Not sure about that controller specifically (I'll have to look up the spec sheets), but there are two styles of dual
battery solar controllers - and I don't mean MPPT and
PWM.
1) Some Dual
Battery controllers will put the main charge into the primary (normally Leisure)
battery, and just a small 1A max trickle into the secondary (typically Starter)
battery.
2) Some Dual
Battery controllers are programmable in terms of the balance between the primary and secondary batteries.
The first type is ok if the idea is to just deal with parasitic losses on the starter
battery, such as from an alarm say.
The second type is much more flexible if the goal might be to charge two separate
battery banks from a single PV array (as I think one poster has asked about?).
I think it is worth pointing out that the Votronic Duo Digital Dual
Battery Solar Controller that is regularly touted as the way to go is one of the first types. For most people who just want a trickle into the Starter
Battery, that is fine, but
it is limited to just 1A maximum into the secondary
battery, no matter how big an array is. Even the 430W Dual Votronic that can put near enough 30A through the controller, only 1A maximum of that 30A will go to the starter - or ANY
battery bank connected to the secondary output.
Brian, your existing panel, based on the size you quoted is almost certainly a 150W Panel as you say.
Say you add another pair of 150W panels - that will give you 450W
potential of
Solar.
The rule of thumb with
solar is 1W of
Solar per 1Ah of
Battery. This would suggest that you will have twice as much
solar as you should BUT .... that rule needs to be adapted depending on the individual and the way they use their camper/motorhome. You said you mainly use your motorhome " ... end sept to April" - At the back end of Sept and in April you would be hard pushed to be harvesting anywhere near to the maximum of the
Solar array and you won't be overloading with
Solar compared to
battery. TBH, if anything, I would wonder if there is much value in adding extra
solar when your usage is mostly over the winter/cooler time of year as the extra it will give you will be marginal I suspect.
It depends if it suits the way you wild camp, but a portable setup where you can angle the panels might be a more effective option? (I am going to assume you don't really want the option of a roof-mounted tilting setup).
If you were camping April to End-Sept, then 450W of
solar into 200Ah of
battery would see the batteries likely refilled every day when wild camping - but even then, you could plan your usage to take advantage of that. If you have an
Inverter, you could use electric to heat the water in the morning, or use electric kettle or ring for breakfast or lunch, knowing you will be back full again for the evening. In that case, I'd stick on as much
solar as I had room for