V belt setup

[Mick]

Need some input recently had to pull the motor to repair a head gasket leak. In the process change the pulley setup. What I have looking at the front of the motor is the alternator on Right A/C on the Left. I have all pulleys in line and can run a single V belt, im using a custom A/C bracket which is mounted where the fuel pump normally is fitted which is how I got all pulleys aligned. What I want to know is there any reason I shouldn't use a single V belt to run the entire system. Any info would be appreciated

Mick

[Ian Anderson]

Mick

How much wrap around do you have on each pulley?
If they are the same you get 90 degrees on each.

I would question if 90 degrees on the crank or wp pulley is sufficient or if you will just get a load of slip

Ian

[Mick]

Ian thats what i am concerned about just not sure what is enough wrap around mainly on the water pump & crank pulleys, any idea what the minimum required would be?

[Rich E.]

Sounds like you just modified your system into a "serpentine" system. A single V belt might not have enough bite on each pulley given that it's only getting, at best, 3 sides of friction for contact. Ever thought of changing the pulleys so you can run a ribbed belt? You'll get much better bite with say a 5 rib belt. It's like 19 points of friction contact when you consider all the peaks and valleys of the pulley.

[Mick]

Did look at serp/rib but decided to try and keep the V belt I think I need to change the bottom pulley to a three groove as the the AC compressor has a double groove pulley fitted. Basically back to square one.

[Ian Anderson]

Mick
Surely a double pulley would suffice.

One for crank wp alternator
The second for crank a/c

Ian

[Chuck]

I am contemplating the same issue.

I run two V belts: Alternator - crank - water pump. And AC - crank - water pump. Generally it works just fine, but the belts need to be tight to prevent slippage. I really wanted to use that second pulley on the AC if possible.

Had contemplated running the alternator pulley to include the AC, but the contact area with the crank and water pump would have been minimal so opted against that idea. I suspect the alternator would have started slipping.

We are in the process of an engine upgrade. I am looking into using a three groove pulley on the crank and running two belts: crank - AC. A single belt would tie the Alternator - crank - water pump. Total of three belts.

Found some pictures showing the current set up.

[clive]

Just finished playing to solve the same problem.

Rich E.s on the money. The contact area of the 6 rib belt is more than adequate for the apparent lack of wrap-around on the crank pulley.

Clive

[Alan Watkins]

Originally Posted by Mick

...is there any reason I shouldn't use a single V belt to run the entire system.

Echoing Ian....Even with good wrap you should probably have a separate belt for A/C and for Alternator, simply because a single V-belt becomes marginal with large alternator loads alone.

As for the presence of a double pully on the A/C compressor; that doesn't imply that it needs two belts. With good wrap (at least 90 degrees, preferably more, on both the load pulley and the crank pulley) it should work fine with one belt on the compressor.

[Chuck]

Alan

Good point.

So would it be better to run the AC only from the crank, rather than the crank and water pump? That would give 180 degrees of wrap.

The alternator belt would still connect the WP and crank.

That means a single rather than dual pulley could be used on the water pump, increasing the clearance to the firewall.

I like that approach. What do you think?

[Alan Watkins]

Originally Posted by CESLAW

Alan

Good point.

So would it be better to run the AC only from the crank, rather than the crank and water pump? That would give 180 degrees of wrap.

The alternator belt would still connect the WP and crank.

That means a single rather than dual pulley could be used on the water pump, increasing the clearance to the firewall.

I like that approach. What do you think?

Most of the time I'm pretty sure the A/C is a substantially larger load than the alternator. After all, the alternator load is (roughly) proportional to the electricity you're using, so if you're just driving around it's not much, until the fans and headlights come on. In my case the fans are 40A. (!)

Peak power consumption of the Sanden compressor in my SPF is about 1.2 kW. An alternator putting out 60A at 14 volts is putting out 0.84 kW Add, say 20% for conversion inefficiency and the alt is consuming a little over 1 kW. So my intuition is to give the compressor the better drive system.

IIRC your idea is exactly what I did: crank direct to A/C with 180 degree wrap; wp, alt and crank on the other belt in a triangle.

That way only the crank needs a double pulley.

[Chuck]

Thanks Alan. Good analysis. Plan to go that route on our upcoming engine swap.

[Rich E.]

Originally Posted by awatkins

Most of the time I'm pretty sure the A/C is a substantially larger load than the alternator. After all, the alternator load is (roughly) proportional to the electricity you're using, so if you're just driving around it's not much, until the fans and headlights come on. In my case the fans are 40A. (!)

Peak power consumption of the Sanden compressor in my SPF is about 1.2 kW. An alternator putting out 60A at 14 volts is putting out 0.84 kW Add, say 20% for conversion inefficiency and the alt is consuming a little over 1 kW. So my intuition is to give the compressor the better drive system.

