archpaladin

So here's a theoretical question for all you electrical engineers out there...... I'm not an engineer myself so I may get my jargon wrong in asking the question, but I'm going to do my best.

I have an AC power source and two loads. One load requires a set amount of power and must always be fully supplied by the source; the other has variable requirements and only needs to take the excess power that the source produces. I want to be able to split the electrical current generated by the source so that the first load will always be supplied with the required amount of power, and that all the overflow will go to the second load. How could I do this?

I want to avoid having to give specific numbers in stating the problem, because I want to be able to change the parameters of the system (like how much power the source produces, or the requirements of the first load) and still come up with a solution. Obviously there are constraints - like trying to power a load with a source that can't supply the required energy - but in asking the question I'm assuming that there will always be an excess of power produced by the source so that there is always overflow to divert somewhere else.

Thanks a bunch.

Lebell

Assuming there is always available "power" (amps), you simply need two separate lines from the pos/neg poles of your source to each device.

That way, you are splitting the amps, not the voltage (parallel wiring). If you put them in a series, like christmas tree lights, then you will be splitting the voltage while the same number of amps flow through each device (series wiring).

The key of course is that your power supply puts out sufficient amps for all devices connected to it.

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stingc

I think that you probably are using the wrong jargon. By "power," do you really mean that, or are you talking about voltage or current? Most sources do not have a constant power output. (Near-) constant voltage sources are most common (your usual AC outlet), and current sources occasionally occur in circuits. Describe physically what you want to do. Is the source a wall outlet? Is this a stereo project?

archpaladin

That's kinda what I was trying to avoid, in order to make it as general as possible. Let's assume this is not a stereo project (though I'm not sure how that would change the problem at all) Use the following as a hypothetical example:

Assume the power source is generated by a human who has nothing better to do with his day then move a magnet through a coil of wire. Basic induction principles tell us that this will generate an alternating electric current. Now, also in the room with the human is a light bulb and a drawer full of electric razors. The light bulb needs a certain amount of current ( / power / wattage? here is the jargon issue) to be on at its appropriate strength, and it must be on all the time because the room has no windows and would be dark otherwise. Also, at any given point in the day, an arbitrary number of hairy men will come in and use the electric razors to shave and leave as less hairy. The electric razors will also require an appropriate amount of current/power to run, but the amount required changes because the load changes. Hence the issue I first posted. I want to split the current/power produced by the source so that the light bulb can be on all the time, and all the excess can go to running the electric razors.

This is obviously an absurd example but demonstrates the kind of problem that I'm getting at. As I said, this was a theoretical question, so I don't want to present too specific a situation because I'm looking for the underlying principle.

a-j

I'm no EE, but have a fascination with electronics. Here is what I would recommend. You would need some current limiting device on the circuit with the razors, and some sort of current detecting mechanism with the light bulb. If the current passing through / power consumed by the lightbulb drops it engages the current limiting circuit connected to the razors. Seems like I've seen this type of thing before with op amps.

But there are probably better ways to do this.

vinaur

Woulodn't you just need a powerful power supply (as in a lot of amps), so it could support all the razors and the bulb at the same time. When the razors are not on the bulb wouldn't be using the whole potential of the supply, but it would still work. You would connect all the appliences with separate wires right from the power supply. I'm not really experienced with electricity, but that's how I always thought of it.

RCAlyra2004

I am NOT and engineer, but worked as an Engineering Technician for a Llarge power production company for many years.

Likely... for an home project you don't need to "Split" the electrical current. As long as the single source of power is large enough and the voltage is regulated to 120 volts the load can change and electrons will flow to where the load is needed, be it razors or lightbulbs.

If you feel that you need to "protect" the Lightbulb from Voltage drops etc and it is actually suffering from a performance problem that is measurable you can install a subsytem that will protect it from power "sags" in the main system by many different means...

stereo system size problem...a capacitor in the circuit for the light bulb, it just helps keep the voltage up/down to where it should be during short 1-5 cycle spikes caused by the power sucking Bass woofer.

A Transformer with a "filter system" built in. The capacitance in a transformer is bigger than simple "capacitors" if used correctly, but this is for BIG projects.

other system.. a battery UPS for the circuit in trouble (convert ac to dc and then back again like a Uniterruptible Power Supply circuit. that battery isolates the Light bulb from surges, spikes and circuit "noise")

Bigger than that...a separate Motor generator circuit. ( a large electric motor that drives a heavy flywheel with a generator attached, or built right in. It absorbs big voltage spikes ( and I mean BIG Fricken voltage spikes and makes nice clean power..mmmmm clean power ...mmmmmmm)

Finally - A Synchronous condenser. This is like a HUGE motor generator set in principle. They are used to maintain the voltage in Transmissions systems (I mean Province/State wide electrical distribution systems. We use Synchronous condensers to manage an smooth out large burps, voltage spikes and even some harmonics occurring in our power transmission systems, where clean power in large amounts is imperitive or customers call and ask us to replace their tv sets after a lightning storm.

If you ensure that the main power supply is big enough it will eliminate the need to split the power in the first place. But like I said if you are avoiding Spikes of usage from something similar to a "Current sucking/ voltage dropping" SubWoofer... You need a big capacitor on the rest of the system.

Analyze the problem... is this a peak load problem? ... and is that throwing the other half of your circuit off (dropping it's voltage internittently causing distortion/harmonics/noise etc.?) FYI Distortion harmonics and noise occurr in all power systems.

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BAMF

put a diode & large resistor in parallel with the light bulb, connect the razors in series after that

RCAlyra2004

YUP! thats it in a nutshell

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the420star

lets look at this in terms of a T... you have something coming in, and two things coming out... Kirchovs Current law states that the sum of currents at a Node, the point where all three things connect is 0. So using this as an example... lets say you have a light blub on one end like you example, that will act as a load a draw a given amount of the current from the system, leaving whatever is left to be used by razor in your example. so we get source(total current) = lightbulb + Razor....so you can see that as long as the needs of the razor dont exceed source - light bulb, then you have adiquate power. i dunno if this is enough info for you, i just banged this out quickly before class... post again if you have more ?s, i am a senior in an EE program... i should be able to clear this all up for you

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undeadninjaz

just wondering, what would that do?