I have a Payne furnace that had a Intermatic wall timer connected to it. The timer was causing the furnace to come on at various times and sometimes just the blower (it'll run all night). If I hit the on/off button on the timer, it'll disable it for 24 hours. I attempted to disable the timer completely according to the instructions, but it didn't help.

The power flow is as follows:

In Power source (black/white/ground) from electrical panel to junction box
24v transformer outside junction box which connects to furnace
Junction box out power source (red/black/white/ground) to wall timer/box
Wall timer box to on/off switch for furnace

I installed a programmable thermostat, but the wall timer still had priority.

I disconnected the wall timer and transformer and made a direct connection from the power source to the on/off switch, but now the furnace seems to "get stuck" at a certain temp. If I turn the heat switch on the thermostat off, then on again, the furnace will kick on again. Also, I've noticed the burners come on several times for short periods, 20 sec or so, with out the blower, and continues to do this for a while. This was happening prior to taking the timer off.

Do I need to put the transformer back on (seems like it should be since it's connected to the furnace) and if so, how do I wire it (I forgot how it was wired originally). Any suggestions?

Any help will be appreciated.

Both the furnace and the thermostat should have contacts marked R or RC, G, Y, Etc. Disconnect all wires going to the timer.

Identify 2 wires coming off the transformer that have 24 V AC between them. Likely to the same color. I have one with 2 yellow wires and a black wire. The black wire is a center tap 12 volts to the others, which you do not use. Connect one of the 24 V wires to a red wire running to the thermostat and the other to a blue wire to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. It may be wired to have the control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan.

If my general info doesn't match your furnace, post back with more details.

Hi Labman, not only did I disconnect the wires to the timer, but also to the transformer (which now I think I shouldn't have, since I don't remember how it was connected. The thermostat (located on the main floor) is connected correctly and works. I doubled checked those connnections.

My problem was with a wall timer that was installed in the basement near the furnace (I just purchased this home and it's only two years old).

The transformer (sits on the cover of the first junction box) has two wires (white/black) that go inside the first junction box, and then another two wires (brown) that attached to the transformer on the outside and goes to the furnace.

The power supply line (located inside the first junction box along with the 2 transformer wires), were somehow connected to a 4 wire (red/black/white/ground) which went to the wall timer (on the second junction box). The wall timer has three wires (red/black/white) which was somehow connected to the 4 wire, including the on/off switch (on the third junction box) (black/white/ground) which then went to the furnace as the power supply.

I'm sorry if I'm not explaining this well enough. I could try and draw a diagram of how it flows it that would help? Also, I have not touched any wires inside the furance, only the ones outside, as described above.

Jim

In my first answer I should have paid more attention to this:

> In Power source (black/white/ground) from electrical panel to junction box
> 24v transformer outside junction box which connects to furnace
> Junction box out power source (red/black/white/ground) to wall timer/box
> Wall timer box to on/off switch for furnace

OK, the furnace was wired so it only had power when the timer was on. If you are not going to use the timer, you need to run black/white/ground from the first junction box to the furnace. You can do this by connecting all the black/white/ground wires in all the boxes. Leave the transformer connected to its black/white and any ground and the 2 brown wires going to the furnace. Leave the red wires at the timer disconnected.

If you never intend to go back to the timer, it would be better to rip it out completely. You could continue to use the black/white/ground wires that went to it and the furnace, or replace them with a more direct, unspliced connection. Keep the shutoff near the furnace. Except for low voltage circuits like the thermostat, all connections must be inside a box that is accessible. Wires must be in a protective covering. In most areas the common NM plastic bundle of black/white/ground is acceptable. Some areas require conduit or flex.

labman, thanks a bunch. It just what I was looking for. One more question, I hooked up the transformer as suggested below and noticed that it got kind of warm. Is that normal? What is the purpose of this transformer, since it's connection goes from the original power source directly to the furnace?

Again, thanks for you expert assistance! :)

Jim

The transformer drops the voltage down to 24 volts which is enough for small control applications but safer than 120v. Lower voltage can use smaller switches, important in thermostats with sensitive controls.

