Mostly PM motor - Joe Flynn motor. My attempt to replicate

[Jetijs]

Finally after more than a month I received my tacX imagic virtual trainer. Will test it now with a bike and then see how I can modify it to work as a dynamometer. Finally some action
Thanks,
Jetijs

[zhorv324]

Good news, I can t wait

[Jetijs]

Hi zhorv324,
I finally got all the things together to connect the motor with the trainer. So far I man not very familiar with the software so it is possible that I am doing something wrong, but the results does not seem very good. At 30V 1.2A input the trainer software shows only 16W of mechanical power. If I lower the voltage to 12v again 1.2A of current is consumed that means 13w of electrical input, and the software shows 10w of mechanical output. Weird. I will fiddle around with the software a bit again, but I think I will have to go with a prony brake. How did you measure the efficiency of your motor?
Thanks,
Jetijs

[zhorv324]

Hi zhorv324,
I finally got all the things together to connect the motor with the trainer. So far I man not very familiar with the software so it is possible that I am doing something wrong, but the results does not seem very good. At 30V 1.2A input the trainer software shows only 16W of mechanical power. If I lower the voltage to 12v again 1.2A of current is consumed that means 13w of electrical input, and the software shows 10w of mechanical output. Weird. I will fiddle around with the software a bit again, but I think I will have to go with a prony brake. How did you measure the efficiency of your motor?
Thanks,
Jetijs

Hi Jetijs, yes the result is pretty weird. I don't have any experience with that kind of software (maybe someone on forum). Another possibility is bad accuracy of software trainer in small amount of mechanical power . I tested my motor with pony brake because of low power,exactly 32w of nominal power. In my experience prony brake is also not accurate but in my case is only way. I would like to have small generator but theirs efficiency is also bad. Another tip for you , how calculate nominal power of your motor. Sum surface of pols on your motor then squaring and divide with 2 (SxS/2). As i say before this kind of motor is very efficiency but not over unity . I hope you not give up hands of experiment on motor at least i not

[Jetijs]

Thanks zhorv324
I just built a quick and messy prony brake from aluminum bar. The length from the center of motor axis to the pressure point is 150mm and at about 1050RPM, the motor pressed about 150 grams on the scale at an input power of 37w. If I calculated it right that gives me about 24w of mechanical output. This number differs from that of the trainer software. This whole setup I have here now is messy and inaccurate, the numbers are jumping around quite a bit I will build a better pronybrake and get better scales and then test it some more.
Also I am not sure I calculated it correctly. Mayne someone can give me the exact equations I need to calculate the horse powers?
Thank you!

[Jetijs]

ok, a quick update.
I am still not sure if I calculate it right but I switched to the bigger magnets and did the test again. This time the motor consumed 54.2w of electrical power and if I calculated everything right, the mechanical power is 55w. I would be glad if someone guided me through all this prony brake measuring process.
Thank you!
Jetijs

[zhorv324]

Sorry I m in rush ,but I use this formula for prony brake HP=2PixNmxRPM/33000 and than HPx746/1000=kW . In your first case Nm=0,23,I think

[Jetijs]

Hi zhorv324,
Thank you for the formula
I made some tests again with my crude prony brake setup. It is hard to get a stable result, because my brake is made out of aluminum and as soon as I tighten it, the motor slows down but it starts to increase the RPMs soon again, I guess the aluminum is ground off on the contact area. Anyway, I managed to get few stable results and it seems promising if I have done everything right. For example I had input voltage of 25.7V and input current of 2.2A, that means 56.5w of input electrical power. At this time the force on the scales was 111grams and the lever length was 150mm, the RPM's were at 2500. So this is 0.1665 Newton meters. Now if I take your formula - HP=2PixNmxRPM/33000
I get:
6.28*0.1665*2500/33000=0.0792HP and that is 59W of mechanical output or efficiency of 104% Right?

This is only one of the stable results I had, some were better and some were worse.
I will make a new prony brake setup from wood and use different scales to confirm these results.
Thanks,
Jetijs

[Ted Ewert]

Nice work J.
You can also use HP calculators on the net for your conversions.

Watts to Horsepowers Conversion Calculator
Horsepower Design Equations Formulas Calculator - Rotating Horsepower
Rotating Horsepower Calculators - Horsepower, Torque, Speed

Ted

[Jetijs]

Thanks Ted
At this time calculations are no problem anymore, the problem is acquiring precise data

Thanks,
Jetijs

[zhorv324]

Thanks Ted
At this time calculations are no problem anymore, the problem is acquiring precise data

Thanks,
Jetijs

Sorry Jetijs i must check this formula on net . It seems it not contains Nm but pound foot(must convert Nm to foot pound) . Anyway god luck with new prony brake .I see now that 1Nm is 0,74foot pound

[Jetijs]

Ok thanks

[Jetijs]

Hi all.
I have tried to get some decent results from the prony brake tests. It is very hard, I am using aluminum braking pads and they tend to heat up and wear off at higher loads and It is hard to get stable working conditions, the RPMs are always changing and the pressure on the scales too. The results are not to be fully trusted at this time, but it seems good. It looks like that the more I load the motor, the better efficiencies I get also higher voltages seem to increase the efficiency. But the harder I load the motor, the more unstable the operation gets. Anyway, so far I have seen efficiencies up to 136%. Even taking in consideration a big margin of error, the motor seems to perform very well. I just need to get a better testing method. It seems I will need to make some kind of braking disc with bigger diameter than the shaft itself, this way even moderate friction could load the motor down considerably without much heat. Because if I brake the shaft itself, very much heat is created and aluminum disintegrates fast thus also the unstable RPM's and pressures.
I am open to suggestions
Thanks,
Jetijs

[Ted Ewert]

I got the same result with my motor when loaded; that the efficiency went up. That's when the magnets really kick in.
I recently built a prony brake you might get some ideas from:
Prony brake - Heretical Builders


Ted

[Jetijs]

Nice work Ted.
Doesn't the acrylic cylinder melt when under greater loads? I tried something similar once on the attraction motor, but since my RPM's were about 3000, the acrylic disc started to melt.