I would like to use a mosfet between two batteries to be able to put them in series when I want ,I left a simplified image of the circuit that I want to realize
,the current that will pass through the mosfet is greater than 30 amps.
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What is the reason for placing the batteries in series? What is your plan to control all the additional switching?
Does it have to be a mosfet or could you use a relay?
What is the max current draw?

 

Most important is how much current do you anticipate as a maximum value? If those are big wet cell batteries cranking a 24 volt deisel truck starter it might be 200+ amps. Really, it needs a 200 amp contactor. And a bit of interlocking software so nothing gets short circuited.

 

I would like to place the batteries (4 volts each) to have a 56 volt battery pack
but I want to load them individually each one then place them in series
so between each two batteries there is a mosfet which will place them in series but when it is not closed the other two mosfets ensure the closing of the circuit (constant current) which will charge them
the problem is that the serialization mosfet will not be able to operate normally with two potentially identical voltages between its drain and its source

 

the battery is a 4volt, 5 amp, 21700 cell, and when the whole battery is placed in series each mosfet will have to support a voltage of 56 volt and 5 amps so not huge

 

Good lord! That will require 41 mosfets if my math is correct. But now only talking about 5 amps not 30+ amps?
Is this constant current generator some form of battery management ?

 

Post # 1 mentions a current of 30 amps.. But now we hear that the plan is for a series stack delivering 56 volts, THE CHARGING MODE WOULD PUT THEM ALL IN PARALLEL to charge from 4 volts. Parallel charging will not work because the 14 cells will not be all exactly identical.
So mosfet switching will be a serious challenge, even at only 5 amps. So the solution is for each 4 volt cell to have a relay , SPDT, 30 amps, to select either the series or the parallel connection scheme. That will work out well and require much less space than having all of those mosfets and their isolated driver circuits to do the switching. But I suggest putting them in series groups of three so that they can be charged using 12 volts.

 

They do make 14s BMS for lipo's as that is a common voltage for E-bikes.
I suppose you could use a commercial charger and P channel mosfet switches on each battery to select the voltage required.

 

My one other question is this: it is implied that this was for a tow vehicle, as in a jumpstart provider. So what sort of vehicle electrical system will survive a 56 volt jumpstart?? The 24 volt zap is bad enough, it damages some non-oem entertainment systems