Comptech SC Alternator Question/Discussion

Hello Everyone,

I was reading about alternators the other day when I discovered something interesting that I have never seen discussed on Prime. For those of you running the Comptech SC, you know that the OEM alternator cannot be used since the installation requires the alternator to run backwards. In order to stick with a Honda OEM part, Comptech used a 1992 Honda Prelude alternator due to its reverse direction.

Now the thing that I found interesting is that the OEM prelude alternator is rated at 90 amps while the stock NSX alternator is rated at 120 amps. This got me thinking; is there any adverse effect for running a 90 amp alternator on a car that is designed to see 120 amps? Part of me thinks that if there was a problem, Comptech would have never developed a system that relied on a part that was not compatible with our car. However, the other part of me thinks if Honda felt that a 90 amp alternator was sufficient, they would have used one. I’m not an electrical engineer and don’t have much knowledge in this area so I’d like to get everyone’s thoughts.:smile:

-Steve

90 A is pretty much. If you use all high current features like hatch defroster together you'll reach that amount. Or if you have an aftermarket stereo. The lights take up to 17 A under braking. In arctic winter conditions with A/C, defogger and lights it needs more current than in warm California.
If you ever excess 90 A the starter battery feeds the rest but only limited time.

I knew this but didn't know the actual amps. This is something all the big stereo guys should know about. In a CTSC car you should really not be using a high powreed class AB amp or worse, multiple amps.

Once you overdrive the system, for an extended period of time, you very well might damage the car's electronics. I have seen this happen. Be mindful of what you are doing. Rear defroster on, lights on, blower on high, stereo with aftermarket amps running altogether is not a good idea.

So is the alternator just a stock 92 prelude or is it modified?

When I had my Comptech, it came in a honda box with a stock number. So I assumed it was just a stock unit.

I am running the comtech kit with this alternator and there is no issue under any loads for the voltage to stay stable meaning that the alternator is handling all the required loads. I would not be worried about the 90 amp rating as the average load is much below this level.

I’ve been having a fairly in depth discussion with another prime member regarding this issue and we have been doing some research together. I ended up finding a shop local to me who has 20+ years’ experience rebuilding alternators and asked them few questions about using a 90 amp alternator in a car that typically sees 120 amps.

The information that I received from them was that running a 90 amp alternator in a car that was designed to run at 120 amps will not do any “real” damage to the car. However, they said that you could potentially run into two problems.

The first problem is reducing the life of your battery because the lower amperage alternator may not be able to sufficiently charge the battery to the correct voltage. He said if that happens, it is not a huge deal because it just means that you may have to change your battery out sooner than you normally would.

The Second potential problem is a little bit bigger. He said if you run a smaller alternator such as the 90 amp one, you are going to significantly reduce the life of the alternator. The reason why is because the car is set up to expect 120 amps so if the maximum output is only 90, then the smaller alternator will constantly be maxing itself out at any RPM range trying to deliver 120 amps. He went on to add that maxing out the alternator every time you take the car for a drive can eventually lead to sporadic electrical gremlins until the alternator just quits. Just to be clear, he said if one does experience these problems, it most likely will not happen overnight, but rather over the course of a few years. I personally have a tendency to believe him because I am on my second CTSC alternator in ~6.5 years and experienced random electrical issues right before the first one went bad.

Now the cool thing is, he said that he can rebuild the one that I currently have so that it produces 120 amps. The price wasn’t that bad either…. $169 and it can be done in 1-2 days. It also comes with a full 1 year warranty. I’m thinking I may just get it done for peace of mind…. To know that my new alternator is now the “same specs” as an OEM one.

Please remind that the car doesn't constantly draw 120 A.

Most of the CTSC alternators had to be changed or revised because their bearings went bad under a strong-tensioned belt.

I have thought about getting a high amp rebuilt Denso alternator. Thoughts?

nsxotic911 said:

I have thought about getting a high amp rebuilt Denso alternator. Thoughts?

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Well, I just got mine back from being rebuilt (see my post above). They said it bench tested at just over 120 amps. As soon as I get around to installing it, I'll give my feedback on if there is any noticeable difference (I doubt there will be any difference you can actually feel, but we will see).

The cool thing is, this company used the OEM pulley and didn't try to put a smaller one on just to get the amperage up.

-Steve

Semnos_NSX said:

Now the cool thing is, he said that he can rebuild the one that I currently have so that it produces 120 amps. The price wasn’t that bad either…. $169 and it can be done in 1-2 days. It also comes with a full 1 year warranty. I’m thinking I may just get it done for peace of mind…. To know that my new alternator is now the “same specs” as an OEM one.

Click to expand...

What did they do exactly?

The kit i bought is older, wonder if i should replace the alternator?

Mike

I don't have anything real scientific to add. However, what I have found with my car is that after driving around town my battery tender always has to charge the battery. It's not even flashing green when I hook it up, which would indicate 80% charged. After going on a few hundred mile trip when I plug in it goes green immediately. My car also has a DA after-cooler and the pump runs the whole time.

