Thread: Dual battery system

Originally Posted by Lukeis

I’m looking for a dual battery system, it willl only be for a 50L waeco fridge from time to
time but it’s possible I will get a winch at some stage.

Does anyone know if I could use something like this? I have already wired up the fridge etc so I just need the additional battery and isolator:

DUAL BATTERY KIT 140AMP NARVA COMPLETE ISOLATOR AND WIRING SYSTEM CABLE 61092 + | eBay

yes, I’m very aware of the triaxide option but it’s expensive and if I can find something 90% as good for way less then that’s a win for me given my low need for it.

Hi Lukeis and unfortunately, it is never as simple as it seems.

That kit comes with 6B&S ( 13.5mm2 ) cable, but you will need 3B&S ( 25mm2 ) for proper winch operation.

What else have you got, such as a tray and so on?

Originally Posted by Lukeis

I’m very aware of the triaxide option but it’s expensive and if I can find something 90% as good for way less then that’s a win for me given my low need for it.

BTW Lukeis, before you do anything, you need to learn how different devices work in your D4.

That device will NOT be 90% as good as one of my isolators. It is more like about 20%.

First and foremost, because that isolator cuts out ( turns off ) when the voltage drops below 12.7v, like most VSR isolators, it is vertically useless for linking batteries while winching. As soon as you start to winch, your voltage will quickly drop below 12.7v, and the isolator will simply turn off, disconnecting the auxiliary battery.

When developing my USI-160 isolator, I quickly realised that even my 12.0v cut-out voltage was still way to high. This is the reason my USI-160 has the unique feature of dropping the cut-out voltage to 10.0v, while the USI-160 is set to WINCH Mode.

And If you forget to reset the USI-160 back to normal operation when you have finished winching, 5 minutes after you turn your motor off, the USI-160 automatically raises the cut-out voltage from 10.0v back up to the normal setting, thus removing the chances of you flattening both batteries while camping.

Next, the very reason my isolators work better at charging auxiliary batteries in vehicles with “SMART” alternators, like your D4, is because my isolators allow up to half the cranking battery’s capacity to be used to assist the powering of accessories while you are camping.

This one function has two primary advantages in vehicles with SMART alternators. The obvious advantage is that you get nearly double the available battery capacity over any other setup, including the one you are looking at, but there is another advantage that very few people are aware of.

Again because my isolators allow up to half the Cranking battery’s capacity to be used while camping, if you have used some of it’s capacity, when you start your motor, the D4’s BMS will see that the cranking battery is NOT fully charged, so it will then run the alternator at a higher voltage for a longer time.

The lower the cranking battery is, when you start your motor, the longer the BMS will keep the alternator voltage high.

This allows both the cranking battery and the auxiliary battery to be charged faster in a shorter drive time.

One more point, with any isolator that cuts out at around 12.7v, because the D4’s BMS continually monitors the cranking battery, while you are driving, if the BMS determines that cranking battery is fully charged, it can lower the alternator voltage below 12.7v, causing your isolator to turn off, and it will stay off until the alternator voltages rises above 13.2v again, and on long trips on open road, this might not happen for long periods of time, making it harder to recharge your auxiliary both because the isolator may be off for periods of time, and when on, the alternator voltage may be so low that it makes charging the battery even slower.

There are quite a few other advantages for using my isolators, but the point is, that isolator you are considering does not have 90% of the functionality of one of my isolators. It is more like about 20%.

Again Lukeis, I suggest you do a lot more researching before you settle on anything in the way of a dual battery system.

Originally Posted by LRD414

I wonder if you’re comparing apples with apples Luke? The Narva VSR kit for $165 gets you the isolator and cabling to connect batteries. The Traxide SC80 isolator alone is $165, so the only difference is the cabling. What about battery tray and hold down bracket plus a mount for the isolator? The basic Traxide kit for $430 includes the tray and isolator bracket and all wiring to suit the space in front of cranking battery.

Perhaps your aux battery is not going in front of the cranking battery and I’m sure the Narva unit would be a good option but I felt the perception of massive cost difference seemed worth further investigation.

Regards,
Scott

Am I missing something? The extra $200 is for a battery tray? I have no idea what they are worth but I would have thought the tray was a $30 item

Originally Posted by drivesafe

Hi Lukeis and unfortunately, it is never as simple as it seems.

That kit comes with 6B&S ( 13.5mm2 ) cable, but you will need 3B&S ( 25mm2 ) for proper winch operation.

What else have you got, such as a tray and so on?

Thanks mate, makes sense.
Forgive me but it’s the $500 price tag I’m trying to avoid, I’ve got no doubt your items are the bees knees but I have new wheels, new tyres, a roof pod, bull bar, spare battery and a few other things on the list of parts to buy so if I need to cut costs it’s going to be with my spare fridge as it runs pretty good on the main battery alone anyway and I have a large caravan fridge which is the main one, the dual battery is just an insurance policy

Luke, the Traxide is a drop in kit with everything done except installation. Cables are correct sizes with crimped ends, auto-resetting cct breakers and battery tray and hold down clamps are supplied and full instructions are provided. By the time you purchase all the cabling and components, measure up, cut to size and terminate cables. It will start to look cheap.

You can always buy just the Traxide isolator and do everything else yourself but I think Tim's kit is very good value.

The cables I can do myself, they are only short so the costs would be insignificant

has anyone sourced their own battery tray?

Hey Lukeis. Do research is all I can say. Yep you can save a few bucks if you purchase traxide basic kit without all the wiring and extras, but only if you can source discount cable etc. I did it that way and got lucky with cable pricing and am more than happy with his kit. One of the flaws of the disco is its poor space for a decent aux battery under the hood. I was dissappointed to say the least. Traxide makes running a fridge in your truck practical due to its 12v cutout. I'm very impressed with how well it works. Can't comment on Tims isolator for winch functionality but I am happy to accept his logic as he know the cars well. Dc-to-dc is a definite disadvantage with an underhood setup where cable runs are very short. Put it this way I've seen my optima yellowtop regularly pull in excess of 40 amp/h for over 30 minutes, and that wasn't including the Varta starter pulling in excess of 25 over the same time period. That's some pretty serious total charge rates, important if your aiming for minimal use of solar. Good luck. Sometimes a few extra bucks means a lot less hassle down the track.

Originally Posted by Lukeis

I have no idea what they are worth but I would have thought the tray was a $30 item

Really? Good luck finding a stainless steel battery tray with custom mounting points to fit in the non-flat, quite small available space and includes a bracket to mount the isolator for $30.