stairmaster

At 4W the alternator IS NOT working against you. At 40W the alternator IS working against you.

don

OM.pdf.

The easy way to do this would be to use an excited-field alternator with a load resistor, in which case the field coil would need excitation power, and there'd be a resistor getting hot in there while you worked.

And on page 45, step 11, they mention the alternator load resistor. This pretty much confirms my surmise.

Yes, they could make a 'green' Stairmaster that would take the energy that you were dumping into the alternator and shove it back onto the grid instead of burning it up. The circuitry would be more complex and therefore more expensive and prone to failure -- and the failures would be of the "flame and smoke" variety. It'd have to be engineered from scratch, which I'll bet that Stairmaster hasn't done for years. Finally, unless you implement things correctly, you run the risk of putting 120V on the contacts of an _unplugged_ Stairmaster -- which means that you need to make sure your electronics engineering team has their heads screwed on straight, and probably means sacrificing some of the 'green- ness' or spending even _more_ money on the circuit.

So you can figure that an 'plain old' Stairmaster is going to do it the cheap and expedient way.

The electronics I designed for an exercise bicycle back in the mid '70's was powered by the alternator, plus the alternator provided variable "resistance"... no A/C source was needed.

Alternator load was simply a big-ass zener equivalent (TL431 plus power transistor on a finned sink), PWMing the field changed the "resistance". ...Jim Thompson

Stairmaster; a device used to reduce floor spaced that needs vacuuming. Mike

Does that TO247 price include a big ass aluminum heat sink?

is

y,

I thought about it.... You are right, the cheapest way to make controlled resistance (mechanical, not electrical) is to control excitation current. For some reason I initially thought that the alternator has permanent magnet and dissipated power is controlled electronically. I wonder why use big ass aluminum housing resistor if same power TO247 MOSFET costs ~10 times less (Digi-Key prices for both)

C40-

grid

.I thought about it.... You are right, the cheapest way to make .controlled resistance (mechanical, not electrical) is to control .excitation current. For some reason I initially thought that the .alternator has permanent magnet and dissipated power is controlled .electronically. .I wonder why use big ass aluminum housing resistor if same power TO247 .MOSFET costs ~10 times less (Digi-Key prices for both)

Because Jim designed the circuit for them 40 years ago and they haven't changed it?

Are you sure they're using a 'good' resistor and not just $0.10 worth of resistance wire?

Not "resistor", "zener". ...Jim Thompson

I was using you as a metaphor for "old smart guy".

C40-OM.pdf.

I was kinda thinking about that as I wrote my post -- I suppose that if you want it to be "modern" you need to talk to a microprocessor, which means either a battery, a cord, or (gasp!) people actually having to _use the device_ to get the microprocessor to come alive.

Elaborating...

Until alternator spins up, a zener presents no load, then the output of the alternator clamps and can suck power proportionate to PWM'ing of field winding.

The TL431 plus NPN power transistor made all functions convenient, including a free power-on-reset. ...Jim Thompson

red

TW > Because Jim designed the circuit for them TW > 40 years ago and they haven't changed it?

TW > Are you sure they're using a 'good' resistor and not just $0.10 worth of TW > resistance wire?

JT > Not "resistor", "zener".

TW > I was using you as a metaphor for "old smart guy".

Much nicer than being a metaphor for "old smart ass".

Does this mean that new exercise bicycles will use neodymium permanent magnets instead of field windings and double as battery chargers in an emergency?

Even better, could a single AA flashlight battery be used to initially excite the field windings and then can it switch to using newly created power to seriously power the field winding? ( A bit of a chain reaction? )

Would that work to charge more AA batteries?

In my day, GM alternators had a mild amount of a permanent magnetism, thus were self-starting (saving a control wire). The draw-back is that there is a minimum load requirement to keep regulation. Thus was born day-time headlights... and you thought it was for safety reasons ;-) ...Jim Thompson

CL-

Oh, so _that's_ why they have all the thumpity-thumpity sound systems! It's so they don't have to turn the lights on!