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Padriac

Variable current indicator

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I am currently gathering the parts to make the Variable DC Power Supply project. I want to include a volt meter and a current meter. I understand how to connect the ammeter but as I understand it the meter will not read anything until a load is applied to the power supply. This could spell trouble if the pot is set for 2 amps and the circut can only tolerate 1 for example. So is there a way to tell what the pot is set for without connecting a project to the supply? Some additional circuitry maybe? Or should I just settle for turning the current pot all the way down, hook the project up, and bring the current back up?

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I do not mean to over simplify this, but perhaps this will also help others:
You cannot have current until the electrons are flowing through your circuit. The current adjustment is a limiting tool. Use the ohm's law calculation to figure out how you will use it. For example, if your power supply gives a potential of 10 volts (set by the volt knob) and your load is 10 ohms, then your circuit will use 1 amp (V/R=I). I am using easy numbers to calculate so it is easier to see. If you limit your circuit to use no more than 2 amps, your circuit will still only use 1 amp. It will not use less and it will not use more. If you change the resistance of the load to 2 ohms (10/2=5), this would give you the potential of 5 amps. However, since you have set your limit to 2 amps, the limit will go into effect at this point and you will not have a melt down. This is great in the case that you accidentally get a direct short in your test circuit. The circuit will not be able to become dangerous. In the case that you forget and leave the current limiting knob too high and you connect a shorted power buss, the current will go up and the system should generate enough heat to pop the fuse if you have made the fuse calculation correct.
I usually start with both voltage and current knobs turned all the way down. You never know when a new circuit will have a short. Best to be safe. Is also cheaper than buying many fuses. I hope this helps to explain it a little better.
MP

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thanks MP. That's what I thought but I was hoping there was some way to tell where the current pot was set when I turned the supply on. I guess I should just print a sticker that says

Turn me down before you turn me on



for the front of the supply. ;D Thanks for the info.

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