I'd like to put one of these in my plow truck. The stock alternator just can't keep up, when you use the plow to voltage drops significantly to about 10volts.

 

In the last couple of years crazy-amp aftermarket alternators have been getting better and better, and producing a lot more current at or close to idle - something that years ago often wasn't the case.

Aside from that problem, another problem is belt slippage because as you draw more current from the alternator it gets harder to rotate - and at some point the difficulty of rotating the alternator exceeds the friction between the belt and the pulley and viola, it slips, then glazes, then burns up.

This is why Ford severe service duty trucks have two medium alternators instead of one huge-*** one - the force required and the friction required to apply that force to the pulley is split between the two alternators and thus, the two pulleys.

So you can use one 130A alternator to drive the normal components of the truck and some accessories, and a second 130A alternator to drive all the high power do-dads - zillion candlepower lights, electric winches, big stereos, et al.

Generally you need a battery to go with the second alternator and if you really want to get fancy you can even rig-up a switching contactor so that you can start and run the truck on either battery/alternator and cover yourself for a dead battery and/or a dead alternator.

While finding a place to shove it is a bit of work, and making DIY brackets isn't always easy, the advantage is since both alternators are "stock" you can get them in a junkyard cheap enough to service what you created going forward, and if you don't like the junkyard route there's an autozombie or poopboys every 20 feet on any major road.

That's my primary reason for disliking high-current non-OEM alternators - when they die, you have to wait for UPS or FEDex to deliver a new one, and if it dies while on vacation, that pretty much sucks (this is why I have a spare alternator in my bedbox, ready to go - "just in case". I do this because alternators never seem to die while I'm in my driveway and only when I'm 500+ miles away)

The key to high-current alternators is to have as much 'wrap' around the pulley that you can, since the alternator pulleys have little surface area to begin with because they're so tiny.

 

unless you get an alternator overdrive pulley

 

or make it easy on yourself and hook up both positive leads of the alts to your battery(s)

 

That's true, and I suppose it's also why I can get away with pulling more power from the alt than the belt is supposed to be good for in a normal setup - I got an idler in there that causes the belt to go full 180* around the pulley, instead of just 150* like it does from the factory - 30* may not sound like much of an increase to some, but they do make a difference...

Which is not always possible - some of us still use V-belts on our engines, there ain't no such thing as a small dual-V-belt pulley, not anywhere near as small as what's available for serpentine belts at least. Also the smaller the pulley the easier it is for the belt to slip on it cause of the less contact surface between the two - you can offset that with more wrap around the pulley as Frederic suggested, but there's only so much you can get out of it...

Have you actually done this? What alternators and VRs did you use? Any details on the wiring, particularly the battery-sensing circuits? Or are you just talking outta yer posterior now...

 

Ford Modules

 

Of course it makes a difference

That 30 degrees is 17% more contact which means it will take 17% more alternator turning resistance above the original Ford design to slip, assuming everything else is the same - belt width, type, compound, pulley diameter, belt tension, etc.

It's no different philosophically as increasing the width of a tire for more traction - a wider tire gives more contact patch to the road and thus more potential traction.

However, just like with a tire, you can overpower it and break that tire free - and that's why locking rear ends are a great idea - half the power goes to one wheel, half to the other and assuming your tires are on smooth, flat pavement that means to spin the tires you have to exceed the friction between BOTH tires and the road, not just one.

Alternators work the same way - if you have two alternators instead of one huge one, the load (resistance of turning the alternators) is split between two pulleys and two sections of the belt - thus it's more likely you won't exceed the "traction" between the belt and the pulley on either alternator.

That's why I prefer dual alts to one huge alt - basic physics.

Well my friend, you just didn't look hard enough because I've bought them



And... I've made them too. A pulley is very easy to make on a lathe and because of the size you don't need a big old 12x24 Clausing lathe like I have - even a 4x8 imported lathe will make a perfectly fine 2-groove alternator pulley.

The "trick" is to monitor and regulate the alternators individually then sum the output, and that's what the module Duramaxfanatic posted does, and it's one solution to the dual-alternator issue however it wouldn't be my first choice for the same two reasons I mentioned above -

1. custom modules/parts/alternators are more difficult to find/acquire when you're stranded because something broke.

2. having completely separate circults (battery, alternator) allows you to use both systems in parallel for more power, however in a pinch you can disable the "broken" circuit and use the good one as your primary circuit - thus start the vehicle, charge the battery, and listen to tunes while you drive home where you can repair the broken circuit.

