Making my furnace variable speed.

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Old 01-06-08, 01:26 PM
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Making my furnace variable speed.

Hello,

I've got two older furnaces (Lennox G8Q3-90 and -105) in a 2400 sqft two story home. As far as I can tell they are original with the house which was built in 1982.

Both furnaces have 4-speed blower motor and what I'd like to do is make use of the variable speeds (low flow continuously, higher when heat is called for). There is no AC unit. I'm not electronically inclined (yet), but it seems conceptually simple enough...

The blower control is a grey Honeywell box that has one push/pull button for manual or automatic, there are no circuit boards. Is there an economical/simple way to do this?

Thanks in advance.
 
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Old 01-06-08, 02:00 PM
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this can be done with a relay, or series of relays without much difficulty but you need something to figure out what you want to control the the system.

what is going to effect the change?
 
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Old 01-06-08, 02:08 PM
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Thanks for the reply.

The fan blower motors have wires for setting low, med-low, med high and high. Currently they are both wired for med-high.

My plan would be to have the furnace blowers on low continuously, then change to med-high when the thermostat calls for heat. I'd also like to have the option of turning off the fan when no heat is called for.
 
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Old 01-06-08, 02:26 PM
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So now, you need to define exactly how things would run such as:

when the fan runs, is it controlled at any time by the thermal switch that makes the fan run now? It can be or it can be over ridden. Obviuosly with the slow speed, it has to be bypassed but when the t-stat calls for heat, do youwant it to go directly to high speed or do youwant it to wait until the thermal switch calls for it and in interim, do you want the slow speed to run or should the fan shut off until the thermal switch calls for fan?

Do you want this to be able to be bypassed altogether and if so, what would the fan setting be in that case?

any other control situations that you can think of would help refine the system.

all in all, not a big hard job that only takes about $1000 worth of parts.




just kidding. you can do it with around $30 or $40 of parts.
 
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Old 01-06-08, 02:58 PM
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Let's see now;

I would want the fan to be controlled by the thermal switch as it is now.

I would want the fan to go directly to the higher speed from the low speed (unless you could give me a reason why I shouldn't do it that way).

I would only want to bypass the continuous low speed, so that the fan would go from off to med-high as controlled by the thermal switch. Currently my thermostat Fan switch isn't hooked up - I'd like that to control the continuous low bypass.

I haven't thought much about further refinements, I think the above would keep things simple and give me the results I'm looking for. ~ or least enough to experiment with for now ~
 
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Old 01-06-08, 06:12 PM
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We would recommend the fanhandler. It does what you are trying to do and does it pretty well. There is a model for almost any direct drive blower. Sometimes it brings out the worst in an OEM motor and can require the replacement of the motor to get smooth operation. Check out their web site (same name as device .com) and you will know if it is for you. Not that expensive when you take out the R&D costs of doing it yourself. I'm not sure if he will sell to an end user but I suspect he may. The owners name is Dick and he is extremely helpful with tech support.

Ken
 
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Old 01-06-08, 06:44 PM
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I suspected there was an after market product that would do the trick ~ I just couldn't find it.
 
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Old 01-06-08, 08:06 PM
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Yikes, you have about 195,000 BTU in that house!?

As Ken said about the fan handler, that would work out for you.. But you want to spend that money on something that is 25+ years old?

I would start saving money, and replace the equipment for something smaller to save on your gas, and get a two stage variable speed system that will be nice to have.
 
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Old 01-06-08, 08:34 PM
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We get cold winters here in Edmonton... sometimes 195,000 BTUs doesn't seem enough. heh...

I couldn't find any price online for the Fanhandler, and I'm not intending on spending a lot of money. I am willing to do the leg work however, so if nap (or anyone else for that matter) can provide a $30-40 solution ~ that's what I'm looking for.
 
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Old 01-06-08, 08:36 PM
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Does both furnace run non stop on your coldest night?
 
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Old 01-06-08, 08:40 PM
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No - not non stop.
 
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Old 01-06-08, 08:54 PM
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if it cycles on and off, then it's oversized. I have no ideal how much this will cost. But more than $100 I'm sure.
 
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Old 01-06-08, 10:41 PM
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I can build this for around $40 bucks. All it needs is a coupple ice cube relays and bases and maybe a switch or two.

it's late so I'll have to hit on this tomorrow.
 
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Old 01-06-08, 11:02 PM
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Thanks a lot nap.
 
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Old 01-09-08, 09:03 PM
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Sorry about leaving you hanging. Time has been at a premium lately.

There are several ways this can be done so let me give one and maybe racraft or o few others will beat it up or at least look at it and toss in any advice they see appropriate.

use a relay with (at least one double throw contact.) an ice cube relay of the correct rating should be fine (note: we are dealing with an inductive load so you need a relay with an inductive load rating greater than the motor FLA rating)

the coil needs to be the same voltage and ac or dc voltage (most are ac but just in case you have something different. check the voltage. Usually 24 but... ). You will need a fan feed wire that is hot all the time. It connects to the common of the contact set. The low speed to the motor connects to the N/C contact and the med-high to the motor connects to the N/O contact of the same contact set. The t-stat also stays connect to the controls it is currently hooked to but the motor feed currently used is disconnected.(see directions further on for this) (if you don;t you could possibly energize two speeds at the same time... not a good thing.)

Now since you are not using the fan control circuit on the t-stat, you can use this to run another t-stat in circuit with the low speed feed between the 1st relay and the fan and connected to the N/C contacts so when energized by the fan on switch, it energizes the relay and actually turns the low speed feed off.

