How to get a 100' or 200' cord with right amps for a 10A electric string trimmer?

[1 Lucky Texan]

How much are those extension cords going to cost?

Did you consider a nice lithium battery powered trimmer? No cords to hassle with or limit your freedom of movement. Might not be much more money overall.

 

[mullins87]

Get a "Yellow Jacket" brand cord. I have four of them, each 100' long. They are construction grade, are 12 awg and are rated at 15 amps. I have a feeling the instruction manual was probably written in the same language as the country the mower was built in, and therefore a translation error is causing the manual to state a maximum of 10 amp rating for the cord.

Think of a cord as a water hose, and think of the electric mower as a spray nozzle. Assume a particular spray nozzle has a 4 gpm flow rating @ 50psi. Please don't check my math, I'm just pulling numbers out of the air for discussion purposes. Let's assume a 1/2" diameter, 50' long hose will flow precisely 4 gpm @ 50 psi. With that hose, the nozzle will produce 4 gpm. Put a 5/8" diameter hose on that nozzle that will flow 7 gpm. Guess what, that nozzle will still only produce 4 gpm. Using too large of a cord with your mower is just like using a larger diameter water hose. However, switch that hose to a 3/8" diameter one that only flows 2.5 gpm, and you'll only get 2.5 gpm from the nozzle. Doing this to an electric motor will burn it up, overheat the cord, start a fire, or possible all three.

Think of electric flow in terms of water flow. The wire gauge is the hose diameter. Amperage is the same as water flow in gallons per minute. Voltage is similar to pressure in the sense that you have to increase it as the wire gets longer to account for voltage drop.

Here is a simple calculator I found on the net.
Voltage Drop Calculator JavaScript

 

[midnite rider]

Hey, thanks for all the quick responses.

For instance, here's an 80' cord reel with 14-gauge. If I plug in a 50' 16 gauge, now I have 130' altogether, which the booklet says should all be 12-gauge. Am I worrying too much? What is the worst that can happen if the total length of the cords = too thin a wire for a length? The booklet says "loss of power and overheating" -- anyone ever fried a trimmer or electric mower like this?

Bill

Just a note about coiled power cords if everything else wasn't enough. Allways fully unwind the reel before you use it. Don't ask me how I know that these 2 things are happening in a coiled extension lead.

The first I'll explain is inductance between the coils If you have 2 coils of cable next to each other and pass a current through either of them then that has an effect on the other - inductance which like you suggest causes a reactance in the cable. This has the same effect as a resistance in the cable and current flowing through it heats the cable. Obviously the more coils you have the greater effect this has (1 coil has 1 effect, 2 coils, 2x effect etc in simple terms)

The second thing that happens is that the coils wrapped round each other prevent the build up of heat in the cable from escaping - so it builds and builds and eventually the cable can overheat. Some reels come with overheat protection.


1 last thing, the rating for a cable in amps is for the cable to be fully unwound - if it is coiled then the current rating drops

 

[bakersman]

Thanks for all the replies and help! It's great to finally have a grasp of these basics.

I'm realizing I'm lucky I didn't burn out a miter saw with a 16AWG cord.

I did think about a battery trimmer, but honestly the batteries on my cordless drill drive me crazy. Going corded is about reliability.

I have a feeling the instruction manual was probably written in the same language as the country the mower was built in, and therefore a translation error is causing the manual to state a maximum of 10 amp rating for the cord.

Yes, exactly! I finally saw in another manual a longer version of the same chart. This chart included additional rows, so under "more than 6 | not more than 10" was "more than 10 | not more than 12". So, they must have just copied the "more than 6 | not more than 10" line into the first manual. I guess it just meant that, for an appliance using between 6A and 10A, these were the *minimum* gauges. It would have been better just to remove the amp range to avoid confusion.

Again, thanks for all the tips. I will definitely be sure to uncoil the cord! I had seen references to that, but I didn't realize the inductance doubled so quickly and dramatically.

 

[Mark Widmer]

Joining in late here, but I've been away from LMF for a long time.

I did think about a battery trimmer, but honestly the batteries on my cordless drill drive me crazy. Going corded is about reliability.

Does your cordless drill use NiCad or Lithium batteries? I've been a lot happier with lithium battery tools, including my Worx string trimmer.

Not sure if it's the battery so much as they just seem to build better charging circuitry when it's for a lithium-powered tool, to protect the battery from overcharging or over-discharging.

 

[txzrider]

I will point out 1 gotha ... with connecting multiple cords... keep the connectors (plugs and receptacle ends) clean and free from dirt or crud, that causes higher resistance in the connections, which cause heat and voltage drop.

 

[dave-m]

put some serious thought into a new battery powered trimmer

a 200' #10 extension cord will be quite expensive and heavy. I can almost guaranty you'll hate dragging it around