Transistor switch acting weird

Other Hardware General Electronics
41

I have relays.
I started with designing and building this circuit with a relay but then changed to transistor as I thought it is the more elegant and correct way to go.

42

I'm quite sure you are wrong.
But try to give correct spot on information.
Instead of writing "5V battery" one could write "12V Agm battery connected to 5V3A step down converter" ..for example..

43

See post #40
If you are still interested let me know, I will be leaving soon.

44

I can buy from Aliexpress and it usually takes about 3-4 weeks for the parts to arrive

45

What information are you missing in order to design a transistor switch circuit that will work under the conditions I've listed in post number 1?

46

I havea circuit that uses a VP2106 MOSFET.
It can't be done with a transistor.

47

I have a few Mosfets on the shelf.
Please post your design and tomorrow I'll see if I have any mosfet I can use.
Thx

48

image
image822×615 6.92 KB

49

Isn't this circuit connecting the (-) from both batteries together at all time?

50

Yes. You did say that would be OK and I don't see why it would not be.

51

It is only ok if i can:

  1. Disconnect this connection (i don't want one battery to charge the other while ignition is off)
  2. Limit the max current that flows to a few miliamps (again, so one battery won't charge/discharge the other while driving)

See post 18

52

I'm not personally missing anything and I gave my answer on my post#10.
Good luck, you are in good hands.

53

That can only happen if the two positives are connected and this circuit does not do that.

again, so one battery won't charge/discharge the other while driving

Again this circuit never commects the two battery positive terminal together.

You need TWO of those circuits, one for each battery.

54

I found two MOSFETs on aliexpress that you could use
MDD3754
IRLML2244

55

Thank you