Cable Sizing & Dc/Dc Chargers

My initial thought was to put a auto solenoid style under my bonnet ,I believe redarc do a good one , and then put the ctek in my camper to charge the 2 batts in there

This way I could run smaller cable from aux bat to rear of vehicle say 8b&s

Yep, a Redarc isolator between the 2 underbonnet batteries and the Ctek either in the back of the vehicle or in your camper would be the common way to deal with your situation. Use a maxifuse or fusible link at the pos on every battery for short circuit protection.

8Ga cable is plenty when you have a Ctek limiting the current (despite what the doomsayers say). Its what I use because I've measured voltage drop (with at least 20 amps current) and it's not significant (when using the Ctek) despite the distance between alternator and Tvan battery). But there's no problem with using bigger cable (apart from weight, cost etc). I use 8Ga because I can get it tinned - haven't found 6Ga tinned cable anywhere and corrosion of cable on campers is a real problem that most people don't know about.

Its also very important to have a good earth between all auxillary batteries and the vehicle's engine (because thats where the alternator's mounted).

Phil

when you say 8Ga cable are you refering to 8B&S cable

all these cable sizes are doing my head in

Dudley

My apologies, 8Ga and 8B&S are the same. Here's a link to what I use:
Whitworths marine 8B&S cable

Duds and others

If anyone is after bulk cable (30, 50, 100m rolls) of just about anything this guy is good for that even after freight costs - search the page for Marine Cables Tinned Copper in his Price list - I think most of his cable is from Tycab and the tycab.com.au site is a good reference for cable sizes and specs and cross referencing Auto (mm), cross section (mm2), and Gauge (B&S).

http://cableandwiresales.com.au/Price_Listb.html

eg. MBS111203-BK-30 8 B&S (112/.3) TCW :BLACK $62.24

As Phil said, Tinned only appears to be available in 8B&S and 2B&S - I used 8B&S for the same reason - corrosion. In fact I try and use tinned for everything.

Much good info in this thread as usual.

I should have said "8B&S and 2B&S in heavier cable sizes", because there are 3mm, 4mm, 6mm tinned available in single and twin, tinned trailer wire, etc.

Ross

my mistake no I wasn't told to charge my main batt but it will isolate when it needs charge so this is fully chatrged first

Hi
A follow up to above
That size cable [pos & Neg] needs to be run the FULL length from tug battery to the charger & from charger to Aux battery

PeterQ

Duds13 posted:
Ross

my mistake no I wasn't told to charge my main batt but it will isolate when it needs charge so this is fully chatrged first

The Ctek DS250 does not allow the main battery to be FULLY charged FIRST
but it does prevent the the load in the van from discharging the MAIN battery

PeterQ

Hi Bill
Yes the Ctek will boost the voltage, lost due to Voltage drop in the cables,
BUT it does that by drawing an even higher current from the alternator!!
More load on small cables even higher voltage lost!!
Power lost in the cables can become quite high
Best to have at LEAST 12V at the Ctek input when under max load !

PeterQ

No argument there Peter.
But having the DC Charger at the end of the long circuit limits the need for extra heavy duty cable and ensures a complete mulit-stage charging process to maintain the batteries properly.
If the Ctek was at the beginning of the circuit voltage drop through the long cable run would be such that the batteries in the camper would not be getting the optimum charging regime the Ctek charger otherwise provides.

I agree 100% with Sandman and Olcoolone. The D250S should be as close as possible to the van battery/s, and away from the under-bonnet heat. I'd use 6 B&S twin to feed it from the engine bay, especially if you are planning on running a 3 way fridge in the van from that same line. If you have an Aux battery under the bonnet it could be charged fairly well by simply connecting it to the vehicle battery through a voltage sensitive relay - not ideal, but probably quite adequate.

Something worth noting - a dc-dc charger such as the 20 amp D250S draws extra current from the alternator to provide the energy needed to increase the battery charging voltage. If the voltage reaching the charger from the vehicle is low due to losses in wiring, the charger will draw extra current from the vehicle to compensate, which then increases the losses, calling for increasing current , resulting in more losses, more compensation, more losses....... For this reason, decent sized cable, 6 B&S rather than 8 B&S, is a worthwhile investment. Also, suggest check that your alternator can handle the extra 25+amps that the D250S will draw.

