Ceap DIY Dual Battery Setup.

Submitted: Thursday, Jul 28, 2005 at 17:30
ThreadID: 25140 Views:13436 Replies:9 FollowUps:16
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I was just having a wander through supercreapy autos (as you do) and noticed they had these little DIY Dual Battery kits. Comes with a Voltage triggered (13.5 in, 12.5 out; same as Redarc I think?) solinoid (with optional manual overide), crimps, some 8g cable and instructions.
All of that for $95 inc GST. Seems reasonable to me. Personally I'd probally use 4g cable but it'd certainally get you started. Also be good for a campertrailer charging setup too so you didn't have to unplug the tralier to disconnect the battery from the car.
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Reply By: Mainey (WA) - Thursday, Jul 28, 2005 at 22:30

Thursday, Jul 28, 2005 at 22:30
Jeff
how big (or small) is 4G and 8G cable, in mm Dia. (of actual metal cable) because to use in a Camper Trailer situation you would need minium 25mm cable to avoid voltage loss at the Aux battery.
AnswerID: 122640

Follow Up By: Member - MrBitchi (QLD) - Friday, Jul 29, 2005 at 08:15

Friday, Jul 29, 2005 at 08:15
Last time I looked 25mm = 1 inch. Geez, mate, you could power the Brisbane CBD through that ;-)
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Follow Up By: Mainey (WA) - Friday, Jul 29, 2005 at 10:43

Friday, Jul 29, 2005 at 10:43
Yeah, I didn’t place "squared" into the “would need minium 25mm cable” :-(

2 B&S is 32.15 SQ MM is 188 AMP
3 B&S is 25.72 SQ MM is 168 AMP
6 B&S is 13.56 SQ MM is 103 AMP
8 B&S is 7.91 SQ MM is 74 AMP

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Follow Up By: Member - Jeff M (WA) - Friday, Jul 29, 2005 at 11:19

Friday, Jul 29, 2005 at 11:19
Umm, yeah I don't think you'd have enough cable in the kit to run all the way back to the camper, you'd need to use your own. The Size of the cable would depend on the size of the battery and or the load in the camper. 8g would be fine for a small AGM running lights etc. 4g Would be better.
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Follow Up By: drivesafe - Friday, Jul 29, 2005 at 19:56

Friday, Jul 29, 2005 at 19:56
Hi Ray, in Australia, there is a standard for AC 240 volt cable but the problem is there is no such standard for Automotive type cable in Autsralia.

When purchasing cable and getting what you want for the currents you want the cable to carry, use the sizing system Mainey used above, the squared area of the copper EG 13.5mm2. This way you can use a chart that equates the squared area of the cable to the exact current capacity of the wire.

Cheers
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Reply By: Ray Bates - Friday, Jul 29, 2005 at 09:53

Friday, Jul 29, 2005 at 09:53
You may think that I am a bit of a dill regarding all these different wire gauges. I was brought up in the old school and work on the old British Standard wire gauge ie Australian Standard wire gauge where the wire was measured by the cross sectional area not the diameter and where the smaller the number the thicker the cable. This is contary to the American standard. I have also noted that some cable manufacturers market their cable on the diameter of the outside insulation so be very carefull when you buy cable
AnswerID: 122672

Reply By: Member - t0me (WA) - Friday, Jul 29, 2005 at 10:55

Friday, Jul 29, 2005 at 10:55
Was it called Mason or Matson or something like that?
If so I fitted one to my Challenger and it seems to work fine. I've not had any heavy duty use of it yet but it was easy to fit. They give you heaps of cable (Decent size cable). I got mine from a 4x4 shop for $99 which was cheaper than the price of it in a battery shop ($129) so $95 seems a pretty good price. States on the pack its perfectly suited to charging batteries of different types (its then up to the charging system to manage to pump out a full charge).

AnswerID: 122680

Follow Up By: Member - Jeff M (WA) - Friday, Jul 29, 2005 at 11:19

Friday, Jul 29, 2005 at 11:19
Yeah I think that's the one.
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Reply By: Member - MrBitchi (QLD) - Friday, Jul 29, 2005 at 11:10

Friday, Jul 29, 2005 at 11:10
With the Redarc solenoid the "optional manual overide" is designed to allow you to use the second battery as a start battery if your main goes flat.

DO NOT ATTEMPT THIS UNLESS YOU HAVE USED HIGH CAPACITY START CABLE!

