Digital Voice and power cuts - mitigation

[Bernie533]

Hi

I am to be moved to digital voice in the near future. A disadvantage of this is that the phone will not work if there is a powercut. 

i am looking at getting the BT recommended cyberpower bbu.  Looking at the instructions this is used to provide temp back up power to the ONT.  does anyone know if i can plug a standard handset direct into the phone socket on the ONT for emergency use if it is powered by a bbu or would i also need a bbu for the smarthub2 ?

Would be grateful for any wisdom from the community as i can’t seem to find out.

thanks

Bernie

[Keith_Beddoe]

@Bernie533 

You would need a separate UPS, as you cannot plug a phone into the ONT.

BT can supply a backup power unit to power the home hub during a power cut, that is assuming that your Openreach optical modem has a battery backup unit. If not, then two separate units  are needed.

Many people already have cordless phones, which would not work anyway, if there is a power cut.

This is for the smart hub 2.

https://shop.bt.com/products/cyberpower-back-up-for-bt-digital-voice-service--non-fttp--091297-FV54....

And this is for the FTTP ONT.

https://shop.bt.com/products/cyberpower-back-up-for-bt-digital-voice-service--fttp--097284-FV55.html

It would be much cheaper to buy a mains output UPS, and plug both the ONT and smart hub 2 into it. 

Something like the Cyberpower BR700ELCD-UK (about £81) would seem more suitable, as you could also plug in any mains powered phones as well.

[Bernie533]

Many thanks Keith, really grateful for the guidance

[Keith_Beddoe]

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@Bernie533 wrote:
Many thanks Keith, really grateful for the guidance

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Its just seems a better option to have one UPS to plug everything in, including any DECT phones.

I suspect that BT have opted for a low output voltage (12V) unit, for customer safety issues, as not all customers would be competent to use a mains output UPS, as its likely someone will plug other things into it, and cause it to overload and shut down. It may also be that people have their ONT and home hub in different locations, so need separate units, adding to the expense.

[Pjay37]

Keith

I hope I’m not butting in. I’m not sure of the etiquette of the forum!
I have been looking for clear information on BBU units and your post was just what I wanted. Because of a mix up over my FTTP installation I have been promised a free BBU unit to cover the mains failute situation, as soon as one is available. This is currently being looked at by Neil (moderator) on this forum.
From what you say it seems I would need two boxes one for the Hub and one for the ONT. Which ever way you look at it this is an untidy solution. I am tempted resolve the problem by purchasing a unit such as the BR700ELCD. The cost is not great, where safety of life is concerned, and it could also provide security for other small electronic items.
I’m out of touch with modern digital techniques in rhis area but I assume the ac output of units like  these is such that it would not invalidate warranties or contractual obligations. Sorry if I’m fussing but my involvement in “converters” goes back to the horrors of vibrators and valve choppers!
Thanks for the information you provided. It was very much appreciated.

[Keith_Beddoe]

@Pjay37 

The UPS is an offline one, in that under normal operation with mains present, it simply passes the mains input, right to all of the sockets. It also makes sure that the internal battery is fully charged.

In the event of a mains failure, an electronic inverter which is powered from the battery, switches in very fast, and maintains the supply to three of the sockets on the top. The other three are only mains powered and are surge protected.

So you have three outlets which are protected from mains failure until the battery runs down. That  enables you to plug in an ONT, a Smart Hub 2, and any mains powered phones.

The UPS output during mains failure, is a simulated sine waveform, which is compatible with all modern switched mode power units like those used on the ONT, Home Hub, and modern DECT phone systems. It will not invalidate any guarantee, as its the same sort of power unit that people use to protect their PC.

The amount of load on the UPS is going to be very low, so it should provide backup for quite a while.

[Bernie533]

If i bought one of these as an emergency power back up to power the ont and the smarthub 2 do you know roughly how long it would keep them running for ?
Excuse my ignorance on this subject and am really grateful for any guidance. Trying to identify if I need to buy the two units from BT shop or a single one like this.

Something like the Cyberpower BR700ELCD-UK (about £81) would seem more suitable, as you could also plug in any mains powered phones as well.

[Keith_Beddoe · Accepted solution]

@Bernie533 

Its a 700VA unit, which is quite large and capable of a 420W load maximum. It specifies nine minutes at 220W.

https://www.cyberpower.com/uk/en/product/sku/br700elcd-uk

The home hub and ONT are unlikely to be more than 40W, possibly much less, so I would expect it to provide backup for at least 45 minutes, possibly more.

[Bernie533]

@Keith_Beddoe 

Many many thanks Keith, genuinely appreciated. I believe there is a 1000va 600w unit as well. I am really grateful for your help.

[Keith_Beddoe]

@Bernie533 

The problem with larger units is that the internal circuitry can take more power that the actual load, so you do not gain as much as you would expect. Larger units are mainly for high power PCs which need time to shut down before the battery runs flat.

Conversion from the 12V backup battery, to 220V, does involve losses.

For those people with electronic know how, the ideal solution for very long outages, would be a 12V battery kept float charged, and then a protected feed from the battery, to the ONT and the Smart Hub, as I think they are both 12V.