Triphasic AC/Heater electrical problems

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  #1  
Old 05-20-12, 09:06 AM
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Triphasic AC/Heater electrical problems

Hello,

My central AC/Heater has 2 electrical problems, I hope someone can give me some guidance on how to resolve these issues. I live in Brazil, and most of the electricians (and AC install specialists) I have hired tend to be of the "tell me what to do" type. They seem to be skilled, but I need to give them specific instructions. There are no enforced AC/electrical codes or inspections.

Ok, I have a triphasic (typical here) central AC/Heater sized at 5 ton (60k BTU). The unit is rated at 5900 watts / 18.8 amps. My house has 3 phases of 50 amps each (plus neutral and ground) coming from the street. The AC unit has its own circuit breaker a 3-phase type "C" 25 amps. The wires from the street to my house are 25mm^2 (about AWG 4) and from the circuit box to the AC unit is 6mm^2 (about AWG 10).

Problem #1: When the AC turns on, my uninterruptable power supply for my computer beeps and the lights in the house momentarily dim. The circuit breaker never trips.

Problem #2: When the heater is being used, every few hours of use the circuit breaker trips. I think this happens the moment the compressor turns on.

It seems obvious that this is due to the high initial power draw for starting the motors. When the AC or heater is running, I measure constrant current draw at 15-18 amps (on one leg). The moment the compressor turns on, my ammeter jumps to a much higher value before returning to 15-18A (can't tell exactly what).

If anyone has any suggestions on how I can begin to figure out how to solve these problems, I would appreciate it. Unfortunately the solution is *not* to simply call a certified HVAC person... because this doesn't exist here! But if someone can give me some suggestions on what to ask the electricians to test, I can do that.

My naive idea is that I need to swap the 25 amp type "c" circuit breaker for a 25 amp type "d" to account for the large iniital instantaneous current draw of the 3 phase motor. Does this sound reasonable? Maybe I should be using a large capacity circuit breaker? The manual says to use a 25 amp breaker, but it doesn't specify the type (b/c/d).

Thanks so much!
 
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  #2  
Old 05-20-12, 11:41 AM
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Considering you are from Brazil and know English rather well, I am assuming you have not always lived in Brazil. I am not familiar with electrical equipment or characteristics in Brazil, can you explain what circuit breaker types "B", "C" and "D" are? I understand that they would all be 25 amp rated, but what is the difference between the three breaker types. Who is the manufacturer of the circuit breakers? Does the heater have electric resistance heat or is it a heat pump?
 
  #3  
Old 05-20-12, 03:35 PM
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CasualJoe, yes I am not from Brazil, I'm from the US.

I am not an electrician (although I have had to learn a lot to deal with electrical issues here) but the BCD types I learned about on wikipedia:

Circuit breaker - Wikipedia, the free encyclopedia

[TABLE="class: wikitable"]
[TR]
[TH]Type[/TH]
[TH]Instantaneous tripping current[/TH]
[/TR]
[TR]
[TD]B[/TD]
[TD]above 3 I[SUB]n[/SUB] up to and including 5 I[SUB]n[/SUB][/TD]
[/TR]
[TR]
[TD]C[/TD]
[TD]above 5 I[SUB]n[/SUB] up to and including 10 I[SUB]n[/SUB][/TD]
[/TR]
[TR]
[TD]D[/TD]
[TD]above 10 I[SUB]n[/SUB] up to and including 20 I[SUB]n[/SUB][/TD]
[/TR]
[/TABLE]

The circuit breakers (manufactured by Siemens) have printed on the things like "B16", "B20" for type "B" 16 and 20 amp respectively. My breaker for the AC says "C25".

I forgot to mention in my original post that the standard voltage here is 127v, like in the US. So for my 3 phase wiring, each leg is 127v.
 
  #4  
Old 05-20-12, 03:47 PM
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"Does the heater have electric resistance heat or is it a heat pump?"

Oops, forgot to answer that question. I believe it is a heat pump. To operate in heating mode, everything runs in reverse (this is what the install guy explained to me). Another bit of evidence, when in heating mode, the compressor blows ice cold air outside.

Doesn't that make it a heat pump?
 
  #5  
Old 05-20-12, 03:47 PM
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What make and model is your heat pump? What is the information on the data plate on the unit? Do you have the manual for the unit, or could you provide a link to an online copy?
 
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Old 05-20-12, 04:07 PM
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Welcome to the forums!

Problem #1: This can be normal. When the AC kicks in the large draw can cause voltage to drop enough to kick off the UPS alarm. I am assuming that it does not say in alarm mode for more then 10 secs.

