What gauge Extension Cord.

[denpat]

I leave my boat in a slip all summer long and charge my trolling battery's at the dock using an extension cord. I have been using a 35' 14 gauge cord for the last couple of years without any problem. This coming season I will be moving to a new slip and will have to use a 100' cord to reach my boat. I have a ProSport 20 plus 3 bank charger and asked this question to ProMariner and they recommended a minimum of 8 gauge cord for that distance. I am no electrician, but that seems like quite an over kill to me. I asked this question to their customer service department and this may be just an overkill to cover any liability they may feel they would have.

I was thinking about going with a 12 gauge cord to cover the additional distance. Does anyone have any information that may help me decide?

[rwl]

I would be comfortable with 12 myself, but I'm not sure the current draw of a charger, I don't think they are that high. With 120v 100' you would still be about 116 volts if I did my math right. That's at 10 amps.

If you go to 10 AWG you would be about 117.5 volts.

The charger should have an acceptable voltage range in it's specs.

Anybody feel free to correct me if I'm wrong in my figures, its been a while since I did this.

PS, your 35 foot cord is costing you ~2 volts now. Again if I am figuring this correctly, I had to get out my Ugly's book!

[Hot Runr Guy]

On this page you'll find a worksheet that allows you to calculate voltage loss based on amp draw, cord size & length, etc. Not knowing what your charger draws, if we use 10amps as the load, a 100' 12AWG cord will lose 3-1/2 volts, so your 120V at the outlet becomes 116+ at the other end. Probably not enough of a loss to worry about.

http://www.powerstream.com/Wire_Size.htm

HRG

[denpat]

I found the specifications on the charger and it is a 20 amp. charger. In the specifications it states "AC in", which I assume is voltage required, was 90-135. Wish I knew more about electricity. Does this information help to determine the gauge requirements?

[1860Angler]

Either a 12 gauge or 14 gauge 100' extension cord will work just fine. At 20 amps with a 12 AWG cord you will loose about 13 volts and with a 14 AWG cord you will loose about 20 volts, either one will keep you well within your 90-135 Volt operating range of your charger. I'd probably go with a 12 gauge cord if it was me, bigger is usually better right!!

[REW]

I really don't think you will have an issue with a 100 foot 14 gauge cord.
Remember your 20 amp 12 volt dc charger puts 20 amps out of your on board charger at 12 volts.

But this means that your on board charger is only drawing 2 amps from your 120 volt AC supply source.

i.e watts = volts X amps.
So, your on board charger is burning up 20X12 or 240 watts of power.

To supply 240 watts of power at 120 volts, you divide.
So, 240 divided by 120 = 2 amps of AC current that is actually running down your extension cord.

To verify any voltage drop just put a cube tape into the end of your extension cord. Plug in your extension cord and then measure the voltage in the cube tap with a good ac voltmeter.

Then, plug in your on board charger, while monitoring the ac voltage on your voltmeter. My guess is that you will see less than a 3 volt AC voltage reduction at the end of your 14 gauge cord which is well within the specifications of your on board charger.

Good luck
REW

[REW]

By the way, here is a copy of the specifications of a 20 AMP Guest on board charger from the owners manual.
Note that the AC current draw at full output from the charger is less than 4 amps. There are always some losses when going from AC to dc and when working with controllers. This is the reason for the slightly larger number than the computed 2 amp draw of the earlier calculation.

But, even at that, the 3.75 amps of ac current will not cause a substantial voltage drop at the end of a 100 foot long 14 gauge extension cord:

7. SPECIFICATIONS
Output:
Charging:
12 Volts DC (min.) at 20 Amps total, 10 Amps each.
Maintaining:
13.30 Volts DC at 0.1 Amps
Input:
Rated AC Voltage
200 – 260 VAC, 50/60 Hz
Current Draw
Amps at full Output 3.75 Amps
Maximum recommended battery size:
For recharging:
Up to 120 Amp-Hours
Maintenance only:
Up to 240 Amp-Hours
Physical Dimensions:
Height:
6 in.
Width:
9.25 in.
Depth:
3.25 in.

[McLoki]

For my Minn Kota charger, these are the recommended extension cord guages for different lengths. (my charger is a 10amp (2 x 5) but it is the same manual for up to their 30amp (3 x 10) chargers...

Minimum recommended AWG wire size for various length extension cords used with the Minn Kota
battery charger:
Length of Cord in feet / guage

25' / 16ga
50' / 14ga
100' / 12ga

Michael

[Lund1993]

I would recommend 12awg because anything on for more than 4 hours is rated 25% higher according to NEC code.

[denpat]

Thanks for all your reply's. I felt like a 12 gauge would be heavy enough, but it was only a guess on my part. Anyhow, I felt the recommendation by the ProSport manufacturer was a total overkill.