Charging second battery from mains via Solar In on DC charger

[miniyazz]

Hi all,

I have a Projecta Pro DCC charging a second battery and due to going away for periods of up to a month or so at a time, was looking for something to keep preferably both batteries topped up when away.

I already have the DCC for which the manual is a bit ambiguous but suggests if charging from solar, it will first charge the second battery and then charge the primary.

It has an unused power in which is intended to be supplied by an unregulated solar panel with 27 VOC max (up to 300W peak).

Coincidentally I also have an AC - 24V DC fridge inverter/charger rated at around 240W maximum so I thought, great, I can just wire that up and plug it in.

It does seem to at least partially work, but I am getting some odd readings from the charging display that suggests it seems to cycle between supplying around 200W to around 20W, and the charger intermittently changes between 'Silent Solar' and standby mode.

Nothing seems to have caught fire yet but I am wondering if this is a safe thing to be doing, if anyone has tried anything similar, and if it will indeed charge the main battery when left to its own devices for long enough.


Below are the three scenarios listed in the manual, which don't seem to make a lot of sense to me - why would it disconnect solar if the auxiliary battery voltage dropped too low? And why would it only charge the main battery when the main battery voltage is above 12.8V? I think someone's become confused when writing them..

Scenario 1: The vehicle’s main battery is below 12.8V and the DCC is in
Power Saving mode.
If solar power is actively available, the DCC Pro will implement silent solar
charging. The LED Glow Ring will indicate aqua green intermittently. In this
mode the main battery is ignored by the solar charging process and all
available power is dedicated to charging the auxiliary. If there is a load
connected to the auxiliary battery, a fridge for example, the DCC Pro will
attempt to match the discharge rate from the auxiliary battery for as long as
solar power is available. If the voltage on the auxiliary battery drops too low,
the charge cycle will be terminated and the DCC Pro will revert to Power
Saving mode. In silent solar mode the Remote Display is disabled in order to
conserve power however pressing the button will ‘awaken’ the display and
the monitor will indicate the auxiliary battery voltage, the charging power in
Watts and display the text SLT SOLAR.

Scenario 2: The main battery voltage is above 12.8V and the DCC Pro is in
a normal charging cycle (boost, absorption or oat).
If solar power is actively available, the DCC Pro will override the current
charging cycle stage and implement primary solar charging (providing there is
sucient power to do so). The LED Glow Ring will indicate aqua green
continuously. In primary solar operation both the main and auxiliary batteries
will be charged simultaneously. Once the main battery voltage has reached
14.5V (or predetermined maximum alternator Voltage) the DCC Pro will release
the main battery and continue to charge the auxiliary battery only. In primary
solar mode the Remote Display is automatically enabled and the monitor will
indicate the auxiliary battery voltage, the charging power in Watts and display
the text PRM SOLAR.

Scenario 3: The main battery is disconnected from the DCC Pro but
remains connected to the auxiliary.
This scenario may occur when the DCC Pro is installed in a caravan or camper
trailer for example, but unplugged from the tow vehicle thereby disconnecting
the main battery supply. If this occurs, the DCC Pro will implement silent solar
charging and it will perform as a stand-alone charging source complete with
MPPT functionality. The LED Glow Ring will indicate aqua green intermittently.
In silent solar mode the Remote Display is disabled in order to conserve power
however pressing the button will ‘awaken’ the display and the monitor will
indicate the auxiliary battery voltage, the charging power in Watts and display
the text SLT SOLAR.

[Kingbrown]

One possibe issue I see with using that 24V power supply as an input to the charger/isolator occurs when there's a heavy load on the charger.
The MPPT feature of the charger/isolator will dither around and load up the solar input until it sees that the solar voltage is falling rapidly.
At this 'knee' point the charger determines that there's maximum power transfer and that's the load that the charger maintains on the solar input.
But with a regulated power supply, it will try to maintain its output voltage when the current is increased, which may ultimately cause the power supply to be overloaded if the demand of the charger/batteries is greater than the capacity of the power supply.
Overloading shouldn't occur if the power supply can handle at least as much as the charger or when the batteries are in a reasonably good state of charge.

An aspect of the power supply that might not be immediately apparent is whether it's DC output is well regulated and filtered or just a rough 24V with a degree of ripple which could upset the charger.

[miniyazz]

Good points, thank you.

Any suggestions on how to keep it topped up easily/cheaply? It is typically parked in a car port so a solar panel probably not an option.

[Bill Parks]

Do you have an isolator between your batteries?
If so the isolator should not allow power to flow backwards from the 2nd battery to the first.
I’ve not got a dc/dc charger on mine just an MPPT controller connected to my 2nd battery.
My roof mounted panel only charges the AGM in the back of my Pajero.
I have 2 solar inputs to the controller so when parked undercover for a few weeks I can hook my portable panel to the controller and just put it outside in the sun.
For the main battery I have run an Anderson plug from the battery to the bullbar. That way I can connect the charger without having to open the hood.
If you do have an isolator you could hook the dc charger to the main battery and it should charge both batteries just as it would with the alternator. That is the way I wired it up on my old Navara and it worked a treat.
You could also connect a 2nd input to your dc charger for a stand alone panel for when it is parked undercover.
Bill

[miniyazz]

Do you have an isolator between your batteries?
If so the isolator should not allow power to flow backwards from the 2nd battery to the first.
I’ve not got a dc/dc charger on mine just an MPPT controller connected to my 2nd battery.
My roof mounted panel only charges the AGM in the back of my Pajero.
I have 2 solar inputs to the controller so when parked undercover for a few weeks I can hook my portable panel to the controller and just put it outside in the sun.
For the main battery I have run an Anderson plug from the battery to the bullbar. That way I can connect the charger without having to open the hood.
If you do have an isolator you could hook the dc charger to the main battery and it should charge both batteries just as it would with the alternator. That is the way I wired it up on my old Navara and it worked a treat.
You could also connect a 2nd input to your dc charger for a stand alone panel for when it is parked undercover.
Bill

Hi Bill,

There is no isolator between them other than the DCC Pro itself which acts as an isolator. But the DCC Pro does have the ability to use the Solar input power to charge both primary and auxiliary batteries simultaneously.

That sounds like a good set-up you have there. I may get a solar panel and do a similar thing.

Thanks

[Turorit]

Good points, thank you.

Any suggestions on how to keep it topped up easily/cheaply? It is typically parked in a car port so a solar panel probably not an option.

Could you put a solar panel on top of the carport & then have an externally mounted anderson plug on your Paj?
You'd need some thicker wiring from the solar panel, depending on the length.

[miniyazz]

Could you put a solar panel on top of the carport & then have an externally mounted anderson plug on your Paj?
You'd need some thicker wiring from the solar panel, depending on the length.

The car port is essentially part of the house (and already has solar panels on it). But I can quite easily set up the portable solar panel in the back garden with a few m of cable when parked up.

Made the order this morning, $229 inc delivery for a 120W flexible/portable 'solar blanket' - folds nice and small for taking out bush too!