Furnace bump timer

I put this circuit together over twelve years ago. I have it installed on my furnace/air condition control. I have a momentary switch near the thermostat, when I push the switch the furnace or air will come on for about

4 minutes (plus or minus). I move an alligator clip depending on season, you can put in a switch. I use it rather than turning the heat/air up and down, for a short comfort adjustment. It runs from a 9 volt battery and has very low standby current, about 80 nanoamps. The battery lasts two or three years. Others can modify for different purposes. If you think of another use, please post it. MikeK
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Reply to
amdx
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Something tells me a capacitor across the coil (1,5) should be added to aid in making sure the armature gets fully moved over with out chatter on the contacts.

That's just me... ignore me otherwise.

Jamie

Reply to
Jamie

Very nice idea and good logic.

I can't help but think the circuit is way over designed with too many components. It doesn't matter to you because you have it built now.

I would have thought a UJT transistor with a simple RC ramp generator but....wait! Yeah another contact on the relay would go a long way to accommodate much simpler circuitry. probably not happening on a latching relay.

Here is something ese you may consider...steal power from the furnace circuit. Hook your common to the one side of the contact and to the other side of the contact make a simple trickle charge circuit with.

furnace connection -> diode -> resistor (say 1K) -> capacitor to common (say

1000uf) -> 9v input.

If the voltage is critical you could insert a 7809 regulator to setady the voltage at 9 volts from the 30 you may get off the trickle voltage stealing circuit or you could use a parallel resistor across the ripple capacitor to drop the voltage down to 9-12 volts. The trickle current has to be light and the cap. big enough to carry the relay coil snaps.

I have discovered the timer input on my HRV system and gor PB to activate it for 20-40-60 by holding it down longer for one, two or three blinks of the feedbak LED on the wall. Short shots of ventilation stuff is nice. You get it when you want it but don't have to find it running your wallet down a month later.

4 minutes (plus or minus). I move an alligator clip depending on season, you can put in a switch. I use it rather than turning the heat/air up and down, for a short comfort adjustment. It runs from a 9 volt battery and has very low standby current, about 80 nanoamps. The battery lasts two or three years. Others can modify for different purposes. If you think of another use, please post it. MikeK
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Reply to
Josepi

I do the same thing by having a humidity sensor(Aprilaire) wired for switch closure on humidity RISE, inserted into the red wire to the thermostat. That way, when I come in from grass cutting or whatever, I just breathe a warm, wet breath into it, and the A/C kicks on promptly, runs for about 15 minutes. And since the thermostat/humidistat is in the hallway near the bathroom door, when someone finishes taking a shower and opens the door, the A/C will kick on within 45 seconds and clear the humidity from the area and remove it from the air in the house. That beats trying to remember to turn the bathroom vent fan off. This arrangement causes the A/C unit to be a whole-house dehumidifier, rather than trying to get a certain temperature. With a 'baseline' humidity setpoint of 35%. My wife no longer gets up in the morning with dry throat and eyes. That makes a big difference to our utility bill in the summer, since a dry 83 degrees is far more comfortable than a muggy

73 degrees. And we > I put this circuit together over twelve years ago.
Reply to
Michael B

I put this circuit together over twelve years ago. I have it installed on my furnace/air condition control. I have a momentary switch near the thermostat, when I push the switch the furnace or air will come on for about

4 minutes (plus or minus). I move an alligator clip depending on season, you can put in a switch. I use it rather than turning the heat/air up and down, for a short comfort adjustment. It runs from a 9 volt battery and has very low standby current, about 80 nanoamps. The battery lasts two or three years. Others can modify for different purposes. If you think of another use, please post it. MikeK
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You have explained and documented your project rather nicely. Good job.

Tom

Reply to
Tom Biasi

Hi Jamie, I noted I have a diode on one coil but not on the other. I don't remember if the diode was added to correct a problem or if it was put in as general good practice and just forgot on the other coil. But the circuit is drawn as has been working for 12 years. MikeK

Reply to
amdx

I can't take credit for the design, I just put it together.

