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Forum Index : Windmills : Power transmission
| Author | Message | ||||
| Jules Newbie  Joined: 08/05/2014 Location: AustraliaPosts: 9 |
Transmitting 48v Ac 40amp max roughly 50m from gererator head to charge controller over 2.5mm standard house wire. Windmill outputs over 3 phases, rated output of generator is 1500w at 36 km/h current wind speed is 15-20km/h so should be outputting around 625w so at 48v this is about 13 amps. Here is the problem, at charge controller amps are bearly cracking 10 and voltage from a single phase is no more than 2-3.5 v I was expecting some loss over 50m of cable but this seems excessive and when I check voltage at the base of the tower a distance of 6m readings are the same. Is it a case of the cable being grossly inadequate and all this loss occuring within the first few meters? If so would this be solved by using 6mm solar cable? Any help would be really appreciated! |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi jules Your voltage mentioned does not make sense to me, please check, while your 2,5 mm cable would be lossey it should do better than you say. Where is your rectifier located? if you run 3 phase AC to the regulator at the controller using the three wires for three phase, losses will be reduced, if you run DC through two wires losses will be increased. The voltage should be checked across phases you may be reading from 1 phase to earth and this will only give you induced leakage voltage. If you are getting 10 amps at the controller into a 48 volt battery load being charged this is close to 600 watts and the calculated output is 625 approx 25 watts loss, sounds more logical. A 6 mm cable would be better of course, when your mill runs up to full output but this is on rare occasions not all the time so it it is not as much of an issue as first imagined, your 2.5 mm cable set as a three wire AC configuration should carry 16 amps with a loss of less than 10% at full load over 50 meters, warm wire on full load as 150 watts approx dissipated over that length. All the best Bob Foolin Around |
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| Jules Newbie Joined: 08/05/2014 Location: AustraliaPosts: 9 |
Hi Bob Reticifier is located with the charge controller at the end of the 50m cable run, 3 phases are transmitted as AC over 3 x 2.5mm cable's. I think I was checking the voltage incorrectly and was only getting leakage to earth as you say. The figures on losses you've given me are reassuring and after a good blow last night generator seems to be keeping my batteries topped up nicely. If I'm only getting 10% loss and 16amps charge at full load I'm happy with this, wont go digging up my trench and laying new cable any time soon. Thanks again. |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
2.5 TPS is seriously underrated for 48V work. 1500W over 3 phase is 500W at say 55V which is ~8.5A losses over 50m would be significant. ripper calculator here http://photovoltaic-software.com/DC_AC_drop_voltage_energy_l osses_calculator.php depends on how you pump in the numbers but losses look like 8-15% to me which is about 5x what i'd like to see, that said if it isnt making full grunt all the time the numbers are slewed.... ME -MORE! Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl What you say is 100% correct for continuous transmission of such power but in my experience over the years maximum power is reached less than 1% of the time unless you are in a continuous wind location and that sadly is not applied to most of us. I would suggest 6mm wire for such installations if done initially but when a 2,5 is already installed unless money is no object it will suffice and accept the losses a very small percentage of the time. It would be good to do calculations as you refer to, but on an actual logging of the mean average output of the mill, if it is averaging 1KW> it would be prudent to upgrade the conductor size. We are in a "make do world" so what we have or can afford is likely to be pressed into service rather than an ideal low loss system used commercially. All the best Bob Foolin Around |
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wallablack Senior Member  Joined: 10/08/2011 Location: AustraliaPosts: 164 |
Here is the link KarlJ posted Sorry KarlJ but the was a gap in it.....GREAT calc though. Foolproof systems do not take into account the ingenuity of fools. |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Jules Small cables, and hence high resistance and the associated losses, become a much bigger problem as the operating voltage gets lower. The 2.5mm2 cables that you have used would be rated for about 25A max (per phase) at 240V, but even this rating accepts that the distance for which cables of this size can be used will be limited. When you drop the operating voltage to 48V, the operating current to transmit a given amount of power is 5 times larger, and the distance over which the corresponding voltage drop (of about 5%) is acceptable at 240V reduces to about one fifth. It gets much worse at even lower voltages, like 12 Volts. As I understand it, your 2.5mm2 cables are already installed, so there is probably not much point in spending money and effort to upgrade them. But wherever you can, always use the biggest cables that you can acquire and fit in a low voltage installation. Regards Don B |
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