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Is thickness of ground wire as important as thickness of the PWR wire?
Posted by
eeguy
on 13 Oct, 2020 17:56
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Hi, I read that if motors draw more current, I need thicker wires. Do I need to choose the thickness of the only the red wire or both the red and ground black wires according to the maximum current that the motors in the system could draw?
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#1 Reply
Posted by
KMoffett
on 13 Oct, 2020 18:27
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I'm confused. Red and black "ground"? Is this a DC motor?
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#2 Reply
Posted by
eeguy
on 13 Oct, 2020 18:40
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I'm confused. Red and black "ground"? Is this a DC motor?
I was taught that by convention, red wire for power and black wire for ground. In the past, I was told that if I use high torque motor that draws a lot of current, I need to use thick wires that correspond to the current draw. I wonder if thick wire means only the red wire that supplies power to the circuit/motor needs to be thicker or both the power and ground wires need to be thicker.
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#3 Reply
Posted by
Cerebus
on 13 Oct, 2020 18:43
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Ponder on why it's called an electric circuit and you'll have your answer.
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#4 Reply
Posted by
james_s
on 13 Oct, 2020 18:54
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I'm confused. Red and black "ground"? Is this a DC motor?
I was taught that by convention, red wire for power and black wire for ground. In the past, I was told that if I use high torque motor that draws a lot of current, I need to use thick wires that correspond to the current draw. I wonder if thick wire means only the red wire that supplies power to the circuit/motor needs to be thicker or both the power and ground wires need to be thicker.
Red and black are commonly used for positive and negative in DC systems. In AC systems both of those colors are reserved for live conductors and should not be used for neutral. Kirchhoff's law states that the current through both wires will always be identical, as mentioned above it's called a "circuit", this may be more clear if you mentally separate the two wires going to the motor and picture it as a circle rather than two parallel lines connected at the ends.
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#5 Reply
Posted by
chrisl
on 13 Oct, 2020 18:55
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Hi, I read that if motors draw more current, I need thicker wires. Do I need to choose the thickness of the only the red wire or both the red and ground black wires according to the maximum current that the motors in the system could draw?
both the red and ground black wires
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#6 Reply
Posted by
eeguy
on 13 Oct, 2020 19:00
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I'm confused. Red and black "ground"? Is this a DC motor?
I was taught that by convention, red wire for power and black wire for ground. In the past, I was told that if I use high torque motor that draws a lot of current, I need to use thick wires that correspond to the current draw. I wonder if thick wire means only the red wire that supplies power to the circuit/motor needs to be thicker or both the power and ground wires need to be thicker.
Red and black are commonly used for positive and negative in DC systems. In AC systems both of those colors are reserved for live conductors and should not be used for neutral. Kirchhoff's law states that the current through both wires will always be identical, as mentioned above it's called a "circuit", this may be more clear if you mentally separate the two wires going to the motor and picture it as a circle rather than two parallel lines connected at the ends.
OK. I am talking about DC systems.
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#7 Reply
Posted by
james_s
on 14 Oct, 2020 05:00
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That only matters in regards to the color coding. You still need a circuit, any current flowing into a load must flow back out.
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There seems to be a little bit of a gap in your understanding of how electricity works.
As some have pointed out, the word "circuit" is important.
You can think of a wire carrying electricity like some sort of pipe carrying water. The current is equivalent to the water flow, a battery is equivalent to a water pump, the voltage is equivalent to the pump pressure, and the load (a motor, a light bulb, a led, anything) is kind of equivalent to a generator.
Imagine a closed water circuit. A pump "pushes" the water upwards, the water then falls down due to gravity and while falling down it moves a generator. The generator is slowing down the water (decreasing the pressure) and finally the water gets sucked by the pump.
The main thing that you have to understand in this case is that, if for some reason you want more water to go through the generator, the first thought is "I should increase the pump's power so the water can travel faster, thus carrying more volume of water per second", but then you realize "oh snap, the pipes are too thin, so if I increase the speed of the water, the walls of the pipes will drag it down, making it way more inefficient, and the pressure created in the pipes will be so high that they might break and start leaking". So you have to put wider pipes. This way when more water flows, the water speed can adjust normally without creating too much drag to the walls. A wider pipe can carry more water per second than a narrower pipe, at the same water speed.
Imagine now that someone asks "But should I make only the top pipes wider, or should I make also the bottom pipes wider?". well, it seems quite obvious, the same amount of water that is flowing at the topp will be flowing at the bottom. If you make the water go easy on the top but not the bottom, then the bottom part of the circuit would have to carry water faster so it can "drain" the top part, thus creating that same drag that I described before.
Electricity is just like this, Whatever amount of electricity goes out of a battery will come back at it. And this happens also for any load. Whatever amount of electricity (current) goes into a motor also comes out of it. The only difference before/after the motor is the voltage.
The same amount of water that goes into a water mill comes out of it. The only difference before/after the watermill is the water height.
Hopefully I explained it clearly and didn't confuse you even more.
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#9 Reply
Posted by
dnwheeler
on 14 Oct, 2020 20:43
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To expand on the discussion of "circuits," don't forget all of the wires, traces, and components in the "loop" must be rated for the current. It doesn't help to increase the size of the wires between a circuit board/switch/relay/whatever and a motor if the rest of the circuit melts down.
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#10 Reply
Posted by
eeguy
on 14 Oct, 2020 20:55
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Thanks. So it is better to use wires of the same AWG throughout the entire system? If connector(s) on commercially available circuit have lower current rating, shall I replace those bottleneck connectors by ones that accept higher rating?
