Do I need a battery Isolator?

OH sorry about the spelling...cut and pasted the draft copy!!!!

I would recommend an isolator.

Read my article on battery power.

Here is an extract:

Isolators
To prevent the starting battery draining from the new connection you need to fit an isolator as well as spike/surge protection and an optional battery monitor. Some isolators have built in spike and surge protection so an external one is not needed, but it is important to know that you have one - most new vehicles have a computer and will possibly be damaged if there is a voltage spike as the two batteries engage and disengage especially at high engine revs when the amperage could be as great as 50 amps at 14 volts or higher. There are 3 basic ways of isolating the auxiliary battery.
Manual Switch
1) You can use a basic battery master switch, which requires opening the bonnet and turning the knob.
2) There is a simple solenoid, which can be fitted with a toggle switch via the ignition to manually engage the charging system.


Automatic Switch
Both these systems work but people tend to forget to switch them on/off and this causes problems especially if the battery is in the caravan and you crank the engine while the switch is on as this can melt the wiring and plugs.

3) So the preferred system is Battery Management or fully automatic system. These consist of voltage sensing relays or "Smart" solenoids. They engage when the engine is running and the starting battery reaches 12.6 volts. They are simple three wire systems and work off the main battery cables between the batteries. There is no need to alter any wiring on the vehicle and they are a fit and forget system!

Yes you can hook your second battery up directly to your main 12V supply.
Keep in mind the following points: during cranking, the current through the starter motor is the sum of the currents from you main battery and the second battery. The amount of the latter depends on some variables, and it could exceed the fuse rating. So it's advisable to have this second battery disconnected while cranking - or you could leave the fuse in doing some experimental cranking and be prepared to replace it with a new one. I hope the fuse is rated lower than the wiring?
Whenever your second battery gets discharged below say 30% before it receives a topup from your alternator, there is a chance that the battery could take in more than its rated maximum charge current, as the new alternator and the heavy duty wiring won't restrict this current.
I'd check the battery specs, for this maximum charging current not to be exceeded is important for good battery health. Again, there are several variables involved which in their sum determine if your second battery will see this excessive charging current or not.
The only way to find out, is again by experimenting. Using an accurate DC current clamp to measure these currents at slightly lower than expected states of discharge @ high ambient temperatures, should help clearing things up.
And last but not least, as soon as you return home or to the park, fully recharge your battery with the mains powered charger of yours (if the c-tek doesn't restrict this...)

I'm sure others will chime in with their first hand recommendations as well, as I'm only seeing things from a battery's health perspective.

If you find any spelling mistakes in my piece, you've permission to keep them :)

Best regards, batterymeister

An isolator would make it foolproof, however if you just start the car before connecting and disconnect prior to turning off it would work.

Thanks for the quick response...
Had a look at the battery boxes like the flyer etc....
I believe they are way to big and will look at adding a isolator.That way I can use the existing battery box and leave it connected if I wanted....
Still interested in what others may have to say....

On charging do members who have dual battery systems under the bonnet top up their AGM battery with a 240 volt charger???
(ie ctek or similar) is there a NEED?

Tag,

If you go for the isolator (and that is preferred) you need to consider the requirement to keep your Anderson plug alive so as to have it available for the boat winch.

If you place the isolator in the existing feed cable from the cranking battery to the winch it will draw its current from the auxiliary battery.

Alternatively, you could place the isolator between the Anderson plug cable and the auxiliary battery, leaving the cranking battery always connected to the Anderson plug and hence the winch.

Either way will work, just personal choice as to which battery supplies the winch.
I would choose the cranking battery to supply the winch.

Tag,

Of course, you could leave your existing winch cabling setup as is and run a new cable from the cranking battery to the auxiliary battery via an isolator.

There is no valid reason why the isolator needs to be placed close to the cranking battery / alternator. If it is more convenient, place it at the auxiliary battery. It will sense the same voltage there before cut-in and if the cable is of adequate size there will be little volt-drop to affect its cut-out.

As has been said, there should be a 50A fuse at each end of the cable close to each battery as a fault on the cable can be fed from either battery.

Your old RedArc would probably be OK. The higher cut-in voltage setting would make little difference to the outcome. Could always change it later if not happy.

" QUESTION...
Can I hook this to the battery pack while driving...?
IT WOULD be disconnected after the days driving...? "

With conditions you state (above) you need nothing extra
(make sure the (+) cable is fused at the battery)

Maîneÿ . . .