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Constant Vigil Sentry Lite DC UPS Review
Posted on 1-Jul-2015 17:03 by timmmay | Filed under: Reviews

The Sentry Lite by New Zealand company Constant Vigil has been released recently. The Sentry Lite is designed to provide backup power to support an internet connection during a power cut, specifically providing power to homes using the new fibre internet being rolled out around New Zealand. The old copper phone lines supplied power to phones and so they worked if the power was off, which isn’t the case with fibre optic internet connections, so if you want your home phone to work during an outage this product is for you.

The Sentry Lite is small, around the size of a pack of cards, though the 7AH battery that comes with it is around 1kg and is around the size of three cans of beer. It costs $135 + GST through their website, including the 7AH battery. At some point a slightly larger 9AH battery will be available at extra cost, and the unit supports larger batteries if you want to purchase them elsewhere.

I was supplied with a demo unit by company owner, Alan Jacks. I’m told the model I was provided is an older model, the newer ones being sold apparently have a couple of extra features such as reverse voltage protection on the battery input, voltage protection of the battery input and extended cables. It’s still a polished unit, appears to be good quality, clearly manufactured on a production line. The units are made in New Zealand to ISO9001 quality levels, according to their website, and come with a two year warranty. Some of the cables received were pre-release hand assembled cables, as you can see in the pictures, production units will come with standard commercial cables. The cables are well labelled, it would be difficult to plug them in incorrectly. I used my own Panasonic 7AH SLA battery for this test.



The Sentry Lite has different options for powering your equipment. This version has two 12V outputs, suitable for my equipment, but there are options for 24V and a split 12V/19V version as well. The Dual 19V/12V model has been custom designed to allow operation of the Asus RT-N56U Router used by several ISP. Customised versions appear to be possible as well.

The unit charges the attached sealed lead acid battery at 400mah, which prevents overcharging or any gas being vented by the battery. A 7AH battery should take around 18 hours to charge at this rate.

The power supply is apparently a good quality unit by NetBit. I know little about power supplies, but Google suggests this manufacturer is used by some very large companies, which suggests it’s good quality. 



Setup was simple. I plugged the unit into the battery, the mains, the ONT, and the router as per the instructions, turned it on, and it worked immediately. It uses one plug pack instead of two, which can help given how many power points are required in some places. The number of cables here stayed constant as there are extra cables required to connect from the unit to the battery. 



I’ve had the unit in operation for the past week, powering my Chorus/Alcatel ONT (Optical Network Termination, like a fibre modem) and my Snap Fritzbox 7390. Everything just worked, I had no problems at all. I did a rundown test, with two people using the Internet connection including some streaming over wired connections it lasted 5h 11m hours before cutting out. No efforts were made to conserve power during the test.

You can see a photo of how I have my system set up below. This is in a high cupboard in a spare room near the centre of my home where I had the fibre terminate, complete with 70s style wallpaper!



Technical Bits

Of course, this being Geekzone, I couldn’t resist taking it apart to see what’s inside. The answer is... electronic stuff. I didn’t learn anything much by doing this, but I’ve included the images in case anyone else wants to know.



Additional Information from Constant Vigil

I asked Alan a lot of questions while I was doing this review, his replies were always prompt and helpful. Below I’ve included some additional information he sent me, reproduced with his permission. This was in response to my questions about:


  • What happens once the battery runs out
  • Any certification done or required by the telcos
  • What testing had been done 

Alan from Constant Vigil: “The Sentry Lite unit will prevent the battery from depleting past typically 11.1V so that it has the ability to recover once power is restored. Where deep cycle batteries are providing the backup power source, the 11.1V threshold can be lowered at time of manufacture to provide a greater period of outage support. Contact Constant Vigil if you have this custom requirement. There may be a little voltage bounce should you get to this end point caused by the battery voltage increasing as the load is disconnected but this would not affect any operation and no adverse voltages are generated. A number of our other customers are also performing these tests based on their configurations including 9Ah battery.

Certification testing is being undertaken but this equipment, operating below 20V, is classified under the old 'Low-Voltage' directive and there are no physical connections to telco wiring which would deem a requirement for any special permits. Some manufacturers like to include filter sockets for RJ45 connections but once you go down that path then certification is much more stringent.

We have been testing this unit for well over a year now with a multitude of various connected equipment and not just in the telecommunication environment although the protection for fibre outage is an obvious interest. Medical and security systems have seen some testing where light power critical support is needed. Indeed we have just last week seen use for LED lighting backup systems. These systems use an existing 12VDC power feed to the Sentry Lite and we provide a regulated 12V output but also charge 6V batteries to ensure surety of supply rather than the conventional 12V types.

The Sentry Lite is by design very simple and extremely robust. All units at production are stress tested to 35W output load and for protection of direct short-circuits and battery polarity inversion and we have maintained production here in New Zealand so that we are in control of the build quality.

We have tested (and indeed further EMC tested) a number of power adaptor types over the last few years and whilst there are a multitude of cheaper variants out there, we have chosen to progress with the NetBit model. NetBit are renowned for their quality and support and over the last 3 years I have only seen one failure from several thousand supplies. As standard we offer a no quibble, two year replacement of the hardware excluding battery.

We currently supply a single Ritar 7Ah battery with the Sentry Lite unit but provide an option to upgrade to the same physical size 9Ah version at time of order.”




Suggestions for Improvement

I made some suggestions to Constant Vigil after my review, some of which have already been done on the production units. These suggestions included


  1. Adding a "charging" or "battery connected" indicator light so users know if the battery is plugged in and working
  2. Adding dual color LEDs that can indicate unplugged/plugged in or “working off mains” vs “working off battery”
  3. Moving the lights to the front of the unit
  4. Providing a switch to turn all lights off
  5. Provide a “battery level” indicator of some type
  6. Provide a USB socket so phones can be charged during an outage

The following responses were received


  1. Will be available in higher end model
  2. May be available in higher end model
  3. One of the reasons for putting keyholes on the bottom was to allow down-facing of LEDs
  4. No reply
  5. Will be available in higher end model
  6. We did discuss the option of a 5V standard USB port but saw this initially as a potential lossy element of the design especially if it wasn’t utilised. We were aiming to use as little power internally as possible for the benefit of powering user connected devices, hence (unlike other designs) the Sentry Lite unit has no processor control, relying on ‘old school’ analogue electronics. OK, maybe not totally old school since no valves or such like, but I am sure you know what I mean? I do take your point though and we should maybe look again at this. 

Alan from Constant Vigil says: "LED switching and battery level indication were available on our previous development where the small to medium business use was considered. In order to provide the lowest cost offering to the residential market, these considerations were removed from the Lite version of the product. The high-end model (in final test stage) includes capability for:


  • Support of two batteries under independent monitoring and charging.
  • Battery charge and health indication. Poor batteries automatically disconnected from circuit.
  • Wifi/Wired Ethernet or cellular connectivity for remote monitoring.
  • Three output ports, with potentially different voltages."


In my opinion the Sentry Lite is a good quality backup power solution for any home that wants their internet connection or phones to keep working during a power outage or during a natural disaster. It has wider application to anything requiring a constant DC voltage at low currents and a variety of voltages. I’ll definitely be buying a unit of my own.


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