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tvkalvas asked

Safety switching on BMS and Blue Smart charger

I am planning on using a Victron Blue Smart 12/20 charger for LiFePO batteries. Reading the manual it worries me as the procedure for stopping charging is described to be done in a definite order with AC switched off before removing connection to battery. Now, if the Lithium battery BMS goes into over voltage protection it will switch a relay removing the connection to the battery. Will this damage the charger? Should there be a separate AC relay controlled by the BMS to remove the AC feed to the charger before cutting the DC path to battery?

battery chargingLithium BatteryBMS
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Joe Greer avatar image Joe Greer commented ·

I have the same concerns. After purchasing a new Bluesmart IP22 24v 12A charger. In my case, there was a charger malfunction at the end if the 1st charging cycle attempted, rendering the new charger completely non functional. I was not present when the issue occurred, but after successfully charging my 200ah 8S LiFePO4 battery, my Overkill Solar 24V 100A BMS disconnected charging current at the default parameter set.


Upon checking the charging status, I found the charger to be warm (not hot, as noted during bulk charging cycle), but all staus lights on the BlueSmart charger were off, and the charger appeared unresponsiive. The battery was fully charged. The charger fuse ohm'd out OK. After waiting 24 hours or so, and draining the battery some under normal load, the charger would not come to life when reconnected. No status LEDs, no connectivity to Victron bluetooth app.


I returned the apparently defective charger for replacement and am now charging my 90% depleted 8S LiFePO battery for the first time with the replacement charger. I plan to closely monitor the absorption charging phase, but am concened that the same issue could repeat itself.

I will report back with results when the charging cycle is complete. Hope this helps, and curious if others have had similar issues.


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1 Answer
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wkirby answered ·

Disconnecting the AC side first is good practice to help prevent arcing that might occur if disconnecting the battery cables first.
As a safety relay, switching the DC cables would not be a problem. Just be sure that the relay contacts are rated for the current and Voltage.

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