UPS solution for ONT and SH2

[stevebrass]

 I am investigating making my own device. Batteries in series to get to 12v connected via an appropriate jack to ONT and router. 

[philip42h]

@stevebrass 

I am similarly tempted, but don't want to "get my hands dirty" and rather hope(d) that someone would sell me a solution ...

It's easy enough to get hold of a 100Ah 12V lead acid leisure battery. On paper that would maintain the ONT and SH2 for up to 40 hours, and I really couldn't ask for more. As a backup battery solution that might work quite well - i.e. charge up before the outage event using a standard smart / trickle charger and deploy when needed.

The key benefit of this approach and, indeed, the Cyberpower 'telecoms' solutions, is that it provides the needed 12V supply without inverter and transformer losses.

Speaking of Cyberpower, they do claim to have a 36W equivalent / replacement for the BT badged solutions (DTC36U12V) that might work quite well. Although it has only a single 7Ah battery it should be able to power both the ONT and SH2 for up to 2.8 hours which might be a reasonable compromise. But I can't (yet) find anywhere that might supply one!

[stevebrass]

@philip42h 

Yes - I was looking at lead acid battery on a trickle charge, as well as a bunch of alkaline.

[JB2016]

@philip42h  

An inverter circuit to convert voltage up from battery to 230V followed by a power supply, either switched-mode or linear, for the 12V for the Hub or ONT, will introduce additional losses that reduce the runtime available from any given battery.  The more efficient solution is float-charging a battery feeding the load (the CyberPower units marketed by BT appear to do this).   No doubt there are other commercial products that work on the same principle and provide a longer runtime than the CyberPower units, but they will inevitably be more expensive.   I suspect you will just have to get busy with the soldering iron.   If you do succeed in finding an off-the-shelf solution, then post a comment at  https://bt-digital-voice.blogspot.com/

[philip42h]

The key benefit of this approach and, indeed, the Cyberpower 'telecoms' solutions, is that it provides the needed 12V supply without inverter and transformer losses.

Speaking of Cyberpower, they do claim to have a 36W equivalent / replacement for the BT badged solutions (DTC36U12V) that might work quite well. Although it has only a single 7Ah battery it should be able to power both the ONT and SH2 for up to 2.8 hours which might be a reasonable compromise. But I can't (yet) find anywhere that might supply one!

I contacted Cyberpower and, somewhat to my surprise, they responded ...

The DTC36U12V is the base product we offer to BT and makes up the ONT and SmartHub2 versions.  They are currently the only partner we ship this product to, so you will need to purchase the units through them.

So it would appear that BT have a monopoly on that product in the UK - that's never happened before ... 🙄

OK, I'm not sure that Cyberpower's statement is entirely correct but mostly so. The BT Cyberpower unit claim to be 24W units - DTB24U12V-BT1. Given that the ONT and SH2 are nominally 12W and 18W respectively, each DTB24U12V-BT1 would happily power either but a single DTB24U12V-BT1 wouldn't power both. The BT Shop has them flagged as "clearance".

A single DTC36U12V, at 36W would happily power both - so I confidently expect to see a BT2 unit replacing the BT1 units in the not too distant future - probably once the existing stock has been cleared. This is entirely speculation on my part ...

But I am not waiting for that - I want to have a UPS solution in place before the next power outage rather than wishing I'd been more proactive when it inevitably happens. So I've order the required pair of units - one each to support the ONT and SH2. It's only money!

Once they arrive, I'll set them up, allow the batteries to fully charge, conduct a simple experiment to get an idea of the probable uptime and post back ... 😉

[philip42h · Accepted solution]

The units arrived on Thursday. One is labelled DTB24U12v-BT1 while the other is labelled DTB24U12v-BT2. They are,  identical units - the only differences being the device connector cables and the instruction leaflets: the BT1 applies to the SH2 while the BT2 applies to the ONT. They are not the 36W unit that appears on the CyberPower UK website.

They arrive with the positive lead from the battery disconnected. I assume that battery is pre-charged and that measure ensures that it stays that way in storage. Nevertheless, I plugged them in, connected the ONT and SH2 and left the system for over 24 hours to ensure that the batteries were as fully charged as they were likely to get.

Each unit has a light to show when the battery is supplying power rather than the mains. According to the leaflet, an alert sounds and this light starts to flash when the battery is down to 45% - i.e. 55% used. So first thing this morning I simulated a power-cut by simply pulling the mains plugs and waiting for the 45% alerts.

Based on the output figures for their respective power supplies I expected the SH2 to draw up to 1.5A and the ONT up to 1.0A. The CyberPower units contain 7Ah batteries so I was expecting an "on battery alert" from the SH2 side after about 2.5 hrs and from the ONT side after about 3.8 hours.

In practice I didn't get an alert from the SH2 until 3.2 hours into the test (I was actively monitoring the test at that time); the ONT alerted after about 10.7 hours (approximately since I was doing other things by then). These alerts occur at the 55% used / 45% left mark. If you believe these figures, then the CyberPower UPS will maintain:

• the SH2 for around 5 hours 50 minutes
• the ONT for around 19 hours 30 minutes

So that's the first few hours of the next power cut sorted as far as communications goes.

The extended runtime of the ONT is rather wasted and I suspect that I could extend the total maintenance time to around 9 hours by swapping the units over after 4h30. Either way, this gives me an uptime measured in hours which is what I wanted.

I'm sure that the actual uptime will depend on the condition of the lead acid batteries and the actual load placed on the ONT and SH2 - well SH2 largely. During the test we used the Internet as we would normally so the SH2 was providing Wi-Fi for a few devices as well as maintaining its DECT hub for 4 DV handsets.

[Mancmonkey]

Thanks Philip!
An absolutely confusing mess from Cyberpower and BT, so unclear that u u need both.

[oldbuffer1]

Been reading the conversation regarding UPS for ONTs and Home Hub 2. I'm awaiting delivery of the Cyberpower UPS which presumably is being supplied to power up the ONT  (or the  Home Hub) since there's only one 12v output. Not much use if one device works with a power cut and the other doesn't. Looking at the specs for the ONT and the Hub I think there may be an outside chance that the single unit might power both Hub  and ONT - if I make up  a suitable splitter cable. Question is, is the power draw sufficient to handle both, is it bad practice to modify the supply in this way, or should I be using two separate UPS devices? I have the Eaton Mini UPS on order in case I need to use both, but I'm trying  to reduce the number of devices clogging up wall space.

[philip42h]

As of a year ago, you needed two devices as per my earlier post. One to power the ONT and another to power the SH2. The devices themselves are identical apart from the cables and connectors - one fits the ONT, while the other fits the SH2. At the time I purchased mine, the only source for the devices with connectors was the BT shop - I couldn't get them directly from CyberPower.

So, I use two devices with different model numbers, and, unless things have moved on, suspect that you should be doing the same.

(The BT Shop is 'down' right now so I am unable to check what is available today)

Our most recent power-cut was last week - 16-00 hours to 03-00 - and the backup solution worked perfectly (at least until I went to bed!)

[oldbuffer1]

Thanks for that. As a matter of interest is there any official ruling from BT on what accessories are available, at no cost, once full fibre is installed in your property. In particular I'm looking at Battery Backup devices and Digital Voice handsets. I had two separate online chat conversations and both persons stated that the BBU plus a couple of standard DV handsets were available f.o.c. When it came to ordering them, the third one told me I had to pay for all of them. Fortunately I retained the transcripts and was able to place the orders  for phones and BBU with no charge. Would a second BBU to power either the Hub or the ONT also be available at no cost. (Battery backup to only one device would be as good as none at all).

PT