Can someone do my electrical maths please?

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Oscarpop

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Trying to work out percentage power loss across a cable run from wind gen to batteries.

Cable is 1.5mm and the power loss is 13.3 ohms per 1000m

I have about a 10-12 m run

The output of the win gen is 5-10amps

Erm, I think that's it. 12v batteries if it helps.

My brain hurts trying to do this , and I know that you lot are very brainy :)
 
power loss in watts or volts drop.


volts drop:
If the cable is 13.3 ohms per 1000m

10 m has a resistance of 13.3 x 10 /1000 = 0.133 ohms.

But the total distance there and back is 20m which has a resistance of 0.266 ohms

Volts drop at 5 amps is 5 x 0.266 = 1.33 volts

or at 10 amps 10 x 0.266 = 2.66 volts

Power loss :

watts = I² x R

so at 5 amps, 5 x 5 x 0.266 = 6.65 watts

at 10 amps, 10 x 10 x 0.266 = 26.6 watts


Multiply all the above results by 1.2 for 12 metres


You need much heavier cable. Aim to limit the volts loss to 3% ie no more than 0.36 volts
 
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If you have a voltage regulated source like a car alternator, a drop of 2 or 3 volts between the source and the battery is disastrous.
Not quite the same with an unregulated source such as a typical wind gen or solar panel.
The wind gen will generate current at 16v if unregulated, some volts are lost in the cable, but the current gets there.
Efficiency suffers but life goes on.
In practice, it will make less difference than you may think, but you need to think about the cable getting hot perhaps?
 
lw395 said:
If you have a voltage regulated source like a car alternator, a drop of 2 or 3 volts between the source and the battery is disastrous.
Not quite the same with an unregulated source such as a typical wind gen or solar panel.
The wind gen will generate current at 16v if unregulated, some volts are lost in the cable, but the current gets there.
Efficiency suffers but life goes on.
In practice, it will make less difference than you may think, but you need to think about the cable getting hot perhaps?
Click to expand...

I agree that the volts drop is more of a problem with a regulated power source than it is with a non regulated one but any excessive resistance will reduce the current as well the volts.

Cable getting hot is not going to be a problem unless sized less than the normal safe working size for the current. 1.0mm² would be OK on that score for 10 amps.
 
VicS said:
... any excessive resistance will reduce the current as well the volts.
....
Click to expand...

Sometimes worth doing the sums to see if it matters in real life.
You really need some sort of I/V graph for the source to work out the real impact.
Sometimes spending a lot on fat unmanageable cable will only make 2% difference on a typical day.
Fat cable is better, but how much better?
 
Wind generator cable

Some wind generators generate and transmit the power to the regulator in 3 phases. This reduces current and voltage losses dramatically. You need 3 wires not 2 but effective current goes down to about 1/6 of the final DC current. Hence the reason power companies transmit power across the country in 3 phases. Also assisted by the very high voltages used.
How???? 3 phases is like having 3 different power supplies which you might imagine are fed by 6 wires.
However if you had 2 12v batteries feeding 2 lamps over a long cable with 4 wires if you connect the batteries +ve of one to -ve of the other and the 2 lamps in series with2 wires coming from the middle of batteries and lamps. Then both circuits can share one of the middle wires. Wheras in actual fact the middle wire carries no current because current is flowing in both directions at once. So the wire can be dispensed with. A quick witted reader will realise we have put 2 batteries in series feeding 2 lamps in series a 24v system. (don't let that confuse you for the analogy.
In 3 phase AC we connect one end of each phase winding to a common wire so we can use just 4 wires instead of 6 for our 3 systems. But if the current in each phase is the same the net current in the centre common wire is zero. So we can dispense with that wire. The timing of the AC sine waves at 120 degrees apart means collectively zero current in centre wire. (we have halved our copper requirement)

But there is more savings because the return for any one phase wire is effectively via the other 2 wires there is more cancelling out of current to give even less effective current hence volt drop.
You might need to draw graphs to see just how this cancelling out works but it does. It enables our high powered electricity transmission systems to operate with less voltage losses in cables.

So OP may be confused that a relatively light wire has been supplied or suggested for the output of the gen. If it is 3 phase then the lighter wire will be fine from gen to rectifier or regulator. from there when it is DC all the usual volt drops occur so use heavier wire to battery. Of course if the rectifier and regulator are in the generator then all this 3 phase stuff is not applicable even though within the windings of the generator advantage will be taken of lower current in 3 phase. What a load of waffle good luck olewill
 
I have an air breeze.

I must admit I am fairly sure I stuffed up when I ordered the wire.

The diameter is 1.5mm2

I re read the info on the wind again last night and I should have much thicker cable.