By this I mean cable capable of carrying around 500amps. You'll fry your electrics and quite possibly start a fire.
AnswerID: 122689

Follow Up By: Member - Jeff M (WA) - Friday, Jul 29, 2005 at 11:23

Friday, Jul 29, 2005 at 11:23
Doesn't the overide just join the batteries? Would cause equalisaition and not be terribally good for the bat's but would give the starter enough to get you out of trouble, that's what I thought it was for anyway...
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Follow Up By: Member - MrBitchi (QLD) - Friday, Jul 29, 2005 at 11:50

Friday, Jul 29, 2005 at 11:50
Yes it does, and if the difference of charge state of the two batteries is large (one fully charged, one flat) then there will be an initial large current flow from fully charged battery to flat battery. Then when you hit the key the starter will draw current from both batteries as they are now connected in parallel. This current will easily exceed the capability of 6mm² cable.
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 29, 2005 at 11:55

Friday, Jul 29, 2005 at 11:55
6mm cable is a lot smaller than 8g that's supplied with it? I use 6mm for my fridge and 8g for my aux fuse box, 8g is like at least twice the size from what I can see... But yeah I know what your saying. As I said at the start, I'd use 4g if it were me (I have done on my own system).
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Follow Up By: Member - MrBitchi (QLD) - Friday, Jul 29, 2005 at 12:03

Friday, Jul 29, 2005 at 12:03
My sparkie made up some cables for me that are actually slightly thicker then the standard earth cable from the main battery. Not sure what gauge, they're about 10mm thick which is about 000 gauge.

Could kick start the Enterprise with them me thinks ;-))
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 29, 2005 at 12:13

Friday, Jul 29, 2005 at 12:13
LOL, good stuff. My Purewave Inverter's running on the same cable they use in the Western Power Transformers. (work sponsered from a mate of mine). It was a bit stiff (not very flexible) but once all in position it looks pretty hardcore! ;-) I figured the Inverter can draw anywhere up to 45amps continuous and it's located at the back of the vehicle so I might as well go over the top and try to eliminate as much voltage drop as possible.

Only trouble when you start using that kind of stuff it is REALLY hard to make it fit neatly in the car and getting it through the firewall.... Well, let's just say it a 3 beer 5 swear word rating. LOL
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Follow Up By: Mainey (WA) - Friday, Jul 29, 2005 at 22:29

Friday, Jul 29, 2005 at 22:29
(QUOTE)With the Redarc solenoid the "optional manual overide" is designed to allow you to use the second battery as a start battery if your main goes flat. DO NOT ATTEMPT THIS UNLESS YOU HAVE USED HIGH CAPACITY START CABLE! By this I mean cable capable of carrying around 500 amps.(end quote)

Mr B, 500 Amp cable would really be overkill... I would suggest, 0 B&S which is 200+ amps, would be the lead of choice as it is H/D starter cable, and nothing higher would be required.
When the Aux is put in parallel to a dead battery you run the risk of loosing it's power as it attempts to equalise with the dead starter battery to a point where the vehicle won't start.

It's far better to by-pass the dead battery totally by disconnecting the dead starter and Aux battery connections at the solenoid and SWAPPING them over and the dead battery will be recharged while you drive : - )
Remember to swap the batteries back to their correct positions after some hours driving or when you get home and you can get it onto a decent battery charger.
When you start off the Aux battery alone as it will do far less damage to your battery system, it would be a deadly problem to be stuck in the bush with two ½ dead batteries.
Was one of the reasons I changed my last isolator system.
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Reply By: Member - Collyn R (WA) - Friday, Jul 29, 2005 at 11:19

Friday, Jul 29, 2005 at 11:19
A few points
The US AWG standard is actually based on cross sectional area - but is expressed in non-related numbers.

'Amp ratings' of cables are totally meaningless in terms of voltage drop. This rating is a fire rating only and indicates the maximum current trhe cable can carry withiout it's insulating melting. Thus a '50' amp cable may have an acceptable 0.2 volts drop over a metre or two, but as much as 10 volts drop over (say) 50 metres.
These ratings also vary hugely depending on insulation material.

The only meaningful indication is conductor cross sectional area in square millimetres - as is used in house wiring. It is the ISO standard. Thus 2.5 mm mains-voltage wiring (in Aust) has 2.5 sq mm conductors.

Auto cable (the stuff you buy from auto parts stores) is rated in terms of overall diameter - that is insulation and all! Thon ONLY information it gives is the size of a hole you could poke it through.

6mm auto cable is not too bad - it's about 4.6 sq mm. 4 mm auto cable is usually 1.8 sq mm - less than half the size most people think is. 2 mm auto cable is about 0.5 sq mm (better than wet string but only marginally). Exact comparisons are not possible as auto cable insulkation thickness varies from maker to maker.

