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Author Topic: Cable length, sizes and components  (Read 9943 times)
w0067814
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« Reply #30 on: January 28, 2009, 11:25:41 AM »

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so to make it short   ,if its so easy  .... what cable then for the  48 volt turbine/generator DC output    for a 100 meter distance to the battery  Roll Eyes

or  does it mean cable costs will  be astronomical

You do not say what power your tubine is, not the acceptable losses. I shall assume 2200w turbine (as mentioned in the OP's post) and 5% cable losses.

I shall also assume that you wish to cyclically charge the batteries in order to get as much charge into them as possible in the shortest space of time. Thus I shall use a cut off voltage of 2.4v per cell as which point at which you switch from constant current to contstant voltage charging.

Cable losses = 2200W * 5% = 110W
Battery Power = 2200W * 95% = 2090W

Battery cut off voltage = 24 cells * 2.4v = 57.6V
Battery Current = 2090W / 57.6V = 36.28A

Required Cable Resistance = 110w / (36.28 * 36.28) = 0.076 Ohms. (Total for 200m).

Work back from Actual cable resistance to get Ohms per km...

0.076 Ohms * (1000m / 200m) = 0.38 Ohms / km.

Using the above table; a cable somewhere near 50mm˛ would be required.

Quote
A dead easy way to calculate the cross-sectional area required (in mm2) is:

A (mm2) = Length x Current/12

The equation allows for a maximum volts drop of 0.4v and takes in to account the cable's return journey so enter the length (in metres) from the battery to the appliance one way ONLY.

So L (one way) x Amps div by 12 = cable in mm2

solving using this formula gives...

Battery Volts + Cable Loss volts = Total turbine volts.
57.6 + 0.4 = 58v

Calculate the current...
2200W / 58V = 37.93A

Calculate the losses of the cable with 0.4V drop...
P = IV
37.93A * 0.4v = 15.17W

Calculate the area required for this using the supplied formula
100m * (37.93 / 12) = 316mm˛

As you can see this figure is very high. As a percentage of total generation the losses are exceptionally small, but I think the cable cost would be prohibitive...
15.17W / 2200W = 0.67%

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Justme
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« Reply #31 on: January 28, 2009, 12:44:07 PM »

I think you missed the bit where he said his voltage from the turbine to the bank was 300v (wild AC over 3 cables).

Ok that calc is normaly used for much shorter & higher loads like inter cell connects & bank to inverter connects.

The other thing is some people will accept a higher loss than others.

Justme
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Stefan (S.T.E.F.)
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« Reply #32 on: January 28, 2009, 02:26:13 PM »

Well, I have decided to have the battery bank next to the house and go for a turbine that produces 300V or so and then rectifies near the batteries. So now I only need to work out the cables for 200m for 300V rather than 48V, should save a fortune.
The dump load problem is still there. Do I connect the dump loads to the charge controller near the battery ?
If yes then I don't have a problem. Oh confused now. All these sales people are driving me in sane !
They just don't seem to know what they are talking about half the time....

Stefan
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Justme
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« Reply #33 on: January 28, 2009, 03:53:53 PM »

Yes or even in the house.
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« Reply #34 on: January 28, 2009, 05:10:08 PM »

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The dump load problem is still there

I have my dump load  in my shed ( it came with my windturbine)  cause was too loud  ( like screaming ) and should have replaced it with a other DC idea    , but i did program the internal relay of the Victron   to start a socket at (in my case at about 30 volt  )   and connected a heater to it,,,,, ideally it was designed to start my  heatpump

I felt more comfy  with two dump loads just in case  Tongue

Billi
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« Reply #35 on: January 28, 2009, 06:15:51 PM »

So it sounds like I can dump via the victron (which I was just told by a sale person that it was impossible). Could I simply connect an electric heater to it to heat my workshop/battery room? I'll make sure I only tinker in there when it's rather windy.
I know we talked about this before, but how about a second battery bank? We still get very windy days in the summer and I don't want to fry the batteries from the outside.... or myself. The second battery bank could be a back up ? No ?

Stefan
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Justme
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« Reply #36 on: January 28, 2009, 06:46:00 PM »

No,

The second bank would need to be kept in a stage of discharge ready for the dump load so would soon fail. You could have two equal banks that are rotated. Say have a 3 day supply via each bank. Use one & charge the other. Costly way to do it.

