Summer 2018 Maintenance Activities

[TerryJC]

Sounds promising but I'm left wondering is you are struggling to solve an issue being exacerbated by the enclosure being used. If there's no good reason to keep the box and we can identify a suitable and if it helps more spacious box, whether it would be better to take the plunge and buy one.

The issue when we designed this system, (which hasn't gone away), is that apart from the RPi 3. which consumes up to 5-6 W during normal operation, we have two Audio Amplifiers that provide up to 12 W each. We wanted to provide a thermal path through the wall of the equipment case without compromising its water and humidity resistance. Plastic IP65 cases provide the environmental integrity, but not the thermal performance. Metal IP65 cases are quite expensive, so we bought the Ammo box as a good substitute.

Whatever kind of case we bought, there would need to be a good circulation of air over the chips on the Pi to prevent the kind of overheating that we are experiencing. The history of the development of this system is strewn with compromises. We were originally going to use a Pi Zero for spares compatibility with the Railway system, but at the time, I was trying to get the two audio channels to work through two USB sockets (the Zero has no audio jack). The trouble is that the Zero only has one USB socket and it needed a better USB hub at a cost of around £35 so we bought a Pi 3 instead. But the RPi 3 runs hotter and is (I believe) susceptible to overheating of the chip on it's underside.

That was why I fitted the original fan, the replacement for which is noisy...

[Penri]

Hello Terry

I wasn't criticising in any way, I was just putting forward an option which has not necessarily been that popular in the past at WMT, ie spending money.

Another thought struck as I was writing, if you did have bigger box, a temperature controlled main fan could be fitted potentially removing the fan noise from the DC supply.

Again, happy to help with implementing any solution you want to go forward with.


Hwyl

Penri

[TerryJC]

I'd like to try the cheap option first, since it only requires a minor modification to the wiring. Re-engineering the layout and environmental design by using a bigger case will require quite a bit of rework, so is probably best done over the winter period when we have the time.

BTW, I didn't read your post as criticism, and I wasn't being defensive; just putting forward the reasons behind the situation we are in.

One other option we could try before ripping everything to bits is to mount the existing case vertically on a false wall (the real walls absorb the sun's rays). This will allow natural convection currents to flow past the chips without the need for a fan at all.

[TerryJC]

I went into WMT this afternoon to replace the 12 V fan with the new 5 V one. When I got there the music was cycling again but it was very hot inside the Minster Tower, the Minster walls were hot and the case of the system was extremely warm to the touch. As to whether the case heat is coming from inside or simply being absorbed from the environment is is difficult to tell. If the former, then the black case is doing a good job, if the latter, then it is contributing to the problem.

After the fix, there is still some hum, (thus proving that the fan being on the 12 V supply isn't necessarily contributing to the problem), but it is fairly quiet compared to how it was. The new fan doesn't run as fast as I'd have liked, but it is now definitely directing the air underneath the Pi.

When I switched back on, the Pi started normally and the music stopped (as it should) at just after 1700. We now need to wait to see what happens overnight, tomorrow morning and in the days and weeks to come.

[TerryJC]

The music was cycling again this morning, so the new fan either didn't help or only helped a bit (it was very hot yesterday).

Over the coming weeks, I'll move the temperature monitoring Pi into the Tower and also consider the possibility of:

• In the short term, putting in a mains timer to turn the power off overnight.
• In the longer term, put in logging code to establish what happens just before the reset.

[TerryJC]

I've taken TempPi out of the Green Box and set it to monitoring the temperatures inside the Minster Tower. One probe is inside the Equipment Case and one is taped to the side of the Power Box (in free air) to give us the temperature inside the Tower at about the same height as the Bells system.

There is no network connection, but it will be easy to plug the SD Card into a laptop to read it.