Second input to 20 amp charge controller

hi all I’m new here but i was wondering if we could add a second input to the 20 amp charge controller so that for example they could be used in a 4wd so that if solar is not good on a day we could charge from the alternator . By the way this design is awsome. good work
regards jon

The alternator generates a voltage of 14.4V for charging the battery already, so we don’t need the step-down converter of the charge controller in between anymore. Or do you think the input should be at the low voltage (battery) side?

There are solutions for 2 battery systems in camper vans already and I guess they are quite cheap. Essentially it’s only a switch to prioritize the battery for the engine and only start charging the other one if the one for the engine is fully charged. Maybe that’s a more simple solution than adding this feature to the charge controller.

Well it depends on the battery type you want to charge. If you want to charge a LifePo4 by direct connection to the alternator it would be a bad idea for several reasons. DC/DC charging would be a valuable feature but I would require a buck/boost architecture with the alternator as input. So no simple solution for this in the Libre solar controller.

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Very old concept. Now DCDC controllers are common because batteries often have different chemistry requiring different charge profiles. Additionally, there may be a third battery in the camper, with a different chemistry again (maybe even 24V while vehicle is 12V).

Suggest user should be able to control point when alternator would override solar and just charge batteries. Applicable to other alternate power sources such as generator too.

Ok, that’s interesting to hear. Is it a buck-boost between the two batteries then? Because a simple buck converter can only convert from high to low voltage, but here each battery could be higher or lower some times. Or is there a separate DC/DC between the alternator and each battery?

hi all i think i have confused some people. I want to be able to run solar and alternator feed so that when there is plenty of sun the pv takes care or he charging but when there is no sun the alternator can charge a bit like the redarc dcdc or bcdc chargers work but nicer cause opensource is the way foward .

Wow, those Redarc BCDC chargers are quite expensive. And yes, they are buck/boost, which is currently not possible with any of the Libre Solar devices. But it should be possible to charge the battery with solar independently and program the firmware such that it switches a relay to connect to the alternator if there is not enough sun available.

Sorry, a bit slow but: REDARC BCDC2420 - will charge a 24V battery from a 12V source. Top quality equipment built for years of under bonnet use in the heat and water working with computer controlled car alternators. The dual alternator/solar models will use both sources if there is not enough solar. (Just to be clear I am also picking up the MPPT-2420-LC with switchable boost output thread.)

What they don’t have is customisable firmware for whatever future battery chemistry.

A couple of cheaper alternatives:

  1. 12V - DCDC10S_DCDC20S_User_Manual.pdf (approx US $100 with free shipping in Australia at time of posting).

  2. 24V - MPPT Solar Charge Controller MPT-7210A LCD Solar Panel Charge Controller DC-DC Boost 24V/36V/48V/60V/72V (US $31.56 with free shipping at time of posting).

Still no customisable firmware.