Not realising the above is the main reason why so many 12-volt fridges (and charging circuits) dont work too well.
Collyn Rivers
AnswerID: 122690

Follow Up By: Member - MrBitchi (QLD) - Friday, Jul 29, 2005 at 11:41

Friday, Jul 29, 2005 at 11:41
In the above scenario (using the secondary as a stert via the overide function) the voltage drop is insignicant as the distances involved would be less then a foot or so per cable. Current carrying capability is the key when starting the car, and momentary current can be in the hundreds of amps.
If you use 6mm² cable then you have a charging system only, not one that can be used for starting.
Redarc recommend 19mm² cable to carry 100 amps continuous.
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Follow Up By: GraemeD - Friday, Jul 29, 2005 at 13:27

Friday, Jul 29, 2005 at 13:27
Hey Collyn, I think I've seen your OKA around. Were you by any chance in York a month or two ago, parked down by the river? If so, I apologise for any unsightly streaks on your paintwork, my wife and I were drooling over it. It looks like just the kind of thing we'd love for doing an trip round Australia, then overland back to Scotland (a very long term dream). :)

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FollowupID: 377890

Reply By: Member - Collyn R (WA) - Friday, Jul 29, 2005 at 16:49

Friday, Jul 29, 2005 at 16:49
GraemeD
Not mine - but there are quite a number of privately-owned OKAs around - probably about 60.

They are a truly excellent vehicles as long as they are properly maintained. One needs to be cautious when buying as many are ex-mining and ex-tour vehicles and have not been well enough looked after: hence the price range: from $30,000 for a rough one to well over $100,000 for a really good one.
Collyn Rivers
AnswerID: 122733

Reply By: Mainey (WA) - Friday, Jul 29, 2005 at 17:28

Friday, Jul 29, 2005 at 17:28
Battery Cable is sized as “mm squared” and is commonly referred to by B&S sizes.
8 B&S is 7.5 mm squared
6 B&S is 15 mm squared
3 B&S is 25 mm squared
2 B&S is 36 mm squared

Automotive wire
1.2 mm squared wire is generally rated to 10amps
2.0 mm squared wire is generally rated to 15amps

So the Redarc spec cable is between 3 B&S (15mm) and 6 B&S (25mm)

Where does the 4 or 8 guage cable fit in with the above size's ? ?
AnswerID: 122743

Follow Up By: Member - Norm C (QLD) - Friday, Jul 29, 2005 at 20:10

Friday, Jul 29, 2005 at 20:10
I found an economical way to get good cable was from an electrical wholesaler. Got 25mm squared double insulated welding cable with what looks like thousands of small strands so it is very flexible for it's size. By Mainey's post it is the equivelant of 3B&S, but double insulated. Got it for about $3.60 a metre from memory. It runs from engine bay through chassis rail, via 175 Amp Anderson Plugs to dual batteries on camper trailer. I measure voltage drop to be .04V. Next to nothing.

When I bought my fridge (a Reefer from Refrigeration Research), they supplied 10mm squared cable for it. Similar to Collyn's post above, they said almost all problems reported to them can be traced to inadequate wire dimensions used. They now supply cable with the fridge to overcome this. To show how poorly educated the industry is on this, two auto electricians have told me that is stupid overkill; 4mm cable is heaps to run a fridge. Didn't use either of them.
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Reply By: Ray Bates - Friday, Jul 29, 2005 at 19:52

Friday, Jul 29, 2005 at 19:52
Just a quick follow up. I have used 4g OFC power cable for my set up from Altronics. It is very flexable as it has many strands in it. The only problem is that you can only get it in red & black
AnswerID: 122764

Follow Up By: Mainey (WA) - Friday, Jul 29, 2005 at 21:57

Friday, Jul 29, 2005 at 21:57
Ray
what colour do you want ? ?

Use red for your pos (+) leads and black for your neg (-) leads

Will look neat and professional, you will always know which lead is active.

What is the actual dimension and amp capacity of "4g OFC" cable ? ?
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Reply By: Member - Duncan W (WA) - Friday, Jul 29, 2005 at 20:06

Friday, Jul 29, 2005 at 20:06
Jeff getting away from all the wire jargon, is this set-up an under bonnet or one of those battery boxes that fits in the back of the bus or van?

Cheers Dunc.
Dunc
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AnswerID: 122768

Follow Up By: Member - Jeff M (WA) - Monday, Aug 01, 2005 at 11:22

Monday, Aug 01, 2005 at 11:22
This setup does not include the battery or battery mounts, so it could be used for either type.
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