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Offline kolias

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Re: Power Supply Unit
« Reply #60 on: January 13, 2011, 08:48:16 PM »
Thank you RICH

I agree with your points and so a metal box will be used for the new power supply unit.

BTW my friend doesn't even know what house wiring is LOL
Nicolas

Offline kolias

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Re: Power Supply Unit
« Reply #61 on: January 14, 2011, 05:19:14 PM »
I went to purchase the capacitors from my local store but I couldn’t find anyone with 50VDC or more neither with 20000uF or more. The closest I found were:

15500uF, 25VDC
10000uF, 25VDC
8200uF, 25VDC
5500uF, 25VDC
34000uF, 15VDC
25000uF, 15VDC
10000uF, 10VDC

Can someone tell me if a combination of the above is suitable?

If not, then I will have to purchase them from the Web

Thanks
Nicolas

Offline Hood

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Re: Power Supply Unit
« Reply #62 on: January 14, 2011, 05:37:19 PM »
No, you need the voltage to be above what your supply is, you may get away with some the same but I definitely wouldnt risk it and definitely not lower. Capacitance is not a problem as you can link in parallel to get the capacitance required but you cant do that with the voltage I am afraid.
If you wish to pay the postage to Canada (I think thats where you said you were) I probably have some capacitors here that I could give you, would have to check tomorrow when I get to the workshop, let me know.
Hood

Offline RICH

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Re: Power Supply Unit
« Reply #63 on: January 14, 2011, 05:37:42 PM »
Nic,
We already told you. The  voltage rating must exceed the output voltage by some amount. The uF can be more than calculated
but preferable not less.

You wouldn't put a circuit breaker or fuse which is less than required for the amps you will draw, it explodes, like wise you wouldn't put
a capacitor  not rated for the voltage you will use.

RICH

Offline kolias

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Re: Power Supply Unit
« Reply #64 on: January 14, 2011, 07:01:46 PM »
Alright, somehow I knew that we can’t add the voltage but wasn’t sure. Yes Rich you told me that the voltage must be higher but you never told me we can add the capacitance but not the voltage LOL. Sounds silly but simply I don’t know about this staff.

Thank you Hood for the offer, sure I don’t mind to pay the postage (yes I’m in Canada) but I don’t know how I can do that. Anyway let me know what is required and I will do it

You would think that I’m in the North Pole because today I spend about 3 hours driving around checking some local stores for capacitors, toroidal and bridge rectifiers but no luck. Mostly they have IC staff.

Thanks
Nicolas

Offline Hood

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Re: Power Supply Unit
« Reply #65 on: January 14, 2011, 07:05:02 PM »
I will check tomorrow and see what I have, hope I remember ::)

Hood

Offline Hood

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Re: Power Supply Unit
« Reply #66 on: January 14, 2011, 07:13:32 PM »
Just thought I better mention something else as you are new to this stuff. Capacitors store a charge and this can be quite a high voltage and they are dangerous because they can discharge very quickly, so never touch the terminals of a capacitor unless you are sure it is discharged or it could cause serious injury. It can take quite a while for a capacitor to discharge naturally so if you need to do any work on the circuit you really need to discharge it first to make sure there is no danger. I usually put a household light bulb across the terminals to do that, not sure if its a standard way to do it but seems to work for me, hopefully someone will chime in if it could be dangerous.
Hood

Offline kolias

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Re: Power Supply Unit
« Reply #67 on: January 14, 2011, 07:43:47 PM »
Thanks for the tip Hood, much appreciated

I'm waiting for someone to chime in and tell me if I can connect the AC ground wire with the DC black (ground) wire. I mean since I will have a metal box to build the unit, do I attach both the AC and DC ground to the metal box wall?
Nicolas

Offline RICH

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Re: Power Supply Unit
« Reply #68 on: January 14, 2011, 10:03:08 PM »
One of the questions to get a ham radio license is:
What is the first thing one should do before working on a power supply or amplifier?
Make sure sure the capacitor's are discharged.

Hood is right on as they can be dangerous. IE; my friend who knew better happen to touch the capacitor terminal, voltage arc  entered the little finger and came out at the thumbs knuckle, which he kind of no longer has. I always waite and then check with a volt meter that it reads zero. A light bulb in a socket works as it acts as a bleed off resistor, but , the meter should still read ZERO. You can have a sized resistor accross the terminals of the capacitor to act as a bleed resistor.

I take the ground wire of the supply cord and bond / attach to the metal case. The DC ground goes to a seperate post which is attached to the cabinet. All DC grounds go to that post.

BTW,

You and only you are completely responsible for all associated power supply building and design. Any and all advice, comments, etc given in this post are not to be considered absolutely safe or correct. The user requesting or using posted information assumes all risk associated with information in this thread.
RICH
« Last Edit: January 14, 2011, 10:04:57 PM by RICH »

Offline kolias

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Re: Power Supply Unit
« Reply #69 on: January 15, 2011, 12:15:12 AM »
Thanks Rich, I like the voltmeter test too and I will use it. The bleed off resistor I will leave it for later until I get to know more about this staff.

Grounding the AC ground to the metal box sounds good and that is what I was planning. The DC black wire I will attach it to a ground bar inside the metal box as you said. I still have to work it out in my mind to see why they have to be separate since indirectly both grounds are connected together (through the metal box) but eventually I will get it.

As for the responsibility of the project of course I know that I’m responsible and nobody else. As you may have noticed I ask a lot of questions, sometimes stupid, and the reason is that I must understand what I’m doing. I will not proceed to build this project until I know exactly what is going on and I feel confident enough to do it.

Thanks for all the help
Nicolas