The Ultimate Cap Dump

[min2oly]

I've had good success using a heavy duty SCR and one zener diode. The sch is below. All I do to adjust the voltage is swap out the zener for a different value. Right now I have a 16V zener on there. So 16V + about 2V that the SCR requires and that's roughly 18 volts over the battery voltage. I felt that this was better than using a 12 V zener because I wanted the battery to always have at a minimum of double the voltage hitting it. When the battery gets up to 15.5V, that's more than the 12V zener would produce on this circuit. I've never blown out one of either of the SCR's shown below either.

Schematic:
[ATTACH=CONFIG]1711[/ATTACH]

A couple different SCR's I've used. The larger one is a 2N1913 and the smaller one says R16RIA60 on it. Found these at my local surplus store. Skycraft Parts & Surplus, Inc.
[ATTACH=CONFIG]1712[/ATTACH]


-Chris

Chris, that nice. I'm glad it's working for your setup.
I have that same SCR. The only thing I've added was an LED from cathode to zener to gate.
Still... when I've moved to larger setups w/ large battery banks - this one is too small and heats up and/or locks up.

Everyone should try it, it is very reliable w/ the right energizer and charge battery.
The drawing in my vid is wrong, but the close up of the actual SCR is easy to see and connected and operating correctly.
Chris has the correct drawing here.
-KR
Patrick

[knagtegl]

I have been playing with a high current SCR to see what you can do with it.
I was also using a zener over the scr and it nicely dumped around 23 V over my battery.
As long as it completely discharges the cap it works fine but when there is a little higher
voltage over the cap than the batt the SCR stays on. This means that you have to shutdown
the input over the cap from the SSG completely. I think the easy way is to short the base of your
SSG Transistors, or in fact the triger coil somehow at the moment the SCR fires.
What I also found is that the cap is leaking over the SCR Gate so you don't want this on all the time
so maybe you want to use a timer like 555 to sample the voltage every second or so and then dump
when voltage is high enough.

Just some thoughts,

Karel

[Catrinisin]

Chris, that nice. I'm glad it's working for your setup.
I have that same SCR. The only thing I've added was an LED from cathode to zener to gate.
Still... when I've moved to larger setups w/ large battery banks - this one is too small and heats up and/or locks up.

Everyone should try it, it is very reliable w/ the right energizer and charge battery.
The drawing in my vid is wrong, but the close up of the actual SCR is easy to see and connected and operating correctly.
Chris has the correct drawing here.
-KR
Patrick

Thanks Patrick. It works almost flawlessly for my actual setup. I did have an issue with too much capacitance one time when my battery got almost full. The SCR would not close again for a few seconds on each pulse. It was strange, it was like a delay before it would re-charge. Lowering the capacitance solved it.

This is a small 3 filer machine. I am in the process of building a larger machine so it's good to know that I need to keep thinking about cap dumps then. I am really tempted to try the full 555 with mosfets circuit. However it is so complicated when compared to this SCR dump or some of the other simple ones. I also don't like how I would have to basically manually adjust it for each load.

Still searching for that ultimate cap dump.....


-Chris

[Catrinisin]

Quick questions guys: Is there any benefit to using more than one capacitor in parallel over using only one capacitor? Since there are two or more "sources" dumping into the battery, does that mean it dumps with twice as much current since there are twice the physical capacitors for instance?

Thanks,
Chris

[Tom C]

Quick questions guys: Is there any benefit to using more than one capacitor in parallel over using only one capacitor? Since there are two or more "sources" dumping into the battery, does that mean it dumps with twice as much current since there are twice the physical capacitors for instance?

Thanks,
Chris

capacitors are like batteries.... in parallel your voltage stays the same but your capacitance goes up. 2 15000 uf caps in parallel becomes 1 30000 uf cap. caps have differing discharge times but it is usually in the nano seconds of difference. it depends if you have a really good new cap or are recycling caps from old power supplies. if anyone runs into the old HP lazerjets or any big printer at a junk yard, the power supply for the fuzer is huge, I have found 50 volt caps in them large Farad ones.

Tom C

[Catrinisin]

capacitors are like batteries.... in parallel your voltage stays the same but your capacitance goes up. 2 15000 uf caps in parallel becomes 1 30000 uf cap. n series the voltage goes up but the capacitance stays the same. its always "1" source. caps have differing discharge times but it is usually in the nano seconds of difference. it depends if you have a really good new cap or are recycling caps from old power supplies. if anyone runs into the old HP lazerjets or any big printer at a junk yard, the power supply for the fuzer is huge, I have found 50 volt caps in them large Farad ones.

Tom C

Thanks Tom. I think capacitance divides down when connected in series fyi. I was just thinking that if two caps were dumping instead of just one, it might dump quicker than if it were only one cap. I know we are talking nanoseconds here so it might be a moot point.

Chris

[Tom C]

Thanks Tom. I think capacitance divides down when connected in series fyi. I was just thinking that if two caps were dumping instead of just one, it might dump quicker than if it were only one cap. I know we are talking nanoseconds here so it might be a moot point.

Chris

yea u r right
Electronics 2000 | Series / Parallel Capacitor Calculator

fun stuff!!

Tom C

[John_Koorn]

Before deciding on adding more caps in parallel, make sure your cap pulser circuit can handle it. Make sure your switching device (BJT, SCR, FET, etc.) can handle the amount of power you are switching through it.