I read that it may not be a good idea to buy wires from Amazon since we don't know if the specifications are correct or not. Is this true? How about Digikey? Is Tinned Copper under Conductor Material the one to choose?
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#11 Reply
Posted by
TimFox
on 14 Oct, 2020 21:01
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Normally, from a US vendor, you would select tinned stranded copper wire of the appropriate wire gauge. The wires available from a reputable dealer such as DigiKey will also specify the voltage capability of the plastic insulation. Stranded wire is better for wiring that may flex in use, but solid wire is normally used in house wiring and is good inside an enclosure where there is no motion of the wire after installation. The expensive option is Teflon insulation, which can withstand higher temperatures (including soldering temperature) at much higher cost. Teflon-insulated wire is normally silver plated instead of tinned, since the coating process would melt the tin and make the stranded wire rigid.
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#12 Reply
Posted by
tkamiya
on 15 Oct, 2020 01:55
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Yes, both black and red has to be thick enough to withstand the current. Both wires will have exactly the same amount of current running through. The only difference is direction of the current.
Since we are talking about motors.... When you first start a DC motor from dead stop, there will be an IN-RUSH current. Motor NOT running is basically a dead-short. So a motor that runs with 10 amp current average, may record peak value of 100 amps or more for a very brief time when it first starts to turn. Once it gets going, it will consume 10 amps, assuming it's the rating. You don't need to use a super thick wire to withstand 100 amps, of course. But you do want it thicker than just barely withstanding 10 amps. Typically, I will just use the next size up and that's enough. If you have a need to start and stop often, you might want to go even bigger.
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#13 Reply
Posted by
tkamiya
on 15 Oct, 2020 02:01
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I buy wires from Amazon all the time. There is nothing wrong with it.
If you are looking for thick wires, some vendors will sell you ALUMINUM CLAD wire. That's an aluminum wire that is copper plated. These are NOT desirable. Just be careful with you read the specification. If it doesn't say Pure Copper, then you need to be particularly careful. CCA is the abbreviation for Copper Clad Aluminum (which you don't want) Also, you'll need to pay attention to insulating material. Vinyl is not good. PVC is ok. Teflon is better but more expensive and perhaps not necessary. It will all depend on what you are doing and the environment your circuit will be running.
As to if you need the same thick wire everywhere, well, anywhere in forward and return circuit where current that drives the motor itself runs, you'd want a good thick wire. Control wires do not need to be thick. Seems you are having trouble visualizing some of the basic principle of electronics circuit. Maybe it will be a good idea to discuss your idea with someone who are more familiar. High current is nothing to be taking lightly, even if voltage is low. Automotive battery for example, at 12 volt, have enough current capacity to melt a wrench if you short circuit it. Then it will likely explode.
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#14 Reply
Posted by
TimFox
on 15 Oct, 2020 02:56
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PVC (polyvinyl chloride) is vinyl.
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#15 Reply
Posted by
tkamiya
on 15 Oct, 2020 03:04
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Don't use wood.
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#16 Reply
Posted by
james_s
on 15 Oct, 2020 04:13
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The problem with buying wire from a company like DigiKey is that it will often be in large packages, like a roll of 500'. For low voltage work you can buy packages of wire in various sizes and colors at any automotive, RV, or hardware store. This is not rocket science, just use wire that is heavy enough to carry the current the motor is rated to draw, and maybe bump it up a size, for example use #10 instead of #12 if you expect it to be starting under load or if the run (length of wire) is unusually long.
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#17 Reply
Posted by
tkamiya
on 15 Oct, 2020 05:59
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What's that insulation material used in old days and still used in some cheap electronics that melts very easily? The kind almost impossible to solder well without some melting/burning? I guess PVC isn't it, but what is it?
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#18 Reply
Posted by
SeanB
on 15 Oct, 2020 08:14
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Would be PVC, often on the cheap end composition wise, so with a low melting point.
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#19 Reply
Posted by
TimFox
on 15 Oct, 2020 15:57
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The technical term for the better grade of PVC is “irradiated PVC”. See the Alpha Wire website. Digi-Key and others stock it. Apparently, the result of radiation is to change the material from “thermoplastic” to “thermoset”. The irradiated insulation is harder to melt when soldering; the usual problem occurs when the insulation is bent close to the solder joint and springs away from the wire. Most electronic wire manufacturers make the irradiated product.
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#20 Reply
Posted by
WattsThat
on 15 Oct, 2020 17:02
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Irradiated PVC is still a thermoplastic material, the treatment raises it’s melting point by cross-linking the long chain molecules. A thermoplastic retains its ability to reach a plastic state when reheated, a thermoset material does not.
The way I remember the difference is that thermoplastics can be recycled/reprocessed, thermosets cannot.
The problem with cheap hookup wire is that it isn’t treated, saving costs. The result is the stuff will melt like butter when subjected to the heat of soldering. The main issue with pvc insulation is that it releases very corrosive hydrogen chloride when overheated/burned and one of several reasons you don’t see it in high reliability applications. It’s why you have trouble soldering a wire that has been overheated, the oxidation is so severe with the tin plating being attacked or outright dissolved.
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#21 Reply
Posted by
TimFox
on 15 Oct, 2020 17:55
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#22 Reply
Posted by
paulca
on 15 Oct, 2020 18:08
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Wow, I clicked as I wanted to know how we got to 21 replies to say.
Yes.
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#23 Reply
Posted by
james_s
on 15 Oct, 2020 18:36
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Because after the question had been answered, discussion went off on several tangents. That is not unusual.