Draining capacitors on power supply - Electronic Circuits Projects Diagrams Free

hfireworks · 16th April 2007, 02:01 AM

I have built a capacitive discharge system for my electronic firing system and I have (9) 200vdc 220uf capacitors that charge up from the power supply.

I am needing to use a resister to slowly drain the capacitors once power is turned off. I am using Dale aluminum RH-560 50W 1.5 ohm on my power supply to generate the 200vdc power load.

I would like to use (1) resister to slowly drain all (9) separate power lines, these are individual power lines but I would like to slowly drain all of them with one resister.

What do you recommend, and do you have a diagram that can be put to use?

j.p.bill · 16th April 2007, 02:08 AM

The caps probably won't care about discharge rate. Old rounded-off screwdrivers used to do the trick real well, although they would occasionally weld onto terminals. If you want to use a switch and have it last, grab a 10 watt 1000 ohm sand resistor and switch it across the caps. Just leave it connected for 10 minutes and all charge will be gone.

hfireworks · 16th April 2007, 02:10 AM

Quote:

Originally Posted by j.p.bill

The caps probably won't care about discharge rate. Old rounded-off screwdrivers used to do the trick real well, although they would occasionally weld onto terminals. If you want to use a switch and have it last, grab a 10 watt 1000 ohm sand resistor and switch it across the caps. Just leave it connected for 10 minutes and all charge will be gone.

My power supply is rated at 35watts.
This is a High Voltage power supply for fireworks discharge and I need something to be internal

I would not rather us a switch.
Can this be left on permanetly, Not the screwdriver done that, I would like to design it on my board so the power supply works as normal but when I turn off power to the supply the cap will drain and not leave high voltage on the board.

kchriste · 16th April 2007, 04:13 AM

Quote:

I would like to use (1) resister to slowly drain all (9) separate power lines, these are individual power lines but I would like to slowly drain all of them with one resister.

Since these caps are not in parallel and are totally separate; connect a resistor of sufficient value and wattage across each capacitor. This is called a bleeder resistor. It's value depends on the voltage across the cap and how long you are willing to wait for it to discharge to a safe level.

hfireworks · 16th April 2007, 04:30 AM

Quote:

Originally Posted by kchriste

Since these caps are not in parallel and are totally separate; connect a resistor of sufficient value and wattage across each capacitor. This is called a bleeder resistor. It's value depends on the voltage across the cap and how long you are willing to wait for it to discharge to a safe level.

You are right they are not in parallel and are totally separate, would I have to use a large 35W aluminum resistor to accomplish this, my power supply is at 200vdc and I am using 220uf caps.

Bleeder resistor is what I am looking for and the discharge time is not relevant as long as it does discharge slowly.

kchriste · 16th April 2007, 05:09 AM

I would use a 1/2watt 150K

hm: resistor across each cap in a trade off between wasted power, heat, discharge time, and cost. Should take about a minute for the caps to discharge to a safe level.

hfireworks · 16th April 2007, 05:14 AM

Quote:

Originally Posted by kchriste

I would use a 1/2watt 150K

hm: resistor across each cap in a trade off between wasted power, heat, discharge time, and cost. Should take about a minute for the caps to discharge to a safe level.

Can you slow down the discharge?

ericgibbs · 16th April 2007, 08:20 AM

hi,
You could use a suitably rated domestic mains filament lamp as a load dump.

In the UK, most domestic lamps are rated at 240Vac, if you chose say, a 25Watt version,
this would drain the caps to zero quickly and safely.

hfireworks · 16th April 2007, 08:28 AM

Quote:

Originally Posted by ericgibbs

hi,
You could use a suitably rated domestic mains filament lamp as a load dump.

In the UK, most domestic lamps are rated at 240Vac, if you chose say, a 25Watt version,
this would drain the caps to zero quickly and safely.

That too is a good possibility, I could place the lamps on my panel, to verify that the power has been drained. However the 200vdc output at 35watts of the lamp will be bright.

I do not want the voltage to drop very quickly, as to be a drain on my main 24vdc batteries to keep the capacitors in full charge during operation.

ericgibbs · 16th April 2007, 08:41 AM

hi,

There are 'pygmy' versions of the lamps down to 15Watts and less, in different colours.
Low energy types, if suitable, as low as 3Watts.

eblc1388 · 16th April 2007, 10:33 AM

Quote:

Originally Posted by hfireworks

I do not want the voltage to drop very quickly, as to be a drain on my main 24vdc batteries to keep the capacitors in full charge during operation.