Just my opinion - if I were to go through all the aggrevation involved in setting up a dual alternator system, I would want to leverage it for redundancy purposes.

The reason why I've made several 2-groove alternator pulleys the first time was for a friend who wanted to attach two 130A 3G alternators to a small gasoline engine whereas he could have portable 12V power at a high current for welding and 12V worklighting.

Amps x Volts = Watts
Watts / 745.7 (one HP) = Electrical HP Produced by the Alternator
HP x 15% Efficiency Loss = HP Loss
HP + HP Loss = Total HP Used

130A x 15V = 1950 watts
1950 / 745.7 = 2.61499 HP
2.61499 x 15% = 0.3922485 hp loss
2.61499 hp + 0.3922485 hp loss = 3.0072385 HP required per alternator.

For two alternators, that would be about a 6HP minimum engine required to drive the two of them.

Since alternators run at a far higher RPM than the engine does due to the mechanical leverage of the pulleys (often something like 8" on the crank and 3" on the alternator), one has to take that into mathematical consideration as well.

So, assuming that same ratio, 8:3, you'd divide the 6HP by 3 then multiple by 8 and get 16HP required as a minimum.

The reality is car engines don't run at 3600 RPM and typically on the highway are at or about 2500 rpm, so the to get the alternator speed in the same ballpark RPM range as it would be on a car engine doing 2500 RPM, you'd change the pulley ratios to something like 2:1 - that would be a 12HP minimum engine.

My friend did that - a 2:1 pulley ratio driven off a vertical shaft, electric start Kohler he ripped off something and that engine produces 18HP.

And there's his totally portable, 240 amp welder, with a little juice left over for a 100W 12V worklight.

To get enough "wrap" on the alternator pulleys, there are four double groove pulleys - one on the engine, one on each alternator, and one between the alternators that wraps the belts around the alternator pulleys about 165 degrees.

Off-topic but I hope it helps someone.

 

Oh, so you're using some aftermarket setup - well you could have just posted that link in your previous post, then I wouldn't have to sound like a jackwagon, lol. By the way, I can't really find any tech info on that website - they obviously make some custom dual-alt control modules, but how they work or even how they install remains a mystery

Apparently, you and me have different ideas as to what a "small" pulley is - my factory dual-groove pulley is 3" OD, the smallest aftermarket dual-groove pulley I've found so far has 2-1/2" OD, hardly worth the effort of swapping it in when I can just bump my idle up 200 rpms (which I do anyways if I'm idling for long periods of time, don't wanna wet-stack the engine) and get the same output... For comparison purposes, the smallest factory serpentine-belt pulley that I know of is 1-7/8" in diameter and is widely available at any junkyard that has '80s Ford passenger cars. Obviously tho with a 1/2" wide V-belt that's just too small of a pulley, don't think the belt will like bending at such a tight radius...


Agreed, 100% - I am all about redundency, that is why my truck can still drive even if the infamous fusible link by the starter relay fries and kills all power to the cab - I will also have full battery charging, some offroad lights, blinkers, GPS and CB

 

I was comparing a factory sized pulley (3") to the above v-groove pulley (also 3")

You can make a pulley that small.

Yeah, it is a tight radius for sure, and I'm guessing why OEMs went with 3". The tigher the radius of the belt around a pulley, the more it has to flex, and the faster it wears out from cracking. That of course would be a bad thing.

I had that in my 81 - two batteries, two alternators, two starter relays, and a toggle switch to select between starter relays.

Redundancy is good, especially when off-roading in the middle of nowhere.

You can actually wire alternators in parallel, by joining the outputs AFTER inserting a huge diode for each alternator. I did that on a friend's Chevy - except I used four 300A diodes in parallel per alternator. That means each alternator can regulate itself and not torture/confuse each other.

The diodes were the bolt-on kind and were wedged between two aluminum plates, and the whole assembly was "potted" in a plastic box with two big screw terminals sticking out.

 

Why did you use four 300A diodes in parallel per alt, wouldn't a single 300A diode per alt be sufficient?

 

I figured that was probably the reason.

 

Thats a very good point. I still think the 95 amp alternator in my truck is a bit underpowerd though.

 

A single 300A diode would be just fine however the purpose is redundancy.

 

Go find an ambulance and pull the dual set-up off it

 

You'll get a good belt wrap (at least on gas motors), if you delete your smog pump.