[TG] [TG11] RS 62157 Cable for A70D - source?

[dave.squared@hotmail.com]

Hi Tom,
Thanks for your time last week. It was good to meet you. As much as the forum is really helpful, a few minutes of conversation gave me a better perspective on how a system should be put together from a data integrity point of view.

In my latest (hopefully last) revision of the layout I have made the following adjustments:
- I have taken your advice and used Seatalk connections wherever possible.
- The only remaining NMEA connections are the 10Hz heading input to the A70D and the interlink to the VHF from the A70D.
- I have added a Double throw power switch such that only the ST2000 pilot OR the 3rd party compass can be powered on at any one time.
- The ST2000 is connected via an unpowered ST connection (red wire not connected) to avoid a power loop (when the tiller pilot is connected and powered up).
- I have made allowance for two mounting/connection locations for the A70D so that I can have it on deck when required or leave it down below when it is not needed on deck. This makes the layout look complicated but it’s not really considering that the A70D cannot be in both locations.

I have some questions for you regarding the proposed layout.

As you can see I have two ST1/STNG converters in the system and I know you are not very keen on this. However, I don’t think thre’s any data loops and I thought this would be better than trying to daisy chain all 8 devices on to one Seatalk bus. This arrangement also reduces the cable run lengths by several meters and makes installation much easier.

Q1: Is it ok to use two converters or should I try to run everything from one?

If I went with one converter instead of two I’d need to put a “T” splice in the Seatalk bus to avoid very long cable runs.
Q2: Is it ok to use “T” splices in a Seatalk bus?

I have read that no more than 5 ST devices should be run from a single ST1/STNG Converter.
Technically, I have 6 devices on my Aft converter (ST60+ Graphic x 2, ST60+ Wind, ST60+ Depth, ST6002 Pilot Controller plus ST2000 Pilot). Only 5 of these are powered from the Converter, the ST2000 Seatalk connection is data only.
Q3: Is it ok to have 5 devices taking power and 6 devices taking data from the single converter?

I could rearrange the layout to have 5 devices on the Fwd Converter (ST60+ Speed, 2 x ST60 Multi, ST60+Wind, ST60+ Graphic) and 4 on the aft converter (ST60+ Graphic, ST60+ Depth, ST6002 Pilot Controller, ST2000 Pilot). However this would increase the length of the cable runs considerably and would involve a lot of extra work.
Q4: Is there any urgent need to redistribute the ST devices or will the proposed layout work ok?

If powering of 8 ST devices from a single converter is a problem, I could avoid this by providing a separate power source to one or other group of them. For example I could make the aft ST/STNG converter cable unpowered and power the 5 aft devices with an external supply.
Q5: What is the best practice for powering a large number of Seatalk devices when ST1/STNG Converter(s) are in the system?

Any other problems/comments with the proposed layout?

Cheers
Dave