Dual alternator?

[FyreDaug]

What concerns do I have to worry about with this?

I have my parts car that has an alt that I will be making brackets to bolt to where the AC normally would, and run an ac belt (with crank pulley) to turn the alt.

Coupel things:
Do both alts need to be the same (they will be anyways)
Do both alts need to be turning the same amount (incase the ac pulley size differs)
Is it okay to run 2 alts to 1 batt? (considering my system is large, a full carputer, 5.1 home theater with 200w to sub. Closing in on close to 55 amps. Major headlight dimmage and what not. Figured this is the quickest, cheapest and most unique way out.

Anyone have anything they would like to add? I plan on doing this within a week. Tomorrow is hopefully stage 1 of my exhaust (making header) :Owned2:

[88eyeguy]

the alternators HAVE to turn at the same rate. DO NOT HOOK UP TWO ALTERNATORS TO A SINGLE BATTERY, you will overcharge it (see results below). connect the second alternator to a second battery in the trunk (or wherever you prefer to put it)and run your audio off of that. be sure that both pullys are turning at the same speed, if that pulley is turning to fast, you will either boil out the electrolyte in the battery or cause it to explode, or both.

i have only seen dual alternators installed once before so just a warning: if you are not familiar with wiring or the charging system, get someone to help you install it all. you could seriously hurt yourself if the installation is incorrectly performed. ever gotten battery acid on your arm? Do your homework, and take it slow. haste makes burned out cars with this stuff.

Oh, and good luck if you decide to do it : )

[FyreDaug]

I was going to use a dry cell battery and run both alts to it. Are you sure it would overcharge and cause damage? What about an alt rated at 120A, Im just simulating that with 60x2. I'm pretty sure I cant run them in series so parallel would be the best bet (or the only one)

[88eyeguy]

just because it's a dry cell doesn't mean that you can't overcharge it. alternators provide enough current to run the electrical systems, but the current has to be stabilized by the battery. a battery can only flow so much current at one time. you would get extra power for the ten minutes (or less) before you smoke the batt., but it won't be worth it. your best bet for two alts would be to use a second battery, man. sorry.

*EDIT* just saw the thing about 120A alt. 120 amp alternator would be a better option (less wiring, no explosions, no fires, everybody's happy.) pretty sure there's a how to on using the 4th gen 90 amp, and you might be able to get it rewound to put out close to 120...

hope that helps

[FyreDaug]

Im sure if anything if I'm gonna use 1 alt I can get any alt to work.

But why would a 60x2A output be really bad compared to 120x1A? Its still 120A output regardless

[POS carb]

The only think I can think of is the alts may not have diodes that are beefy enough to handle another alternator running parallel or their voltage regulators may interfere with eachother (i.e. if one is set a bit lower than the other it'll never do any charging)... That battery blowing up idea is possible too but w/e man its your car; I wouldn't do it and I've done crazy rigs to my electrical system!

FYI I run a custom wound alternator with a huge RV battery in the trunk and a 3 farad capacitor... absolutely no dimming.

[FyreDaug]

Thats a little more expensive than I was thinking. You see, I have the alt. The cables. And the bracket material. Just need to do some welding/bending and drilling.

What other alts are around 100A? I'll be able to make it work aslong as it spins the same direction with any bracket. Theres the possibility of a 4th gen one that I can just throw in there, but I was hoping for a couple extra A than 90.

[88eyeguy]

your battery can output hundreds of AMPS, yes. amps do not (over)charge batteries, volts do. the battery supplies the current (amps) needed to start the motor, then it supplies the electrical systems with power as well. the battery would drain itself if not for the alternator. the alternator is only connected to the battery and to ground. it produces AC voltage which it rectifies into DC voltage to use on the electrical systems. it then flows the current back through the battery, both to charge it (a constant process), and to provide the extra power needed for the car. since this is a constant process, neither the battery nor the alternator has any kind of "automatic cutoff" for when the battery is fully charged. if you supply to alternators to one battery, you will not only double the amperage, but the voltage as well. this is what would cause a battery to overcharge and, quite literally, go boom. that is why the 120 AMP alternator is a good option, being that it will only supply the necessary voltage to the battery to maintain the proper charge.

whew...long breath.

Andy

[FyreDaug]

Well that makes sence then, I guess I must have forgot about double voltage aswell. What about an external voltage regulator? Or somehow.... wiring them in series

[88eyeguy]

a voltage regulator could be an option too. i wouldn't suggest wiring them in series, since you could end up with the christmas light problem: one goes, and it all goes down. then everything would be running off the battery. that's up to you though.