Oops! Yes the transformer will be warm, but not too hot to touch.

Hello, Labman. I am trying to hook up a 24 volt transformer to use for hot wire cutting foam. I have plans and instructions I downloaded but they were not helpful.

This is a radio shack Transformer 273-1512b. I first wired a dimmer switch to a Ground Fault Outlet and indicator light and all works fine.

There are three wires like you talked about on this transformer. Two on one side a are black and I assume to be my leads to the wire cutter. There are three on the other side, one black and two yellow.

You said the black is a "center tap 12 volt to the others". I have no idea what that means but I did disconnect it from the ground but I'm still blowing fuses and the circuit breaker.

My latest attempt has been to have one yellow wire hooked to the white wire source and the other to the black wire source (I put a two pin plug on the yellow wires and am plugging it into the ground fault outlet. The green is hooked to the ground screw on the outlet.

I have included two jpgs showing the setup. You can see how I wired the transformer. The scramble inside is due to twisting the outlet and I have fuse holder I'm not using now that I have the ground fault outlet.

Can you tell me how to hook this up? I'm gettling close to blowing myself up trying to figure this out.

Attached Images

  

You want the pair of black leads connected to the incoming power. The pair of yellow leads connect to the foam cutting wire. The dimmer switch should be able to be connected between any of the 4 wires and the wire it would otherwise be connected to. If you connect the incoming hot wire to it, in the off position, nothing will be hot except the wire to the switch.

You won't use the third black wire. Fold it over and tape is so it never contacts anything.

Thank you for replying so fast Labman. I would not have guessed the wire hookup since the black wires (input) were smaller than the yellow (output).

It still doesn't work, however, there is progress, no blown fuses. That has been exchanged for a smell of burning transformer. In fact, I think I may have burned it out. When I plug it in, I hear it and shortly thereafter smell it and subsequently see smoke. I have it hooked up to the "hot wire cutter" and am getting no voltage reading.

I also rewired it the way it was described in the orignal plans, sound smoke, but no voltage. http://[email protected]

So I have tried it with the ground fault outlet and without it and the results are the same: No hot wire.

My next move is to buy another transformer because I don't trust this one. This also tells you how little I know about these things.

Is there a sequence or something I missed?

The diagram in the link is about what I suggested, except it has the fuse and indicator lamp. What are you using as the cutting bow? It needs to have a high resistance to keep from drawing too much power and burning up things. The fuse insures when something burns up, it is the cheap, easy to replace fuse.

For your next try, start with the dimmer cranked all the way to the left. Once on, slowly turn it up, giving the cutting loop time to get hot enough to cut without drawing too much power. Once you have it working, you may want to make a mark so you can quickly return to about the same setting.

I burned up a couple of transformers on my furnace before adding a fuse to it. When I replaced the furnace, I discovered the chipmunks had chewed the insulation off the thermostat wires. Worse than Labs.

Hello labman,

I got a new transformer today and hooked it up, black wires power lead, yellow wires load and it works! I had really cooked the other transformer.

This morning I took apart two battery chargers I happen to have to see if there was anything useful there, but both were solid state and had stuff I didn't recognize.

I have cut foam with them before and they worked OK, but there was very little control which was achieved by moving the clips on the cutting wire up and down to get the right amperage. Ideally, from my reading, you want about 5 amps from 24 volts.

The project is to cut foam model airplane wings and the airfoils are nothing to trifle with. You want accuracy. Now I will have much more control.

Thank you very much for your help.

Hi Labman. You seem to have a ton of knowledge about transformers. I'm very new to electronics and want to make sure I learn all I can before I attempt anything too complex. Currently, I'm working on a project to make a remote-controlled sliding glass door opener for my dog. I have a 24v wheelchair-ramp motor that I would like to use. I'm thinking of going off this schematic for the power conversion: http://www.zen22142.zen.co.uk/Circuits/Power/unreg.htm
I've changed the diodes to 1N4002s at the suggestion of someone. I think I have a grasp as to what most of the things on the schematic represent, but the Rload is still new to me. I'm not sure if it's a resister or what. Also, after reading the previous posts in this thread, am I right in thinking that the black wires in the 25.2v transformer are going to connect to the power in the wall and the yellow are connected to the circuit? A thought just occurred to me, will the Rload be the motor? (as you can see, I'm extremely new to this)
As far as assembling this goes, what would the best way be? I have a gen.purpose PC board from Radio shack but am not sure if that's needed.

