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hvac control and ammeter

Hi all,

I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

I'd like to monitor the current that the unit draws. Typically I would
use a small resistor in series, but at these currents even a small
resistor would burn. How is this typically done without starting a
fire? I do not have a fireplace to accomodate :)

I'm also planning on using a relay (Potter & Brumfield K10P-11D15-12,
rated for 15A, 1/3HP, 120VAC) to control the unit. Is this sufficient?
Since the motor is an inductive part, are bleeder circuits of some
sort typically included to gracefully remove current, or is the relay
designed to handle a little spark?

A couple side questions:
What does AFL stand for in the context 8 AFL @ 120VAC?
How is the horsepower specification used, for instance the 1/3HP for
my relay? Does it mean it can power a 1/3HP motor?

Cheers,
Chris
 
D

delo

Jan 1, 1970
0
For current measurement You can use an Hall effect sensor like those
produced by LEM.
Its only necessary to pass a single mains wire (phase) into a hole...
bye
delo
 
F

Fred Bloggs

Jan 1, 1970
0
Hi all,

I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

Yes, but that breaker does not trip instantaneously, there is a delay.
The relay/switch whatever in the tstat supplies that current
instantaneously.
I'd like to monitor the current that the unit draws. Typically I would
use a small resistor in series, but at these currents even a small
resistor would burn. How is this typically done without starting a
fire? I do not have a fireplace to accomodate :)

Don't bother trying to monitor it, it can vary greatly depending on
operating conditions like start-up counter-torque from whatever the
motor is driving.
I'm also planning on using a relay (Potter & Brumfield K10P-11D15-12,
rated for 15A, 1/3HP, 120VAC) to control the unit. Is this sufficient?

Only if your motor loading is < 1/3HP...
Since the motor is an inductive part, are bleeder circuits of some
sort typically included to gracefully remove current, or is the relay
designed to handle a little spark?

The relay may even require that inductive spark to preserve its contact
material, don't worry about it.
A couple side questions:
What does AFL stand for in the context 8 AFL @ 120VAC?

Amperes Full Load
How is the horsepower specification used, for instance the 1/3HP for
my relay? Does it mean it can power a 1/3HP motor?

Duh
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
Hi all,

I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

I'd like to monitor the current that the unit draws. Typically I would
use a small resistor in series, but at these currents even a small
resistor would burn. How is this typically done without starting a
fire? I do not have a fireplace to accomodate :)

Don't do it. If this were your own home, I'd still suggest that you not
mess around with the wiring. But as you are likely to burn down the
homes of other renters as well as your own, this is all the more a bad
idea.

AC current is typically measured using something called a current
transformer. They have a side benefit of providing isolation between the
high voltage circuit being monitored and the monitoring equipment
connected to their secondary (which I can already visualize bursting
into flames).
I'm also planning on using a relay (Potter & Brumfield K10P-11D15-12,
rated for 15A, 1/3HP, 120VAC) to control the unit. Is this sufficient?
Since the motor is an inductive part, are bleeder circuits of some
sort typically included to gracefully remove current, or is the relay
designed to handle a little spark?

It appears to be OK.
A couple side questions:
What does AFL stand for in the context 8 AFL @ 120VAC?
How is the horsepower specification used, for instance the 1/3HP for
my relay? Does it mean it can power a 1/3HP motor?

AFL = Amps Full Load

If a device has a horsepower rating, that indicates that it is suitable
for use with a motor up to that size.
 
J

Joerg

Jan 1, 1970
0
Hi all,

I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

Usually the rotor is not locked on a motor :)

If you do that for more than a few seconds three things can happen.
Either the circuit breaker pops, or the thermoswitch begins to cycle, or
smoke billows out of the motor.

I'd like to monitor the current that the unit draws. Typically I would
use a small resistor in series, but at these currents even a small
resistor would burn. How is this typically done without starting a
fire? I do not have a fireplace to accomodate :)

You can use a clamp meter. Contactless. You open the clamp and then
close it around one of the motor wires (not both). Harborfreight has
meters like that for little money, don't know how good they are.

I'm also planning on using a relay (Potter & Brumfield K10P-11D15-12,
rated for 15A, 1/3HP, 120VAC) to control the unit. Is this sufficient?
Since the motor is an inductive part, are bleeder circuits of some
sort typically included to gracefully remove current, or is the relay
designed to handle a little spark?

That relay sound a bit wimpy for that purpose. At least for my taste.

A couple side questions:
What does AFL stand for in the context 8 AFL @ 120VAC?
How is the horsepower specification used, for instance the 1/3HP for
my relay? Does it mean it can power a 1/3HP motor?

WRT horses I've seen rather bizarre statements for motors that sure
sounded like the marketing guys had gussied them up a bit.
 
R

Ross Herbert

Jan 1, 1970
0
Hi all,

I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

Who decided that the HVAC was to be connected on the same wiring
circuit as domestic lighting? GPO's and lighting should be on
individual circuits as should HVAC. Having HVAC on the same circuit as
lighting is simply a disaster waiting to happen.
 
F

Fred Bloggs

Jan 1, 1970
0
I'm working on designing a thermostat that controls the heating and
cooling unit in my apartment, and which in turn I can monitor and
control via the computer. The current thermostat is a Honeywell T6169
line voltage (120VAC) unit. The sticker on the back shows the
following ampere ratings:

Full load: 8A
Locked rotor: 48A
Resistive: 13A

48 amps seems like quite a bit! In fact, the circuit breaker for the
unit (lights in the room are on the same circuit as well) is rated at
15A.

I'd like to monitor the current that the unit draws. Typically I would
use a small resistor in series, but at these currents even a small
resistor would burn. How is this typically done without starting a
fire? I do not have a fireplace to accomodate :)

I'm also planning on using a relay (Potter & Brumfield K10P-11D15-12,
rated for 15A, 1/3HP, 120VAC) to control the unit. Is this sufficient?
Since the motor is an inductive part, are bleeder circuits of some
sort typically included to gracefully remove current, or is the relay
designed to handle a little spark?

A couple side questions:
What does AFL stand for in the context 8 AFL @ 120VAC?
How is the horsepower specification used, for instance the 1/3HP for
my relay? Does it mean it can power a 1/3HP motor?

This is the tstat
http://customer.honeywell.com/techlit/pdf/63-0000s/63-9174.pdf
....and you're not going to improve on that. The *real* problem is that
the landlord has you locked out of adjusting it and you want to bypass
it. Isn't that right?
 
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