I'm thinking it may be a good idea to have mine rebuilt as well.
Semnos_NSX would you mind PM'ing me the info of the shop that did yours?

Thanks,
Chris

Don't PM it, just post it. It's good info to have.

cmc140 said:

However, what I have found with my car is that after driving around town my battery tender always has to charge the battery.

Click to expand...

According to the graph posted above a stronger alternator won't help you. What would help in your case would be to use a smaller pulley for the alternator to keep rpms and current delivery higher but only if your battery would run empty.

Interesting post. When I refreshed my car 2 years ago, I experienced similar problems. I have a SOS supercharge,intercooler,added HID lights and stereo.
Since the refresh, I have replaced one alternator in such a short period of time. When the ambient temperature ran between freezing and 85 f, the charging system worked flawlessly.In particular,all was perfect at idle.However, when the outside temperature hit in excess of 90 f , my volts would drop from a mean of 14 to say 12 at a stop light. Once I got moving again ,all was perfect.
Checked the charging system in its entirety ....voltage drop test...wiring. et....no apparent issue. So I had the company that rebuild my industrial motors check it out....heat sink!!

So ...they built the alternator with a ceramic coated housings which can handle high heat, additional copper wire windings in the stator, soldered connections coated with special silicone to reduce corrosion and protect against high heat and vibration,....pulley size remained unaltered...problem resolved still at 90 amps.

goldNSX said:

What did they do exactly?

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They dissembled the entire alternator and replaced every component with better quality parts to bump up the amperage. The main and most crucial part that gets replaced to help raise the power output is what they call the "stater". This is the copper wire that you see inside.

TURBO2GO said:

Don't PM it, just post it. It's good info to have.

Click to expand...

The company is called RAS inc. (Riverside Alternator and Starter). The owner is a really cool guy and has been in the business of rebuilding alternators for over 20 years.

I haven't installed mine yet because I decided to replace my SC belt while I had the alternator out. I had to order the belt so I am waiting for that to come in. I'm sure everything will work fine, but I don't want to vouch for this place until I verify that everything works as promised.

(951) 354-2373
9960 Indiana Ave. Suite 3
Riverside Ca, 92503

goldNSX said:

According to the graph posted above a stronger alternator won't help you. What would help in your case would be to use a smaller pulley for the alternator to keep rpms and current delivery higher but only if your battery would run empty.

Click to expand...

Hi goldNSX,

I don't see a graph, but based on research I did, I was told that using a smaller pulley is just "low quality" way to up the amperage a little bit. the smaller pulley just spends the alternator at a faster speed thus forcing it to produce a little more power. However, the internals are not designed to handle this constant extra bit of power so reliability becomes an issue. The guy who rebuilt my alternator used the OEM pulley.

Again, I'm not an electrical engineer, so I'm not claiming to know everything about this subject....:smile:

Semnos_NSX said:

Hi goldNSX,

I don't see a graph, but based on research I did, I was told that using a smaller pulley is just "low quality" way to up the amperage a little bit. the smaller pulley just spends the alternator at a faster speed thus forcing it to produce a little more power. However, the internals are not designed to handle this constant extra bit of power so reliability becomes an issue. The guy who rebuilt my alternator used the OEM pulley.

Again, I'm not an electrical engineer, so I'm not claiming to know everything about this subject....:smile:

Click to expand...

Where has the graph gone to?

From the graph in SM 23-100 you can see that at idle the alternator can maximal 50-60 A at 12 V. Above 3k rpms Amperes are maxing out. The rising rate of the alternator's current delivery at low rpms very high, so speeding it maybe 10% higher will result in +10 A at idle. This could be enough to let the battery charged around town.

I agree with you that it touches reliability but 10% is not that big of an impact.

Too bad your company is so far away. It's expensive to send a parcel from Europe to the US and the shops in Europe are expensive too.

goldNSX said:

Where has the graph gone to?

Click to expand...

oops, i must have deleted it when i added the question. Sorry.

Mike




This is from a load test machine so i don't know how different the real world is. Be careful changing pulley size because at redline, 10% would be running the alternator near 20,000 rpm.


Here it is again.

Thanks for the info. I think I'll send mine out this winter for a rebuild, just as a precautionary measure. I'll report back if it makes any difference.

Thanks again,
-Chris

FYI - For my engine rebuild project I just went online to Amazon.com and bought a complete alternator for $200 shipped.

This is a remanufactured one, BUT it is rebuilt direct by Denso to tighter controls than other rebuilds may be. It looks brand new, and came with a new pulley already installed.

Dave

Edit - Also bought a Denso-rebuilt starter too from Amazon super cheap. No need for core charges or time spent dropping off/picking up your stuff.

i have ha good luck with starters and alternators for my fishing boat in Bristol Bay AK. from this site...found this link I believe the far left of the 3 would be the right one to get rebuilt. correct me if I'm wrong

http://www.dbelectrical.com/c-8286-regular-output.aspx

What about this one?


HIGH OUTPUT 130 AMP ALTERNATOR 1992-1996 HONDA PRELUDE



And this one says new NEW ALTERNATOR 1992-1996 HONDA PRELUDE 100amp