SR-71

I have plans to put on an underdrive pulley system. I may consider an electric water pump, if I can find one for daily drivers that fit GM. (All I find so far is for Mustang.)

But I've been thinking. Is there a system anywhere to drive ALL the belt-driven accessories (water pump, power steering, and A/C) with an electric motor? I've seen that the 2008 Tahoe Hybrid has an electric-driven A/C system, but I haven't found any details.

Does anyone know how much power it takes to drive all three? If I could find a good, brushless DC motor, I could probably fabricate a drive system. I can find all sorts of info on how much an underdrive pulley saves, but nothing on how much total power the three systems actually drain off the motor.

Supervisor42

So what would you drive the great big alternator that's going to be needed to power the electric motor with?
If it's a 406 that runs the 1/4 mile in 12.6 and gets 28.6 MPG at 65mph, I wouldn't touch it...

Guest

There are electric power steering pumps out there but as I understand it, its quite complicated and a rather large motor to drive something with that much hydraulic pressure.

Meizere for one makes an electric water pump, I have one.

Air_Adam

If I understand correctly, you are trying to drive all your accessories - including the alternator - with an electric motor.

If I'm correct, then what you are trying to do is what people have been trying to do for hundreds of years - build a perpetual motion machine. It would have to be a system that creates more power than it uses to run itself (more alternator output than the motor would require to drive everything, including alternator.)

If you figure out how to do that, let us know - and patent it. You'd be sitting on a goldmine!

SR-71

No. Note that I didn't list the alternator.

I'm just trying to consider possibilities. There's enough talk that even underdrive pulleys aren't worth the cost for their little return. But since the new hybrids drive all their accessories with electric power, I thought the question was worth asking.

The "Bang for the Buck" principal probably will rule against it, but it's worth looking into.

I bet it would take less alternator than some of you guys' big boomdie-boom stereo systems!

I'm trying to break 30 mpg and still stay in the 12's.

Batass

Well thats obviously not possible, so he'd still need to run the alternator off the motor.

Alternator load is going to increase a lot. You have to decide what rpms you want to turn the motor.

So you'd convert mechanical power into electrical, back into mechanical. I think the gain would be minimal.

However acceleration plays a big part in power loss, so that might increase.

SR-71

Yeah, that's another question. When would alternator load become the same as driving the accessories by belt? Electric motors run at 80% plus efficiency. Gas less than 40%. So an electric motor draws less to do the job than the gas engine does.

I know an electric fan is less load than a pump-mounted one, so an electric fan increases power and mpg. Same with an electric water pump. Takes less power off the engine to run an electric water pump than a belt-driven one.

So the question becomes, how far can you push that? Can you drive only an alternator off the engine, and run all the accessories electrically, and be ahead of the game on power and economy?

There are arguments against an electric pump that if it fails, you have no cooling. Some pumps aren't recommended for daily drivers. Some are. Some say the Mr. Gasket pump drive system isn't safe for daily drivers. But then I have a certain amount of insecurity about the serpentine belt. If the belt blows, then I lose cooling, steering, AC-- everything. But it's easier and cheaper to replace a belt than an electric motor. More to think about.

I'm basically just trying to stimulate discussion on it, to consider the possibilities.

Supervisor42

Well, for $15 you can do what I did to free up power. Put in a WOT switch/relay to interrupt the A/C clutch and sleep the alternator. It turns them both into idler pulleys.
Since you have electric fans you can still have them working off of the battery at WOT. The engine doesn't spend that much time at WOT so the battery won't get run down.
This leaves only the water pump and P/S pump using power from the belt during WOT, everything else is an idler pulley. And if you're going in a straight line, the P/S pump isn't using jack.
The big horsepower hog of the accessories is the alternator.
It is powering the cooling fans, headlights, and the HCAV blower motor (and an occasional 2000 watt amp). It's easy to make an alternator "not charge" with the exciter wire.

For mileage: Verify that both cooling fans stay off at highway speeds. If the air dam is working, it supplies much, much more air than the fans. That's why the factory turns on the fans at such a high temperature. If they're off during cruise, they take zero horsepower. (people with their fans on a manual switch, pay)

Electric water pumps: There are several reasons why the factory hasn't gone with electric pumps.
The belt driven one goes faster as the engine goes faster.
This is very convenient as the engine needs more cooling the faster it runs. Electric pumps are either on or off. If you have one that moves enough coolant for WOT, then it is wasting power at cruise. Also when you change rotational power into electricity in the alternator and back into rotational in the electric motor there is inefficiency and energy lost as heat in both parts. So switching to an electric pump will actually cost you MPG.

The only time electric pumps make sense is at the dragstrip, where the cooling system can continue to run after the engine is turned off. This lets a much smaller radiator be used saving a lot of weight because it is full of water. Ask a drag racer if weight is important...