Vortex1:

QuoteSince there is a finite amount of energy per pulse, it takes more pulses of energy to charge the cap from say 4 to 5 volts than it does from 1 to 2 volts

E(J) =1/2CV^2.

Exactly.  This also implies the following:  If you take your 20,000 uF electrolytic capacitor and charge it to 20 volts then you can discharge it with a precision resistor to make an accurate measurement of it's capacitance.  Pick a 1% resistor so that it discharges by 63% in at least a minute or more.  Measure the seconds to reach the 63% voltage discharge point to measure the RC time constant.  Then just punch in the numbers and get your accurate capacitance value.

Then connect the fully discharged capacitor to the JT and time how long it takes the JT to charge the cap to 10 volts.  Then take your scope and measure the JT frequency as accurately as possible.  Put at least 20 cycles of the JT waveform on the scope display.  Then pull out the 10X time-base button and fiddle with the horizontal offset and make a precise period measurement for 20 cycles.  Crunch that back and get the precise running frequency of your JT.

Now you know how many seconds it took for the JT to charge your precisely measured capacitor value to 10 volts.  You know exactly how much energy is in the capacitor and you know the precise JT frequency.

You have all the numbers to calculate the JT output power in watts and the energy per spike in milli-Joules.

To go the full distance, you could use Gotoluc's average DC current measuring meter that he built with big capacitors and a shunt resistor.  This was designed by Poynt .99.   You could make an accurate power consumption measurement for the JT circuit itself as viewed from the batteries perspective (actually the DC current measuring output, factoring out the shunt resistor).  From above, you have an accurate power consumption measurement of the output power from your JT.

It is a bit of work to set up, but once you got good at it you could make performance measurements of any JT circuit setup in 20 minutes and then start experimenting with tweaking the design.  The only measurement that counts is power out vs. power in.

One big caveat as I think about this a bit more.  There is a problem with using Gotoluc's DC current measuring system - you are changing the load on the battery from what it is supposed to be; pulsing current of a low amperage value to an even lower DC current value.

This problem can be worked around.  You would have to measure the output impedance of the battery first, and I am not going to get into that.  Now that you know what the output impedance of the battery is you can make quite accurate inferences of how much energy is being lost in the battery for the actual very low DC current flow, vs. what would be happening in "real life" if Gotoluc's measurement jig was not there.  It is a little bit complicated and it would probably only make a very marginal difference on your output power vs. input power calculations as described above.  The important thing is to be aware of it.

MileHigh

MileHigh

How would you feel about putting the capacitor under test in the negative feedback loop of a power op-amp. Using the dual slope integration method you could autozero the cap, then ramp to vthreshold with the +input on vRef+, at the threshold, switch to vRef-. Count time on ramp up and ramp down. Compare the times, should be equal (if vRef+ and vRef- are equal) unless dielectric absorption or excess energy is present in the cap. Also vRef- can be made much larger, say 10x for 10x faster discharge, thus time differences would be a ratio of the reference voltages.

Hi Vortex1:

It looks perfectly feasible, I assume that's how capacitance meters work.  For a large cap though the old tried and proven exponential decay way is easy and accessible to anyone and can be quite accurate.

MileHigh

Agreed, but finding the 63% point can be a little tricky on an analog scope. I have used the integration technique with a few more parts than is shown and a counter timer chip to get very accurate measurements of dielectric absorption etc.

In spare time I am a consultant to High Energy Corp, capacitor manufacturer. Catalog pdf's available from their site http://www.highenergycorp.com/

Quote from: MileHigh on December 10, 2009, 09:13:00 PM
Truthfinder:

Your comments about the ampere-hours don't make sense.  It doesn't work like that for ampere-hours.  However, you acknowledge the issue of one battery discharging into the other battery, as does Paul.  This is not a healthy situation.  It can also happen towards the end of the life of the two batteries.  The one that starts to die first and becomes the load for the healthier battery.  So at the beginning and at the end, you loose energy and potentially damage the batteries.

Chances are noting is going to happen in most cases with small batteries.  However you never know, a small alkaline battery can source quite a bit of current.  It is simply bad practice and should not be done.

I had a glance at a Magnacoaster instruction manual once.  That fool Richard shows a diagram with big car lead-acid batteries wired in parallel.  That is insane and very dangerous.  If you submitted a product like that to UL for approval they would refuse you and behind your back laugh in your face.

For higher-voltage batteries you can give them a common ground and then use diodes to bridge all of the positive outputs together.  Then you can get your big current and avoid thermonuclear meltdown at the relatively small price of a diode voltage drop.

Albert:

I hope that you studied my mini treatise on battery voltages for you.

Paul:

Love your swagger.  I find it very ironic that you say "discharge the batteries."

Are you acknowledging that the UC capacitance is a function of voltage, which is what I have been saying the whole time?

This is where you loose it.  Forgetting about the JT, all you can say when you run a test like that is you were able to make a measurement of how much energy could be extracted out of the battery under these conditions with a certain error margin.  You can't make any sort of statement about COP.  Plus a certain type of battery will have a certain average energy content with some sort of standard deviation, and if you want to get picky the mean and standard deviation would be set on a batch by batch basis.

Albert:

Let me briefly describe what's going on when a JT generates a spike.  The transistor switches on and current flows through the coil in the JT "transformer."  When the transistor switches off the energy in the coil (1/2 L i-squared) will become a voltage+current spike that goes through the diode and then into the cap.  It can be a cap or an ultracap, either one will absorb the energy in the spike.  That's it, there is no magic.

I can suggest a little experiment.  Take a standard JT circuit and connect your scope to the LED to see the pulses on your scope when the LED fires.  Then replace the LED with a 50-ohm resistor, and look at the scope.  Do the same for 500 and 5K ohm resistors.  You will see that the larger the resistor value, the higher the voltage in the spike, and the shorter the time of the spike.  This is showing you how a discharging inductor reacts to different loads.

Then change the 5K resistor for a regular 25-volt 20,000 uF electrolytic cap and look at the scope.  The voltage spikes are now gone - completely gone.  However, each time the JT fires the voltage on the cap increases, like a step.  You will also notice that the rate of the voltage increase starts to slow down the higher the voltage on the capacitor.  Do you know why this is happening?

MileHigh
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mh : )

yes richard in my opinion has no idea what he is building ...
sorry but true .. 

any how .. i have over come this ... lol

and sir yes i do know why you speek of this problem ...

YOU SEE I HAVE PULSE MOTORS THAT ACCELERATE INSTED OF SLOWING WHEN I TAKE WORK FROM THEM... hummmmm

i find the more i remove the faster they spinn ... so if i remove a high voltage .. i get a verry high spin factor ...  and if i only burn a tiny amount ...  it allows a constant highspeed spinn ... i then can pulse from any number if coils i like ... rectify to a cap ... and it WILL NOT SLOW down sir!


WILLIAM : ) im no richard.... lol  ; )