Battery Isolators

woohoo we have one of them in Melbourne, what do I ask them for?

Actually, not so.
If the fully charged battery has a voltage of, say, 12.7v at no load, there will be an initial current flow and the voltage of both will rapidly settle at a voltage well above 12v. The current flow is well within safety limits for the batteries. The characteristic of lead acid batteries is that little charging occurs below about 13.0v, so after the initial current there will be not much change in the amount of charge in either, and little current flow.
For example. It takes 45 hours to recharge a 100% discharged battery to 90% charge at a voltage of 13.0v. (from a reference I have) So if the voltage is 12.3v the time would be essentially infinite because the voltage is way below that at which the battery accepts significant charge.

So what you get is an almost fully charged battery and a slightly charged one even though they are connected together. Only a charging voltage above about 13v will equalise the charges because the flat battery will accept current and the full battery little.

As an aside,
When the NRMA jump starts a vehicle with a flat battery using one of those portable battery packs there is no great spark when it is connected.

There are some good references to the characteristics of lead acid batteries on the web and these have been quoted in this forum recentlly Unfortunately I have not got them to hand right now.

Phil, have you got access to a data logger. If you have, and you hook it up to a Redarc battary isolator and second battery, you will find the modern batteries are quiete different to the older technology batteries. If they were not, I would not be using one in association with my solar panels.

At the end of the day, there is not to my knowledge any battery isolator system that you can buy off the shelf ready to install in a vehicle that is automatic that will adequately charge a second battery in the manner that would be ideal. If there is one, I would love to see and hear about it.

Ozi, another case of showing my ignorance.
My pre EFI GQ dual battery system has cranking battery connected to deep cycle via 90 amp cable and a simple isolating switch (Pirhana I think - "isolated "red knob is removed). Has worked well for 3 years with same batteries. Overnight plus - I use switch.
Question and advice please - am I living dangerously??!! I have read the REDARC Tech info with interest.
Thanks
Mike
Ps You can see I am not too technically minded!

Mike, not, not at all. It works, and you don't have all the electronic goodies today that are fitted to petrol and diesel vehicles. What I do like about the Redarc unit, it is fit and forget.

The other reason I like it, you can easily bring in your second battery in an emergency if it is fitted with 1BS but preferably 2BS battery cable and mounted under the bonnet.

Mike the sort of system you have there we used for many years before we got all these lovely electronic goodies to make life easy. Because it is not the latest and greatest, does not mean it is not good or functional.

Mike my philosophy is we are here for a short time, so make it a good time and help others as you would hope to be helped. Life is like agriculture, if you so bad seed, you reap a poor crop.

Ozi, VMT for your reply. I ndo appreciate your responses (crawling here!), but seriously trhanks.

Ozi, VMT for your reply. I ndo appreciate your responses (crawling here!), but seriously trhanks.

Cut off in my prime! David where is spellcheck!
Ozi, glad I live for another day!
Mike

Mike, your system is actually better than say a manual solenoid system as it won't cause as many problems with surges, etc.

Personally I would forget to switch it on or off and then I wouldn't be happy, so I spent my $$$ for convenience.

Reading the Rotronics website, I cannot get excited about them at all.
Having a system that is independent charge and has a diode in the circuit - OUCH! I could not see how you could possibly justify the cost on a Rotronics system. You would be substantially better spending that amount of money on a solar panel if you had a place to mount it full time. I just *love* my solar panels. It is like gold mining, I love it, getting money out of the ground for nothing, solar panels are the same, money from heaven to charge your batteries and run your gear.

Yep I agree about the solar panel.

The rotronics system doesn't rely on diodes and has the smallest voltage drop of any system, including solenoids. It doesn't charge both batteries simultaneously via diodes, it charges one at a time so the alternator only senses that battery. This allows the alternator to recharge each battery in less time that it takes to charge both together.

All of the vehicles electrical connections (except the starter cable) are removed from the main battery and connected to the switch box.

Eric, I'm interested to hear what you have to say. Can you email me? cullenmarkd@hotmail.com

Cheers.