Backup power
There are lots of ways of providing Backup power. This article introduces the various options, with their main features. Some of these have their own articles that go into the option in more detail.
Power options
Generator
Issues to consider:
- how to detemine power needed
- noise
- maintenance
- cost
- service life (often very short)
- 2 strokes and starting reliability
- the Cult of the Listeroid
- connecting to mains wiring
Torch
Battery torches tend to turn out to have flat batteries. Rechargeable batteries are worse in this respect, with quite high self discharge rates.
Wind-up and shake torches don't need batteries, so are more likely to work when they haven't been used in ages. They don't run long on a charge, but can be useful to see to get another power source running.
LED torches give out less light and light of lower CRI, but run longer, are much less prone to bulb failure and are far more robust.
Gas lighting
Despite being historic technology, gas lighting has some advantages over electrical power. The main one is its long term reliability, which is hard to match using elecrical kit. Gas lights can be expected to work for decades without attention or failure.
Gas cylinders don't discharge in storage, so power is always there ready to go. This contrasts noticeably with rechargeable batteries, which are prone to either
- being flat when wanted if not left on trickle charge
- having limited life if left on trickle
A small camping lantern will produce more light than a 60W incandesent light bulb for several hours at maximum brightness. If longer run time or less light is required they can be turned down to give long run times, 10 hours or more depending on cartridge size. Note that often maximum brightness is achieved at below maximum gas output, since at full the flame can be not ideally positioned.
The quality of the light is quite good, and much better than the low CRI and high CCT types of electric lighting, such as LEDs and cool white fluorescent tubes.
Gas lights produce a lot of heat due to low efficiency, and with suitable care this can be used to cook or heat water. Even a small camping gas light will put out around 400w of heat, which is enough to cook on.
The high heat output means it should be put somewhere it can't be knocked over in use. Hanging from the ceiling is often practical.
Putting foil round half the globe produces nearly twice the level of forward light.
Cost per volume of gas varies widely for different cartridge types. High gas cost lights can be uneconomic purchases, even if cheaper initially.
UPS
Uninterruptible Power Supplies provide a mains feed that's not interrupted in the event of a power cut. The switchover to internal battery is instant.
Large whole building units are available, but nearly all UPSes sold are plug-in items intended to run one or a few low power appliances, typically a computer system. Small cheap units may only manage minutes of backup time.
To avoid disappointment, the required capacity of UPS should be calculated before purchase, otherwise its likely to fail to deliver the run time wanted.
Laptop
A laptop is often a practical way to get computer time during power loss.
Where TV is wanted to sedate the kids, a laptop with a USB TV card can be cheaper than a UPS to run the main TV, and of rather more use.
Extra batteries can give more run time. As well as expensive Li-ion laptop batteries, laptops can be run off lead acids with higher capacity and lower cost per hour, or an iron carbon battery. Manufacturer's instructions should be followed in such cases.
Lead acid battery, charger, invertor
A good option for people that already have most or all of the parts. However the necessary bits and leads need to all be to hand when the power cut happens, and the battery must of course be charged and ready.
Candles
Though basic, candles are a workable way to provide occasional lighting. £1 buys a lot of tea lights, but not a lot of light level.
Candles are associated with significant fire risk, so its only sensible to use some means to keep the candle safe in use. Wall sconces are effective, placing the candle high up out of reach, especially of young kids.
Always keeping candles and matches in the same place makes finding them in the dark easy. Finding them in a new location can be a hopeless task in the dark.
Emergency escape lights
Non-maintained lights will light up automatically when mains power fails. (Maintained units are designed for a slightly different job.)
Run time typically 1-3 hours, typical cost £15-20.
Fluorescent units generally give more run time due to the much higher efficiency of fluorescent tubes.
Rechargeable torch
These are left permanently on trickle charge. Some can be set to come on automatically when power goes off. Available light output and run time vary.
Fluorescent torches generally give better run time, since the fluorescent tube is much more energy efficient than the filament bulb.
All share one defect, limited battery life, and will require re-celling after so many years. Cells with higher capacity can give longer run time if required.
Iron carbon battery
The home made iron carbon battery can provide plenty of power at any chosen voltage during a power cut. These are stored dry, and water is added to activate them. Because of this, shelf life is indefinate.
Construction cost is trivial, they're easily replenished after use, and can be built to any size for any load requirement. Very large batteries are quite constructable.
Luminaire backup pack
Mains fluorescent lights are available with a battery backup pack built in which will light the tube when mains fails. Be aware that battery operation is usually at much reduced power. While popular in commercial premises, this is not one of the cheaper options for domestic use, expect to pay anywhere in the region of £80 or so. They also aren't generally styled for domestic use, but this issue is easily sidestepped with trough installation.
