Emergency lights..... Discuss

[Rod Speed]

While that is true, having it done when you have unacceptible downsides with the cataracts does ensure that you do have acceptable vision in those eyes before risking anything.

[Animal]

One thing I learnt about backup lighting is that none are long term reliable. Gas lights are, and they're cheap.

[Rod Speed]

What did they do about need for glasses afterwards ?

I initially thought that it couldnt be possible to have the new fixed focus lens never need any glasses, but turns out its more complicated than that.

My BiL had his done just after Xmas last year and does need reading glasses but they claim that the surgeon stuffed that up.

I need mine done but I deferred it due to covid, and then the bugger who used to show up in my town doing it retired.

There is now a new one showing up but we are just getting a new covid surge so I'd rather wait till that is over.

The only downside with my quite severe cataracts is that I can't get my drivers license renewed because we have to be able to read the right line on the eye chart and I can't do that reliably although I can still drive fine and occassionally do that illegally.

[SH]

The emergency lights I have been looking at have a jumper internallt so you can switch between maintained and non-maintained.

S.

[Martin Brown]

A dumb one that has a ~fixed 15v supply in series with a resistor will not quite murder the battery but it isn't very good for it either.

Charge rate is always (V_in-Vbatt)/R

So it varies between (15-10.8)/R = 4.2/R (flat) to (15-14.4)/R = 0.6R when fully charged. However the supply voltage also tends to rise a bit when the current draw deceases. Most do have a discharge cutoff limit to avoid damaging the battery by too low a terminal voltage.

They do vary a lot. Only the cheapest and nastiest have no measures at all to protect the typically SLA battery from harm. Mine have a pretty crude diode arrangement so that from nearly flat the diodes conduct and it quickly charges at C/3 to a terminal voltage of about 14v then the diodes stop conducting and a bleed resistor tops it off at C/20 ish.

The whole thing is made a bit more complicated by the way output voltage of the rectified AC rises as the current drawn falls. ie

_______|r|_____________|R|______ V_in | |_____ I_out, V_out==V_batt |---|>|---|>|---|

Once V_batt gets to 14v the parallel diode stops conducting.

Initial charge rate when flat = (V_in-V_batt-1.2)/r

Final trickle charge = (V_in-Vbatt)/(R+r)

R ~ 15r

I only have previous generation iron transformers (ie fluoro not LED based ones) and they each draw about 5W continuously when they are on and warm to the touch (and produce about 20W of fluoro light when the mains fails). They are warmer when the inverter is actually running.

NB Cheapest and nastiest UPS devices can only just about survive running at maximum load for the length of time that their battery can provide for.

In the interests of true DIY solutions then if you can solder then 3 white 3W LEDs in series onto a heat sink and a ~15v wall wart to charge an SLA in a similar configuration to as described above with a relay to hold the LED circuit open whilst there is mains would be a DIY option.

At 1A a 7Ah SLA will last a good 6h or so of intermittent use.

[SH]

Actually thinking about this a bit more.....

What about a 2nd 63A CU that is fed by a UPS with extra battery and the UPS is then connected to a standby generator.

The low amperage circuits like lighting, alarm, CCTV, smoke dets and boiler are then wired through a DPDT relay (one for each RCBO) with the relay coil energised by the original CU.

When power fails, the bank of changeover DPDT relays then switch the low current circuits over to the 2nd CU (which have the same RCBO's duplicated for each circuit) and this secondary CU is connected to the UPS and Genny.

This then allows instant switchover of all lighting circuits and smoke dets, boiler, CCTV and alarm to UPS and my route to the generator location is fully lit to allow me to to then start the genny and then the UPS can then be energised back up to through powering rather than discharging its batteries.

(I need the outside floods to see my way across the garden to get wood from the woodstore for the woodburner)

From an IET wiring regs point of is the above permissible with warning labels on both CUs about some circuits being energised during a power cut? It no different to a PV array with a battery is it really?

[The Natural Philosopher]

Good grief. Cant you feel your way to a torch by your bed?

