VM188 - Fixed timing and possible calibration

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1

Hi all,

excuse my many questions, I also just try to confirm some information I read up before:
What I want to do:
I want to use the VM 188 timer board to start and stop (one time shot) the charging of my electric car.
I understand that there is no quartz on board so the timing is not 100% accurate (and I do not care about 5 minutes plus/minus)
What my intention is (and maybe someone can point me to the correct values:
I want fixed start delay times. I want to do this by replacing the potentiometer with fixed value resistors on a multi contact switch.

Question 1:
I need delay start and hold power:
So I can start my charing in 2, 4, 6, 8, 10, 12, 15, 24, 48, 60 hours time and charge (hold power) for 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 6 and 10 hours
What would be the resistor values required to achieve roughly this timing?

Question 2:
If nobody can tell me:
I could set the timer to seconds and find out the value by just adjusting the potentiometer so long until I have the right timing and than use this value with a fixed resistor. But for this I have to know: If I have the setting to 5 seconds, would (if I change the jumper to hours) this also be about 5 hours, or do I need to configure the potentiometer really on the hour setting?

Question 3:
How high is the repetition accuracy of the timer once set?
I have a stable power supply providing 13.5 to 14V (Car battery, the voltage will probably not drop below, since when the car is at a stand still the 12V Lead battery is constantly charged by the traction battery and kept full. The 12V lead battery would only drop in voltage while driving with “everything on”. But then I would not need the timer while driving anyway)

Questions 4:
Do I understand correctly:
The timer will start the moment it is connected to power. So since this board would be permanently powered up I would need a push button to interrupt the power supply for a short time and this would act like a trigger button to start the timer? Is there a minimum time the power to the boards needs to be cut so it starts correctly?

Thanks plenty for having some answers.

Markus

2

1 & 2: We’d recommend to set the potmeters for the desired time in seconds, to avoid having to wait too long during testing.

Next, desolder the potmeter and measure its setting with an ohmmeter. Do not measure it in-circuit.
Finally, replace potmeter with two fixed resistors of the correct value. It might be a good idea to still include a small pot between the two fixed resistors, for fine tuning.
Once you’ve found the correct time setting, you can simply change the jumper setting from seconds to hours, but keep in mind that a small error in seconds is multiplied by 3600 when set to hours.

3: In theory, the controllers are internally trimmed to 1%, but external factors can lead to up to 5% deviation.

4: Yes, power will have to be interrupted to restart the cycle. Experimenting will show how long it will have to be interrupted. Should not be more than say a couple of seconds.

3

Thanks, about what I would have done and expected. :slight_smile: