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Ok for those of us who Bottom Balance our batteries have slim pickens out there for equipment options leaving us to be creative. The Initial or Bulk Bottom Balance is simple enough. We recieve our new batteries, wire them in parallel, discharge to 2.5 volts, and we are set to go. All we have to do is install them in series, and charge up. Ready to go fast down the road.
However over time due to self discharge rates and parasitic losses (natural aging) we incur an imbalance and thus need to rebalance the pack. That is a PIA to do if you have to remove them and wire in parallel again like we did to start with. Well I guess that is fine for a informed DIY who knows what they are doing, but eliminates other DIY and any commercial consumer application. Then it dawned on me how to get around the problem. Not that I think it would have any real commercial market potential because the commercial world is stuck in Top Balance for various reasons.
But what hit me is, why not do it the exact same way a commercial Top Balance BMS works except in Reverse using Vampire aka Bleeder Boards. Instead of Turning On at 3.6 volts and Turn Off at 3.5 volts, why not Turn On equal to or greater than say 2.6 volts, and disconnect at 2.4 volts?
Does not need to be a lot of current. All one needs is about 1 amp load to do a corrective aka Maintenace Bottom Balance. I built a prototype for a 3S LiPo pack I use on RC planes. So if I burned it up, no big deal. At .25 amps worked perfectly on 3 AH 11.1 volt LiPo. I just used the JST Balance plug already on the battery to BB. At 1-Amp drain is less than 4 watts of power per cell board. Real doable using off the shelf components. Example 5-Watt 2-Ohm Power Resistor and a FET switch.
I do not see any reason this could not be scaled up, especially for folks using LFP on Off-Grid Solar using 8S and 16S. Just make a Balance Wire Harness hard wired to the batteries to a Balance Plug. On an EV just as simple, just more cells in series.
So when the time comes, drive the EV until Turtle or Limp Home mode activates to do the bulk discharge, plug the Balance Port up to Bleeder board to finnish the complete Balanced Discharge aka Bottom Balance.
Anyone else try this, or have comments good or bad? Just keep it friendly and constructive. This is NOT a Top Balance vs Bottom Balance debate.
THX
Dereck
However over time due to self discharge rates and parasitic losses (natural aging) we incur an imbalance and thus need to rebalance the pack. That is a PIA to do if you have to remove them and wire in parallel again like we did to start with. Well I guess that is fine for a informed DIY who knows what they are doing, but eliminates other DIY and any commercial consumer application. Then it dawned on me how to get around the problem. Not that I think it would have any real commercial market potential because the commercial world is stuck in Top Balance for various reasons.
But what hit me is, why not do it the exact same way a commercial Top Balance BMS works except in Reverse using Vampire aka Bleeder Boards. Instead of Turning On at 3.6 volts and Turn Off at 3.5 volts, why not Turn On equal to or greater than say 2.6 volts, and disconnect at 2.4 volts?
Does not need to be a lot of current. All one needs is about 1 amp load to do a corrective aka Maintenace Bottom Balance. I built a prototype for a 3S LiPo pack I use on RC planes. So if I burned it up, no big deal. At .25 amps worked perfectly on 3 AH 11.1 volt LiPo. I just used the JST Balance plug already on the battery to BB. At 1-Amp drain is less than 4 watts of power per cell board. Real doable using off the shelf components. Example 5-Watt 2-Ohm Power Resistor and a FET switch.
I do not see any reason this could not be scaled up, especially for folks using LFP on Off-Grid Solar using 8S and 16S. Just make a Balance Wire Harness hard wired to the batteries to a Balance Plug. On an EV just as simple, just more cells in series.
So when the time comes, drive the EV until Turtle or Limp Home mode activates to do the bulk discharge, plug the Balance Port up to Bleeder board to finnish the complete Balanced Discharge aka Bottom Balance.
Anyone else try this, or have comments good or bad? Just keep it friendly and constructive. This is NOT a Top Balance vs Bottom Balance debate.
THX
Dereck