# 10Hour Timer using a 555/4040

#### Wendy

Joined Mar 24, 2008
22,990
I have a Ni Cad battery Charger as part of a Black and Decker Ve3rsa pack system. They recommend a 14 Hour charge the first time you charge them. I have basically ruined one set of batteries forgetting to pull them out of the charger in a timely manner. I measured the power supply to the base it is approx. 9V AC unloaded. So I'm going to try and built this circuit before I order a new set of batterys.
I'll protoboard it first before making a final build, I'll post my results as I proceed. The signal feeding the SSR is not finalized. at this point, since I'm not sure how my SSR will handle the signal going to it.

#### click_here

Joined Sep 22, 2020
545
You would usually put the +/- in series with R7/D5

#### Wendy

Joined Mar 24, 2008
22,990
This is very much a WIP. I expect multiple revisions in my schematics before I am done. Vcc is +5VDC for now it will be assumed. The 555 will be a 555CN.

#### Wendy

Joined Mar 24, 2008
22,990
So here is where I am tonight. I thought about using a 7805 regulator but decided on a zener instead. Once I know the max current requirements I'll figure out the resistance needed.

#### AnalogKid

Joined Aug 1, 2013
10,113
I'm all for whipping up a home project. But ...

1. You have around 70 mA of peak combined LED current. That puts the power dissipatiion in the zener resistor at around 0.5 W, so you'll want tu use at least a 1 W resistor to keep the tempeerture down. Consider powering the LEDs from the bridge output/C2 directly, rather than after the zener diode's dropping resistor (reference designators?). The same power dissipation is spread out over five resistors.

2. In fact, you can eliminate the zener altogether since all of your parts are rated for greater than 11.4 V operation.

3. A CD4060 both eliminates the 555, and allows smaller timing components (because of its two extra divide stages), small enough that C1 would not have to be an electrolytic.

4. A $7 lamp timer at Wal-Mart times things in 1/4 hour increments. You lose the incremental indicators, but you're on the air 2 minutes after you get home from the store. ak Last edited: #### MrSalts Joined Apr 2, 2020 2,096 4. A$7 lamp timer at Wal-Mart times things in 1/2 hour increments. You lose the incremental indicators, but you're on the air 2 minutes after you get home from the store.

ak
But, is that "good enough" or "the best"?

#### AnalogKid

Joined Aug 1, 2013
10,113
best what?

#### AnalogKid

Joined Aug 1, 2013
10,113
Post #4 -

1. R10 is shorted out on the proto-board.

2. When the circuit is started by resetting the 4040, the Q12 output goes low. As this is connected to the 555 Reset input. won't this freeze the oscillator?

A work-around is to replace that connection with a small signal diode between U2 pin 1 and IC1 pin 2/6. This will override the current from the timing resistors and stop oscillation when Q12 goes high after 2048 counts. The same method works with the CD4060.

3. Your 555 symbol is pretty small, and this might be too much clutter, but I think it would be better if it had a bubble on pin 4 to show that it is an active-low input.

ak

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#### MrSalts

Joined Apr 2, 2020
2,096
best what?
I've no idea -its in the OP's signature line. I assumed it was a requirement.

#### AnalogKid

Joined Aug 1, 2013
10,113
Umm ... no. A tagline is not a project requirement.

ak

#### MrSalts

Joined Apr 2, 2020
2,096
Umm ... no. A tagline is not a project requirement.

ak
Umm... I see more and more humans have trouble digesting humor.

#### tsnyder

Joined Nov 7, 2019
3
Why not buy a 110 vac countdown timer (mechanical or electronic) and plug the Black and Decker Ve3rsa pack charger into it? All you need is the countdown timer which are available at most hardware stores.

#### Wendy

Joined Mar 24, 2008
22,990
The whole point is to freeze the oscillator when the charge is done. I may add a short beep when it finishes to signal me in addition to the green LED. Like I said this is a WIP. I am not using a battery and my outlet space is very limited. I have to have the wall wart anyhow. So this seems a better long time solution. I'm both exercising my one handed solder in skills as well as my mind. After I finish this I'm going to have to replace one or two Nicad batteries anyhow so I want to get this done before I buy them. I hate Nicads. They all eventually get trashed.

#### peterdeco

Joined Oct 8, 2019
484
I find it hard to believe (and disturbing if it's true) that Black and Decker would produce a charger for their tools that will allow the battery to overcharge. The battery on every cordless tool I own can be left on charge indefinitely without damage.

#### click_here

Joined Sep 22, 2020
545
I'd say that this is a warranty issue - I don't know where you are, but in Australia (by law) if you buy something new that is faulty or not able to do what it is intended for you have the right for refund or replacement.

#### Wendy

Joined Mar 24, 2008
22,990
B&D in my opinion, makes some of the shoddiest tools you can buy. A lot like Harbor Freight, if you need it it can get you there. But buyer beware.

These tools sat unused in my garage until I could have my home fully modified for wheelchair access (the stroke was in June 2016).

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#### Wendy

Joined Mar 24, 2008
22,990
OK, latest revision. While I drew a Sonalert circuit in, I did not put in in the protoboard layout yet. PNP transistors are red.

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#### AnalogKid

Joined Aug 1, 2013
10,113
Just to be clear, you want D1-D4 to show the remaining time in the charge cycle, not the elapsed time - right?

ak

#### Wendy

Joined Mar 24, 2008
22,990
True, it is a count down timer. Which is count up timer inverted by the PNP transistors