Another Dual Battery Wiring Question

[AK7 Senior Member Find all posts View Profile Close AK7]

I've searched and read a bunch of dual battery threads forums but can't seem to find the info I need. Can anyone help please?

• I have all the cables, lugs, SBI12, ARB tray, etc. Wanting to set up the Auxiliary battery as accessories only (as per Bazza's Pic in this thread). The positive lead to the fuse box attaches to the original battery via a right angled bracket (see attached pic). What are people doing to extend the cable to the SBI12? ie. Cut & join or bolting together with an eyelet? I'd kinda like to keep that right angle bracket in the unlikely event that I'd like to revert back to stock setup but it's not major...
• If I have circuit breakers, should they be in the same layout as per Bazza's Pic? But with 200A breakers for use with the SBI12 override function? Some people mention not having circuit breakers at all. Could someone please explain the reasoning behind this?

Thanks

[Bazza Senior Member Find all posts View Profile Close Bazza]

Hi AK7,
In my wiring set up only my secondary fuse box is connected to my auxiliary battery, not the vehicles fuse box. I assuming you wish to connect the vehicle's fuse box as well. I saw no need to do this as all my high load accessories, radios, additional lights, fridge, ect, are all now connected to my secondary fuse box as shown in my pic that your referring to. As for the CB's, they are there to prevent a dead short either damaging the battery, Redarc unit or causing a fire. You could use fuses in their place but CB's are more convenient, but you should use one or the other.
Bazza

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Not sure why you would want to relocate the factory cable from the main to the auxiliary. The auxiliary is used for specific loads like fridge, maybe lights etc. Leave the factory stuff on the main battery. So what you need is to run a cable from the main battery to the "main" side of the isolator and then run a cable from the other side of the isolator to the auxiliary. I have always put a manual cct breaker between the main battery and the isolator so I can switch it off if necessary. How you set up the power supply from the auxiliary is really open. You can run a main cable to a fuse box and then run to your auxiliaries from there or simply have fused cables running to the +ve terminals on the auxiliary. Depends really how many loads you want to feed.

My set up is a bit different because I am using a DC DC charger in the back of the car with the auxiliary mounted under the charger. I have 4 loads off the auxiliary. Fridge and volt meter which run through a 6 fuse Baintech fuse box which has a single 8 B&S cable run from the +ve and -ve bus to the auxiliary battery terminals and a dual USB and single 12V socket which I have wired direct to the auxiliary battery with fused cable. I did it this way because these were an afterthought and it was easy to put them on the lid of the battery box and just drop the cables onto the auxiliary.

If you have a lot of consumers off your auxiliary then I would suggest using a fuse box. If you have some high current draws like an air compressor or in my case a dual motor air compressor then run a single cable (6 B&S or so) to a fuse bank (ANL type fuses because the fuse boxes usually are limited to 30A per connection and then a total draw depending on the size and brand) and then connect your consumers up there. I still have to do this for my main battery as I have the 6 B&S feed to the DC DC charger, twin 6mm2 (fused at 40A each) cables to the compressor, spot lights, volt meter and sometime in the future DRLs all connected to the +ve terminal on the main battery. The -ve terminal fares better since I use chassis earth for a few items. I will mount up a fuse bank on top of the main fuse box in the near future.

[AK7 Senior Member Find all posts View Profile Close AK7]

Thanks for your responses

Hmmm. I wanted to (also) be able to have existing accessories on the auxiliary battery (ie lights, aircon, radio, 12V & 240V outlets). I hadn't considered a secondary fuse box for additional high load devices but thanks for the idea - will definitely do that later when a few more mods are made I guess that setting up the way you guys are suggesting using the over-ride feature could function in the same manner that I'm after. I might be getting myself a bit confused here (or over complicating things), in a parallel setup is there no voltage drop?

Bazza, regarding circuit breakers, sorry I should have been more concise! I was wondering why people would set up like this without fuses or circuitbreakers... Seems to be tempting fate. I've gone out and bought all the gear to run with 25mm² CSD cable and was thinking 100A fuses between the batteries and SBI would suffice...?