Andy

[FyreDaug]

Where would I find a regulator that could do what I need? it would be from 27-29V input and output 14.5 right?

[Versanick]

Voltage regulators are not expensive. Two alternators won't overcharge a battery, just like one won't. You can, in fact, disconnect your battery once the car is running. If you're afraid to overcharge it, run 4 gague wire from your battery to a switch that you can turn off while the car is running.

So remember the points:
You don't need a battery for the car to run once it is running, probably unless your stereo is hitting as hard as it can and you're idling at 500rpm..

An alternator won't be bogged down channeling or creating electricity if nothing is taking electricity. You don't need an alternator for your car to run, but your battery will die in short time.

Your battery will not overcharge. It doesn't overcharge on the highway with one alternator. It won't overcharge with two alternators. Newer batteries won't take charge past a certain point. It's not chemically possible.

Voltage regulation is a good idea. Your car already does that, but good luck with the wiring. Consider running 4 ga wire from the second alternator to a switch. Keep the switch off most of the time, and have it on when your stereo is on. If you want.

There are a million ways to do this. I've never seen a battery overcharge outside my cousin overcharging his battery for his outboard motor on his fishing boat. Different batteries.

If you guys have seen some battery overcharging with a certain type of battery, I'd like to see it. I would suggest that it won't happen.

edit: And your voltage won't double. Your potential amp output will. Remember, a 120A rated alternator won't CONSTANTLY put out 120 amps to everything in your car. your car doesn't need that much to run. It will put out high amperes to a dead battery, a pounding stereo, or some other such high-drain activity. Take by example when your car is idling at night, and you suddenly turn your headlights on, and your idle drops slightly. Your alternator is THEN encountering the increased 20A requirement, and your engine actually has to work to turn it (in other words, a path for energy to be used is created. electron flow to your headlights is uninhibited by your headlights turning on) or some other such thing.

[FyreDaug]

Will it be a 24V system then?

[Versanick]

12V-14.5V... really all the same. Everything in your car is set to run 12V. More is better, but too much is probably a bad idea. 24V is way too much. 15V will be fine. Your car might be able to regulate the voltage. It's been a long time since I've messed around with alternators. I can get back to you and post again about it.

Some alternators on newer cars come with built in voltage regulation. they put OUT 12-15V, and regulation is taken care of that way. This eliminates a lot of electrical problems that can arise, and have arisen. I don't know what year the cutoff is or about when they got big. Could be brand new.

[Versanick]

Wiring in series is what can give you 24V. Your home and car are all mostly wired in parallel. That way you can turn something on or off without breaking the entire circuit.

Some things are at advantage to be wired in series. I wouldn't think alternators would be on that list.

[FyreDaug]

Yeah theres been some misinformation in here. I missed the part with parallel not giving 24V. My bad.

Anyways, there really shouldnt be any problems with dual alts is there? Would the engine load be greater than say a single 120A alt? I need more electrical juice, but I want to sacrifice the least amount of power I can. If a bigger alt is the best bet, I'll get one out of a 4th gen for simplicity and bolt er in.

[Oldblueaccord]

Yeah theres been some misinformation in here. I missed the part with parallel not giving 24V. My bad.

Anyways, there really shouldnt be any problems with dual alts is there? Would the engine load be greater than say a single 120A alt? I need more electrical juice, but I want to sacrifice the least amount of power I can. If a bigger alt is the best bet, I'll get one out of a 4th gen for simplicity and bolt er in.


Misinformation yeah say that agian. 88 eyeguy you way off on your assumtions. I'd goto the library and get a book on basic electrical principle and read it.

Fyre the easiest and cheapest thing I think you could do to up your reserve capacity (amps) is add another battery to the system. It be cheapest and simplest in your case. Also the Yellow top optima I have runs about 13.2 volts at rest instead of the 12.7 a regular car battery runs.

The next thing would be go with a larger alt. I have recomended serveral times the AC Delco type alt. you see advertised in Summit racing for about $100. There 100 amp rated and a one wire hook up. Meaning there internally regualted and one wire to the battery is all you need. Very popular option with the hot rod crowd. You would have to make a custom mount for it.

You want to make sure your wire can handle the x-tra amp load. Guage your wire accordingly to your amp rating always.

And to finally anwser your question I have actually seen a car with 4 alts. It was on an older 70's Chevy Caprice when I lived in Rocheester NY in the late 80's. The guy had somekinda huge radio setup in this car with like an anteaae I never had seen that went from the rear bumper to the front. I guess it was a short wave.


wp

[Blkblurr]

The real problem with running two alternators is that they must produce exactly the same voltage or you will get reverse currents flowing between the alternators and the batteries. This is not good. If one alt is producing 13.3 volts and the other is 13.6 volts, you have a difference of .3 volts that gets a current flowing when you don't know it. The extra power has to be disappated and this usually happens by heating up something. Usually the regulator until it blows.

