Uniselector mini project.
T i m
I would like to use a uniselector (got) to step to its next position
upon connection to a mains supply (through 'X' circuitry). This will
probably be at one_per_day time intervals.
Ideally said circuitry would consume as little energy itself as
possible.
What I'm actually trying to do is 'cycle' an intelligent low current
(.5A) but quite expensive charger to a range of smallish 12V lead acid
batteries. Once each battery is actually charged (probably elsewhere)
it will be kept topped up by said project applying said charger once
every Y days (where Y could be 25 as I think it's a 25 way selector).
I could use (make) a 240 ac to 50V DC PSU (assuming the uniselector
was designed to run at that) and then create a suitably long one shot
pulse on power-up (charge cap?). I could probably even just use one
mains digital time switch, energising the uniselector 'step' cct for
one minute, again via a suitable charge cap (so the coil isn't left
energised for longer than needed)?
Ideally though both the charger and the stepper sides would be power
cycled at the same time (to ensure the charger was reset). Or the
charger de-powered when the selector is pulsed (so the selector isn't
actually switching the charge current).
Ideas welcome please. ;-)
Cheers, T i m
KR
Use a DC supply to run it, and (say) 2200uf electrolytic in series.
This will hold it in for a couple of seconds upon power up. If it is
not long enough, use a larger value cap. It would be a good idea to
put a diode across the coil, with the K (stripe) to the positive to
prevent back EMF from the coil possibly damaging the capacitor over
time.
Note that this will pulse the coil once every time you turn on the
power, it will not pulse again until the power is turned off and on
again.
I have used this method in the past with relays to provide a power on
delay and it has worked well for over 10 years.
T i m
wrote:
>> I would like to use a uniselector (got) to step to its next position
>> upon connection to a mains supply (through 'X' circuitry). This will
>> probably be at one_per_day time intervals.
>>
>> Ideally said circuitry would consume as little energy itself as
>> possible.
>>
>
>Use a DC supply to run it, and (say) 2200uf electrolytic in series.
Would you make summat (transformer, bridge rec, cap) or just get a
wall wart sorta thing?
>This will hold it in for a couple of seconds upon power up. If it is
>not long enough, use a larger value cap.
Understood. My original thought (to keep the residual current down)
was to just half_wave_rectify the mains and use that with the cap idea
as once up to potential there shouldn't be much in the way of current
(if both charger and this circuit were powered from the same mains
timer etc). It's just the coil could initially have more than 50V
across it (zener?) and I'm not sure how it would cope with un smoothed
half wave rectified current? How much current do transformers draw
when there is little load?
>It would be a good idea to
>put a diode across the coil, with the K (stripe) to the positive to
>prevent back EMF from the coil possibly damaging the capacitor over
>time.
Understood.
>
>Note that this will pulse the coil once every time you turn on the
>power, it will not pulse again until the power is turned off and on
>again.
Yup, exactly what's needed. As long as the cct can reset quickly (so
that would be down to a 'bleed' resistor across the cap presumably)
then the timer could just provide a 1 min off time. If not I guess 15+
mins (as per the mechanical timers) may be required
>
>I have used this method in the past with relays to provide a power on
>delay
That's another thought, slugging the start up of the charger to after
the selector has stepped. It would be quite easy to (safely / easily)
cover that with two cheap digital 24hr time switches [1] but a single
solution would be 'cleaner'.
> and it has worked well for over 10 years.
Yup and KISS often means at least I actually getroundto doing it. ;-)
Cheers, T i m
[1] Charger timer turns off.
<short delay>
Stepper timer turns off.
<delay to bleed cap>
Stepper timer turns on.
Charger timer turns on.
<~24hr delay>
GOTO [1]
josephkk
Sounds like a great application for a stepping relay. Typical specs: 10,
20, 25, 40, 50, and up to 100 steps; 2 to 10 poles; 250 V, 2 A.
Next; trying to find one.
New ones can be had, but are spendy:
http://www.surplussales.com/switches/SWLedex-1.html