I'd like to see your design!

Thanks, MikeK

Reply to
amdx

since a dry 83 degrees is far more comfortable than a muggy

73 degrees.

Amen to that, I bought a dehumidifier to run just to bring humidity down to 40%. I can run the temp 5 degrees higher and be more comfortable than with lower temp and higher humidity. It is not the solution though, the dehumidifier produces a lot of heat and wherever room it is is gets hot. New SEER 15 installed recently, won't know till summer how it does with the humidity/temp issue. Cool idea with the humidistat wired into the cooling circuit. Or is that a dry idea? :-) MikeK

Reply to
amdx

Well thanks, I use paint for schematics, although it could have a few extra features that would really help. Such as when you want a six sided object like this,

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I worked around it, but "draw a line at angle xx" would be nice. MikeK

Reply to
amdx

My thermostats are all digital, but what I ended up with was this rule...

If the humitidy is above 50%, for every 2% above 50%, lower the temperature setpoint by 1 degree F, up to 5 degrees. So if I set the temp at 75, it's allowed to cool as low as 70 to make it more comfortable, and it can bring the humidity down faster. As the house dries out, the temperature slowly increases back to the original setpoint.

I learned the hard way that letting the house warm up above the setpoint if it's dry is NOT acceptable to my wife. However, it's always OK to cool it down more.

Reply to
DJ Delorie

It's most likely the relay you are using has it's mechanics designed to get past the load swing point of no return before the contacts that is maintaining the coil current opens. My thoughts were to have a cap on the opening coil to help it give a little more time to make sure it gets over the hump.

We've worked with those kind of dual coil latching relays before and had issues when the applied duty cycle of DC current to the coil was not always long enough and the relay would either switch back or sometimes get stuck in the middle. The fix was to place a cap across the coil with a blocking diode. I've seen some that come with these components already in them.

If it works, that is all that matters.

Jamie.

Reply to
Jamie

I have my thermostat at 73 degrees, since it's the humidistat that will actually turn it on.

Reply to
Michael B

This has even lower standby current:

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--Winston

Reply to
Winston

That's a great idea Winston! Only down side is cutting the hole in the wall for the box. Thanks, Mikek

Reply to
amdx

(...)

That's easy.

This is a 'low voltage' use, so you don't need an official stud- mounted box in most jurisdictions. Locate studs in the wall and outline the location of your new switch between them.

Drill 3/8" holes to define the inside corners of the box and use your keyhole saw to cut out the plug in the middle of the outline.

Use a respirator and have a vacuum ready. This is dusty business.

Fold the tabs of one of these nifty 'box eliminators' into the hole and use two sheetrock screws to secure the end of the tabs so that they grip the edges of the opening.

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Use your fish tape or fish rod to pull the cable from the opening into the wall and attic. Connect both ends of the cable and drop a generous 12" service loop of cable into the wall behind the switch. Affix your switch and cover plate to your box eliminator.

Use a slightly damp cloth to clean the area of sheetrock dust.

Hey Presto! A clean looking custom installation!

Piece of cake.

--Winston

Reply to
Winston

If that's still too big of a hole, use one of those plastic "pancake" surface mount boxes. Then all you need is screw holes and a small hole for the wire.

Vaughn

Reply to
vaughn

But check clearance first!

The timer switch is fairly deep.

This might work, but it has been "whomped with the 'ugly stick'":

--Winston

Reply to
Winston

For drywall?

Draw the outline and use a utility knife to cut a deep grove along the lines. Then cut groves to opposite corners. Whack with a hammer and peel out the scrap. VERY little dust created.

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--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.
Reply to
Michael A. Terrell

The paper backing would tear out the back side of the drywall in the corners. It wouldn't be visible but it would be a weakness in the 'rock where a crack could form. Filleted corners reduce the chances of cracking.

--Winston

Reply to
Winston

So everyone was wrong for generations? You can't trim the backing with the knife?

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.
Reply to
Michael A. Terrell

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