Power Distribution Board Question

[yash101]

I do not get this thing about amps and volts. Most people think that it is amps that kill. Why is it that if you have 12,000 volts and 1 microamp, you can still die a painful death? Isn't it wattage that kills?

So, you may be wondering how this goes with this topic:
Well, the traces would probably break down if you had a high voltage and low amperage because the wattage will still be high. Wattage is Voltage times Amperage. A supercapacitor of 1 volt will do the same damage as a 12 volt battery outputting a tenth of that amperage.
Using Ohm's law below:
If the trace has a resistance of 1 ohm, 10,000 volts at .0001 Amps would equal to ten watts.
With the same resistance, 1 volt at 10 amps would equal ten watts.
That is the same amount of energy. No less, No more! The only difference is that in the first scenario, there is a high pressure and low flow. In the second scenario, there is a lower pressure but a higher flow. It is more-or-less the same as converting potential energy to kinetic energy and back!

Ohm's Law:
I = E / R
E = I * R
R = V / I

General Power Law:
P = I * E
E = P / I
I = P / E

P: Power
E: Voltage
I: Amperage
R: Resistance

Guys, Please let me know if I am misunderstanding physics here!

[MrForbes]

In electronic circuits, the size of the conductor must be large enough to handle the current. And the insulation (or trace spacing) must be good enough to handle the voltage without arcing.

We look at current and voltage specs separately in most cases.

But power....watts...that is important because of the heat that must be dissipated.

It's not a matter of understanding the physics of Ohm's Law. It's a matter of understanding the engineering requirements for the different properties of electricity.

[Chris_Ely]

Originally Posted by yash101

I do not get this thing about amps and volts. Most people think that it is amps that kill. Why is it that if you have 12,000 volts and 1 microamp, you can still die a painful death? Isn't it wattage that kills?

12000 Volts and 1 micro amp will not hurt you. When you get shocked when you touch a door knob, for example, that shock can be well over 100,000 Volts. Amps is what does the damage. You are correct in Ohm's law and the Power law, but the amperage that you list is not high enough to cause pain. See this Wikipedia article. http://en.wikipedia.org/wiki/Electric_shock

[Brandon_L]

There are much, much better options out there then the current FRC Power Distribution Board.

As MrForbes stated, something like the pre-2009 control system pd components would work fine - and probably be cheaper. I can't imagine you needed anything too fancy.

[Al Skierkiewicz]

Where to start?
Lets do the volts vs amps question. GFI breakers are designed to trip off at less than 4-6 ma since above that level is the current that seems to interrupt the heart function with regularity. However, at much less than 120 volts (the RMS value) the skin and body resistance will limit that current. That is why you can touch the terminals on the 12 volt battery and not be harmed. 48 volts on the phone line can give you a really uncomfortable tingle. This is all assuming you do not already have some electrical issue with heart function or have a pace maker. As you increase voltage the induced current will change. If the current is limited in some fashion, the high voltage still can cause other effects like local skin burns and muscle damage.
As Jim has pointed out above, high voltage requires precautions with insulation and exposed conductor spacing. The transmitter I work on has a 35,000 volt, 2 amp power supply. The wiring has a multi-layered insulation that requires regular replacement to prevent it breaking down. All the parts that are at this elevated voltage also have an anti-coronal design so that the voltage has a uniform field around the parts. This prevents discharge and the accompanying arc burns and localized welding of parts. There are no sharp edges on anything in the high voltage cabinet. Yes, at 2 amps, the wiring really needs to be only #22 wire. However it is larger than that simply to support the insulation and other factors. The overall diameter is about 1/4".
On to the power rating, yes the 35kV@2 amps gives you 70kW which is the amount of work that can be performed and this transmitter is generally capable of making 30kW at full power due to inefficiencies and head room. Here is where things get a lot more complicated. The RF at that level behaves much differently than DC of the same peak voltage. Even at low currents, severe muscle damage can occur with severe burning. The currents tend to flow at the surface of conductors and depending on frequency can penetrate the body to varying depths.
As to the PD, the conductor spacing, board composition and other factors would easily handle at least 50 volts and likely 100 volts DC. (The electronics as I mentioned above are designed for 12 volts and will be destroyed at 24 volts and above.) However, whether the PD would pass electrical laws (i.e. NEC) for those levels is unknown. I think that the WAGO is speced up to 300 volts. However, the current PD in my opinion, is far superior to the power distro used in earlier years. At least you do not need multiple tools to terminate wires and it is much easier to mount and use.

[Andy Brockway]

Don't you just love it when Al breaks it down for us non electrical guys!

[EricVanWyk]

The FETs controlling the blown breakers would become marginal. They are rated at 25V, so you are right up against their rating. It would become possible for a voltage spike to push you well past their rating and blow them.

The PTC fuse for the regulated 12V supply would be well out of spec and no longer provide protection.

The 12V power supply indicator LED may burn out.

Most of the input capacitors for the power supplies would be over-volted. This would likely cause part failure (which would become self-clearing, loudly and with odor). It would definitely cause severely increased noise on the output.

The 12V regulated power supply would not be in regulation.

Depending on what year PD you are using, the 5V supply might pop.


The quick summary is that the PD design could easily be tweaked for a 24V input, with most rework for the 12V supply, but it wasn't.