Latching Solenoids anyone?

[Al_The_Man]

Anybody happen to use Latching solenoids in an application? If so were there any downsides?
Was Intermittent coil type used used or was pulsed mode coil used?
Al.

[Geof]

I used some many moons ago. I don't know what type When the solenoid was energized it rotated a little cam which operated a small microswitch then the next energization rotated it further to release the switch.

The system I built with these ran ten cycles a day, 365 days a year for seven years without problems.

[Al_The_Man]

Yes I have seen those, I was looking at the plunger type.
This is a mobile application so it need to be power conscious.
Al.

[john_100]

the only relays I know of have
two coils , one to set the relay and the other to reset it
i think they had a magnetic bias ?

do you have something in mind that you want to do with relay logic ?

I would expect an electronic solution to be less expensive

but not as much fun



John

ps- you answered the question before posted my reply

[Al_The_Man]

I think you are thinking relays, these are mechanical actuator solenoids.
http://www.blpcomp.com/productinfo/solenoids4.php
Al.

[john_100]

a quick search on ebay and I found OMRON ELECTRIC make what i'm thinking off

the first one i found is omron G6AK-234P a 2 pole pcb mounting relay
with 10 pins for the 2 coils and dpdt contacts

searched ebay for latching relayand found ---

http://cgi.ebay.co.uk/RELAY-12V-2POL...item3cb16e6fd6

for info look at http://www.reuk.co.uk/Latching-Relays.htm

John

[Geof]

Originally Posted by Al_The_Man .....This is a mobile application so it need to be power conscious. Al.

How power conscious do you want to be? The type I used took a fraction of a second pulse to latch, the same to unlatch and didn't draw anything in between.

[john_100]

Hi Al,

looking at the diagram of the latching solenoid
the only downside I can see is the need to pulse the current through the coil in both directions with a some thing like a "H" bridge circuit

if power consumption didn't matter a dual coil would be easier to control
and still save on coil heating -- ( 1 to hold in ,1 to pull in)

but in your case If you need the solenoid to be held in for any length of time
the power saving will be the over riding factor

John

[Al_The_Man]

Originally Posted by Geof How power conscious do you want to be? The type I used took a fraction of a second pulse to latch, the same to unlatch and didn't draw anything in between.

Being portable I obviously want to save on power draw, the types I have looked at come in three coil styles and wattage, continuous, intermittent and pulse.
As per my initial post, I wondered if any difference was found between intermittent and pulse, e.g. Intermittent = 1 minute on 3 minutes off and pulse = 100ms on and 900ms off?
Each get progressively higher in consumption, but different in duty cycle.
Al.

[RomanLini]

Al, I've used latching relays (not solenoids) and they were pulse type. Providing your minimum supply voltage is known you can use quite a low pulse duration and a hbridge driver for polarity.

You can also drive then with a half-bridge and a large series electro cap (4700uF?) but this requires that the output of the half-bridge stays stable for the entire duration which will probably not be as energy efficient as your half-bridge must remain powered up.

One issue may be holding force, they will only have the latch mechanism keeping them in either state so you won't get much holding force at all.

Something I have used for good result in high efficiency door latches etc is to use a little RC servo, these are very energy efficient because of the high gearing and will usually remain in position after full power down (you still need a mechanical latch detent). You can also get quite a high throw force although likewise only a low holding force based on the latch. One good point is that you can drive them direct from a microcontroller pin or a 555 timer, you don't need any power electronics.

[Al_The_Man]

Originally Posted by RomanLini Something I have used for good result in high efficiency door latches etc is to use a little RC servo, these are very energy efficient because of the high gearing and will usually remain in position after full power down (you still need a mechanical latch detent). You can also get quite a high throw force although likewise only a low holding force based on the latch. One good point is that you can drive them direct from a microcontroller pin or a 555 timer, you don't need any power electronics.

That was another option I was considering by means of a stepper, but I will look into the RC option, Don't these have a resistance to back feeding? If so will it still need the detent?
Al.

[RomanLini]

If you keep the RC servo powered up, and keep supplying the control signal to it they hold position. If there is no load they use maybe 5mA to 20mA, if there is load applied it will hold the same position but use maybe 50mA to 1000mA depending on the load applied.

But if you move the servo to the new position and power it down it will use zero power, but then the holding force will be small and depend on having a small latch detent etc. That's the way I've done it for electronic cabinet locks etc with a bolt-type latch that doesn't require much holding force.