battery cable size

Submitted: Friday, Dec 16, 2016 at 17:52
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Hello there , I'm asking a question regarding what battery cable size for a second battery approximately 4 ~4.5 metres away to boost a flat main battery in the event that it might happen at some odd occasion :-(
vehicle is ranger px diesel will be fitted with red arc battery isolator switch ?
how many amps would a ranger starter motor draw approximately in this circumstance wld you say ?? any thoughts ....
Cheers Nick b
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Reply By: TomH - Friday, Dec 16, 2016 at 20:18

Friday, Dec 16, 2016 at 20:18
Either 2 or 3 Gauge (2 B & S) would be good Toyotas use that between the twin batteries in the 100 ser..
You will need the little push button in the cab to make the isolator do that.

Where is the battery going, to be 4m away
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Follow Up By: Member - nick b - Friday, Dec 16, 2016 at 21:06

Friday, Dec 16, 2016 at 21:06
thanks for your reply : under the tray behind the cab ~ extra cab
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Reply By: Rangiephil - Friday, Dec 16, 2016 at 23:29

Friday, Dec 16, 2016 at 23:29
If you only want it to help start if teh main battery goes flat, I suggest you would be far better off with one of those LifePO4 battery packs that fit in your hand.

For a couple of hundred dollars you will save carrying 25-30Kg around and the cost of wiring and an isolator.

Regards Philip A
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Follow Up By: Member - nick b - Saturday, Dec 17, 2016 at 06:38

Saturday, Dec 17, 2016 at 06:38
Im wanting the extra battery anyway for camping etc & i have to run wire to charge it so might as well run a heavy wire to jump start .
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Reply By: Hoyks - Saturday, Dec 17, 2016 at 00:07

Saturday, Dec 17, 2016 at 00:07
How often do you get a flat battery?

For me it is a extremely rare event, so I didn't wire up the car to have redundant systems like that. To make it work you not only have to have heavy cable that can cope with the power, but a relay that can handle a large number of Amps running in both directions, as well as fuses that can take it too. After the cable has snaked its way around the engine, cab and chassis you probably have a meter or more than is ideal.

What I did do is have the cable enough to charge the 2nd battery and a heavy earth cable from the 2nd battery to the chassis.

If I need to self jump start, then I run a single jumper lead between the positive terminals and start it that way.
9 times out of 10 you are just giving the starter battery a helping hand, rather than full amps to start from the 2nd battery, for that 1 in to where the main battery is fried, then you may as well just replace it with the 2nd battery and head for town.

... and get the dealer to switch off the smart charge 'feature'. My BT50 doesn't have it and we have nowhere near the battery issues that Rangers seem to have.
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Follow Up By: Member - nick b - Saturday, Dec 17, 2016 at 06:59

Saturday, Dec 17, 2016 at 06:59
Turning off smart charge wld be something i"d like to do aswel but wanted to find out a bit more of that that does ? ?
Regards the bat cable it will be as u say, + ~ + terminal on batteries with red arc switch .

These vehicles have the lights coming on when the door is ajar & i are offen on my own.
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Follow Up By: Frank P (NSW) - Saturday, Dec 17, 2016 at 08:51

Saturday, Dec 17, 2016 at 08:51
I agree with what you're doing, Nick. I have a similar setup in my BT50 so I can start off the second battery and winch off both. I have had a flat or nearly flat crank battery a number of times due to the quirks of the Ranger/BT electrical system so it has been worthwhile.

Also, larger cabling will promote better charging of the second battery, especially over the long cable run.

For your second battery, choose a dual purpose deep cycle type that will tolerate the occasional high amp output. I have an SSB AGM which seems happy enough, though I do use a programmable dc-dc charger which provides exactly the right charging parameters.

Turning off the Ranger's smart charge system has no ill effects, only benefits, so if I were you I'd do it. It is especially important to do it if you are not using a dc-dc charger for your second battery. If you don't, the second battery will never get adequately charged and will die a premature death.

I'd do the dc-dc charger anyway, but you'll find divided opinion here about that. It is essential if you choose to leave the smart charge system operative. If you do it, I suggest you get one with an inbuilt solar regulator. Perfect for camping. Redarc make a couple, but I like the Enerdrive DC2DC which has adjustable current output, among other things.
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Reply By: Sand Man (SA) - Saturday, Dec 17, 2016 at 08:27

Saturday, Dec 17, 2016 at 08:27
Nick,

A second battery to run a fridge, etc. is usually of a deep cycle type, providing lower amps over a long period and a deep cycle battery is not generally suitable for use as a starter battery which requires high amps for a short period.

You really need to determine what your primary use is for each battery and obtain a suitable battery type to use for each specific purpose.