Problem #2: During normal start up a motor (which an AC unit has a couple) will draw up to 3 times the normal running current. Most circuit breakers are similar to a time delay fuse and can handle this inrush current for a few seconds or so.
This would not happen after the unit has been running for a couple of hours. You have something else happening. I suggest putting on your ammeter and watching the current until the breaker goes.

In the US we really only have two types of breakers that are widely used. Inverse time, which is the most common and instantaneous trip circuit breakers. I have not heard of a B, C, or D circuit breaker. I do know that you may not install a larger amp breaker then listed on the units nameplate.
 
  #7  
Old 05-20-12, 04:33 PM
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"What make and model is your heat pump? What is the information on the data plate on the unit? Do you have the manual for the unit, or could you provide a link to an online copy? "

The brand is Springer Carrier is is called a "Split Versatile 60000BTU" the specific compressor/blower parts are 42BQA060510HC and 38CQD060535MC.

Here is the download link for the Owners manual:
http://www.springer.com.br/Download/279-2-1

Here is the download link for the Operation and Installation manual, note specifically page 76 which has the pertinent electrical info for my model:
http://www.springer.com.br/Download/279-2-2

The manuals are in Portuguese, so good luck!

I took a photo of the data plate on the unit, now I need to figure out how to post a photo to this forum.
 
  #8  
Old 05-20-12, 04:43 PM
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Problem #1: This can be normal. When the AC kicks in the large draw can cause voltage to drop enough to kick off the UPS alarm. I am assuming that it does not say in alarm mode for more then 10 secs.
You are right, it beeps once then returns to normal, less than a second. It kind of sucks, because I work on my computer, and these occasional UPS beeps startle me.

Problem #2: ... This would not happen after the unit has been running for a couple of hours.
Normally I would agree with you (and you may be right). But my current theory is that since the the heater unit doesn't run constantly, it turns on and off every 15-20 minutes, the tripped breaker is happening the moment the compressor turns on. My theory is unfortunately based on no evidence, since I have yet to sit there for a few hours with the ammeter waiting for it to trip.

I suggest putting on your ammeter and watching the current until the breaker goes.
Ugh, yeah, I probably should do that.
 
  #9  
Old 05-20-12, 05:15 PM
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Thanks for the links.

I took a photo of the data plate on the unit, now I need to figure out how to post a photo to this forum.
See How To Include Pictures.
 
  #10  
Old 05-20-12, 05:19 PM
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Well, I can't figure out how to post an image, I guess I will just type out what is written on the data plate of my compressor.

Voltage range: 198/242V
Voltage nominal: 220V
Phases: 3
Hz: 60
Air Flow: 6420 m^3/h (3779 cfm)
R-22: 3200g (112.9 oz)
Cooling: 58000 Btu/h (61193 Kj/h)
Cooling: 18.8 amps
Cooling: 5900 watts
Heating: 58000 Btu/h (61193 Kj/h)
Heating: 18.6 amps
Heating: 5865 watts
Model: 38CQD060535MC
Series: 0811B11129
Circuit Breaker: 25A
 
  #11  
Old 05-20-12, 05:43 PM
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sometimes if you move the a/c breaker closer to the main breaker in the panel it will stop the dimming from happening. Another thing you can do is add a hard start kit to lower the compressor starting amp draw.

521 Compressor Saver - Residential Installation Video - YouTube
 
  #12  
Old 05-20-12, 07:11 PM
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hvactechfw-
Thanks for the YouTube link, that was informative. One thing I learned is that (according to the video) the "lock rotor amps" specification for the compressor tells you how much current is needed to start the motor. Makes sense now!

Anyway, I looked in my manual and while my compressor's rated at 18.8 amps when running, the lock rotor amps is rated at 127A! This comes from the 5th line down on page 76 of the installation manual I linked to earlier.

That seems like a really high number to me, and maybe (?) the root of my problems. My type "C" 25 amp circuit breaker is rated to trip (if I understand that wikipedia page correctly) at 5x 25 amps = 125amps for instantaneous tripping current. Right at the limit of what the compressor is drawing.

Wow, these "hard start kits" sound ideal for my problem... unfortunately I'm pretty sure I won't find them for sale in Brazil. But, I'll look.
 
  #13  
Old 05-20-12, 08:36 PM
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You can always find just about anything on the internet and have it shipped to you.
 
  #14  
Old 05-21-12, 06:30 PM
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It sounds to me like the hard start kit might help your problem too. I am thinking you are also getting low voltage from the street as the compressor starts, hence the UPS beeping problem. I am thinking probably some poor connections at the utility connections. Hopefully, if you get a hard start kit installed, your problem will be solved.

I see one other possible solution. Move back to the U.S.!!
 
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