question

@Totomundo

Panels of different types don't usually work well together. Often the power is just pulled right down anyway and then not working at great efficiency. Are they the same VOC and amps?

If not then the extra power can dissipate through the other panels creating hot spots (and sometimes fire). Do the panels have good blocking diodes? If they are the same VOC it may work. Are you planning on series connecting it in, or paralleling the three?

https://www.victronenergy.com/mppt-calculator check your calculations though, the VOC is the most important figure, if at min temps you do not go over the 75v input in series, then it can work, not as well as it would with matched panels.

Firstly, 50w from a 200w flexible panel system installed on a vehicle roof is not normal. I had a 4x50w lensun array on a T4 for 2.5 years (after which they de-laminated) in a series/parralel config and I would get max power of about 160w (max hit in 2 years, normal high level would be 120w. I would get over 400wh/day (which is all I use)

I have now gone to a 250w rigid and its working well but it is a weight hit.

As prev. poster, don't mix your panels on the controller. Even if your original ones are in parallel and the portable is the same type, it would still be a bad idea for a few reasons. Firstly the portable one may be in a different situation (like not in shade), secondly, your original ones are massivly under performing so don't drag the portable down too.

I suggest getting a second portable 75/15, or if thats too much value, get a PWM for the portable (they are pretty low cost). This has the side benefit that you can use the portable to charge the leisure battery or the vehicle battery (assuming that I understand your use case correctly)