Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: Mastermime on February 20, 2013, 07:01:04 PM

Title: Verification of Charging Circuit
Post by: Mastermime on February 20, 2013, 07:01:04 PM

Hi guys,

Last question for this project.
I am building this  charging circuit (left side of schematic) and I feel like I am doing something wrong.  Perhaps shorting something out?

I feel like something is up with my transistor configuration is up.  My understanding of them is not complete, but I thought I got the gist of it

Thanks


Please help quick

Title: Re: Verification of Charging Circuit
Post by: jwatte on February 20, 2013, 07:38:38 PM

I think the NPN has the collector/emitter reversed if you consider the battery a load for the charger. Using a MOSFET may be better. You also need a current limiting resistor on the base, and perhaps a base bleed resistor between base and ground, too.

What is supposed to happen when the switch is left vs right? As far as I can tell, when the switch is left, it will attempt to parallel the two batteries, whereas when it is right, it will attempt to series them.

Btw: I would not hook that circuit to the rest of the pieces until it worked exactly like I want. Too much risk of burning things!

Title: Re: Verification of Charging Circuit
Post by: Mastermime on February 20, 2013, 08:33:43 PM

Thank you for such a quick response.  You are exactly right, run in series, charge in parallel (I only have a 7.2v charger).

Quote

I think the NPN has the collector/emitter reversed if you consider the battery a load for the charger

I'm not sure if its my schematic skills or my misunderstanding.  In my circuit, I have emitter connected to ground of the top battery and the collector connected to the ground line of the charger.  Is this correct?

I think my schematic is correct.  No shorts right?  I dont want to ruin the batteries.

Quote

Btw: I would not hook that circuit to the rest of the pieces until it worked exactly like I want. Too much risk of burning things!

I dont!

Title: Re: Verification of Charging Circuit
Post by: newInRobotics on February 21, 2013, 02:29:06 AM

What are You trying to achieve with Your charger-transistor-batteries circuit?

Title: Re: Verification of Charging Circuit
Post by: jwatte on February 22, 2013, 12:44:54 PM

The implicit answer I deduce from above is to be able to charge the batteries without removing them using only a 7.2V charger.

The arrow in a transistor should point in the direction of conventional current. When charging, conventional current will go the other direction than the transistor arrow points.