I have purchase all my batteries for my efoil project and now it’s time to solder them.
The plan is to have a 40V 32AH battery made of 8 parkside powertool batteries of 20V and 8AH (I know it’s more like 18V).
I understood that to add voltage you need to put them in serie and add capacity is done with parrallelle but still there are several options and I don’t know which one is the best, especially for batterie life length and how to empty them in an equal way.
Some additional comments : the equivalent of my battery would be 10S 32AH. I know it would have been better in 12S or 14S but I didn’t want to solder many cells wo I preferred to combine Parkside powertool batteries of 5S 8AH, so I was stusk to 10S or 15S but my ESC flycolor 160A has a maximum of 14S.
I’d go for ption 3 but with the connection point for plus and minus in the middle of the pack, if you have the room then you can use 8awg wire for the connections and the difference in voltage drop will be negligible.
Most BMS don’t allow for series connection, or only series connection of a limited number of packs.
When an individual BMS shuts off, it turns off the FET, which opens the circuit. This means that the FET could then have a higher potential voltage across it than it can handle. It should be possible to see if this is ok by looking at the spec sheet for the FET in the power tool BMS to see if it can handle the higher voltage.
Great comment! Didn’t think of this, if any bms trips then there will be a flyback voltage spike at full assembly voltage (and more) which the packs might not be built for.
I think there are a few other components in each battery bms that need to be able to take the full voltage, mainly input voltage regulator and caps.
I thought about it and a bms shutdown during riding, regardless of cause, can also damage the esc so this can’t be allowed. The undervoltage setting in the esc should be set conservative, adding a smart bms with voltage displayed on your phone could be a good idea, this way you could monitor the status of the battery better.
Depending on which parkside batteries they are, some are designed for series connections. Most of the lawnmowers and chainsaws run on 40v which means 2 batteries connected in series.
I know it’s been demonstrated on YouTube a few times that even the Daly BMS can be connected in series, as long as the esc is set to cut off before the battery BMS does.
Option 2 would mean you don’t over-volt anything, but there’s always going to be some risk when chaining BMS together…
Thank you @Larsb for your feedback. In fact, I only have 6mm2 wires (~10 AWG), so I might go with Option 4. Moreover as I am using this type of fuse, I could connect each of the 4 positive (red) wires of the 4 batteries to the fuse with a M6 pod with eyelet screwed on it.
Concerning the 4 negative (black) wires going out of the 4 batteries, they need to be connected to the ESC. So I will solder the 4 wires (10 awg) to 1 wire (10 awg) who will be solder to the ESC. To solder the 4 wires to 1 wire, I don’t know the right technic, I am going to do a big torsado of the 4 wires around the one and solder everyting and put in a shrink tube. If there is a more efficient technic or a type of connector that could plug 4 to 1, I am interested
Absolutely, this the project of @nicolasLGM which I am trying to replicate in an efoil version ! I have seen these “orange connectors” to connect wires, but I couldn’t find one doing 4 to 1.
Thank you @Strongarm , @Larsb and @Jezza for raising this potential issue. I can confirm you that the parkside battery I used are sometimes used in serie by Parkside (ex lawn mower) to reach 40V (36V). Here is the model, it the same used by @nicolasLGM , there are called smart battery as you can pilot them by bluetooth to set current parameters
As I am not good in electronics, I am not sure I will be capable to add a general BMS on top of the 8 batteries. So do you think it could be feasible to put a fuse between the battery in series (4 fuses on the purple wires) ?
I used 10S4P with 4 lidl parkside batteries to efoil, works perfectly, really no need to add a general BMS.
I added a 150A fuse between the 10S4P pack and ESC.