[FyreDaug]

The real problem with running two alternators is that they must produce exactly the same voltage or you will get reverse currents flowing between the alternators and the batteries. This is not good. If one alt is producing 13.3 volts and the other is 13.6 volts, you have a difference of .3 volts that gets a current flowing when you don't know it. The extra power has to be disappated and this usually happens by heating up something. Usually the regulator until it blows.

That kind of makes sense, but what about a one way resister through each alt? So the current wont go back (if it actually does)?

It makes sense to me though, but what kind of background do you have that on? I'm pretty sure it would be hard to have the exact same output, even if its mV, its still different somewhere in multi alt cars.

Maybe I should just try it...

[Blkblurr]

That kind of makes sense, but what about a one way resister through each alt? So the current wont go back (if it actually does)?

It makes sense to me though, but what kind of background do you have that on? I'm pretty sure it would be hard to have the exact same output, even if its mV, its still different somewhere in multi alt cars.

Maybe I should just try it...

You would need a voltage regulator designed to have two voltage inputs. and a single output. A one way resister is a diode. It would have to be huge to handle the current of the alts. You then would still have different voltages at the battery or point of connection that would generate heat. My back ground is Electrical engineering with my specialty in automotive assembly and test equipment. It just happens that one of my projects a few years ago was an alternator test line for Ford. I think separate batteries is the best way to go for two alts.

[88eyeguy]

FyreDaug- you have my advice, take it or leave it

Oldblueaccord- FYI, i was reading through my automotive electrical principles textbook while posting; if therefore, you disagree with my information, I encourage you to take up that debate with God or whatever you think is in control of the laws of physics before making baseless accusations against someone you don't know.

End Rant, End Advice, End Post

[FyreDaug]

Okay, but what would the 2 different voltages have to do with anything? They will both be charging the battery and whatever is left will go to the car. I just dont see a problem, I used to have a weak alt in one of my old cars, so I would run the car and have a high current batt charger hooked up to it aswell so I could drive it.

I never blew up a battery or anything, the alt was still giving about 20A (enough to run the car without anything on) and the charger was 25A I think.

[Oldblueaccord]

Okay, but what would the 2 different voltages have to do with anything? They will both be charging the battery and whatever is left will go to the car. I just dont see a problem, I used to have a weak alt in one of my old cars, so I would run the car and have a high current batt charger hooked up to it aswell so I could drive it.

I never blew up a battery or anything, the alt was still giving about 20A (enough to run the car without anything on) and the charger was 25A I think.



Well no alts have voltage regulators built in. Have since early 70's. So they taper there charge off as they battery voltage increase. Old car the voltage regulator was a separate box and :bowrofl: it was actually a mechanical relay in there. The alt. is actually AC and it has a rectifying curcuit changing it to DC voltage. There a neat way to make a AC welder by taping the AC part of an alt. to make a portable welder set up.

Electricians here at work arent sure it be a problem but one had the idea that the second alt. would charge a second separte battery for accessories that way there wouldnt be a conflict if you will.

Fyre Im a little behind the times but there has got to be away. these kids now days with those killer amps and 15 speaker setups are doing it. Could try and see what there up too. My day 6x9's in the trunk where the shit. :uh:


wp

[FyreDaug]

Oldblueaccord, thanks for the input. I know there has to be a way and I want to figure it out.

But again, what would produce more of an engine load, 60Ax2 alts or 120Ax1 alt?

[Oldblueaccord]

Oldblueaccord, thanks for the input. I know there has to be a way and I want to figure it out.

But again, what would produce more of an engine load, 60Ax2 alts or 120Ax1 alt?


Thats a good question but i have no idea. I have heard and seen number that they might pull 10 hp at high high rpms. Alotta bracket racers dont run them because of that. Its gonna be a trade off.

wp

[FyreDaug]

Yeah I just dont know where I want to do the trade off

[88eyeguy]

120A alt. wll pull about 2.82 horsepower under full load. two 60A alternators will pull about 2.78 horsepower.

[Oldblueaccord]

120A alt. wll pull about 2.82 horsepower under full load. two 60A alternators will pull about 2.78 horsepower.

Could I ask where you got these numbers from and at what rpm?

TIA


wp

heres the alts i was thinking of. Its there summit brand.

http://store.summitracing.com/default.asp?target=partdetail.asp&autofilter=1&part=SUM%2D811001&N=4294925143+400304+4294839060+4294880793+42948807 41&autoview=sku

hope the link works its 89$ 100 amp internally regulated.

