well the beat goes on with the alternator selection process. In a bit of a quandry here. I spoke to the Derale Fan guy today and he says they recommend 140 AMPS generator / Alternator for cars that are running the fan I am putting in. I should clarify: the fan is a 50 AMP draw: 25 for each of 2 fans. YEEEEEEow!!!!!

Ok here is my logic for picking a 94 amp GM SI alternator. I had a 37 AMP alternator and the car was running fine. Now if I add 50 amps worth of load with the fans...as in 25 + 25 = 50 and even if I assume that I was using ALL of the 37 amps I had then 37 + 50 = 87 which is still less than 94. My assumption was that with a 94 Amp SI I would have had a MINIMUM extra of 7 amps and possibly more if my 37 amp unit was not totally taxed.

Am I missing something here???? Seems that way back when in school all ya had to do was add up the draw of all the accessories and figure out the total. As long as you supplied at least that much to the system you were OK. Right? Has some rule of electricity changed? This is the same as my house ( I know AC not DC ) but fundamentally...when you add central air conditioning you gotta up the service from the pole same issue here. I added the load of the central A/C built in a little extra buffer and there ya go?

Asking just my opinion sort of limits you. I don’t have all the answers and many responses always lead to a better answer. Yes, the 94 amp will work. You already know you have little headroom over what you need and what you have. However, it will work. If you decide later on that you want to add something, like a CD stereo, you may have to upgrade again. My personal opinion is I’d rather stay with GM products on the car. That way if something dies on the road, I can get a replacement. If I remember right the only non-GM aftermarket electrical part I mention is the Wells regulator. If one of those were to go out, there are other regulator replacements that are easily obtainable.

I appreciate your answer but I did take the opportunity to talk to a few other folks. I have the same question posed to another friend here in Atlanta. No answer back yet fro him. Also a freind called today (on another subject) who is an electrical engineer so I bounced it off him also.

I thought I was OK with my calculations and you are right another upgrade might be needed but honestly I don't see the CD and such going in the car. I, like you, like to stick with Gm stuff and I don't like the Brand X anything especially electrical.

My experience has almost ALWAYS been that the GM stuff is more than adequate for what it was intended to do. I see this hot rod clutch and that hot road whatever and then I usually see..."It did not fit like it should have" "Comp Cams always go flat" "Richmond Gears Always howl" "It makes too much fan noise" "The tech support guys are dopes" Things like that, especially with electrical stuff, scare the daylights outta me.

Thanks for the feedback..... Enjoy the holiday

Oman

You are correct in that the 94A alternator will produce enough current to run everything and charge the battery but only at driving speeds when it is turning fast enough to produce 94A. That's probably why the 140A recommendation because it will produce more current at idle.

An alternator requires about 2400rpms to begin producing decent output current. Typically, the pulley ratio is 3:1 so your 800rpm engine idle is 2400rpm at the alternator. Check a store or 2 and see if any of the 12SI alternators they carry have a performance test sheet included. This would show the current vs rpm output when it was tested. Take your idle rpm times the pulley ratio (use 3 if you don't know) and then check that rpm for the output on the curve. You need probably 55-60A to maintain battery voltage when idling.

After all this, the discharging of the battery has to be offset by recharging the battery so you just need to know from your driving habits if this could be a problem. If you know most driving doesn't include much idling then it doesn't matter if you're discharging the battery while idling. A 50A discharge doesn't have much effect on the battery even if applied for a few minutes of idling. The alternator will re-charge once you begin moving again and get the rpm's up.

Peter

Thanks again Peter!

Consensus is that it will work....trouble is if I get into a low charge situation with the battey the system gets marginal. Operating both of the fans and charging the battery could get too close for comofort.

I am thinking that IF I go with the 94 amp unit and I have trouble I can always ditch one of the fans freeing up 25 amps of charging potential to rejuvinate the battery. My issue with this approach is that I don't drive the car much and most likely the battery is in need of some level of charge whenever I take the car out.

I am thinking I have the opportunity to step up to a new alternator from an aftermarket source...A friend just bought a Tough Stuff 140 and I respect his technical ability and sense for quality very very much. His choice would likely be my choice IF I move to 140 amp. The issue I have with that choice is that it is not a GM alternator. Parts might become problematic at some point in the future and I don't like that idea..on the other hand I don't like the idea of having marginal charging capacity in the mix eather.

Decisions decisions decisions. My head tells me go with the 140...my gut tells me..."It ain't GM" and that gives me heart burn. Then my head tells me "Yeah but the GM is only available in a Delco Remanu. and that ain't new where as the Tuff Stuff or Power Master if I went that way is new!

Decisions Decisions Decisions

Any suggestions?????

Once you're driving down the road you shouldn't need any fans at all so that'd be the time to charge the battery. Knocking it down to even 1 fan should easily allow the 94A alternator to work.

Personally, I don't really like 1-wire alternators much. I like having the idiot light and remote voltage sensing wires.

From the tech refernece you can get a 105A CS type alternator if you ask for one from a 1988 Olds Firenza 2.0L engine with EFI and AC. The CS is supposed to produce more current at idle than the 10SI or 12SI so it may be a better choice.

I haven't any experience with a 94A alternator and this type of load to see what happens. But, I'm trying a 20A fan (have to actually measure it still) on a 10SI alternator (63A maybe?) and initial voltage testing shows me that the voltage at idle is good with just the fan and still OK with the fan and lights. This would likely ratio up to what you're proposing. I still have to do further testing.

Peter

The more I read about the one wire the less I like them. Just seems like a lot of work for a cleaner 1 wire install. I guess it is neat but if a few extra wires on the alternator were all I had to look at might be I would remove them. Given all the clutter under that hood a couple of more wires just don't matter. As for the electrical issues related to one wire your thinking is kinda the same thinking I am doing.

I gotta upgrade because I only have a 37 right now and I am leaning heavily to the 140 Tuff Stuff or Powermaster. Just seems like the hot ticket. I hope that is not HOT in terms of fire just hot interms of the right way to go. Since I cant get 100 + amps out of my lowly 37 amp alt I am just gioing to save it as a spare for my Vette and move to something new.

The Tuff Stuff and Powermaster are just about the same price as the reman. Delco 12 SI if you consider that I have no turn in core against the Delco purchase so I guess it is a no brainer?

Anyone have experience with Tuff Stuff or with Powermaster???? I hate opening that can of woms but forewarned is forearmed.