Alternator voltage control

[nicknorman]

At last I have got around to some measurements. I had been taking the Smartgauge readings for voltage as Gospel, but I know that my SG does not agree with my voltmeter so all these are all taken using my clamp meter/multimeter.

 

These were taken with RPM (sensed from alternator reading 1100. The pulley rations indicte that this should mean that the alternator is running at about 3000RPM.

 

B+ to case voltage = 14.36

D+ to case voltage = 14.46

Battery voltage = 14.22

 

Current out of the alternator at 10A

 

Are these reasonable?

 

Nick

So you are dropping 0.14v at 10A, which seems a little on the high side. At 70A it would be 1v. Of course you will be dropping voltage in the -ve path as well as the +ve. You might get some improvement by finding out exactly where the voltage drop is, and remedying it (or more likely, them).

 

Otherwise, you say you have set the alternator to limit at 14.2v (-ish) and that is what you are getting at the batteries. That you are only getting 10A into them at that voltage presumably means they are at a fairly high SoC.

 

Looking back at this thread I tend to agree with dave and disagree with snibs (I dare to do that now he's left!) - the voltage regulation of an alternator is fairly soft and it won't be giving 14.2v at high current. But in your case, you should be able to improve things by having less voltage drop in the wiring at the alternator's max output.

Edited April 17, 2015 by nicknorman

[Theo]

Thanks, Nick.

 

I think that I will redo the measurements at the beginning of the day when the battery voltage is a bit lower. I will have a go at measuring the voltage across each of the terminals and see where the resistance is high.

 

N

[nicknorman]

As a start, do alternator B+ to battery +ve, and alternator case to battery -ve with high current, then work along the +ve path and then the -ve path to identify what is dropping voltage.

[Theo]

As a start, do alternator B+ to battery +ve, and alternator case to battery -ve with high current, then work along the +ve path and then the -ve path to identify what is dropping voltage.

Thanks, Nick.

 

I will do this and let you know the results.

 

N

PS and , Why has Snibs left? Nothing I said, I hope.

 

N

[nicknorman]

Well probably best if you search for his departing thread.

[Theo]

Alternator B+ to battery +ve, = 0.336V

 

Alternator case to battery -ve = 0.286V

 

At this time B+ to casing was 14.25V

 

Both at 43A

 

Which means that I am wasting 4.4% of the power that the alternator is generating. To me this is fairly insignificant in terms of energy loss but will the voltage drops be significant in terms of the regulator?

 

 

N