That is some Great Stuff,, I am just learning so everything helps...
Maybe a little more information on my part will help...
The 2 middle bottom squares are Solar Charge Controllers, I have 1 for each battery.. So charging through the cable might not be an issue??
I have 1 solar array to a combiner box, out of the combiner box I have 2 circuit breakers. 1 circuit breaker going to the batteries SCC.. When Bat 1 is charged, I shut the breaker off for bat 1, which puts the SCC to sleep and turn on the breaker for bat 2 to charge...
question from above:
I didn't get why you want to separate / rejoin / separate your parallel batteries - maybe you could explain more?
Chemistry of batteries, different Capacity, Age difference of batteries..
I basically only want to parallel the battery for a few milliseconds to swap between them to maintain power to the loads..
Reason for using the make before break circuit... With what ever means to prevent the inrush current between batts
Currently I use a off/1/both/2 switch for each battery, with a 25 ohm resistor through post 1 for precharge...
Thanks again!! if more information is needed I will try to explain what I am trying to accomplish better..
As said above, connecting 2 separate large 200AHr batteries together when at different charge voltages/SoC is problematic.
If connecting directly by just relay, "large" currents will flow until the batteries equalize charge state - could spike to 100's of amps. Currents would flow more like up to several minutes. This can be dangerous & stressful for cables, batteries & contacts (MOSFETs similarly high stress). Batteries likely to get damaged, contacts weld, etc like already mentioned. It's a bad idea.
At the very least you would want something like a "precharge system" with eg high wattage (eg 100W) resistor approx 0.5 to 5 Ohms in series (depending on pack voltage).
You'd have a resistor in series with each battery and a relay across each resistor.
Battery carrying load, relay = closed, joining battery, relay = open. Current flows for a while vs resistor, batteries get close, 2nd relay closes.
However, from your picture & application description, just having the load supplied via the two diodes would prevent one battery dumping current into the other. Since the chargers are separate, charging is no issue.
You could safely add/disconnect either battery at any charge state.
Only the load would see a step up in voltage if a higher charged battery was connected. No large currents would flow.
Like also said above you need large diodes (depending on load).
This is how some UPS's already operate internally.