Another Dual Battery Wiring Question

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

What he said. The radio switches off after 30 minutes according to my wife so I could see a benefit in wiring that to constant power on the aux. 12V sockets can be run off the aux as can the fridge power. The rest? Do you want to run your wipers or rear demister with the engine off?

Anyway up to you, let's know what you decide. Maybe list the ancillaries you need with the car off and see if the gestalt of PP can come up with ideas.

And yes Derek is Derek Bester of ABR Sidewinder. Sorry I assumed that fitted. Derek is a nice bloke and quite clever. Not that i have ever met the guy, just exchanged a few emails and he helped a workmate sort out the wiring in his Ovlov for power to the camper. What a nightmare that wiring is for anyone who wants to stuff with it.

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What controls the radio to be switched off after 30 minutes? Merely moving it to a different power source may not change this.

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

Interrogating the boss yielded many screams and much pain but I endured this and for the benefit of PP discovered that when the 'key' is on acc and the radio on it automatically turns off after 30 minutes. Why or how no idea. However the whole shooting match shut down not just the radio so I would surmise it is a timer on the power supply not the radio.

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

Just a guess, because I've never tried it, but given that the "acc" mode is just a press of the starter button I would assume that it is all controlled by the computer and the computer assumes after 30 minutes that it has been left on by mistake and switches off. Probably a reasonable assumption given the nature of the vehicle, i.e. not a tradies ute that is likely to be left with the radio on! In terms of this thread this is both a benefit and a nuisance. A benefit in that the battery (probably) cannot be flattened accidentally by leaving "acc" circuits switched on, and a nuisance in that if you want to listen to a test match you'd have to keep pressing the "go button" every 30 minutes!

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

zzsstt is spot on, actually remember reading it in the manual somewhere. things you do when you get a new car

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

All your questions have been answered in previous posts. But just for the sake of it:

Q1/ why do people swap....

Answer. They don't. Derek (who trades as ABR Sidewinder) sells an auxillary battery wiring kit that allows the "factory" battery to be relocated to the passenger side of the vehicle. This is done solely because the driver side space is smaller, so it allows a smaller battery (still perfectly adequate) to be used as the "factory" battery, and a larger "auxillary" battery to be fitted on the passenger side to run fridges etc. The factory battery, wherever it is located, is still used for ALL factory functions. The auxillary battery, wherever it is located, is only ever used for aftermarket products like fridges.

Q2/ Is there anyone with this configuration..

Answer. If you're talking about Dereks approach then there is no problem at all. If you are talking about what you propose (splitting the factory wiring between two batteries) I would seriously doubt that anybody has ever done it.

Q3/ Aside from essential service...... is there a reason it should not be used.

Answer. Because it serves no purpose and is a huge amount of work. (See also Answer 4, below)

Q4/ If power loss is such an issue....

Answer. I think you are confusing too many issues. Temporary disconnection is not the problem. The problem is that you are proposing splitting the basic vehicle functions between two batteries. That serves to create an additional single point of failure (if either battery is dead the car won't go). It also raises concerns of voltage control etc. - which battery does the management system look at to decide it is fully charged? Potentially the management system (hanging from the fuse box) will see a "full" battery and reduce the charge rate whilst the "starter" battery is still near death. I suspect there are many other potential problems, but as the configuration serves no apparent purpose there seems no reason to go looking for them!

I am still uncertain of exactly what factory fitments you would be using that would risk draining the battery. There's really only the radio, tiny inverter and ciggie lighter socket, all of which require the ignition to be left on unless they are rewired, and none of which are really designed for long term use with the car stationary. If you want to use an inverter for long periods, or anything powered from a ciggie lighter socket, it is surely easier and far less risky to install a conventional auxillary battery and leave the basic functioning of the car the way Toyota designed it.

Outstanding. Thankyou Now I see why that idea is not a good one. I'd heard people mention "moving the starter battery" and presumed they meant moving the starter motor to the auxiliary battery. I never mentioned or considered splitting the devices in the fuse box. It was either the whole fuse box or the starter. Not a great deal of work to do that.

As for power usage, I will be getting other auxiliaries as time passes (fridge, CB, winch, etc). At any given time I might want to use headlights, internal lights, radio, etc. without the motor running. Very rarely though. I have had to do this in the past and drained car batteries as a result. Now that I have an automatic vehicle, having some form of battery redundancy system is important to me. Jumpers won't cut it - there's not always someone around who can help. Whatever the option is, it needs to be built into the car.

Interrogating the boss yielded many screams and much pain but I endured this and for the benefit of PP discovered that when the 'key' is on acc and the radio on it automatically turns off after 30 minutes. Why or how no idea. However the whole shooting match shut down not just the radio so I would surmise it is a timer on the power supply not the radio.

Interesting. If that's the case, it wouldn't be surprising if there was a low voltage cutoff mechanism as well. I hope you came through that saga unscathed. As for your wife, if she does it to you again, give her another 30 minutes in there.

