What guage wire for 120 foot 110V ext cord to 45 amp Iota battery charger? - Page 3 - SailNet Community
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post #21 of 31 Old 09-19-2008
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Originally Posted by sailingdog View Post
Cam-

Can you please point me to where you can buy a 30 Amp 50' dock cord for $50???
Sure...pretty close:
Marinco Ultra White Cord Set - BoatersWorld.com

$60 bucks each + 10% off on $70 total purchase.

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post #22 of 31 Old 09-19-2008
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Jim...the 11 amps max draw was right from the spec sheet. So 1320watts at 120V ....so yeah...the efficiency IS in the 40% range.

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post #23 of 31 Old 09-19-2008
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Jim, I should have been more direct. If I understand the situation correctly, the suggested project solution involves connecting a 20'cord to a 50'cord to another 50' cord. What I would humbly suggest is buying a 120' piece of 10/3 SO or SJO (or any other sunlight resistant cable designed for hard use) cable along with a good quality male and female cord end to fit the existing so as to avoid having to make so many "temporary" waterproof connections.

All tape is not equal...all 3M tape is not equal either...3M 33 and 3M 88 are very high quality products. 3M used to, and still may make some "consumer" grade stuff that was obvioulsy aimed at a low price point, I can't recall the product number but a few years ago it was in that 1$/roll range. Good tape will be $5+/roll. I have had good success with liquid electrical tape as well.
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post #24 of 31 Old 09-19-2008
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Limit the load on the extension cord. It's fine to have #10 guage wire but you're going to have a devil of a time finding male and female plug ends rated for the wire. You'll need plug ends rated for thirty amps and you're not going to find those at the Home Depot. You're also going to find that, if you find a 10gg extension cord in that length you're going to have a bit of weight on your hands.

Trying to run too much on one cord is hard on all components and could cause lasting damage to the appliances.
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post #25 of 31 Old 09-20-2008
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Cam, the iota spec sheet says max current is 11 amps. The specs also say it has an operating efficiency of 80% which would mean that the actual draw when the output is 45 amps @ 12 volts would be about 6 amps @ 120 volts. Here's a voltage drop calculator: Voltage Drop Calculator .You want a voltage drop of 3% or less.
Note that we are talking 2 different types of loads, one inductive one resistive. With inductive loads the current increases as the voltage decreases. With resistive loads the current decreases as the voltage decreases. A battery charger is an inductive load and if the amperage is too high it will at best shorten it's life expectancy and at worst fry it. The water heater is a resistive load lower voltage and thus amperage will decrease it's efficiency.
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post #26 of 31 Old 09-20-2008
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Ebs...I'm afraid I do not understand your point. If MAX input current is 11amps at 120VAC...and MAX output current is 45amps (one would assume at bulk charge rate of 14.5VDC or so...then at some point the comparison is 1320watts of draw...producing 652 watts of charging. Now it may be that the max draw is only quite brief and that only 815Watts or so is needed during the full charging cycle on average? I don't see what an inductive load has to do with it as the Dockside Voltage never varies and the amp draw is clearly stated as 11amps max. I agree that 80% efficiency would imply only 6 amps draw from dockside...but it is clear that 11 amps can be drawn and we know a water heater will typically draw 1500 watts or 12.5 amps...so we are looking at the possibility of 22-23 amps being drawn by those two appliances + whatever else might be using AC like computers, TV's etc.
So...where am I going wrong or what are you trying to explain to my dense skull!?

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post #27 of 31 Old 09-21-2008
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Cam I just question one of the 2 figures in the spec sheet. At max output its either 11amps with 41% efficiency or 6 amps with 80% efficiency. If 11 amps is a momentary draw then it need not be considered. We need only be concerned with the "run" draw. Or one of the figures is incorrect. As far as the voltage is concerned the voltage at the dock outlet is the same but once you run it through an extension cord you get voltage drop in the extension cord. The voltage at the far end of the extension cord is going to vary depending on the length, gauge and amperage.
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post #28 of 31 Old 09-21-2008
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oh...OK...we are in agreement then. It is just a question of what spec to believe as one is obviously wrong. I chose to believe the 11amp number since it is part of the UL certification whereas the 80% efficiency number could be most anything. As far as voltage drop goes...it is 3.5% at 120 feet of 10 gauge at 20 amps so is essentially immaterial.

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post #29 of 31 Old 09-21-2008
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If the charger were purely a resistive load, it would not need 11 amps. However, it is an inductive load and probably has a power factor of around 0.7 The power factor is defined as the power used divided by (volts times amps used). Thus, the max amps being pulled through the cable are 140% of what you would calculate assuming a resistive load.
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post #30 of 31 Old 09-21-2008
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EBS...AHAH!! I've found the answer I think to what you were talking about with reactive/inductive loads. Looking at the manual for the 45amp charger I found an interesting spec...it said:
Max WATT DRAW...842.4 (VA watt draw 1296)
Note this is remarkably close to the numbers we've been discussing where VA watts would be MY measurement and the 842.4 number would be close to the 80% efficiency number! Note the RATIO is 65% between the two numbers.
Doing some research on VA watts vs. Watt draw...I came up with these statements:


VA in AC circuits is "reactive power" and has nothing to do with real power.
Loads such as induction motors, do not act as pure resistors, but like
inductors. Inductors and capacitors draw AND supply power back into their
power source. Induction motors supply current BACK into the power grid ever
half cycle. These currents tend to somewhat cancel out, but are still there.
If I supply 10 amps on a wire for 1 second, then reverse the polarity and
try again, the net current flow from end to end was zero, but 10 amps were
flowing for 2 seconds.

It would seem that
the volt-amp refers to the maximum power flow, while the Watt refers to a
time-averaged power flow. In AC circuits, Power flow varies as a sine
function. The "root-mean-square" rate of flow is approximately 65% of the
maximum flow.


Mystery explained! Your instincts were correct!! Thanks.



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