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Old 08-30-2018, 08:52 AM   #1
Pete_89T2
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Default Measuring alternator charging current

After another "110A/high output" took a dump just 4 months out of warranty, I decided I needed to find a way to measure charging current to characterize my FC's charging needs as various loads are switched on & off. I found this little gem on Amazon for about $17 shipped that does the trick:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Basically it's a hall effect current sensor ring that you slip over the B+ alternator charging wire. They have 100A and 400A versions; I opted for the 100A version. You wire power to the little circuit board, either via a 9V battery or hard wire it to the car's 12V switched supply. Since I didn't want to permanently install it, I went the 9V battery route.

The resolution on this sensor is rather course, about +/- 0.2A per spec for my 100A version, which is useless if you want to use it to help find parasitic loads/shorts when the key is off, but was fine for my purposes - charging current characterization where +/- 1A resolution will do.

After installing my new alternator (more on that later), I installed the sensor ring, and temporarily mounted the display/battery to the dash and went for a drive. Here's a few observations:

- For the 1st few minutes after starting the car, current draw is much higher than what I was seeing as "steady state". Steady state for my car (no additional loads, but engine running) was around 18~20A. Same loads but within < 5 min after start, and I'd see about 50A. I attribute this to the fact that on start, the battery discharges a bit, and the alternator is trying to bring it to a fully charged state ASAP. During this higher current draw period voltage will read 14.5V, and will drop to about ~13.6 as the current draw drops to its steady state 18~20A figure.

- Whenever my main e-fan kicked on, I saw a brief 20A inrush (added to whatever the steady state was), which dropped to about 10A while fan is running. Oddly enough, just the brake lights impose a similar 10A load, with much less of an initial inrush current. Think it's time to replace all those halogen bulbs with LED equivalents!

- Full boat current draw on my car at idle, with AC on max, main E-fan & stock Aux E-fan running, headlights, fog lights, brake lights + rear defroster on was 95A. So it would seem my new upgraded 110A alternator is keeping up, but there's little headroom there, which explains the short life. Bottom line lesson learned is that I need to (a) reduce electrical loads where possible and (b) move up to a 150A rated or more alternator.

Regarding my alternator, I figured I'd call the vendor I purchased the dead one from, tell him about its early demise and see if they would be willing to do anything for me. Since it was 4 months out of warranty, I figured best case I might get a 10% discount on a new one. Instead they asked me to just ship the dead alternator back, and as soon as I could send them a tracking #, they had a new replacement alternator on its way to me for free. The shop is Ace Alternator & Starter motors in Whittier, CA, and they sell on Ebay. Shipped the dead alternator out to them on a Friday and I had a new one in my car the next Monday






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Old 08-30-2018, 12:21 PM   #2
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Or just get rid of all those luxuries and go basic.

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Old 08-30-2018, 01:20 PM   #3
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I never read anything but bad reviews for the "upgraded alternators." Shortened life and low voltage at idle speeds seem to be the common complaints. A few companies make claims against the latter (IR Performance offers a S6 alternator upgrade) but I'm skeptical. Have you considered one of the "common" upgrades like a S6 (100A) or Ford Taurus (130A?) alternator? Based on the loads you listed there isn't much you can do to reduce them. LED taillights and perhaps a more efficient/variable speed e-fan are probably the best options.

I'm in the process of upgrading my charging system as well. My car has significantly less sources of draw. Outside of the "normal loads" the only additional loads are the electric cooling fan and cabin blower motor. My biggest issue is low voltage at idle due to the Racing Beat underdrive pulleys. I had a Banzai Racing alternator pulley but it was eating belts for some reason. I'm going to try a S6 alternator with their v-belt pulley next. Hopefully that will bring up the idle voltage and the extra current headroom can't hurt. LED taillights in the future too.
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Old 08-30-2018, 03:32 PM   #4
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^Same here, high output rebuilt alternators tend to be a crap shoot. Although the one I have (110A vs the stock 80A) doesn't have any problems with maintaining voltage at idle speed. I'm using a dual belt pulley, but it's not an under drive type.

An S6 alternator wouldn't be an upgrade over what I have now - I know the "rated" 110A alternator I have now is putting out at least 100A, as I was able to get my 100A sensor to read an over range condition (displays FFF when > 100A) by flipping on everything shortly after starting the car, when current draw maxes out. Thought about the Taurus alternator, but don't like the fitment - too tight with the stock TMIC. Someone needs to publish an alternator cross ref database that you can drill into by technical specs - case/mounting dimensions, electrical output/interface & pulley specs.

Going with LED equivalents for everything outside except for the headlights & fog lights will reduce power consumption by roughly 85% (e.g., a 27W halogen 1156 gets replaced by ~3.5W LED, for similar light output), so I'll be doing that soon.
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Old 09-01-2018, 09:31 PM   #5
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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.


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Old 09-02-2018, 08:24 AM   #6
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Quote:
Originally Posted by RETed View Post
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.

Quote:
Originally Posted by RETed View Post
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.


Quote:
Originally Posted by RETed View Post
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.

Quote:
Originally Posted by RETed View Post
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?

Quote:
Originally Posted by RETed View Post
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.
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Old 09-08-2018, 01:50 AM   #7
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That's awesome! I've been thinking about stuff like this lately too.

I've had the upgraded alternator from IRP on my FD for almost 10 years now. The original one failed pretty quick and I suspected it was due to using an underdrive pulley that was too large. Ihor swapped that one out for me and I started using pulleys that were either stock or closer to stock diameter and haven't had a problem since.

I've used an Odyssey PC680 and a Braille battery of similar size at different times and I wasn't super happy with either of them, although when I got the Braille battery years ago I hooked up a battery tender and I don't remember having any issues with it other than one time when I couldn't plug in the tender and I guess an interior light was left on all night. I've continued using the battery tender with an Optima Yellow Top and Optima D51R and haven't ever had any issues.

I think I'll be getting one of these sensors to see just how much I'm stressing the system. Thanks!
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