Verification of Charging Circuit

[john444]

Hi Mastermime,

Both of your schematics appear to short the lower battery through the switch.
I don't believe the transistor (or FET) will do what you want.

Afraid I agree with Zener, to charge the batts in parallel and operate them in series,
a multi-pole switch would be easiest.
But, you cannot operate at the same time you are charging.

Good Luck, John

[mastermime]

ok I will use a switch. something like this (attached) is what you're thinking? What should I do about gnd?

[mastermime]

Ok now I believe I'm understanding transistors correctly. So now when the SPDT switch is in the correct position and the charger is plugged into the XLR port, it will introduce the parallel connection by sending a signal to gate connecting both grounds. When the charger is unplugged the connection between ground is broken and when the switch is flipped, the connection between the positives will be broken.

I hope I got that right

[mastermime]

Please help

[adafruit_support_bill]

I believe that john444 and Zener have given you some excellent advice.

[john444]

Hi Mastermime,

Sorry for the delay. I've had a motherboard failure that has kept me off the internet.
Regarding your circuits:
The one Feb 16 will place the batteries in series to run your circuit.
However, only the lower battery will charge.
The Feb 18 schematic has the NPN transistor's C&E inverted and shows nothing
to limit current into the base.
In my opinion, using a switch is the better solution to your problem.
Although, you will need a 3PDT switch.
I need to install some drivers before I can attach a schematic.

See if this description makes sense to you-
The lower Batt always connects to GND.
however, both the + and (-) of the upper Batt need to be switched.
the upper Batt + connects (through one pole of the switch) to [your circuit]
or to {the + of the lower Batt}.
The upper Batt (-) connects (through a second pole of the switch) to
[the lower Batt +] or to {the lower Batt (-) ie. GND}
I would use a 3rd pole to disconnect the charger from the
Batts when the Batts are in series, powering your circuit.

John

[mastermime]

Wow thank you for the nice response

I have one day left to get this done. I really appreciate this, but I do not have a 3pdt switch and I already have the transistor installed. If I had more time, I would definitely use your idea for the sake of simplicity, but I'm on a huge timecrunch.

No shorts right?


Thanks a lot! You saved me

[john444]

Mastermime,

Sorry, you still have issues. I'm not trying to beat you up, only want to help.

1 when the switch places the Batts in series to operate the rest of the ckt,
the transistor will be turned-on because the base has about 14.4-mA into it.
If the transistor has a gain of 100 then you will be pulling about 1.4-A from
the lower Batt.
2 the 7.2-V charger will be connected to the two Batts or 14.4-V.
That may or may not be ok for the charger.
3 with the switch in the 'charge' position, you still have the transistor shunting
current from the lower Batt, just not as badly as before.
4 the lower Batt will have .3 to .6-V more across it from the charger than
the upper Batt. because of the voltage drop across the transistor.
5 the rest of your circuit is now connected to only 7.2-V instead of 14.4-V

Some of these may not be terrible issues but #1 is a biggie you probably
cannot live with.

Sorry for the bad news.
John

[mastermime]

Ok in that case, I think I will search as hard as I can tomorrow for a 3pdt switch. I may need your help wiring it up tomorrow. thanks for the helpful advice even if it was bad news! lol

[mastermime]

Ok in that case, I think I will search as hard as I can tomorrow for a 3pdt switch. I may need your help wiring it up tomorrow. thanks for the helpful advice even if it was bad news! lol

[john444]

I'll see if I can't get you a drawing loaded up tomorrow using the computer at work.
John

[mastermime]

Wow you're a great guy. thanks a lot

[john444]

OK, here you go.
C1, C2, C3 are the common terminals on your 3PDT swtich.
In the 'up' position you can charge the batts in parallel.
In the 'down' position your other circuit is connected.
The dashed line indicates that the switch poles are mechanically linked
so that they operate together.
Good Luck, John

[mastermime]

ok thanks a lot for this! I reapply appreciate this!