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Old 13th March 2014, 06:09 PM   #151
SRMcGee is offline SRMcGee  United States
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120 VAC . . . 1uF . . . 1440R
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Old 13th March 2014, 11:31 PM   #152
AJT is offline AJT  Philippines
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so now we have values that work.....
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Old 10th August 2014, 12:37 PM   #153
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Hi everybody here.
I am building a Regulated PSU for a modular synth, it is a big one.
I am using a 300VA toroid trafo, 230V primay, 15-0 & 15-0 secondaries.
My filters are two 10000uF caps, using two 25amp bridges and two LM338 regulators.
The idea is getting +15 and -15 volts 5 Amps.
Should I need a soft start? I believe that I should, but after reading the whole 16 pages of the forum still I am not sure if this soft start is suitable for Regulated PSUs.
Any advise will be apreciated.
Thanks a lot in advance.
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Old 10th August 2014, 01:12 PM   #154
AndrewT is offline AndrewT  Scotland
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The 300VA should run with a T1A, or T1.25A, mains fuse.

The 300VA will probably not start on that size of fuse, so you will need to fit a soft start.
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Old 10th August 2014, 03:36 PM   #155
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Thanks a lot AndrewT for your really fast answer.
I was reading carefully all the posts and as far as I can understand I should use C9 1uf/400v R15 to R18 1K5 5W. Right?
R= 230x230/5/30 = 352.67 comercial value: 360R
360R x 4:1440 ohms commercial value 1K5
Is that right or I am doing something wrong here?
Thanks a lot!
Guillermo
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Old 11th August 2014, 08:17 AM   #156
AndrewT is offline AndrewT  Scotland
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This is a direct to mains powered project.

If I discuss details of how to build this, or how to modify, I risk being sin binned for breaking Forum Rules.

What I have answered
Quote:
Should I need a soft start?
is a general question that is not specifically direct to Mains.
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Old 11th August 2014, 09:34 AM   #157
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Many thanks Andrew, I got it.
Don't worry I'll find the way.
cheers.
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Old 11th August 2014, 11:54 AM   #158
AJT is offline AJT  Philippines
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Quote:
Originally Posted by JRC4558D View Post
Hi everybody here.
I am building a Regulated PSU for a modular synth, it is a big one.
I am using a 300VA toroid trafo, 230V primay, 15-0 & 15-0 secondaries.
My filters are two 10000uF caps, using two 25amp bridges and two LM338 regulators.
The idea is getting +15 and -15 volts 5 Amps.
Should I need a soft start? I believe that I should, but after reading the whole 16 pages of the forum still I am not sure if this soft start is suitable for Regulated PSUs.
Any advise will be apreciated.
Thanks a lot in advance.
get a mains switch good for at least 10 amps, i do this all the time...no need for soft start...
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Old 11th August 2014, 04:08 PM   #159
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Hi AJT, thanks a lot for your answer.
I have another PSU (51X Group DIY Lunchbox) and I did that (big switch), the Toroidal Transformer there is 250VA and I had to place a 3.1Amp fuse because the fuse was blowing everytime I turned it on.
I think for this new one which has a 300VA toroid I should use a 4 Amp fuse t avoid it blowing, then reading the all the posts I think a 4 Amp fuse will be almost useless. Am I wrong? That's why I ask for a suitable soft start.
Unfortunately I haven't got enough knowledge to be really sure about it and the consequence of not fiting one.
Cheers.
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Old 11th August 2014, 04:13 PM   #160
Mooly is offline Mooly  United Kingdom
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I'd imagine a 4A time delay fuse would be fine for 300va. It must be a delay type though (slow blow) which will be marked something like 4AT or T4. I've used T6.3 fuses with no problem on a 650va toroid.
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