Wire Gauge and plug Size

[Mides]

Originally Posted by JohnRobHolmes

Good call, added in to the tech.

I'm flattered.

Thanks everyone with all the help. It has been REALLY REALLY REALLY informative.

I came across this:
http://www.powerstream.com/Wire_Size.htm

For 16 gauge wire, it looks like maximum amps for chassis wiring is 22a and maximum amps for power transmission is 3.7a. Now i'm not sure what these numbers mean, but I heard EddieO and John talking about 80a peaks, but for that you would need 9 or 8 gauge wire going off the chart.

In this process I think I have just fried my brain.

[Charlie-III]

Originally Posted by NicholasMides

I'm flattered.

Thanks everyone with all the help. It has been REALLY REALLY REALLY informative.

I came across this:
http://www.powerstream.com/Wire_Size.htm

For 16 gauge wire, it looks like maximum amps for chassis wiring is 22a and maximum amps for power transmission is 3.7a. Now i'm not sure what these numbers mean, but I heard EddieO and John talking about 80a peaks, but for that you would need 9 or 8 gauge wire going off the chart.

In this process I think I have just fried my brain.

Keep in mind those amp values are for continous loads, short peak loads can be much higher without being an issue.
As to "power transmission" vs. "chassis" wiring, they are "derating" the amp values in power transmission since they assume very long wire runs. At that point resistence losses become a major factor generating heat.
Stick with the "chassis" amp values. Actually, stay in the 12-16ga range and be happy.

(PS, a little "brain fry" here & there is OK, actually it's good!)

[Manning]

Originally Posted by JohnRobHolmes

..
. One thing that many people don't consider (or may not be aware) is that motor amperage and battery amperage are not the same since we use digital speed controllers. The basic formula ignoring inductance influence is [Motor phase amp = Battery Amps x (1/duty cycle %)]. At half duty cycle (50% throttle basically on voltage based ESC systems) the motor amperage will be 1/.5 or twice that of the battery amperage. At 10% duty cycle motor current is 10x battery current. Eddie, if you logged 120a at about 50% throttle, that is a burst of 240 amps on the motor side of the circuit.
.......
Eddie- just grabbed my old radio. A Magnum PCM 1024. I think you are few years older, I'm a spry 29! My back doesn't think it is so young though

I thought the 1/2 the volts with the same load = double the amps only worked in the AC world. With DC, 1/2 the volts with the same load = 1/2 the watts. Apparently I'm missing something. (E=IR and all that...)

So where does the extra amps come from if the battery isn't seeing them and the motor is? If the esc 'on' time is only 1/10 sec, then it's off for 9/10 sec, and theres zero current flow during the off time, right? I think we're back to the average current thing again. Also seems like the batteries wouldn't like 240 amp spikes much, and there would be more "brown outs" then actually happen.

I have a Mag PCM that still works great.....and yes, the black 1700SCRC's were the friggin bomb when they came out......

[indiana mudcat]

Ohm's law, Watts law, they don't change at all for AC vs DC. There's been some talk about half throttle and half voltage, correct me if I'm wrong, but the ESC always passes full voltage regardless of throttle position, the cycle just speeds up for more throttle.

IMO the average draw over a run means nothing, it's the peaks that you need enough power to feed. I don't pay any attention to Mah and C seperate at all when choosing packs. I break it down to the cont and burst amp ratings, then compare pack size to amps available. Then I go for the highest power in the smallest package.

[Charlie-III]

Originally Posted by indiana mudcat

Ohm's law, Watts law, they don't change at all for AC vs DC. There's been some talk about half throttle and half voltage, correct me if I'm wrong, but the ESC always passes full voltage regardless of throttle position, the cycle just speeds up for more throttle.

IMO the average draw over a run means nothing, it's the peaks that you need enough power to feed. I don't pay any attention to Mah and C seperate at all when choosing packs. I break it down to the cont and burst amp ratings, then compare pack size to amps available. Then I go for the highest power in the smallest package.

True, there is only a single Ohms law & Watts law......the law doesn't care is the voltage is straight or alternating....
As to the ESC, depends on what you run. Granted a looong time ago it was a resistor, thus it regulated voltage applied and generated heat for the escess.
Newer ESC's are just fast switches for the most part (PWM = Pulse Width Modulation....basically the on/off times, the more "on" the more power to the motor).
Keep in mind, part of what happens is the inrush current to "fill" the motor winds which can be HUGE! Then you turn off the power and some of that power runs back to the ESC due to the collapsing magnetic field of the motor windings. Basically how an ignition coil works.
Small wire size, poor connections, long wire runs can all reduce the efficiency of the ESC and lead to other issues. The motor caps try to suppress some of this field collapse (along with brush arc) in brushed motors.
Brushless motors are 3-phase motors, switching 2 phases is what changes motor rotation.

