Solar charging when car has a dcdc charger


Well-Known Member
sorry if this has been covered before, i couldn't find an answer I am looking for.

I am looking at one of these , to permanetly put on top of my canopy :

I currently have an auxillary 12v circuit in the car, which is wired to an auxillary battery, which is charged by a redarc DC-DC charger (redarc bcdc1220). My auxillary circuit is isolated completely from my starter battery and car circuits (except through the dcdc when car is running).

I have an auxillary power socket in the tray already ,along with various other things wired into my aux circuits (inverters, fridges and stuff)

The above solar unit comes with a standard power regulator (no MPPT) ... which I'd ideally like to install in the canopy also, and simply hardwire it into my existing auxillary circuit in the canopy ... straight into the 12v auxillary circuit and thus into the battery.

What happens when i am driving, and my DC-DC charger is dumping power into the circuit 20amps (its input Is alternator) at the same time as my solar regulator also dumping in? (5 amps or so).
Both connected to battery directly along with loads.
Will the redarc get confused because it sees a higher voltage coming in from the solar reg and cut out thinking it has no work to do? Or would the solar reg see high voltage from redarc and decide to cut out / float ?
I do know that my redarc every 100seconds stops charging and checks the battery voltage to reassess.

Sent from my iPad using Tapatalk HD
Last edited:


Well-Known Member
Not sure how that will work but you can get a Ctek DC-DC which has a solar input then will decide which to use.

Another option would be just to wire a relay to disconnect the solar once the ignition is on?


Well-Known Member
Yeah I know I can replace the dc dc Mac man but don't want to. Cost and hassle. I just want to throw panel on roof with its regulator and wire it into my aux battery.

If I did get a new dc dc id go the bcdc1225 redarc which has Builtin solar. Don't want the bcdc 1240-40amp (alternator struggles with load at night as it is but that's an unrelated factor).

I'm hoping they would just get along. Doing some tests at moment by plugging in my acdc projecta charger and then monitoring both to see what reactions are. The redarc actually seemed to go into absorption mode pretty fast but then that's because she's fully charged. Might run battery down a bit and then do some better test.

Of course the projecta isn't the best charger to pretend with because it's 7 stage and too smart (it went off into some recon loop when the redarc got involved as it got confused).

Most importantly can't be assed having to run seperate cables from the back of vehicle all way to front so hopin to tap into existing aux circuit

** Sent from tapatalk**
Last edited:


Well-Known Member
A PWM does not handle partial shading of the panel as well as a MPPT regulator. Just saying in case that matters with your setup.

My suggestion would be to phone Redarc and ask them. They have an excellent tech section who have always been most helpful with my silly questions.


Well-Known Member
Yeah think a call into the silly questions department is in order.

My only real concern is whether the solar contribution (already regulated) to aux would somehow trick the redarc into floating when it shouldn't and therefore missing out on valuable Charging from it.

Ie the redarc sees 13.4v or whatever and goes ok I sleep now ...

Guess I need to suss out what voltages each of the equipment makes decisions on that will probably dictate it. From what I understand the solar stops at 13.4v assuming full charge whereas redarc stretches out to 15v

Sent from my iPad using Tapatalk HD


The minimal fuss solution is what Mac suggested. Wire a relay to isolate the solar panel when the engine is running.

If the red arc see's the voltage increased due to the solar panel when the engine is running you loose out on 20amps from the alternator just to get nominal 5amps from solar.
Relays are cheap.

Checkout my ride in My Colorado build Thread!!!


New Member
I admire that you have taken the decision to use solar panel to run your car. I hope you have got the answer to your question here. I stay in Perth and I was really intrigued about the discussion about solar panel which was going on here. I am of the opinion that solar energy is the future and is the most reliable and cost-efficient source of energy. I would like to know your opinion about it.


Well-Known Member
This thread is ancient and obselete guys.. have since been through several solar setups , MPPT chargers and all is well in the world lol