Extensions Cords

[nickao]

One of the things that rarely gets mentioned about extension cords is that the majority of the voltage drop actually occurs at the plugs, not within the length of the wire. So the last thing you want to do is use a bunch of short cords to make a long one.

Another thing that's a little interesting is that the resistivity of 12 and 10 gauge cords is not much different. 12 gauge cord is 1.5 ohms per 1000 feet (or 0.15/100), and 10 gauge cord is 1.0 ohms per 1000 feet (or 0.1/100). So for the voltage drop on a 100 foot (200 foot round trip) power cord with 15 amp load, you are looking at 3 volts versus 5 volts, due to the wire.

So the wire size isn't as big of an issue as the quality of the ends. Once you get into the 12 gauge cords, they usually have pretty good quality ends, and definitely do on 10 gauge cords. It's really the 14 gauge cords where you are going to run into significant problems right off the bat.

The comment on the cord ends makes total sense to me, thanks.

 

[Rip Van Winkle]

I believe that universal motors are more about frequency than about voltage.

No, you have that backwards. They are called "universal" for the very reason that they are generally frequency independent, including being able to accept DC power.

Universal motors can usually handle DC voltage, but the fancy electronics a lot of tools come with now are not necessarily made to. The fancy electronics, which provide things like constant speed under load, overload protection, variable speed, switch cutoff incase of power interuption, etc. are usually not used in tools made for use on DC current. On their newest series if angle grinders, Fein chose to produce some models without the electronic modules, and specified those were safe to use on DC current. For at least a couple decades before then, almost every Fein tool contained the fancy electronic controllers.

 

[Rick Christopherson]

Universal motors can usually handle DC voltage, but the fancy electronics a lot of tools come with now are not necessarily made to. The fancy electronics, which provide things like constant speed under load, overload protection, variable speed, switch cutoff incase of power interuption, etc. are usually not used in tools made for use on DC current. On their newest series if angle grinders, Fein chose to produce some models without the electronic modules, and specified those were safe to use on DC current. For at least a couple decades before then, almost every Fein tool contained the fancy electronic controllers.

That's not quite correct either. That's why we can have variable speed and brushless motors in our cordless drills and other tools. The difference between AC PWM and DC PWM is the type of transistor commonly used for each. Triacs are very simple switching transistors, but they need the zero-crossing of an AC signal to turn off once they get turned on. MOSFETS are more common for DC.

 

[Holmz]

The motor controller will be adding or removing voltage to maintain the target PRM up till it gets to the rail. It is probably more about loaded RPM than unloaded RPM.

Sort of. With Pulse Width Modulation, the voltage is always line voltage, but it gets turned on and off rapidly to approximate a lower voltage on average.

Assuming that they turn on the power on on the trailing side before the zero crossing, then they have both a lower voltage and a lower integrated voltage.

I believe that it is the current is what generates the magnetic flux, so the voltage is only there to push the current along.

So unless one is really pushing the saw along with a lot of intent, then even if the voltage is 10v low, it would be hard to tell using the saw until one actually 'puts their back into it'.

 

[JimD]

The power that a motor makes is a function of its use of both voltage and current.  It is correct to think of voltage as pressure in a hose and current the water.  But the work the motor can do is analgous to the flow of the water.  If it flows faster (higher voltage) it can do more work.  If more is flowing it can do more work. 

There is merit to the notion that we are less likely to burn up our tools by using too small an extension cord if we keep the tools lightly loaded.  At light loads, they pull less current so the additional current that comes from the reduced voltage may not cause them to exceed their capacity.  That is somewhat challenging to consistently accomplish.  Boards have knots and wild grain.  It isn't hard to forget and get up around the tools normal limits and at the end of a long cord that can destroy the tool.  But if you are careful, lighter loads can help offset the long cord.

Another way to think of this is to think about what happens when our power providers get too much load on their system for their generators to supply.  That causes voltage to go down, but only slightly, a few volts maybe at most 10%.  About the same as our long cords.  The utilities get lots of claims for appliances that are damaged by the slight undervoltage.  Not everybody has a claim but lots of people do.  I think that's like the fact that we can often get away with too long a too small cord.  But if we keep doing it, eventually the wrong tool will be on the wrong load and be damaged. 

 

[antss]

So, is it most people's contention that the only drawback to 10/3 cords is that they cost more ?

This is the same crowd that frequents a board about tools where the average cost is what $350-$400 ?

Seems similar to the folks that buy a high $$$ car and moan about having to put premimum gas in it cause it's 20 cents a gallon more. 

Like saving a few bucks on gas and extension cords is going to allow you buy more BMWs and Festools.  :

 

[Holmz]

So, is it most people's contention that the only drawback to 10/3 cords is that they cost more ?

This is the same crowd that frequents a board about tools where the average cost is what $350-$400 ?

Seems similar to the folks that buy a high $$$ car and moan about having to put premimum gas in it cause it's 20 cents a gallon more. 

Like saving a few bucks on gas and extension cords is going to allow you buy more BMWs and Festools.  :

Maybe a Telsa, and then justify using the cord for that too...  [wink]

 

[antss]

Tesla chargers and extension cords are a no no.

 

[Klemm]

So, is it most people's contention that the only drawback to 10/3 cords is that they cost more ?

This is the same crowd that frequents a board about tools where the average cost is what $350-$400 ?

Seems similar to the folks that buy a high $$$ car and moan about having to put premimum gas in it cause it's 20 cents a gallon more. 

Like saving a few bucks on gas and extension cords is going to allow you buy more BMWs and Festools.  :

for some users the extra weight on a 100 ft 10-3 might also be a factor.
Feel the cord you are using after running your tool for a while. The temperature rise of the cord is a good indicator of the resistance the cord is offering. The energy consumed for heating the cord won't be available to run your tool at the far end.
Rick's comment about connectors is spot on. Just compare the effective contact in a high end HUBBELL conector to the little stampings in your everyday cord male and female plugs.
Hans
Hans