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Follow Up By: Nomadic Navara - Saturday, Dec 17, 2016 at 15:04

Saturday, Dec 17, 2016 at 15:04
Despite deep cycle batteries being tailored of low current applications they still make excellent starting batteries in an emergency.
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Follow Up By: Sand Man (SA) - Saturday, Dec 17, 2016 at 18:40

Saturday, Dec 17, 2016 at 18:40
Peter,

Your classification of "excellent" is a bit exaggerated mate. Perhaps "adequate" is a more appropriate word and then mainly for a petrol fueled vehicle.

Take a common, popular and quality AGM Battery such as a Fullriver DC105-12.
It's CCA rating is a mere 660A, hardly an excellent rating for a large diesel engine.

As far as permanently wiring a second battery up to use as a means of starting "in an emergency", I think the extra cost and effort is wasted.
How long would it take to uncouple an auxiliary battery, or use another vehicle's battery and a set of leads to jump start?
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Reply By: The Bantam - Saturday, Dec 17, 2016 at 11:36

Saturday, Dec 17, 2016 at 11:36
There are people who will insist on a particular size and so forth ...... but auto electrics is always a compromise.

lets start with the starter .... most small diesel starter motors draw in the range of 100 to 150 amps at stall will a battery at full voltage.
The actual cranking time is very short in terms of electrical loads.
The actual cranking current may be considerably less than the stall current perhaps as low as 60 to 80 amps.

if you are considering winches, most have a 6ish Hp motor that will draw in the range of 400 amps stall and a couple of hundred amps on typical winching

Factory starter wiring in most vehicles is very light compared to the ideal.

I wont talk in wire guage because we live in Australia and all calculations are made in mm2

Many commercial jumper leads are lighter than 10mm2.

10mm2 would be in my opinion an absolute minimum ..... it would be perfectly adequate for charging the battery and delivering AUX loads from the alternator.
However it's probably pushing things a bit far to crank off ...... but it would probably get you started in most cases.

Any bigger will make bugger all difference to charging efficiency, at those lengths.

I typically use 10mm2 solar twin to feed switchboards and 50 amp andersons, because it is redily available, easy to handle and the bang for buck cable in that size range

If you are expecting to crank, I would be looking at 20mm2, because it is commonly available and still not too big to handle.

It would be the minimum I would look at If winching ..... 25mm2 seems only a little bit heavier but if you are winching you need every extra but of help you can, and it still is a handleable size ...... some would go to 30, 35 50 or 70 mm2 but it starts to get expensive and hard to handle

for comparison and because people insist in talking in American wire guage.
#8 is a little smaller than 8mm2
#4 is a shade larger than 20mm2
#3 is about 25mm2
#2 is about 32mm2
#0 is just under 50mm2

As for the "ranger foolisheness" good luck with that.

cheers
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Follow Up By: Member - nick b - Saturday, Dec 17, 2016 at 11:56

Saturday, Dec 17, 2016 at 11:56
Thanks for your reply. I was looking at 26mm2 @ $12 p/ m looked to as a good size .
As you say its only very short time to start the vehicle .
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Follow Up By: The Bantam - Saturday, Dec 17, 2016 at 12:40

Saturday, Dec 17, 2016 at 12:40
http://www.springers.com.au/product/647/Square-25.6mm-Single-Red-Cable

remember if you are going to crank or winch you can not use fuses or circuit breakers so you need to be pedantic with your mechanical protection.

you may be able to get that up the right size of braided PVC hose with some talk and a draw wire

If you don't already have one there are good battery lug crimpers available from a number of sources

cheers
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Follow Up By: Frank P (NSW) - Saturday, Dec 17, 2016 at 15:28

Saturday, Dec 17, 2016 at 15:28
"remember if you are going to crank or winch you can not use fuses or circuit breakers "

This intrigues me, Bantam. Why can't you? What about a fusible link?

I measured the current my second battery contributes during winching. It's under 300A. I installed a 300A fuse at each end of the positive link, near each battery.

I realise that a fuse may affect the efficiency of a large fat cable, but I have the peace of mind that if some clown T-bones me and crushed bodywork cuts into the cable somewhere I'm not going to have a dead short supplied by two batteries and the accompanying risk of fire. Well, not in that circuit, anyway.

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Follow Up By: The Bantam - Saturday, Dec 17, 2016 at 18:12

Saturday, Dec 17, 2016 at 18:12
Pretty much no factory built motor vehicles have fuses or breakers in the high current starter circuit. ..... right from motorcycles to heavy trucks

Sorry peace of mind is not worth a cracker if it is false.

Ever seen a high current DC fuse go off or seen the results?

If you have even a 200 amp fault ....... that is welding currents, it will burn big holes in the body work, throw sparks and molten metal everywhere.

If you have a 200 amp breaker of fuse ..... that will hold up a 150 amp fault indefinitely, burning holes in what ever is the contact point.

