Changeover switch between isolated and non-isolated SMPS supplies?

[zenerbjt]

Dear Engineers,
We have a battery powered circuit as attached. Usually the isolated DCDC SMPS module supplies the load. But every so often one battery is removed for charging etc, and we still need power to the circuit….so we then have the relay (as shown) which switches between the isolated and non-isolated 5V and Gnds. It “changeover switches” them together.

What worries me is that charge pumping through the isolated SMPS may mean that even with the 1MEG equalisation resistor, there may end up being significant potential between the battery ground and the isolated ground?

…especially since there are actually four isolated converters in the real circuit (not just the one as shown).

Do you think there is any chance of this “charge pumping” causing a significant difference in the potentials of isolated and battery grounds?

 

[Diver300]

There could be a significant voltage between the different grounds, but it doesn't matter.

There whole isolated circuit has little capacitance to ground, so there is very little charge that has to be dissipated to get them to the same voltage when the relay operates.