 | Home > Technical > cable weight for split charge |
 
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| diesel_jim Member Since: 13 Oct 2008 Location: hiding Posts: 6112   
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if you're using a nice heavy duty relay to join both batteries, or indeed a fancy electronic split charge unit, you'll want to use the same size cable that comes out of the alternator (as it will be the same current going through said cable)
off the top of my head, i think its about 25mm cable, multi-strand. although, if you're going to be doing some seriously heavy winching/battery drain, it might be prudent to upgrade it to 35mm, especially if you fit a higher output alternator (the td5 is a 120amp alternator, Tdi's about 85-100amp, depending on spec) |
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6th Jul 2012 8:40am |
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| BigRuss Member Since: 15 May 2010 Location: Norfolk Posts: 2785 
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The question is what are you using it for and do you really need it? Russell
2011MY 110 XS USW Black |
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6th Jul 2012 8:44am |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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On the other hand, if it's just for a second battery to power a fridge and lights, then you can use something much lighter. As Russ said, depends what it's for. Darren 110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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6th Jul 2012 8:46am |
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| mobilecentre Member Since: 05 Mar 2012 Location: Evesham Posts: 645
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And is it really a split charge or relay to parallel two batteries together?
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6th Jul 2012 8:47am |
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| tatra805 Member Since: 16 Aug 2011 Location: Dolany Posts: 436  
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join in
If the alternator runs the batteries will be joined, can you join manually? (eg nat luna has a pushbutton for that) if yes: which users will be switched on at that moment? eg, if this is a winch, i saw a lot of cooked splitcharge systems as these had a 200A rated solenoid and the winch was pulling more than that. Say the solenoid is strong enough, then size the cable to the solenoid, eg same thickness as battery cable. If no: for charging purposes only: current the battery will take to charge is roughly 10% of its Ah rating. Take 8A per mm2 of cable rating. eg 100Ah battery = 10A charging current = 1.25mm2 in reality 1.5mm2 should be enough For each consumer which you will run from the second battery,at the time battaries are joined (by running engine or manually) add the amps to that. (if your alternator is running the current will come from that one as internal resistance of battery makes it easier to take it from the alternator) Eg Fridge 5 amps Lights 20 amps Inverter 50 amps This totals 85 A = 10.6 mm2 reality 15mm2 If you plan on having a winch, or ever using the aux battery to start the car (eg when main is drained): - chech rating of solenoid of your splitcharge system, these are normally not able to handle this type of currents. Most of the time they are between 80A and 200A rated. If the solenoid is not able to handle 500+ Amps, route a normal battery cable between the + poles of both batteries over a 1000A rated manual switch. This way your splitcharge system can do its work and in case of an emergency (starting, winching those last couple of meters, etc) you can couple the batteries using the manual switch. (and in case your splitcharge system will stop working (yes it will i guarantee it) you can still manually join while driving to charge your aux batt) 2 cents  |
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6th Jul 2012 9:54am |
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| BigMike Member Since: 13 Jul 2010 Location: Lancashire Posts: 2253
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thanks all. very useful
it's a blocking diode split charge / relay. I had the same on my 90 and it worked flawlessly in various difficult conditions. The third battery is to run fridge, 2 gps's, small inverter for camera batteries and handheld radio batties, cb radio. it only joins when it sense the "correct" voltage (i'd have to check what it is) and it also joins if the main batteries do not have the requisite charge for starting. |
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6th Jul 2012 1:23pm |
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| mobilecentre Member Since: 05 Mar 2012 Location: Evesham Posts: 645
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KISS - use 35mm2 cable
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6th Jul 2012 1:24pm |
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| big steve Member Since: 24 Dec 2009 Location: hertfordshire Posts: 2456 
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Buy welding earth cable 2015 2.2 tdci hardtop xs
3.2 conversion DONE 238bhp and 707nm torque and thats just the start ;-P hybrid turbo in build -done ready to fit ashcroft atb in transfer box 6 speed auto in build |
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6th Jul 2012 1:44pm |
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| BigRuss Member Since: 15 May 2010 Location: Norfolk Posts: 2785
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Wow 3 batteries! You trying to run your own nuclur plant? Russell
2011MY 110 XS USW Black |
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6th Jul 2012 2:14pm |
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| mobilecentre Member Since: 05 Mar 2012 Location: Evesham Posts: 645
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Seen a few triple battery systems all in the seat box - tight to say the least!
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6th Jul 2012 4:11pm |
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| bpman Member Since: 21 May 2008 Location: Oslo Posts: 8069 
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I used the same weight cable between the earths and the +ve feeds with a lighter cable to the aux fuse
 Click image to enlarge together with a BlueSea controller from MobileCentre  |
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6th Jul 2012 5:49pm |
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| diesel_jim Member Since: 13 Oct 2008 Location: hiding Posts: 6112
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The trouble with using "light" cable is when you either forget, or someone else plugs something with a heavy current draw in, and melts it. Or the situation arises (somehow) that you need to use the second battery for something, and you think to yourself "
 , wish i'd used bigger cable" 
IMO better to do it once, properly. |
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6th Jul 2012 9:04pm |
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| Retroanaconda Member Since: 04 Jan 2012 Location: Scotland Posts: 2683 
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I used 16mm˛ cable between my batteries and the split charge relay (X-charge). This gives me about 110 amps I think. More than enough for charging current and anything I can draw off it. My auxiliary fusebox is fed through a 100 amp fuse.
In the event of needing to self jump start, I would just hook a jumper cable from one battery to the other. |
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6th Jul 2012 9:07pm |
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| bpman Member Since: 21 May 2008 Location: Oslo Posts: 8069
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yes, I plan to upgrade the cables to the aux fuse box as soon as I see my mate who is a marine electrical engineer who has all the right tools to do the crimping .. update with pics to follow. You also need to be mindfull of the overall rating of the fuse box, i think its' either 50amps. |
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6th Jul 2012 9:11pm |
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