Choosing correct size alternator

[vintovka]

I have what i believe to be a standard oem 65 amp alternator on my 54 with a 350 crate in it. Biggest amp draw is the big spal fan at 40 amps. ALt light came on occasionally with fan use. Think i need a bigger amp alternator. See there's 100, 120 and 150 available. Suggestions?

[kwmech]

100 would suffice.

[vintovka]

Thanks. What i was thinking. Its a shame however i have a brand new in the box 65 amp sitting on the shelf. Would seem a waste of time the swap it out with same results. I see lots of 100 amp alts everywhere from amazon, summit ect. Any recommendations on brand that's reliable and cost effective???

[RustyPile]

I put this one on my '71 BBC.. Powers everything, including twin fans on the radiator.. Best part about is I didn't have to dig around on Amazon or any of those other online sites.. Got if from a locally owned independent parts store right here in town...

https://www.remyautomotive.com/singl...?partNum=20223

[truckster]

I've used DB Electrical starters and alternators for several years with good results.

[vintovka]

Thanks looking at them now. So if i have a bigger alternator it might not drop my voltage down to 12 volts when fan is engaged???

[RustyPile]

Originally Posted by vintovka

Thanks looking at them now. So if i have a bigger alternator it might not drop my voltage down to 12 volts when fan is engaged???

You don't need a physically "bigger" (larger) alternator.. What you need is one with higher output, one that meets the demands of your electrical system.. 10SI and 12SI alternators are all basically the same physical size, but come in varying output (amperage) ratings.. These two designs have the voltage regulator built inside the alternator, commonly referred to as "internally regulated". The alternator described in my link should be of sufficient output to keep up with your entire electrical system. If your charging system is designed for an external voltage regulator, you'll have to make some minor changes to the charging system wiring..

[Tom]

Just put the biggest one in and then you don't have to worry ever. Simple enough.

[Dead Parrot]

The stock 3 wire 12SI has a few more amps of output at idle speed compared to the older 10SI. 4~7 IIRC. Won't cover the 40amp from your fan but might limit the lights dimming when you are at a stop light. 94 amp seems to be one of the stock sizes. The 12SI case has better cooling as well.

3 wire has the advantage of being able to connect the voltage sense wire to the junction box and make up for any voltage losses in the main alt wire.

You probably want to go with a larger main wire as well.

[vintovka]

Used an online calculator which estimates my load at 83 amps. So far this looks best and probably won't require heavier wire. Just hope i can just hook it up like the existing 2 wire. This may be the one i use:

https://www.summitracing.com/parts/tff-7127d9

[RustyPile]

Originally Posted by vintovka

Used an online calculator which estimates my load at 83 amps. So far this looks best and probably won't require heavier wire. Just hope i can just hook it up like the existing 2 wire. This may be the one i use:

https://www.summitracing.com/parts/tff-7127d9

Not knocking Summit at all, I buy from them all the time... That is NOT the alternator you want.. It is a 10si and the one you want is a 12si.. Same physical dimensions but way different on the inside.. Also cooling is much more efficient.. I can buy two 94 amp 12si alternators at the local parts store for the price of that Summit "high performance" alternator....

At 83 amps, yes, you'll at least need to increase the wire gauge between the alternator and battery.. Upgrading the charging system is very seldom "plug-and-play"....

Not sure what you mean by "existing 2 wire".. Where are these "2 wires" connected on the alternator??

What part of the suggestions posted on this thread do you not understand?? Please ask questions.. A poorly designed and/or altered electrical system can lead to a fire or meltdown..

[vintovka]

Thanks. Will post some pics soon of what i have right now.

[vince1]

My go to retrofit alternator is a CS130 as can be found on an 89 Pontiac Safari. It has the V pulley or for other applications there is also the serpentine pulley. They are around 100 amps and I find that they charge much better at idle than the older style 10si's.

[vintovka]

Took all the advice and visited local alt/gen repair guy. He tested output at battery and right at battery. Said the wiring done by the much mentioned Oregon pot head mechanics was really bad and needed redone. Also said alternator is like 20 amps to small. Recommended all new 100 amp with 8 or 9 gauge direct to battery. Has only 12 and it looks well cooked. Will proceed after next SS check.

