CharlieD93

So I recently bought a 240 amp alternator from Mechman Alternators for my 1998 GS300, now I have one problem. Every time my rpm's goes past 5k and I let off the gas my battery light comes on, I did not have this issue with my stock alternator. I have upgrade to 1/0 gauge KnuKonceptz Wire for my the Big 3 Three, although for my power run I have a 4 gauge run (I have no amplifiers yet, so I believe it won't draw the full the 240 amps but will pull stock load for now which is somewhere around 100 amps). I have copper lugs, an XS Power D3400, a new Goodyear Gatorback Belt, and also added an inline fuse. I have done everything that was asked and I still have a problem. Does anyone have any insight? I am wondering if it may have to do with the stock power wire being still connected and the fuse box being overloaded with power? I don't think that is the case, though not 100% sure, any information will help. I am also linking a video of the battery light coming on past 5k rpms.

https://www.youtube.com/watch?v=sI-Q...ature=youtu.be

DosyBoy

iTrader: (1)

I was told always buy OEM when it comes to the alternator on these vehicles...

CharlieD93

I would go back with OEM like you say, but I am going to be running over 2000 watts in the next month and was told/also what I have researched, that a High Output Alternator would be needed to run all of that. That way I wouldn't have my headlights blinking, fry the OEM alternator, and have my amplifiers going off on me. But I do understand that OEM is always better, but will not work for my setup, thanks Flocko for being the only one to respond!

Bhubb18

Check what voltage is being produced. Could be a dud alt?

CharlieD93

The alternator is charging, so its not a dud. I sent it to Mechman 2 weeks ago and they fixed it and sent it back. It had a very loud oscillating sound that I knew wasn't right. I have another video to show there isn't any voltage spike when I let off at 5,000 rpms. So for it to still be a dud alternator, I would be very disappointed in there repair department. My voltage does fluctuate some between 13.3-14.2, whenever I turn on an accessory it just starts to plummet in voltage until I turn that accessory back off. I emailed Mechman and "they said it is a very strange problem but it sounds like you have it all wired up correctly." So my installation is all good, which would point back to the alternator, but I do not want to have to pay for shipping twice in 2 weeks. IF anyone has put on ANY aftermarket alternator on there GS and had the same problem or didn't have a problem at all, please let me know how to fix this.

Sphan519

I had the exact same problem when i put in my 240a mechman alternator as well which was 2 weeks ago. I gunned it and the battery light would come on a for a split second. i had a half an inch shorter drive belt installed at the time and i thought that it was belt slippage at high rpms. I emailed mechman and they told me to look at the front face of the alternator where the pulley is to see if there was any black powdery residue build up, i swiped my finger across it and there was indeed a black powdery build up. So i went out a bought another half an inch smaller belt than what i already had on which makes my current belt 1 inch shorter than the original belt.

I'm not sure if that fixed the problem but ill hop in my car tomorrow and gun it to 5k rpm to see if i get the same results.

Spyder78

iTrader: (7)

Sounds like sphan519 might be right. I did a lot of research before I choose my alternator. The biggest issue for me was finding one which could use the oem length belt and put out a lot of amps. I went with a 270 amp dc power alternator and have no issues.

CharlieD93

Yes Sphan519 please let me know, I did try a smaller belt and it didn't help, but it wasn't a gator back like they suggested, I got a gator back belt that was for my car, maybe it is still slipping but I did get what they recommended. And spyder how much did you spend on the 270 amp dc power alternator? I just checked their website and they don't have our model car on their list, did they custom make it for me as well?

CharlieD93

Spyder78, you think you could do the 5k rpm test for me? Just to see if it is the Mechman and not just all aftermarket alternators. I am pretty sure it is only with the Mechman alternator, but if you do that test for me and let me know your results, I would greatly appreciate it.

tdciv

is the belt lose check the voltage at 5k rpm

CharlieD93

The belt isn't lose, my tensioner pulley is fine, my voltage is/stays at 13.8 at 5k rpms, my battery light just comes on for a split second, here is the other video that shows no voltage spike/drop at 5k rpms.

tdciv

from what i see its the regulator do you have a ext regulator?

2GSKaizen

iTrader: (1)

That device you are testing for the voltage spike with isn't going to update the display fast enough to show a voltage spike or drop. To get a truly accurate picture of the voltage output at a specific RPM you would need to hook it up to an oscilloscope and watch. Same problem for people trying to get 02 sensor readings with a voltmeter.

CharlieD93

True, but I do not have an oscilloscope on hand, that was the best I could do, my DMM also just died on me, so I would use that. I do not have an external regulator, thats not the problem unless it is indirect. My issue is the battery light coming up for a split second, that's all. Every other forum and Mechman points to the belt, but I got what they recommended, so then it points back to the alternator, but it was just fixed... so I am still trying to figure it out.

tdciv

regulator must be bad on it thats why i asked if you did or not the bad news is you need to send it back

i run the same alt on my 2jz-gte and it works fine