Consider that at 200 amp fuse or breaker will typically hold for twice its rated for 1 minute and 1.5 times its rated for a hour ... unless you get something specy

The consequences of any sort of high current DC fault in a motor vehicle can be dire.

Yes you battery will deliver those very high currents, any decent sized battery will deliver 500 to 700 amps for a few minutes no problem

You want to avoid high current DC faults at all cost, this makes mechanical protection THE priority.

then there is the cost and physical size of effective high current circuit protection

the higher the current the less and less viable and effective DC fuses and breakers are in the installation and the more you MUST rely on mechanical protection and good practice.

Above 120 amps is where the practicality of circuit breakers in DC car electrics starts to deminish considerably. ....

Even a 120 amp breaker may hold up a 200 amp fault for a minute ..... in that time considerable damage can occur

In any high current DC circuit in motor vehicles, the matter demands great respect, circuit breakers and fuses at this current will provide very little protection.

cheers
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Dec 17, 2016 at 20:02

Saturday, Dec 17, 2016 at 20:02
.
Much of what Bantam says is appropriate.

If a cable of a size capable of handling typical starter current of up to 300A accidentally shorts to the body or chassis, a current in the order of 1000 amperes or even much more can eventuate from a typical 100ah lead acid battery, including AGM types. This fault current is likely to result in a vehicle fire or even battery explosion.
Fuses that can safely limit this fault current are available but they are of industrial specification and expensive. OEM starter cables are unprotected from fault current but are generally located such that faults are unlikely to occur.

Locating remote batteries such that long cables are integrated within the bodywork is difficult to achieve the desired safety without thorough and expensive arrangement. I would not recommend the proposal of back-up cranking batteries located some 4 metres away. There are safer alternatives. The need for assisted cranking should be very low if proper maintenance is practiced, so the simple provision of carrying adequate jumper leads should suffice. They have the added advantage of being available for use between other vehicles.

In the case of a desire for using a second battery to assist with winching, the provision of isolating switches at each end of the heavy interconnect cable will ensure safety. If this cable serves also as the regular interconnect between cranking and auxiliary batteries then a 60A fuse across each switch provides a protected conductor for when the switches are open.

If there are any doubts regarding the extreme currents that can be realised, try Googling "lead acid battery fault current" or click on this link for a very comprehensive technical White Paper on the subject.

Cheers
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Follow Up By: Frank P (NSW) - Saturday, Dec 17, 2016 at 20:42

Saturday, Dec 17, 2016 at 20:42
Bantam,
Thank you for your detailed reply. Now that I've read it I recall that you've written it all before, so thanks for your patience in doing it all again. I have used quality cabling and enclosed the positive in split conduit for its whole length. Not as good as hose and talc, but the best I can do.

Allan, thanks for your explanation and recommended configuration. It's logical now that you've described it. I believe I can readily modify my setup to comply.

Thanks again to you both.
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Follow Up By: Zippo - Sunday, Dec 18, 2016 at 18:14

Sunday, Dec 18, 2016 at 18:14
Allan, the AGM's I use are Yuasa UXF100-12's (because of the price I paid ....) and their specs quote initial short-circuit current as "~3500A". And those are designed for telecommunications applications.

Any half-decent 100Ah battery should deliver >2000A initially into a short-circuit, which is why you need some resistance in your leads if you want to try DC "field welding".
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Dec 18, 2016 at 18:50

Sunday, Dec 18, 2016 at 18:50
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Yes Zippo, I expressed my values conservatively in order to be credible. The practical "short circuit" in a vehicle will contain some resistance and inductance which limits the current from what can be expected from a solid busbar directly across the terminals. Furthermore, within milliseconds of a fault occurrence, gas bubbles form on the plates raising the battery's internal resistance thus limiting the current.
Nevertheless, you may well realise 3500A from your Yuasa UXF100 batteries.
The link that I provided provides much more detail re fault currents.

In the case of DC field welding, my heavy duty jumper leads provide some resistance and I carry fence wire which can be pressed into service as a series resistor. The kit has yet to be used in anger but in the backyard it worked well with 3mm electrodes on 10mm steel and 24V. Certainly as good as my hobby welder. Would probably need some series resistance for panel welding. One way of providing this would be to attach the 'earth' lead a bit remote from the weld site.
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Follow Up By: The Bantam - Monday, Dec 19, 2016 at 14:16

Monday, Dec 19, 2016 at 14:16
People wonder whay those of us who know a little about batteries and electrics get so damn fussy about what is done and posted.

The consequences of reasonably foreseeable faults can be quite dire and spactacular.

Time and again we hear of "freak accidents" ....... to those of us who know, most of these "freak accidents" are far from freakish.

Much of the time what is required just requires some sound information and a bit of forethaught, before beginning the job.

