hot rodding an alternator, how?

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
 
Last edited:
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.
 
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!
 
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.
 
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 $$$.
 
Last edited:
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
 
Last edited:
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

Again, up at the outputs you are looking for just rewinding a stator isn't going to cut it - think 20hp through the poxy little bearings, shafts etc that are in even a good quality commercial vehicle alternator - you are talking about exceeding design limits by factors of 100. It could literally rip the alternator apart before it acheived full output. As for 900A capable diodes - last time I saw anything like that they were mounted to a chassis rail of an 18-wheeler to get enough cooling.
 
im not trying to go the entire 900amp in just one shot. right now i have room for 4 alternators and depending on the day of the week i might have all 4 running at 150 amp each im right around 600amp (atleast on paper). if i can just boost them by 50-100 amp output each ill be right in the ball park of where i need to be.

there seems to be no shortage of stuff like this on ebay or around the internet

300 Amp High Output Suburban Chevy Truck Van Alternator: eBay Motors (item 250329603263 end time Nov-11-10 10:51:41 PST)

they claim 300 amp and i guess it all comes out that 4mm bolt on the back? when i see stuff like this it atleast made me wonder if these claims are remotely possible or if they are just flat out lies. or i even just wonder what they could have done to this thing to pretend it can make that much power for any amount of time.
 

infinia

Member
2005-05-15 9:51 am
SoCal
Marine designers have been dealing with this for years, Most modern designs have 2 seperate charging circuits, one for the stock starting battery. And another using a high output alternator for the deep cycle house batts. Remember the max amps is a percentage ~ 10-20% of the total AH of the house bank to keep from overheating the batteries and retain their lifetime. see http://www.pyacht.com/balmar-alternator-guide.pdf
 
I guess my ?? would be, how long will this load last, how much time its on/off.
you can get a lot of strong alts, most to me are known from car audio, that will deliver power easy. Then you have few batterys and you can draw a lot of peak power and also constant

How big is the engine you think on putting on alts?

under 1500$ I think you could co it easy
 
Last edited:
the engine im using is a 425hp caterpillar, its a commercial truck. my running lamps can be on for 12 hours at a time. its only 2kw but still i would like a few kw all day long. the car audio ones i have seen i wouldnt trust they seem to physically small, the ones i have seen seem to be designed to fit into a honda.

as aardvarc pointed out im drawing serious horse power from my engine im not sure how a honda could have the flywheel horse power to just donate 20 hp to an alternator load without stalling. my engine is somewhere around 10 times larger and it bogs right down and starts adding fuel to compensate for engine loading.
 
i dont have any pictures but it isnt very spectacular. its just 6 bulbs like this one on my mirrors (3 each side)

GE 45220 4522 PAR46 13V250WLNDG Light Bulb - Buy 250 watt (19.2 AMP) 13 volt PAR46 Screw Terminals Base #4522 Sealed Beam Incandescent GE Light Bulb Online at ServiceLighting.com

then just 4 of these on the bumper but each one holds 2 bulbs and i swapped them out for 100w H3 bulbs instead of the 55 watt

http://www.princessauto.com/trailer...53-6-1/4-x-4-3/4-55w-utility-flood/spot-light

its a commercial truck and i drive into pretty remote parts of northern canada, plus its fun to wear sunglasses while driving at night. (i look super cool). the round sealed beams dont last very long but they are cheap and bright (around 20$ each)

so...
250w x 6 = 1500w
+
8 x 100w = 800w

for a grand total of 2300w
 
I thought that the lack of total darkness near the north pole at certain times of the year was due to the tilt of the earth. Now we know it's just you driving around at night.

In a few more years, high power LEDs will become cheap enough to replace most of the incandescents you're using now. That will decrease the current draw and increase the life span.

Have you thought about using HID lamps? They last much longer than incandescent lamps.
 
What a load of uninformed fantasy...

Cheers!


Nice to met you aardvarkkash10.
I was generalizing my statements please don't let that confuse you too much. And most of my reference was based on modern IRA type off the shelf gear < keeping it affordable and away from the more complicated setups>

IRA type alternators do shut off from excessive heat caused by excessive load factors like excessive shaft speed and load. They offer a safe albeit limited and controlled 12 volt management package and they are off the shelf items. Electronic shutdown has nothing to do with clutches, but it does the same as a clutch would if it were mechanically feasible.
The days of relays mounted on the firewalls controlling alternators three feet away are pretty much gone by the way side, as out dated and unreliable, especially in today's advanced electronically controlled times we live in. Plus most modern engine control systems will not allow for the wide margins of operation that older less sophisticated system have to offer.

plus in most cases where very high power is needed on a constant basis most setups have small generators mounted on board that deliver power regardless of vehicle engine speed issues. And vehicle engine speed is very relative to any alternators output hence the over drive pulley used by most heavy duty alternator setups so the alternator will develop higher then normal output power at idle.

nice to met you and I hope this clears up some of the fog I apparently generated that caused your comments..Cheers...