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Old 10th June 2004, 12:31 AM   #1
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Default Soft Start Circuit With Multiple Transformers

as the title says, my amp which will probably never gte made is going to have multiple transformers (not sure how many yet, atleast 3... maybe 6 or 7.. lol) they are 250VA each, and I believe (though I have no tested yet) that when powering up a few of these at once, it will be bye bye fuse... so, my idea, is to connect them in sequence.... so... when I flick the power switch, the centre transformer instantly gets power, 2 seconds later, the next 2 transformers are powered up, then the next 2, then the final two... all 2 seconds apart, then 2 seconds later again (unless I don't need to do this) the rails will be applied to the amplifier PCBs..... alot of mucking around I know.... but I like the idea.. 3 or 4 relays, and a simple circuit... any ideas or sugestions?? THANX!!
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Old 10th June 2004, 12:40 AM   #2
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If you have 10A 230V in aus as well, you can power up 1kVA at a time, the bigger deal is actually to do so with the load disconnected from the trafo. So if you power them up in batches of 4*250VA and connect the load a second or so after that you should be fine.

The startup power required by a trafo is 5*nominel rating, the mains fuses will tolerate the startup if calculated 2.5 to 3* nominal rating of the trafo.

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Old 10th June 2004, 12:44 AM   #3
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Quote:
Originally posted by Magura

The startup power required by a trafo is 5*nominel rating, the mains fuses will tolerate the startup if calculated 2.5 to 3* nominal rating of the trafo.

Magura

wouldn't that depend on the size of the core? powering up just one of these transformers with nothing on the secondary causes enough load to cause the voltage to drop enough for the lights to flash dimmer for a fraction of a second (like a fridge does when the compressor kicks in)
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Old 10th June 2004, 12:50 AM   #4
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Quote:
Originally posted by SkinnyBoy



wouldn't that depend on the size of the core?

Yes, and the core size is dependent of the VA rating if the trafo is constructed correctly

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Old 10th June 2004, 12:51 AM   #5
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Quote:
Originally posted by Magura



Yes, and the core size is dependent of the VA rating if the trafo is constructed correctly

Magura

these toroidals have cores about as large as a 500VA toroidal.... lol
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Old 10th June 2004, 12:56 AM   #6
Magura is offline Magura  Denmark
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What can I say...in that case id start them up in batches of two.

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Old 10th June 2004, 12:57 AM   #7
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Quote:
Originally posted by Magura
What can I say...in that case id start them up in batches of two.

Magura

hey... they might not be THAT big... lol someone take a pic or 2 of a 250VA toroidal with a CD sitting ontop, and resting against the side.... ol
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Old 10th June 2004, 12:58 AM   #8
Magura is offline Magura  Denmark
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Or look up the dims. at www.trafoshop24.de

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Old 10th June 2004, 01:07 AM   #9
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Quote:
Originally posted by Magura
Or look up the dims. at www.trafoshop24.de

Magura

ok..... my toroidals are about....

Outside Diameter: 130mm
Inside Diameter: 40mm
Height: 65mm

that includes the wire lol which (assuming that site includes the windings in their dimensions) is the same as a 400VA toroidal


EDIT: they weigh about 4kgs each (hard to get an accurate weight, no decent scales :P)
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Old 10th June 2004, 02:03 AM   #10
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Well, 400VA or whatever else they might be similar to in size...the math is still the same

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