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Author Topic: DC wiring help please.  (Read 1730 times)
Stevie D
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« on: June 21, 2010, 01:06:44 PM »

Folks I wish to connect up my batteries in a more efficient manner than the current sprawl in my tiny battery shed. Free up a bit of space and make it look a bit more profesional. I've a week off soon so would like to do this and insulate before the winter - just in case it's as cold again this year Cry

System is 24v for off grid holiday cabin, 1kw windmill, possible future pv when funds allow, and lister cs with dc head.

I have plenty of heavy welding cable and crimps etc.  my concern is the differing length of cables between +ve / -ve between strings?

Something like this - sorry forgot to take the camera with me last time i was there.



Intention is to run a bus bar either side and have a common point for connecting loads etc, should this be at opposie ends i.e top or bottom or from the middle.

Should the bus bar be shorter?

Is it just a bad idea?

Inspiration came from here - http://www.wagonmaker.com/newbatt.html, and looking at this http://www.smartgauge.co.uk/batt_con.html although I'm note sure my interpreation is good. banghead

Thanks

Steve





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Off grid 400ft2 log cabin
640ah 24v VRLA battery pack - it was Free :-)
700watt (1000 watt peak) windturbine
60amp Dump load controller
Chinese thermal solar tubes
Resol Solar pump station
50amp ex military dc genset - now coupled to  Lister cs 6
3kw Sterling Invertor
HalcyonRichard
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« Reply #1 on: June 21, 2010, 02:35:09 PM »

Hi Stevie,
              Looking at the whole system I have a few observations.

1/ For each battery "pair" connected across the busbars. You should ideally have the same
length of wire. It does not matter if this is on the positive or negative side of the pair
of batteries or both.(i.e. +ve length + -ve length = same for all pairs of batteries)

2/ The power losses in the wire is fractions of a watt. So I would make up the wires all
the same length. So you have short and long negatives and short and long positives. Pretty
much the same as your diagram. But I would make them long enough to connect to a star point.
Then connect this star point to the invertor/wind input. Thus the busbar is just a long bolt.

3/ By doing 2/ you balance the pairs to have the same resistance in series which should
balance any charging/discharging currents.

Regards Richard


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martin
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« Reply #2 on: June 21, 2010, 02:57:43 PM »

the best advice - http://www.smartgauge.co.uk/batt_con.html Wink
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guydewdney
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« Reply #3 on: June 21, 2010, 09:48:42 PM »

clean contacts and good crimps are more important than identical wire lengths. If you have that much wiring to do - get a proper ratchet crimp tool if you dotn have one already.
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Stevie D
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« Reply #4 on: June 22, 2010, 05:05:31 PM »

Thanks folks!

Richard - you've more or less answered my question - ref the long and short +ve's and -ve's cables, and busbar, thought that might be the answer.

Guy - yes got a proper set of crimps Wink

Steve
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Off grid 400ft2 log cabin
640ah 24v VRLA battery pack - it was Free :-)
700watt (1000 watt peak) windturbine
60amp Dump load controller
Chinese thermal solar tubes
Resol Solar pump station
50amp ex military dc genset - now coupled to  Lister cs 6
3kw Sterling Invertor
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