load current

k1jroth · 25th November 2004, 01:53 PM

I`m trying to design soft start circuit for 2x40V 1000VA toroid and
filter capasitors (63V 144000uF).

I think that resistors in primary coil with relay should do it.
Secondary coil is the problem because of the capasitor load current.

I`m thinking resistor in series with capasitors and when they are loaded Zenerdiode will turn the relay on. (relay shortcuts resistor)
Same relay to capasitors and primary coil resistors.

How can i calculate load current and load time with specific resistor?

Please help beginner.

boholm · 25th November 2004, 02:04 PM

(40 volts *1.4 ) - 0.6 or 1.2 volts = about 55 volts.

At startup the capacitor is uncharged and therefore acts as a shortcircuit: 55 volts / 0 ohm = infinite ampere.

Due to internal impedance in the transformer and the diode bridge, the max. current will be more modest, but it will still be large.

Why not build this:

http://sound.westhost.com/project15.htm

peranders · 25th November 2004, 04:07 PM

Absolutely max inrush current is huge. Measure the DC resistance of the primary winding. Take 230 x 1.4 = 322 volt and divide this with 3-5 ohms = 100 A!

Best way to start up this huge power supply of yours is to have 100 ohms 7-10 watts wirewound i series with your primary winding and then let a relay bypasss it after 1-3 seconds. If you have this device on the primary side you don't have to deal with so high currents as if you had it on the secondary side. The rectifier bridge will probably handle this well with any extra parts.

With a current probe (using hall elements) connected to an oscilloscope I measured 77 A peak for my 600 VA/ 4 x 22000 uF PS (+- 60 volts) This extremely high peak lasts only one or a couple of mains periods. Since you have a huge capacitor battery maybe the current peak will be streched a bit in time.

Sch3mat1c · 25th November 2004, 04:36 PM

Quote:

Originally posted by k1jroth
I`m trying to design soft start circuit for 2x40V 1000VA toroid and
filter capasitors (63V 144000uF).

Wouldn't have to if you used smaller caps.

Tim

peranders · 25th November 2004, 04:51 PM

Quote:

Originally posted by Sch3mat1c

Wouldn't have to if you used smaller caps.

Tim

Check my title at the left

djQUAN · 25th November 2004, 05:00 PM

I have only a 500VA toroid with eight 10000uF caps. dims the house lights. I definitely need a soft start installed soon.

25th November 2004, 01:53 PM	#1
k1jroth diyAudio Member Join Date: Nov 2004 Location: tampere	load current I`m trying to design soft start circuit for 2x40V 1000VA toroid and filter capasitors (63V 144000uF). I think that resistors in primary coil with relay should do it. Secondary coil is the problem because of the capasitor load current. I`m thinking resistor in series with capasitors and when they are loaded Zenerdiode will turn the relay on. (relay shortcuts resistor) Same relay to capasitors and primary coil resistors. How can i calculate load current and load time with specific resistor? Please help beginner.

25th November 2004, 02:04 PM	#2
boholm diyAudio Member Join Date: Apr 2004 Location: Copenhagen	(40 volts *1.4 ) - 0.6 or 1.2 volts = about 55 volts. At startup the capacitor is uncharged and therefore acts as a shortcircuit: 55 volts / 0 ohm = infinite ampere. Due to internal impedance in the transformer and the diode bridge, the max. current will be more modest, but it will still be large. Why not build this: http://sound.westhost.com/project15.htm __________________ Best regards Bo

25th November 2004, 04:07 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Absolutely max inrush current is huge. Measure the DC resistance of the primary winding. Take 230 x 1.4 = 322 volt and divide this with 3-5 ohms = 100 A! Best way to start up this huge power supply of yours is to have 100 ohms 7-10 watts wirewound i series with your primary winding and then let a relay bypasss it after 1-3 seconds. If you have this device on the primary side you don't have to deal with so high currents as if you had it on the secondary side. The rectifier bridge will probably handle this well with any extra parts. With a current probe (using hall elements) connected to an oscilloscope I measured 77 A peak for my 600 VA/ 4 x 22000 uF PS (+- 60 volts) This extremely high peak lasts only one or a couple of mains periods. Since you have a huge capacitor battery maybe the current peak will be streched a bit in time. __________________ /Per-Anders (my first name) or P-A as my friends call me

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25th November 2004, 05:00 PM	#6
djQUAN diyAudio Member Join Date: May 2004 Location: manila	I have only a 500VA toroid with eight 10000uF caps. dims the house lights. I definitely need a soft start installed soon.

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