Pajero Owners Club of South Africa

Great stuff!
I don't know about you, but after such a project I can't decide what was the best part of it - the end product or the knowledge I gained.
You now have more knowledge of a 2-battery setup than most!

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There's a slight problem with my design (or design philosophy) it seems - specifically using one DC battery (as opposed to the car battery) to drive the other.

You see the DC-DC charger has a low voltage cut off at 12.5v (I assume this is to keep the main battery from going below 80%), so I will never get the full value of allowing a DC battery to be discharged beyond 80%. This effectively makes the first DC battery redundant.

Ok so help me out here... As per my previous post.

What I was wanting to achieve was having two auxiliarry batteries. One a permanent fixture in the vehicle, charged by my current NL setup. The other was a temporary one for extended trips, using the first auxiliary battery to charge the second. This would mean the second auxiliary battery was always being charged, even when the vehicle was stationary.

However, given the situation specs below, while the charger will accept a voltage of 10.5 to 15V from the aux battery, it will only charge the second aux while the engine is running, like a normal split charger.

So effectively my thoughts above are thrown out of the window, and my thinking is that I have actually bought the wrong charger.

The only way round this to achieve what I want is some way of swicthing from one aux battery to the other once the voltage has dropped below a certain threshold.

Thoughts?

http://www.hcdpelectronics.co.za/
Switch ON voltage : > 13.3V (on Ignition input)
Switch OFF voltage : < 12.5V (on Ignition input)
Charge input voltage : 10.5V to 15V (on Car & GND connection)
Solar Panel input power : 180W max
Input current : 17A max plus load current
Output voltage : 14.2 +/-0.1VDC
Charge current : 12A max
Operating temperature : -10 to +45 degrees Celcius
Dimensions : 145mm x 130mm x 68mm
Weight : 820 gram

OK, I don't quite understand one thing.
The specs give switch on voltage of 13.3V, but also a charge input voltage of 10.5V.

I don't quite get it.
I thought that it would charge from a source with an output of 10.5V?

Have you tried using a source other than the alternator as input to the DC-DC charger?
(Such as a battery at 12V?)

I looked at your wiring diagram again.
If you chose to use a solar panel, you would flip the toggle switch to SP, not so?
So if you want to charge from the aux battery, it will substitute for the SP, which means that if the engine is not running, you will have to select SP.
Check with Manie whether I understand it correctly.

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Perhaps some salient emails between myself and Manie might help.

Me: I intend to use it in conjunction with an Aux Battery in the engine bay which charge a battery in the back of my vehicle via this charging unit. The Aux battery in the engine bay is charged via NL split charge

Manie: Perfect – keep in mind that our DCDC12A is not waterproof.

Me: Just one question. On opening it I noticed you had connected the battery protector to the load side of the charger, which confuses me a little. The DC-DC charger disconnects on low voltage, so am I right in understanding that the charger protects the source (car) battery from low voltage? But it doesn’t protect the battery that it itself is charging from low voltage?

Manie: The power for the load side comes from your second battery when the engine is not running. We therefore connected the under voltage lock-out unit to the load. You should now connect your loads to its output terminals. The dcdc charger will automatically disconnect itself from the main car battery if the car voltage drops below 12.5V

Me: Effectively what I have is the first auxiliary battery in the engine bay – it is to this that the DC-DC charger is intended to be connected. Now if the charger disconnects at 12.5v I’m not getting the full value out of the first battery.

Have I got my thoughts and configuration wrong? Sorry if it seems I’m asking silly questions.

Me Again: It’s me again – revisiting the spec sheets the ignition input is the one that detects the 12.5v – 13v on/off scenario.

But your spec sheets says the charging voltage is from 10.5v on the car input. Am I right in saying that if I bridge the ignition and car inputs as per your alternative wiring diagram, the same situation will happen i.e. the charger will switch off at 12.5 v? So how then can the charger operate at a low of 10.5v on the car and ground inputs unless one doesn’t use an ignition input?

Manie: For the preferred wiring the following:

The ignition line is only a voltage sense line that should be connected to a voltage source close to the battery (switched ignition wires normally have a vey small voltage drop).

If your main +Car and GND wires have a drop of say 3V at 17A and the alternator delivers 13.8V it means that the DCDC12A will see 13.8-3=10.8V at its input terminals and will still charge at 14.2V provided that the ignition sense line stays above 12.5V witch it should because there is less than 0.01A being drawn on this line (it is only a sense line)

Normally the DCDC12A is connected to the car’s main battery/alternator and acts as a dual battery switch which separates the main battery and auxiliary battery if the main battery drops below 12.5V (engine switched off).

Hope this explains the operation.

My last Q for which I am awaiting a response: Does this mean this isn’t actually the ideal scenario for using two auxiliary batteries (one being charged by a solenoid system, and the other as a “plug-in” when needed) to effectively increase ones capacity for extended trips?

I read CATS' post again, and his simple but efficient setup is what I would advise as well.
I would have asked Manie to advise me how to set that up, using his charger.

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What it looks like I have to do to achieve what I want is to run a second set of cables from the cranker to the back and have the dc-dc system a backup of the first NL system. Then build in a switch to cut over from one to the other when necessary.

Not only do I have redundancy but a simple cut-over if needed. And also have solar capability

The question is. Will the alternator be able to handle the load or am I missing the point?

Simon

Lets gets this right. What is your goal exactly? Do you want to install an occasional third battery in the rear of the vehicle to extend your staying power only every now and again?
You already have a second battery with NL system in the engine bay and thick cable running to back of vehicle where fridge etc gets plugged in? I assume the fridge connect to this plug by Brad Harison type plug?
I assume the above is yes in my explanation below.

I would connect the dc dc charger to the cranking battery and install it somewhere permanently in the rear of your Pajero out of sight. I would then make a very short cable from the output side with a Brad harison type plug again. Your third battery in box will then have two brad harison connections. One used as input from dcdc and one used as output to fridge. Connect a nl battery monitor and once battery goes flat unplug the fridge from this battery and plug into second battery using the plug. You thus have two similar plugs in the rear where you can connect. If any of the two systems (nl solenoid or dcdc) fail it will still be able to work normally and independantly from the other. You manually need to unplug the fridge but my experience was that the dcdc is so efficient in keeping the deep cycle battery topped up that I seldom if ever need to do this. You can also plug in a solar source into the dcdc if you have this available.

This basically is what my system looks like, except that my rear batteries are 2 and it is permanently installed. Thus 4 batteries in the vehicle and another two in the Xplorer.

CATS
I have edited this post now 4 times to try and be clear, does it make sense?
With all my editing I missed your post Simon, which basically agree to what I say. The alternator will handle it.

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Christo, your assumption on my goal is correct. So we're in agreement on what I should do. But I wont make it a permanent installation. My one aim was to be able to take the system out for a portable solar arrangement when I get the money for a panel. I then still have a battery in the car for when I'm mobile, and leave the panel behind.

I guess I hadn't thought through exactly what I wanted but the redundancy and a manual cut-over crystalised my thoughts somewhat.

And I think I will get a second battery protector, there being one for each battery