Running two alternators on same car?

[j-c-c-62]

Dual Alternator Kits

Those solutions are for seperate 12V systems, and make a lot of sense in those applications, but mine is a single system and must remain so.

 

[Photon440]

Those solutions are for seperate 12V systems, and make a lot of sense in those applications, but mine is a single system and must remain so.

If you have low draw, why not just rely on the engine mounted alternator?

 

[j-c-c-62]

If you have low draw, why not just rely on the engine mounted alternator?

Two fans, electric water pump, EFI, fuel pump, etc

 

[Moparfever65]

In my mind two alternators would be less efficient than one heavy duty alternator. More parasitic drag. The only reason I can see would be either for redundancy in case of failure, or if you can't get one with sufficient amperage.

 

[j-c-c-62]

In my mind two alternators would be less efficient than one heavy duty alternator. More parasitic drag. The only reason I can see would be either for redundancy in case of failure, or if you can't get one with sufficient amperage.

Well, the fans, fuel pump, electric water pump, etc are all in the rear of the car, or maybe less than 4' from where a DS mounted alternator would locate. That load right there may approach 90+A, and running all that from the front is just more downside with a trunk mount battery. Additionally, this split/asymmetrical charging system favors rear and low COG placement for both units. Any additional parasitic drag is an acceptable tradeoff.

 

[Jeff Peterson]

Obviously, my needs are different than the op's, but a plow draws 400+ amps, especially if your trying to "stack" the snow, imagine doing this hundreds of times a day/night, then my setup starts to make sense.

 

[451Mopar]

Question? Where and how is the rear alternator mounted?
I could see having a driveshaft driven alternator on a truck with a 2 part driveshaft driven near the carrier bearing with the alt mounded to the frame.
Having the alt mounted to the axle and driven off the yoke, the alternator mounting will take a pounding from suspension travel, and the wiring will be moving with the suspension, so it would need to be secured with clamps to not pull on the alt output stud. It is also in a lower position where it might get damaged.

 

[j-c-c-62]

Question? Where and how is the rear alternator mounted?
I could see having a driveshaft driven alternator on a truck with a 2 part driveshaft driven near the carrier bearing with the alt mounded to the frame.
Having the alt mounted to the axle and driven off the yoke, the alternator mounting will take a pounding from suspension travel, and the wiring will be moving with the suspension, so it would need to be secured with clamps to not pull on the alt output stud. It is also in a lower position where it might get damaged.

All your concerns all valid and will have to be dealt with. The first car I expect to try this on will be a Magnesium Dana 60 live axle with a 3-point coil over suspension. The Final car if it works will be an IRS set-up, so no direct vibration/road bump issues, as it will be solid mounted. All will seldom be street driven and will run off yoke mounted pulley so no geometry changes as rear moves being alternator is mounted to the rear. I see rain/puddles as my biggest concern. Dirt cars use this solution with a live axle, and I cannot imagine a tougher beating then that application. Of course, they may only last a race or two? The alternator will not be lower than the fuel cell so there is that, but the car will be set to run low.

 

[j-c-c-62]

Obviously, my needs are different than the op's, but a plow draws 400+ amps, especially if your trying to "stack" the snow, imagine doing this hundreds of times a day/night, then my setup starts to make sense.

Not clear, what is drawing that much current in this snowplow application?

 

[451Mopar]

All your concerns all valid and will have to be dealt with. The first car I expect to try this on will be a Magnesium Dana 60 live axle with a 3-point coil over suspension. The Final car if it works will be an IRS set-up, so no direct vibration/road bump issues, as it will be solid mounted. All will seldom be street driven and will run off yoke mounted pulley so no geometry changes as rear moves being alternator is mounted to the rear. I see rain/puddles as my biggest concern. Dirt cars use this solution with a live axle, and I cannot imagine a tougher beating then that application. Of course, they may only last a race or two? The alternator will not be lower than the fuel cell so there is that, but the car will be set to run low.

