Measuring alternator charging current

[RETed]

I picked up a cheapie (made in China) inductive clamp DC current meter off Amazon a few years back for $35 and it comes in handy.
It also does voltage and resistance with included test leads, so for the money it was worth it to me.
Keep in mind that these inductive DC current meters are only relatively accurate, so readings on the low side should be taken with a grain of salt.

It's been years since I've upgraded to an FD alternator...
...and I haven't looked back.
The stock FC alternator are just not powerful enough, especially at idle.
Even my current FD alternator, I run an artificial 900RPM idle (thank you Haltech) to keep idle voltage above 13.0VDC.
Mind you, I am running a big twin electrical fan set-up that draws ~25A of current when on.

A few years back, I was killing alternators left and right.
This was due to the FC not being a daily driver.
I tracked this down to an overzealous Sears / Die Hard battery charger that was bumping charging voltage over 16VDC(!!!) when set to 200A cranking mode.
(At about the same time my MX83 alternator die, and I went through a bunch of those due to the stupid battery charger too.)
So, at this point I had a half dozen alternators sitting in front of me...
I thought it was going to be a simple process if changing out the voltage regulators, and I was going to end up with a bunch of "brand new" alternators!
Boy, was I wrong - it turned out the overly high battery charger voltage was zapping the diodes in the rectifier.
And, it wasn't easy - or cheap - to find replacements; in fact, some of the bare rectifier modules cost more than buying a "brand new" alternator!

Hold on - there is a moral to this story.
Being ambitious with this "project" I started to look for bare diodes to repair these damaged rectifier modules - nope, not easy or cheap.
Lower current ones (20A) were relatively easy to find, but 30A or higher wasn't easy.
It didn't help that our alternators (in fact most Japan / import ones) use the smaller profile diodes.
On top of that, doing the actual replacing on the rectifier model was a royal pain in the ass!
The rectifier modules are usually coated in this tough epoxy.
I use a pencil torch to burn that coating away to remove each diode.
I gave up after I killed the first module as the heat killed everything around it.
Now, these rectifier modules comes with 4 pairs of diodes.
Each diode pair has a + and a - diode type, so you need 8 total to overhaul each rectifier module.
The 20A ones were around $5 each - cheaper if you find a deal (i.e. surplus sale).
$5 x 8 is already $40.
Now, the FC alternators were loading with 20A diodes - so do the math, 20A (per pair) x 4 80A - this is your theoretical maximum.
My FD alternators were loaded with 30A diodes, so that's a 120A theoretical max.
All those "upgrade" and "high current" alternator you see in eBay all run the same rectifier models, so the FD ones are max out at 120A.
So those FD alternators rated from anywhere from 100A, 120A up to 130A, 150A, 180A, 200A all use the same rectifier module - max out at 120A.
So effectively, anything over 120A is bullshit.
Lesson learned.

Side note, I have had pretty good "success" with the eBay seller "ace_alternators" for my FD alternator replacements.
One cavaet, they don't seem to last longer than 2 years - keep that in mind.
For under $100 every 2 years, that doesn't seem to be that bad of a price.
The other eBay seller I use is BNR Parts, but watch out with the overratings as these guys like to tout 150A, 190A, 200A rated FD alternators which is basically impossible.
Outside of the insane overratings, the BNR Parts alternators last about the same - about 2 years for me.

These alternators do a legit 90A - 100A at full tilt, which is enough for me at this time.
I only have a small stereo set-up with a single 2 x 75W amp right now.


-Ted

[Pete_89T2]

Originally Posted by RETed

Even my current FD alternator, I run an artificial 900RPM idle (thank you Haltech) to keep idle voltage above 13.0VDC.
Mind you, I am running a big twin electrical fan set-up that draws ~25A of current when on.

I'm running a higher idle as well, 950, thanks to AEM Infinity, but even if I dial it down to 750~800 RPMs, I'll still see voltage between 13.0~13.8. Due to the big street port, engine idles a bit rough down that low, which is why I let it idle higher.

Originally Posted by RETed

A few years back, I was killing alternators left and right. This was due to the FC not being a daily driver.
I tracked this down to an overzealous Sears / Die Hard battery charger that was bumping charging voltage over 16VDC(!!!) when set to 200A cranking mode.

That makes a lot of sense... if not daily driven, even a fresh battery will lose a fair amount of juice upon cranking/start up, and then your alternator will be working hard initially to bring it back to full charge. At least that's what my current measurements are telling me. More amps produced over longer time = more heat = quicker alt failure. I've been using a small trickle charger/battery tender to keep my battery fresh when the car sits in the garage between rides. Hopefully that practice will minimize the amount of time after start up that my alternator has to crank out the 50+A to get the battery back to full charge, and help the alternator last longer.

Originally Posted by RETed

I thought it was going to be a simple process if changing out the voltage regulators, and I was going to end up with a bunch of "brand new" alternators!
Boy, was I wrong - it turned out the overly high battery charger voltage was zapping the diodes in the rectifier.
And, it wasn't easy - or cheap - to find replacements; in fact, some of the bare rectifier modules cost more than buying a "brand new" alternator!

I didn't have as many alternators to play with, but I had the same initial thoughts, and came to the same conclusion - those diodes are the choke point! PITA to replace, PITA to acquire and too $ to be practical.

Originally Posted by RETed

All those "upgrade" and "high current" alternator you see in eBay all run the same rectifier models, so the FD ones are max out at 120A. So those FD alternators rated from anywhere from 100A, 120A up to 130A, 150A, 180A, 200A all use the same rectifier module - max out at 120A.
So effectively, anything over 120A is bullshit.
Lesson learned.

Ebay crap aside, this makes me wonder how those expensive high-output (150A+) builders like Mechman are doing it - Where do they get their rectifier diodes from?

Originally Posted by RETed

Side note, I have had pretty good "success" with the eBay seller "ace_alternators" for my FD alternator replacements.
One cavaet, they don't seem to last longer than 2 years - keep that in mind.
For under $100 every 2 years, that doesn't seem to be that bad of a price.

If your ebay "Ace Alternators" is located in Whittier, CA, that's the same shop I used. This last alternator lasted for a year + 4 months, and they were nice enough to still honor the 1 year warranty on it. The prior alternator I purchased from them lasted almost 3 years, but that was before I went E-fan, and I probably fried that alternator with a high power charger like you did. Long story short, but as we completed the harness wiring of the AEM Infinity and were attempting 1st start at Brian's shop in CT, battery was worn down and we tried to get her started on his mega charger - not much doubt that must have fried the alternator. Managed to get the car back home to MD by using one of Brian's spare alternators.