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Old 1st December 2012, 01:37 AM   #21
evanc is online now evanc  United States
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Just wanted to chime in with my implementation of the soft start board. My new amp has 240kuf in the solid state power supply plus another 1.2k for the tube supply. I initially chose .33uf for c9. The relay would not latch. I added another .33uf for .66uf total and the board is working as it should. The boards I have gotten from DIYaudio are great, and the excellent build guides are appreciated.
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Old 1st December 2012, 05:59 AM   #22
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Thanks for the feedback Evan.

Cheers!
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Old 5th December 2012, 01:16 PM   #23
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I'm building this soft start for my latest amp. Could somebody suggest to me a Farnell's part number for suitable relay for this circuit ?

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Old 5th December 2012, 01:27 PM   #24
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Perhaps this could help...

G5LA-1E 24DC - OMRON ELECTRONIC COMPONENTS - RELAY, PCB, SPDT, 24VDC | element14 Philippines
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Old 6th December 2012, 12:14 PM   #25
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Quote:
Originally Posted by JojoD818 View Post
Thanks jojo

Any recommendation for R, C9 and fuse value for a 300VA 230VAC traffo to works at ideal condition for the soft start ?
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Old 6th December 2012, 12:20 PM   #26
AndrewT is online now AndrewT  Scotland
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Be very careful changing C9.
This is a direct online mains powered project.
It is usually forbidden to discuss this on this Forum. But for some reason the usual LIFE SAFETY rule has been ignored.

As for mains fusing a close rated fuse for 300VA and 230Vac is 300/230 = 1.3A

Use a T1.25A

If this works reliably, then try reducing it to T1A and see if that works reliably.

It's OK , I have reported my own post for those that think commenting on other's decisions is inappropriate.
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Old 6th December 2012, 12:40 PM   #27
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Quote:
Originally Posted by AndrewT View Post
Be very careful changing C9.
This is a direct online mains powered project.
It is usually forbidden to discuss this on this Forum. But for some reason the usual LIFE SAFETY rule has been ignored.

As for mains fusing a close rated fuse for 300VA and 230Vac is 300/230 = 1.3A

Use a T1.25A

If this works reliably, then try reducing it to T1A and see if that works reliably.

It's OK , I have reported my own post for those that think commenting on other's decisions is inappropriate.
Hmmmm

I'm using a Novutem 0300P1-2-025 Toroidal 300VA 2x25V o/p Nuvotem 0300P1-2-025 to be exact and recommended fuse is 6.3AT. So why there's so much different ???

IMHO his discussion & suggestion might save my life
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Old 6th December 2012, 12:50 PM   #28
AndrewT is online now AndrewT  Scotland
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An inductive load needs a very different start up fuse from a resistive load.
The "normal" fuse for an inductive load is:
fuse rating = VA / Vac * 3

300VA / 230Vac * 3 = 3.9A
Use a T4A. Most transformer will start with a T4A, some will need a higher fuse rating.
Some will start reliably with a lower fuse rating.

But this is not close rating of the fusing.
That T4A will pass 8A for many seconds and in extreme cases can exceed half an hour before rupturing.

How much heat will the faulty equipment generate if 7A or 7.5A or 7.9A is passing for 30minutes? What happens if the faulty equipment is unattended?

That's where close rated fusing offers a big safety advantage. But transformers need a soft start to allow close rated fusing to be adopted.

Yet another unhelpful post?
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Old 7th December 2012, 07:37 AM   #29
AJT is offline AJT  Philippines
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Quote:
Originally Posted by AndrewT View Post
I think there should be some "design" notes added for the current limiting resistor values.
The 4 resistors R15 to 18 are specified @ 180r.
Is this for 110/120Vac and/or 220/240Vac?
Is this for 200VA to 1000VA transformers and/or any size transformer?

I know from experience that 45r (180/4) works on 220/240Vac for medium sized transformers in the range 200VA to 500VA.

But smaller transformers would need higher value resistors and larger transformers would need lower value resistors.
I expect that 110/120Vac transformers will generally require lower value resistors to effect similar current limiting.

A simple table showing VA & Vac combinations with appropriate resistor values would be very useful to less experienced builders.
the reason for using a startup limiting resistor is to prevent your switch from being arc welded at turn-on, in my super leach amp build with a 2kva power traffo, i used a dale 10 ohm/50 watt aluminum clad power resistor, time delay of about 3 seconds....i used a power switch rated for 15amperes...and 20 years later, the amp and its switch is still good...
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Old 7th December 2012, 10:14 AM   #30
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Tony View Post
..............super leach amp build with a 2kva power traffo, i used a dale 10 ohm/50 watt ...........time delay of about 3 seconds...............and 20 years later, the amp and its switch is still good...
Quote:
. . . . . . . . . .Vac
VA . . . 115Vac . . 230Vac
100 . . . . 270r . . . 390r
200 . . . . 180r . . . 270r
400 . . . . 120r . . . 180r
800 . . . . .82r . . . 150r
1600 . . . . 68r . . . 120r
Tony and others who feel the need to read my unhelpful posts:
The 10r Tony has used for 20years is equivalent to four (4) 40r resistors in parallel (R15 to R18 inclusive). Looking at the table that I put up for discussion I see the progression from 270r down to 68r for the range of transformers from 100VA to 1.8kVA (on 110/120Vac).
Tony's 2kVA (is this on 220/240Vac?) is just beyond that range and 40r would seem to fit almost exactly into the extrapolated range of values.

Thanks Tony for that evidence.
Has anyone else got evidence (pro/con) to put up for discussion?
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