Adding a Watch Winder Battery Monitor

Most of the cheaper watch winder units do not have a battery monitor to warn you of exhausted batteries. Here is a low cost circuit which you can add to your existing control board. Please be reminded that if your watch winder is new, opening the unit, removing or adding any circuits would void all warranties.

Labels: DIY watch winder, watch winder features

Watch Winder's Battery Life

Many users are also concerned about battery life of their watch winder. Unless you want to keep your precious timepiece in a safe without any power outlets, one should then be concern. Otherwise, like me, the AC mains would be eventually used for my homemade watch winder project.

Just out of interest, let’s see what the battery life of a watch winder would be like.

Example:-
1) A motor draws about 60mA when loaded with a watch in its winding cup.
2) At rest, the circuit draws about 4mA.
3) If I use 4xAA dry cells, it has capacity of about 2500mAH for 20mA loads.

In the 950TPD mode,
2500mAh/4mA = 625 x 39 = 24375/24 = 10156/30 = 33.8 months

Explanation: -
The motor does not continuously turn, meaning drawing continuous 60mA, so I’ve taken the minimum current for calculations. Note that the motor remains at rest about 90% of the time.

Here’s what I did…
Divide battery capacity with motor current, and then multiply by the ratio of the sequence (Total cycle time divide by ON time). I’ve used my own sequence for this calculation.

Next, I divide by 24 hours to determine the number of days.

Lastly, I divide by 30 days to know how many months the battery pack can power up this unit.

Theoretically, it should have enough juice for approximately more than 30 months, or about 2.5 years. (90% of 33.8 months).

From this exercise, you will noticed that battery life depends on 3 important factors:-
a) current drawn by the motor,
b) battery capacity, and
c) winding sequence ratio of ON and OFF times.

So, hypothetically if I have a higher battery capacity and a motor that draws lower current, I can perhaps extend the battery life. The winding sequence would then be dependant on the motor rpm.

Labels: DIY watch winder, winding sequence

Electronic Parts for Homemade Watch Winder



These are the confirmed parts I’ve used for this project. This circuit is not commercially viable. Please DO NOT use this for other than your own personal project.

Parts List
R1 2K2, Carbon Film Resistor $0.05
R2a 1M0, Carbon Film Resistor $0.06
R2b 1M2, Carbon Film Resistor $0.06
R3 220R, Carbon Film Resistor $0.05

C1 220uF, 16V, Electrolytic Capacitor Free, got it from my junk pile

T1 2N2222, NPN Transistor $0.30
T2 2N3906, PNP Transistor $0.30

LED1 Power Indicator, any color, 3mm Free, robbed from my nephew’s toy

SW1 Rocker or Toggle Switch Free, taken from a junk HP printer
RS1 Slide switch, 2way $1.50

M Small DC Gear-motor, 6V Free, taken when shop staff wasn’t looking,
Just kidding. It’s from my junk pile.PCB Stripboard, Copper $1.20

BH Battery Holder, 4xAA $1.50


Total cost is (SGD)$5.02 with FREE parts were salvaged from my junk pile.

So with the above circuit, I’ll have a two TPD selection. The housing could be built using scrap parts too. It’s a simple way to demonstrate the working principles of a watch winder.

Labels: Circuits, DIY watch winder, homemade watch winder