Aux batteries and charging advice needed

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Posts: 1
Joined: Thu Aug 12, 2010 11:55 am
Town: Potchefstroom
Vehicle: Hilux 3. D4D 4x4 D/C
Real Name: Jaco

Good day all you clever people

This accountant need some advice.

Currently this is my electrical set-up as attached.
Krag van bakkie.png
Two auxiliary batteries:

1. 100Ah AGM in the load bin.
2. 80Ah Regular high cycle in engine bay (chose high cycle due to effect of heat and faster charging).

I have "two" sources of charging the batteries:

1. HCdP HPP1 MK5 Power panel (14.2V DC to DC 12A, ; 240V AC 12 A; 1 x 100 W Solar panel) - this question however more relates to the 12v DC to DC charger.
2. Alternator via NL Intelligent solenoid - Alternator measured at 14V output measured using digital multi meter if worth anything.

(PS I know the alternator effectively charges both batteries no matter what, but one option is directly and the other is via the DC to DC charger)

I have a three way marine isolator switch that I can use to select which battery (or both) supplies power to the Power panel.

Other for the wiring running from the main battery to the HCDP Power panel as 12v input, which is 10mm2, all the other wiring is 16mm2. Battery in the load bin is close to the Power panel. Only long distance for wiring is from engine bay to load bin.

My "standard" set-up is such that the isolator switch is set to 1, meaning, when driving, the alternator directly charges the high cycle aux battery in the engine bay, while the AGM aux battery in the load bin is charged via the DC to DC charger.
When not driving, the aux battery in the load bin supplies the power to the various outputs (fridge (80 l NL double; some LED lighting and water pump). If the power becomes low, I can switch the isolator switch to 2, so that the high cycle battery in the engine bay supplies the power to the loads. This is really the back-up battery.

My questions are as follows (the more I read, the more I get confused!):

1. How will charging be impacted if the isolator switch is set to 3, meaning both batteries are connected in parallel. Now the alternator supplies both batteries as well as via the DC to DC charger. What will happen? My view is that the Power Panel will pick up that the battery (ies) are fully charged since it will read the battery power as 14V, the output of the alternator. I therefor think the Dc to DC charger will do nothing and all charging will be done just by the alternator.

2. How will you set the isolator switch when driving and when parked?
2.1 Again, my view and understanding: If my comment above holds true, while driving it will be best to set the switch to 3, and let both batteries initially be charged by the alternator . After about two hours, one can switch the isolator to 1, so that the AGM aux battery in the load bin is charged via the DC to DC charger. My reasoning: Faster initial charge directly by alternator and then later by DC to DC charger (although looking at the output of the alternator at 14V (and higher amps) and the DC to DC charger of 14.2V (max 12 Amps), I don't think the impact will be significant?).
2.2 When parked: Maybe first use the high cycle battery in engine bay, and then if power is low or going to bed, switch to AGM battery in load bin? Don't think it will work to switch to 3 and connect the batteries in parallel, since they are different types of batteries?

Any wise advice or suggestions will be welcomed, also if you think I should do something different.

PS I have another AGM battery spare, which is the same size and age as the one currently in use, but it doesn't fit in the engine bay, and I am worried about heat there, and also don't have space in the load bin for another battery. I have a double cab Hilux (2006 D4D) and no trailer.

We plan a trip to Botswana in July, where we will alternate camping one or two nights at a camp site (Nxai, Moremi, Chobe) and quite a lot of driving and game viewing even on the double stay days.
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