[Gwagensteve]

This might be a really dumb question, but,,,

Is there any reason I can't run two alternators charging the same battery(ies)?
I'm aware of winch cars running two complete charging systems with a second alternator isolated from the vehicle charging system, but that's not what I want to achieve.

Here's my pulley setup:



It's all stock vitara. The aircon pump provides tension for the belt on the LHS of the engine, which runs the power steer. As I don't have A/C (and don't need an engine driven compressor) the A/C pump is just sitting there acting as a big, heavy belt tensioner.

My plan is to install another falcon alternator in that position. More than giving me 200A peak, it's really allowing me to keep up with demand at low engine speeds, when I might be airing up (60A of compressor) or of course, heaven forbid, if I ever fit a winch

Will it work from an electrical point of view? I can't see why not, but I'm keen for feedback.

Steve.

[Bugsta]

It can be done but you will want some kind of isolation protection/controller circuitry. If you just parallel them, and one fails, or they become different, it could cause one or the other to overload itself or the battery.

http://www.amplepower.com/products/dac/index.html

[Gwagensteve]

I'm not sure I follow that Bugsta. How can the battery be "overloaded"? If I parallel them and one fails, why can't I just pull the IG+ lead from that alternator, thereby disabling it?

It doesnt matter if one alternator does most of the work (as per the web site) as one does all the work right now. It's only for when draw outstrips supply, typically at low engine RPM.

The tach signal thing is irrelevant as that's a diesel issue.

Steve.

[31zook]

Are you going a 24V winch/lights set up? that would be awesome.

What are you trying to achieve?

[rick1970]

I just fitted a second alternator to my Rangie. Was running 1 x 65amp Bosch, fitted another so now 130amp total. It has dual N70 batteries linked by a simple HD solenoid when the ignition is on, so starts on both batteries.

Second alternator is mounted where the a/c comp was and is wired up with its own warning lamp (3w) for the excite side of things. B+ for the second alternator is running to the second battery, so in a pinch i can pull a wire and seperate the two systems.

Seems to work a treat. Went from 12.5v at idle under full elect load (inc 500w of lights) to 13.9v @ idle.

Was told by an auto sparky to rig it up like this and he told me it was once a quite common conversion before big amp alternators were common place.

[Gwagensteve]

31zook wrote:

Are you going a 24V winch/lights set up? that would be awesome.

What are you trying to achieve?

Nope, no 24V setup.

Two reasons. I can't remove the A/C pump without adding a tensioner to that belt. For the stuffing around fitting a tensioner, I might as well fit a cheap 100A falcon alternator to act as the tensioner.

Next: The most amps I've seen the stock alternator deliver is about 45. (this is normal for a 60A alternator) At idle, with the fans and the compressor running, I'm drawing upwards of 70A, without any lighting running. Sure that's only ever a temporary situation, but I'd much rather tip in what I'm taking out and not experience volt drop. I'm auto so I can't bump start. I'd like enough alternator to meet demand at all times except starting (and winching, should that happen)

Ricks setup sounds like what I'm shooting for, but I'm not running second battery and I see no reason to. All the more with dual alternators.

I don't need two batteries linked together for starting as I have 800CCA of optima, and I'm not key starting like with a manual. Also, with EFI there's no reason to excessively crank - its going to start or it's not.

Steve.

[jdk81]

As far as I can tell....

You might need to set up a second light to alert you if the 2nd alt has issues.
You will need to run the voltage sense wire to the voltage sense wire on the other alternator.
Alt output with a fuse to the battery.
Both alts should work at approx the same capacity, sharing load.

A elecmagician might provide better input (looking at Jrzook)

[Trypt]

I cant see why it cant be done on a sierra.

Competition sound cars/trucks (the ones with 100k stereos) run upwards of 3 alternators for 12v supply.
most ive seen is 4.

They dont run duramax's and big block's so they can go fast or sound good its so they can crank 4 300amp alternators!!!!

[Blakey]

Gwagensteve wrote:

This might be a really dumb question, but,,,

Is there any reason I can't run two alternators charging the same battery(ies)?
I'm aware of winch cars running two complete charging systems with a second alternator isolated from the vehicle charging system, but that's not what I want to achieve.