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

You jump start off your auxiliary. Usually enough juice in both to get the engine going, my experience anyway.

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

You jump start off your auxiliary. Usually enough juice in both to get the engine going, my experience anyway.

Cool. Weren't you saying that setup is not a good idea? Or are you referring again to having jumper leads and jumping with those?

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.

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

A typical auxillary battery setup has a solenoid that connects the two batteries together when it senses that the alternator is producing power (the voltage produced by the alternator to charge the battery is higher than the "full" battery voltage). When the engine (and hence the alternator) are stopped, that solenoid disconnects the auxillary battery, so whatever is connected to the aux battery can no longer deplete the factory battery. An addition to this system is a manual triggering of the solenoid via a switch. This allows the two batteries to be connected together to provide extra power in the event of a flat factory (starter) battery. However such a system should rarely be required, because the factory battery shouldn't ever be depleted! It is, in fact, more frequently used to allow the auxillary battery to assist with winching, especially when the engine has drowned or stalled. Whilst such a solenoid override is not hard or expensive to install, I personally have never bothered. It is one extra thing to go wrong, and as I carry jump leads I can always connect the batteries with them if the need arises. I would never fail to have jump leads (how would I weld without them?) so it is not a problem!

With regard to your list of future accessories, the fridge will obviously run from the auxillary battery. The winch however should be connected to your factory battery, it is more suited to the high current production needed by a winch and can draw from the alternator directly, rather than through the solenoids and fuses that will exist between the alternator and the auxillary battery. The UHF can be installed to either battery, it draws very little power. I always install them on an ignition switched circuit from the factory battery because then they power down when I turn off the car and I don't have to remember to switch them off. Saying that, my work vehicles (where the radio and UHF are left on all day) are all key started (so can be left in "acc" mode without a 30min power down!) have no auxillary batteries and I've never had a problem with the radio and UHF depleting a battery. For things like UHF and radio, you might also consider handheld/portable units for use when the car is not running. They avoid having to turn the volume up and annoy other people, having to leave the car doors open in the rain, having to run across the campsite only to find that the UHF has picked up static or a truckie and not your mate, etc. etc.

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

I was referring to jumper leads or a dedicated start with both batteries set up (in addition to any isolator to charge the auxiliary) and not just tripping the basic isolator to connect the two. Given the cost I would just go for the extra heavy duty jumper leads. Mine are hand made from old commercial welding cable. Heavy but effective.

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

A typical auxillary battery setup has a solenoid that connects the two batteries together when it senses that the alternator is producing power (the voltage produced by the alternator to charge the battery is higher than the "full" battery voltage). When the engine (and hence the alternator) are stopped, that solenoid disconnects the auxillary battery, so whatever is connected to the aux battery can no longer deplete the factory battery. An addition to this system is a manual triggering of the solenoid via a switch. This allows the two batteries to be connected together to provide extra power in the event of a flat factory (starter) battery. However such a system should rarely be required, because the factory battery shouldn't ever be depleted! It is, in fact, more frequently used to allow the auxillary battery to assist with winching, especially when the engine has drowned or stalled. Whilst such a solenoid override is not hard or expensive to install, I personally have never bothered. It is one extra thing to go wrong, and as I carry jump leads I can always connect the batteries with them if the need arises. I would never fail to have jump leads (how would I weld without them?) so it is not a problem!

Thanks. Winching is one of the things that I want this setup for. It's not about how often the setup is there. It's about having it there in case it ever does happen. Akin to nobody liking being bogged, but the sensible ones have recovery equipment on hand "just in case". What equipment they have on hand is ultimately down to personal choice. I have a good set of jumper leads. I don't want to have to use or carry them. That's just personal choice.

With regard to your list of future accessories, the fridge will obviously run from the auxillary battery. The winch however should be connected to your factory battery, it is more suited to the high current production needed by a winch and can draw from the alternator directly, rather than through the solenoids and fuses that will exist between the alternator and the auxillary battery. The UHF can be installed to either battery, it draws very little power. I always install them on an ignition switched circuit from the factory battery because then they power down when I turn off the car and I don't have to remember to switch them off.

The winch will get cabled by an auto-elec. The rest of the stuff I'm not too worried about yet. As long as the config I use can accommodate additional devices, it's all good. One other thing I'll likely add down the track is a decent 220-240VAC inverter and run all sorts of things off it (within the capacity of the inverter).

For things like UHF and radio, you might also consider handheld/portable units for use when the car is not running.

I'm after a Uniden UH078 SX-NB. I want to be able to use it in my work cars as well. I'll wire in an antenna into the Prado. If ever I (or the next owner) want to install a head unit, the antenna will already be in there.