So basically (exisiting fuse block):
Aux Batt --> CB 100A --> SBI12 --> CB 100A --> Start Batt --> Fuse block/starter motor

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

If you ever plan on using the override feature to link the batteries to start the engine (not something I think is a good idea anyway) you will just trip the 100A CCT breakers. Just carry jumper leads if you think you need the back up.

There is no advantage to running factory loads off the auxiliary. Don't bother.

[Pete t pops Junior Member Find all posts View Profile Close Pete t pops]

on the side winder site it mentions using "moving" the start battery to drivers side & using the original battery location for 2nd battery. the advantage being that the new smaller battery could be used for starting & larger orginal battery location (replaced with deep cycle) for camping duties etc. I'm kinda interested, probably just to prove that i can do it more than actually needing to do it.

Ps I am planning a system similar to "the ultimate dual battery setup" (bottom of page redarc wiring guides)
http://www.redarc.com.au/handy-hints/wiring_guides/
But with an ignition sourced on/off switch for overide connection instead of momentary switch, this will allow me to have the bcdc look after the 2nd battery most of the time (therefore extending battery life), but when im camping and only driving for a half hour that day i will select the override switch to on, turning off the bcdc & connecting both batteries together. which will allow the alternator to slam as much current as possible into the 2nd battery(optima) in that short period. Possibly with leighs voltage booster put in for trips away.

[zzsstt Junior Member Find all posts View Profile Close zzsstt]

The BCDC is designed to manage the optimum charging of the aux battery and overcome any voltage drops associated with modern alternators or long cables, and batteries with specific requirements that differ from the primary battery. If your configuration doesn't involve such issues, why fit a BCDC at all?

My setup uses a BCDC with MPPT control, but I use a "normal" Redarc solenoid to control a charging cable that supplies both a BCDC at the front (connected to the aux battery) and an Anderson plug at the back. The plug connects to a second BCDC in the camper trailer. When the engine is running this circuit is live and both the camper trailer battery and car aux battery are charged by their respective BCDCs. I also supply switched 12V to the input selectors on both BCDC's, such that when the engine is running (and for the trailer when it is connected to the car) both BCDCs select "alternator" input. When the car is not running, both default to solar input. Because the additional charging circuit is isolated from the main battery by the Redarc relay, when the car isn't running if I plug a solar panel in to the anderson socket on the rear bumper (rather than having the trailer plugged in) the car BCDC will charge the aux battery from that panel. I didn't bother doing ABR's battery swap trick, because the aux battery in the car only runs the fridge and can be charged by solar if required. I also saved weight by using a 60Ah LiFePO battery that gives the same usable capacity as a 100Ah deep cycle, but weighs only 10kg or so. It is happy to run the Engel for at least a couple of days under most conditions, and if I'm not driving I just plug a solar panel in to the Anderson socket. I also like to keep a decent sized primary battery because it runs the winch. If I ever need to parallel the primary and aux batteries (I haven't ever needed to in the past) I'll use jumper leads!

[AK7 Senior Member Find all posts View Profile Close AK7]

If you ever plan on using the override feature to link the batteries to start the engine (not something I think is a good idea anyway) you will just trip the 100A CCT breakers. Just carry jumper leads if you think you need the back up.

I don't think it's a good idea either, but if the accessories are running off the same battery as the starter is, then you need to use the override to be able to start the car if that battery goes dead, yeah? I don't see the point in carrying jumpers (for starting your own car) if you have dual batteries - kinda defeats the purpose of keeping the starting battery in good state...

Also, if I do go to 200A breakers, it's probably a good move to go to 32mm² cable then for the higher Ampere rating, yeah? 25mm² CSD is only rated to 215A...

There is no advantage to running factory loads off the auxiliary. Don't bother.

