So, I have six identical 4s 5200mah 50C Lipo packs that I’m currently using in a eMountainboard build. The way I have them configured is 8s12p….meaning (2) 3 packs plugged into a diy xt60 parallel adapter, then those are plugged into diy xt60 series adapter. The reason for configuring this way is bc I’m using a Hobbywing Max6 ESC and 8s is the max allowed. To charge I’ve been using two separate but identical Hobby balance chargers along w parallel charging boards. Well, unplugging everything to charge and plug back together is getting old and wanting to attach a BMS to this pack. How would I go about doing this? Would I just solder each corresponding balance lead from each parallel pack together into one (splice and solder all of the 1st balance wire of the 3 paralleled packs to merge them to a single balance wire, which would then go into BMS, and then repeat w the remaining balance wires)? Can I get by just using one BMS or do I need two separate BMSs? Any help is appreciated. Thanks in advance.
Need help adding BMS on multi pack lipo battery
- Thread starter Atxraider
- Start date
If you want a permanent "merger" best to atomise the cells do a capacity test on each, ideally ESIR as well, discard near-EOL outliers and then build 8x paralleled groups, each group matching total capacity best you can.
You then have one monolithic 8S pack, one decent 8S charger will deal with it as a single pack, and only one BMS to worry about.
You then have one monolithic 8S pack, one decent 8S charger will deal with it as a single pack, and only one BMS to worry about.
Some analysis, to clarify the situation first:
First, the probably wrongly-labelled scenario: 8s12p. If you have 12 parallel packs (which is what 12p means, since the 5200mAh packs typically are only 1p themselves, no paralleled cells), with 8 packs in series (each with 4 cells in series), then you have a 24s 12p battery pack when they are assembled for use on the board; this is 288 cells. If the 8s is only 8 cells in series, then that 8s 12p would still be 96 cells. I expect this would be a rather large pack that probably wouldn't fit on or in the board.
Since there are only six packs of 4s, then this means you almost certainly only have a total of 24 cells (6 packs x 4 cells each). If they are wired for an 8s setup, then that's two 4s packs in series. If there's six packs, that means all wired together there'd be 8s 3p.
Assuming the latter configuration is correct, then these are the necessary things to add to / change from your existing discharge setup:
-- Parallel the balance lead sets of the most negative set of three packs, and then separately parallel the balance lead sets of the most positive set of three packs. If you have the space, then to simplify the work you could use paralleling boards like you do for charging. Then wire those to the BMS, in the correct order for that specific BMS. (it would need to be a BMS capable of running just an 8s battery). If you wire the BMS connector up to two matching connectors to your paralleling boards, then you can just plug it into them. Then when you later need to replace packs, or if you must test them separately to find problems, etc., then you can just unplug things instead of cutting wires or desoldering.
If the most positive balance lead of the most negative pack is electrically connected to the most negative balance lead of the most positive pack, then only one of those is used to connect to the BMS (or they are connected in parallel to the same BMS balance pin). With an 8s pack, there will be a total of 9 balance wire connections, if the BMS includes a ground pin on it's balance connector. If it uses the main pack negative as the ground pin, then there will only be 8 balance wire connections, one for each cell group's positive end.
Before connecting the completed balance lead set to the BMS, measure each pair of wires, starting at the most negative, and verify there is only one cell's worth of voltage between any pair. If there is more or less, then something is probably miswired and must be fixed before connecting to the BMS to prevent damage.
-- Route the main negative wire from the XT60 that normally goes to the controller instead to the BMS's P- pad.
-- Route the main negative wire from the packs' final paralleled XT60 instead to the BMS's B- pad.
-- If the BMS has a C- pad, this is used for the main negative wire from your bulk charger (that outputs the voltage needed to charge 8 cells in series).
-- The main positive wires route just as they do now; most BMSs don't connect to those. If your BMS does have a main positive connection for it, then you wire that to both the controller's and the cells' main positive wires.
First, the probably wrongly-labelled scenario: 8s12p. If you have 12 parallel packs (which is what 12p means, since the 5200mAh packs typically are only 1p themselves, no paralleled cells), with 8 packs in series (each with 4 cells in series), then you have a 24s 12p battery pack when they are assembled for use on the board; this is 288 cells. If the 8s is only 8 cells in series, then that 8s 12p would still be 96 cells. I expect this would be a rather large pack that probably wouldn't fit on or in the board.
Since there are only six packs of 4s, then this means you almost certainly only have a total of 24 cells (6 packs x 4 cells each). If they are wired for an 8s setup, then that's two 4s packs in series. If there's six packs, that means all wired together there'd be 8s 3p.
Assuming the latter configuration is correct, then these are the necessary things to add to / change from your existing discharge setup:
-- Parallel the balance lead sets of the most negative set of three packs, and then separately parallel the balance lead sets of the most positive set of three packs. If you have the space, then to simplify the work you could use paralleling boards like you do for charging. Then wire those to the BMS, in the correct order for that specific BMS. (it would need to be a BMS capable of running just an 8s battery). If you wire the BMS connector up to two matching connectors to your paralleling boards, then you can just plug it into them. Then when you later need to replace packs, or if you must test them separately to find problems, etc., then you can just unplug things instead of cutting wires or desoldering.
If the most positive balance lead of the most negative pack is electrically connected to the most negative balance lead of the most positive pack, then only one of those is used to connect to the BMS (or they are connected in parallel to the same BMS balance pin). With an 8s pack, there will be a total of 9 balance wire connections, if the BMS includes a ground pin on it's balance connector. If it uses the main pack negative as the ground pin, then there will only be 8 balance wire connections, one for each cell group's positive end.
Before connecting the completed balance lead set to the BMS, measure each pair of wires, starting at the most negative, and verify there is only one cell's worth of voltage between any pair. If there is more or less, then something is probably miswired and must be fixed before connecting to the BMS to prevent damage.
-- Route the main negative wire from the XT60 that normally goes to the controller instead to the BMS's P- pad.
-- Route the main negative wire from the packs' final paralleled XT60 instead to the BMS's B- pad.
-- If the BMS has a C- pad, this is used for the main negative wire from your bulk charger (that outputs the voltage needed to charge 8 cells in series).
-- The main positive wires route just as they do now; most BMSs don't connect to those. If your BMS does have a main positive connection for it, then you wire that to both the controller's and the cells' main positive wires.
Atxraider said:
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