Justme
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30 x 58mm panel 259L TS
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2 x Victron Multiplus II 48/5000/70
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« Reply #37 on: January 28, 2009, 06:56:53 PM »

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So it sounds like I can dump via the victron

My victron multi plus has a internal relay i can configure /program (with the VE configure software) to  what ever i want  to dump /use excess power  , that the battery cannot absorb ( but to keep the battery healthy you need to make sure  that she is charged fully sometimes / every week  and that needs some time  Tongue)

In relation to your expectations on surplus power  Grin  ....  i always was fooled and expected more performance ....

Be it wind , PV, or Solar thermal .....  but after a while they all got my best friends  Grin


Quote
We still get very windy days in the summer and I don't want to fry the batteries from the outside.... or myself. The second battery bank could be a back up ? No ?

Perhaps you now think i am mad but i will store power on my land , by digging a lake /dam to store about 100 kwh of power  in form of a water battery that then can be utilised  to charge the one and only  Lead -acid battery

But if you find out , that your windturbine is over performing , then i guess you are able to deal with that  after installed her  Wink


Billi


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« Reply #38 on: January 28, 2009, 07:39:43 PM »

I do like the set up that american bloke has with a hydroligiser to use up all the excess summer power making hydrogen & then he uses that fuel to make elec in the winter.

Justme
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30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
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BMV 700
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48v 1000ah
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Bill H
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« Reply #39 on: January 28, 2009, 10:43:18 PM »



Perhaps you now think i am mad but i will store power on my land , by digging a lake /dam to store about 100 kwh of power  in form of a water battery that then can be utilised  to charge the one and only  Lead -acid battery

But if you find out , that your windturbine is over performing , then i guess you are able to deal with that  after installed her  Wink


Billi


Well Billi, what an excellent idea - and why not !    Not sure about the physics and engineering that might be needed - would obviously need a good head - I know you have a few slopes around there - but 100kWh seems pretty do-able with a reasonable amount of land and and in a windy old place like yours  Wink  should be easy to add enough generation......  It is  Cool

Very best - and it would/will be a real learning for all on the forum.  If you need some help when it comes to the heavy lifting - PM me !

Bill

« Last Edit: January 28, 2009, 10:46:45 PM by Bill H » Logged

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billi
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« Reply #40 on: January 29, 2009, 06:33:31 AM »

Bill

I have about 22 meter head and a little stream ( between 0- 30 l/s ) and   a small valley  that i can  dam  to a lake holding roughly 6000 m3  of water ( dont tell the planning office  police ) That lake i want to build anyhow as a feature

The waterturbine (arrived a week ago)  uses 36 m3  an hour  for each KW  produced  so if i drain the lake for one meter (and leave 2 meter in)  that can produce ideally then 55 kwh  so enough power to keep us going on not sunny days  ( but had 4.5 kwh PV power yesterday  Grin)
its hard to know how fast it will refill cause depends on rain )

I hope that that idea replaces the diesel back up  generator (charging batteries )  or  to power a heatpump

 ( i donot trust cheapish  windturbines anymore since mine came down 3 weeks ago  surrender)

Will see 

Billi the Kid

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« Reply #41 on: January 29, 2009, 07:38:27 AM »

Stefan

here is  the description (ignore the grid connection in this case )  of how it  works  so basically you could use that relay to power what you like in your house

http://www.victronenergy.de/upload/documents/DC%20solar%20system%20with%20a%20MultiPlus%20inverter-charger.pdf

Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Bill H
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« Reply #42 on: January 29, 2009, 09:41:56 AM »

Billi, so, are you going for some kind of pumped storage ?  do you have the space for a 2000cub meter 'lake' near the level of the tubine?  or is the 'once through' solution enough ? 

Going pretty seriously off-thread here - maybe we should move to the Hydro threads  tomatosplat

cheers

Bill
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« Reply #43 on: January 29, 2009, 05:30:00 PM »

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Billi, so, are you going for some kind of pumped storage ?  do you have the space for a 2000cub meter 'lake' near the level of the tubine?  or is the 'once through' solution enough ?

the lake is 22 meters higher than the turbine (will be) and for the start its not pumped  cause cannot dig a second  lake next to the turbine  Huh 

So i decided  to just open the lake  as a backup  and feed the turbine and then figure out more ideas

One is a RAM Pump to fill the upper lake( trickle charge )  from a small stream i have with no or small head
the other sure is  my engine powered waterrpump  to pump water 22 meters up with a hydroturbine attached to the outlet  wackoold

will see

Billi
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« Reply #44 on: January 29, 2009, 08:54:06 PM »

I have enough room for a lake but no head, so some kind of electric appliance for the dump load. How about electric underfloor heating for the bathroom ?

Stefan
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