The Ultimate Cap Dump

[James Milner]

not just "any" cap will do. find one with a value that helps the front end be more springy.. not too big not too small is that a good electrical engineer term? Tom C

Tom, do you mean a low ESR cap roughly slightly larger than the joule output of the battery in one magnet pass?
Now how to calculate that joule output?
James

[Tom C]

http://www.youtube.com/watch?v=v3-HwZMThzQ so changing the L or the C will change things. the L is fixed by its construction and wire size, so we change the C. I am not a physics guru by any means. but I get the concepts..... so even if you get lost in the math, listen to what he is saying ABOUT the circuit. works on both sides of the monopole.

Tom C

[aln]

Thanks Tom, useful info. Springy, I get it now after watching video. aln

[James Milner]

Tom, just thinking a about this a little further.
Are you suggesting, or have you tried working out your magnet pass speed in milliseconds and the used the known inductance of the coil and worked out the capacitance required? For exactly that oscillation speed?
Thanks
James

[Tom C]

James,

no I have not, I am more of a hunt and peck kind of guy, grab a few caps and swap em around. on my project list is a cap box where you can switch out different uf caps.

Tom C

[Catrinisin]

Hey guys, i finally built a more permanent comparator on a perf board. I've been wondering about the size caps here. For our 12 volt needs, shouldn't we go with smaller voltage caps, but with the same capacitance?

Here is my logic: JB knows what he's doing and his comparator was built for 36 volts. Double that and you get about 72-80v that you would be charging these caps to; fully utilizing the 15,000uF of capacitance in each cap. If we modify the circuit for 12v like we've been tinkering with, and still using 80v caps, only charging to about 32v max; aren't we then only using less than half the overall available capacitance? Shouldn't we shoot for say 35v caps with the same capacitance?


Hmmm...

-Chris

General rule of thumb is tall skinny ones, not short fat ones. Generally tall skinny ones have a lower ESR (Equivalent Series Resistance) and will charge and discharge faster that short fat ones.

Unfortunately they are usually more expensive The ones that JB used in the large comparator (15,000uF 80v) are about $12-$15 each.

John K.

[John_Koorn]

Hey guys, i finally built a more permanent comparator on a perf board. I've been wondering about the size caps here. For our 12 volt needs, shouldn't we go with smaller voltage caps, but with the same capacitance?

Here is my logic: JB knows what he's doing and his comparator was built for 36 volts. Double that and you get about 72-80v that you would be charging these caps to; fully utilizing the 15,000uF of capacitance in each cap. If we modify the circuit for 12v like we've been tinkering with, and still using 80v caps, only charging to about 32v max; aren't we then only using less than half the overall available capacitance? Shouldn't we shoot for say 35v caps with the same capacitance?


Hmmm...

-Chris

Chris,

My opinion on why the rated cap voltage is high - 80V for a 12v charge battery - is that as the cap charges its impedance gets higher and harder to charge. So if you only charge a cap that is rated at 80V to 25V, it's going to get there faster than if you use a 35V cap.

Just my opinion, I'm no EE

John K.

[BobZilla]

Yea along what John K is saying ,, the impedance is the biggest difference. But I have noticed that the closer to filling a cap the more punch it seems to have. I have some 50v 15k, 40v 33k, and 75v 60k and have used all of them. They all will work so it may be a splitting hairs concept but impedance does play a part, especially if you are trying to balance the front and back.

One example I could give is comparing the 75v to a 45v. The 75v can reach 25v very quickly and it is actually the larger capacitance but if you have an analog meter to watch it it is kind of a fluffy charge, it gets there right away. A smaller one will jump to say 15v just as quick but then there is a noticeable climb upwards, as if it has to pack it in there more densely.

I'm not saying one or the other is better but just offering some observation I have made with my caps.

[Nofear]

Impedance and rate of charge are the right arguments for picking the most appropriate cap, in my opinion.
One can plot the cap voltage vs time or in other words the rate of charge and choose the cap that gives you the desired voltages while it is still in the linear region. I mean by that before the saturation orcap voltage flatten out.
It's essentially the same thing John K said....A bigger cap charges faster. Or you could be a bit more surgical and plot your cap voltage with a osci as explained above.
Good Luck

NoFear.

Chris,

My opinion on why the rated cap voltage is high - 80V for a 12v charge battery - is that as the cap charges its impedance gets higher and harder to charge. So if you only charge a cap that is rated at 80V to 25V, it's going to get there faster than if you use a 35V cap.

Just my opinion, I'm no EE

John K.

[Catrinisin]

Thanks everyone, this is good information. I think I'm going to experiment with a couple different voltages and see what I get with charging and what I see on the scope.

Chris

[Ed_Morbus]

Hi all, I want to make a cap pulser I add a schematic,
I hope it may to place on the forum.
wants an expert check to or schematic is right.

thanks.

[min2oly]

Hi all, I want to make a cap pulser I add a schematic,
I hope it may to place on the forum.
wants an expert check to or schematic is right.[ATTACH=CONFIG]2881[/ATTACH]

thanks.

Have you tried it out yet?

[min2oly]

Here's one that dumps at a higher voltage:

these both dump all the way down to the charging batteries voltage, not like the comparator types.

[Ed_Morbus]

Yes for me works whit se schematics

[hobbyrobotik]

Hi Ed_Morbus,
if your circut really works as you replied to min2oly, your schematic here is nonsense.
please check this and post a correct drawing.

regards

Hi all, I want to make a cap pulser I add a schematic,
I hope it may to place on the forum.
wants an expert check to or schematic is right.[ATTACH=CONFIG]2881[/ATTACH]

thanks.