I am just trying to figure out how much power I am losing by not upgrading the cable.

I figure that even with very large cables I am going to lose say 5%. If I am only losing 10% with my current cable, then I am not that fussed. However if it is up to 20% then it needs to be added to the list of jobs to do.

In the 2 months that I have had the unit, I have seen it peak at 7 amps output in a blow. I have a 10amp slow blow fuse in it and that is still intact.

My rationale for all this malarkey was that the cable I have is about the same thickness as domestic cable and rated at 15amps.

Now in my defence here, I did all my previous maths and research the night after a crazy wedding. where i spent the last hours before passing out, walking around with a cigar in one hand while swigging from a bottle of drambuie
 
You seem to be getting current in to the battery, despite the thin wire, if the battery is near fully charged then you don't want too much current. Remember the charging current is dependant on what charge is already in the battery.

Interesting theory by William_H about only 1/6 th current. It wasn't like that when I learnt 3 phase theory! You can't get current from nowhere. The DC current out must be the same as the AC current in. The savings on the electrical distribution are because of the use of transformers to change the voltage, and hence the lower current at higher voltage where the power loss is proportional to the square of the current.
 
Oscarpop said:
My rationale for all this malarkey was that the cable I have is about the same thickness as domestic cable and rated at 15amps...
Click to expand...
A 3V voltage drop at 230V is OK, at 12V it's not so good.

William_H said:
Some wind generators generate and transmit the power to the regulator in 3 phases. This reduces current and voltage losses dramatically. You need 3 wires not 2 ...
Click to expand...

No, you need 4 wires, not 2 :)
 
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prv said:
Ouch!

Surely it was obvious as soon as the order arrived that this was not suitable cable for charging a battery? It's what I use for my LED cabin lights!

Pete
Click to expand...

it is the same thickness as domestic wiring for say a kettle, and is the same diameter as the wires for the rest of the 12v appliances.

Although as already stated I realise that I have made a schoolboy error here.:o
 
nigelmercier said:
A 3V voltage drop at 230V is OK, at 12V it's not so good.



......
Click to expand...

A 3V drop may make surprisingly little difference.
It depends on the output impedance of the generator at any given RPM.
Some generators give nearly as many amps into 17V as they do into 15V.
All wind generators should be designed to cope with significant cable loss, by their nature they tend to be a bit remote from their batteries.

Less cable loss is nearly always good, but the improvement may be disappointing when you get down to measuring it.
If the generator is roughly constant power, reducing the cable loss to 1V from 3 will improve the peak charging into 14.5V by 17.5 /15.5 or 13%
At average wind speed, the current is less, so the losses are less, you might be looking at
16/15 which is only 7% more current.

In reality, it is often the long slow charge that your battery needs, rather than peak performance in strong winds.
You could try doubling up with temporary cables and measuring the difference in charge current, if the generator manufacturer cannot provide the V/I curves.
 
William_H said:
Some wind generators generate and transmit the power to the regulator in 3 phases. This reduces current and voltage losses dramatically.....ll
Click to expand...

Olewill's post I think is slightly off the point, but taking the AC from the generator and rectifying and regulating it close to the battery makes a lot of sense.
If the generator regulated to say 15V at source, any voltage drop above 0.5V would severely limit charging. It is not like a regulated (car) alternator, for a good reason.
 
lw395 said:
A 3V drop may make surprisingly little difference.
It depends on the output impedance of the generator at any given RPM.
Some generators give nearly as many amps into 17V as they do into 15V.
All wind generators should be designed to cope with significant cable loss, by their nature they tend to be a bit remote from their batteries.

Less cable loss is nearly always good, but the improvement may be disappointing when you get down to measuring it.
If the generator is roughly constant power, reducing the cable loss to 1V from 3 will improve the peak charging into 14.5V by 17.5 /15.5 or 13%
At average wind speed, the current is less, so the losses are less, you might be looking at
16/15 which is only 7% more current.

In reality, it is often the long slow charge that your battery needs, rather than peak performance in strong winds.
You could try doubling up with temporary cables and measuring the difference in charge current, if the generator manufacturer cannot provide the V/I curves.
Click to expand...

well I hope that you are correct. 7% is more than acceptable.:)
 
nigelmercier said:
Quote:
Originally Posted by William_H
Some wind generators generate and transmit the power to the regulator in 3 phases. This reduces current and voltage losses dramatically. You need 3 wires not 2 ...
Click to expand...
No, you need 4 wires, not 2
Click to expand...

4??
Three phase uses only three wires.
I think they've changed the colours now but they used to be coded red, blue and yellow

Look at electricity transmission towers Usually two circuits, three wires in each,

34886_Pylon.jpg
 
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