ST Generator Efficiency ?

[veggie]

Does anyone know what the average efficiency is for the ST style generators when running in the "sweet spot". The ST-3 in particular.
As I understand it, the newer design brushless 3600 rpm heads used on today's "screamers" are about 92%.
I was wondering if the ST heads fall in the same efficiency range.

Veggir

[veggie]

Bump !!!

Any ideas at all regarding ST head efficiencies?
I'm trying to get an idea if they are much more efficient than a 24 volt Delco industrial DC alternator rated at 55%

[broncodriver99]

I have never seen a documented number. If I had to guess I would say in the 75-80% range at best. I have seen documentation on similar type designs albeit western designed and built and those seem to all be in the high 70's% efiiciency. I would think it very unlikely that the ST heads could match much less exceed those numbers.

What 2 pole heads are you seeing that are obtaining 92% efficiency? I went through all of the Mecc-Alte catalogs that had smaller generators in their range and I don't remember seeing anything above ~82%.

On the DC side so far the most efficient alternator I have come across is the Delco 28si in the 24V flavor. It is 76% efficient according to Delco.

[veggie]

Hi Bronco, I read the 92% effy somewhere when I bought my 3600 rpm 4kw Brushless Voltmaster head.
I have since tried to find the specs but I can't.  I'll take you word for it that an effy in the 70's is more realistic and that's what I am finding elsewhere too.
My reason for the info is that I was evaluating the difference in overall system efficiency when running a 24 volt Delco 26si vs an ST3 gen head for charging a battery bank.
If the efficiencies were close, I prefer the DC alternator because it's not sensitive to engine speed and I can run the Lister at wherever speed I want. 
However, if the AC alternator is considerably more efficient, the fuel savings could add up to a significant amount over several years.

[dkmc]

How difficult would it be to do some testing and determine efficiency of each?
Power in VS power out?

[ThomasEriksen]

Interesting topic…A quick search gave me Power (kW) = Torque (Nm) x RPM / 9550 so need to measure torque on shaft and rpm, there are shaft power meter, but those I found was for ships propeller shaft.Output power is simple to measure by power meter then divide that by shaft power and exaction power. Warning if answer is greater than 1 you found free energy and will either receive a Nobel prize or hunted by big power company, most likely math is wrong

[dkmc]

It's really about time someone's built a dynomometer for these engines. Not me tho....

[cujet]

It has been quite some time since I've done these calculations, so everything is by memory. However, being rather nerdy, I do tend to like playing with numbers.

My 20/2 Listeroid is run at 850 instead of 1000 RPM. It's well tuned and makes about 18HP. It will produce 11,500W with the ST15 head. The generator head efficiency seems to be about 85% at this point in it's operational range, about 76% of rated max output. I am not using the Z winding, instead I'm regulating and filtering the output of one 120V leg, in an attempt at producing a smoother sine wave.

In the end, the generator head is not terrible. But the power pulses of the engine do result in the typical lister flicker.

[veggie]

cujet

Thanks for the numbers. All the research I have done regarding DC alternators states that the average efficiency is around 55%.
So it would seem that the ST generator is far more efficient at making power.
A difference of 30%  (85 compared to 55) is considerable.
In other words, my engine with an alternator would have to work 30% harder to make the same power as an ST head.