Here's my pulley setup:



It's all stock vitara. The aircon pump provides tension for the belt on the LHS of the engine, which runs the power steer. As I don't have A/C (and don't need an engine driven compressor) the A/C pump is just sitting there acting as a big, heavy belt tensioner.

My plan is to install another falcon alternator in that position. More than giving me 200A peak, it's really allowing me to keep up with demand at low engine speeds, when I might be airing up (60A of compressor) or of course, heaven forbid, if I ever fit a winch

Will it work from an electrical point of view? I can't see why not, but I'm keen for feedback.

Steve.

should be fine DC can be put in series for more voltage or ie 24V or paralleled for just simple 12V you shouldn't really need any separation protection as the rectifiers already in the alts will have sufficient diode protection for feeding back into the alts windings. but you can add something if you wanted to be safer.

adding 2 100A alts will have a total output of 200A Unless they are in series. from an electrical point of view it will be fine.

its only AC that you need to be careful with when connecting together.

[Bugsta]

Gwagensteve wrote:

If I parallel them and one fails, why can't I just pull the IG+ lead from that alternator, thereby disabling it?

Well you can, but how would you know.

The site I posted was just an example. First one I came across, to demonstrate they exist.

I have never done this, but based on my knowledge of electrical/electronics, as in any multiple supply situation, you need to manage them or you can end up with issues. If one fails, it could draw the B+ voltage down causing the other to increase its output thereby over supplying the battery. Just one scenario. Probably many others.

[Reubs]

Gwagensteve wrote:

Is there any reason I can't run two alternators charging the same battery(ies)?
I'm aware of winch cars running two complete charging systems with a second alternator isolated from the vehicle charging system, but that's not what I want to achieve.

You can -

Both alternators need to have the same output curve (same model - same regulator) otherwise one will be doing all the work until it reaches its maximum output so-to-speak.

The Bosch alternator book I was reading when researching for my alternator upgrade specifically mentioned this scenario.

Gwagensteve wrote:

If I parallel them and one fails, why can't I just pull the IG+ lead from that alternator, thereby disabling it?

As has been mentioned, you will need a seperate alternator light for each alternator. I'm pretty sure it's the alternator light (L pin) being connected that switches on the regulator - not the IG pin for sensing system voltage only - the reason many universal fitment alternators have 2 wires (warning light & output) only.

[Blakey]

the sense is what turns the alternator on or if you have a IG terminal that turns it on. it turns the regulator on and off which controls the internal DC excitment coil inside the alternator. that without that there is no current or voltage output from the alternator as there is no magnetic lines for the coils to cross to create power. if you look at a wiring diagram for most alts the light terminal isnt connected to the regulator its only conected after some diodes internaly so when the alternator fails to output there is a difference between the 2 voltages on either side of the light so it lights. it doesnt do any switching

and you will need something to stop the alternators figting each other for the system voltage. ie when one turns on it will bring the voltage up so the other alt will thing the voltage is high so it will turn off or be low and when you get a fully charged battery and both alts might turn on and off at a high frequency causeing problems and major headachs.

The problem will be getting them to load share properly as they are not designed to do that.

IF you can find some alternators that do not have a rectifier or regulator attached so you can put a single external one on then that will work perfectly and you will get perfect load sharing and not have the problem of 2 regulatorrs fighting each other. (but now you will need exactly the same alternators as you would be joining AC not DC) and i do stress they need to be the same including the pully, if you are joining AC unless you shorting phase to phase faults.

[twitchy]

Just turn the AC into an endless air & put a decent fuggen alternator on............ simple really.

[royce]

I have no idea how it would work, but I would be interested to see an amp gauge on each charge lead to see if they bounce back and forward to each other.

[3cyl]

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

[Blakey]

royce wrote:

I have no idea how it would work, but I would be interested to see an amp gauge on each charge lead to see if they bounce back and forward to each other.

they shouldn't be able to send charge to each other as rectifiers cannot work backwards because of the diodes only allow current in one direction. so they cannot feed each other but the regulators for the Voltage can fight each other, make one or the other turn on and off repeatedly or leaving one completely off thus being pointless having 2 alts as one is not outputting.

