DCDC and solar charger query

4x4PlayNT

Unfortunately this is a problem faced by many systems where there are 2 charging mediums used at the same time, the one putting out the greatest voltage will 'shut off' the other.

Short of using a single unit that will accept charging current from both, or more than one, source the only way would be to fit a relay to the Solar panels that will 'switch off' the solar panels when the vehicle ignition is on.

Regards
Athol

If the charge voltages of the 2 devises are even similar, they will play happily together.
I use solar at a boost voltage of about 14.8V and direct charging from the alternator at about 14.4V and they will both contribute charge together - up to 30A from the solar and up to 70A from the alternator. As the batteries come up in charge, the alternator input will gradually drop away.
Cheers,
Peter
OKA196 motorhome

4x4PlayNT

Have you actually parked the vehicle, had the solar running through it's switchmode MPPT unit to batteries AND had the engine running through it's DCDC charger and measure/seen what the charge input is really doing? That way you will know if they conflict.

Some MPPT chargers run MPPT when in BULK, bit switch to PWM when in absorbtion or float.
The alternator to DCDC will do same all the time but drop through it's charge regime.
Unless you try it you won't know if they fight each other. If each one is momentarily stopping it's charge to read the system voltage for it's micro processor to decide what to do next instant, then they may conflict as the voltage fluctuations are being varied from each source.

Not hard to have an opening relay to turn off solar input while travelling as Athol mentioned.

I have used solar through PWM AND direct alternator charge at the same time but when there is switching waveforms and pulses of charge from two sources to the same point it is worth checking before that long drive.

What brand dcdc is it? If it combines dc sources and has mppt like most do, just plug the panels straight into that and keep the other mppt for if you have an emergency. You might be over thinking it.

While on this topic what if you have solar but no dc-dc charger? I have straight from alternator to aux battery through 2x 100amp fuses and solonoid to protect the tug battery.
Altetnator is 110amp. Solar will be 250w (not purchased yet).

I think you will find with the Redarc dc to dc charger that there is a relay to be purchased that switches the Solar connection off when the ignition is on. So when driving the solar panel is doing nothing but when the car is switched off the solar panel will charge.

It will be a matter of suck it and see, some controllers will play happily together others won't. Generally when batteries are low and can accept the entire output of both chargers the chargers will be in current limit mode and both will supply their maximum outputs. It is when the current flow drops below the maximum of both chargers that problems may start, one charger will try to hold its voltage and the other will push it higher causing it to back off more, current drops, the charger that backed off then tries to increase it again and so the cycle repeats.

At this point of time the batteries will most likely be in a fairly high state of charge anyway unless the chargers have very high output capacity or there is sever interaction you might be better off just leaving both working if they are each putting out a fair charge rate, ie if one is putting out 20A and the other is cycling between 5A-15A then your still getting extra into the battery so let them play. If however both a badly interacting with each other and your only getting say 5A out of each but one on its own will give 20A then your better off turning one charger off.

And just when I thought I had all aspects of charging my van batteries sorted out - along comes another curly one.

Yesterday I was feeling quite comfortable having worked out how to go about using a genset to 'top up' the batteries if the situation arose - and now we have a new case to consider - 'possible CONFLICT between charging systems - and as it hasn't been mentioned by any of my installers as the units were added, I am hoping it won't be an issue - but as mentioned earlier we will just have to 'suck it and see'.

My systems now consist of the original CTEK MPS25 which is purely a 240 volt charger - I see no issue there - particularly as I can switch that off quite easily.

The next unit installed not long back and not tested yet is a Jaycar 'Powertech' 4 stage 40A DC - to DC unit to charge purely from the alternator through the Anderson plug and only whilst the engine is operating.

The latest came with the addition of solar panels - an Enerdrive ePower PWM 30A unit.

Each of these is wired separately down to the batteries.

It may be 2 or 3 weeks before I can test it all, but I will most assuredly advise if there are any dramas.

In the interim, if 4x4PlayNT has an issue or anyone else with a similar arrangement I would appreciate any feedback thanks.

Good luck with it all everyone, life was so much simpler back in the dark ages - a tilley lamp and old army tent weighing a ton - we didn't know what we were missing. Ignorance is bliss...

Cheers - Phil

I have 200watts of solar on roof of car and dcdc charger in boot that feeds 2 x 130amp gel fullriver batteries. Solar via a MPPT reg. in 3 years I have never had an issue and batteries always charged up. They happily co-exist being on all the time (naturally dcdc is only on when ignition is on).