Reducing wire size in a long run

[HenryVG]

I'm trying to get some design plans down for a first wind system. I have a site that will require a 100 foot run from the tower to the battery bank and so I was planning on winding my turbine for 48V to allow me to use smaller guage wire for the run. But if I do this, do I have to then use a 48V battery bank or can I run the 48V into a 12 V bank and have the batteries hold the voltage down? Or will this negate the benefit of having the 48V turbine? I'd like to use my existing inverter, which is a 12V, but don't know if by mixing voltages like this if I'm really screwing myself up.

Is there a strong reason for keeping all parts of the system at the same voltage?

Henry

Fixed the typo. Can't upset the ladies.

[strider3700]

I suppose a long run would reduce my wife's size but I'm not brave enough to tell her that

Back on topic

You can't run 48V into a 12V bank,  It will limit the voltage from the turbine to 12V.  You can get charge controllers that will knock the 48 down to 12V  but I don't know anything about them other then they exist.

[Off grid in Tonopah]

While I assume you made a Typo in the title......... I'm not going to touch this one

[phil b]

You might put your figures into a voltage drop calculator.

http://nooutage.com/vdrop.htm

[Flux]

Ignoring the title bit as being beyond my help, your proposal is crazy. If you connect a 48v turbine to a 12v battery it will be a disaster. Firstly it will stall so badly that you get very little out and that will probably save you from a stator burn out. You will not achieve any reduction in line loss as the battery will determine the system volts not the alternator. The potential current output of a 48v alternator is 1/4 that of a 12v one so you loose all ways.

One day when a commercial mppt wind controller is available you will be able to do that but at present it is just not viable.

The only logical thing to do is build a 12v alternator and use heavier cables or be sensible and change to 48v. There is another possibility that to me seems crazy but would work at a cost. That is to use a small 48v battery connected to a 48v -12v converter to charge your main 12v battery. The MX60 would do this very effectively but the cost would be much higher than replacing an inconvenient 12v inverter for a sensible 48v one. Put the 12v inverter on ebay change to 48v and never look back is my advice.

Flux

[s4w2099]

Ive done that but its very far from ideal as you mentioned. This setup will need two charge controllers to prevent damage to both of the 'banks'. The one connected straight to the mill and for your real bank.

maybe a simple home made buck converter woudl work?

[ibedonc]

only way = increase gen volts higher volts = lower amps and smaller wire , that is the route I am going and > 250v

[s4w2099]

Ohh, no my mistake. Only one charge controller at the main bank should do it.

[DanB]

I have to second everythig Flux said.

One other comment..  100' is not too bad.  If you decide to stay with 12V (which I wouldn't unless its a small system that will always remain small) then a 100' run doesn't seem so bad.  Cables get expensive... but it's only 100'!

There are two people in this canyon who have 10' dia 12V machines over 350' from the batteries running on such light cables it would make most people shudder...  and in high winds they lose more than half their power - but in low/average winds (say 10mph and 120 watts output or so) they're reasonably efficient.  Their machines run a bit faster than I'd like but they seem to be holding together fine - one of them is over 4 years old.  In that sort of situation it's nice to furl really early.  So it depends what you want/ need - but when you think about losses in the line think of 'energy over time' which might seem much smaller than the huge losses you suffer when the wind is blowing 30mph.

12V systems are very limited though and this may be the time to upgrade.  The value of your existing inverter is small (obviously because it's only 12V) compared to the cost of the whole system.

[Nando]

48. volts generator to 12 volts battery is for me a good choice if you add a charger converter to it, specially if it is a MPPT charger, but in addition you will need a ELC ( Electronic Level Controller)for 2 reasons.
    
1. to protect the charger from over voltages specially when the battery bank is full and the wind mill is un-loaded.
   
2. to protect the wind mill from over speeding and to set the furling point of the mill.
   
   

Also, you could use the ELC for heating purposes.