My second battery is about 3 meters from the main .. it's cabled in 25mm2... yes I have tucked the cable up realy tight under the body and tied it in well as well as threading both hot and cold cables thru reinfoirced hose......... it took me a good half an hour laying under the vehicle on a creeper looking for a route that I was happy with.

people including big manufacturers ARE way too slap happy with this stuff.

The three most dangerous and frequently dismissed as requiring better attention in touring vehicles and boats are.

Battery housings and wiring.
Non-mains 240V AC supplies
Gas containers and anything gas related.

There ARE significant life threatening accidents every year, associated with these 3.

cheers
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Follow Up By: Allan B (Member, SunCoast) - Monday, Dec 19, 2016 at 15:16

Monday, Dec 19, 2016 at 15:16
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Yes Bantam, I agree with all of that.

In particular, the only "Freak Accident" I could envisage is belting around the bend and running smack into a five-legged cow! lol
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Reply By: 9900Eagle - Saturday, Dec 17, 2016 at 20:28

Saturday, Dec 17, 2016 at 20:28
Nick, I have a set of jumper leads that I made up with top quality battery clamps and 70mm welding cable. Those leads are long enough to go from my 2nd battery in the tray to the main battery.

Reason I have this setup is as Bantam and Alan have said, you really can't protect high current wiring of that length in a vehicle unless you have either unlimited space or unlimited money for the protection. A HRC fuse of say 600a will be around 200mm long

My fridge battery is an agm and I am not worried about it starting the engine if needed, so far I haven't needed it.
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Reply By: Member - nick b - Saturday, Dec 17, 2016 at 22:44

Saturday, Dec 17, 2016 at 22:44
In reply to some comments :
The battery i'm using is one that i have moved around from vehicle to van etc, its a dual purpose 100ah .
There are a lot of good suggestion here , but keep in mind this is a simple quick fix jump start in the event that i might get a flat battery just at the wrong time .
so if i use 26mm2 size cable over ~ 4.5 meters be ok
In the L/C i have the charging wire that runs to the back of the wagon inside the chassis from engine bay & is in an air hose for insulation from any damage .
cheers
Cheers Nick b
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Reply By: TomH - Sunday, Dec 18, 2016 at 10:41

Sunday, Dec 18, 2016 at 10:41
While your protection methods are commendable, there are situations where other members concerns are valid.

EG if you have cable through the chassis and you get rear ended and the chassis ends compress and short the cable, disaster looms.
One can only protect against the expected but must allow for the unexpected also.

Personally if I couldnt get the second battery under the bonnet I would use my heavy duty Jumper cables for a flat battery
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Follow Up By: Member - nick b - Sunday, Dec 18, 2016 at 10:51

Sunday, Dec 18, 2016 at 10:51
thks : In this case ....Its a charge size cable & is fused .
Cheers Nick b
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Follow Up By: The Bantam - Monday, Dec 19, 2016 at 16:22

Monday, Dec 19, 2016 at 16:22
The only reason I can think of that you would run a cable to the extreem end of the chassis is for a charging cable for a caravan or a portable battery pack ..... in that case I would probebly be running 10mm2 twin to a 50 amp anderson and it would be protected by a 60 amp breaker.

A lot of people have the idea that running things inside the chassis rails is a good thing, but there are several reasons why it may not be.

In most 4wds, ya best route is on the underside of the body which is well above the chassis and out of harms way.
On caravans and trailers, rigid PVC conduit attached with double sided saddles is about as good as it gets

I have seen lots of damage to cables on caravans and trailers where the cable enters and leaves the chassis rails.
AND people tend to drill, screw and weld on trailer chassis rails without looking inside them.

cheers
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Follow Up By: TomH - Monday, Dec 19, 2016 at 16:35

Monday, Dec 19, 2016 at 16:35
I ran mine down the top of the right hand rail where Mr Toyota had thoughtfully already ran a wiring loom so I just cable tied my heavy cable to that. No problems in two years and 60,000km
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Follow Up By: Member - nick b - Monday, Dec 19, 2016 at 17:48

Monday, Dec 19, 2016 at 17:48
re my earlier comment , In the L/C ~ landcruiser~ i have the charging wire that runs to the back of the wagon inside the chassis from the engine bay & its in an air hose for insulation from any damage . It is fused on the battery end & on the other end ~ camper battery via Anderson plug at the hitch ....
Its is a charging wire only ~ 5 to 10 mm2 ,,
regards to damage , yes i might have a smash or rub & wear a hole in it .
the vehicle has done many thousands of km's . Kimberlies , cape york , birdsville etc over many years ..... so far so good :)
cable ties could break or burn or i could put a screw through it :(
And
As someone once said to me " its only as strong as its weakest point !! "

I would like to thank every one for there comment suggestions & thoughts
very much appreciated
cheers

Cheers Nick b
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