Alternator- Parasitic Drag?

[Doc Sprocket]

This one's a little outta my department, so if you know anyhthing here, feel free to throw it in!

As many of you know, I'm plugging away at a racing mower build. I have recently torn down a parts engine, and was examining the flywheel. I had a though- which occurs occasionally...

I'm quite restricted in what I can do to the engine in this build class, so I'm examining a two-fold "cheat".

We all know that a lighter flywheel allows an engine to spin up a wee bit easier. Now look at all those BIG magnets! What if I remove them? It will lighten the flywheel a bit...

Now, the question- By removing the magnets and therefore eliminating the alternator, is that going to free up a fraction of a pony? I have absolutely no idea how much drag the alternator creates... But I do know that I don't need a charging system for racing. The rules state that I have to have a functional starter- they don't say anything about not being able to manually charge the battery between races!!!

Is it worth doing?

EDIT- There are 12 magnets, I circled one in red.

 

[machinist@large]

This one's a little outta my department, so if you know anyhthing here, feel free to throw it in!

As many of you know, I'm plugging away at a racing mower build. I have recently torn down a parts engine, and was examining the flywheel. I had a though- which occurs occasionally...

I'm quite restricted in what I can do to the engine in this build class, so I'm examining a two-fold "cheat".

We all know that a lighter flywheel allows an engine to spin up a wee bit easier. Now look at all those BIG magnets! What if I remove them? It will lighten the flywheel a bit...

Now, the question- By removing the magnets and therefore eliminating the alternator, is that going to free up a fraction of a pony? I have absolutely no idea how much drag the alternator creates... But I do know that I don't need a charging system for racing. The rules state that I have to have a functional starter- they don't say anything about not being able to manually charge the battery between races!!!

Is it worth doing?

EDIT- There are 12 magnets, I circled one in red.

ut: If you're not putting a load on it, it shouldn't make much difference one way or the other.

Why don't you just whip out your race prepping bench dyno and do some pulls and let us know how it works out!!

 

[Doc Sprocket]

If I had a dyno... LOL

I don't think the alternator will drag much if the battery is fully charged- I'm just trying to debate if the combination of the two factors (in removing the magnets) is actually worth the effort... ? 'Cuz I imagine they'll be a bugger to remove!

 

[r97]

I would gut it, keep the flywheel lighter, and reduce the drag. I'm no expert either, but it would make sense to me that the output of the alternator is equal to the power the engine uses to drive that system, once you factor in the inefficiencies that is. If your charging system is always creating power, and the regulator just shunts everything to ground that isn't used, then I would bet you could see a somewhat noticeable increase in usable power. If your charging system is one that only generates electricity when it is needed, then removing the charging system probably wouldn't gain much, just as long as the battery isn't drained too much from starting.

Once again this is a topic I'm still learning myself, so my post is fully open to corrections!

 

[machinist@large]

If I had a dyno... LOL

I don't think the alternator will drag much if the battery is fully charged- I'm just trying to debate if the combination of the two factors (in removing the magnets) is actually worth the effort... ? 'Cuz I imagine they'll be a bugger to remove!

I'd be more concerned with throwing the balance out on the flywheel (that they would be a to get out is a given). Does this use the Ignition coil for the voltage pick off or does it have a separate coil for charging? Remove the coil, and you should remove any chance of adding drag. Just my

 

[Doc Sprocket]

The magnets shown (and the corresponding stator) are solely for the charging system. There is a magnet embedded in the exterior rim of the flywheel for the ignition coil, and a separate coil.

I'm not at all concerned about the balance. I know darn good and well that I could chip the magnets off, and use a dremel or similar to remove all remaining traces of magnet and epoxy.

EDIT- A stock photo of stator

 

[machinist@large]

The magnets shown (and the corresponding stator) are solely for the charging system. There is a magnet embedded in the exterior rim of the flywheel for the ignition coil, and a separate coil.

I'm not at all concerned about the balance. I know darn good and well that I could chip the magnets off, and use a dremel or similar to remove all remaining traces of magnet and epoxy.

EDIT- A stock photo of stator

You just answered your own question (as well as mine!!) Pull the stator and you're done; if the magnets have no coils to excite a charge in, then there's no drag from them.

And it saves you the trouble of chipping them out......

 

[Doc Sprocket]

You just answered your own question (as well as mine!!) Pull the stator and you're done; if the magnets have no coils to excite a charge in, then there's no drag from them.

And it saves you the trouble of chipping them out......

... you forgot about the lightening of the flywheel...

 

[machinist@large]

... you forgot about the lightening of the flywheel...

UUMMMMM.... keeping the magnets gives torque; harder to stall out (yea, yea, thats it).... oh wait this is supposed to be a race motor?

 

[machinist@large]

Any decision, Yea or Nea?

 

[Doc Sprocket]

No decision yet, and no hurry, either. Was hoping a few more of the "notorious" folk around here would chime in. Either way, I've still got lots ahead of me, and the flywheel's dead low on the "to-do" list.

 

[dman]

i signed up just to say this but if your going to do that then get a deep cycle battery so u don't kill what u have

 

[Doc Sprocket]

i signed up just to say this but if your going to do that then get a deep cycle battery so u don't kill what u have

Not a bad idea- thanks... Why not take off your coat and stay awhile?

 

[dman]

i would but idk much about building a racing kart im trying to get help on my new project right now

 

[Doc Sprocket]

i would but idk much about building a racing kart im trying to get help on my new project right now

We do a whole lot more here than racing karts!!! You might of missed it, but this thread is in relation to a racing LAWNMOWER I am building. We also cater to fun/yard karts, homebrew stuff, mini and pocket bikes, bar stools, whatever!

Heck- whatever YOUR project is, if no other category covers it, you can put it in the "Other Projects" section!

 

[jamyers]

Gut it.
You don't need a battery charger on your lawnmower, you'll have one in the pits.
Lighter flywheel will spin up faster.

 

[augidog]

so long as you can do the job properly, gut it and remove all doubt & all drag by any definition...there's a bit of mass involved, so it seems to me you'll even affect temperature to a small degree (pun intended.)

gut (simplify) the wiring too, and you'll be able to "hot-swap" the battery. i'd calculate the absolute smallest battery needed for a reliable start, then i'd get two and i'd keep one on the tender & ready to go for the next start...which btw we know is the best way to maintain SLA's anyway.

 

[Doc Sprocket]

You do make some compelling points. I have no problem doing the work thoroughly and competently. After chipping as much of the magnets off as I can, I would finish the surfaces with a sanding drum on my Dremel. All related charging wiring would indeed be deleted, I have all the appropriate diagrams.

 

[dman]

my project is on here look up "electric lawn kart" maybe you could help

 

[Tymoto21]

Not to bring up a dead thread but.....

An alternator will draw up to 5 hp per 100 amps of current draw you have.
So 1 hp is just above 700w BUT that alt is 60% efficient if your lucky. So Lets say your kart needs 500w to keep everything working. You are sucking almost 1.5hp away.
So if you take a DC amp meter and measure the current you are using. Times your voltage to get watts. Then devide total watts by .6 as a efficiency and that should give you an idea on hp lost.

It may only be 100w or so which is not much to worry about