Thread: Dual Battery Time Again

Hi Babs and this will probably start the usual debate, but Babs, what do you think you will gain by fitting a DC/DC device?

Because what you have posted up about what you want to do with your vehicle, means you are actually creating a lot of disadvantages by fitting one.

Originally Posted by drivesafe

Hi Babs and this will probably start the usual debate, but Babs, what do you think you will gain by fitting a DC/DC device? Because what you have posted up about what you want to do with your vehicle, means you are actually creating a lot of disadvantages by fitting one.

Drivesafe I have no idea whatsoever when it comes to electrical. I have no idea what the unit is that I took the photo of, he is proposing this and I'm not doing anything until I get some advise of the forum here.

My last battery setups were done through the mechanic and trusted him to give me the right setup.

Please feel free to give me your thoughts on this, I appreciate all input. Cheers.

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Hi Babs, there has been much heated discussions on this topic, but if you listen to the people that actually do these things for a living and understand batteries and how they charge - not just your local Autolec or Mechanic who are generally just dealers for these devices, then you will find that not only don't you need one, but you will also find that your auxiliary battery will take longer to charge. Your cars alternator is the best device to do this, and it's already there.

Do yourself a favour, have a chat to Tim (Drivesafe who answered your first post) - click the link in his signature - his number is there, then buy the system he recommends - he won't try and sell you something you don't need and his systems are unmatched in the industry. I run one in my L322 and it is brilliant, and does more than you might think. He backs his products and has first rate after sales service.

No, I have no association with him, but as an Electrician I understand more than a lot do on this subject and I've found his knowledge on the subject unmatched.

(Ok Tim, you can send me this months cheque now)...

I did have a traxide fitted to the fender......

Have now fitted 3 x basic rearc isolator a to the three work cars

I did have a basic redcarc but the desert killed it. Now I use a Narva voltage sensitive relay , cost $44. This works fine for and keeps things simple.

I was directed to Traxide (by Justinc) and from my experience with dual batteries in my TD5, fitted with a Traxide system, as well as from reading his posts in this forum, I don't think you can go wrong if you follow his advice.

Just waiting for Tim to recommend something.

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Hi folks, after a PM exchange with Babs, I'll post up the advantages and disadvantages of different types of Dual Battery Systems ( DBS ) for Babs, but this may be of assistance to others.

I'll will have to do it in sections as I am flat out filling orders, and if you have any questions or disagree with my posts, please feel free to reply.

DC/DC devices first. These devices are the most over rated form of battery charging.

The advertising for these devices claim they can charge a battery to 100%. They even imply or outright state that an alternator can not fully charge a battery to 100%.

While both claims are correct, both claims are an exaggeration, and for the very same reason.

If you have a low auxiliary battery, unless you drive long enough, then an alternator will not full charge that battery, but the same is the case when using a DC/DC device to charge that same battery.

Unless you drive long enough, there is also no way a DC/DC device can fully charge a low auxiliary battery. But this is something you never find in all the grossly exaggerated advertising and this is lying by omission.

The reality is that if you have a low auxiliary battery, you are highly unlikely to drive long enough to fully charge the battery, no matter what type of charging you use.

But depending on the type of battery and how low it is when you start your drive, an alternator can usually have a battery in a higher state of charge at the end of a drive than what a 20 amp DC/DC device can.

Using a 40 amp DC/DC device, then you can bring many batteries to a higher state of charge than an alternator can, but if the battery is something like an Optima, then an alternator will easily charge this type of battery up 40% quicker than even a 40 amp DC/DC device can.

If you are just topping up batteries, then a DC/DC device can in many cases, do it in a shorter drive time, but if you drive for periods of 3 three or more hours, an alternator will still achieve the same charging level.

The one situation where the use of a DC/DC device can be advantageous is where you have a setup that uses thin cabling for connection between the cranking battery and a battery in the rear of a vehicle, or in a caravan or camper trailer.

It would still be cheaper to replace the thin cabling with decent size cable but some situations do not allow for the changing of the cable size, so a DC/DC device can be a big improvement in charging capability.