Thread: 12 volt power efficiency.....

Not professing to be an expert in this...but....if the alternator isn't delivering enough voltage to charge the battery you have a problem. Also, in a 4x4, surely you'd want to ensure the starting battery was charged before you started charging the aux, wouldn't you? Even if you didn't, most battery controllers have an override so you can immediately start charging both.

You're never going to get a 100% full charge to any battery anyway, but without the expensive smart chargers I've been looking at recently, I think this is true of any battery charger, whether alternator or a 240v one.

If your aux battery is being discharged by whatever you have plugged into it then the charger will be trying to top it up all the time, what is the chance of this dragging your main battery down below the voltage required for starting. Can you set up some device to shut it down when voltage gets to the critical level.


Martyn

Originally Posted by Bushie

If your aux battery is being discharged by whatever you have plugged into it then the charger will be trying to top it up all the time, what is the chance of this dragging your main battery down below the voltage required for starting. Can you set up some device to shut it down when voltage gets to the critical level.


Martyn

You could wire the supply to the inverter through a relay activated by your ignition. Still undecided as to the benefits of going the inverter way as opposed to a normal dual battery setup.

Originally Posted by Feral

I am looking at installing a dual battery setup in the back of my D2. At this stage I am not sure if the auxillary battery will be permanently mounted or used in a battery box.

The general way that most people do is to use a dual battery controller which will charge the aux. battery. All this is wired using the proper specifications of wiring and fuse, circuit breakers, etc.


There is another way which is beginning to be more prevalent in the caravan industry.

The plan is to use an inverter and a battery charger to charge the aux. battery. Of course this will be wired correctly using proper fuses, circuit breakers, etc. For those who are concerned about 240v being introduced into the vehicle, the position of the inverter and battery charger will be protected by the left storage bin. I will have a spark/high voltage label clearly displayed to protect other users.


Now the theory that decides which way to go is that with the dual battery controller is that it only begins to charge the aux. battery AFTER it charges the mains. When it does this it will only charge as efficiently as the alternator can deliver so if the aux. battery does not receive 13.8v it will not be charging.

With the inverter and battery charger system, the inverter will work even though the voltage may drop to 12 volts. This in turn runs the battery charger which delivers 13.8v or more to the aux. battery. The inverter and battery charger are all protected by their onboard protection systems and will automatically shut down if any issues arise.

Its all to do with the 'state of charge' of the battery. If the aux. battery is fully charged it will run longer.

Will it work ?

Is there anything I have missed ?

I have read so much info on the whole deal...its information overload

I think perhaps you are thinking waaay too deep. Its got some serious losses doing such a conversion. perhaps 30% depending on quality. To top up the main battery will only take like 30 secs, in most cases, to replace the starting losses. Assuming it starts the second battery above like 13.5V or whatever, my FL atleast would link them up instantly after starting. I would be only using the charger theory you mentioned if you wanted to charge the secondary off a screwed main, but thats not real bright or useful. Stick with a dual battery controller and be happy in its reliability.

An alternator at decent rpm is like half a dozen decent battery chargers running together.

IMHO atleast.

Cheers!

Originally Posted by Feral

With the inverter and battery charger system, the inverter will work even though the voltage may drop to 12 volts. This in turn runs the battery charger which delivers 13.8v or more to the aux. battery.

If the main voltage supply drops to 12V you have a problem and the last thing you should be worrying about is charging an auxillary battery.
I really don't see how this is a beneficial system. You are converting 12VDC to 240VAC and back to 12VDC. With heat losses at every conversion, you will be wasting alot of power. Why convert to 240V??
A conventional dual battery setup works well and is far less complicated than the system you are describing.
I think that the advantage in a caravan is so that the battery can be charged while on a powered caravan site.

Originally Posted by awabbit6

If the main voltage supply drops to 12V you have a problem and the last thing you should be worrying about is charging an auxillary battery.
I really don't see how this is a beneficial system. You are converting 12VDC to 240VAC and back to 12VDC. With heat losses at every conversion, you will be wasting alot of power. Why convert to 240V??
A conventional dual battery setup works well and is far less complicated than the system you are describing.
I think that the advantage in a caravan is so that the battery can be charged while on a powered caravan site.

Have to agree,
add to that the cost of a decent inverter+decent battery+wiring etc. Would work out more than a proven basic and reliable dual battery setup

Sorry for how abrupt this is but there is no polite way to address the suggestion of driving around with live 240 VAC in a vehicle, especially a 4x4 it is nothing short of lunacy.

Besides the fact that it is totally unnecessary as any alternator can easily charge two batteries at the same time and contrary to all the BS, they can be FULLY charged by the alternator, IF everything is set up properly in the first place.

The situation of having ordinary vehicles ( Tour Buses have 240 VAC on board but there are major differences between them and normal vehicles ) is getting more and more attention for different emergency services departments and I would not be too surprised if it is not made illegal before too long.

For less than the cost of a battery charger or an inverter ( let alone the combined cost ) you can buy a third battery and your alternator can not only charge them both but can do it quicker than an inverter/battery charger set up can, plus you end up with twice as much stored power.

Sorry Feral, it just can’t be made 100% safe and as there is no legitimate reason for doing it in the first place, why do it at all.

I agree with the above comments. I can recommend Smart Solenoids from the USA retailed by ARB. We've used many of these on boats and crane-equipped vehicles at work as well as one each on my two personal Land Rovers. Never had the slightest problem with charging big dual battery setups and they give you emergency starting as well. The only better system that you could install would be a marine battery management system such as those made by Adverc, but I think that this sort of thing would be over the top for an auto installation. The problems that modern ambulances have with their huge dual alternators is that they fry the Hell out of the batteries. You can have too much of a good thing.