Altenator Sizing

robins44 · Member Joined: 29 Dec 2007 Posts: 632 18797.16 points

1990 Chevy K1500
Optima 750 cca yellow top
Msd 6al2 box
Msd multi step retard box
Two holley hp 150 pumps, 1 running only unless spraying
1 flex a lite syclone fan, may change later
Normal stereo stuff

Have just a cheap old school 40 dollar alternator on it right now and when at the dunes with the fan running continuously the voltage would drop off. Looking at powermaster alternators and not sure which one to get. Money is not an issue but is a big 200 amp alternator way over kill? 1 wire or 3 wire?

Truck was getting up to 220 on test hill at silver lake when running up to the top on a cool 70 degree day, and I want to make sure that the fan is getting full power before I go dropping big bucks on a twin electric fan setup.

As far as the getting hot, I have a 160 degree thermostat, high volume weiand water pump, and a summit aluminum radiator, fan is bolted to a shroud. Can get pictures, cruises down the road at 180 190, touches 200 when romping on it.

Thanks

Cody

clay · Posted: Fri Aug 29, 2014 5:26 pm Post subject:

One thing to try is go by a starter / alternator shop and ask what they can do to help you out. Sometimes they can upgrade what you already have to a higher output setup for less money than buying something else outright and end up with better components. What does the drive ratio (pulley sizes) look like? Completely factory stuff or aftermarket? Hopefully not an under drive setup. On the fan - where do you get power from? They can easily get into the 30 amp range and a supply directly from the battery through a relay is almost a must. 10 ga. wire would be minimum size to run to minimize voltage drop. Clay

robins44 · Member Joined: 29 Dec 2007 Posts: 632 18797.16 points

Fan is wired up with a summit relay kit. The draw on that fan is 17 amps. Don't really have the time to swing in to a alternator shop, was hoping to just order something from summit. Nothing invested really into old alternator, and don't want to wait for them to build it. Just don't know if I need something like this lol. Does look pretty b.a. though!

http://www.summitracing.com/parts/pwm-478068

Cody

SMOKEmUP · Posted: Sun Aug 31, 2014 1:46 pm Post subject:

Do you what size the alternator is now?

10sec.et · Posted: Sun Aug 31, 2014 6:27 pm Post subject:

unless you have something like a Lincoln Navigator with a high wattage stereo system, there is absolutely no reason to run that much alternator. about half of that will do just fine. expecially on what youre doing. stay away from one wire alternators too. they dont charge for shit at low speeds.

robins44 · Member Joined: 29 Dec 2007 Posts: 632 18797.16 points

No clue what size, just a cheap reman old school gm v belt altenator from local hot rod parts store.

Paul P · Posted: Sun Aug 31, 2014 9:30 pm Post subject:

Simple to do a current survey on your car. Connect an inductive clamp on current meter over the positive cable. Turn on everything in the car and see what the drain is. Add 50 % or more depending on the selection of sizes available and that is the alternator size you need.

I think the Chevelle had something in the 45-55 amp range for totals. What is typical is 100Amp. I have a 94Amp out of a late 80s GM vehicle for the car now. Works fine. No issues.

Paul

af2 · Posted: Tue Sep 02, 2014 3:56 pm Post subject:

robins44 · Member Joined: 29 Dec 2007 Posts: 632 18797.16 points

Thanks guys, that was exactly what I was looking for. So far so good with the yellow top, some love them, some hate them.

Cody

10sec.et · Posted: Thu Sep 04, 2014 10:35 pm Post subject:

i dont like the Optima batteries. if they fully discharge, they dont like to come back. you really need a charger specifically for AGM batteries. im happy with my walmart battery. i can get a replacement any time anywhere.

Big Dave · Posted: Fri Sep 05, 2014 9:01 am Post subject:

A 200 Amp alternator isn't overkill electrically as it will only out put the amount asked for by way of the field windings being energized. So a 200 Amp alternator will cheerfully provide you with 55 Amps all day long.

The disadvantage of that large a capacity is in the physical size of the case (will it bolt in place of your current SI-10 Delco now, or is the case larger in diameter?), and of course the cost. You can actually weld with a 200 Amp alternator to do field repairs if set up properly. Which is another point against the 200 and that is if your wiring can support that much current flowing through it without melting. You will definitely need to go to an 8 gage wire to the battery from the alternator as the factory sized 10 to 12 gage wire will melt at full out put (older vehicles used smaller gauge wires as they had only a 36 to 64 Amp capacity alternator to deal with).

Big Dave

10sec.et · Posted: Fri Sep 05, 2014 11:49 pm Post subject:

ok Dave, you have my interest.... tell me how to weld with that Very Happy

good point on the 8 gauge wire. i always add that when i wire a car regardless of the alternator. dont forget to put some sort of fuse or fuseable link on that wire though. i caught a car on fire that had the charge wire too close to the header.

Paul P · Posted: Sat Sep 06, 2014 7:12 pm Post subject:

if he uses the factory 1990 wiring the system it should hold fine for 100 amps as that size was available for those years. I do agree if he goes big he needs an 8 gauge wire.

Big Dave · Posted: Sun Sep 07, 2014 9:58 am Post subject:

Paul P · Posted: Tue Sep 09, 2014 12:57 pm Post subject:

No current control kind of makes it good for just about nothing but heavy gauge steel in the range of it's output.