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Old 25-03-2008, 19:15   #1
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Windchargers and Voltage Drop Question 4 Experts.

I'm adding a windcharger to my boat. I already have it and plan on hanging it in the foretrangle as I did on our last boat.

What I don't understand is why with the windcharger and the variable speed of the wind I need to be concerned with voltage drop.

If I'm putting out enough just to push my batteries to charge what does it really matter if my voltage drop is 3% or 10% or hell even 15%. So I loose a little in the transmission. So what.

I'm concerned because on this boat I've approx a 30' run to the inside of the boat and most likely 40' to the electrical panel. At that run lenght and with the charger capable of putting out 15 - 20 amps I need about a 2 guage wire. YUCK!

So for any of the experts out there if anyone could explain to me why I need to go to a 2 guage vs smaller I would appreciate it.

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Old 25-03-2008, 19:43   #2
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The only issue is if you run 20 amps and the wire is too thin it will heat up and start your boat on fire. The voltage drop means nothing in those terms. The physics of 20 DC amps in a wire is not a debatable question. Not sure what wind charger you have but mine never did better than 10 amps. I always though 8 amps was a gift that I only saw one time for an extended period. BYW you measure the ground plus the positive distance. A mast off the stern is a shorter wire.
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Old 25-03-2008, 20:02   #3
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Know someone that lost his thumb in stern mounted pole. Yeah, he screwed up. But I don't carry one when sailing for that reason. To easy to screw up. You've confirmed a little of what I thought. BTW I've a center cockpit so the difference won't be quite that much. However; is there any formula that figures then how hot the wire can get at what voltage drop? Inquiring minds want to know. Mine.

Thanks for the answer.
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Old 25-03-2008, 20:11   #4
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Quote:
However; is there any formula that figures then how hot the wire can get at what voltage drop?
Yes, the charts will tell you what the voltage drop will be but not the temperature of the wire if you go too thin. The voltage drop is also a function of temperature. A hot day in a big wind would probably do you in if you hit 20 amps. It's the amps number you need to question to back into a reasonable number for the wire size. My old Four Winds cut out at 40 knots due to the counter balancers. I never saw them do it.

Where did you get the 20 amps number from? The difference from 10 to 20 is a lot less wire but still pretty hefty in terms of $/ft times 2.

Aft pole mounted wind gen disasters are quite gizzley. Limbs and finger don't fair well. Winch finger disasters are equally disgusting. So too as are fan belt confrontations. Boats are not a safe places.
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Old 25-03-2008, 20:21   #5
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If the wind generator has a regulator built in such as an Air x, the regulation takes place at the source. If it's set say at 14.4 volts, when it's putting out 10 amps and you have skinny wires to your battery bank, you may only be getting 13 volts to the batts.
If you had decent wiring, your batteries would charge up a lot faster. The regulating voltage would more closely mirror the battery voltage.

So what's wrong with hiking up the regulator voltage to make up for the crummy wiring job? Nothing until you have a light wind day and the batteries are close to full. The current coming out of the wind generator is less, but the battery voltage can climb because the voltage drop through the wiring is less with the reduced current.
The batteries will boil unless you are there to monitor them.

Imho you don't need 2 ga wire, but if it were me, I'd go with at least 8 ga.

Another way to do it is to put the regulator near the battery bank.
That's what I did with my house (a real house not my boat) system.
As we live on an island and power outages are a fact of life in the winter, we've got an Air X on a piling with nearly 100' of wiring to the battery bank for house power/inverter. I built a regulator and put it in the house next to the batteries. The Air x regulator is turned up all the way, thus effectively removing it from the system.

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Old 25-03-2008, 20:37   #6
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If you use lighter-gauge wire you will have charging loss (and I'll explain why), but heating with a 20A current will not be a problem. For example, building wiring codes allow you to carry 20A in a #14AWG wire when it is in free-air, and 15A when it is bundled with other wires in a conduit. A #14 wire can carry over 150A before the wire melts (the insulation goes much sooner, of course).

You can't ignore the voltage loss you will get in the wire (and as was mentioned, the distance that counts is the total length of both wires). Your wind generator will put out a certain current into a particular voltage. It will deliver less current into a higher voltage, and more current into a lower voltage. This voltage is determined by the voltage of the battery being charged, and the resistance of the connecting cables (and the current flowing in the cables). The more wire resistance, the less current the generator will deliver to the battery.

Once the battery has sufficiently charged to where the regulator reduces the charging current the cable resistance becomes less important. But it is during the maximum-charge portion of the charging cycle where you get the most bang for your buck.

There are different regulator types that can make the analysis even more confusing, but none of them can eliminate the effects of wiring resistance.

You can no doubt go lighter on the wiring, and everything will still work. You will pay a price in longer charging times, and reduced power available on your boat. A rough estimate isn't too difficult to make, perhaps the loss won't be enough to matter to you.
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Old 25-03-2008, 22:34   #7
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Others have already said it but to simply, where to you want the power to go; into the battery (and therefore to useful loads on board) OR into heating up the wires from the windcharger.
Small wires mean higher resistence to current flow; higher resistance means more power (heat) is generated in the wires; means less power is available to electrical panel.
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