I was referring to jumper leads or a dedicated start with both batteries set up (in addition to any isolator to charge the auxiliary) and not just tripping the basic isolator to connect the two. Given the cost I would just go for the extra heavy duty jumper leads. Mine are hand made from old commercial welding cable. Heavy but effective.

Just to clarify, you're saying going through the isolator is a bad idea? And that having an extra cable between the two batteries with a manual switch is a better option? I'm assuming so - just want to be 100% clear. It's something I've considered and would be more than happy to install. I saw the over-ride and thought that might be a good option, but I have noticed hardly anyone uses it. Thanks again Another good reason why I ask questions on this forum

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

The winch is just about the easiest thing to wire up, it's just two great big cables straight to the battery. The only addition to this setup would be a whopping great big isolator switch if you're concerned about the "watch me use a paperclip to cut this car in half" trick!

I would never go anywhere without jumpers leads. They allow me to connect two batteries (including the one in my camper trailer if required) if I need to jump start my own vehicle, they allow me to jumpstart other peoples vehicles, and they allow me to weld if required. They also provide me with a source of heavy duty cables and connectors should a battery lead or earth wire get broken. I have even used jumper leads to run a winch in another vehicle - a guy bogged his ute, then went and got his wifes 4WD and bogged that, then he borrowed a neighbours Land Cruiser and flattened it's battery by winching with the engine off. I used a non-winch vehicle with jumper leads to both start the 'Cruiser and assist it to winch out the two bogged vehicles. For the amount of space they take up they are (for me) an essential item, and every vehicle I own has a set. As you say, personal choice!

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

I already have a good set of jumper leads. I just want an inbuilt way start the car if ever the starter goes flat - or better still, a failsafe to prevent the starter battery going flat.

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

I already have a good set of jumper leads. I just want an inbuilt way start the car if ever the starter goes flat - or better still, a failsafe to prevent the starter battery going flat.

I understand, it's just that I (and probably many others) believe that the best approach is a simple auxillary battery, either supplied via "smart" solenoid or a DC-DC charger if the battery is of a different chemistry to the factory battery. This achieves the aim of preventing the factory battery from being flattened by after market extras like fridges and avoids running lengths of heavy cable twice round the engine bay. To keep this system as simple as possible, because the more switches and solenoids are incorporated the more potential there is for things to fail, it is my opinion that a set of jumper leads achieves the other objective of providing a way to start the car should the factory battery go flat. That combination is simple, proven and reliable (given quality components), and additionally provides the other benefits of carrying jumper leads as described above. The only downside to such a system is that in the (hopefully) unlikely event of having to cross connect the batteries the driver has to open the hood and connect 4 clips. The advantages are that it cannot fail due to a stuck or flooded relay, and it cannot be activated by accident and inadvertently drain both batteries - a switch can be left on by mistake! To prevent accidental activation, most cross-connecting systems use a momentary switch with a relay, either the "smart relay" itself of another parallel relay, but then we are back to multiple relays, switches, high current fuses etc., all of which will work perfectly until you really need them at which time they will (according to Murphy) fail to operate.

As you said above, nobody wants to get bogged or stuck with a flat battery. But building a complex, expensive and potentially failure prone system just to avoid using a set of jump leads in an emergency is not something I would do. Personal choice though.

If you do choose to install an inbuilt cross connect, be aware that you will need to wire it all up with heavy cable and suitably rated fuses, switches, relays etc. A standard charging circuit for an auxillary battery would use much lighter cable and fuses, for example a small Redarc smart solenoid without "start assist" should use 8mm^2 cable and 60amp fuse, whilst the "start assist" version of the same solenoid specifies 19mm^2 cable and 100amp fuse. In fact, to start a diesel from cold I would personally move up to a higher rated smart solenoid, and the next one up the Redarc range specifies 32mm^2 cable for "start assist" duties. Given that my 9500lb winch draws 340A, if I intended cross connecting batteries to run it I would install cable, fuses etc. to suit - and that would be 32mm^2 at minimum.

Alternatively, given that initially you will not have fridges etc. and a winch would be connected to the factory battery anyway, I return to my earlier suggestion of an "emergency jump-start pack" in the boot. Plug it in to a ciggie socket and it will sit there, always charged and always ready to be used. It's cheaper, easier and achieves every objective......except being able to be used without leaving the driver seat! Out of interest, that was exactly the approach I took with a Discovery I used to own. Fitting a second battery was tricky because of the cramped engine bay, so I replaced the factory battery with the biggest and best battery I could find. I ran my fridge through a voltage cut-off (standard practice, whether or not a second battery is fitted) to prevent it from flattening that single battery, and then carried a jump-start pack for emergencies. I never used the jump start pack, but it was nice to know it was there.....

Not wishing to be rude, but can I ask; Is there a particular reason why you want a push-button system rather than having to use jumper leads? It seems slightly odd, because winching and recovery require lots of physical effort and a degree of thought, whilst connecting jumper leads seems trivial!