im new to this Site and new to the Hobby . My Girlfriend and me are building our first Campervan ( VW T5 ) together .
I came across the function of the SmartShunt where you can also read your starterbattery´s voltage . Great i thought , i wanna have it .
I´ve looked across the documentation of the SmartShung and found the Diagramm on how to Wire it but im not sure with which Wire Thickness .
Since I only have to read the Voltage with not mich current going through the Wire´s something like 4mm² or 11 AWG should be enough for it or is my thought wrong ?
Im talking about the Wire where the red arrow is pointed
If you mean the large negative cable then the size of that depends on the rest of your system. If you have a single alternator charging both starter and domestic batteries either directly, through a combining relay or a DC to DC charger that cable could carry a high current and need to have a suitability large area. If you can be sure that it will only take the measuring current then a small cable such as 1.5mm2 would be OK but 4mm2 would be physically more robust.
Im using a 30amps DC DC charger that ist sitting between the Starter and domestic battery , only 1 alternator .
So i guess because a 16mm² ( 11awg ) ist supporting the Power ,the “measuring” cable should only get the voltage but no high current ?
My Idea is to get a 4mm² cable in each crimp that ist coming from the Starterbattery which are going in the DC DC charger , that way i should get the Reading from the Starterbattery ? Or am i thinking wrong ?
If your 30A DC to DC charger is non isolated then you can have 40A flowing through the common negative between the starter and domestic batteries. This is the remainder of the circuit. Your common battery negative has to have at least the same size as the positive cables on the DC to DC charger.
Oh sorry i forgot to day that . Im running the isolated charger so i have a negativ and positiv 16mm² cable running from the starterbattery to the charger and from the charger to the domestic battery .
So my Idea should Work with 4mm² for the voltage readout ? Sorry but im new to this stuff , i know mechanics but i have Limited knowledge to electrics
OK, isolated DC to DC charger so there should not be any large current flowing so the lead at 4mm2 should be OK for the voltage measurement.
However, you need to make sure that there is no way high current can flow as this is the only link between the 2 systems. If you have a fault between a positive cables on the domestic system to the vehicle body / chassis then the fault current will pass back through the small negative wire. The SmartShunt auxiliary voltage is really designed for systems with a common negative. The small negative wire would have to be fused.
My view is you either need to keep the 2 systems isolated ftom each other or decide they share a common negative and have a thick wire between the 2 that is the same gauge as the positive battery cables.
Even thought that i have the isolated charger i thought that connecting the “livingroom” negative to the Chassis wouldnt be a bad idea or is it ?
I guess it could work the way i described it but to be sure i will put a fuse on each the aux and negativ cable just to be extra sure , with a 1Amp fuse it should break before anything bad happens
