The Stovebolt Site Forums The Shop Area The Electrical Bay Downside to a high amp alternator?

I probably don’t NEED anything more than a regular old GM 10si. But stumbled into a deal for a 12si rated at 150 amps.

Obviously, if I was going to put very high loads on the charging system, I would choose my wire gauge accordingly and fuse or breaker things for that sort of amperage. I will make sure my wiring is somewhat oversized, regardless. For conversion purposes, let’s just assume I would never need any more charging capability than the 60ish amps of a 10si.

Is there any downside to having “too much” alternator? I assume it takes more power to turn one, but isn’t that proportionate to the load placed on it? Or does it turn harder all the time?

It won't take any more power to turn one than a smaller output alternator given the same amp output. Like you said, proportionate to the load placed on it. Maybe a little more load when revving the engine because of the possible higher inertia from more mass in the rotor, but that's not significant.
You can have it available for when you install the gnarly stereo system in it so you can blow the doors off with the volume.

There will be a heavy surge current immediately after startup to recharge the battery from the drain of the starter. Once that is accomplished the alternator will only produce enough current to meet the load of the ignition, lights, etc. and keep the current going into the battery high enough to maintain the voltage at whatever the electronic regulator is designed to do. Usual current flow into a fully charged battery will be around 5-10 amps, regardless of the max capacity of the source- - - -generator or alternator. Upsize at least one wire gauge on the main charging lead over what's needed to handle the smaller alternator- - - -maybe 8 instead of 10, for instance.
Jerry

Exactly!

Just what Jerry said. I have a 100 amp alternator. I don't care about a stereo system but I have A/C and I have 2 electric fans...one that works based on radiator temperature and one that runs constantly when the A/C is on. And there are reasons I don't just use one fan for both that have to do with the design of the AD radiator. I also have HEI and that will have some inrush current at first. And I have electric wipers and dual horns. It works fine for me.

The 150 amp. alt. will put too much load on the belt. The 6 cyl. engine has a very small contact area on the alt. pulley. The belt will squeal & glaze the belt & pully. All the late model vehicles with high amp alt. use Serpentine belts.
Most of the time the bat will not be low enough to put a large demand on the charging system, but we all know at times we leave something on for a while or it takes longer then normal to start the engine especially in cold weather or after it has set for a long period of time. That is when a large amp. flow takes place.
You might get by by over tightening the belt but that puts a stain on the water pump.
The 60 r so amp alt. is all you need for the standard accessories. The original gen put out about 30 amps & 0 or almost at idle & we drove them for many years that way.
The alt. is a tremendous improvement but there is no reason to go overboard.

George

Tell me about the radiator design thing….

I haven’t pulled the trigger on this yet. I’ll probably wait too long and the opportunity will pass anyway

It is a 3 core aluminum radiator I bought on Amazon years ago. Sitting on the back side is a Spal puller fan (adjustable---thermostatically controlled) and this mounts onto a thick aluminum shroud I bought from Old Air Products. It has 4 corner vents and rubber flaps that drop down when air flow is light. Then the A/C condenser sits in front of the radiator and in front of it is another (smaller) Spal fan which is wired to automatically go on any time the compressor is engaged. The fact the radiator is 3 cores and has smaller gaps between the fins than the original by apx 40% means it needs some help with airflow to make it as efficient as possible...the old (original) radiator/fin design had plenty of airflow, however the fact air passed through faster meant it gave up less heat in the process. Especially in slow moving traffic. That is where you notice the benefit of an engineered fan greatly. And there is with the A/C extra heat being generated. Sort of the same thing as your home central A/C unit and the fin design it uses. The condenser and compressor outside today usually use 3 bladed (some 4) fans which are larger in diameter, spin faster and suck a larger volume of air through fins which are larger but closer together than the old style which you could see through. They do this to maximize the SEER. Most of them use fins which wrap around the refrigerant tubes in a circular fashion so more heat can be thrown off faster. If you go out there in the dead of summer, when the compressor is running you will feel a good amount of heat being thrown off out the top (or side if you happen to have a horizontally oriented system)...all a part of the effort to make it run less frequently.