Electrical Load VS Mechanical Load

[SHGWAG]

One thing I've always wondered, due to being a newb at most things electrical.

Say you have a vehicle with the following belt driven accessories:

Water Pump

Power steering

Fan

If you remove these things, & replace them with the electrical equivilants:

EWP

Electric P/S

Electric Fan

This obviously reduces the physical load on the crank / engine making it "Produce more power"

However, this would place more load on the alternator correct?

Now, I get that an alternator is a magnet spinning inside a coil.

My question is: Does electrical load cause greater physical resistance for an alternator to turn?

Thereby placing more physical (Mechanical) load back onto the crank. If that makes sense?

Someone smart will answer this in one post.

[Simon]

My question is: Does electrical load cause greater physical resistance for an alternator to turn?

Thereby placing more physical (Mechanical) load back onto the crank. If that makes sense?

Absolutely.

It takes some high power calculations to figure out which option is better, mechanical or electrical driven.

I would get rid of the mechanical fan. Leave the mechanical water pump and power steer to be honest.

Although I don't know you situations 100%

Even things like amps and large audio systems can increase fuel usage heaps.

People often think that electricity in cars just comes from the battery in there, forgetting that it has to be replaced by the alt.

[Spencer]

Basic answer

Yes an alternator changes the the small field current to keep a constant output. Thus putting more load on the engine as more load is put on it.

It still takes the same ammount of energy to move the same amount of water or air no matter if its mechanical or electrical driven. Then theres losses in the mechanical - electrical conversion (alternator is only 50-60% efficient)

As far as I see the savings of electrical devices in this situation is that they can be controlled better and only be run when needed, or at varying speeds/loads.

[Unclejake]

An EWP delivers something like 80lpm regardless of the revs but adds a constant load to the crankshaft via. the alternator.

A mechanical waterpump delivers variable lpm depending on revs and therefore is a variable load on the crankshaft but the optimum water reticulation is probably happening at medium revs.

The load an EWP puts onto the crankshaft at high RPM will therefore be less than the mechanical waterpump.

For this reason an EWP can free up horsepower where you really need it and will provide better cooling at low RPM (like when stuck in traffic with reduced airflow over the radiator).

The horsepower gains are not significant with the EWP but the HP gains with an thermostatically controlled electric fan vs. a direct drive mechanical fan can be significant as the mechanical fan is doing nothing but robbing horsepower over 60 kmph

Summary: Pushrods

[Hemi]

this explains why your car suddenly loses load if you jump it and unhook the batteries etc .

and lose the mech fan , whaat hell no .. keep that stz .. good for burnouts etc can suck a blackman off your sister etc

[mikuni]

As far as I see the savings of electrical devices in this situation is that they can be controlled better and only be run when needed, or at varying speeds/loads.

This. Link computers (along with probably all aftermarket ecu's and more than like some top end factory systems) can be made to shut off the alternator under wide open throttle conditions. If you think about track use you are probably only on WOT 30% of the time, if that so it still gives you 70% of the time to replenish the battery charge.

In a completely unrelated tangent, some race cars run the power steering pumps on dummy axles because the overall losses are reduced compared to running it straight off the engine. Would suck at low speed though.

[Unclejake]

^ If you looked hard under the throttle pedal of a certain race car you may see a momentary off switch wired up the exciter wire to the alternator

[forced]

This. Link computers (along with probably all aftermarket ecu's and more than like some top end factory systems) can be made to shut off the alternator under wide open throttle conditions. If you think about track use you are probably only on WOT 30% of the time, if that so it still gives you 70% of the time to replenish the battery charge.

In a completely unrelated tangent, some race cars run the power steering pumps on dummy axles because the overall losses are reduced compared to running it straight off the engine. Would suck at low speed though.

It doesn't need a computer to do it.

Not very clever though because when you shut down the alternator the voltage drops, So instead of running off about 14 V it drops to 12V or less. There's a corresponding drop in ignition voltage and injector voltage, the drop in injector voltage affects the "dead time" (Slower to open) and hence the AFR. Just a bit but it's still an un needed variable.

Mitsi AWS uses a diff driven pump for the rear steering, no doubt others do to.

Steve

[84_S12]

At full load a 90A alternator is about equivalent to a 2hp electric motor working against your engine

[Simon]

What he said^

And why have your energy converted from mechanical to electrical to mechanical at a power loss of like 50% when the cars life is 98% road and 2% track?

/ perpetual motion...

[SHGWAG]

I see.. cheers guys. The penny has dropped

[UTERUS]

[useless post] reminds of this boat i had the misfortune of working on once, you could have the inverter and battery charger on at the same time. The dude honestly thought converting 12v to 230v and back to 12v was going to charge his batteries [/useless post]

[David]

Remember there is two ways to disconnect an alternator.

Electrical : By putting a electrical contractor between the battery and the alternator.

Mechanical: By installing a clutch to the front of the alternator.

Both have problems, Electrical cutting in and out can blow the diodes in the alternator (Need to install capacitance with a current limiting resistor) between the alternator and ground.

Mechanical (can use an Air-con clutch). When pulling the clutch in on a high current load, the sudden load can send the V belt flying. This depends on the number of poles (size), capacity and the mass of the internals of the alternator and how fast the electrical load will react. (Need a meaty belt to overcome this but courses more mechanical losses).

In all disconnection is a big paid in the butt. Just remember to turn your sounds down and your rear windows demister off when dragging off from the lights.

Back to the original question. If it’s an older car with no power steering. It’s likely to have an old non-viscous fan and inefficient water pump, robbing power away. (All running off one belt). Yes the change to an appropriately suited thermostatically controlled electrical fan and pump will give a good efficiency% gain and a better ¼ mile and could use less fuel. You may have to consider upgrading that stressed out old alternator. Remember you’re putting all your eggs in one basket now, and this is your weakest link. The same could be said for a dirty old V belt running all the old stuff. If a V-belt breaks on you, you can find one not far away and not for much and change it with some junk tools out of you boot. A new alternator is not so easy when you break down on the side of the road.

As we know spending $1000 on gear and saving $30 on fuel a year, or knocking 0.04 seconds of a ¼ mile time doesn’t add up. The most important question is does it make my engine bay look good?

For a late model car it’s unlikely to help: It’s all about looks. It’s most likely you’ll just upset that harmony of the motor and will lead to a breakdown some ware down the track. As always have a person well prepared to point the blame at when it happens.