computer controlled latching relay

Thread Starter

nemo1986

Joined Mar 4, 2009
8
Hi

I am working on a project to design a self contained cooler for a group project and I am working on the electrical system. The cooling system works by using a ammonia vapor set up to cool the food. Now I have the heating coil I am going to use but the problem is I need a latch relay to open the circuit under two conditions 1. it will shut down after a certain amount of time or the pressure changes or if the heating coil goes above a certain temp. This setup will be monitored by a computer system that will be chosen by another member of my group. My professor recommends That I use a parallel port set up but I can't find what I want or I am missing something. It will monitor a 120VAC standard wall socket at a current of 5-10 A.
 

Thread Starter

nemo1986

Joined Mar 4, 2009
8
latching relay. I need something that will kill the voltage when the computer detects that the ammonia has evaporated or something goes wrong with the coil.
 

beenthere

Joined Apr 20, 2004
15,819
Try a P & B S89R11DAC1-12 (actually now a part of Tyco). It's 12 volt DC impulse latching DPDT, 15 amp contacts. Digi-Key has them as part #PB513 @ $45.38.
 

Thread Starter

nemo1986

Joined Mar 4, 2009
8
Try a P & B S89R11DAC1-12 (actually now a part of Tyco). It's 12 volt DC impulse latching DPDT, 15 amp contacts. Digi-Key has them as part #PB513 @ $45.38.

And this can be controlled by a separate computer and can be open and closed by the same computer?
 

beenthere

Joined Apr 20, 2004
15,819
Anything that can apply 12 VDC to the coil can control it. You wil need some external hardware for that, but a resistor, logic level FET plus suppressor diode, and a 12 volt supply are about the only components necessary.
 

Thread Starter

nemo1986

Joined Mar 4, 2009
8
what size resistor we talking about? If this works out then you just helped mesolve three weeks of headaches I needed to find this, a heating coil and a 12-14.8V battery that would last around 6-7 hours and a heating coil I found the heating coil and a 14.8V battery 9Ah (133 Wh, 7A rate) that should workout fine. Hey do you control the discharge by wire guage or do I need something else for that. Cause I will be honest batteries were never my strong suit.
 

beenthere

Joined Apr 20, 2004
15,819
Here's a schematic of the hookup. Any logic HIGH pulse lasting a couple of 10's of milliseconds will operate the relay. It will change and hold state with each pulse
 

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