Gallery, Projects and General > How to's
How to Make a Power Supply
Darren:
Thank you Tim,
Understood that perfectly and it even made sense to me :clap:
Now I know why they use huge 1 farad caps in car stereo setups :thumbup:
It's funny how people go down different paths for similar uses. That is, I use voltage regulators with much less uf for valve filaments which are low voltage and high current.
Maybe I should try what is being suggested for Erics situation and see how it sounds, it might be simpler but it does really depend on the resulting sound.
I don't know how much you know about valves?
With indirectly heated types we can use AC voltage to heat them and get away with it. With directly heated valves (which I prefer) this only seems to work with lower voltages of up to around 4V helped with the use of hum buckers. Above that they hum too much so we then switch to DC heaters.
My largest transformer has taps at 3,3K and 4.2K and I must try these higher supplies with my larger valves one day.
But as you can guess, that presents a whole new set of issues.
:thumbup:
Darren:
Back to the power supply that is the subject of this thread.
I have spent some time testing and measuring the circuit under load with one 24V motor as shown in the pictures.
The unit has been left on overnight at the max stressful 2.5V low speed setting with a 24V input from the transformer. The temperatures of the regulator have been monitored and I'm happy to say it's still running :D
Max temp recorded of the regulator has been 88deg C, but it typically sits at 74 deg.
I have come to the conclusion that given a larger heat sink this supply could run 3 motors at the same time.
Below you will find the data as recorded, I hope this information will help those that wish to see a more in depth technical side of the goings on.
I will continue this thread to show how to increase the current output capabilities by adding one, two, three or even four power transistors.
Done properly this will provide a very powerful and possibly dangerous outputs depending on how you handle it.
I accept no liability if you follow my examples, I'm merely providing a demonstration. Not forcing you to copy, that would be your choice and yours alone.
The data recorded as follow, sorry the formatting has become a little lost transferring it onto here, but it should still be clear enough.
Motor V I W
H Speed 31.6 0.4 12.64
1/2 Speed 15 0.26 3.9
Low Speed 2.5 0.15 0.375
Regulator V I W
H 4.8 0.4 1.92
M 21.6 0.26 5.616
L 33.9 0.15 5.085
Pot V R I W
H 28.9 5000 0.00578 0.167042
M 12.6 2500 0.00504 0.063504
L 0 0 0 0
V=Volts I=Current in Amps W=Watts R=Resistance in Ohms
Ohms Law V=IxR
Watts W=VxA
LM338 Voltage Regulator Max Values
Current 5A Continous With extra cooling 7-8A 12A Peak Start up such as motors
Wattage 24V = 120W 24V = 192W 24V =288W
Temperature 125Deg C
Ref: http://www.datasheetcatalog.org/datasheet2/8/0ujhh2scud4dfop1xfyut2u2qopy.pdf
spuddevans:
--- Quote from: Darren on May 16, 2009, 04:49:31 AM ---It's funny how people go down different paths for similar uses. That is, I use voltage regulators with much less uf for valve filaments which are low voltage and high current.
--- End quote ---
True, there are many ways to get the same results. Would I be correct in remembering that valve heaters have a constant current draw? If so that would be why you can use smaller uf caps, and especially if you use a choke as well. Constant current draw requires less uF than intermittent current draw.
--- Quote ---I don't know how much you know about valves?
With indirectly heated types we can use AC voltage to heat them and get away with it. With directly heated valves (which I prefer) this only seems to work with lower voltages of up to around 4V helped with the use of hum buckers. Above that they hum too much so we then switch to DC heaters.
--- End quote ---
Not a huge amount, I always wanted to build a nice high-end type valve amp for the hi-fi, but got scared off by the price of decent quality output transformers and the scarily high voltages involved. (I dont mind working up to 200-240v, but most of the designs I looked at were 600-800v :bugeye:)
Do you use Valve rectifiers for the HT supply?
Tim
Darren:
--- Quote from: spuddevans on May 16, 2009, 02:33:30 PM ---
Would I be correct in remembering that valve heaters have a constant current draw?
Not a huge amount, I always wanted to build a nice high-end type valve amp for the hi-fi, but got scared off by the price of decent quality output transformers and the scarily high voltages involved. (I dont mind working up to 200-240v, but most of the designs I looked at were 600-800v :bugeye:)
Do you use Valve rectifiers for the HT supply?
Tim
--- End quote ---
Yes the heater current is constant, can be anything from 0.3 - 10Afor the sort of valves I use.
Typical power valves are around 3-5A 3.15-10V
Output transformers new are a price, £200 a pair is about average, I think my dearest for the 833's cost me around £450 the pair and that is middle of the road.
But, you can get pretty good results with old radio ones and the mains transformers are handy too.
Then again 9V toroidal used in parafeed also works well for outputs and these are cheap.
I have about 3-4000 valves to play with, some are valued at £1,500 a pair (no I didn't). My main little amp uses PX4's (a vintage triode from the 1920's about £100 each) That is valve rectified but I also use silicon sometimes.
My 833 amp uses silicon rectifiers. But I do have a few mercury rectifiers that I could use instead. It's the 1,500VDC that limits what you can use here because of voltage breakdown issues.
If you still want to build a valve amp let me know, I have about half a ton of mains transformers and could do with slimming them down a bit. A real understatement !!!
For caps, I have many, no idea how many but the PIO's alone fill about 3 large stacker boxes. If you want to use electrolytics those disposable cameras with flash are hiding one of the best quality ever made, little Rubycons that can take some hammering 100uf 300V.
I'll takes some pictures for you. Valve amps are easy to make :thumbup:
Regards Darren
spuddevans:
--- Quote from: Darren on May 16, 2009, 04:10:21 PM ---If you still want to build a valve amp let me know, I have about half a ton of mains transformers and could do with slimming them down a bit. A real understatement !!!
--- End quote ---
I would love to build one but if I take up another hobby(or resurrect an old one) I think my better half will explode. I already have a long list of jobs to do around the house that keep getting put off, I dont think I should push it.
Back when I was big into electronics I did consider building one of the Hi-Fi World valve amp kits, I built a pair of floorstanding speakers from one of their kits and loved them, still use them as part of the home cinema system.
--- Quote ---I'll takes some pictures for you. Valve amps are easy to make :thumbup:
--- End quote ---
I'd like to see some of your electrical handywork, that'd be great :thumbup: :thumbup:
Tim
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