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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
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Posted: Sat Jan 07, 2012 8:34 am Post subject:
Re: The Drum Cookbook PSU Subject description: V quick and easy query. |
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Hi
Im building the psu from the drum cookbook.
I havent got the 1000uF 35v+ caps on hand, will increasing to 2200UF have any detrimental effect? Its c3 and c4.
Im monumentally skint at the mo so if can use parts i have it would be awesome.
Many thanks, Ben |
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inlifeindeath
Joined: Apr 02, 2010 Posts: 316 Location: Albuquerque, NM
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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
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Posted: Mon Jan 09, 2012 12:13 am Post subject:
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Thanks
I thought as much but just wanted to be sure.
Cheers ben |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
G2 patch files: 1
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Posted: Mon Jan 09, 2012 6:40 pm Post subject:
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The only "potential" problem with using over rated caps in a PSU is that when it's first turned on, if the caps are completely discharged, the inrush current which tries to fill them up, may blow a fuse, or,.. in the worst case scenario, your transformer. (I'd say that would be pretty rare!)
When empty, they are effectively a momentary short circuit. _________________ What makes a space ours, is what we put there, and what we do there. |
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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
Audio files: 2
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Posted: Tue Jan 10, 2012 2:24 am Post subject:
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Hmm... ok.
On a scale of one to ten, how likely is that, at a guess (prob asking the impossible here!).
Alternatively, isnt two in series about 1000uF?
Sorry, i know these are pretty basic queries. PSUs (probably quite rightly!) worry me/make me want to be 101% sure in my own mind.
Cheers. |
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Tim Servo
Joined: Jul 16, 2006 Posts: 924 Location: Silicon Valley
Audio files: 11
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Posted: Tue Jan 10, 2012 1:35 pm Post subject:
Re: The Drum Cookbook PSU |
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Paradigm X wrote: | Hmm... ok.
On a scale of one to ten, how likely is that, at a guess (prob asking the impossible here!).
Alternatively, isnt two in series about 1000uF?
Sorry, i know these are pretty basic queries. PSUs (probably quite rightly!) worry me/make me want to be 101% sure in my own mind.
Cheers. |
Going from 1,000uF to 2,200uF isn't likely to cause any problems unless your transformer is underspec'd or you have a very low rated fuse in there. If it is a problem, something like a 10 Ohm 1/2W resistor in series with each supply (one in series on the +V, one in series with the -V) before the caps will limit the inrush current.
Oh, and two 1,000uF caps in parallel is 2,000uF. In series they will give you 500uF.
Tim (Inrush Current sounds like a good band name) Servo |
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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
Audio files: 2
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Posted: Tue Jan 10, 2012 2:44 pm Post subject:
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its 40va transformer so should be fine. was specd by a mate who knows what hes doing for a mixer psu i never got round to fixing. 1A fuse. For The Liquid Hihat which is just 4 cmos chips so should be more than plenty. Need to measure current draw
Many thanks ben
ps yes inrush current does sound like a modern love kinda band |
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Sound
Joined: Jun 06, 2006 Posts: 842
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Posted: Tue Jan 10, 2012 3:44 pm Post subject:
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2200uF capacitors is fine.
1A fuse is too big.
The transformer you said is 40VA. What is its voltage rating? |
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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
Audio files: 2
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Posted: Tue Jan 10, 2012 4:10 pm Post subject:
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it say 2x18v
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1419542
hmm, i bought th 1a fuses as thats what henry says to aim for in his book. hping to use for more modules later...
maybe i shouldnt be doing this i clearly dont know enough, i was guided ny a mate whos an ex electrical engineer, who seemed to know what he was talking about. this was intended for a mixer, +-15v and 48v phantom...
thanks |
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Sound
Joined: Jun 06, 2006 Posts: 842
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Posted: Tue Jan 10, 2012 5:08 pm Post subject:
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This is a good transformer.
You must choose a slow blow type fuse, also called anti-surge fuse in order to avoid it to be blown when you turn on the power supply.
A rule of thumb for choose the current rating of the fuse is to calculate one and half times the current rated on the primary.
So, we have a 40VA 36VCT and for example 230V VAC of Mains Voltage.
We know that current in primary to current in secondary is inversely proportional to voltage in the primary to voltage in the secondary.
Ip/Is=Vs/Vp
We know:
Vp=230
Vs=36
To know current on secondary Is for a 40VA transformer:
40=V*A
40=36*A
A=40/36=1.1
Is=1.1A
To know current on the primary:
Ip/Is=Vs/Vp
Ip=(Vs/Vp)*Is
Ip=(36/230)*1.1
Ip=0.172A
Now
I fuse=Ip*1.5
I fuse=0.172*1.5
0.172 * 1.5 = 0.258
So for this example, a slow blow 250mA will do the job.
------------------------
I recommend use IEC connector like (farnell) JR-101-1-FRSG-03 with crimp terminal and insulating cover farnell code:3625515 and farnell code:3625515 for a very neat and safe result.
And
1) Turn-off AND disconnect physically the cable ALWAYS that you want to service the power supply.
2) Before turn-on the power supply, be sure ALWAYS, that no any cable , no any conductive part at 230V is without protection.
3)If the housing case is conductive connect it ALWAYS to the earth of the connector. |
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Sound
Joined: Jun 06, 2006 Posts: 842
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Posted: Tue Jan 10, 2012 5:20 pm Post subject:
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4) Be sure that filter capacitors are discharged, before work on the power supply
5) ALWAYS use a correct sized fuse. A transformer connected without fuse with secondaries accidentally shorted could result in fire.
Paradigm X wrote: |
maybe i shouldn't be doing this i clearly don't know enough |
you must know how to deal with mains voltage to build a power supply. There is danger of electric-shock http://en.wikipedia.org/wiki/Electric_shock |
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Paradigm X
Joined: Feb 15, 2011 Posts: 363 Location: Null and void
Audio files: 2
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Posted: Wed Jan 11, 2012 10:18 am Post subject:
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Thanks Sound
Ill have a good read thru a bit later.
Cheers, Ben |
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