Connecting thick gauge cables
Submitted: Sunday, Aug 14, 2016 at 09:16
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AeolusRicky
I have some 3B&S 25mm2 cable that I am using for a dual battery set up. The Redarc BCDC1240 I am using has 8B&S 9mm2 cable coming out of it for the connection. When I was in the US we had stepdown butt splice connectors that I would crimp and use for this but I cannot find them anywhere so I have 3 options. 1 - crimp together 2 butt slice sleeves and insert them into each other. 2 - solder the cables together by inter-twisting the wires and cover in heat shrink. 3 - crimp a lug on each cable and bolt them together. I have all of my own equipment hydraulic crimper, soldering iron etc. I am more interested in safety over money or a slight voltage drop. The cable run is only going 6-7 meters and the reason I am using 3B&S is because I have hundreds of meters of it for free.
Any other options, ides or suggestions would be appreciated.
Reply By: Allan B (Member, SunCoast) - Sunday, Aug 14, 2016 at 10:17
Sunday, Aug 14, 2016 at 10:17
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Hi Ricky,
Technically, there is nothing wrong with reducing the number of strands of the 25mm cable to permit it to fit a crimp sleeve sized to accept the 9mm cable from the Redarc charger. The reduced section of the 25mm cable still has the same current-carrying capacity as the 9mm and there would be immeasurable volt-drop over the centimetre of reduced cable.
Strip 1.5 cm of the 25mm cable then work around the cable with side cutters until it fits the crimp sleeve. Cover the entire sleeve and a couple of centimetres up each cable with heat shrink (maybe two layers) for a secure and neat
junction. Somewhat tidier than lugs and bolts.
AnswerID:
603378
Reply By: Bob R4 - Sunday, Aug 14, 2016 at 13:17
Sunday, Aug 14, 2016 at 13:17
Stripping some wire strands from the larger cable, crimping, and sealing with adhesive lined heat shrink, and then a second layer of the same heat shrink longer than the first layer would surely provide a good electrical connection, and good moisture exclusion.
I've never had an issue with any such connection in my experience, particularly in marine/boat situations, so surely must be more than adequate with auto applications.
Simple too.
Solder can sometime create hard points around the join which would be subject to possible fatigue.
Bob
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603384
Reply By: Zippo - Sunday, Aug 14, 2016 at 19:24
Sunday, Aug 14, 2016 at 19:24
I'm with AllanB regarding DECENT crimps (not those pissy Faston/QC types) vs soldering, and I CAN solder!
Soldering creates stress points where flexing loads will be concentrated, far more than crimping. In addition, it is NOT trivial to get the right amount of heat and even heat distribution when soldering bigger cables like those you are faced with.
Rather than pursuing unequal butt splices, a method I often use is to find the splice connector size that will allow BOTH cables to enter (EDIT: from opposite ends) and overlap them for the full length of the splice.
AnswerID:
603393
Reply By: Member - John (Vic) - Monday, Aug 15, 2016 at 01:42
Monday, Aug 15, 2016 at 01:42
Your other option is to put a fuse such as an ANL or Midi fuse in between the two different gauges of wires and use a suitable crimp lug in and out of the fuse holder.
Aside from the fuse helping to protect the BCDC charger and system as a whole it fixes the issue of trying to connect the two wire gauges.
This is just what I did when mounting my BCDC charger, I put an ANL fuse holder on the positive lead into the BCDC and one on the output to the secondary batteries, bracketing the charger.
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Follow Up By: Nomadic Navara - Monday, Aug 15, 2016 at 09:35
Monday, Aug 15, 2016 at 09:35
Unless you have a battery (or other high current voltage source) on each end of the wire you should have only one fuse in the line. Every fuse in line causes a voltage drop. The extra fuses also are an extra potential source of problems.
I think Zippo's method is the best way to go.
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873041
Follow Up By: Member - John (Vic) - Monday, Aug 15, 2016 at 13:42
Monday, Aug 15, 2016 at 13:42
Umm you do have a battery on each end of the wire.
Input current comes from the start battery whilst being charged by the alternator, up to 14.2v, in my case the ANL fuse has almost zero impact on voltage drop.
On the output side the BCDC raises the voltage to suit my AGM's 14.5v so certainly no voltage drop there either.
It's also the way Redarc recommend you wire the unit to protect the system as a whole.
Redarc BCDC wiring diagram
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