Electric components to toggle DC motor polarity

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Hi spec,
I like the design of your toggle circuit with the latching relay. I don't see any problem the OP could find with this circuit as he has done with all the other suggestions.

Les.
 
Les Jones said:
Hi spec,
I like the design of your toggle circuit with the latching relay. I don't see any problem the OP could find with this circuit as he has done with all the other suggestions.

Les.
Click to expand...
Thanks Les,

Like many of my posts, it is based on the information from others, in this case Tony Stewart. I didn't really know that much about latching relays. Until Tony posted the Panasonic data sheet, I remembered latching relays as quirky things that were best avoided. I didn't know that they are now reliable and respected components.

It is surprisingly difficult to make a two state flip-flop with a single clock input.

I could not find a three pole changeover latching relay, thus two relays had to be used instead of one.

Limit switches could be incorporated but I though it better to keep the circuit as simple as possible. Perhaps limit switches would alow an absolute system? I'm not sure that limit switches are necessary to protect the motor though.

At th moment 12V relays are specified but 9V may be better. I will do a full analysis and optimization if the OP has any interest that is.

spec
 
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Hi spec,
I have only used a latching relay in one application. It was to allow switching my shed alarm on and off from two different places in the house without running an extra cable. (I had a few sparecores in an existing cable but not enough for a normal two way switch circuit.) The latching relays I had (Which I originally bought as normal relays.) only had one coil. I have tried to work out a way to make them toggle but the circuit became too complex. The thing about your circuit that I like is the solid way you ensure that the capacitor is fully charged so that it does not try to pulse the coil after the contacts have changed over. I notice that suitable latching relays (Such as **broken link removed**.) are available on ebay for about £3.50

Les.
 
Hy Les,

It seems that you have done a lot of designing and building, whereas my stuff is just theory, at the moment anyway. Afraid I was spoilt at work: someone else did all the hard tasks: machining, PCB layout and even design proving.

I soon realized that the essence of a single trigger flip-flop is to steer the trigger depending on the toggle state. There used to be a standard circuit in the RTC logic days but I couldn't find it.

Nice find , the £3.50 relay.

spec
 
spec said:
Limit switches could be incorporated but I though it better to keep the circuit as simple as possible.
Click to expand...
Limit switches would be advisable in practice though, and over-current sensing might also be needed, as sooner or later the mechanism is likely to be jammed by chicken crap . But let's not add too many bells and whistles for now.
 
Yes limit switches would be the Rolls Royce approach but they do add complications.

Some of the small motors I have messed about with seem to be quite happy stalled, but of course with an industrial grade higher power motor stalling would cause overheating. The simple solution might be to fit a simple current limiting circuit.

spec
 
Once again, this design:

could not be more simple and it appears to meet the OP's basic concept, notably:
dcwatson84 said:
The problem with that is that I do not want the system to consume *any* power when it is offline
Click to expand...
NO power used when between operations and positive stop design with little opportunity for "drift". One "limit" switch. No power reversals.

Now, decidedly not an elegant electronic solution and it would require some mechanical construction and alignment, but having followed this thread from post #1, there sure has been some impressive ink generated...
 
If I'm not mistaken , cars use stall current sensing coils to stop power windows and use PTC's in manual closed positions or bimetallic thermal protection switches , such that manual over-ride disables the switch after a few seconds then lasts for several seconds after that.

One could use a PTC for this purpose and use a more sensitive coil across the PTC to perform some other task similar to end stop. Now they probably use current sensing active latches.

Ford uses a "Generic Electronic Module" (GEM)to cut out motor current "unlatch" in response to an "express down" switch command. The guts of the GEM are a mystery.
 
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If you intend using latching relays, be aware that their coils can't be powered for lengthy periods. Here's an extract from a Shrack datasheet :
 

Brilliant cowboybob.

spec
 
Had an "ah ha" moment today...

I'm pretty certain I can do exactly what I described with 2 switches, 1 SPST relay and 1 DPDT relay. I'll have the switches tomorrow to test and will report if it's successful.
 
If you post the schematic of your idea we should be able to tell if it will work.

Les.
 

cowboybob - I can't really tell how the limit switch is activated? In addition (and perhaps more importantly) one of the downsides of my motor is that it lifts by a string on a reel, so unless I take it apart and assemble complex gears (which I cant) then I need the system to be the standard forward/reverse model. Thanks for the design though! I'll have to keep the cam setup in mind for future projects as it is very elegant mechanically!
 
Les Jones said:
If you post the schematic of your idea we should be able to tell if it will work.

Les.
Click to expand...
I'd need a few tips before I could draw one that makes sense..

I see how to depict switches/relays in a schematic. However, for relays, how do I depict the through-path as well as the control-path (the wire that controls the relay). I see how to show the through-path, but I dont see how to show the control-path. In my system both would need to be shown for it to make sense. Forgive me if my terminology is way off, im simply describing what Im talking about as best as I can . Please correct me if there are accepted terms for this stuff.
 
Wait... I may have answered my own question... The "coil" represents the control path right? So what about DPDT, is it just represented by two coils? i.e. two SPST?
 

Instead of the "bumps" picture a depression where a roller microswitch sits along the edge, The micro would stop the motor when sitting in the groove. The timer, just has to give it a nudge for an amount of time less than 1/2 a revolution. If you have a timer with a 1 minute resolution and it takes less than a minute to open the door, the method won't work as designed.
 
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