Replacing R/R for better MPG?

[cyclopathic]

I am looking to replace the OEM Shunt type R/R with series unit, and if my math correct depending on speed this should give me 3-13% MPG improvement?

OEM stator is rated at 35A (420w) and this is constant load due to shunt type R/R. The actual electric load is 190w less, which with series unit should reduce engine drag by 0.26hp.

Per calculator depending on speed (35-65mph) road+aero load is 2-10.3hp, so the 1/4hp drag reduction should give ~3-13% improvements.

Am I missing something?

I suppose at lower speed the stator output will be less than max, so 13% is over-estimate.

[Grant-53]

If we are talking about a generator system then minimum drag is when there is no current in the field windings or the armature is not moving. The core of the field coils will have some residual magnetism so there will be some slight output with the armature moving. A clutch on the armature shaft could control it such as used on an AC compressor though there would need to be enough current from a battery to engage it.

[ProDigit]

Just remove the alternator, and install an exhaust driven turbine driving a generator.
Really, you don't need an alternator, are better off with a rotating exhaust turbine.

[stiletto2]

Originally Posted by ProDigit

Just remove the alternator, and install an exhaust driven turbine driving a generator.
Really, you don't need an alternator, are better off with a rotating exhaust turbine.

That's just gotta be a joke. If such a thing existed and was viable, we'd be using it already I'd think. Back pressure would reduce performance and if it were made so that it wouldn't do that so much then it probably wouldn't be able to keep up with enough charging. A couple little windmill generators at the bar ends charging a pack of Lithium ion batteries on a no alternator/generator engine would probably be just as effective. (or just as ineffective as the case would probably be) If real, then I'd want to see a source.

[ProDigit]

Back pressure trades top speed for torque, so your MPG should go up, as well as your acceleration.

As far as an exhaust driven turbine, powering an alternator, no one invented this yet.
But if you want to ride alternator free, the exhaust is a good place to harvest the energy from.

[ThermionicScott]

Originally Posted by ProDigit

Back pressure trades top speed for torque, so your MPG should go up, as well as your acceleration.

As far as an exhaust driven turbine, powering an alternator, no one invented this yet.
But if you want to ride alternator free, the exhaust is a good place to harvest the energy from.

A lotta "shoulds" and "ifs" and "no one ___ yet" in there. We like tested and proven stuff on this forum.

[ProDigit]

Originally Posted by ThermionicScott

A lotta "shoulds" and "ifs" and "no one ___ yet" in there. We like tested and proven stuff on this forum.

Nothing works tested and proven 100%, however, back pressure allows more hot exhaust in the cylinder to warm up the incoming cold air/fuel.
It's a proven fact to increase torque and MPG. That's why many manufacturers do this especially for small bikes, and performance cars as well, using exhaust back pressure valves, or some form of restrictive exhaust can.

[ThermionicScott]

I was talking about the exhaust-powered alternator, obviously.

[ProDigit]

I think trying to disconnect an alternator, is just as unproven.

[ThermionicScott]

Originally Posted by ProDigit

I think trying to disconnect an alternator, is just as unproven.

Nope! There are folks on here who have run A/B/A tests of alternator deletes, and good discussions of the pros and cons surrounding them.