Tesla PowerWall Backup Gateway Grid Outage Detection – UPS Still Required

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The Tesla PowerWall 3 solar PV inverter and battery storage system provides the ability to automatically disconnect from the grid and power the site from its batteries in the event of a grid outage – including topping up the batteries from solar generation during the outage. The component that handles this is the Backup Gateway 2 which is installed next to the meter, in the outdoor GRP cabinet.

The installation engineer was very positive about the performance of the switch-over from Grid supply to Battery supply, based on their experience testing this by manually triggering a switch-over while the grid connection was still live, with no flickering of lights or resetting of appliances. The official Tesla specifications (which I’m struggling to find to reference here) are much less optimistic and note it can take a few seconds to switch in a real-world power outage scenario – especially when there’s a brown-out rather than a clean break in the supply. Clearly that’s long enough for most appliances to reset.

It’s typical to have a couple of short-duration power outages every year – perhaps as a consequence of the overhead 11kV supply and the way that is connected to the rest of the grid. When the grid power went away for a second or two the other day the Backup Gateway did not react (at all? – there was certainly no message to say it had gone off-grid) and the network switch and router in the Outbuildings lost power for long enough to reset. The equivalent devices in the House are already protected by an Uninterruptible Power Supply (UPS) so stayed online.

That prompted me to add a UPS to the networking equipment in the Outbuildings – something I was planning to do anyway, but I had decided to wait for some real-world experience first (in case the Backup Gateway did react quickly enough after all).

I’ve had good experience with second-hand APC UPS equipment over many years and the smallest and cheapest APC model I could find on eBay was the Back-UPS CS BK350EI which runs from a single 12V 7Ah lead-acid battery (very widely used as backup batteries for alarm systems so readily available and competitively priced). While this UPS is only rated for 210W and won’t run for more than a few minutes at full load it seems perfect for covering a few seconds of outage while the Backup Gateway kicks in, powering the Outbuildings’ network router and network switch (including the CCTV cameras and Wireless Access Points supplied via PoE from that switch).

While a rack-mount UPS would have been nice, those tend to be much more expensive and – importantly – the smaller rack-mount models need much more expensive batteries.

APC Back-UPS CS (BK350EI) located in the network rack in the Outbuildings Plant Room

The UPS was only £17.99 without a battery (including free shipping) and a new Yucel 12V 7Ah battery was only £15.49 from a local electrical wholesaler that specialises in alarm system equipment and hence has a pretty quick stock turnover for those. (The same battery would have been £27.49 from Screwfix/Toolstation, with more risk of getting one that has been in stock for months.)

The APC BK350EI UPS has three IEC 60320 Type F socket outlets (in fact the photo on that Wikipedia page is of an almost identical UPS) – plus another socket that is only surge-protected, not also battery-backed. It was supplied with two Type E to C13 cables which are ideally suited to powering devices like the UniFi network switch which has a C14 plug connector. In order to power devices which demand a standard UK BS 1363 socket (e.g. because they use a power adaptor integrated into a BS 1363 plug) it’s necessary to use an extension lead with a Type E socket. While re-wirable Type E sockets are available (and I’ve used a good quality one successfully before – and struggled with poor quality ones) it’s generally better to cut the C13 connector off the end of a pre-made Type E to C13 cable and wire that to something like a 3-way socket outlet adaptor.

These small APC UPS devices don’t support the ‘SMART’ monitoring network cards which the larger models (aimed more at business deployments) do, but they still provide an option for USB connectivity via a non-standard cable (APC AP9827) with an RJ50 (like an RJ45 but 10-way) plug at the UPS end and a USB Type A connector at the other end. Genuine APC cables are very expensive but much cheaper equivalents are available via eBay. While an 8-way RJ45 plug will physically fit into a 10-way RJ50 socket and only 4 pins are actually wired, those include pins 1 and 10 so it does need to be a 10-way plug.

Rainwater Pipework Labelling

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One risk with having two separate water pipework systems in a building, where one set of pipes carries Drinking Water supplied from the mains and the other set carries Rain Water, is that it’s important to ensure the right pipe is connected to the right appliances – especially when new connections are being added some time after the original pipework was installed. Accidentally connecting to the wrong pipe won’t be obvious since both pipes carry cold water, but Rain Water is not safe to drink (and must not be allowed into the water supply network).

In the Outbuildings (as opposed to the House) it helps that the pipework is exposed so it’s not too difficult to trace the pipes, but the regulations rightly specify that the rainwater pipework needs to be clearly labelled at suitable intervals.

It seemed sensible to label both sets of pipes, for extra clarity, and to follow the BS1710:2014 guidance for the label colour scheme. This uses Green as the background colour (to indicate a Water pipe) then various other coloured band(s) to indicate the type of water and the source. RM Labels offer a nice range of pipe labels and valve tags and I settled on:

  • For the Drinking Water pipes, their Drinking Water Pipe Marker PMW32a which has a Blue band, indicating “Potable water derived from the public water supply”
  • For the Rain Water pipes, their Rain Water Pipe Marker PMW59a which has a Grey band (to indicate a source other than the public water supply) and a Black stripe (to indicate the water is non-potable).

While it is of course necessary to follow the label colour standards and professional plumbers should be familiar with the colour codes, I’m not sure who else would know what the Grey, Black and Blue bands mean – but the text makes the pipe contents clear too.

“Rain Water” and “Drinking Water” pipe labels attached to insulated 22mm copper water pipes

One minor problem is that these labels don’t stick very well to polythene pipe insulation – especially in cold and damp conditions – so I opted to over-wrap the labels with the sort of clear sticky film intended for wrapping paperback textbooks (visible as a shiny band in the photo). That film is cut long enough to wrap over onto itself, which should help it stay in place.

(An alternative would have been to use slightly different labels that are supplied on a roll and which wrap all around the pipe by themselves, e.g. Drinking Water Pipe Banding for Potable Water from Public Water Supply – Self-adhesive – PB001PWPWS and its equivalent for Rain Water.)