Also make sure that the wires or traces can handle large surges of current. The larger the better.

Check the circuit for heat, if anything is getting hot you are losing too much in heat and need to add more devices or thicker wire/traces. If you have to parallel more devices, make sure they are matched.

John K.

[min2oly]

Now we're talking folks :-)
This is some good info. The basics are always very important, in fact most important!

So, what do we have, back to triggering the SSR - one wire in one wire out.
Try and keep it simple like the SCR/zener combo.
Now we know.

1. We can get a positive voltage(battery supply) between the two negatives. That is, with 24v in a CAP and 12 volts in our charge battery, connect the two positives and we have 12 volts available between the two negatives. this is where our power comes from.

2. We need to send a pulse across the SSR's input in order for the output to connect the two negatives and discharge the 24v into the 12 volts (sticking w/ the above analogy).

3. We now need a reliable method to send this pulse not on a "timed" basis but driven by the difference in voltage between the cap and the charge battery.


So how can we do this reliably when the zener has so many conditions that make it lock up and flow like a river over a dam rather than a ram pump?

Can we put the zener under a condition that it sees less voltage after the dump?

Should we ditch the zener all together?

Should our timing be driven by the difference rather than a set zener?

post a circuit, let's have some fun, no harm in trying.

Might have to try some of that nocturnal egg hunting... :-)

-KR
Patrick

[forelle]

Hi to all,
i have built this cap dump circuit and it works very well,the voltage goes up to 25 and then it dump every 1.5 sec but you have to give the wheel a resistance,otherwise the SCR don't switch off.JB said the bikewheel charges better when it's not only free spinning( for this he has the fan).I have it in my livingroom and i don't want wind at the moment,maybe in summer,so i took a hoseclip,a piece of leather and a screw.Now you can easy controll the resistance.The amps from the drivingbattery didn't change but the rpm go down from 160 to 140.
SCR BT152 from NXP
5 LED white 3.1v
cap 22000µf 80V and a neon(better a GDT with 75v,or a cap with 100v)
Here are the pictures.

[min2oly]

Hi to all,
i have built this cap dump circuit and it works very well,the voltage goes up to 25 and then it dump every 1.5 sec but you have to give the wheel a resistance,otherwise the SCR don't switch off.JB said the bikewheel charges better when it's not only free spinning( for this he has the fan).I have it in my livingroom and i don't want wind at the moment,maybe in summer,so i took a hoseclip,a piece of leather and a screw.Now you can easy controll the resistance.The amps from the drivingbattery didn't change but the rpm go down from 160 to 140.
SCR BT152 from NXP
5 LED white 3.1v
cap 22000µf 80V and a neon(better a GDT with 75v,or a cap with 100v)
Here are the pictures.[ATTACH=CONFIG]1719[/ATTACH][ATTACH=CONFIG]1716[/ATTACH][ATTACH=CONFIG]1717[/ATTACH][ATTACH=CONFIG]1718[/ATTACH]

Hi Forelle,
that's an interesting use/positioning of the LED's. Nice job on the pulley system.
so what's going on different w/ the charging of the cap when you place a load on the wheel with your setup?
Thanks for sharing that, will give it a try...

[forelle]

Hi Forelle,
that's an interesting use/positioning of the LED's. Nice job on the pulley system.
so what's going on different w/ the charging of the cap when you place a load on the wheel with your setup?
Thanks for sharing that, will give it a try...

Hi min2oly,
i am not sure what the difference is.Please can you tell me exactly what and how i should measure.The cap goes down from 25v to the batteryvoltage with and without the resistance but without resistance it doesn't switch off.Gatetriggercurent Bt152 is 3-32ma maybe a bigger one would work without resistance.If you want scopeshoots tell me from where.
Have a nice day.
Oliver

[min2oly]

Hi min2oly,
i am not sure what the difference is.Please can you tell me exactly what and how i should measure.The cap goes down from 25v to the batteryvoltage with and without the resistance but without resistance it doesn't switch off.Gatetriggercurent Bt152 is 3-32ma maybe a bigger one would work without resistance.If you want scopeshoots tell me from where.
Have a nice day.
Oliver

Hi Oliver,
That is very nice how you have it set up, simple and sweet. 3-32mA might be a bit much for a small build, but perhaps that current is not being used up???
sometimes these switches can pass the current on to the charge battery.

Slider also mentioned using a resistor there, this is how he controls, makes sure, the switch turns off and does not lock up. I would not change a thing as long as it's working efficiently, If you are just wanting to experiment, it's always fun to build another, pop it in and compare the two.
-KR
Patrick

[min2oly]

What’s up people :-)

Almost there!
Great ideas here – Keep them coming!

Wouldn't it be nice if someone who already had a nice simple adjustable voltage driven circuit jumped in and showed us the quick down and dirty reliable method... not calling anyone out here, just say’n…

Most if not all of you will figure out how I did it w/ this next video. I will post the final part 4 in the end anyway.
Ok Part 3, enjoy:

Only one final step left. A few people have already PM’d me that you get it and I am also very impressed with a couple of the circuits that have been provided.
-KR
Patrick

[min2oly]

I forgot about this video:

John and Chuck go over some stuff and run into the SCR lock. We can learn from the conversation they are having, as to why it does lock. I just like watching these over again. I always gleam something I missed before...

-KR
Patrick