Dual Battery Charger

[Noel]

Thought this may be of interest, It works a little different to most other aux battery units as it uses both batteries until the voltage reached 12V then isolates the main battery giving longer battery life with still enough power to start the engine.
SC40 Unit
http://www.traxide.com.au/

[TOMUCH]

Noel, I believe that nearly all, if not all of them operate in a similar way...but usually its 13V cut in... (when the start battery has 13V across it, the isolator then connects the AUX battery and charges it.. however I cannot see the point in stressing your cranking battery (not designed to be drawn down like that) by discharging it to 10.5 volts to get a bit longer run time for your fridge. Unless you are using AGM (eg: LIFELINE BATTERIES)or similar batteries for both start and AUX this has the potential to reduce the life of your start battery (especially in cold climates) and could potentialy leave you stranded if you dont have another vehicle to jump from. Be careful.. make sure you fully understand what your getting. Remember there are no free lunches.. Cheers TOMUCH

[TOMUCH]

Actually, after studing the wiring diagram a bit closer, it appears that to achieve the 10.5 V run down, you need to have two of these things fitted. the second one allowes the AUX battery to to be discharged only ... whilst the other one isolates the Main battery.. again, cant really see the point.. most fridges have an auto cut out. and if you leave the lights in the rear tray on all night, they still wont damage the AUX battery to a point it cant be used.. the only up side is the unit is cheap at $99+ Postage, and will certainly isolate your start form your AUX as shown...but not that cheap at $198+ if you need two of them. Cheers TOMUCH

[Noel]

I think the main battery is isolated at 12V, Which wouldn't stress it but it may save the aux battery from stress as taking any battery below 10.5v will cause damage. from my research the problem with charging batteries is the lower in voltage they are taken down to the charge time is greatly increased as they drop in voltage Eg a battery taken down to 10v will take 8hrs driving to charge fully when driving where a battery will charge from 12v to fully charged in 1hr there are a few sites that will give you exact times therefore if you can use a little of the stored power from the main battery with no risk of not being able to start you motor your batteries will charge in a much shorter time as the voltage is higher to start with very handy for people traveling. Also I believe Engel have removed the low voltage cutout on there new fridges

There is a lot in a dual battery setup at first glance they seem very simple but it is great to have some input and discussion on this subject
Noel

[Macca]

From the lifeline battery owners manual
State Of Charge Voltage
100% 12.8 or greater
75% 12.55
50% 12.2
25% 11.75
0% 10.5

12volts is less than 1/2 charged (AGM type batt)
might have trouble getting ECU to work when cranking reduces voltage further. Have heard something about 11.5v minimum.
Check ou the Bisolator at www.sidewinder.com.au
I have had no trouble with mine and the remote switching to "connect" both batteries is handy while winching. Cost $179.95
Macca