Alternator issues

[Mikexx]

9 hours ago, Sir Nibble said:

You compared two maximum outputs at two different speeds. Think of it like this. The alternator spins at a speed S. Output is around 10A at 13V, 130W. Reconfigure the same alternator and at speed S it gives 30A at 14V, 420W. The extra power has to come from torque because S is the same in both cases. The potential for the original alternator to produce more at higher speed is irrelevant since not only is increased speed a contributor to overall power but is not achievable anyway, which is why the alternator has been modified.

 

I'm still not sure where my argument is flawed. If there is any misunderstanding I apologise. I do feel the need to point out that in generall the higher the rotor speed the higher the output for any given star or delta configuration or number of turns, up to some aymptotic output. As you say the potential for the original to produce more at higher speed is only relevant if the increased speed is achievable.

I think the diagram below best illustrates the difference between an alternator with a set number of stator turns and another with twice the number. Changing from delta to star will be similar, except the improvement in cut-in speed with be sqrt(3) and the max current for star configuration would be 1/sqrt(3) of delta. What the graph does show is that at some point in speed the alternator with the lower number of turns will have a greater output.

 

[ditchcrawler]

This topic is sort of dragging me back 50 years to colege days which are not coming to the surface very well.

[WotEver]

On 08/05/2017 at 19:52, Mikexx said:

I'm still not sure where my argument is flawed.

I believe you answer it yourself when you later write...

On 08/05/2017 at 19:52, Mikexx said:

the potential for the original to produce more at higher speed is only relevant if the increased speed is achievable.

The increased speed isn't achievable. This is a given and is why the alternator has been modified. It's a slow revving engine with a too-small engine pulley, meaning that the alternator spins slower than its design speed. 

So, let's talk not about an unachievable theoretical maximum speed, lets instead talk about the one fixed speed that the engine is rotating at when cruising down the cut. At that speed (which is the real, actual speed that it operates at) the modified alternator is now putting out three times the power than before it was modified. Therefore the torque required through the belt is three times as much. 

[Mikexx]

13 hours ago, WotEver said:

I believe you answer it yourself when you later write...

The increased speed isn't achievable. This is a given and is why the alternator has been modified. It's a slow revving engine with a too-small engine pulley, meaning that the alternator spins slower than its design speed. 

So, let's talk not about an unachievable theoretical maximum speed, lets instead talk about the one fixed speed that the engine is rotating at when cruising down the cut. At that speed (which is the real, actual speed that it operates at) the modified alternator is now putting out three times the power than before it was modified. Therefore the torque required through the belt is three times as much. 

I take your point and the/my misunderstanding.

I was trying to say that max torque with a standard winding, would be the same torque as a modified winding. As you say, and I agree, the max torque with the standard winding may never be achieved for a slow revving engine/camshaft drive.