Dual Battery

[snow]

Ok. if I had a brain, ShaneJ i didn't notice the in your diagram that the ignition was off and the relay was open so yea the main battery wouldn't be touch, so i'am guessing to get the size of a relay go see an auto electrain, I also like Joel's way with the VSR relay as well, thanks guys 2 good options and a diagram just what i was after i'll let you know down the track how it turns out

Didn't know there was that many from brizzy here maybe it's the new board huh i was beginning to think them sandgropers had pinch everbody

cheers snow

[ShaneJ]

Once we get some stickers available and advertise the site a bit more hopefully we'll get some more Bedford members.

Comet batteries at Geebung can help you out with a good relay. They keep them in stock there.

[alien8]

My Bedford is at my mates workshop at Redcliffe at the moment getting some body work done. I'll give you a shout once I get it back.

Hi Shane, your bedford wouldn't happen to be at KCF Rallysport and being worked on by Keith would it.

[ShaneJ]

That's the place, but Keith if off work for a bit.

You know him?

[snow]

thanks for the help ShaneJ, i'am on the western side of brissy 1st i'll try on this side other wise over to your side

 cheers snow

[Clance]

Basically you should be thinking about how big a battery can you fit, and less about how small and cheap a battery you can get away with, the larger the battery the less percentage wise you will be draining it, and the longer it will last both in power usage and battery life, with the extra advantage of more capacity when needed.
Hot Tip …Batteries love being fully charged, they don’t like being discharged at all, they like it when you only take them down to 50% of their capacity and then top them back up soon after, they will lose capacity and die quickly when left discharged for long lengths of time.
The Battery Isolator.
The battery isolator is a device that allows the cars alternator to recharge the auxiliary battery while protecting the cars starting battery from discharging, if these batteries are simply linked together you run the very real risk of draining them both to a level that you can not start the engine, and there are many other reasons why you should not do it this way.
So hence we have the battery isolator, there are many different methods used to isolate the batteries, most use some form of solenoid, this is an electronic switch that can handle large (charging) currents, much more than standard switches can, and they are operated by applying a small amount of power to them, this is turn actuates a solenoid that links the batteries together so that large currents and be passed between the batteries.
There are many ways to operate these battery isolators, some much better that others.
The cheapest way is that you manually turn them on and off, I call these idiot switches, because sooner or later some idiot (and I’ve been there) will forget to turn the switch on (no charge goes into the aux battery) or off at the right time (and then the starting battery gets drained as well).
Another way of doing it is to have the solenoid turn on as soon as you start the engine up, and turn off when you shut down the engine, this has been the cheap way of doing it for many years, but it’s far from ideal.
I believe the best way for most situations is to use a VSR (voltage sensitive relay) activated solenoid, and the one I like the best and use is one of the most inexpensive ones, it does the job very well, and as good as, and sometimes better than many of the very expensive ones too.
The Redarc Smart Start battery isolator and how it works.
 
When you start your engine the Redarc works by first letting your starter battery recover it’s charge, it lets it achieve 13.2 volts, at this point that battery has about as much charge in it as it's going to get, once the Redarc sees this 13.2 volts it closes the contacts on the solenoid, this links both batteries together for charging purposes.
The next thing the Redarc is looking for is 12.5 volts, in other words you have shut down your engine and started to draw power from the batteries, so very quickly the voltage across both batteries will fall to 12.5 volts, as soon as the Redarc sees this voltage it will open the solenoid contacts and isolate the batteries, leaving your starting battery for starting and your auxiliary battery for auxiliarying ;-)
The Redarc Smart Start battery isolator is rated at 100Amps constant duty with a surge capacity of 400Amps, it has silver contacts unlike some of the cheaper ones that have copper (silver is much better), the Redarc also has spike protection so it won’t upset the delicate electronics on newer vehicles.

[Clance]

This is the Redarc VSR Solenoid that I use in my motorhome, I've been using it for thre years now and have not had a flat battery yet. The wiring is basically the same as Shanes relay method it's just that these are voltage sensitive.

[ShaneJ]

The problem with those redarc jobs is that the transistor in the voltage sensing unit starts to get lazy after a while. With out enough current the main relay doesn't close hard enough to make good contact for high current to pass through.
I had one fitted in my 4x4 up until a few weeks ago to charge a third battery in the back and I had this very fault with it.

[ben]

far out i dont know whih way to go now!!!! relay or Voltage sensor..

maybe ill flip a coin!!!
ben

[ShaneJ]

A plain ol relay is cheaper