Adding charge controllers in parallel

When adding more solar panels (or other inputs) in the future is it good practice to add another charge controller in parallel with the original, or does a new larger unit need to be procured to run solo?

The answer is...it depends. If your current charge controller can handle the additional current or voltage (depending on how your array is configured) then there is no reason to add another. I would suggest an array configured in series to get the highest possible voltage and a single appropriately sized MPPT controller properly connected directly to your house bank.

But if the existing battery charge controller is max'd out then can they be added in parallel? I'm wondering if there might be a problem where one charger shifts into float but the other doesn't, or some other conflict.

Parallel controllers can be a bit of a pain in the butt but can work in parallel. A single larger controller would be my choice.

If you do parallel make sure the programmable parameters are identical.

As long as all the inputs use the same voltage setpoints (which IMO should be adjustable) not a big issue.

In most cases isn't the controller already running in parallel with engine alt and 110 volt charger? So adding another charging source does not seem to be a problem. You would also gain some redundancy.

Parallel operation of solar charge controllers, engine alternators, gensets running shore power chargers, etc. is possible and usually works ok. Each device will have a different, sometimes a lot different charging parameters. When the batteries are low then all will put out near maximum, unless it is too high a percent of the batteries amp hour capacity. That limit is usually stated as 25% for FLA batteries, maybe double for AGMs.

As the batteries become more fully charged, say about 75%, one or more of the devices may switch to float, but that is ok because at that point the batteries can accept less current anyway so it doesn't matter.

But if I had my druthers, I would have one large solar controller rather than two in parallel.

David