I was think live axle. IRS makes sense to me. The race cars usually run small light weight alternators, so less mass and could be mounted higher?
You will need to figure the alternator to driveshaft pulley ratio for the speeds you are planning to get the best output from the alternator without over speeding it.

 

[j-c-c-62]

Regarding speeds, the available yoke pulley sizes are rather limited in this application, meaning I'll likely be looking for a rather small alt pulley, which is counterproductive when combined with a high amp alternator. Well the mass has to be somewhere on the car for the amount amps I need, so it might as well be low and at the rear and on the centerline. Unfortunately, it adds to the unsprung mass, but with the Mag Dana 60 I should just be back to my starting point is my thinking. We'll see.

 

[Jeff Peterson]

Not clear, what is drawing that much current in this snowplow application?

The hydraulic pump is powered by an electric motor and your always trying to raise the plow with it loaded with snow to pile it out of the road/lot, and with mine being a power “vee” that’s just more load on the batteries.
I just guessed on the amps, this is from Boss plows website
ONLY 243 amps, but again many times over and over with hardly any recovery time in between.

 

[j-c-c-62]

Wow, that like 4 hp?
Surprised that in your case with a separate alt they did not upgrade to a 24V or higher system

 

[451Mopar]

Regarding speeds, the available yoke pulley sizes are rather limited in this application, meaning I'll likely be looking for a rather small alt pulley, which is counterproductive when combined with a high amp alternator. Well the mass has to be somewhere on the car for the amount amps I need, so it might as well be low and at the rear and on the centerline. Unfortunately, it adds to the unsprung mass, but with the Mag Dana 60 I should just be back to my starting point is my thinking. We'll see.

Post some pics when you get it done. It sounds interesting. Is the drive a cog belt like on an external dry sump pump?
I was just thinking a setup like that might need a clutch or mechanical diode / sprag for when the car stops it will slip the altenator belt trying to stop the alt also.

 

[fourgearsavoy]

Completely unnecessary IMHO. New cars have all your accessories and more and they don't use 2 alternator. Just put a good charging system on the car with a good internally regulated alternator and not one of those one wire units. I had the same equipment on my car and the Denso unit from a Toyota pick up was more than up to the task. Just think about all the options are on your modern car and think about your plans.
Gus

 

[j-c-c-62]

Completely unnecessary IMHO. New cars have all your accessories and more and they don't use 2 alternator. Just put a good charging system on the car with a good internally regulated alternator and not one of those one wire units. I had the same equipment on my car and the Denso unit from a Toyota pick up was more than up to the task. Just think about all the options are on your modern car and think about your plans.
Gus

I saw this setup on the GT3 class Lexus? at Sebring 12 hrs this weekend. It's a rear transaxle I believe with a Magnesium case and they went so far as to also relocate the starter.
The physical size of the alternator appears to be rather small IMO considering all the electrical requirements on a night raced endurance high level factory backed sports car, unless they also have another engine mounted alternator.

 

[Photon440]

I saw this setup on the GT3 class Lexus? at Sebring 12 hrs this weekend. It's a rear transaxle I believe with a Magnesium case and they went so far as to also relocate the starter.
The physical size of the alternator appears to be rather small IMO considering all the electrical requirements on a night raced endurance high level factory backed sports car, unless they also have another engine mounted alternator.

View attachment 1821508

If that's a Denso alternator, they're often rated for 130 Amps when used on a Lexus LX470, so should have adequate power delivery.

 

[fourgearsavoy]

The Denso unit on my Savoy is only 80 amps and it works great. As posted above the Lexus unit is compact so it fits in a very tight engine bay. 130 amps would be more than adequate. Make sure you get a genuine Denso reman or new $300-$500 not cheap but will last hundreds of thousands of miles.

 

[65CopCar]

I don't know the answer. But I will trow out some thoughts from an electrical engineering perspective.