[Colin Bignell]

To find a torch, all I need to do is reach into my breast pocket (or on the bedside table if I am in bed) for my mobile phone. Rechargeable torches hang by the front door and I could find those by the light of the emergency light over the stairwell.

However, moving around my house in total darkness would be hazardous. Far too may things to walk into or trip over and I certainly wouldn't want to get my toe caught in one of the rat traps I always keep set, even when I don't know any rodents are around.

[John Rumm]

Well as you move to more commercial targeted kit, you tend to get more commercial prices!

To be fair my example was a bit excessive - you don't need 4 hours at full load, and it may be that a smaller power UPS with external batts is available - that was what came to hand quickly. Even a cheap 450VA UPS hooked up to much bigger than usual SLA batts (mounted externally) might do the trick. (assuming they inverter does not have a temperature profile that limits max run time)

Your bog standard Solar PV will use a grid tied inverter, and so can't function without mains power. More sophisticated systems designed to time shift consumption however should be able to work without external power.

There is no easy answer to the sizing / run time questions since they are interdependent. The KVA is more related to max the power of the inverter rather than the battery (assuming it can provide adequate current to meet the power demand of the inverter). The run time is dependant on the capacity of the batts, and the load on the inverter.

[Jim Stewart ...]

oh goody

[Animal]

Gas backup lighting is so much easier. Cost of light: £5-20, probably a bit more now Installation procedure: screw in a hook Battery life: 1 lifetime Self discharge: none Run time: much longer than any battery based system Reliability: vastly better Outputs: about 60w equivalent of light with 400w of heat. Will boil water & cook things, though not very quickly.

[Colin Bignell]

Does it come on automatically when the power fails though?

[Harry Bloomfield Esq]

I would be wary of relying entirely on a generator starting, if my life depended on it, batteries are something I would have more faith in.

[charles]

Many systems rely on batteries at first, until the generator is running.

[George Miles (dicegeorge]

someone wrote: What about a 2nd 63A CU that is fed by a UPS with extra battery and the UPS is then connected to a standby generator.

ive seen an electrician on youtube wiring up a battery bank to a house which is charged by solars and by off peak electricity then powers the house at night, and switches some circuits over to batteries in a power cut.

g

[Martin Brown]

If for no other reason than to turn over the generator to start it!

If it is mission critical then you do have to do monthly or three monthly tests depending on how crucial it it. It is very embarrassing if the emergency backup doesn't kick in and work as intended on a test.

That happened on our site once and did a lot of damage.

[Martin Brown]

I think you must include a specific type of fail safe isolation switch over keywords "Automatic Transfer Switch" to isolate your premises. Some dodgy bodge of relays in a diecast box won't cut it.

Line engineers lives are at stake.

You will have to be selective of what you put onto the system. The generator can probably tolerate a fridge or freezer motor starting up from cold but a computer type UPS could see it as a fault condition.

Lights shouldn't be a problem but starting up powerful motors can be.

You probably want an automatic start on the generator as well as on the switchover. These installations do not come cheap.

Probably better to keep a bit more wood indoors then to avoid having to do it during a power cut. It doesn't make much sense to insist on being able to do absolutely everything as normal during a power cut.

Most PV arrays and batteries are grid tied. They cannot operate without mains power from the grid for them to sync to. There are ones that can be configured to operate in a free running mode but again you would need an Automatic Transfer Switch to isolate your home from the grid.

[Andrew]

Even people with 20/20 vision would struggle when plunged into (total) darkness, which would be the case unless there was some moonlight or light from a fire.

[Andrew]

I know someone who thought he had a cataract in one eye, but the optician said no, your eye pressure is 33mmHg and you have Glaucoma, so off to the eye hospital with you.

The eye hospital agreed with the original diagnosis but did say there was the beginnings of a cataract (but didn't indicate what could be done). They just prescribed eye drops of something for 6 months.

[Andrew]

Am I the only one puzzled by the way people use the phrase 'gaslighting' ?. The generation that seems to like this word have almost never experienced illumination by gas so what is the point of using it ?. 'Spotlighting' or even 'footlighting' I might understand.