The Mighty Volt
1 MW
Hi.
I am trying to build a battery pack for frequent use, and dare I say it, mis-use.
This pack will be dropped into a ruck-sack which is then used in the usual fashion. It will have to deal with frequent handling, the risk of being dropped, frequent disassembly at a sub-pack level, etc.
The pack in question will be small, 4Ah minimum, 8Ah maximum, but high voltage, 100v, 32s, LiFePo4.
Considering its high-voltage, high discharge and relatively low-capacity nature, the pack will find itself being often removed, charged, balanced and re-installed.
The idea here is to conceive a build which does not rely on traditional Signa-Lab/Fechter-Goodrum-Hecker/Cammy/Ping BMS formats.
The idea is to retain flexibility, limit the volume of wiring, platforms, plastic bits and pieces etc which can get in the way and get broken or snagged so easily.
At the same time, the pack will need to be capable of rapid charging, rapid discharging, effective balancing and with some form of LVC protection.
This battery is intended for my BMX build, which will be more of a drag bike than a cruiser. The nature of "dragging" means high-amperage discharges, a perfect environment for cells getting out of balance or forcing a runt cell into a steep decline.
Ideally the pack will be so somebody can travel to a deserted car park, BMX park etc, let rip, then return to their car and charge the pack off the 12v cigarette lighter socket.
Here is my plan thus far:
Take 4 A123 cells {either 18650 or 26650}, glue them in parallel, weld them, then solder on some shim. This creates a 1s4p unit, the most basic unit of the build.
Take 8 of these completed strips, and join them in series, making an 8s4p block, the second most basic unit. 4 of these units will be made up.
Take each 8s4p sub-pack and terminate them, +/- spade ends, heavy duty.
Then solder on one of these:
Connect each 8s4p sub-pack up in series to make a 32s4p final pack.
I did this on an 8s1p experimental strip this morning.
These pigtails have 9 wires, 8 black and 1 red. I wired the red to the first positive terminal, the next black to the negative terminal of that same cell, and then a black wire, in turn, to every other negative terminal, finishing on the last negative terminal.
I then hooked up my multimeter and found that I could measure the individual voltage of each cell in series, as so:
The small probes are just bits of solder I wedged in so I could take readings.
This pigtail, would it fit into the Turnigy 8s Accucell charger??
Are there any 8s LVC monitors that I could plug into it??? Would what Geoff57 was selling be of use in this regard? For those not familiar with Geoff57's product, here is the link http://endless-sphere.com/forums/viewtopic.php?f=31&t=21695
Finally, I need some sort of foam insulation. The sub-packs are wrapped together but left in such a way as their series connectors can be broken apart in a hurry. That is to say, the battery can be quickly broken down into a collection of 8s4p units without actually changing its physical form, with the 4 sub-packs still physically joined {with duct-tape, insulation} but electrically disconnected.
When the time comes to charge, I would hope to break the battery down into its 4 constituent sub-packs, I might either do a quick current-limiting charge with a Meanwell Limiting charger and then do a balance charge on the Turnigy 8s Accucell, or I might just use the Accucell to begin with though I appreciate that this would be slower.
If anyone has any suggestions they would like to make about any of this then I would be most grateful. I will be going ahead with the build using some circumspect 18650 A123, just to get the feel of the build and use it to work out any wrinkles in my methodology.
I am trying to build a battery pack for frequent use, and dare I say it, mis-use.
This pack will be dropped into a ruck-sack which is then used in the usual fashion. It will have to deal with frequent handling, the risk of being dropped, frequent disassembly at a sub-pack level, etc.
The pack in question will be small, 4Ah minimum, 8Ah maximum, but high voltage, 100v, 32s, LiFePo4.
Considering its high-voltage, high discharge and relatively low-capacity nature, the pack will find itself being often removed, charged, balanced and re-installed.
The idea here is to conceive a build which does not rely on traditional Signa-Lab/Fechter-Goodrum-Hecker/Cammy/Ping BMS formats.
The idea is to retain flexibility, limit the volume of wiring, platforms, plastic bits and pieces etc which can get in the way and get broken or snagged so easily.
At the same time, the pack will need to be capable of rapid charging, rapid discharging, effective balancing and with some form of LVC protection.
This battery is intended for my BMX build, which will be more of a drag bike than a cruiser. The nature of "dragging" means high-amperage discharges, a perfect environment for cells getting out of balance or forcing a runt cell into a steep decline.
Ideally the pack will be so somebody can travel to a deserted car park, BMX park etc, let rip, then return to their car and charge the pack off the 12v cigarette lighter socket.
Here is my plan thus far:
Take 4 A123 cells {either 18650 or 26650}, glue them in parallel, weld them, then solder on some shim. This creates a 1s4p unit, the most basic unit of the build.
Take 8 of these completed strips, and join them in series, making an 8s4p block, the second most basic unit. 4 of these units will be made up.
Take each 8s4p sub-pack and terminate them, +/- spade ends, heavy duty.
Then solder on one of these:
Connect each 8s4p sub-pack up in series to make a 32s4p final pack.
I did this on an 8s1p experimental strip this morning.
These pigtails have 9 wires, 8 black and 1 red. I wired the red to the first positive terminal, the next black to the negative terminal of that same cell, and then a black wire, in turn, to every other negative terminal, finishing on the last negative terminal.
I then hooked up my multimeter and found that I could measure the individual voltage of each cell in series, as so:
The small probes are just bits of solder I wedged in so I could take readings.
This pigtail, would it fit into the Turnigy 8s Accucell charger??
Are there any 8s LVC monitors that I could plug into it??? Would what Geoff57 was selling be of use in this regard? For those not familiar with Geoff57's product, here is the link http://endless-sphere.com/forums/viewtopic.php?f=31&t=21695
Finally, I need some sort of foam insulation. The sub-packs are wrapped together but left in such a way as their series connectors can be broken apart in a hurry. That is to say, the battery can be quickly broken down into a collection of 8s4p units without actually changing its physical form, with the 4 sub-packs still physically joined {with duct-tape, insulation} but electrically disconnected.
When the time comes to charge, I would hope to break the battery down into its 4 constituent sub-packs, I might either do a quick current-limiting charge with a Meanwell Limiting charger and then do a balance charge on the Turnigy 8s Accucell, or I might just use the Accucell to begin with though I appreciate that this would be slower.
If anyone has any suggestions they would like to make about any of this then I would be most grateful. I will be going ahead with the build using some circumspect 18650 A123, just to get the feel of the build and use it to work out any wrinkles in my methodology.
Fails the first use
