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I have three identical lead acid batteries. All three batteries are on a common ground since they power different components on a same circuit. I have three independent "intelligent" chargers whose charging outputs are on isolated grounds.

I wonder if there is a counter-indication of charging all three batteries at the same time when on a common ground (their positive poles are disconnected from the main circuit, of course). I know this could be charger-specific, but if anyone knows anything about it.

Here is a quick schematic of what it is (would be) like when charging:

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Kirchoff's Current Law says you will be fine. \$\endgroup\$ – Matt Young Mar 13 '14 at 13:42
  • \$\begingroup\$ Yes, that's what I suspected but those chargers are a bit expensive so... ;) But thanks for the confirmation! \$\endgroup\$ – Doombot Mar 13 '14 at 14:19
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The significance of the "isolated ground" is that it can be connected to any place in the circuit without consequence. (It isn't really a "ground", but a negative or return lead. Ground usually implies a common connection.) So, it is allowable to connect it to chassis ground, and it is allowable to connect it to another charger's return lead. It probably could even be connected to another charger's positive lead in order to create a higher series voltage (though you don't need that here).

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  • \$\begingroup\$ Ok I will check this out and keep you guys in touch! Thanks! \$\endgroup\$ – Doombot Mar 13 '14 at 13:30
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If the batteries are disconnected from the loads, there is absolutely no issue with charging them all at the same time.

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  • \$\begingroup\$ If the load can tolerate the charging voltage (usually no more than 14.2V for the so called 12V lead-acid) the load may remain connected. \$\endgroup\$ – Nick Alexeev Mar 13 '14 at 4:10
  • \$\begingroup\$ Nick is correct, no issue even if the loads are connected, except the voltage is a bit higher and the charge time may be longer if the loads are active. \$\endgroup\$ – John D Mar 13 '14 at 4:15
  • \$\begingroup\$ Ok I will check this out and keep you guys in touch! Thanks! \$\endgroup\$ – Doombot Mar 13 '14 at 13:29

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