[Manning]

If all we care about are peaks and inrush current, then we all are running much too small of wire, and definitely too small of batteries. But it seems to work OK.

OK, I'm guessing there are at least two people on RCC that have motor dynos.

How about doing a test? Don't change anything but some wire leads on the motor. One set of runs with 8" of 12 awg Dean's noodle wire on the motor terminals, and a set of runs where the 12 awg is replaces with 18 awg and post the results. Easy. The 8" wire run is just my guess as the average length between the esc and motor. Feel free to change that to anything that's realistic.

Once upon a time I had access to a Tekin dyno, but I couldn't get much useful info out of it.

[Charlie-III]

Originally Posted by Manning

If all we care about are peaks and inrush current, then we all are running much too small of wire, and definitely too small of batteries. But it seems to work OK.

OK, I'm guessing there are at least two people on RCC that have motor dynos.

How about doing a test? Don't change anything but some wire leads on the motor. One set of runs with 8" of 12 awg Dean's noodle wire on the motor terminals, and a set of runs where the 12 awg is replaces with 18 awg and post the results. Easy. The 8" wire run is just my guess as the average length between the esc and motor. Feel free to change that to anything that's realistic.

Once upon a time I had access to a Tekin dyno, but I couldn't get much useful info out of it.

I have a "home brew" motor dyno, have to see if I can do the test you are asking for.
Not really sure any dyno will capture the info you are asking for. But hey, we brought it up, least we could do is try & measure it.

Using other systems, I absolutely know it makes a difference, not sure how measureable it is in this application.
As I stated before, many other factors can negate a difference in wire ga size.
In the pan car world (a couple of decades ago.....) you could see the difference.
With LiPO's (and newer NiMH's) power is so abundant, who gives a rats butt??
But, there is a difference.

[EddieO]

The tekin dyno was probably one of the worst made. You could get pretty much the same info out of a voltameter and a couple of motor stands....

The test would not be very easy with most dynos. The Turbodyno and Fantom would be a TON of work to switch over the wires...its just not very practical. You would have to dissemble the units and solder on the main circuit board. While I am not sure on the fantom, I know the TD45 can skew results if you mess the wires.......just to switch wires sizes would be a TON of work.

I think it's doable on the robi, but still would take some work to make the leads up. The robi test leads plug in, so its possible to do with a little work. If I get time, I will make up another set of leads and do a test. I gotta keep everything the same though length wise and plug types, so it will take a few parts.

Later EddieO

Originally Posted by Manning

If all we care about are peaks and inrush current, then we all are running much too small of wire, and definitely too small of batteries. But it seems to work OK.

OK, I'm guessing there are at least two people on RCC that have motor dynos.

How about doing a test? Don't change anything but some wire leads on the motor. One set of runs with 8" of 12 awg Dean's noodle wire on the motor terminals, and a set of runs where the 12 awg is replaces with 18 awg and post the results. Easy. The 8" wire run is just my guess as the average length between the esc and motor. Feel free to change that to anything that's realistic.

Once upon a time I had access to a Tekin dyno, but I couldn't get much useful info out of it.

[Manning]

No, don't rewire the thing, just add the wire in question to the existing leads. Don't go destroying anything. It's not worth that.

[EddieO]

I am not positive on the fantom, but on the Turbodyno you cannot increase the wire lengths, as there is something weird about the programming that will effect the numbers.

It's actually pretty easy on the robi, I just gotta pick up some banana plugs and a reciever pack plug, along with the wire. I basically would just make two identical sets in all aspects except wire size. I could even do it for like 12, 14, 16, 18.

Later EddieO

[Caustic101]

Im all for bigger fatter wire, Both in my RC where there is 14 guage as I couldnt get a hold of better, thicker wire that still has flex, damn small towns with no LHS.

And also in my truck where it gets 00 guage wire for the amps and charging system

[Charlie-III]

OK, here is another thought for some of you regarding wire size vs. amp draw.
Think of jumper cables for your car, you could be pulling upwards of 600 amps @ ~13VDC to start a car with a dead battery. This is with a ~4ga jumper cable which is NOT rated for that load. The difference is that:
1-It's usually less than 20'
2-It's only for a few seconds.

