There are bound to be people here running solar power on their boats, caravans etc. Maybe someone can answer this for me.

I want to run a DC-DC 20 amp charger from my caravan (house battery) to charge a second battery. Is there any tech reason why this cannot be done?

The details...The "experts" told me, or rather insisted and in some cases DEMANDED that what I have done cannot be done. So I done it and proved them all wrong.

I have a 120 watt bi-fold 12 volt panel, which I re-wired in series to make it a 120 watt 24 volt panel. It is mono. It then runs through a 12/24 volt 20amp auto switching MPPT controller and charges the 120AH van battery...That is the part the "experts" say cannot be done !! I have been running this set up now for 2 years, so I have proven it can be done. What this achieves is awesome charging ability. I run an Engel on freeze mode, some LED lights, charge the laptop, watch some TV, etc and use about 50 to 60 AH per 24 hours. On most days the house battery reaches float by 10 in the morning (the experts say that cannot be done too) and on a good day by 9 AM. Even with the Engel running on freeze, the battery stays at float all day until the sun goes down.

I am clearly producing a lot more power than what I am using. So I thought I might run that excess power into a second battery which I can then use to run the inverter. The biggest thing I would run off the inverter is my little washing machine which is 230 watts. So about 23 to 25 amp draw for about 12 minutes. It's a 1000 watt (2000 surge) sine wave inverter (as apposed to a modified square wave !!).

Both batteries are wet cell LA. The house battery is sealed valve regulated calcium wet cell, 120AH. The second battery is open valved lead wet cell, 100AH.

The instructions say the DC-DC is intended to be used as a dual battery charger. But they make no mention of solar. I don't want to burn out my brand new DC-DC charger the first time I plug it in :)

Thanks in advance for any advice you might have.

Cheers
Neil