[joeblow]

3cyl wrote:

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

What he said. I ran dual alts about 10 or more years ago....what a freakin waste of time.

[Dr_Snapid]

Hey steve, can your ac 'compressor' be rigged up to pump up ya tyres? That would be cool

Edit: OK I just learned what endless air is

[Bugsta]

3cyl wrote:

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

...Or by utilising a control circuit designed for the purpose.

[fordem]

3cyl wrote:

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

Whilst this is true for alternators in general - we're discussing automotive alternators here, they have rectifiers and output DC - phasing is NOT an issue.

[Bugsta]

Found this from the same company witha litle more digging...
http://www.amplepower.com/products/sarv3/index.html

[31zook]

Possible or not, I still don't see the advantage. Is it like the old twin stick debate?

[rick1970]

31zook wrote:

Possible or not, I still don't see the advantage. Is it like the old twin stick debate?

For my application there is maybe an advantage. On the Rangie, the alternator is driven off a dual pulley on the p/s pump Too much extra load and the p/s pump belt slips. Second battery places the load on another pulley (ex air con compressor), so i get the extra charging capacity for the 3 x batteries (when camper trailer is hooked up) with no extra load on the p/s belt. Also the Rangie picks up the tacho signal from a phase on the alternator, so the drive ratio needs to be kept the same, which makes mounting a single larger alternator to run off its own belt that little bit more diffucult (if i want the tacho to read right). Dual alternators was an easy out.


With a basic inductive amp meter, i had a reading of 40amp from one alternator, 35 from the other. Batteries flattened a bit, ligts on, camper not connected. Needle held fairly steady, but this was with a very basic tool.


In an ideal world, a single 120amp alt on a mulit rib belt would be preferable, and i would go this way when it gets a 4.6L put in.

[3cyl]

fordem wrote:

3cyl wrote:

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

Whilst this is true for alternators in general - we're discussing automotive alternators here, they have rectifiers and output DC - phasing is NOT an issue.

I was referring to a previous post where someone suggested to use remote common rectifier and regulator.
2 alternators on one battery will act like 2 compressors with 2 pressure switches on 1 receiver, 1 will do most of the work.

[royce]

31zook wrote:

Possible or not, I still don't see the advantage. Is it like the old twin stick debate?

Alternators do bugger all at low revs, so with fans and lights and pumps running you drain the battery quickly

2 alternators doing bugger all is still twice as much as 1 so might be enough to keep the batteries going flat, just having a single big alternator possibly isnt any better unless it can do a lot of amps down low

Have the same trouble with the big pink thing, at night idling it can draw 70 amps, doesnt take long for the battery to get to the point where stalling it can be trouble

[3cyl]

Could you drive the alternator faster?

[SierraDan]

With overdrive pulleys at cost of some engine power.

[Blakey]

3cyl wrote:

fordem wrote:

3cyl wrote:

You definitely won't be able to connect 2 ac alternator outputs together unless you synchronize them, on vee belts that won't be possible. They'll be a dead short if they're out of phase.
I reckon 1 good alternator and 2 good batteries.

Whilst this is true for alternators in general - we're discussing automotive alternators here, they have rectifiers and output DC - phasing is NOT an issue.

I was referring to a previous post where someone suggested to use remote common rectifier and regulator.
2 alternators on one battery will act like 2 compressors with 2 pressure switches on 1 receiver, 1 will do most of the work.

they would act like that only if you parallel them after the rectifiers ie DC side. if you parrallel them on the AC side before the rectifiers. it will be like a normal AC generator and will share load fine. just need a common rectifier and regulator. and it will work fine. just have to make sure the AC is synced or it will short out in your face when you turn it on.

[3cyl]

The sync was the problem I was talking about and being belt driven I don't see how that's possible. Then with the common reg the 2 alts won't be exactly the same efficiency and 1 will output higher than the other on a common rotor input.
I reckon twin alternators is an inefficient way to charge 2 separate batteries and a difficult and inefficient way to charge 1.

[royce]

3cyl wrote:

Could you drive the alternator faster?

Then you are posed with overspeeding the alt, which is something to consider with engines that can rev over 6k