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what kind of power supply?

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nyeboy2000

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I am a novice in electroincs with a question about powering two small devices. The specs are 14 amps and 9 volts on one and 9 amps and 15.4 volts on the other. I am guessing that I need an AC to DC power supply. But what do I need to look for when I buy it? Is this range of power standard?

Thanks
 

kinjalgp

Active Member
14 and 9 AMPS are very high currents. No doubt you'll get power supply of this rating in the market but be sure of what you are doing because short circuit @ 14 amps can easily cause fire. Are you aware what are those 2 devices?
 

nyeboy2000

New Member
when you say 14 amps and 9 amps is a lot, can you give me a comparison to some other items and their currents. For instance, an item with low amps and an item with amps comparable to the 9-14 range
 

kinjalgp

Active Member
But before that I would like to know what are those 2 devices which requires such high current.
 

kinjalgp

Active Member
When I said high current, I compared it with currents in electronic circuits which are generally of the order of few hunderd milli-amps or sometimes few amps except for power amplifiers. So I was wondering which device is eating so much of current. The best suited power supply would be SMPS as even a compact sized PS can cater considerable amount of current.
 

nyeboy2000

New Member
Can you tell me more about SMPS? What is the price range for something like that? What else would I need as far as fuses or other? Also more about any possible safety concerns. I really appreciate all of your info. Thanks.
 

kinjalgp

Active Member
SMPS (Switch Mode Power Supply) is a kind of PS similar to one used in computers. As compared to bulky transformers it is quite compact and has many other featutes too like good output regulation, less ripple etc. I don't have idea about pricing of SMPS of 14A and 9A but a computer SMPS will cost you around US $10 which has a 12V output capable of giving 10A and 5V @ 25A.

Regarding safety, a fuse is always good to use whose capacity will depend upon your load current requirements.
 

nyeboy2000

New Member
Where can I buy a SMPS and how is it powered? What else will I need to be able to adjust the voltage and current that it outputs?
 

kinjalgp

Active Member
Well, a normal computer SMPS is available in any computer hardware shop. It is powered from AC mains 110V/220V. Normally the outputs of SMPS are a fixed voltage but by changing the component values you can vary it.
 

Gene

New Member
An example might be a car brake light which pulls about 2 Amps - about the same as a 27" color TV. Of course the TV is AC and that's a different situation but hopefully this will give you an idea of how hot 14 Amps is - please be careful. When you said powering "two small devices" and then said 14 Amps, something didn't sound quite right. Could it maybe have been mA (mili-Amps)?
 

nyeboy2000

New Member
It is a cooling device and I have learned that electric heating and cooling devices can use very high current. I would like to learn more about any precautions I should take or any pointers on how I should setup the initial testing of this device. If you have any thoughts on this I would appreciate it.
 

Gene

New Member
Since you got everyone's attention with the high current thing, you should simply be sure to insulate all connections well. I'm sure you must have heard somewhere that current kills - not voltage; so don't be fooled by the low voltage of this circuit. I think a key word would be, 'respect.' Be aware when the thing is plugged in to the house power as you are working and please know that electrolytic capacitors (which you will surely use) hold power - lots of it - even when the thing is unplugged. Last thought . . . when you are done, put the power supply in a well vented, closed metal box with proper fuses. Good luck!
 

nyeboy2000

New Member
The figures I have given, 9 volts and 14 amps, are maximum values for the device. I will not necessarily be running the device at full capacity. Assuming I want to run at 54 watts, I could run it at 9 volts, 6 amps or 6 volts, 9 amps. Is there any possible advantage to running it at 6 volts 9 amps? In other words, is it always the case that I should run with lower amps and higher volts if I have the choice? If so, why would anyone want to run a device with such high current and low voltage?
 

star882

New Member
nyeboy2000 said:
Can you tell me more about SMPS? What is the price range for something like that? What else would I need as far as fuses or other? Also more about any possible safety concerns. I really appreciate all of your info. Thanks.
SMPSes are power supplies that convert the incoming AC into DC and step it down.
Avoid naked PCB power supplies if you can, there is 170v on the bottom of the board(340v if 240v). :shock:
My friend Caitlin Williams got a shock from an unplugged fluorescent lamp that caused her to wet herself. :lol: :lol:
The cap in the lamp is only 220uF.
I have seen 2 680uF caps in a dell power supply.
BTW, I reverse engineered an old dell power supply from a p133.
That dell power supply used a LITEON power transformer(at first, I thought they only made CD-ROM drives).
There is only one switching transistor(well, only one big primary transistor, as there is a smaller transistor in the 5VFP supply, and several big transistors on the secondary side), but it is a high-power IGBT boobie(20A, 900v) in a TO-3 case.
The primary caps are 680uF each, for a total of 1360uF(most PC power supplies have only 2 470uF, or 940uF total)!
The coil in a flyback regulator cannot be called a true transformer.
My friend Christina Mahoney designs SMPSes alot, and she said that a true transformer has instants where power is going in and out at once, but the coil in a flyback converter never has an instant where power is going in and out at once.
When the transistor is on, current flows through the primary winding, and energy is stored as a magnetic field in the core.
When the transistor turns off, energy flows out of the core into the secondary circuit.
In other words, it is like using a cup to transfer water from one container to another.
She also explained the switching frequency.
Higher frequencies allow higher power density, because power goes into and out of the coil faster(back to the water analogy: it's like filling the cup and emptying it faster, so a smaller cup can be used).
 

mechie

New Member
Current Kills ?

Gene made a comment that "current kills", this is true, but Ohm's law is on your side!
V=I*R therefore I=V/R --- for the current to be high enough for you to even feel it your body resistance must be low enough to pass that current at the available voltage.
I have NEVER even felt a tingle from 24v supplies even outdoors when I get rained on (soaked), 50v is fine for me when I am dry.

nyeboy2000 asks "should (I) run with lower amps and higher volts if I have the choice?" --- This will be a trade-off you must make; higher currents means bigger conductors, higher voltages means more insulation (taken to the extreme).
Unless you have a complex load on the power supply you will end up altering current and voltage simultaneously; reduce the voltage and the current will also decrease (Ohm's law again!).
If you can arrange the load to use a higher voltage I would do that as it allows smaller currents and therefore cheaper regulation.
 
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