Hilux battery system (CTEK Smart pass-D250S) Voltage drop/cable size

Submitted: Sunday, Jun 01, 2014 at 18:18
ThreadID: 108056 Views:8268 Replies:6 FollowUps:12
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Hi All

I posted a thread on the 19-5 re DC-DC charging and setting up a battery system in a mates Hilux. Just wanted to post an update of what we have planned and see if anyone can see any major issues.
As a coincidence the battery and the alternation died last week and both have been replaced. Auto electrician said voltage output was only 13.2v with new alternator and that this wouldn't fully charge the AGM's we are putting in the car. Interestingly when I put my multimeter on the battery terminals it showed 13.8v, thoughts anyone? I tested my Troopy and it registered 14.2v at battery so it seems like the Landcruiser alternator might charge at a higher rate.
Two 130A/h AGM's will be going in the far left rear of the tub, a tight fit, we have made up a tray and all seems good on that side of things. We will be using the CTEK D250S dual and Smart pass.
Just so I understand this right, this will raise the charging voltage from the alternator whilst it charges the batteries up to 80% give or take a bit, it will then switch over to the DC-DC function of the D250S duel for the final top up of batteries, it will then switch and bring the starting battery up. We will also be having two 50 Amp Anderson plugs under the rear tow bar. One will feed solar from a 80W panel via the CTEK whilst the other will go directly to the batteries for use with a CTEK 25A charger ran from either mains or generator as needed.
I think the above is correct but if anyone can see any issues or that I've misunderstood anything please feel free to comment.
My mate bought some cable from an auto supplier the other day but I am concerned it may not be large enough. It is 6AWG or 13.5mm2
Depending on which route the cable takes we will either be looking at a 5 or 7.5 metre run. Mate wants to bring cable into tub behind rear left tail light (7.5 m run), or we can shorten it by bringing up through tube floor but he doesn't really want to do this. It would be a 7m run to the smart pass then a .5 m to the batteries, then 6 metres back to fuse box under bonnet. As the draw from accessories wont be real high, say max of 10A I think the
13.5 mm2 back to the fuse box should be fine? They have then supplied him 8 B&S or 7.91mm2 to run from fuse box to his various sockets he plans to put in. The longest run (I hope) will be around 6 metres to the furthermost socket. Calculating the Vd from batteries to fuse box and then adding this to cable to sockets, I come up with around .15Vd, so should be fine.
I am concerned however that the draw from the two batteries when discharged will be quite high and that 13.5mm2 will be inadequate. Though this is of course the whole idea of what we are hoping to achieve, a high charge rate. Thoughts on this?
By my calculations if the batteries are drawing 80A (and providing the above system can provide this) to keep Vd to .193v (this is to the smart pass then + 50cm to batteries) I would be needing to use 0B&S or 49.2 mm2. This is also calculated at 25c and it is bound to be hotter than this. At 40c it would be .224v
Collyn Rivers states that .15-.2 Vd is acceptable. If I go to 1 B&S at 40c Vd would be .279v. B&S 00 or 64.9mm2 will see a Vd of .182 If I allow for the full 7.5 Metres from front battery to rear via the smart pass.
Or am I completely mistaken and the smart pass and charger are going to render my ramblings above irrelevant? If so please explain.


Thanks

Lyndon
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Decide now what you will,
Place faith not in tomorrow
For the clock may then be still

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