Zone Control

Hi all,

I have a slight problem that I need to resolve. I have to control 5 zone motors on two daikin a/c units. The zone motors themselves I believe are advantage air 24V AC units. They need to be driven with a switched active to open and close. The question is does a change over relay like to be in one state over another. What I mean by this is by default it is NO I believe. If the zone is switch to NC and it stays in this position indefinately what are the down sides / side effects to the unit. Otherwise should I just use Blind Relays?

If anyone has had any experience with zone motors i would appreciate your input. I am not sure if the motors can move once they have either fully closed or fully opened by the pressure of the air it is controlling. If this is the case thn blind relays wont work.

Thanks
Arthur

 

I'm slightly confused by these two statements. You refer to 24V AC, yet then refer to switching active, which would be 230V (in Aus.). It's an important distinction because it affects the solution.

An L5504RVFC Change-over relay has a preference for the Normally Closed state. The relays are non-latching so the NC contact will be closed when power fails. It draws a little extra power in the On state to provide power for the relay coils. You can configure them to go to any state you like when power returns.

The L5108RELVP is suitable for up to 30V ac/dc only, but it does offer a cheaper way to get plenty of change-over contact channels. It has a strong preference for the Normally Closed state. Whenever there's a power failure all channels are forced off, which closes the Normally Closed contact. At power up, all channels will be in the NC state. The power consumption is exactly the same in both the On and Off states.

The preferred state is implicit in the names of the terminals: "Normally Open (NO) and Normally Closed (NC)". What that means is that when the C-Bus Group address is Off, power will be sent to the NC terminal. When the Group is On, the NO terminal gets power. That's why the label for each of the two output terminals for each channel starts off with "Normally...".

The Shutter Relay may/may not suitable for your application because it's output only remains activated for a short period of time. It's suitability will depend on the exact behaviour of your zone motors. If they're spring-close or spring-open, they'll just close or open again once the Shutter Relay output turns off.

 

I misread this as "does a change over relay like to be in one state or another". It reminded me of the time we had a request for dimmable relays

 

Can you please elaborate on this. My understanding is the relays are the latching type. If a relay is activated and the power fails does the state not stay the same ?? (like the 12 channel 240v relay module)
do you have some circuitry that detects the power fail and has enough dying gasp power to put all relays into the NC state. By power fail you mean CBUS power fail. How does this unit handle phase failure which may take out enought cbus power supplies to make the cbus network unworkable but still have a voltage on the bus. When full c-bus power returns what happens?

Charles

 

I have spent a bit of time working with Advantage Air motors. (Built a Variable Temp Controller.)

They have a range of motors (both 24v and 240v). Do you know exactly which motors you are dealing with? Are they a few years old or a new installation? Did Advantage Air supply a simple on/off controller or a variable controller?

Assuming you have the standard on/off damper 24v motor: The motor will drive full open or full close upon power application. Air flow is not relevant and does not move the damper controlled by the motor. The motor itself has full throw cutout switches. So you can leave power applied in the correct direction or switch off after a reasonable time. The 240v motors take about 30 secs to make a full movement.

Because the motor has internal position switches, it is important to fit the motors with damper correctly angled to the motor position. So be careful if you ever remove one and re-install it.

As others have said, use the "normally" feature of the relays. I would suggest using the normally closed contact to open the damper to avoid air con damage. Don't worry about the power off state, since if CBus has no power the air con damper motors just open and that is a safe state (for normal installations, esp. houses).

Andy.

 

No probs, Charles.

The relays are latching, so they don't consume any power except at switching time.

That's exactly what happens. The unit is designed to turn off all the relays when there's a C-Bus power failure. Enough energy is stored in the unit to do this.

What you're really asking here is how the unit handles C-Bus brown-outs, since the unit is bus-powered. When the bus voltage drops below 15V the unit stops operating the relays. The chances of successfully getting a C-Bus message across the network below 15V are pretty much zero anyway, but this ensures that all units stop working at the same network voltage. When the microprocessor finally is about to die, it fires off the relay drive circuitry to turn all the relays off.

If the voltage went below 15V, but the unit didn't reset, the state of the relays won't have changed, so it just picks up from where it left off. If the voltage dropped low enough to cause a full reset of the unit then normal power-up rules apply, where all the relays are off and the internal levels for the groups are 0. The MMI mechanism will clean up any discrepancies if some units on the network did/didn't experience a reset and share the same groups.

 

Hi Arthur

I've only just had a chance to read this post.

This product (the 8 channel ELV relay) has been purposely designed with a number of applications in mind. Yours is one of them.

Air conditioning damper control usually operates with power to open, power to close. The damper has 'common', 'open' and 'close' connections (3 wires/terminals). It also contains a limit switch that cuts power to the driving solenoid once the swing arm is in position. Below is a typical circuit for this (note, the limit switch included with the damper in series with the solenoid)


The other (main) type used is a power to on, spring return (to off). With this type, simply drive the solenoid using the n/o contact.

Hope this helps

Cheers

 

Thanks guys! It does look like the new product is the best way to go. I currnetly have a 4 channel change over relay module that I will return.

Andy@Mandoon - The zone motors are 24V AC and it is a new installation. Advantage Air zone controllers were suppied but were not to our liking so I placeda DLT next to the thermostats to control the zones. I simply told the installers of the HVAC to give me tails to all the zone motors and would take care of the control myself.

Conformist - The trick would be to wire up at least one zone in the opposite state to the others to make sure the system always has at least one zone "open" to allow air to flow, otherwise it will blow the duct work off the unit. That is how I currently have it wired up in the 4 channel din unit. The issue I was concerned about was the impact of leaving a channel in the NO state for a long period of time ie days/weeks/months is there any down side to the long term life of the unit. But since the ELV unit is latching it eliminates this issue

Are the units readily available at the moment?

Thanks
Arthur

 

Yes, there is stock on the shelves

 

Not too sure about if the following is possible with the Daikin but, if you have on/off control of the (Daikin) unit, you could use some logic to ensure that the unit will only run if at least one zone is on. If all zones are off (ie someone switches off the last zone), you then shut down the unit. I always used to program systems that way.... simple and user friendly