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Old 27th December 2009, 10:08 AM   #491
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Quote:
Originally Posted by AndrewT View Post
that capacitor is rated 1u5F @ 400Vac and captioned on the pcb @ 630Vdc.
It appears the soft start is using mains voltage and dropping the excess voltage using the capacitor to leak working current through the high impedance of the capacitor. It will pass ~ 100mAac from 240Vac 50Hz.
It's not a nice way to do it, but when competantly designed it does work.
Be careful the soft start is working at mains voltage!!!!
Hi Andrew

Do you think this method of powering the soft-start circuit would cause the bulb to light?

Thanks
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Old 27th December 2009, 10:20 AM   #492
AndrewT is offline AndrewT  Scotland
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no.
You wired it up wrongly.
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Old 27th December 2009, 10:52 AM   #493
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Andrew has probably recommended a fuse rating to protect the amplifier. You can add such a protection, although amplifier protection with fuses is not really effective. The fuses are either too big to avoid damage or so small that the amplifier is useless due to continuous nuisance blowing.

Each transformer secondary must have a fuse directly behind it even before the rectifiers. Short-circuits and overload can happen in the wiring, the rectifiers and the capacitor bank, and the primary fuses cannot provide protection in all possible cases.

I don't want to reverse engineer that soft-start module from photos, so let us wait for the manufacturer's response. Maybe it uses a simple type of SMPS to convert the 240 VAC to 12 VDC. If not, it would indeed waste a lot of energy.

David
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Old 27th December 2009, 11:15 AM   #494
AndrewT is offline AndrewT  Scotland
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Andrew T. has recommended fuse ratings to allow the amplifier to perform as an amplifier with reactive speaker loading and yet never suffer nuisance blowing.
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Old 27th December 2009, 11:45 AM   #495
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Quote:
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no.
You wired it up wrongly.
Highly likely.

Click the image to open in full size.

The soft-start came pre built, but without any instructions.
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Old 28th December 2009, 10:42 AM   #496
AndrewT is offline AndrewT  Scotland
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That looks good.
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Old 28th December 2009, 10:51 AM   #497
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Hi Andrew

That's how I have always had it wired

So maybe there is a fault with the soft-start or I need slightly higher rated fuses. The bulb tester didn't indicate a fault when testing all of the other parts.

This is so frustrating due to my lack of knowledge!

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Old 28th December 2009, 04:59 PM   #498
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Hi Richard, thanks for the Christmas brain teaser I have no idea what the answer is
I tried the voltdrop part of the cct and voltage was reduced to 6V ac, lightbulb tester glowed (60W bulb) and the cct drew 20VA.
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Old 28th December 2009, 05:59 PM   #499
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The relay coil is rated with 0,9 W at 12 V, hence draws 75 mA. 240 V x 75 mA = 18 W plus the consumption of the rest of the control circuit. It seems the manufacturer relies on the 15 capacitor to dissipate most of the waste heat. Pretty scary in view of everybody striving for energy efficiency.

Richard, would you publish the manufacturer's name, so that everybody can avoid buying from him?
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Old 28th December 2009, 07:29 PM   #500
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Originally Posted by pacificblue View Post
The relay coil is rated with 0,9 W at 12 V, hence draws 75 mA. 240 V x 75 mA = 18 W plus the consumption of the rest of the control circuit. It seems the manufacturer relies on the 15 capacitor to dissipate most of the waste heat. Pretty scary in view of everybody striving for energy efficiency.

Richard, would you publish the manufacturer's name, so that everybody can avoid buying from him?
No, the reactive feed is non-dissipative. See EDN PDF for more information.
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