Thanks in advance for any help from you!

Breckbone

I think the rload and lload has to do with resistance and inductance. An electric motor resists current very differently than a toaster. Shouldn't make that much difference in a power supply. I am not sure how to calculate it, but you get less DC volts once rectified, than the AC you start with. You might need more like 50 VAC to produce 24 volts DC. Maybe the easiest way would be to look around at battery chargers for one that produces 24 volts. Motors are not as fussy about ripple as electronic devices.

Wow... fast reply. Thanks. I hooked up the motor via the schematic I found and it seems to work fine. I'm not sure of the best way to connect everything, though. I just have the diodes and cap twisted together. I used wiring caps for the wall plug to the transformer. Eventually I plan to build a box to mount the motor in and am assuming that soldering the diodes and capicator and wires together is an approach, but then to I just leave them sitting inside the motor box? Should I use electrician's tape and cover everything?

Thanks for the help.

Breckbone

I wouldn't pack things too tightly in a box. The diodes give off heat, perhaps too much to dissipate in the motor box. If you try it, and it does become hot, you could always put it in a bigger ventilated box. Tape sometimes comes loose eventually, but I can't think of anything better.

Great... Thanks for the helpful suggestions! Now I just hafta figure out the remote part of it. I was thinking of using a receiver from an old rc car... not quite sure how to implement it yet. A doorbell reconstructed might work, too... anyway, off to more reading. Thanks again.

For my basement cutter I prefer to use a powerstat/variac (ebay $20) rather than transformers. For my portable foam cutter I use 3 radioshack 24 volt 2 amp transformers wired in parallel to heat a 53" nichrome wire rated 1 ohm per foot resistance. When I tried to use 1 trans by itself it overheated, so I bought 2 more. Now they get warm but not hot. I like this setup rather than 1 larger trans because with the dimmer on full, the wire gets just a little too hot (not unsafe) instead of burning up. (FYI-A 12 volt 650watt transformer i tried would only power about 20" and an ATX power supply will only power about 10" of same wire.) I use a timer and a GFCI extension cord so I don't get shocked and don't leave the damn thing on!

1: I've read that wiring transformers is questionable, something about they can be out of phase and this can be a problem? Can anyone shed some light on this? Am I OK since these are all the same model trans?

2: I believe that trans wired in parallel increase the amperage not voltage is this correct? (e.g. my 3 trans can provide up to 6 amps-so now the wire is not overdrawing the transformers, which is why the trans are only warm and not melt-down burn your hand hot-yes?)

3: please let me know if I'm doing anything stupid :)

4: p.s. to be clear, when I say I wired the transformers in parallel:
I wired all the primaries up to the gfci cord so there is 1 black from each transformer on the positive and 1 blk from each tran on the negative of the cord. From the secondary I hooked up 1 yellow from each trans to the pos and 1 yellow from each tran to the negative side of the nichrome wire, so that there are 3 yellows running to my hot wire on each side. This is an example of transformers in parallel yes?


TIA,
flafla

Household current is more hot and ground than negative and positive. At any one time, one end of an AC coil is positive, and the other negative, but constantly switching. If both primaries and secondaries of the 3 transformers had obviously right and left wires it would be fairly easy to wire them up in phase. Other wise, you have about one chance in 4 of getting them right. Since you have it working, you must have connected them right, and yes what you describe is parallel. If you connected the secondaries out of phase, a positive end to a negative end at that time, it would draw unlimited current until something overheated and burned up.

I am sure I would have done it differently, but what you are doing, seems to be working. The GFI does protect you from a number of possible problems.