Do I have enough power?

Alan (California Radiant) Forbes

I've got a Taco ZVC 406 powering nine Watts manifold actuators. The Watts spec's. say each powerhead is rated at 2.5 W(VA), but printed on the actuator itself it says 1.6 W. The ZVC controller has a 40 W transformer, so 9 actuators x 2.5 W per actuator = 22.5 W, so I should be good to go, no?

Joe Mattiello

Hi Alan
your math is correct; the actuators add up to approximately 22.5 VA load. the ZVC406 is equipped with qty 2 40 VA transformers wired in parallel which is more than enough capacity to handle your load. Hopefully this was helpful.

icesailor

I don't know what to tell you. Taco 57* zone valves have a rating of .9 amps. They use a 40VA transformer for 3 valves. A 40 VA.24 volt transformer will open three valves at once. It will open any 3 in any order with more heads. 3 in any sequence. They might open 9, but only three at any one time. If you put a 60 VA 24 volt transformer, it will open 4 valves.

Taco Technical Support is OUTSTANDING. It always has been.

hot_rod

Ice, I thought VA is Volts X amps?

24V X .9 = 21.6 VA

So how do three .9 A draw actuators "fit" unless you saturate the transformer or hope they don't all call at the same time.

icesailor

hot rod said:

Ice, I thought VA is Volts X amps?

24V X .9 = 21.6 VA

So how do three .9 A draw actuators "fit" unless you saturate the transformer or hope they don't all call at the same time.

It might be.

All I knew and cared about was that Taco said that a 40 VA, 24 volt transformer would operate 3 valves. That the marking on the valve head said .9 amps. That if you put 4 valves on a 40 VA transformer, only three would open at the same time. If you had four valves, you used a 60 VA transformer and all valves opened. Or, you used two 40 VA transformers and wired them so that only 3 valves were operated. Seven valves required three 40VA transformers. No one stocked 60 VA transformers where I worked.

Maybe were saying the same thing. All that was important to me was that the heat anticipators on thermostats was set to .9 amps or higher so the zone valves didn't cycle excessively.

That's what my Amp Mate was for. Checking thermostat control wiring amperage. At least we don't have to deal with Honeywell Series 10 3-wire thermostats and controls anymore.

Alan (California Radiant) Forbes

That's what I love about this business. Nothing is ever straightforward.

ChrisJ

VA is volts x amps. That's why it's volt amps.
It often differs from watts depending on what the power factor of the load is. Inductive loads such as motors typically have very low power factors where restive loads have very high power factors.

You can have a 120V 3A load that only draws 150 watts but it's still 360VA. What's the difference? For residential and likely most commercial you're only paying to run 150 watts but your equipment must handle 360VA because the current consumption is still there.

If you're dealing with 24VAC and inductive loads then watts is NOT the same as VA. I highly suspect zone valves are likely inductive loads and you may find the VA rating to be far higher than the wattage rating.

ChrisJ

I don't know if this is the same Watts actuator or not but,

"Specifications:
Each actuator will consume 2.5VA (2.5W)
at 24 Volt power with max end switch load
of 700 mA. A typical 40 VA transformer will be
able to power 14 actuators."

Interesting they claim the VA and W consumption is the same. Either way, they're claiming you can run 14 from a 40VA xformer.

SWEI

ChrisJ said:

"Specifications:
Each actuator will consume 2.5VA (2.5W)
at 24 Volt power with max end switch load
of 700 mA. A typical 40 VA transformer will be
able to power 14 actuators."

Interesting they claim the VA and W consumption is the same.

That's because it's a wax motor, which is about as close to a purely resistive load as you can get.

Mark Eatherton

I was told by some master electrical friends (radiant window co-inventors) that when you exceed the VA capacity of a transformer, assuming the windings can withstand the amperage being drawn, that the loads connected will be shorted power (Volts) which will cause them all to open partially (assume heat motor of Synchron motored devices). You will know when the transformer has been forced beyond its ampacity. It lets the all critical smoke out of the transformer...

