| Rarkov |
Hi,
I have just modelled up a power supply in Duncans Power Supply Designer II. The circuit uses a choke directly after the rectifier. The amp is it providing has 5A (I think) rail fuses. I assume I need a choke that is rated at 5H and 5A?! These must be huge!
Can anyone tell me if this is right - and Where I can get them?
I can give more information / graphs on request...
Thanks,
Gaz
BTW - If these chokes don't work out - I will be using a high power potential divider! |
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| Rarkov |
Just speaking to Brian Sowter - He says that a 5H 5A Choke would be well over 100kg! How would I fit that is a monoblock?! He suggested using a solid state regulator - so that it is I think.
Thanks,
Gaz |
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| promitheus |
| what exactly do you want to power up ? |
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| roddyama |
Hi Gaz,
There are a couple things you need to check. As you found, a 5H choke is huge. 5mH sound more like it. The other item is that when I’ve used Duncans’ program in the past, I would set the load as a constant current draw. Your PSU is only providing 10mA to a 5kohm load.
Try it again with 5mH and 5A constant current.
Rodd Yamas***a |
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| Rarkov |
Hi,
The amplifier is a Randy Slone designed MOSFET 140W-200W class B amp. It needs +-55V to operate at those ratings.
When I replace the resistive load with the 5A constant current load - the rectification goes out of the window! I can't make it look like a normal graph at all! Even when I change the choke to a more reasonable value!
Edit:
If I only pull 1 Amp and leave the choke at 5H - I get a response alot like a very underdamped impulse response with huge overshoot.
Gaz |
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| promitheus |
I don´t know about this PSU design programm but I agree that 5H is a little too big. 5mH is I think more logical as stated before.
Also I would split the capacitance in half and use 2 caps on either side of the coil in a pi configuration. It works better and is easier to find smaller caps. |
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| Rarkov |
Hi,
The 13.6mF cap represents 2 6.8mF in parallel. Obviously 5H is a normal kind of value for Choke Input Supplies - but as it has been pointed out to me - That is for hundreds of voltages and mA!
I got quite good results from the Choke-Cap-Choke-Cap-Load configuration - when drawing a resitive load!
Gaz |
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| UrSv |
You might also want to change the diodes from 1 A types (which indeed would blow up used here) to something more suitable like a 35 A bridge or similar. If using the supply for Class B amp I would also not use a choke supply but normal C supply or possibly CRC.
/UrSv |
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| HBarske |
Rarkov,
your schematic shows 30 Ohms for the 5H coil. You are going to lose 30 volts on your voltage rails for every ampere of current you draw.I can't imagine this is meant to be serious... |
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| promitheus |
I would always use a 25 or 35 A bridge. The cost of this part is so small why use a smaller bridge?
I always use caps across the bridge diodes to lower RF noise getting in the PSU. |
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| Rarkov |
| quote: | Originally posted by HBarske
Rarkov,
your schematic shows 30 Ohms for the 5H coil. You are going to lose 30 volts on your voltage rails for every ampere of current you draw.I can't imagine this is meant to be serious... |
It's my PSU skills that are the joke! Let me put this another way.
I have a 35A rectifier. The output of my Xformer-Recifier-Cap-Cap PSU is 70V. I want it lower than that (55V ish). I suggested to a friend that I would be using a potential divider and he suggested a choke. SS regulators have also been suggested.
What is peoples preferred method of changing voltages (without buying a new xformer)
Thanks,
Gaz |
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| Christer |
Rarkov,
I am afraid the preferred method is to buy a new
transformer. They are expensive, but it will save you a lot of
trouble. Second to that, you may try to rewind the one you've
got, but that ís usually quite a lot of work.
Otherwise,
1) Linear voltage regulator. Will waste a lot of power and
dissipate a lot of heat.
2) Switching regulator. Much better efficiency, but difficult
to design and higher risk of failure.
My suggestion:
Get a new transformer. Keep the other one for future projects
or try to sell it to somebody building a bigger beast than you. |
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| Rarkov |
OK, OK, You win!!!
Maplins have been kind enough to order in some 40V varients so the output voltage will be 56V. Because I have not soldered them - They will let me swap them, even though it is outside the 14day limit! Thanx guys!!!
I was getting worried anyway - because the caps are rated at 63V...One wrong wiring...!
Thanks alot lads! Great help! ;)
Gaz |
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| Jakeh |
That saved a lot of trouble...
Still not a huge amount of headroom on those caps, so definitely a wise choice to change the trafo.
Jake |
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| Rarkov |
It's just as well that they did exhange them...they had to redeem themselves. When they delivered the xformers, caps, bridge rectifiers and switches etc. they put the box down somewhere. When I picked it up - the box looked like it had been thrown from a 10 floor high building! It crumpled in my hands!
I had a look at the capacitors and they were bugg**ed! They was dents and holes in the sides! I took them back and one lad said - they should be alright!!! ;) Like I was going to build my first major PSU with dud / dangourous caps!!!
Anyway - they did change them in the end! ;)
Cya,
Gaz |
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| Rarkov |
Hi,
It does - but I can't find how to design dual polarity PSUs in PSU Designer II. I haven't looked that hard - but it wasn't obvious when I did look.
Gaz |
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| Elso Kwak |
Hi Rarkov
The program you are using is for tube amplifiers. |
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| Rarkov |
I know this is its primary function. It does, however, have an option for solid state design.
I will try on PSpice tonight. As soon as I add a current drain on the end - the results go wild!
Gaz |
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| Christer |
Rarkov,
Which of Sloanes amps are you building? |
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| Rarkov |
Hi,
It is in his Audiophile Source Book. About in the middle there is an amp that he quotes 'as his favourite of any type'. He publishes about 6 or so pictures of built and commercial versions. It is rated at 140W(8Ohm) 200W(4Ohm) @+-55V and he gives instructions on converting to 300W versions or even a 400W version (@ +- 68V). I believe it is the last amp in the chapter?
Hope that helps.
Gaz |
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| Christer |
OK, I assumed it was a design from his Power Amplifier Manual.
Could still be one of those, but then it is difficult to tell without
having booth books. |
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| Rarkov |
I'd actually really recommend the source book. It's got some interesting circuits in it. Also some bloody stupid ones - such as an expandable equaliser that looks like it could cost £200 for the components alone and the same again for a circuit board that size!!!
I think they're invaluable references though. I also have Doug Self's book...But that is slightly more technically minded!
Gaz
P.S. I don't think it is published in the Cook book... |
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