Using a CD4066 a 4 switches

Thread Starter

chrischrischris

Joined Feb 18, 2012
303
Hi. I was wondering if someone could help with this question. I have a remote control mono wing foam glider that uses 4 x AA NiMh rechargeable batteries. The are not removeable as they are glued in the middle of the glider. Currently they are connected in series to produce around 5V and I can only charge them is series (not ideal).

As 1 or 2 of the cells are now on their way out, I'd like to build a small circuit so that I can balance charge them individually. To do this I first thought of inserting a switch between cell 1 & 2 (pos/neg), then another between 2&3 and also one between 3&4. However this is too manual when charging. I then thought of using a CD4066 as it's a quad bilateral switch. What I'd like to do is, when I power the glider up via a switch, this also powers the 4066, which in turn connects the 3 sets of Vcc/Vdd of the 4 batteries so the glider works. When I switch off the power, the connection drops so I can charge the batteries independantly. However, there seems to be quite a bit of resistance in the 4066. Can someone explain/make a better suggestion.
 

Bernard

Joined Aug 7, 2008
5,788
Like #2, but fire up your hot wire cutter, or connect the cells together with MOSFETs controlled by 4066 & some form of drivers for FETs.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
303
Sorry, not gonna happen. The 4066 is for switching low level signals not power.
Yes, I was guessing as much. I'm therefore now looking at PN222A switching transistors. I'll sketch it up and ask if someone can tell me if it will work. On the breadboard it "seems" to work.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
303
What is the drain on battery?
Sorry Bernard, I'm not exactly sure. The 4 x AA 2700mAh batteries are running 2 small servo motors, the receiver, 2 flashing LEDs (for a bit of night flying!) and a small beeper (in case I loose the glider). From experience, fully charged batteries last around 5 to 6 hours continuous flying if that helps.

How do you plan to control the switches?
I am now planning to utilise on 1 single slide switch as I currently have. Can someone please comment on my Fritzing layout? Would this work?
AA charging.jpg
 

Alec_t

Joined Sep 17, 2013
12,149
That layout won't work :(. The servo supply negative should be from the fourth cell. The first cell is permanently drained by the 10k resistor.
Why not just use a 3PDT slide switch to connect the cells?
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
303
That layout won't work :(. The servo supply negative should be from the fourth cell. The first cell is permanently drained by the 10k resistor.
Why not just use a 3PDT slide switch to connect the cells?
Yes, I placed the note on the wrong negative - it is on the 4th cell neg.

R4 (the 10k you mentioned), I think is in the wrong spot. It should have been from the centre pole of the switch to the ground of the first battery. The idea is for it to be a pull down resistor to the bases of the transistors (to ensure they don't turn on by static or the like). Is that correct?

A 3PDT slide switch - I was going to, however I can seem to find a mini slide switch that has 2 positions and 3 poles.
 

Alec_t

Joined Sep 17, 2013
12,149
If you google '3pdt slide switch' several vendor sites pop up. Note that the current-switching ability of switches is less for DC than for AC (because of contact arcing problems), so 'mini' might not be quite as small as you'd like. Nevertheless, even a moderately-sized switch will likely be smaller and weigh less than the combination of a 'mini' SPDT one plus the associated electronics needed.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
303
If you google '3pdt slide switch' several vendor sites...
Thanks Alec. In the end I went and bought 2 mini double pole slide switches. I think however my original circuit does work (with the removal of the 10k and the change in neg supply). Weight - well I'm building a timer for a beeper and flashing LEDs, hence the reason. Never mind, I'll go with the 2 switches - much simpler. Ta.
 
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