ESP32 based NiMH Smart-Charger Circuit Questions

[timfis]

Hello,
I'm currently designing an ESP32 based NiMH Smart Charger. I have 3 Circuits (floating, Charging Circuit, Battery internal resistance measurement circuit), which shall be connected one by one to the NiMH battery if needed. An automatic reverse polarity changer circuit shall be applied before as well. Currently I thought about relais, but those are not that durable and I want to get rid of possible mechanical failures.
Overview:

Charging Circuit (default for CN3085):

Internal Resistance Circuit:

Now my questions:

1. Can I use a H Bridge IC as polarity swapper (Like a L293D but with more Amps), or does it need to be a fancy MOSFET H Bridge? I want the voltage drop to be as close to 0V as possible, so a simple diode bridge rectifier circuit is a no go.

2. How do I connect those 3 circuits to the Battery without relays? Since they all use GND at some point, it should be possible to just put a PNP MOSFET on the positive rails right?

I appologize for my mistakes and dumb thoughts. I'm a newbie in designing HW circuits, so please be kind! Thanks in advance for your help!

~ Tim

[jim-p]

@timfis

Since they all use GND at some point, it should be possible to just put a PNP MOSFET on the positive rails right?

If in the floating configuration the battery ground can be connected to the charger ground, then yes but you may need back to back MOSFETs to prevent reverse flow

Actually, what you want to do can be accomplished with one P-MOSFET and one N-MOSFET.

[timfis]

Ah okay. So if I understood correctly, it would be better to put PNP and NPN on each positive and negative circuitline, so that I don't have the reverse flow and a floating state if all MOSFETS are off?

[jim-p]

No there is a much simpler way to do the whole thing with only ONE PMOS and ONE NMOS

[timfis]

Oh do you mean like this? (since the Internal Resistance Circuit gets GND only from the NiMH and is practically isolated?)

Edit: That doesn't make any sense. The NMOS wouldn't trigger at all, since it's isolated from GND. My bad. I really don't get it

[jim-p]

The CN3085 will shut down if Vin drops below the battery voltage. So if you put a PMOS on Vin you have basically disconnected the IC from the battery and the only thing connected across the battery is the 10uF cap.

Next for the internal resistance measurement, you can do this.

[timfis]

Oh! That makes totally sense! Thank you so much!
One last question: What ist the best way to solve the Reverse polarity problem? One fellow Maker built a H Bridge to compensate for that. Ist there a simpler way? Here is his circuit:

[jim-p]

I thought that your reverse polarity circuit was just a protection circuit. Not sure how you would do it