1. I have measured as much as 120VAC from the output of car alternator - someone mentioned 17 volts
2. If not hooked up to the battery, you do have have 3 phase full wave rectifier ripple (if it was on a 60 hz system it would be 360 hz). A car alternator is a 3 phase synchronous generator, or can actually be a 3 phase motor too! I forget exactly, but I believe alternators are like 12 - 14 poles so the frequency is very high. The battery for all practical purposes sinks the AC ripple, minus IR drop. But I don't believe there are any real harmonics associated with this ripple.
3. Things get a bit squirrely when trying to figure out exactly what is happening because of all the voltage drops in the wiring and ground.
4. The way the regulator works is that it looks at voltage at a point in the system, and then increases or decreases alt field to balance out the regulated voltage. If you had 2 alternators and two voltage regulators, one alt would hog the load because one VR would always be satisfied so would reduce the field causing that alt to put out minimal current . In essence, the 2 voltage regulators would be fighting themselves, especially if they are sensing voltage at the same point. If the voltage regulators were internal to the alt, then the sensing point changes and voltage drops come into play and one alt would put out more current than the other but both would be producing at least some current - maybe, depending on voltage drops. If you have one VR feeding 2 alternators, unless the alternators were 100% electrically balanced, one alt would hog more load than the other, but might be just by a little or by a lot.
5. It is not hard to make 2 alternators work where they put out the same current, its just not with a conventional VR. One method that comes to mind is have one alt as the master with a voltage regulator, and the other be a current follower of the master, but now you are sensing current not voltage. There are other methodologies that would work.

 

[j-c-c-62]

I don't know the answer. But I will trow out some thoughts from an electrical engineering perspective.

1. I have measured as much as 120VAC from the output of car alternator - someone mentioned 17 volts
2. If not hooked up to the battery, you do have have 3 phase full wave rectifier ripple (if it was on a 60 hz system it would be 360 hz). A car alternator is a 3 phase synchronous generator, or can actually be a 3 phase motor too! I forget exactly, but I believe alternators are like 12 - 14 poles so the frequency is very high. The battery for all practical purposes sinks the AC ripple, minus IR drop. But I don't believe there are any real harmonics associated with this ripple.
3. Things get a big squirrely when trying to figure out exactly what is happening because of all the voltage drops in the wiring and ground.
4. The way the regulator works is that it looks at voltage at a point in the system, and then increases or decreases alt field to balance out the regulated voltage. If you had 2 alternators and two voltage regulators, one alt would hog the load because one VR would always be satisfied so would reduce the field causing that alt to put out minimal current . In essence, the 2 voltage regulators would be fighting themselves, especially if they are sensing voltage at the same point. If the voltage regulators were internal to the alt, then the sensing point changes and voltage drops come into play and one alt would put out more current than the other but both would be producing at least some current - maybe, depending on voltage drops. If you have one VR feeding 2 alternators, unless the alternators were 100% electrically balanced, one alt would hog more load than the other, but might be just by a little or by a lot.
5. It is not hard to make 2 alternators work where they put out the same current, its just not with a conventional VR. One method that comes to mind is have one alt as the master with a voltage regulator, and the other be a current follower of the master, but now you are sensing current not voltage. There are other methodologies that would work.

Thanks, I believe we are both on the same page here, this is not a simple straight forward question. #4 above zeroes in on that. My initial thinking was to have two slightly different voltage set points, the engine driven alternator always in circuit with engine running, being of lesser current output, with its VR set slightly higher and the larger current driveshaft (DS) driven alternator with a VR set slightly lower, to kick in when voltage started to drop when the current began to exceed the engine driven alternators output.

That begs the question, does the engine driven alternator effectively go idle charging wise when it sees the enhanced voltage from the DS alternator comes online?
And does the engine driven alternator come back online smoothly when the DS driven alternator surpasses its output rating and/or the DS/car stops?
I fully understand actual testing will give the final answer here I suspect, unless a case is made this idea is determined to be dead in the water.

"Smoothly" above is only one of a number of words that might apply here.
The other detail not mentioned with my recent added pic above, that alternator is effectively rear mount, but really engine driven, as it is FW driven.