Cable Sizing & Dc/Dc Chargers

Submitted: Wednesday, May 08, 2013 at 17:47
ThreadID: 102091 Views:14005 Replies:5 FollowUps:21
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Hi all

I have been trying to sort out my dual battery system and run power to charge a couple of battery's in my camper

I have been advised to install a CTEK D250s Dual under the bonnet to manage the charging of my main start battery and the aux battery (currently Ii have a Cole Hersey switch in the drivers foot well) under the bonnet and then run 10mm cable to an anderson plug at the rear of the vehicle to then run to the battery's in my camper

I am a little confused with the cable sizes I think I should be using 6B&S as my cable from the CTEK to the anderson plug/

any thoughts?
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Reply By: Member - Phil G (SA) - Wednesday, May 08, 2013 at 18:07

Wednesday, May 08, 2013 at 18:07
Your Ctek limits the current to 20 amps, so cable size is not as critical. I use 8Gauge marine cable with mine (= 85A cable) but 6B&S (140Amp cable) is what most people would use.

But if you have both your car's aux battery and your camper's batteries after the Ctek, that is a lot of battery sharing the 20amps.
AnswerID: 510591

Follow Up By: Duds13 - Wednesday, May 08, 2013 at 18:17

Wednesday, May 08, 2013 at 18:17
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
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Follow Up By: Member - Phil G (SA) - Wednesday, May 08, 2013 at 21:42

Wednesday, May 08, 2013 at 21:42
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).
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Follow Up By: Duds13 - Wednesday, May 08, 2013 at 21:49

Wednesday, May 08, 2013 at 21:49
Phil

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

all these cable sizes are doing my head in

Dudley
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Follow Up By: Member - Phil G (SA) - Wednesday, May 08, 2013 at 22:06

Wednesday, May 08, 2013 at 22:06
My apologies, 8Ga and 8B&S are the same. Here's a link to what I use:
Whitworths marine 8B&S cable
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Follow Up By: KenInPerth - Thursday, May 09, 2013 at 09:26

Thursday, May 09, 2013 at 09:26
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.

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Follow Up By: KenInPerth - Thursday, May 09, 2013 at 10:01

Thursday, May 09, 2013 at 10:01
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.
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Reply By: Ross M - Wednesday, May 08, 2013 at 18:31

Wednesday, May 08, 2013 at 18:31
Did I read correctly, has someone recommended the Ctek to be charging the main start battery?
Your alternator should be charging the main battery otherwise if you have CRD or EFI engine, air con running, heater blower, wipers, headlights etc etc you may need two or more Cteks just to keep the main battery receiving sufficient charge to prevent it becoming flat. This is not a solution.

A ctek is normally run off the main battery and then charges other batteries.
I would prefer the Ctek to not be in the engine bay at all because when it is heated by the 70 degree C under bonnet temp the Ctek will derate so IT doesn't overheat.
This may mean when travelling the Ctek will be HOT and derate and just supply a piddly small amount of current to the trailer while you think it is pumping out 20 amps for the two trailer batteries.
Not much use having a Ctek doing that.

Can you use appropriate wiring to the rear of the vehicle or trailer and have the Ctek either at the rear of the vehicle or better still mounted in the trailer near the batteries it is charging.

Ross M
AnswerID: 510594

Follow Up By: Duds13 - Wednesday, May 08, 2013 at 18:35

Wednesday, May 08, 2013 at 18:35
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
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Reply By: oldtrack123 - Wednesday, May 08, 2013 at 19:07

Wednesday, May 08, 2013 at 19:07
Hi
First, the DC to DC charger should be as close as practical to the Aux battery IN the camper

The cable size will depend on the cable distance between the tug battery & the DC to Dc charger in the CAMPER & will be either a gauge size or cross sectional area of the COPPER core
6 B&S [copper core 4.1mm dia] as you have suggested would probably be adequate.

Advised 10mm cable??
is THAT the Copper core diameter?[I think not] or the overall dia, over insulation, which means absolutely nothing!!

PeterQ
AnswerID: 510597

Follow Up By: oldtrack123 - Wednesday, May 08, 2013 at 19:12

Wednesday, May 08, 2013 at 19:12
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
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Follow Up By: oldtrack123 - Wednesday, May 08, 2013 at 19:19

Wednesday, May 08, 2013 at 19:19
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
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Reply By: Sand Man (SA) - Wednesday, May 08, 2013 at 19:11

Wednesday, May 08, 2013 at 19:11
The Ctek D250S Dual is best placed at the remote end of the cable run. (ie close to the camper batteries).
This will reduce the need for extra heavy duty cable from the starting battery as any voltage drop at the remote end will be boosted back to optimum level by the DC Charger.

As has been stated, your starting battery can be managed quite well by the vehicle alternator and the DC Charger would be wasted in the engine bay, at the start of the charging circuit.



Bill


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Follow Up By: oldtrack123 - Wednesday, May 08, 2013 at 19:24

Wednesday, May 08, 2013 at 19:24
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
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Follow Up By: Sand Man (SA) - Wednesday, May 08, 2013 at 19:43

Wednesday, May 08, 2013 at 19:43
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.

Bill


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Follow Up By: Member - John and Val - Wednesday, May 08, 2013 at 19:44

Wednesday, May 08, 2013 at 19:44
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
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Follow Up By: Member - John and Val - Wednesday, May 08, 2013 at 19:48

Wednesday, May 08, 2013 at 19:48
Ooooops..... Sorry Olcoolone - I really meant Oldtrack123 !!

Cheers

John
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Follow Up By: Sand Man (SA) - Wednesday, May 08, 2013 at 19:55

Wednesday, May 08, 2013 at 19:55
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!
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Follow Up By: Keir & Marg - Wednesday, May 08, 2013 at 19:59

Wednesday, May 08, 2013 at 19:59
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
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Follow Up By: Duds13 - Wednesday, May 08, 2013 at 20:20

Wednesday, May 08, 2013 at 20:20
Thank you all for your advise

I think I now know what I need to do
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Follow Up By: Duds13 - Wednesday, May 08, 2013 at 20:29

Wednesday, May 08, 2013 at 20:29
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
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Follow Up By: Member - John and Val - Wednesday, May 08, 2013 at 21:33

Wednesday, May 08, 2013 at 21:33
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

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Follow Up By: Duds13 - Wednesday, May 08, 2013 at 21:42

Wednesday, May 08, 2013 at 21:42
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?
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Follow Up By: Member - John and Val - Thursday, May 09, 2013 at 07:57

Thursday, May 09, 2013 at 07:57
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
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Follow Up By: KenInPerth - Thursday, May 09, 2013 at 09:51

Thursday, May 09, 2013 at 09:51
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
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Reply By: Sand Man (SA) - Thursday, May 09, 2013 at 07:15

Thursday, May 09, 2013 at 07:15
Dudley,

Have you considered a Sidewinder Flyer to contain a second battery in the rear of your vehicle, close to where your fridge will be?
This would eliminate the need for a second battery under the bonnet and provides a connection socket for your fridge.
The Flyer comes complete with all wiring, etc. and incorporates an isolator to protect the starting battery.

Sidewinder Flyer

I use a Flyer in my vehicle which contains a 100Ah AGM battery to run my fridge.
To connect my camper up, all I require is to install a patch lead from the Flyer's Anderson connector output and run it out the back of the tailgate to connect to the camper.
This basically connects the auxiliary to the Ctek D250S charger in the camper and then to the two AGM batteries installed in it.
(I have a Waeco 65l upright in the camper)

Bill


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