Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

[oil pan 4]

I have found with electric cooling pumps don't bet on getting more cooling capacity than you bargin for.
I use a electric pump that draws 10 amps and the company claims it can cool a "2200hp big block chevy" maybe that is a drag strip, sled pulling motor or methanol engine.
At "55GPM" drawing 10 amps is just enough to cool a diesel engine that is making no more than 30hp or 40hp while going down the highway.

[MetroMPG]

Dipstick raises a lot of good points - good cautionary reading for noobs who get excited about the relatively large potential fuel savings, but haven't really thought things through.

His advice seems to boil down to: this isn't a mod that should be done half-baked by someone who doesn't understand the consequences of implementing it wrong. I fully agree with that!

[JackMcCornack]

I'd like to put an alternator cut-out switch on my 32 horse Kubota diesel that will disengage the alternator (electrically--it has a one wire alternator) at full throttle. Will this improve fuel economy? I think yes, 'cause I'm giving my car a removable roof this summer, which will add a bit of weight, and according to my back-of-envelope calcs this alternator mod could give me a (worst case) extra half horsepower at full throttle which means I won't need any engine mods to keep my present (limited) performance. Does this make sense to anybody?

Also, should I do this with a relay? Probably so (rather than have long current-carrying wires 'twixt alternator, foot switch, and battery), and hooked up as NC; so how much will the current draw for a relay negate the alternator disconnect advantage?

[ecomodded]

After reading that someones electric cooling fan used 10 amps i had to look for a lower amp option. For the Flex-A-Lite brand, the amperage's vary from 28 amps to 5.2 amps. They have one 5.2 amp fan and one 7.7 amp.
A 9 or ten amp electric fan is the small size, a lot of them draw around 20 amps.
It appears Volkswagen has used the same fan in its diesel and gas 4 cylinder motors.
If my current electric fan dies, i will look for a lower amp fan.
Flex-a-lite Electric Engine Cooling Fans

[Christ]

Originally Posted by JackMcCornack

I'd like to put an alternator cut-out switch on my 32 horse Kubota diesel that will disengage the alternator (electrically--it has a one wire alternator) at full throttle. Will this improve fuel economy? I think yes, 'cause I'm giving my car a removable roof this summer, which will add a bit of weight, and according to my back-of-envelope calcs this alternator mod could give me a (worst case) extra half horsepower at full throttle which means I won't need any engine mods to keep my present (limited) performance. Does this make sense to anybody?

Also, should I do this with a relay? Probably so (rather than have long current-carrying wires 'twixt alternator, foot switch, and battery), and hooked up as NC; so how much will the current draw for a relay negate the alternator disconnect advantage?

Innit like 1 or 2 watts for a starter solenoid (form of relay) to actuate the big copper plate inside against the terminals? I'd think there would really be no noticeable degradation of performance, although your lights might dim some (haha - dim sum) at full pedal.

[Christ]

Originally Posted by ecomodded

After reading that someones electric cooling fan used 10 amps i had to look for a lower amp option. For the Flex-A-Lite brand, the amperage's vary from 28 amps to 5.2 amps. They have one 5.2 amp fan and one 7.7 amp.
A 9 or ten amp electric fan is the small size, a lot of them draw around 20 amps.
It appears Volkswagen has used the same fan in its diesel and gas 4 cylinder motors.
If my current electric fan dies, i will look for a lower amp fan.
Flex-a-lite Electric Engine Cooling Fans

On both my diesel Golf, and now the Festiva, I have no cooling fan. Don't let your car idle for any longer than you have to, and channel as much air through the radiator as you can by keeping airflow from going around, over, or under it.

Cooling fans, installed on the already piggish cooling systems of today's cars, are actually unnecessary. They're designed for a lazy market that likes the supposed convenience of leaving their car idle forever.

The only time it might be warranted (the cooling fan) or necessary, is if you're leaving the car on to utilize A/C. Even then, it's fairly easy to make a relay setup that will also turn a smaller, maybe 5A cooling fan on when you turn the A/C clutch on.

Removing the fan actually increases cooling capacity, also. It makes it so the air doesn't have an obstacle to move around. This is pretty easily identified because the airflow through the radiator moves the fan - obvious flow reduction.

[MetroMPG]

Originally Posted by JackMcCornack

I'd like to put an alternator cut-out switch on my 32 horse Kubota diesel that will disengage the alternator (electrically--it has a one wire alternator) at full throttle. Will this improve fuel economy?

It depends (TM).

If you are interrupting alternator load only temporarily, then the energy taken from the battery will have to be replaced by the alternator when you switch it back on, negating any temporary savings (owing to conversion losses).

I don't think the alternator delete/off mod works unless you are primarily running from the battery, and then using some other power source to recharge it.

You could conceivably control the alternator intelligently to take advantage of the best times to recharge the battery, ie. during throttle-off fuel cut or actual friction braking. Those opportunities are more common in sub/urban driving than on the open road (limiting usefulness for my typical driving).

[MetroMPG]

Originally Posted by Christ

On both my diesel Golf, and now the Festiva, I have no cooling fan.

OT - but I'm pretty sure I had a mid-80's Toyota Tercel that had no fan at all, from the factory.

[JackMcCornack]

Originally Posted by MetroMPG

I don't think the alternator delete/off mod works unless you are primarily running from the battery, and then using some other power source to recharge it.

In my case I'm using it to add a bit of full-throttle oomph, which allows me to get performance equal to having a slightly larger engine, and the fuel savings comes from not having to drag that bigger engine around when I don't need it. Probably of no significance on a big engine, but gosh, if I could replace the 17hp engine (say on an XR3 or other small trike) with a 16hp engine and an alternator switch, mileage might improve a few percent. My issue now is keeping the 0-60 time under 18 seconds...and it's 17 seconds and some change at present, and I'm going to be adding a bit of weight, so I may need all the help I can get.

Originally Posted by MetroMPG

You could conceivably control the alternator intelligently to take advantage of the best times to recharge the battery, ie. during throttle-off fuel cut or actual friction braking. Those opportunities are more common in sub/urban driving than on the open road (limiting usefulness for my typical driving).

I was considering putting a big, tall geared alternator in the system, with an air conditioner clutch that engaged whenever the brake lights lit, but for how little I use the brakes, the weight of a second alternator would cost me more mileage than the regenerative braking would gain me.

[MetroMPG]

Originally Posted by JackMcCornack

if I could replace the 17hp engine (say on an XR3 or other small trike) with a 16hp engine and an alternator switch, mileage might improve a few percent

Makes sense. And seems strangely similar to the economy justification for adding a turbo to a smaller engine.