# Typical values and danger of circuit components

1. May 31, 2009

### xianyang

Hi guys,

I am a physics graduate, currently working in an experimental lab. Before coming here, I have no solid experience in lab stuffs. Anyway I enjoy working at lab a lot.

The first task I have is to learn and master a programable DC source (Yokogawa 7651). To do this, I personaly think that I need some knowlegde for the following:

1) What are the typical values of voltage, current, resistance of a circuit? I would like to know the typical values of them ranging from as small as table circuits to industrial circuits.
2) How dangerous is a value of voltage, or current? I think we can calculate the power consumed by the whole circuit by a simple estimate P=VI=V2/R=I2R. However, this is for the whole circuit, rather than for a small object such as our body when coming into contact with the circuit. Make it precise, is there anyway to calculate the power that our body will be receiving from a circuit, given some neccessary information?

I would appreciate if you guys like to share with me you says or some links that answer to the above doubts.

Thanks,
Xian Yang

2. Jun 1, 2009

### vk6kro

Looks like a nice power supply although the front panel is confusing. Maybe with the instruction book it may become clearer.

It can generate 32 volts at 120 mA. These are quite safe for you to touch unless you apply that voltage to a large inductor. In that case, you could get a large voltage generated.

Many electronic devices would not stand 32 volts and may be destroyed. So you would have to be aware of that.

Devices like electrolytic capacitors have voltage ratings that can be less than that and they also have polarity requirements.

LEDs and Zener diodes have to have a series resistor that must be appropriate for the device and the power source.

Otherwise, you should perhaps set up a few small projects to learn how to use it. Keep the voltage low for a while until you get used to it.

I guess it could be used for calibrating other measuring equipment like digital voltmeters, rather than actually powering equipment with it.

3. Jun 1, 2009

### LewisEE

When I hook up the power supply to my circuit and turn it on, the first thing I look to see is how much current the circuit is drawing out of the power supply. I don't know what exactly you will be doing, but most circuits you throw together on a breadboard won't need more than several mA. Of course, check the data sheets and your circuit before you flip the switch so you have an idea of how much current there should be. If you see the current jump up to a couple hundred mA or over 1 A, something may be wrong. Current at this level is extremely dangerous.

Make sure that if you use electrolytic capacitors, you have them biased properly because they can get damaged, smoke, and even pop out at a high speed.

Make sure that if you use op amps you are properly biasing them because they too can easily be damaged.

As vk6kro said, you may want to keep voltage low to start with. But especially keep current low; once you get above a few mA you need to be careful.

4. Jun 1, 2009

FYI,

Capacitors do blow up violently when hooked up badly. They also release lots of smoke (white with purpleish tint in my case).

However, if you don't have your face over them when it blows up then you should be fine. If you do then stop breathing, turn off the PSU and go wash your face.

I'd recommend you build a few simple circuits, LED/resistors then put in switches and so on.

120 milliamps is not a lot, but it should drive a couple LEDs

5. Jun 1, 2009

### vk6kro

The most dangerous component you could encounter is another power supply.

This one may be well prepared and protected from other power sources, but it might not.
If it encountered a higher voltage, you may well blow up some extremely expensive components or turn your power supply into a heap of scrap.

So, always ensure that any circuit you apply it to has the power disconnected by pulling the plug from the wall. Also, capacitors, especially electrolytic capacitors can hold a charge for a long time and need to be discharged before any testing.

6. Jun 2, 2009

Thanks guy!