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 Forum index » DIY Hardware and Software » Thomas Henry designs
Re: The Drum Cookbook PSU
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Paradigm X



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PostPosted: 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



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PostPosted: Sun Jan 08, 2012 7:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

no, it may actually provide more stability. bigger the better in this case!
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Paradigm X



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PostPosted: Mon Jan 09, 2012 12:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks

I thought as much but just wanted to be sure.

Cheers ben
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Uncle Krunkus
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PostPosted: Mon Jan 09, 2012 6:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.

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Paradigm X



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PostPosted: Tue Jan 10, 2012 2:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm... ok. Confused

On a scale of one to ten, how likely is that, at a guess (prob asking the impossible here!). Laughing

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



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PostPosted: Tue Jan 10, 2012 1:35 pm    Post subject: Re: The Drum Cookbook PSU Reply with quote  Mark this post and the followings unread

Paradigm X wrote:
Hmm... ok. Confused

On a scale of one to ten, how likely is that, at a guess (prob asking the impossible here!). Laughing

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



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PostPosted: Tue Jan 10, 2012 2:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Razz
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Sound



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PostPosted: Tue Jan 10, 2012 3:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Tue Jan 10, 2012 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

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...

Confused 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



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PostPosted: Tue Jan 10, 2012 5:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Tue Jan 10, 2012 5:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

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:

Confused 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



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PostPosted: Wed Jan 11, 2012 10:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Sound

Ill have a good read thru a bit later.

Cheers, Ben
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