installation of the Data Logger was her car running consistent or inconsistent?

Put the alternator from your car that graphs good onto her car, and her bad one that graphs bad on your car and compare.

If any / all graphs bad on her car and good on your car you need to look else ware.

quote:

Originally posted by SCDIV1:
Put a good meter on it. A Fluke, see what it reads. They move around very easily so if it reads pretty steady without bouncing around I would not know what to say. ?

Make sure your belt is tight and wire connections are tight. That’s probably a non issue though.

Now that you mention it I checked it with my meter when we were warming it up Sunday and it definitely wasn’t rock solid. Didn’t think much of it at the time. Thought about belt too but it’s tight, and can’t see a belt slipping that “perfect” to be the same each time.

quote:

that is a huge dip at the shift

That’s the electric shifter

quote:

To OP my question is this. Prior to the installation of the Data Logger was her car running consistent or inconsistent?

It had inconsistent 60’ times but good/normal mph. 60 would move a lot, .02 even .03. Installed data logger, did some slo mo videos, made a shock adjustment and tire pressure change at the same time we ran the borrowed alternator then the two new ones. Car has been good since.

quote:

Originally posted by 183N:

quote:

that is a huge dip at the shift

That’s the electric shifter

I know why it's there, just that it is a huge dip. Mine barely moves with my electric shifter.

Mine is rock steady even with the electric shifter. On the shift it drops about .5volts. mine is a huge gm stock corvette.. Think 160amps because I used to run efi and went thru batteries like crazy. Left it in there with the carb setup. Don't care if it costs me ET.

Is your belt slipping? Wire size feeding battery?

Take it off and take it to a reputable shop and have them test it. This will eliminate all the in car variables.

For anyone who needs a good meter

I have 2 Flukes and they are pretty much the go to meter in my world.

An older Model 83
A newer model 117

Both measure Frequency/Hz or Cycles per second as it was known for years.

Your std USA power is 60 HZ.....

Its a very use full thing when you work on machines that have no way to read engine RPM....like diesels and welding machines and generators....

The 117 is a lower cost meter and has many features...
My 83 is in my racecar trailer...Its 25 years old....has been repaired by Fluke a couple times...

I use the 117 at work everyday.....they cost around $150 I think.....the 83 I bought for $200 used....

quote:

Originally posted by CURTIS REED:

quote:

Originally posted by 183N:

quote:

that is a huge dip at the shift

That’s the electric shifter

I know why it's there, just that it is a huge dip. Mine barely moves with my electric shifter.

My old ECAE alt could not keep up with the demands. At an idle it was 13.8v but going down track it showed battery voltage (12.xx) on the grid data and would dip way down under 11v on the shift. Never would have found this without the grid.

My new Powermaster is @14.8v idle and @13.8 going down track. It still dips 1 volt on the shift but I know why. I have a Biondo solenoid wired thru a relay. At one time (pre-grid) it was hooked directly to the delay box and was accidentally switched to normally on, it started smoking. It still worked so I didn't replace it, might be time to get a new one.

From the log you posted, the alternator isnt charging very well at idle. In my experience that can cause some consistency issues if your not charging the battery regular. Basically the load on the alternator will change based on the state of charge of the battery. IMO the point of having an alternator is to maintain the state of charge on the battery, and it isnt doing that if it's just charging going down the track.

One think to try, disconnect the alternator, and fire up the car and see if the oscillation is still there? If it is, you need to look elsewhere.

What electrical components do you have?

Is this a single wire alternator?

My stock gm alternator, the type used by GM throughout the 80s and 90s, puts out 13.3 all the time, idle or WOT. It is only a 105 amp unit, very small, and having EFI and dual 30 amp fans I need a lot of juice!

Your alternator may not have enough output or a bad regulator.

There should be NO oscillation like you are seeing! The battery acts just like the worlds largest filter cap, without it, yes, you will see the ac waveform from the alternator.

The electric shifter dropped it 1.2 volts when I borrowed my friends alternator. I’ll have to check the amp draw of the shifter solenoid, maybe it’s going bad...I’m sure it’s original to the car, 2005.

Bill, it’s a 1 wire alternator and ignition is msd 7al3. The graph was steady with a borrowed alternator.

Mike I agree should not be seeing it - just hard to believe I would get 2 alternators in a row that do it.

Going to do some testing on it this weekend. The divisional is in town, I’m racing SC but she’s not so I’m going to see if I can replicate the issue in the pits then put my alternator on it and see what it does.

My car with the same alternator is 13.9 at idle and 14.5 steady going down the track.

Put the oscillating alternator on my car this weekend and made 3 time shots and a first round win in SC and the graph showed a perfectly steady 14.65 all the way down the track. Waiting for it to stop raining to finish the race today.

Don’t get how a different alternator was good in her car but this new one was bad in her car but good in mine. Guess I should try a new battery??