[88eyeguy]

an electrical principles reference. one hp is roughly equal to 746 watts, and watts are determined by multiplying amps by volts per accessory (i.e. alternator). if you multiply 120A by 14.5 volts you get 1740 watts. then divide that by 746 to determine the number of horsepower. add about 20% for "mechanical and electrical losses", and you get a good estimate of the horsepower required to run an accessory at full load. i'm not sure what rpm though, and i'm not entirely sure that it matters. if it's at full load during idle it should pull the same hp as at 6k rpm.

[FyreDaug]

Nice, either way its not that bad. I figured it would be worse with 2 alts.

[Blkblurr]

Don't forget you twice the mechanical friction from belts and bearings with two alts. You need to add that to the equation.

[88eyeguy]

i think that was included in the 20% addition for electrical and mechanical losses.

[FyreDaug]

Well I will try this soon you guys and let you know the results. I have a digital volt meter in my car (which reads 14.6 with nothing on, 14 with computer, 13.2 when system is cranked, and it dips into 12's with headlights on)

I want to overcome that. I'll let you know later. Anything else I should know?

[mouchyn]

another thing to consider is the weight of two alts vs. 1.

two alts might require .1HP less than a big single alt, but you have to weld up custom brackets, use custom belts, and find a way to make it all fit.

with a single 120A alt, installation will be easier, troubleshooting will be easier, and it will weigh less -- which should make up for the .1HP extra it takes to turn the bastard.

[FyreDaug]

Not neccesarily. The brackets are a breeze to make, I will use the stock AC belt (and ac pulley on the alt) and I'm sure a 120A alt will weigh more than a single stock one anyways.

Plus 120A alt will cost lots of money, this will cost me maybe 10 bucks for misc wiring and some metal to use as a bracket.

[Blkblurr]

an electrical principles reference. one hp is roughly equal to 746 watts, and watts are determined by multiplying amps by volts per accessory (i.e. alternator). if you multiply 120A by 14.5 volts you get 1740 watts. then divide that by 746 to determine the number of horsepower. add about 20% for "mechanical and electrical losses", and you get a good estimate of the horsepower required to run an accessory at full load. i'm not sure what rpm though, and i'm not entirely sure that it matters. if it's at full load during idle it should pull the same hp as at 6k rpm.

When I do the math on this I get the same answer in either case. As one would expect using this formula and calculating in the % of loss. What will be more actual is that the mechanical load caused by the friction of the pulleys and belt will be greater on the dual alts than on the large single alt. This is not taken into account properly by applying a percentage loss.

[FyreDaug]

Well its either $100+ or $10. I think the 90$ in my poor pocket is best right now. I dont wanna wreck this alt by drawing too much off of it, so this is an insurance for me too.

I could also wire up a switch for the positive output of the alt so I can turn it on only when needed, reducing the general load during regular driving and giving me the power when I need it. Its like a Vtec'd alternator. :D:D
Would that work though? It wont see an electrical load when theres no + going out of it so it would spin freely right?

[Blkblurr]

That's true in a sense but the electrical need of your car is what provides the load to your alts. If you had two alts, you would split the load between them. You would still have the mechanical load no matter what. If you put a switch on the alt, make sure the switch is on the field wire and not the output. It would take quite a switch to handle the output. I don't think it's the way to go anyway.

[TheWatcher]

I finally got around to reading this entire thread. Based on what I have read so far, I have no doubt that the dual alterator project will fail. Dual alternators can sucessfully be accomplished, but none of the posts I have read so far is definitive or even lays out a complete plan of attack. I'm not a big believer in dual alternators, but every car has a different mission in life. Good luck Fyredaug, I would suggest putting off the project until you have a solid plan of attack.

BTW, 3 years of electronics and some knowledge of a sucessful dual alternator project says that none of the posts quite have it right. Either they are mistaken or missing a key element.

Peace.

[FyreDaug]

From all the replies Ive got from here I dont think the dual alternator thing is something I will do, the 4th gens are 90amps right? I can get one of those to work no problem, so thanks for the help

[mouchyn]

From all the replies Ive got from here I dont think the dual alternator thing is something I will do, the 4th gens are 90amps right? I can get one of those to work no problem, so thanks for the help

get one like that and rewind it for a higher output. bump up your idle speed a tad and you'll be fine.

[mouchyn]

by the way. if any of you guys are serious about dual alternators, it's not hard. the easiest way is with two batteries to isolate the different charging systems.

http://www.caraudiomag.com/technical/0206cae_alternator/

www.google.com is your best friend.

