vic wrote:
It would definitely draw a lot less amps for the same speed.
Like Jesse, I can’t see how there can be any significant difference. Electrical motors have very high efficiency (except for some types when they are starting). Since the work required to turn the engine is the same, the current must be the same as well.
vic wrote:
Just imagine a tiny motor at 20 000 revs driving a reduction gear to have the same revs on the crank: It would definitely draw a lot less amps for the same speed.
That’s nonsense. As what_next wrote, gearing doesn’t change power required to turn a crankshaft (well, actually it does, there will be some additional losses, but that’s really besides the point). As long as voltage stays the same, current flow must be the same. Such change cannot be due to addition of gearing. PS: Assuming voltage stays constant, current draw depends both on torque and speed of a motor.
Airborne_Again wrote:
Like Jesse, I can’t see how there can be any significant difference. Electrical motors have very high efficiency (except for some types when they are starting). Since the work required to turn the engine is the same, the current must be the same as well.
This difference is really there. Have done quite some starter overhauls and tests of them on the test bench. The output RPM on a lightweight starter is also much higher than on and old heavy weight starter. Heavy weight starters are generally better as well, especially as they contain old style bendix. Newer bendix quality is very low, and nowadays few starters make their TBO.
The motor construction is completely different, direct drive, versus geared – permanent magnet design.
For sceptics:
MZ heavy weight version – direct drive, 2240 Watt / 11.1 Ft/Lbs load
MZ light weight version – 4 to 1 gear reduction and PM, 4200 Watt / 10.0 Ft/Lbs load
sorry, your numbers can not be true as I read them:
light weight version: about double power motor, 4:1 reduction and yet still same torque ! There is some big mistake here. The reduction must be a a speed up really.
How much faster turn these light weight starters the crank in reality, if so ? I say max twice as fast as the direct drive old iron. So with reduction gear of 4:1 max amps will still be lower than with direct drive, no reduction. And when talking of real reduction gear of say, 4:1 and same crankshaft speed as before, you will need a motor one quarter of the power but four times the motor shaft speed for same crank speed. So you will obviously have only one quarter of amps as the torque will be upped by the gearing – right ? Certainly when you want a starter to perform higher cranking speeds you will need more power from it. Anyway, it is a simple matter of reduction gear theory how big the electric motor has to be: When you have a gear reduction of 1000:1 your motor only has to provide one thou of the required torque with obvious minimal electric current flow at that.
25 will be fine.
Thx Jason!
vic wrote:
sorry, your numbers can not be true as I read them:
light weight version: about double power motor, 4:1 reduction and yet still same torque ! There is some big mistake here.
This are the specifications from the overhaul manual and test specifications. My pratical experiance with the testing and overhaul of starters agree with the specifications in this manual.
Feel free to disagree. It’s like in the Alternator topic where you seem to compare different products. The information given on this forum by me is based on experiance with the actual products. I guess you can not compare all products they way you want to compare them.
