Re: Urgent help required: Star vs Daisy chain wiring for aircon control am I screwed

["Keith Doxey" <ukha@xxxxxxxxxxx>]

Hi Chris

--- In ukha_d@xxxxxxx, "christopher purves"
<CHRIS_PURVES@M...> wrote:

> Each unit in the chain (including external units and the
touchscreen) has an
> f1 and f2 signal connection.
>
> Originally Daikin told our installer to wire as a 'star' back to
the
> touchscreen location which required a single 2 core cable to each
indoor and
> outdoor unit back to the touchscreen which of course they did. In
effect
> join all f1's together and all f2's together and attach to f1 and
f2 on the
> trouchscreen.
>
> However when speaking to Daikin today, Daikin are claiming the
internal
> units must be wired in a daisy chain (one to the next).

The reason for specifying a Daisychain is that the cable run must be
terminated at each end to avoid signal reflections which could
corrupt the data.

With Starwired, you will have unterminated stubs of cable which the
signal will hit the end and bounce back possibly causing corruption.


> Can we just ignore their comments and wire it a as a star ?
>

There are two factors that affect how bad the reflections will
be.....
1. the length of the unterminated stub
2. the speed of data transmission.

In a domestic environment the cable runs are probably quite short
and I would imagine that the data rate would be reasonably slow as I
cant imagine there is that much information flying about

Whether you "can get away with it" I wouldnt like to say :-(

> Certainly CBUS can be wired as either.
>

Probably because they designed it with Star wiring in mind.

Did you put in a single pair cable as specified, or have you used
CAT5 which has 4 pairs (or some other data cable with more than one
twisted pair)?

If you have used a multi pair cable you can still fake a daisy
chain. Send the signal to the unit on the first pair and return on
the second, then join that to the first pair of the next unit etc.

It doubles the length but RS485 is designed for long distancee comms
anyway so shouldt be a problem.

HTH

Keith