# Line losses A/C vs. D/C

Discussion in 'The Projects Forum' started by floomdoggle, Dec 31, 2008.

1. ### floomdoggle Thread Starter Senior Member

Sep 1, 2008
217
2
Hi all,
I finally got my first real windmill built. What I am wondering is, where should I put the rectifier. Right off the motor? Or right before the battery I am charging? I know about wire size, (even though more info would be appreciated), so I will be running 12 ga from the windmill to the battery.
I had heard that A/C is better to run longer distances. I am talking only about 100'. But the more efficient the better. Figure about 30V max.
Dan

2. ### SgtWookie Expert

Jul 17, 2007
22,198
1,800
Right before the battery.

3. ### floomdoggle Thread Starter Senior Member

Sep 1, 2008
217
2
Thanks Wookmeister,
As always, you are one of the best.
Dan

4. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Yes, it is better to use AC for long distances because electrons do not travel around the circuit but they vibrate around a point. In DC electrons travel around the circuit.

5. ### SgtWookie Expert

Jul 17, 2007
22,198
1,800
Here's a voltage drop calculator page:
http://www.stealth316.com/2-wire-resistance.htm

If you have a 100' run from the alternator to where the battery is, you'll actually have a 200' loop.

10A through a 200' loop of AWG 12 will get you a drop of around 3.243 volts.

If you're using a standard full-wave bridge rectifier, you'll have an additional voltage drop of somewhere between 1.3v to 3v, depending upon your load current and the rectifier's rating. If you want to reduce the loss in the bridge, you might consider using Shottky diodes or a synchronous rectifier.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
7,018
682
The advantage of AC is the ease of transforming voltages/currents. The main disadvantage of AC is skin effect, but that only comes into play for large diameter wire that has to carry high currents.

7. ### leftyretro Active Member

Nov 25, 2008
394
5
The advantage of using DC vs AC vs given wire gauge size has to do with 'skin effect' of AC current that tends to travel on the outside of the wire rather then being able to take advantage of the whole wire diameter. This is frequency dependent and may have no particular disadvantage in your case.

You would have to search for the applicable formula to see if the effective resistance differences is worth the effort. All things being equal, there would I think be an advantage to having the rectifier down at ground level for easier access.

Lefty

8. ### Ron H AAC Fanatic!

Apr 14, 2005
7,018
682
Skin depth at 60Hz is about 8.5mm. The radius of AWG 12 wire is ≈1mm, so AC vs DC is a toss-up as far as losses are concerned.

9. ### leftyretro Active Member

Nov 25, 2008
394
5
I figured 60hz would not be significant, however for a wind powered AC generator I have no clue as to it's frequency. Would vary if it's direct drive or gear driven and of course would vary with the wind speed. So I left the calculations for the OP.

Apr 14, 2005
7,018
682
Good point.

11. ### floomdoggle Thread Starter Senior Member

Sep 1, 2008
217
2
Ron, Lefty, Mik, Wookie,
Thank you al.
Dan