I have a Victron 12V 30A charger. I need to charge the 48V 4S2P bank to 100% SOC before syncing to Victron Smartshunt so SOC can be tracked going forward. Also, I might repeat it on other setups I am helping others with.
I wired up a 4 way parallel connection with a 100amp dual busbar and MBRF fuses (50A Blue Sea Systems) for each of the positive terminals. The charger is connected to busbars diagonally to keep the round-trip resistance for each of the four connections about the same. I did measure it with a micro ohm meter for each of the four connections - about 6 milliohms round trip (1.5mohm for negative, 4.5 ohm for positive with additional resistance from fuses).
However, as soon as the second battery is connected to the busbar, it seems arcing happens in the last terminal connection to be made since now the two battery groups are in parallel, and will try to rebalance (but should be small as calculated above). It seems arcing was strong enough to blow two fuses (no short-circuit here - all connections were tested with 4 wire method for small variations in resistance, and against short-circuit).
Before starting, I confirmed that each of the battery group had equal voltage - max 10mv difference with multimeter. 3 were less than 5mv difference (i.e., identical on DMM). So, max balancing current should be 10mv/6 mohm ~1.7a.
So, it seems to me I have missed something here. 50A fuses shouldn't blow when batteries in the bank (which is not connected to anything else, not even the charger - so, open circuit) are resting and are at very small potential difference, no more than 10mv (checked with both Klein and hioki DMMs).
I have couple of questions:
- Is there some kind of higher inrush current (especially, since I used Andersen connectors to connect the pair of clamps for each group to corresponding paired connection on busbar, correct polarity, no short-circuit in connections)? That would blow out some of the fuses? If this is the case, how would one go about calculating the inrush current?
- Are there any kind of inductive switches that I can use for each of the four connections, to turn them on one by one, and avoid arcing when the connection is switched on, through smoother current introduction?
BTW, to repeat, polarities are correct, no short-circuit, no loose connections (checked via 4 wire resistance meter).
I am aware of battery equalizer and have one of them. However, it is very convenient to be able to parallel charge the batteries using a slow 12V 30A charger like Victron, and have them balance nicely through paralelization. Useful once in a while. I am aware of alternative approaches like charging one group at a time, and using the equalizer to smooth out the differences. I am very curious about what I got wrong above, and will very much appreciate knowledge sharing from those who have already solved this.
Please feel free to ask if anything not clear. BTW, batteries are 12v 410Ah PowerQueen (in case any questions about BMS behavior). There is no balancing current flow at rest (verified with hioki clamp meter after 0 adjustment).
I wired up a 4 way parallel connection with a 100amp dual busbar and MBRF fuses (50A Blue Sea Systems) for each of the positive terminals. The charger is connected to busbars diagonally to keep the round-trip resistance for each of the four connections about the same. I did measure it with a micro ohm meter for each of the four connections - about 6 milliohms round trip (1.5mohm for negative, 4.5 ohm for positive with additional resistance from fuses).
However, as soon as the second battery is connected to the busbar, it seems arcing happens in the last terminal connection to be made since now the two battery groups are in parallel, and will try to rebalance (but should be small as calculated above). It seems arcing was strong enough to blow two fuses (no short-circuit here - all connections were tested with 4 wire method for small variations in resistance, and against short-circuit).
Before starting, I confirmed that each of the battery group had equal voltage - max 10mv difference with multimeter. 3 were less than 5mv difference (i.e., identical on DMM). So, max balancing current should be 10mv/6 mohm ~1.7a.
So, it seems to me I have missed something here. 50A fuses shouldn't blow when batteries in the bank (which is not connected to anything else, not even the charger - so, open circuit) are resting and are at very small potential difference, no more than 10mv (checked with both Klein and hioki DMMs).
I have couple of questions:
- Is there some kind of higher inrush current (especially, since I used Andersen connectors to connect the pair of clamps for each group to corresponding paired connection on busbar, correct polarity, no short-circuit in connections)? That would blow out some of the fuses? If this is the case, how would one go about calculating the inrush current?
- Are there any kind of inductive switches that I can use for each of the four connections, to turn them on one by one, and avoid arcing when the connection is switched on, through smoother current introduction?
BTW, to repeat, polarities are correct, no short-circuit, no loose connections (checked via 4 wire resistance meter).
I am aware of battery equalizer and have one of them. However, it is very convenient to be able to parallel charge the batteries using a slow 12V 30A charger like Victron, and have them balance nicely through paralelization. Useful once in a while. I am aware of alternative approaches like charging one group at a time, and using the equalizer to smooth out the differences. I am very curious about what I got wrong above, and will very much appreciate knowledge sharing from those who have already solved this.
Please feel free to ask if anything not clear. BTW, batteries are 12v 410Ah PowerQueen (in case any questions about BMS behavior). There is no balancing current flow at rest (verified with hioki clamp meter after 0 adjustment).
