Caleffi Troubleshooting

Alan (California Radiant) Forbes

I've got a short in a 4-zone system; keeps burning out the transformer.  I don't know if it's in the thermostats or the Caleffi zone valves (not telestats).  Does anyone know the resistance reading on a good Caleffi motor?



Alan

bill nye_3

Trouble

Alan, don't know the answer to the resistance question, but... How about an inline fuse holder? Cheap money. I used to change a lot of transformers on first co. air handlers. A little fuse is way cheaper than transformers.

Alan (California Radiant) Forbes

Even cheaper

is a transformer with a circuit breaker...................at least for testing purposes.  

BobC

isolate

It's more likely a solenoid coil that's shorting out. Put a slow blow fuse in line with the transformer output. If you can, disconnect all the valves and then reconnect them one at a time, and then activate that valve till a fuse blows or the transformer output voltage dives.



Those transformers should be impedance wound so they don't fail with a short on them. Of course the company accountant would never allow that because it would cost a few bucks more.



Bob

Alan (California Radiant) Forbes

Troubleshooting

I'm going over there this morning and I'll ohm out all the coils.  They should all be close except the one that's shorted.



Thanks for the tips.



Alan

hot_rod

which actuator, Alan?

is it this Z-one motorized spring return valve? Here is the spec sheet that shows the current draw.



Also a graph that shows the current draw of the thermal-electric actuators, and the motorized ball valve type that caleffi offers.



The current draw on a thermal actuator, regardless of the brand, depends on how cold the valve is when it is activated since the wax needs to warm from that temperature. Rarely do they pull full current on start up unless they are in a very cold ambient temperature condition.



Notice also that a thermal actuator (blue line) only pulls a high current for a short period of time.



Caleffi now offers a low current draw thermal actuator also, 6 per 40VA transformer are allowed. The trade-off is a slower opening time (lower wattage actuator)



Let me know if you need more info.

Alan (California Radiant) Forbes

Caleffi

Thanks, Hot Rod.  I believe they are the Z-Ones, but what I need is a rating of the coil resistance.  When I test a water solenoid valve on a shower steam generator, a reading of 560 ohms tells me it's a good valve.  If it's a lot lower than that, it's a short.  I just want to know that resistance figure for a good Caleffi valve coil.



I'm just leaving for the job now; more when I return.

hot_rod

under the hood

of the Z-one zone valve is a small synchron motor and an end switch, if the valve was ordered with the switch option.



Basically a motorized zone valve motors open, and stalls, becoming a 5W heater, so they get pretty warm to the touch



If it is a 24V/ 5 W motor then 5 divided by 24 =.2 which is what you should read on the ohm meter.



Also you can use the handy calculator at online calculator.com. Plug in the two known numbers and it will tell you the other. So here I plugged in 24V and 5W and it gave me resistence.

hot_rod

under the hood

of the Z-one zone valve is a small synchron motor and an end switch, if the valve was ordered with the switch option.



Basically a motorized zone valve motors open, and stalls, becoming a 5W heater, so they get pretty warm to the touch





Also you can use the handy calculator at online calculator.com. Plug in the two known numbers and it will tell you the other. So here I plugged in 24V and 5W and it gave me resistence.



Opps I read the wrong line, here is the conversion and the formula shown below.

hot_rod

cover off

connect ohm meter on motor leads, yellow and orange

bob_46

Resistance

HR I don't think your formula will work. Your formula only works with DC. With AC

inductive reactance jumps in. You can measure the resistance with an ohm meter and use your formula to determine current draw but when you install the motor in a AC circuit it

will draw far less current than your formula predicts. The inductive reactance caused by

AC current in the winding will cause the apparent resistance ( impedance ) to be much higher than what your ohm meter measured . A zone valve motor is wound so that even

when stalled the impedance is so high that the motor can't draw enough current to hurt it's self.

hot_rod

tell me more, Bob

if it's a true resistance AC load does the "simple" Ohms law apply? Can the formula be used to predict the resistance on this type of motor, accurately? Or does the resistance change as the motor winds then stalls?

Alan (California Radiant) Forbes

On the job,

all the Caleffi Z-One zone valve coils gave a reading of 22-23 ohms, so they were all good.



I found the short when I disconnected a neutral wire from the transformer to the "C" terminal on the 4 thermostats.  This additional wire (other than wires to RH and W) provides power to the thermostat so you don't need batteries. I did a continuity test between C and RH to see if the short was in the thermostats, but they all checked out OK.  I surmised that the short was somewhere in the wiring to one of the thermostats.



Thanks for all your help.



Alan

bob_46

Ohm's law

Ohm's law applies if the load is a pure resistance like a water heater element or electric furnace element. If the load involves a coil like the winding in a motor or a solenoid as soon as the current flows you have inductive reactance. The impedance will vary as the rotor spins or as the armature enters the solenoid etc. I don't know how to calculate impedance .

bob_46

Current draw

Using HR"s calculator and the resistance that Alan measured the Z-valve would draw one amp and 25 watts when because of inductive reactance it really draws .3 amp and 5watts.

Jean-David Beyer

I don't know how to calculate impedance .

I do, but I will let wikipedia do it.



https://en.wikipedia.org/wiki/Electrical_impedance



If you are trying to calculate it for something like a real motor, there are problems because of non-linearities; i.e., where the inductive reactance (or capacitative reactance) changes as a function of speed or load on the motor.