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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #1 ·
My upgraded cooling fans proved too much for even the upgraded alternator and it died. I called Driftmotion and discussed with Aaron. He suggested using a device that kind of delays the fan activation over a brief time, pulsing the current, so that the alternator isn't getting hit with the full start-up draw all at the same time. Is anyone familiar with this and if so, what advice do you have in installing this?

(Note: this certainly makes sense. If there was a way to make one come on and the second with a slight delay it would make no difference from a cooling standpoint once both were spinning but would certainly avoid the huge initial draw of both coming online simultaneously.)

As always, thanks in advance.
 

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Cant say Ive heard of that outside of electric cars. I know the mk2 MR2 alternator is a direct fit and puts out way more amps. Stock Supra is 70 amps, MR2 110 amps. The MR2 had electric power steering which is why its so much more beefy.
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #3 ·
I have a 140A unit from Driftmotion but also have aftermarket electric radiator fans. They draw 15A each but I don’t know if they draw more on start up.
 

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1990 White NA/Blue Interior
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I have a 140A unit from Driftmotion but also have aftermarket electric radiator fans. They draw 15A each but I don’t know if they draw more on start up.
I’ve heard mixed reviews about the alternator (I just installed one myself), that they fail fast and are the same as the eBay ones. Maybe someone else can chime in.
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #5 ·
I just had a long conversation with one of my close friends who is an electrical engineer. He thinks the pulse width modulation module from Driftmotion is the way to go. That will continuously vary fan speed from 0% to 100% depending on temperature so it will never have the hard surge of 100% start-up.
 

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I made a stupidly simple low-side switched PWM controller for my Mondeo fans (a good 30A startup each and over 20A continuous), works a treat on the factory alternator.

It'll work, just make sure to get a controller rated for the proper current.
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #7 ·
The module from driftmotion says it is rated for 65 A. The data sheet on these fans say their normal draw is 13A each so 65 should be more than enough.
 

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The failure of the alternator has very little chance of being related to the fans. You have a battery in parallel with it with 500 CCA that can more than handle any surge current from the fans. Note that the ABS pump draws 50A and its not killing anything. I'd chock that alternator failure to infant mortality and unknown heritage. Its why I try to stay with Denso replacement parts.
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #9 ·
I think I know why it died. I completely forgot that driving home on my commute last week, a drive that takes 45 minutes, the highway was shut down and we got diverted off the highway through some back roads not designed to handle that level of traffic. I spent 2 1/2 hours in 95° heat sitting still on these roads. My fans ran the entire time trying to keep the car cool. I knew sitting wasn’t good for the car so I started watching the gauges like a hawk. I noticed the aftermarket digital voltage reading on my instrument panel dipping down into the low tens for extended periods, in fact I turned off the AC to reduce the load. I am pretty sure the fans were at max draw continuous for the better part of an hour and a half until I finally cleared the construction and accident detours. In hindsight I should have pulled into a parking lot and just shut the car off once I realized what was happening.
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #12 ·
It’s being replaced under warranty. I am willing to spend money for a better one if available. I have read people also put dual alternators on cars. If I can do that with better quality 70A alternators I am willing. I lack knowledge, not funds.
 

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1987 Toyota Supra
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I just stick with OEM units and just have them rebuilt.
The box store alternators are junk, my guess is the diode bridge / rectifying section that goes out.

Pi has it right.
Fast acting transient loads aren't damaging the alternator, it usually just can't react fast enough to cover the whole initial hit when a load turns on.
The battery acts as a load buffer during that time, taking up some of the slack.
I'm talking milliseconds, before the load handoff happens.

I am still on my original alternator, just with new guts.
Still works great.
 

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OEMs switch their fans on and off all day. My volvo has 20 years and 250k miles on the same alternator and fan and I live in a hot climate. There's no excuse for this. Its just a crappy alternator rebuild.
Pi has it right.
Fast acting transient loads aren't damaging the alternator, it usually just can't react fast enough to cover the whole initial hit when a load turns on.
The battery acts as a load buffer during that time, taking up some of the slack.
I'm talking milliseconds, before the load handoff happens.
Totally agree with these two statements. I would find it hard to believe switching loads with a relay or the fans on for 2 hours would kill an otherwise normal, healthy alternator. I may have missed it, but what is the draw form the fans?
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #15 ·
15.2A each. I am hoping this is simply a new alternator with a manufacturing defect. They are Maradyne TA12A3001.
 

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90T
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The 7MGTE 1990 alternator is rated at 80A. That was deemed sufficient for the 3 cooling fans on the 7MGTE with A/T.

There is a 100A MR2 OEM alternator that came on 91-92 models with electric power steering. That might be a viable upgrade although I don't know for a fact that it is drop in compatible.


Rewinding an alternator for higher current involves using thicker wire and less turns, which means higher peak current but poorer perfromance at low rpms. Personally, that is a bad trade in my opinion.
 

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Discussion Starter · #17 ·
I get a new 140A for free due to warranty. I think I will order a Denso unit to keep on hand just in case. I am feeling that since my block and head were rebuilt and I replaced the transmission it wouldn’t be a bad idea to keep extra 7M accessories on hand “just in case.”
 

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15.2A each. I am hoping this is simply a new alternator with a manufacturing defect. They are Maradyne TA12A3001.
I'm not an electrical guru by any means, but I would suspect that (i.e. not that the fans are killing the alternator). The MR2 upgrade may be worthwhile in the future as it is a Denso part as well... I'm just not that familiar with the application in the 7M. But per the guys above, it works. It may not be needed however
 

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15.2A each. I am hoping this is simply a new alternator with a manufacturing defect. They are Maradyne TA12A3001.
Yeah, I agree it's not going to be a problem for you. My fans draw more than the factory alternator can supply at nominal speed, let alone at startup. It's a whole different story.
 

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As I understand it, initial draw is a spike of amperage, which settles into a constant rate of draw. I believe most electrical components are rated in terms of this "constant" capacity as the initial draw is often just for a very brief moment.

Anyway, I had a wiring issue with my fans that caused them to literally melt the wires. Some of that good ol' "knowledge" at work, I suspect, folks that think they know everything, but the results of their work emphatically say otherwise. So, I put each fan on its own circuit. The wiring ain't pretty, but this was merely an experiment for me, and everything worked out great:



Edit: Just look at that beautiful bearded bastard. That just reeks of a guy who isn't afraid to tinker, and will likely light something on fire accidentally.
 
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