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stmbtwle

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Reply with quote  #11 
Fine, but then you need a power source to unlatch the magnet. We're looking for one that releases when the power fails.

There is another type of solenoid that has a built in circuit that reduces the current when the solenoid is engaged. Common on older diesel engines. Cut the power and they release. Overkill, but they should work.

https://www.ebay.com/itm/New-Fuel-Shut-Off-Solenoid-Replace-For-Lister-Petter-Solenoid-SA-3405T-366-07197/302106298375?

https://www.alliedelec.com/guardian-electric-a420-066053-00/70161933/
https://www.alliedelec.com/deltrol-controls-53753-82/70733453/

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LAT39

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Reply with quote  #12 
Here is an idea just for the sake of stimulating more ideas.

I read a thread on another forum some time ago where a guy wanted to control a relay with a single IO pin on a microcontroller.  The suggested solution was to use a latching relay and a capacitor as crudely illustrated below:

[SolenoidControl-Single_IO_pin] 

The idea is that when the IO pin is "HIGH", current flows through the solenoid setting the relay and eventually charges up the capacitor.  When the IO pin changes to "LOW" the charge stored in the capacitor provides the reverse current to reset the relay.

I haven't attempted to calculate the size of capacitor required to power a door lock actuator, but I imagine it may be quite large.  The equation is I=C*dv/dt.  Solve for C and plug in your best guess at current, voltage drop and switching time.  And obviously an IO pin on a microcontroller isn't going to work, but a power transistor and a comparitor to monitor supply voltage might get you there.  This simple circuit solves that "continuous duty" problem since the capacitor blocks DC.

Rick H Parker

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Reply with quote  #13 
Solenoid Circuit.png 

On power up current flows through the Solenoid pushing the plunger to magnetic lock damper closed position. When the capacitor is charged to the supply voltage, current through the solenoid drops to zero.

When the power goes down, the capacitor discharges through the Solenoid and resistor pushing the plunger to magnetic lock damper open position.

Eliminates Solenoid continuous duty but does not eliminate continuous load on the power supply.

V+/R would need to equal or exceed the current need to overcome initial inertia of the plunger.  Capacitor would need to store enough energy to move the plunger from one position to the other.







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Rick H Parker
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stmbtwle

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Reply with quote  #14 
I think if the resistor were moved to the other side of the solenoid as shown, an ordinary solenoid could be used.

Solenoid.jpg 
When the system is powered up the (normally closed) snap disk would allow current to rush through the solenoid into the capacitor, pulling in the solenoid and closing the vent.  Once the capacitor is charged the only current will be that allowed by the resistor, which should be just enough to hold the solenoid without burning it up.   When power fails or the snap disk opens at high temperature, current stops and the solenoid drops out and the vent opens.  Probably a 100 ohm, 10w resistor would work, can't speak for the capacitor.  I think it would work with a door-lock actuator, too.

Though for all the aggravation I think a continuous-duty solenoid (if available) would be better. The capacitor and resistor could be dispensed with.


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Rick H Parker

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Reply with quote  #15 
Quote:
Originally Posted by stmbtwle


Solenoid.jpg

Though for all the aggravation I think a continuous-duty solenoid (if available) would be better. The capacitor and resistor could be dispensed with.


Would need to be a spring loaded solenoid to insure the damper returns to the open position. The load of the spring will increase the amount of current required to keep the damper in the closed position.

The idle current might be high, lower or about the same as my circuit.

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Rick H Parker
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stmbtwle

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Reply with quote  #16 
The idle current would probably be higher but still low. BUT you can use a common solenoid. I'd still go with the continuous-duty solenoid, a motor drive, or a servo.
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pianoman8020

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Reply with quote  #17 
I am planning to add a 12VDC  4" fan to the inlet ducting attached to a 140 deg snap switch and 12v battery. A single charge on a larger battery would be enough for a day or two of operation in a backup situation. I also have a small tickle charger that could be attached to the battery when line power is good. I am tempted to not use the 140 deg. switch and turn to fan on when ever 120 vac is missing. I would have a better chance of keeping the temp. lower to start with.

In the summer when the collector is covered the temperature runs 10 Deg.F over the outside ambiate temperature.

Jim for IL 
stmbtwle

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Reply with quote  #18 
I think you could do fine with just a PV panel instead of a battery. If there is no sun, the collector won't overheat anyway. If you already have the battery, use it, but think about the PV for a later date.

An adjustable buck converter can manage the PV output.

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Solar is like the wind. It may be free, but putting it to work isn't!
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