Delco alternator efficiency white paper

[mobile_bob]

there has been a long held belief by many that automotive alternators are only 50% efficient on average

this up until the last year or so was a belief i shared without question, however after doing some research
i am finding this is not necessarily the case or rather need not be the case.

the following link was posted on another forum a while back and i thought it might be of interest to some
and would also be a lead in for a much more indepth report to be published here in the next few weeks.

the report will be on the results of my research into the modification and use of automotive alternators for use
in non automotive applications, namely fixed speed operation with better control strategies.

the following like is from Delco and is an interesting read

http://www.delcoremy.com/pdfs/High_Efficiency_Alternator_White_Paper.pdf

note*
i am keeping a copy of the pdf on my puter should the link fail down the road, not sure yet how to post
the complete text or the pdf in its entireity here, or if it is legal to do so.

bob g

[rl71459]

Good Read!

Thanks Bob

[PsycoBob]

Bob- if you can post it, the link has failed.

[gregger2k]

Try http://www.delcoremy.com/Documents/High-Efficiency-White-Paper.aspx

[JLMTECH]

Hi Everyone,

Thanks MobileBob. I found a white paper on the Delcoremy.com/documents/high-efficiency-
white-paper.aspx. This might be the one you have referenced for automotive alternators. This
paper has efficiency curves for partial loads and various RPMs. The alternator tested maximum
output seems to be 160 to 200 amps.

I have been seeking partical load data for automotive alternators.

For charging batteries, the efficiency curves verify the improvement you obtained by increasing
the output voltage to 24 volts and higher by reducing the losses in the diodes. The paper indicates efficiencies of 60-70% at 14 volts with large diode losses. Increasing the voltage to 28 volts should reduce the percentage diode loss by about half so that the overall alternator efficiency is increased.

Also shown are partial amp load curves. For your design, reducing output current below maximum (40% to 60%) increases efficiency.

The most interesting (unexpected) result shown is that the best efficiency is obtained around
2000 RPM for alternator speed. I guess this means that alternator speed should be just enough to
provide minimum cooling to match the maximum current draw.

Larry

[mbryner]

At higher and higher alternator speeds wouldn't efficiency suffer from cooling fan drag?

[Lloyd]

One thing to consider.

Our application, is completely different then the down the road application.

First we use the alt to charge the bats, not produce on-board power. Our run-times are only when needed,(to replace x amount of current back in the bats) and the output voltage is usually 14.5 during the bulk/absorption time, at a fixed speed. The higher the v-out the better the eff..

So we need a fixed amount of current to charge the bats, so if we run the alt at lower speed our total output drops from 160 amps to 120 amps from top speed to 2000 rpm, that's a 580 W/hr drop in out-put, so that means we have to run the engine longer to put the fixed amount of current back into the bats.

Life is always about balance, we really need to find our balance for this application, bc I don't think we can extrapolate the eff...curves from this paper.

I am a big believer in running the alt at a much higher voltage and using buck regulation to get back down to bat voltage, either transformer or switch mode rectification.

Lloyd

[mbryner]

Thanks for posting that white paper.   It's a good read.   I just finished reading it and it answered some of my questions.

[admin]

JLM/Larry

along with lower diode losses (as a percentage of the total) we also have significantly less stator losses

typical automotive 24volt alternators, either rewind the stator with more turns than the 12volt counterpart, reconnect in wye, or both.

all these thing significantly increase stator resistance and losses.

they have to do those things in able to get to  charging voltage at engine idle and low relative alternator speeds.

this is why a 12volt alternator overdriven to provide 24volt nominal charging can be much more efficient than simply going out
and buying a 24volt alternator,,, at least for our purposes where we are more likely to either be running at a fixed speed or a relatively narrow
speed range.  we don't really care about engine idle low rpm performance "and" also having to stand up to 4 or 5 times that speed too.

we can pick a speed and engineer our drive to provide the rpm range we wish to operate in, we can then re purpose a 12volt alternator to run at 24, 48 or whatever higher voltages we want, change out the diodes and end up with something that is very efficient. 

certainly there are other more efficient ways of getting up the mountain, however none can compete economically with this system.

in my opinion of course

bob g

[JLMTECH]

Hi Bob G, Et al,
I find the more winding in a 24 volt alternator interesting.
I understand that pumping cooling air is another big loss.
Lower rotor speed has less pumping thus higher efficiency.
Is the cooling different?
Larry