[FyreDaug]

holy typo batman, Im sorry it should have read

From all the replies Ive got from here I dont think the dual alternator thing is something I will do, the 4th gens are 90amps right? I can get one of those to work no problem, so thanks for the help

Should say something I WONT do. a 90A one will do, maybe if I can find one thats higher I'll use it, but the 4th gen ones dont seem to be a WHOLE lot of work

[ace69247no13]

i have done the two alternator thing in my camaro you have to use a second battery and seperate the two system +'s you use a common ground which is anything on the car not + it actually is easy and no the alt's do not need to spin the same speed they are their own circuts if you have any other ??? how to do this send me a pm

[lostforawhile]

i have an easy suggestion for your alternator problem, hook up the two alternators, but use a single pole double throw switch to switch between the two different field current circuits,that way you can run the heavy duty alternator when you have the stereo going and the normal alternator when you don'tr need all that extra current. an alternator needs field current to function and if you cut that off the alternator quits charging. the extra alternator won't need that much horsepower to run when it's not charging. when an alternator is charging the magnetic forces generated are what causes it to use so much horsepower. that horsepower is required to overcome those forces. a single pole double throw switch will let you only select one or the other not both . make sure you use fusible links or something to protect both circuits. and don't try to run the heavy duty alternator with the factory circuit to the battery. connect the output directly to your battery. with a fusuble link of course. I thought about doing this with an early civic alternator as a backup, because our alternator is so hard to get out. the old civic alternator is tiny, but it's great for an emergency backup. does anyone know where that thread is about the 4th gen alternator?

[TheWatcher]

by the way. if any of you guys are serious about dual alternators, it's not hard. the easiest way is with two batteries to isolate the different charging systems.

http://www.caraudiomag.com/technical/0206cae_alternator/

www.google.com is your best friend.
Haha, I knew I read about this somewhere. I had all the information in my head. This is the article I read!

No one mentioned keeping the two systems isolated, so I told them it would not work. I did not want to go into detail, because I didn't want to encourage them. Sometimes a little information is worse than no information. :)

Peace.

[Blkblurr]

Haha, I knew I read about this somewhere. I had all the information in my head. This is the article I read!

No one mentioned keeping the two systems isolated, so I told them it would not work. I did not want to go into detail, because I didn't want to encourage them. Sometimes a little information is worse than no information. :)

Peace.
I said it in this thread at post #20- the last line.

[88eyeguy]

It was also said in the first paragraph of post #2.

[lostforawhile]

the reason i suggested switching between the fields is to make the load on the engine eaisier,you don't need both alternators going all the time. if you switch off the one you aren't using, it's much less load to turn it. only run the heavy duty alternator when the stereo is cranked up or something

[TheWatcher]

I said it in this thread at post #20- the last line.
Oh, I should have said "No one mentioned keeping the two systems isolated with a relay switch."

Peace.

[Blkblurr]

Why would you need a relay switch? Just keep them totally separate.

[lostforawhile]

because if you don't need all that extra current all the time,you can turn off the extra alternator so it's less drag on the engine. it doesn't take much horsepower to turn an alternator that isn't charging. it's when the alternator is charging that it's takes so much horsepower to turn. in other words run the smaller alternator when you don't need all that extra current and therefor it takes a lot less power to turn it,only run the heavyduty alternator when you are going to run a lot of stuff.the more amps an alternator puts out,the more horsepower it takes to turn it under full load.

[Blkblurr]

because if you don't need all that extra current all the time,you can turn off the extra alternator so it's less drag on the engine. it doesn't take much horsepower to turn an alternator that isn't charging. it's when the alternator is charging that it's takes so much horsepower to turn. in other words run the smaller alternator when you don't need all that extra current and therefor it takes a lot less power to turn it,only run the heavyduty alternator when you are going to run a lot of stuff.the more amps an alternator puts out,the more horsepower it takes to turn it under full load.

If the battery is already charged and you aren't using whatever is connected to the alt. You won't be causing much drag/ magnetic resistance or whatever you choose to call it. You won't have much current flow.

[lostforawhile]

If the battery is already charged and you aren't using whatever is connected to the alt. You won't be causing much drag/ magnetic resistance or whatever you choose to call it. You won't have much current flow.
even with the battery charged,the alternator is still using load when it's running. an alternator usually puts out about 13.5 volts, it has to have a higher voltage then the batttery to cause current to flow in it. all the battery does is provide current for starting and a reserve when the amp requirment exceeds what the alternator is able to produce,nothing runs off of the battery under normal circumstances the alternator powers the vechicle.