It is similar to running more gas fired appliances on a given meter, exceeding the capacity of the meter. All appliances still fired, they are just under fired.

In testing transformers for efficiency, I have found that until they are loaded to the max, their power factors can be fairly low, and these were connected to resistive loads (radiant windows), as verified by a Kill a watt meter. And when loaded to the max, they got hotter than a $2.00 pistol.

As others have pointed out, the chances for extended run times of all zones occurring at the same time are slim, and probably not worth losing sleep over. :-)

ME

hot_rod

Most 24v transformers read 26, 28, even as high as 30V out of the box, until you start loading them. Unless you have an accurate version built

Also the current draw on a heat motor type ZV is only for a short period. I suspect that is how you get away with move valves than the math shows

If the power is out, and all valves call on at the same time, you will pull that full load for maybe 15 seconds or more, it depends on the temperature of the heat motor when it powers.

I put some in the freezer overnight to see how that changes the draw.

Most manufacturers now have low current draw actuators, allowing as many as 3 on one relay connection. Keep in mind the low current draw actuators take much longer to open, they have smaller heaters around the wax motors, is all.

I think some of the zone relay boxes with two transformers split the outputs, 3 outputs on one transformer, 3 on the other for example in a 6 ZV control. So be careful when wiring a bunch to one output.

This chart shows the draw of the different types of zone valves, heat motor, motorized open/ spring return, and a motorized ball valve style.

Abracadabra

Keep in mind that transformers are rated in Vrms and "most" common DMMs read Vpeak. So that 24V transformer will "read" higher on your DMM than 24. (Unless you have a rms setting on your meter)

ChrisJ

Abracadabra said:

Keep in mind that transformers are rated in Vrms and "most" common DMMs read Vpeak. So that 24V transformer will "read" higher on your DMM than 24. (Unless you have a rms setting on your meter)

I assume most if not all of these transformers are laminated core type? If so, it's normally to see a few volts higher unloaded due to poor regulation. A toroidal type is always more stable but costs more.

I checked the xformer on my boiler a few months ago and want to say I saw 28V unloaded and high 25s loaded. This was using my Fluke 179 DMM which is a true RMS meter.

I believe p-p of 24v rms would be almost 34 volts and almost 40 volts for 28v rms


I'm not sure what most guys use out in the field, but I highly recommend a Fluke 179. It has many options including a quality thermalcouple and a good bright backlight.

http://www.amazon.com/Fluke-ESFP-True-Multimeter-Backlight/dp/B00012Z0V6

SWEI

Abracadabra said:

Keep in mind that transformers are rated in Vrms and "most" common DMMs read Vpeak.

Actually they read Vp-p and then do some math on it which assumes they are reading a sine wave. Not generally an issue until the wave changes shape or harmonics show up.

hot_rod

Mike up at our office uses an O scope to check and log power info.

He has been finding some wild stuff with various electronic t-stats. Some "leak" as much as 20 V back in the off mode. Others clip the top 1/2 of the sine wave. Plays havoc with relay boxes. I see more and more relay box manufacturers adding a list of disclaimers for various t- stats.
Sometimes adding a resistor works, others not. I think Uponor still sends a 750 or 1000 ohm resistor along with their stats.

icesailor

All my RMS Multi-meters came from Sears. Some one company makes them all in China. Buy one brand, its the same as all the others.

Years ago, I bought a really nice Amprobe Amp Clamp. Then it was recalled. The recall list was like a who's who in the instrument world. All made in China.

ChrisJ

icesailor said:

All my RMS Multi-meters came from Sears. Some one company makes them all in China. Buy one brand, its the same as all the others.

Years ago, I bought a really nice Amprobe Amp Clamp. Then it was recalled. The recall list was like a who's who in the instrument world. All made in China.

You're actually comparing a TOL Fluke product to a Sears product?

icesailor

ChrisJ said:

icesailor said:

All my RMS Multi-meters came from Sears. Some one company makes them all in China. Buy one brand, its the same as all the others.

