| Author | Message | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: N/A |
I am planning to use DuoTherm Penguin 13,500 BTU/h roof airs, due to height restrictions. Unfortunately, it seems that technical information regarding these units is difficult to come by. So, as it happens, I goofed on the planning and did not leave any way to run wires for the remote thermostat system that DuoTherm offers for these (my AC wiring for them is already in place). I did not realize, when I did my design, that the internal 'stats on the shroud-controlled units never shuts off the blower. I've got most of what I need for the work-around, which involves standard programmable wall thermostats (which will also run the Webasto for heating) that I will have switch a 24 VDC relay or contactor in the AC supply for the appropriate unit. So far, so good. However, I'm having a heck of a time sizing the contactors for this application. Any of you good people who has a knowledge of this particular unit and its operating characteristics, as well as an understanding of the dynamics of motor-starting contactors, please help with the following questions: DuoTherm calls for a 20-amp breaker. I see that running amps on the unit should be around 14-16 depending on temperature differential. That makes sense to me in thermal trip mode, because the running current will be less than 80% of the handle rating. But I'm assuming a much higher starting current, which I would guess to be closer to 60a or so. I have to believe that a 20a breaker would trip magnetically, unless it is the time-delay type. Can anyone tell me what the actually starting current is, and for how long? In sizing a relay to control these, if the relay has to "make" the starting current, I will need to use a motor starter type contactor, with an AC-3 rating for the starting current (or is it AC-2?). I don't think I'll have any trouble "breaking" the running current (16 amps) with even a standard 20-amp relay (or will I?). So the next question is: if the unit is sitting idle with no power applied, but the controls are set on cool (and the temperature is such that the internal stat will call for cooling), and then AC power is applied to the unit, will the compressor try to start instantly, or is there some hysteresis in the internal circuitry (such that my control relay does not have to "make" the entire starting current)? Apologies in advance for cross-posting to two boards! -Sean | ||
| Jayjay (198.81.26.104) Rating: N/A |
Last question first: The system will not start with high head pressure, (high amp load) the fans system will run first, then the compressor will kick in. First set of questions: A Square D or equivalent thermal magnetic breaker fed with #12 AWG wire, will hold quite well. They are designed to take up to 700% of rated curent for a brief period, just for this type of condition. Your contactor can have a coil rated at 12/24 DC, or 120VAC, with contacts rated at 20A. AC. The wire feeding the coil can be quite small,(#22 AWG)since they pull something in the 250 to 450 MA range. Potter Brumfield or Allen Bradley make a nice line of light ( NEMA Size 1) starters and contactors. I doubt that you will need a starter, with "O.L. Heaters" though. I think I caught everything, but any further questions you may reach me off the 'Board at: jarjaje@wmconnect.com Cheers...JJ | ||
| Tom Connolly (Tomconnolly) (64.58.196.218)
Rating: N/A |
My DuoTherm's have a delay, the fans start with power applied then between 1-3 minutes later the compressors, the two have only started at the same time a couple times and once when the hot water heater, convection oven and a few lights were on, at that time I tripped a 60 amp main (2 tied 30's). I use a 100 amp contactor like the kind from a HVAC unit, with a 1 minute time delay for my automatic transfer switch and have never had a failure opening and closing at full load + - 60 amps, although I can say the 6500 onan has tripped a breaker a few times starting everything. I would go with the motor starting contactors and rate them for use at 75% of continuous duty. Tom C | ||
| woody48348 (66.208.219.185) Rating: N/A |
Sean, I have 3 13,500 Duotherm units on my Eagle and each unit has a 20amp CB to protect the AC, and the 12VDC is supplied to only one of the units, 18GA wire through a 5amp CB. All the units are then linked with a telephone cable, and communication and voltage supply to the other units is through this telephone cable. There is no need for a relay. Bob. | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: N/A |
Bob, I think you must have missed the part of my post that says I no longer have the ability to run any more wires to the A/Cs. Each of the three units has a 120VAC power cable and that's it. I believe the system you are talking about involves Duotherm's low voltage control system, which requires extra wiring to the units. Correct me if I misunderstood. -Sean | ||
| woody48348 (66.208.219.185) Rating: N/A |
Sean, I'm sorry, I missed it. If you are wanting to switch each of the 120VAC input for each unit through a relay, to be controlled by your thermostat, you will not be able to run the fans separately unless the thermostat calls for A/C. There will be no 120VAC to the unit unless the relays is thrown. Bob. | ||
| Tom Connolly (Tomconnolly) (64.58.196.218)
Rating: N/A |
Sean, I personally would work on a way to get the control wires run, you would be surprised at the places a wire can be installed after the fact, when you have the correct tools in the hands of experience. I managed to put both my 110vac and control wires in place after my walls and ceiling were completed and the cavities were spray foamed too! I used my construction photos to pick the route, then fed glow rods (tracking the rod tip location with a stud finder) I used the rods to pull brass sash chain, that I pulled back and fourth to saw a path in the foam, then lubed up the wires with pulling gel and pulled the wires through with the chain! If you don't see a way check with a good alarm wiring technician before giving up. Tom C | ||
| R.C.Bishop (128.123.221.211)
Rating: N/A |
Great post, Tom..... Where there's a will,..there's usually a way!  RCB '64 Crwoon HWC | ||
| R.C.Bishop (128.123.221.211)
Rating: N/A |
Please.........make that Crown.... RCB | ||
| Doug Dickinson (Dougd470) (65.161.188.11)
Rating: N/A |
An Idea Have you thought of using X-10 technology to control a solenoid in the unit? There is a lot of control stuff available that might work |