Cheers

John

Ooooops..... Sorry Olcoolone - I really meant Oldtrack123 !!

Cheers

John

Just to confirm the cable sizes I use, The Flyer I have in the rear of the vehicle comes with 10mm2 twin core cable.
The patch lead I use to connect the camper cable is also 10mm2.
The camper also has 10mm2 cable which was OEM supplied.
All I did was install a 30 amp fuse and the Ctek at the end of the cable run and before the batteries which connect to the output of the DC charger.

All good!

The D250S includes a temperature sensor which needs to be placed on the camper battery as close as possible to the positive terminal of that battery, ie the D250S needs to be in the van, not under the bonnet. I've just installed one and it is doing a great job of keeping the 100Ah AGM at 14.3 volts (ie fully charged). Thank you Kulkyne Campers who were way cheaper than anybody else. No affiliation!Kulkyne Campers website

Thank you all for your advise

I think I now know what I need to do

John

You mentioned a voltage sensitive relay as being ok

What would you suggest as a better option

I' m hoping to only do this once

Dudley

Dudley,

With the under-bonnet Aux battery close to the vehicle battery, there are minimal losses so the Aux will get close to the charging voltage that's available to the cranking battery. Assuming the Aux is an AGM type, it would benefit from slightly higher charging voltages than will be available at the cranking battery. It would be preferable if it had the benefit of a dc-dc charger to kick the voltage up enough to charge that last 10-20%. (That % is a guess and will vary with charging time, temperature and condition of both batteries.)

I'd put the D250S in the van, but adding a second dc-dc charger to deal with the under-bonnet aux battery really isn't justified in my opinion. (We can get carried away with optimising and too easily overlook the fact that "perfection is the enemy of the good" !!)


A question - Do you really need the aux battery under the bonnet, or might it be possible to move it to the van where the D250S can look after it? (I expect you have a fridge in the vehicle, in which case you do need a battery for it in the vehicle.)

HTH

Cheers

John

John

Yes I have a 50lt Waco in the back of my nissan patrol wagon plus some lighting for when we are fishing

I've just been looking at the Redarc SDI 12 isolator thoughts?

Hi Dudley,

I haven't used the SBI 12 isolator, but it's pretty expensive. ABR Sidewinder is a member of this site and I've been pleased with the quality of their gear. They offer this isolator at a much more reasonable price.

A thought - I've been assuming that the under-bonnet aux battery is an AGM type, which will ideally need a bit more voltage than will be available. If it's a wet battery, or a gel type, (probably not gel, as they don't like the under-bonnet temperatures) you could get away with using a high current schottky diode as an isolator. (eg Three of Jaycar's highest rated MBR735 devices, paralleled, would handle 20 amps and cost less than $5.) ( Diodes introduce a voltage drop so are generally unsatisfactory for this sort of use. Schottky diodes have a lower forward voltage and may be ok if you can tolerate a small drop.)

Cheers

John

Duds - just to add a bit more ..

What I have done is similar to John is saying re using 2 chargers.

I have one Ctek "in vehicle" on a 120AH battery right next to a small fridge/freezer (mainly for good cold beer) and in the van I have another Ctek on the house batteries - both are driven directly from the Alternator. Alternator must be capable of initial start up requirements though when both Cteks kick in (potentialy another 40 Amps for a while).

As others have said, the Ctek should be with the battery so the temperature sensor is placed on the battery.

Voltage drops are also critical as people have said - according to the Ctek spec you have to have minimum 12.8V at the Ctek to ensure it will not drop in and out at higher (20A) currents. So tinned coppper, minimum number of connections and terminals, and good quality connections and crimping is a good rule of thumb. I use an Anderson plug to get from vehicle to van rather than the trailer plug which is usually cable size limiting and a screw terminal.

For info from the D250S Dual manual
The charger starts charging the target battery when the supply voltage exceeds 13.1V for 5 sec (engine on).
The charger stops charging the target battery when the supply voltage drops below 12.8V for 10 sec (engine off).

http://www.ctekbatterychargers.com.au/uploads/3/6/2/9/3629451/d250s_dual_manual.pdf