IIRC your idea is exactly what I did: crank direct to A/C with 180 degree wrap; wp, alt and crank on the other belt in a triangle.

That way only the crank needs a double pulley.

This is also the way I routed mine. Only needed to offset the AC pump. Make sure your alignment is dead on or at high rpm to decel your belt will want to walk off. Ask me how I know

[Cliff Beer]

One minor point to contemplate....the more driven items off of a single belt, the more chance there is that one of them will have a bearing seizure, leaving you stranded by the road. If you have a separate belt for WP from A/C and alt then if the A/C/alt belt fails you can still get home with a functioning WP. The serpentine belts are OK with many driven items running off a single belt as they have greater longevity than the old style v-belt.

If you did decide to go with a single v-belt, you could always get a longer belt and add in a spring loaded tensioner (flat side of belt, use a serpentine tensioner) on the side needing greater wrap.

[Bob Putnam]

Originally Posted by awatkins

Peak power consumption of the Sanden compressor in my SPF is about 1.2 kW. An alternator putting out 60A at 14 volts is putting out 0.84 kW Add, say 20% for conversion inefficiency and the alt is consuming a little over 1 kW. So my intuition is to give the compressor the better drive system.

IIRC your idea is exactly what I did: crank direct to A/C with 180 degree wrap; wp, alt and crank on the other belt in a triangle.

That way only the crank needs a double pulley.

A couple of other things you have to include in the power-draw comparison:

An alternator can put out 90% of it's maximum power at 15% of it's maximum rpm. Therefore, the maximum required torque is highest at low rpm (assuming high draw), and much higher than what it would be with linear output.

The alternator pulley is much smaller than the AC pulley, so the force required at the pulley groove (for generating equivalent torque) is higher.

[Alan Watkins]

Originally Posted by Bob Putnam

A couple of other things you have to include in the power-draw comparison:

An alternator can put out 90% of it's maximum power at 15% of it's maximum rpm. Therefore, the maximum required torque is highest at low rpm (assuming high draw), and much higher than what it would be with linear output.

The alternator pulley is much smaller than the AC pulley, so the force required at the pulley groove (for generating equivalent torque) is higher.

Good points. That at least equalizes the two and may even argue for reversing my proposition.

[Chuck]

Originally Posted by Bob Putnam

A couple of other things you have to include in the power-draw comparison:

An alternator can put out 90% of it's maximum power at 15% of it's maximum rpm. Therefore, the maximum required torque is highest at low rpm (assuming high draw), and much higher than what it would be with linear output.

The alternator pulley is much smaller than the AC pulley, so the force required at the pulley groove (for generating equivalent torque) is higher.

So is that why it is usually the alternator, not the AC, that is most likely to squeak at start up, but then quiets down once the revs get up a bit?

[Alan Watkins]

Originally Posted by CESLAW

So is that why it is usually the alternator, not the AC, that is most likely to squeak at start up, but then quiets down once the revs get up a bit?

I suspect so, since when the alternator gets going the first thing it sees is a partially discharged battery from having just started the car. So it immediately has to push a bunch of current into the battery to make up for what the starter took out. On the other hand the A/C compressor clutch is disengaged (I assume) when the car first starts up.

The other option we have independent of which load goes on which pulley is to increase pulley wrap by using a longer belt and an idler pulley(s). The rules there are that the idler needs to go on the back of the belt (probably obvoius) and it should be located on the belt run that is unloaded (i.e.the side where the belt runs from the crank toward the load). All you need is a ball bearing, a spacer to hold it away from the bracket, and a nut and bolt to attach the bearing. It can also be the belt adjustment if you put it in a slot rather than a hole.

[Chuck]

Originally Posted by awatkins

The other option we have independent of which load goes on which pulley is to increase pulley wrap by using a longer belt and an idler pulley(s). The rules there are that the idler needs to go on the back of the belt (probably obvoius) and it should be located on the belt run that is unloaded (i.e.the side where the belt runs from the crank toward the load). All you need is a ball bearing, a spacer to hold it away from the bracket, and a nut and bolt to attach the bearing. It can also be the belt adjustment if you put it in a slot rather than a hole.

But there is that pesky space problem. My alternator and AC compressor are as close to the engine as possible and squeezing any more pulleys or belts would be a challenge. How about dropping from at 100 amp plus alternator to a 75 amp alternator? By definition its maximum output would be less. I suspect 75 amps would be sufficient to drive the ignition and the cooling fans without difficulty. Less likely to get a slipping belt with less current demand . . . . . then go with the your original idea to run the AC off the crank pulley only. . . . .

[Rich E.]

I think we are bordering on analysis paralysis here. If your not gonna run a serpentine system just run two belts, make sure they line up, put on the proper tension and have at it.

.02