hot rodding an alternator, how?

[scampo77]

im not sure if this is the correct forum or not, but where can i find out more about alternators specifically how to make them produce more power.

can anyone comment on what the choke point of an alternator is? physical size? rectifiers? etc...

[alexcd]

I would try a car audio forum, but what do you hope to gain? Voltage? Current? Both? If you plan to dismantle an alternator be aware the voltage pre-regulator is very high and dangerous. Don't go probing around!

[1moreamp]

physical size? rectifiers? etc...

You got the picture, most high output units are cut down 18 wheeler 24 volt versions reset for 12 volt at very high current. They get hot they shut off just like car amps, so size is important for heat emission surfaces, and higher current diode packs which are internal to the unit. Other then that its the pulley on the shaft which determines where the power is made on the RPM curve.
Except for the IRA units not too much has changes in the last 50 years. About the only thing that has change drastically is the demand we put on them nowadays.... I don't rebuild them. I buy what I want from RV sources etc...Hope this helps some


Oh a fast hot rod is to change the pulley on the shaft. This increases the rpm of the unit at idle so the alternator has a higher output. BUT it will increase shaft speed and at high engine RPM the alternator will most likely shut off due to excessive shaft speed

[scampo77]

i rebuild alternators all the time and im quite familiar with the different parts but i have never given any thought to the parts im changing out for new ones. the alternators i have now are huge maybe a foot long and a 10 inch diamater. from asking around to starter/alternator guys they all seem to be saying the same thing "physical size counts" but these ones are rated at 150amp. i see teeny tiny ones in car audio magazines and ebay rated at 300 amp and i got to thinking how this is done. i cant imagine they would stand up to that for very long before melting off of the engine.

i am still trying to retain the 13.8v but i need it to be closer to 6-900 amp supply. my engine only revs to 1700 rpm anyway and i suppose im not opposed to changing pulleys, but i was really hoping to find the difference between the amperage ratings of these alternators.

[aardvarkash10]

Originally Posted by 1moreamp

physical size? rectifiers? etc...

You got the picture, most high output units are cut down 18 wheeler 24 volt versions reset for 12 volt at very high current. They get hot they shut off just like car amps, so size is important for heat emission surfaces, and higher current diode packs which are internal to the unit. Other then that its the pulley on the shaft which determines where the power is made on the RPM curve.
Except for the IRA units not too much has changes in the last 50 years. About the only thing that has change drastically is the demand we put on them nowadays.... I don't rebuild them. I buy what I want from RV sources etc...Hope this helps some


Oh a fast hot rod is to change the pulley on the shaft. This increases the rpm of the unit at idle so the alternator has a higher output. BUT it will increase shaft speed and at high engine RPM the alternator will most likely shut off due to excessive shaft speed

What a load of uninformed fantasy...

Alternators are rated at output current - typically 55amps or greater.

THE "choke point" as you put it is the winding of the stator - the outer ring in which the current is developed.

The stator is wound to produce a particular output current - the output voltage is regulated, typically elecrtonically. The combination of wire gauge and winding design in the stator sets the current output.

Obviously everything downstream from the stator has to be up to the job of passing that current - diodes, cabling etc.

Most manufacturers have alternators that are supplied in a range of output capabilities - say a 55, 70, 90, and 110 amp, all with the same basic design, just different stator. Often there is no externally visible difference between them. Sometimes the high output ones have a slightly larger stator.

The output rating of the alternator is all well and good, but don't forget that at 110 amps @ 14 volts you are trying to pass a serious current through the B+ cable to the battery (and by implication, from the battery onward). This is current you can arc-weld with and far beyond the design spec for the original cable. Fires have happened because of this. Its pointless upgrading the alternator without upgrading the B+ cable SIGNIFICANTLY.

On top of that, the alternator is not designed to supply its full output continuously - its design duty cycle is probably closer to 25% maximum.

Size, while being important for efficiency of generation (the greater diameter the better) is pretty much irrelevant for cooling - that is acheived by the fan which pumps air through the alternator - diodes first, then everything else downstream of them.

They do NOT shut off when they get hot - they just get hotter and hotter until they fry.

Most alternators will put out around between 1/2 and 2/3 of their design maximum current at engine idle if they are pulleyed correctly - its pointless putting a smaller pulley on to try and acheive greater output at idle as you will probably then exceed the maximum rotor RPM at high engine speeds, leading to catastrophic failure of the alternator's bearings and/or rotor.

They do NOT shut off at high shaft speed - they don't have a clutch to acheive this fantasy effect - they just keep on spinning until the cetrafugal forces cause them to explode.

Sigh. Find a good qualified auto electrical specialsit to get some advice for your specific model of car and requirements.

Cheers!

[aardvarkash10]

Originally Posted by scampo77

...but i need it to be closer to 6-900 amp supply. my engine only revs to 1700 rpm anyway...

900 amps at 14 volts is 12.5kW!!! Thats around 20 HP in old speak! WTF are you running - the Grateful Dead's arena rig? In a steam locomotive?

[scampo77]

I'm compensating a lot for loss and i would really like to aim for the 1/3 to 2/3 loading and not the full peak of the 12kW, and the redundancy of multiple alternators is great.

i have spoken to quite a few alternator guys and it arouses quite a few raised eyebrows and even yells to the back of the shop "hey ed come up here for a sec you have to hear this!!" but all of them are in the same position as me, which is more of a repair technician and not much about the design aspect. so its why i ended up coming here to see if i can figure out a field winding to rotor ratio (if such a thing exists). then it would be just a matter of finding large enough rectifiers. some of the other ideas are military grade 300amp alternators at 1600$ each but guarantee 300 amp at 12v for 5 years 24/7 no problem at all, also shaft driven generators or even someone recommended an a/c generatror (im not sure how that would work). all of these seem expensive or not really worth it, and it seems easier to just keep bolting 150 amp alternators all over my engine

the load is too much to explain here but to start its, 2kW of driving lights and 6kW of radio plus welders and other tools.

[aardvarkash10]

what is your load duty cycle? Your most practical solution may be large deep cycle battery bank and a decent 300A alternator.

Once you are over 300A you are in shaft drive territory really - getting over 5kw through a belt drive system is expensive and complicated to acheive reliably. Certainly you'd be talking either mutiple V belts or possibly toothed belt a la a supercharger. THink $$$.

[scampo77]

thats what i have now, I'm using forklift batteries

i dont mind machining chain or gear drives to drive a a shaft, but i would still need to know how to work with the field windings vs rotor strength. i would think driving a system would be the easy part and building or buying the field windings/rotor is what seems to be hanging me up. all the other shaft driven stuff i find seems to be like a generator to make 110v ac so not much of a model unless i want to start with switching power supplies or transformers which is a whole other mess

[aardvarkash10]

In that case I suggest a direct coupling to the Hoover Dam...

Aircraft stuff may be interesting to you - often @ 48V which would be easy to distribute to your forklift batteries, and available in high output continuous rated. Not cheap however!