This is what we are alluding to when we speak about short burst loads vs. continous loads. While the cable "can" handle the short burst, it WILL be an issue if carrying that load for any length of time. It WILL also get warm when loaded that much for any length of time.

[JohnRobHolmes]

Originally Posted by Manning

I thought the 1/2 the volts with the same load = double the amps only worked in the AC world. With DC, 1/2 the volts with the same load = 1/2 the watts. Apparently I'm missing something. (E=IR and all that...)

Our ESCs are fundamentally AC machines. Whether they switch from -12 to +12v with a pretty sine wave or from 0 to +12v with a nasty square or trapazoid wave, the alternating aspect is still occurring.

The wattage and all that is still the same when averaged over a time period of at least one AC cycle.

[Manning]

What I was thinking of is the where you go from a 120VAC motor to one for 240VAC of the same power the current is halved. But the wattage is the same so the current would be halved. If you take the same dc motor and up the voltage the current increases, but the power increases as well....too many cookies and Mt Dew.

Can anybody tell I'm stuck at the in-laws and really bored?

[JohnRobHolmes]

The 240v motor would be 1/2 the KV of the 120v motor if it was rated the same power. If you don't change the motor speed the current and power will increase when voltage is increased. Doesn't matter what type of motor it is.

We can do the same thing with a DC motor. Use a 40t motor on 4s, or a 20t motor on 2s. Ignoring brush and commutator efficiency they should be able produce the same power, just at a different voltage and amperage.

[Charlie-III]

Originally Posted by JohnRobHolmes

The 240v motor would be 1/2 the KV of the 120v motor if it was rated the same power. If you don't change the motor speed the current and power will increase when voltage is increased. Doesn't matter what type of motor it is.

We can do the same thing with a DC motor. Use a 40t motor on 4s, or a 20t motor on 2s. Ignoring brush and commutator efficiency they should be able produce the same power, just at a different voltage and amperage.

Hmmmm...seems to me, when reading AC motor rating labels, that the amp value shown for 120VAC is twice what it is at 240VAC, you can then size smaller feed wire since the load is lower (wire sizing is based on amp draw, NOT voltage.....well, not until the volts go way up, like over 480VAC)
This is part of why a window A/C unit only goes so large on 120VAC until it is required to double the voltage (to 220/240VAC) so the wire size does not get out of hand by halving the amp draw..

Motor speed remains the same.

Quick example for a single phase AC motor... http://www.grainger.com/Grainger/DAY...ers&cm_vc=FFTS

[Manning]

Originally Posted by JohnRobHolmes

The 240v motor would be 1/2 the KV of the 120v motor if it was rated the same power. If you don't change the motor speed the current and power will increase when voltage is increased. Doesn't matter what type of motor it is.

We can do the same thing with a DC motor. Use a 40t motor on 4s, or a 20t motor on 2s. Ignoring brush and commutator efficiency they should be able produce the same power, just at a different voltage and amperage.

Yes, hence my "too many cookies and Mt. Dew" comment.

Wayyyy back in the days of RC oval racing, I had attempted to explain why a rc (DC) motor draws more amps on more voltage under load, to a air conditioner repair guy that dealt with AC motors all the time. All he knew was that if you replaced a 1hp 120VAC motor with a 1hp 240VAC motor the current halved.

So, any dyno runs yet?

[Charlie-III]

Originally Posted by Manning

Yes, hence my "too many cookies and Mt. Dew" comment.

Wayyyy back in the days of RC oval racing, I had attempted to explain why a rc (DC) motor draws more amps on more voltage under load, to a air conditioner repair guy that dealt with AC motors all the time. All he knew was that if you replaced a 1hp 120VAC motor with a 1hp 240VAC motor the current halved.

So, any dyno runs yet?

Ummmm.....OK, so you are ignoring my AC motor link for a dual voltage AC motor that SHOWS the amps drop 50% when you double the voltage??

I have to think DC vs. AC motors are different. Or, prove me wrong.

[JohnRobHolmes]

Induction VS. Permanent magnet motors can certainly act differently depending on design. The induction motor you linked likely has an automatic field coil regulator that changes the rpm per volt of the motor based on input voltage. It either has that, or it has a way to change the speed with hard wiring field coils in parallel or series depending on input voltage.

[Manning]

Originally Posted by Charlie-III

Ummmm.....OK, so you are ignoring my AC motor link for a dual voltage AC motor that SHOWS the amps drop 50% when you double the voltage??

I have to think DC vs. AC motors are different. Or, prove me wrong.

I'm agreeing with you. Apparently I can't write what I'm thinking. Or, I have no idea what you are talking about. One or the other.