When was the last time you saw a wood router running at less than 25,000 rpm? I haven't seen any flying brushes yet? Typical alternators have a max rpm of 12,000 rpm.
Why do you think slip rings aren't made of copper or a copper alloy like commutators?
In an alternator the field windings are rotating. They are energised with current through slip rings. The current through these slip rings is in the order of a max of few amps. It is this current which is used to control the charging voltage/current.
In a dynamo the field winding is stationary and power is picked off the rotor. An alternator is effectively a dynamo inside out with a rectifier stack to do the commutating.
The windings of an alternator are very different to a dynamo and hardly compare. The field rotor looks more like a bobbin with interleaved fingers. This as you suggest is more rugged than the rotor windings on a dynamo. Nevertheless you can find some very high speed ac/dc motors built on the "dynamo" principle.
The message from "Fred" contains these words:
Not the same thing at all. Slip rings aren't switching the current every time the brush passes a segment as there are no segments.
More importantly, the sliprings only carry the excitation current, which is quite low.
So what is your point exactly? Are you saying that the maximum rotational speed before destruction occurs is *higher* in a device with a commutator?
Obviously the maximum possible rotational speed will be limited by many factors. Amongst those will be the size of the device. What is the diameter of the commutator in a router motor compared to the diameter of the slip rings in a car alternator?
Again, in the context of what I was explaining, what is the point of this question?
Chris
No. The commutator on a dynamo handles the full output - so has to switch perhaps 30 amps with all the associated burning of both brushes and copper.
The slip rings on an alternator don't have to switch and carry a much lower current.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Fred" saying something like:
Charging current is determined by the resistance of the battery and the supplied voltage.
That lad Ohm had the right of it.
Yes the apparent internal resistance increases as you near full charge.
I can see that being true when you start the car but, once charging starts, won't the electrolyte be heated due to the charging process?
Brian
& anyway if you meter it it doesn't put it's full output into a battery.
Hi Brian,
Normally a car's charging system is not dumping 90 amps into a 50 amp hour battery. But, you are correct in that extended charging at rates greater than C/4 (where C is the amp hour capacity of the battery) will cause the electrolyte to heat. Once over 125 degrees F, the positive grid corrosion is accelerated. The good news is that most car batteries are recharged within the first five minutes of running the engine and the electrolyte does not have a chance to heat up significantly.
Kindest regards,
BiLL......
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