12v battery & 12v lights
Fluorescent lights give several times the run time per light output than filament Lamps. A practical option where mains voltage isn't needed.
Its possible to feed 12v wiring to every room, and add a relay that switches a 12v lighting system on when mains fails. This may be an attractive option when carrying out work that permits running new low voltage wires, such as major redecoration, rewiring, installing a wired network, etc. See Low Voltage Wiring.
There are 3 types of lead acid battery. Deep discharge batteries and SLA are suitable for permanent installations. A battery borrowed from a car will do for occasional use. Lead acids require correct treatment to avoid early failure.
A Lead acid battery requires a few minutes of maintenance every couple of years to last well.
Glowsticks
Low light output and high price, but long shelf life, completely safe to give to kids and keeps them amused.
Glow in the dark tabs can be added to door handles to help small children navigate the dark.
Paraffin lamp
Old fashioned pressurised paraffin & lamps (Coleman, Petromax etc) are much cheaper to run than gas canister lamps, but a little knowledge & time is needed to get them started. They burn pressurised boiling paraffin and are not the safest lighting option.
Nothing
Most people choose no back up power, and are quite happy to sit in quiet for once. It can be a nice break in a hectic life, and quite refreshing.
Choice
The usual question that's posed when choosing is 'What do you want power for?'
- lighting
- ch/hw
- tv
- computer
- freezer
- cooking
- etc
What will that cost, and is it worth it? Now, more realistically, what will do?
Services
Cooking
If power for cooking is needed, as well as the above options it can be provided by any of:
- disposable charcoal BBQ tray
- wood/coal fire
- gas stove, either mains, bottled gas or camping canister type
- paraffin stove
- and maybe self heating instant meals
If considering these options, bear in mind that old fuel cookers such as paraffin types can sometimes produce significant CO, and will require good ventilation or use outdoors.
Some mains gas cookers cut the gas off when they get no electrical power, some don't.
Phone
Wired phones connected direct to the line should continue to work in a power cut. Not all companies keep as much reserve run time at the exchange as BT.
Mobile phones may stop working as most cell towers have no backup power source. A mobile with a flat battery will of course be dead - obvious, but sometimes overlooked.
Cordless phones stop working if the base unit doesn't have a built in rechargeable battery. Those that do should continue to work for a fair time if the battery is serviceable.
Internet
Dialuppers using a land line should have no problem for a while. Wireless mobile net access will suffer the same fate as mobile phones, and usually stop working.
Broadband services require power to the modem to work, otherwise net access stops. Any routers will also need power if you want them to work.
TV
TV aerial systems that include an amplifier will play dead during a power cut.
Set top boxes and anything else the aerial signal runs through will also want power providing, or won't co-operate. However its not hard to connect the aerial lead direct to the TV to just get the 5 main channels.
Computers
Desktop systems and CRT monitors are both power hungry. Cheap plug-in power backups won't run these for long, and in some cases won't run them at all. Laptops are more practical.
Desktop systems with a CRT monitor on a UPS suffer a particular issue: if the monitor is off when power is lost, switching it on tends to glitch the backup power, which often resets the computer or shuts down the UPS. This is due to the high initial current consumption of the degauss circuit in nearly all CRT sets. Even a 1kVA UPS can be caught out by this in some cases.
CRT monitors can be modded to sidestep this problem by putting the degauss circuit on a switch, and normally leaving it off, but few would bother for domestic use.
Hot water
Some gas fired hot water systems can work without electicity, most won't.
Fires with backboilers and gravity circulation work with no electricity.
Space heat
Some gas wall heaters work without mains, some don't.
Portable gas & paraffin heaters all work with no mains. Old paraffin heaters produce CO if the flame is adjusted wrong, or the wick needs trimming, so these can't be considered safe for everyone. Any more than the odd flicker of yellow in the flame indicates incomplete combustion, and thus CO output. Knocking these heaters over is also a familiar cause of house fires.
Business use
When using backup power for commercial premises, its helpful to estimate how much business is lost in one power cut, and roughly what this value adds to over say a 10 year life of a power backup system. A quick calculation shows that UPSes are a no-brainer for many businesses.
Bear in mind that power cuts are in practice due to on-premises faults as well as supply outages, and that getting an electrician generally takes many hours.
Connecting to house electrical circuits
Care should be used in doing this, as its quite possible to kill or injure a linesman if the right safeguards aren't in place. Integrating the backup power source with the whole house wiring is more involved than most DIYers are willing to do. Running an extension lead from power source to appliance is a simpler option.
Wiring Design
Its possible to choose what appliances you want to work in a power cut, and provide a separate circuit to run them, possibly with a UPS to keep the circuit alive for a while. Very few of us go that far, but some will wish to at design time.