[vintovka]

Since last posting i broke my rule and got talked into a 93 amp alt from NAPA see link below. Yes i read them the riot act and they are well aware i have a hot line to some top NAPA guys so they assure me its wonderful and they will honor the lifetime guarantee. Apparently they have been listening as losing market share does get your attention. It weighs much more than the original and is listed as a 33si. Has a plastic fan and a ground lug. Now planning to run a number 4 direct to battery or starter and a number 9 to main fuse. Your comments advice recommendations and possible castrations are welcome.

https://www.napaonline.com/en/p/RAY2134356

[jeffahart]

Originally Posted by vintovka

Since last posting i broke my rule and got talked into a 93 amp alt from NAPA see link below. Yes i read them the riot act and they are well aware i have a hot line to some top NAPA guys so they assure me its wonderful and they will honor the lifetime guarantee. Apparently they have been listening as losing market share does get your attention. It weighs much more than the original and is listed as a 33si. Has a plastic fan and a ground lug. Now planning to run a number 4 direct to battery or starter and a number 9 to main fuse. Your comments advice recommendations and possible castrations are welcome.

https://www.napaonline.com/en/p/RAY2134356

I have a 140 amp alt. I run a #4 straight to the battery and use an inline 200A breaker. I have an old electric winch and onboard compressor. I have potential for pretty massive power draw, I use #4 ground wires also. But for you, over kill on the big #4 can't hurt... as long as you have your hands on it and you can keep the #4 out of the way. I lug and slug all the connections and use mil spec battery terminals.

j

[RustyPile]

Originally Posted by vintovka

Since last posting i broke my rule and got talked into a 93 amp alt from NAPA see link below. Yes i read them the riot act and they are well aware i have a hot line to some top NAPA guys so they assure me its wonderful and they will honor the lifetime guarantee. Apparently they have been listening as losing market share does get your attention. It weighs much more than the original and is listed as a 33si. Has a plastic fan and a ground lug. Now planning to run a number 4 direct to battery or starter and a number 9 to main fuse. Your comments advice recommendations and possible castrations are welcome.

https://www.napaonline.com/en/p/RAY2134356

33si??? Never heard of such a thing.. "33si" isn't mentioned anywhere on your link that I can see. The "plastic fan" and grounding lug is common to all 12si alternators.. If you follow the link I posted in post #4, you'll see the Remy is exactly the same as the one you purchased from NAPA.. I paid $49.84 for my 12si 94 amp alternator.. And my alternator has the same lifetime warranty... Having said all that, I'm glad you got their attention, and talked them into adjusting their prices...

[vintovka]

Originally Posted by RustyPile

33si??? Never heard of such a thing.. "33si" isn't mentioned anywhere on your link that I can see. The "plastic fan" and grounding lug is common to all 12si alternators.. If you follow the link I posted in post #4, you'll see the Remy is exactly the same as the one you purchased from NAPA.. I paid $49.84 for my 12si 94 amp alternator.. And my alternator has the same lifetime warranty... Having said all that, I'm glad you got their attention, and talked them into adjusting their prices...

Says 33Si on spec sheet that came with it. I weighed it and it like half again the weight of the old 12si. It is the heaviest one i ever installed and arms are still recovering. After all i paid $78 OTD. which is about "right" given the recent devaluation of the dollar. Been to the supermarket lately?? Will add i thought it weird they and i felt better it was made in Mexico and not china, and it was available. May be able to finish running all the wiring today and will report back if anyone cares. Mechanics in the 4th Quarter is a real challenge.

[RustyPile]

Originally Posted by vintovka

Says 33Si on spec sheet that came with it. I weighed it and it like half again the weight of the old 12si. It is the heaviest one i ever installed and arms are still recovering. After all i paid $78 OTD. which is about "right" given the recent devaluation of the dollar. Been to the supermarket lately?? Will add i thought it weird they and i felt better it was made in Mexico and not china, and it was available. May be able to finish running all the wiring today and will report back if anyone cares. Mechanics in the 4th Quarter is a real challenge.

OK, I did some research. There is a 33si series alternator, but it's certainly not the one in your NAPA link....
It's this one..

https://www.jittruckparts.com/delco-...ing%20Shopping


It's a Delco Remy 24 volt unit for big trucks. and it is a heavy piece.. Certainly not the alternator for your truck.. Sounds more like they spoon fed you some NAPA hype.. You go ahead and put it on your truck and enjoy the fireworks when you hook it up.....

[vintovka]

If you scroll down the specifications on the attached link it reads that it is a 33si and 12 volt. The second link is to the Delco specs on 33si type alternators. The come in both 12 and 24 volt and supposedly much better than the 12si. Interesting to see that si numbers go to over 40 now and that all are considered heavy duty. After 50 years as a registered professional engineer i tend to believe facts over conjecture. Any further comments, inquiries or information on this thread have been moved to my signature link below.


https://www.napaonline.com/en/p/RAY2134356

https://www.delcoremy.com/alternator...el-family/33si