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Yeah I gave up on Ali - they wanted my passport and seemed like everything short of an anal probe
I do a lot of small circuits but have all the tools and usually can quickly identify the limitations of what should be attempted at the small scale - I don't mind spending some time/money on these "hobby" electronics but I have limited time for it
Whatever you choose to do good luck.. if looking for advice I've got plenty of background with this type of stuff... do it just about every day ;-} -
Not sure what you mean by the battery dying but P-ch MOSFET's in the above are disconnecting the bat+ and leaving the bat-'s connected together as a common ground which everything can use as a negative reference
When N-ch's are used typically they are disconnecting the bat- so no longer a common negative reference... not a deal killer but it complicates things to have to use a common positive reference (need to sense both batteries), especially at electric bike voltages, and the above can't handle that
It is possible with charge pumps to use N-ch's in the high side but that's an entirely different drive than what you all have in that circuit (again start from scratch) and will complicate things, especially at electric bike voltages
But hey I'm just an old guy that's been around the block for a long time and know there's plenty of new tricks this old dog can learn -
There are very good reasons you *never* (and I mean never) see PMOS in electric bike current paths
Breaking the negative side is not as trivial as it may seem since now you lose your reference for voltage sensing with anything remotely resembling that circuit above
I guess I'm just saying that I'm of the notion the circuit above brings next to nothing for electric bike applications... that trying to make it work will take more time than just starting from scratch...
But go ahead and prove me wrong! I'd truly enjoy it -
I think the greatest issue is the P-channel MOSFET's doing the heavy lifting which isn't practical for bike battery voltages and currents
Once you replace them with N-channel the whole rest of the circuit goes out the window for the most part since now the negative side is what's getting broken which is entirely non-trivial
Oddly enough I've got a station with battery back up in my shop right now (just finishing this failure analysis project today ironically) that was toasting batteries and the problem turned out to the the LVCO disconnecting the negative (which is what N-channel's will do) and another connection to battery negative causing the failure of the LVCO to disconnect the battery and over-discharging the battery...
Regardless, these are reasonably simple circuits at the fundamental level... it's just the details that make them challenging... -
I don't think it is terribly useful for bikes
The back to back MOSFET's are P-channels and would need to be changed to N-channels (at much higher Vds) to get reasonable Rds(on) and everything on the left would need to get swapped around (inverted) to deal with that
The logic is far too low of voltage and looks made to detect only whether not a battery is present and above 4.38V... it would be possible to regulate a lower voltage for the NAND gates and use dividers on the threshold detectors I suppose but there is still the issue that now the logic needs to drive the MOSFET's relative to bat+ and that will throw the voltage detect all out of kilter
I suppose it could be done but personally, I'd just start from scratch and create something optimized for bike batteries
One of the really big challenges with doing something like this for bike batteries is going to be getting all the heat out of the back-to-back MOSFET's -
Not really
A quick look at the numbers in the datasheet and:
15A through 1 diode you will be dumping somewhere around 10-15W (figure 1 in data), 30A closer to at least 25W and dropping voltage at least 0.5V @15A (figure 7) and approaching a full volt at 30A
It will get hot, hot, hot and the heat is just wasted battery power - at 30A the temperature will depend on the heat sink (without one will just fry, they don't even specify the thermal impedance to ambient)
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