Accessory drive

[Telco]

Hi, new member here. Read a lot of the posts, pretty impressive what some of you have done.

Has anyone tried building an accessory drive system that uses an electric motor to drive the accessories instead of using the engine? I was thinking that this might solve some of the problems with killing the engine for coasting, if the accessories were driven by an electric motor. You'd need a larger alternator driven off the engine, and a deep cycle battery, but this would allow the AC, power steering pump and water pump to be driven at one speed at all times. This would have the effect of eliminating variable speed steering boxes that make it harder to steer at highway speeds and easy to steer in town, but wouldn't affect steering systems that don't have this. It would allow the power steering to work at all times. Adding a Hydroboost braking system would also allow power brakes to work at all times, not to mention not having to worry about the air conditioning not working properly. This would also eliminate a lot of drag on the engine.

Thoughts? I come from the performance world and like the idea of not having drag on the engine on a WOT pull, but thought I'd post this idea up as a safety issue for you fellows. I'm kind of an oddball because I believe you can have a high power engine that gets good mileage with proper planning.

[omgwtfbyobbq]

Manufacturers are doing this with mild hybrids, but you need a few deep cycle batteries to run the A/C w/ the engine off. The others are relatively small iirc. Overall efficiency would go down too, since going engine->alternator->battery->motor->device is less efficient than
engine->device, so you won't see much in terms of gains unless you go alternatorless and/or charge the batteries separately. Otoh, if you really want A/C that bad when the engine's off, you could go for it. For braking, I'd just go with a boosterless system. No need for power brakes on a 2-3000 lb vehicle imo.

[Telco]

You know, you'd think so but not necessarily. When you remove the mechanical clutch fan you remove about 30HP of load, but you don't add 30HP of load at the alternator. If you did, then converting to an electric fan would do little for you. When I made the switch my fuel economy went up 2MPG and the power increase was great, especially in the upper RPM band. Even when the fan was running there was no perceptible difference in power. Then, some of the experimental hybrids that only use the gas engine to run a generator, which then drives the wheels, is getting way better mileage with the same power as a comparable gas-only engine. You'd think that going direct from engine to accessory is more efficient but I have to wonder. I can see why the manufacturer won't want to do this, it'll add a lot of complications and an expensive electric motor under the hood to take the place of a 20 dollar belt.

I think I will look at this, unfortunately I can't mess with it until the kids move out, starting this time next year. No cash available for special projects until then, I'm doing good to do what I am doing with my truck as it is. After all, the kids come first!

[omgwtfbyobbq]

30hp of load? On what engine? I'm saying that running everything connected to a belt through battery power and a larger alt would be less efficient than your current setup, not that switching to an electric fan from a mechanical fan w/ clutch alone is going to drop efficiency.

[Bill in Houston]

It seems like a small motor running the water pump might be a good efficiency boost. Not sure if it would be worth it to mess with any changes on the PS or A/C...