turn on my timer circuit when a DC motor stops running

Thread Starter

sdowney717

Joined Jul 18, 2012
705
making a delay off timer | All About Circuits

The above timer I made works good for years now.
This is the situation
On the boat, you have a head (electric pump toilet).
I press a momentary switch that starts the timer circuit (runs 10 seconds) and the head empties itself in a Marine Sanitation Device called a Lectrasan.
The Lectrasan has a rotary timer switch. You turn it all the way round to activate the MSD Lectrasan.
Lectrasan has 2 mixer motors, 2 chambers divided by a titanium electrode assembly that has 20 amps DC running through it into the effluent water, it turns the water in hypochloric acid killing the bacteria. So first mixer runs and a few seconds later, other mixer runs and the electrode pack turns on for a minute, then the cycle ends, finished.

So it leaves the purified waste in the device till next flush of the head.
I would like to kick on the head flush again with my timer circuit activated to flush it out with clean water at the end of every Lectrasan cycle.

What is the easiest way to do that?
Is there a simple circuit that detects the motors stopping that can then trigger my timer circuit?
 

olphart

Joined Sep 22, 2012
99
Hi, many ways, one is using the electrode at power on as the inactive edge of a flip-flop clock.
At power off the F/F output changes. Use that to start a timer to a relay that parallels the momentary switch.
The timer also resets the F/F.
I'd use 4000 series logic (up to 18V) and a 555 as timer (up to 200mA output) to most any small relay.
For low idle power the F/F could drive a mosfet to energize the relay, which also resets the F/F.
This might need a capacitor to lengthen the relay on time.
Good Hunting <<<)))
 

MisterBill2

Joined Jan 23, 2018
9,908
The first thing to do will be to examine the rotary timer on the "lectrosan" device to understand what options may be possibly. It seems like it may be a mechanical timer. If it is a spring driven timer with internal cams to operate mechanical switches then possibly a new cam is a solution. If it is an electric motor driven timer then using the motor signal to start another timer could be an option. Is it possible to provide either an actual circuit drawing, or at least a more detailed description?
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
yes a mechanical timer inside a metal box. You turn a handle, and it winds back down with several wire connections on the timer.
One of the connections turns on a relay to power the electrode pack. A couple little leds or neon lights turn on as the motors come on.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Hi, many ways, one is using the electrode at power on as the inactive edge of a flip-flop clock.
At power off the F/F output changes. Use that to start a timer to a relay that parallels the momentary switch.
The timer also resets the F/F.
I'd use 4000 series logic (up to 18V) and a 555 as timer (up to 200mA output) to most any small relay.
For low idle power the F/F could drive a mosfet to energize the relay, which also resets the F/F.
This might need a capacitor to lengthen the relay on time.
Good Hunting <<<)))
thanks for that, do you have a schematic diagram I can look at?
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
The first thing to do will be to examine the rotary timer on the "lectrosan" device to understand what options may be possibly. It seems like it may be a mechanical timer. If it is a spring driven timer with internal cams to operate mechanical switches then possibly a new cam is a solution. If it is an electric motor driven timer then using the motor signal to start another timer could be an option. Is it possible to provide either an actual circuit drawing, or at least a more detailed description?
ok, I will look for one, somewhere i have the original manual.
The timer is like a cylinder shaped thing.
 

MisterBill2

Joined Jan 23, 2018
9,908
OK, the simplest way may be to add an external switch linked to the timer, all inside the box. Or, since it seems that the goal is to run a motor that is already controlled by the box a second time, possibly a different cam. OR, possibly not, given that I have not seen it at all.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
here are some pics from manual. However I noticed the manual says the waste gets treated 4 times before all the fluid is entirely displayced.
But I still think it would be better to leave it in a fresher state by an extra flush at the end of its cycle
20210909_193504.jpg20210909_193426.jpg20210909_193345.jpg
 
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