I'd like to be able to run all auxiliaries (and later on any additional auxiliaries) without fear of draining the starter battery (and not having to run the engine to prevent that drain).

on the side winder site it mentions using "moving" the start battery to drivers side & using the original battery location for 2nd battery. the advantage being that the new smaller battery could be used for starting & larger orginal battery location (replaced with deep cycle) for camping duties etc. I'm kinda interested, probably just to prove that i can do it more than actually needing to do it. Ps I am planning a system similar to "the ultimate dual battery setup" (bottom of page redarc wiring guides) http://www.redarc.com.au/handy-hints/wiring_guides/

That seems to be exactly what I'm thinking of (but without the change-over relay and BCDC) and moving the starter cable rather than the fuse box cable. Maybe I should just do that... I don't suppose you know how people are people extending the starter cable to reach the other side? Just replacing the whole starter lead or screwing/crimping to the existing cable (and obviously insulating the join)? Would love to do a setup like that but can't justify it at all

[Pete t pops Junior Member Find all posts View Profile Close Pete t pops]

So AK7, for your setup the most important thing to you seems to be being able to run the original 12volt outlets + stereo for a long time & still be able to start it with confidence at after that? You dont seem too worried about additional stand alone outlets off an auxilary battery for a fridge or whatever.

My suggestion would be to setup your sbi12 as per the redarc wiring guide "always start from both batteries" and put a supercharge allrounder in as your main battery. With no loads off the 2nd battery it would always be there fully charged to help start after using stereo etc.

or am i on the wrong track...., ps i am not an auto elec just a 12volt hack that cant bair to pay anyone to do basic wiring

[zzsstt Junior Member Find all posts View Profile Close zzsstt]

I don't think it's a good idea either, but if the accessories are running off the same battery as the starter is, then you need to use the override to be able to start the car if that battery goes dead, yeah? I don't see the point in carrying jumpers (for starting your own car) if you have dual batteries - kinda defeats the purpose of keeping the starting battery in good state...

The only things that run from the starter battery are the things that Toyota fitted, and things that are only used when the vehicle is running (like spotlights, winches etc.). Extra "camping" loads like fridges and camping lights run from the aux battery. Under those conditions the starter battery should never be depleted, and the batteries never need to be paralleled together to start the vehicle. I would suggest that other than in cases of actual battery death (failure, not depletion), the only possibility for parallel connection of the batteries would be in extreme winching scenarios when the engine had died.

As stated by a previous poster, moving factory loads (i.e. standard fittings) from the starter battery to the aux battery is not required. Toyota intended them to be connected to the starter battery and they are either powered via the ignition switch or permanently "on" by design (i.e. security codes for radios etc.). Unless the car has been altered (badly) or is faulty, there should be no loads on the starter battery that would deplete it in a time frame shorter than several weeks. Moving just the starter cable would appear to result in the starter motor running from one battery, and EVERYTHING else running from the other. Apart from the issues of charge management and cross connection that result from that modification, even conceptually this would appear strange because the car wouldn't start if EITHER battery was depleted or failed, because you need power to the controls (ECU etc.) as well as the starter motor!

If I have misunderstood and you are simply considering, in effect, moving the starter battery to the passenger side by extending the battery leads (rather than the "starter leads") then you still require the additional relays etc. to manage your auxillary battery, wherever you fit it!

[zzsstt Junior Member Find all posts View Profile Close zzsstt]

So AK7, for your setup the most important thing to you seems to be being able to run the original 12volt outlets + stereo for a long time & still be able to start it with confidence at after that? You dont seem too worried about additional stand alone outlets off an auxilary battery for a fridge or whatever.

Many builders, farmers etc. have a stereo (and UHF) going all day in their parked car whilst they are working, without ever even considering that the car won't start at knock-off time. When I'm building fences my Hilux is often parked at 7.30am and left until 4.00pm or later with the UHF on and the radio playing. The standard battery and wiring has never failed me, nor did it in my previous Hilux. In this situation I'd suggest perhaps a standalone "jumper pack" would be the cheapest and easiest approach to provide that "ring of confidence"? Plugged in to a cigarette outlet to maintain it's charge without any mofications to the vehicle, it's always there and can start other peoples cars as well! Just a thought!

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

If you want to swap everything over to the other side then go right ahead. Make sure you post pics. It should be as easy as extending the +ve and -ve cables across in front of the radiator to the new smaller starter battery. As for cable size the bigger the better. And then run another big mother cable back to the auxiliary from the isolator next to the main battery.

I know you say that Derek recommends this on his site but even he didn't do that to his 150 unless he has done it recently and not updated his build which is of course possible.

If you want to run ALL the factory auxiliaries off the auxiliary battery and just have the main battery for starting the car then you will need to do some wholesale wiring changing. Before you start make sure you have access to the factory wiring diagram and a good automotive electrician if you aren't yourself.

As I said earlier I cannot for the life of me understand why you would bother to do this. If all you want is an alternative power supply to run the radio without flattening the main battery then just swap this over and have a separate dedicated supply for noise. Interior lights etc as well? You can easily have some LED light bars running off auxiliary sockets from your auxiliary battery. More flexible and probably better light.

When I set my DC DC charger up I read the 'ultimate dual battery set up' and was really left wondering why. Are you going to also run solar in feed? The DC DC chargers have their own auto voltage on and off as well as a trigger wire to tell the charger when to wake up (blue wire). This I have connected to a circuit that is on when the ignition is on. Lots of places to steal this signal from. Under the bonnet you can tap into the dark green wire running to the windscreen wiper motor up over the brake master cylinder or if you have the auxiliary battery inside the car any of the power sockets or in my case the light green wire that sits near the 220V inverter that connects to a 12V outlet in the GXs. This way the DC DC charger is asleep until the engine is on and the alternator is running and then some 30 seconds later the DC DC charger wakes up. Using a changeover relay you can have a solar in feed on the normally closed connector and the feed from the main battery on the normalyl open connector, fire up the engine and the relay flips over and then the DC DC charger takes its power from the main battery/alternator.

I have just finished wiring a camper with a Redarc isolator and their BCDC1240. 6B&S goes from the main battery to a 100A manual cct breaker thence to the Redarc isolator and to the back of the car and an Anderson plug. When the camper isn't connected you can trip the breaker and the Anderson plug carries no voltage. Connect the camper to the Anderson plug with the cct breaker closed and current flows to a pair of terminals under the camper. From there power runs to the OEM camper fuse and distribution box and also to the changeover relay terminal 87. Again the good old Britax beast that will accept 10mm2 cable. The power from the car goes to this normally open contact on the relay. That contact is paralleled to the DC DC charger trigger wire (blue wire) and changeover relay terminal 85 to switch the relay when the car is running. Also at the changeover relay the normally closed contact (87A) is connected to an Anderson plug under the camper where a solar panel can hook into. The -ve terminal is connected to a tapped hole in the chassis, a common point in the camper distribution box and also a common point for the two 120AH auxiliary batteries and changeover relay etc. Quite a neat set up even if I say so myself.

In this case there is no additional battery in the car nor is there a fridge in the car that needs power. The 3 way fridge in the caravan will run with the car running and then on gas or 240V if someone else is paying!

During the second day of the install his main battery went flat which was the result of the radio going, doors left open and lights on AND a battery that was down to about 60% electrolyte. So we jump started the car with some 70mm2 cables. My jumper leads.

So my suggestion is decide if you want to do as Derek suggests and therefore run some new cable across the engine bay to the RHS and fit a smaller battery for starting and all things OEM and then fit the isolator or if you are going to use a DC DC charger then mount that near the auxiliary.

I don't know how many PPers have ever been caught with a flat battery and unable to start their car but it has happened to me twice in about 30 years of 4wding. Both times my wife was the one inconvenienced and both times she walked over to the shed and grabbed the jumper leads and jumped the car off the auxiliary, then drove to a place to buy a new battery. She's a keeper for sure.