Years ago, I bought a really nice Amprobe Amp Clamp. Then it was recalled. The recall list was like a who's who in the instrument world. All made in China.

You're actually comparing a TOL Fluke product to a Sears product?

No, my point is that Sears doesn't make any of their tools. Someone else in China/Asia does.

There are no electronic tools that are 100% Made In USA.

ChrisJ

icesailor said:

ChrisJ said:

icesailor said:

All my RMS Multi-meters came from Sears. Some one company makes them all in China. Buy one brand, its the same as all the others.

Years ago, I bought a really nice Amprobe Amp Clamp. Then it was recalled. The recall list was like a who's who in the instrument world. All made in China.

You're actually comparing a TOL Fluke product to a Sears product?

No, my point is that Sears doesn't make any of their tools. Someone else in China/Asia does.

There are no electronic tools that are 100% Made In USA.

I'm really disappointed in Sears mechanics tools now too.
They all seem to be cheap Chinese junk.

BobC

i own about 6 DVMS - fluke 75, 8060 (3), and an old 8100 with nixie tubes.

There is a big difference between a good meter (Fluke, HP, etc) and the Chinese knockoffs. The cheap ones work but they have limitations and they will never last as long as my 8100A (1974).

Bob

SWEI

ChrisJ said:

using my Fluke 179 DMM which is a true RMS meter.

I bought a 189 (basically a 187 with sample memory, which as it turns out I rarely use) about ten years back. It's phenomenal -- and I say this as an original owner of an 8060A (and current owner of an 87, two 12's, a 337, a 568, and more.) A 287 would be the current equivalent, and if you haven't used a recent dual display Fluke, you really are missing something.

Larry_52

All this talk of high pf is a bit misleading since it is a ratio that can swing from lag to lead. If the current and voltage in sine wave form are in synch then the pf is 1. If current wave load lags the voltage wave then it will start to move in voltage lead direction to .8 for most induction motors. But if the load is capacitive the current may lead the voltage wave and you have a pf of .8 in the other voltage lag direction.

VA= apparent power or useful energy
W= true power or total energy
VAR= Reactive power or not useful energy
pf= ratio of true power over apparent power

Xfmrs tend to add capacitance to a circuits depending on loads. Xfmrs are not typically expressed in pf ratios as it is the load that determines the pf. A strictly resistive load will have a pf of 1 and voltage/current are in synch. If you are right on the edge of apparent power rating with an inductive load adding a capacitor to the xfmr 2ndry will correct the pf to the desired ratio of 1.

So when you read the pf of a typical xfmr 2dry winding that has no load you will see that that the pf is possibly .8 but in the voltage lagging direction opposite of inductive loads voltage leading direction. That means the xfmr is consuming energy but no useful work is being performed which all xfmrs do sitting idle.

icesailor

And for many, if the motor doesn't work, or the appliance doesn't work, change the motor, or change the board. When you have the ability to pinpoint the bad resistor on a board, you still change the board.

Time is money.

ChrisJ

icesailor said:

And for many, if the motor doesn't work, or the appliance doesn't work, change the motor, or change the board. When you have the ability to pinpoint the bad resistor on a board, you still change the board.

Time is money.

Very true.
And some of us make our money troubleshooting board level problems.

bob_46

"ELI the ICE man" with inductance (L) voltage (E) leads current (I)
With capacitance (C) current (I) leads voltage (E)

icesailor

@ChrisJ:

And some will replace a whole boiler over a bad contact to the board.

ChrisJ

icesailor said:

@ChrisJ:

And some will replace a whole boiler over a bad contact to the board.

Or leaky fill valve!

SWEI

bob said:

"ELI the ICE man" with inductance (L) voltage (E) leads current (I)
With capacitance (C) current (I) leads voltage (E)

Haven't heard that one in awhile. But I still use it (along with SOHCAHTOA) on a regular basis.