Nando

[DanB]

Yes - I agree Nando... if somebody is able to build such a beast by themselves - which very few can, I think that needs to be made clear.  There is no such product yet - and even when there is it will be fairly expensive and limited to perhaps 60 or 80 amps output (which isn't really that much at 12V).  I'm fairly certain that such products will exist in the near future - when you consider their limited current capacity though they don't make much sense for 12V systems.  Money/time might be better spent settling for some inefficiency and a slightly larger machine.  (the first/best investment of time and money would be to increase the system voltage)

[HenryVG]

A couple responses:

1. PLEASE don't send a copy of the original title to my fiance. Now I see why spellchecking will never replace re-reading.
   
2. I'm getting a good education here. I kept thinking that the alternator and the battery are separate. Now I see the main thing I need to consider is the SYSTEM. Thanks for making that so clear.
   
3. Also thanks for the direct feedback about not trying to save a 12V inverter at the expense of designing my system around it. I can always use that 1500W job on the sailboat to run the coffeemaker if I don't want to just EBay it.
   
4. I now see that the 48V alternator to the 48V battery bank (with a charge controller and dump load)through the 48V inverter to the 110v house power is the most simple way to go. And a lot less expense than putting up the 12V alternator and running this all through 12V, then doing it over when I want to do the 'real' system. Adding more complexity just means I'll screw something else up.
   
   

Thanks for the feedback

Henry

[thyristor]

Hi Folks!

        If at all practical, why not put a small shed at the base of the tower which houses the 12V battery and inverter, then run the 110V AC to the house on relatively thin cables? This is what the power utility companies would do (albeit on a larger scale). Just a thought!

[snowcrow]

One thing you can do if it is a 12v PMA, is to remove the rectifier from the PMA and put it in a deep plastic outlet box with a grounded outlet. Use the ground as one of the legs. Find yourself a good heavy duty grounded cord, cut off the female end, and connect it the 3 phases. You now have AC traveling most of the long run, with very little loss!! AC don't have to make a round trip like DC does, thus you can use smaller wire!!!

Blessings, Snow Crow

[TomW]

Snow crow;

AC don't have to make a round trip like DC does, thus you can use smaller wire!!!

Sorry, but thats not correct. Any electron flow [voltage] needs a complete circuit. Out and back.

Sorry to burst your bubble but that statement is just flat wrong.

Cheers.

TomW

[TomW]

RossW pointed out I should have used "current" not voltage in the above comment and he is right. Don't tell anyone I agreed with Ross, OK?

T

[thyristor]

I have to agree with TomW. Another point: Where I live, regulations state that an earthing conductor may only be used to carry fault current and not for any other purpose.

[rossw]

A wire is a wire. Surely, it would only be an "earthing conductor" if one end of it is connected to earth?

I know, we're arguing over interpretation, and it would probably depend on how good you were at talking to the inspector, and how stubborn the inspector was, if it ever came to be found!

At the end of the day though, the colour of the insulation makes no difference to the wire itself. The CONVENTION of using green for earth is just that - a convention. I don't see them banning green hookup wire for anything other than earth....

(Ultimately though, there is proper 3-phase wire which doesn't have a green - I don't know how much more expensive it is, but you can buy 25 and 30 metre, 15 amp extension leads here for about $6, which is almost certainly much cheaper per metre than 3ph cord)

As an alternative - I wonder what would happen if you <cough>accidently</cough> wired a  3-pin socket wrongly at the mill. Plug in a standard extension cord.... if you plug the extension cord in any other socket, the green wire would be carrying the "earth" so the lead would be fine. The mill might be earmarked as "illegal" due to bad wiring, but you can unplug it while the inspector is there I guess...

I'm sure this world is getting over-regulated just to keep shiny-bums in jobs. Some of these regs are just red tape for the sake of it!

[snowcrow]

Well... I guess you could buy a 220 AC cord for more money. That would give you the 3 phase wires and a ground, just to keep the inspectors happy!!!!

[ghurd]

Today, I ran a length that should have had more than a few #6 CU, but it was just about as efficient (maybe 1.8% vs. 2.1% loss ) to run #1/0 AL.

Three conductor #1/0 AL (USE) cost less than 2 pieces of #6 CU (THHN).  Wire prices often change.

It caused a few minor issues with connecting CU to AL, and #1/0 to multiple #12.  Nothing major.

Saved hundreds of dollars.  And an entire day of labor.

G-