I would suggest that if you have need to start off both batteries then use a separate circuit as shown on the Redarc site with bigger breakers and the larger of the two isolators they offer. Assuming you are driving in the snowy at the peak of the cold season. Or just buy some decent jumper leads for the one in 760 million time that you try and start the car and the main battery has gone flat.

Like I said at the outset if you want to do the whole rewiring thing then please go ahead and make sure you post pics of your journey. For me it would be way too much effort for negligible (if measurable) return.

If you want pics of either of the set ups I have recently done then just ask.

By the way these two threads might help you too...

http://www.pradopoint.com/showthread...n-Sbi12-system

http://www.pradopoint.com/showthread...Redarc-or-Ctek

Without reinventing that particular wheel or opening up the debate again I wouldn't bother with the DC DC system unless you are charging different types of batteries; lead acid and AGM for example. I did because I am. And if you are running an AGM battery give good though to getting it out of the engine bay because it is probably too hot in there (ABR make a foil/foam battery shield that seems a good investment) for it and they are really heavy mothers.

Michael

[zzsstt Junior Member Find all posts View Profile Close zzsstt]

ABR make a foil/foam battery shield that seems a good investment

I completely agree with everything else you said, but I would need to see "numbers" to believe the battery shield does anything at all. Insulation, no matter how good, can only ever slow down the rate of heat transfer. If the battery was encased in a massive thickness of insulation it would, nonetheless, eventually heat up to the same temperature as the rest of the engine bay unless it also had some active cooling process. A thin sleeve of insulation, like the battery shield, will delay the rate of heating only marginally and make no difference to the final temperature. Perhaps if the engine is running only for a few minutes the battery might stay a fraction cooler, but over the course of an hour or two the battery will get to exactly the same temperature. And, of course, the insulation will keep it warm for longer when the engine is switched off!! That is before we consider that charging a battery tends to make it hotter, and the insulation prevents that heat escaping!

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

zzsstt actually insulation can and does isolate temperature. It is a property of such materials. There is a temperature gradient across the material irrespective of exposure time. For example high temperature piping can have superheated steam running inside at 550C and 20MPa with metal temps pretty much the same temperature, two layers of insulation later and the outside cleading is less than 57C. Yes the ambient temp is less again but there is not many kW of radiation happening. The converse is also true, we build a room (for the want of more explanation) that is 350C inside 55C outside and filled with pipes and supports. Piping at 550C is insulated to keep it hot and mild steel supports are insulated to keep them cool. But here is not the place to discuss thermodynamic properties of insulation. Top and bottom of the battery will be the same with or without the shield but if made from the correct material the sides will be cooler. I don't however know anything about the shield which is why I said "seems".

[zzsstt Junior Member Find all posts View Profile Close zzsstt]

zzsstt actually insulation can and does isolate temperature.

No, that is simply not true. Insulation slows the flow of energy. In the examples you quote, there is a temperature gradient because there is a cooling process at work. For example, there is a temperature gradient in your pipe insulation because the ambient temperature outside the insulation is low, relative to the steam. The rate of energy flow from inside to outside is less than the rate at which the outside cools (radiates the heat to the atmosphere), so the outside remains "cool" relative to the inside. If you turn off the steam, under your theory the inside of the pipe should stay hot forever - it doesn't! In the same way, the steel fittings are insulated but unless they have a means to transfer heat away (probably they are actually connected to the outside structure and so conduct heat away) they will also slowly heat, and eventually reach the same temperature as their surroundings.

In the battery example if we assume the battery is completely enclosed then it has no cooling. The insulation will slow the rate of heating, but even if just 1J per hour gets to the battery that joule has nowhere else to go, so the battery will heat up.

Insulation results in a permanent temperature gradient only in the case where one "side" is being actively heated and the other side is being actively cooled - even if the "active" process is simply the addition or removal of energy to another large heatsink (like the atmosphere). In a static situation the transfer of energy through the insluation, no matter how slow, will eventually cause the temperature of the two sides to equalise.