Along with this, I would place a single pole double throw switch in circuit with the fan power feed tapped before the thermostatic switch (the klixon switch that normally turns the fan on from the heat in the heat exchanger). One of the load sides will go on to continue that same circuit and the other load side contact will be the feed to the new relay setup. This way, you can flip this switch one way and everything will work as before the new controls.. The other way, the new controls will be utilized.

hopefully some of the other guys will take a look at this and critique. The mind has been tired lately and I don't want to smoke your furnaces.

I'll take another look at it tomorrow to check throught it again as well.
 
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Old 01-11-08, 10:54 PM
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Alrighty then - I think I've got some reading to do... =)

I'm going out of town - but I'll let you know my questions when I get back.

Thanks again.
 
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Old 01-12-08, 04:32 AM
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What you will have is a multi speed blower, not variable speed. It will probably suffice for your experiment. Especially on your budget.

Ken
 
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Old 01-12-08, 10:10 AM
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he does have a multi speed motor. All I was doing is providing a means to allow use of more than one speed as needed or desired.

a true variable speed motor is a totally different animal.
 
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Old 01-12-08, 04:57 PM
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I know that the motor is multi speed. I was making the distinction between variable speed and mulit speed. the fanhandler senses temperature of supply air and varies the speed of the motor infinitely from the minimum setpoint to the full speed of the tap it is connected to (usually high). That way the condensor can chill the evaporator before it begins to discharge air that is not cool and it tends to dehumidify better. In heating mode it also ramps up and down to attempt to maintain a constant supply temperature. The multi speed relay setup you are creating will probably make the house more comfortable at times and since it costs next to nothing, there is little to lose. I would suggest a way to make it easy to bypass the new control so that troubleshooting does not require knowledge of the new circuit. That way someday a service tech won't come across it and freak out.

Ken
 
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Old 01-12-08, 05:27 PM
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I would suggest a way to make it easy to bypass the new control so that troubleshooting does not require knowledge of the new circuit.
please notice:

Along with this, I would place a single pole double throw switch in circuit with the fan power feed tapped before the thermostatic switch (the klixon switch that normally turns the fan on from the heat in the heat exchanger). One of the load sides will go on to continue that same circuit and the other load side contact will be the feed to the new relay setup. This way, you can flip this switch one way and everything will work as before the new controls.. The other way, the new controls will be utilized.
one switch is all it takes to do that.


the problem I have with the fanhandler is it does not state in any of the literature I found how it slows the motor. the clain this thing has been around since 1961 so I have a hard time believing it is a vari freq drive, which it how you need to vari the speed of a PSC motor. If you use a pot, like you would with a shaded pole motor, you may get some variation but at what costs. You will get variation due to additional slip (read: heat inducing ) Often it is the cost of the motor since a PSC motor is an "economy" design and is not typically intended to be overloaded and live.

So, any literature on the fanhandler that speaks to the method employed to slow the motor?



what my set up does is simple; it is what JetJock asked it to do and at a price within his budget parameters.
 
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Old 01-13-08, 05:00 AM
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The fanhandler connects to the neutral wire of the blower motor and controls its speed through (I assume) changing the ac waveform. On some motors it can make them noisy. They sell a good quality motor that can operate with the controller and not hum but I have only needed to replace one motor and I have installed close to ten of those units. It solves various system problems and comfort problems but I don't think it has a use on every job. It makes things work better on a zoned duct system, or an oversized system. The cost is around $150 if I remember correctly so you must reap a benefit before that cost can be overlooked.

Ken
 
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Old 01-13-08, 08:49 AM
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Ken, if you get a chance, I would really like to learn more about this fanhandler and since you apparently have used it and understand it to some extent, I figure you are my best shot at more info.

Do you any technical literature?

How about a patent number if nothing else (I hate the USPTO site but sometimes you have to do what you have to do).

btw: this site lists a 240 volt version for $600.http://www.negative-ion-generators.c...pping_cart.php
 
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Old 01-13-08, 09:23 AM
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I finally found some info.

We control the motor’s speed through phase control. This means clipping the sine wave both above and below the zero line. The very critical aspect here is that the FanHandler cuts the sine wave at exactly the same voltage above the zero as it is below. If you do not do this precisely, you end up with a direct current component to the AC signal. AC to an induction motor drives it forward and a DC component acts as a brake. (The way big screw machines and lathes are stopped is to hit them with DC; they stop within a few revolutions.) DC in our application will cause heat and burn up the motor. The FanHandler’s circuitry avoids the DC component. We’ve been building just about this same circuit since the early 1960’s (GE helped us develop the control). Many companies have tried to do the same thing but with cheap triggering methods (like dimmer switches). These cheap controls will ruin a motor.
Phase control? Ah, sure, if you want to use that term. They state they "clip the sine wave" that is a fancy way of saying they reduce the voltage. Not only do they reduce the voltage but by clipping the sine wave, they actually turn off the power to the motor for the period of time it is clipped. No wonder they speak to worn out motors and cheap motors having problems. You have to have a tight motor just to be able to handle the abuse this thing throws at the motor.

Not only that, but they try to use the old "baffle them with BS" approach to their information. Double speak and pseudo-technical jargon doesn;t sell me.

This is not an acceptable method for altering the speed of this type of motor. If you doubt me, call the motor manufacturer and ask them if they will warranty a motor if you use one of these things.
This is why you do not see a bunch of other companies selling similar devices. If it were this easy, there are many well known manufacturers that would have similar devices.

Sorry Ken but I'll have to pass on this thing.

I would look into VFD's if you want to retrofit a variable speed system.
 
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