Why bleeds the capacitors and drain energy while the system is in standby/use? Fits a 24V relay at the supply side to switch OFF the bleeding resistor when 24V supply is healthy.

If all the 9 capacitors have a common negative connection, then it might be possible to connect up all positive terminal of the capacitors to a common point using blocking diodes and discharge all 9 capacitors with a single resistor.

Optikon · 16th April 2007, 01:32 PM

Use some 250V mosfets with bleed resistors in drain. One button press (tied to all the gates) could turn them all on and discharge each C with its own resistor. BTW, you do not need high watt ratings for the discharge resistors in this case because they are not always in circuit dissipating power. They only switch in when you signal to discharge.

hfireworks · 16th April 2007, 02:41 PM

Quote:

Originally Posted by eblc1388

Why bleeds the capacitors and drain energy while the system is in standby/use? Fits a 24V relay at the supply side to switch OFF the bleeding resistor when 24V supply is healthy.

If all the 9 capacitors have a common negative connection, then it might be possible to connect up all positive terminal of the capacitors to a common point using blocking diodes and discharge all 9 capacitors with a single resistor.

So typically using the 9 blocking diodes to prevent backflow from the 9 Capacitors I can connect all 9 capacitors to a block and using a single switch to discharge all 9 capacitors into a single resistor.

So, if I switched all 9 capacitors into a single resistor, I would have 9 200vdc 220uf caps. Would one Dale RH-50 50watt 1.5k aluminum resistor handle that kind of power to drain?

If that were the case I could add a swich, possibly a high power SCR, or Darlington Pair or a relay to a toggle and add an LED and discharge.

hfireworks · 16th April 2007, 03:07 PM

Quote:

Originally Posted by Optikon

Use some 250V mosfets with bleed resistors in drain. One button press (tied to all the gates) could turn them all on and discharge each C with its own resistor. BTW, you do not need high watt ratings for the discharge resistors in this case because they are not always in circuit dissipating power. They only switch in when you signal to discharge.

I havn't used mosfets yet but read a little on them, I am beginning to se the bigger picture on this now, The design is popping into my head.

Since the capacitors have an abundance of power stored, could connecting all 9 of them create a surge on the resister?

hfireworks · 16th April 2007, 03:10 PM

Quote:

Originally Posted by j.p.bill

The caps probably won't care about discharge rate. Old rounded-off screwdrivers used to do the trick real well, although they would occasionally weld onto terminals. If you want to use a switch and have it last, grab a 10 watt 1000 ohm sand resistor and switch it across the caps. Just leave it connected for 10 minutes and all charge will be gone.

I am curious as to the 10 watt 1000 ohm sand resistor I have not seen one, what are the characteristics of these?

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16th April 2007, 02:08 AM	(permalink)
j.p.bill	The caps probably won't care about discharge rate. Old rounded-off screwdrivers used to do the trick real well, although they would occasionally weld onto terminals. If you want to use a switch and have it last, grab a 10 watt 1000 ohm sand resistor and switch it across the caps. Just leave it connected for 10 minutes and all charge will be gone.

16th April 2007, 05:09 AM	(permalink)
kchriste	I would use a 1/2watt 150Khm: resistor across each cap in a trade off between wasted power, heat, discharge time, and cost. Should take about a minute for the caps to discharge to a safe level. __________________ --- The days of the digital watch are numbered. ---

16th April 2007, 08:20 AM	(permalink)
ericgibbs	hi, You could use a suitably rated domestic mains filament lamp as a load dump. In the UK, most domestic lamps are rated at 240Vac, if you chose say, a 25Watt version, this would drain the caps to zero quickly and safely. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

16th April 2007, 08:41 AM	(permalink)
ericgibbs	hi, There are 'pygmy' versions of the lamps down to 15Watts and less, in different colours. Low energy types, if suitable, as low as 3Watts. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 16th April 2007 at 08:43 AM.

16th April 2007, 01:32 PM	(permalink)
Optikon	Use some 250V mosfets with bleed resistors in drain. One button press (tied to all the gates) could turn them all on and discharge each C with its own resistor. BTW, you do not need high watt ratings for the discharge resistors in this case because they are not always in circuit dissipating power. They only switch in when you signal to discharge.