Motor shorting out circuit

[bonxer]

I have a motorized coin sorter/counter. You drop the coins into the top, it spins them around and drops them into the correct slots, and reports the number of coins in each slot on an LCD. The entire thing that I find 'funny' is that the unit has a wallwart that gives it 6v DC to the motor. But for the counter and display, it requires two AAA batteries! A unit that plugs into the wall in order to function needs batteries for additional functionality! :? So I throw on a few quick parts to get around 3 volts parallel to the motor and remove the need for batteries. While the machine is switched on, everything is fine. The motor runs, the display is on, and it counts. As soon as the power switch is turned off, the display is instantly killed. This was not the situation when I tested it with the 6v, diodes, cap, and display alone. The display would stay on for a good minute or so. But as soon as I integrated it back into the case and connected it to the switch, it stops working whenever the switch is opened. Shouldn't the diodes be preventing the cap from discharing to or being shorted by the motor?

 

[eblc1388]

Friday the thirteen, what do you expect??

Anyway, I don't know the reason why but the following would definitely works.

 

[Nigel Goodwin]

This was not the situation when I tested it with the 6v, diodes, cap, and display alone. The display would stay on for a good minute or so. But as soon as I integrated it back into the case and connected it to the switch, it stops working whenever the switch is opened. Shouldn't the diodes be preventing the cap from discharing to or being shorted by the motor?

I would suggest the answer is simple! - the capacitor in the 6V power supply was keeping the LCD running, NOT the one near the LCD. With the motor connected the PSU capacitor rapidly discharges, leaving the LCD to discharge the capacitor near the LCD.

What size is the capacitor near the LCD?.

 

[bonxer]

I would suggest the answer is simple! - the capacitor in the 6V power supply was keeping the LCD running, NOT the one near the LCD.

But the switch was disconnecting any capacitance in the DC adapter from the display. I don't remember the value of the capacitor I used last night, but I shall see about using a larger one.

 

[Nigel Goodwin]

I would suggest the answer is simple! - the capacitor in the 6V power supply was keeping the LCD running, NOT the one near the LCD.

But the switch was disconnecting any capacitance in the DC adapter from the display. I don't remember the value of the capacitor I used last night, but I shall see about using a larger one.

Are you sure you were switching it off, and not just unplugging it from the mains?.

 

[Oznog]

You need an actual reg going to that LCD. A wall wart is a crudely regulated power source, a 6v rating may give you 9v with no load. The electronics are more sensitive than that.

You may want a diode on that motor to protect againt power spikes.

 

[bonxer]

I have physically removed the wires so that the diode chain, capacitor, and lcd are the only things left on the circuit. The top of the diode's anode is left floating. So yes, in that regard I am sure that there is no interaction with the power supply in that regard.

As for the DC supply itself, it is a stable 6.06v.

 

[audioguru]

1N4148 see-through diodes with a bright light on them?
Then they leak a fair amount of current. :lol: