inverters, power cuts, generators, CH, etc.

[Stephen]

Hello,

We had a power cut for three hours last night. I happened at the worst possible time: just as we were getting cold, dark, and hungry.

We have oil fired central heating and it was frustrating that we had a tank full of oil but could not use the CH because we had no power for the boiler. This got me thinking that perhaps I could buy a cheap inverter and run the boiler from a car battery.

The boiler instructions say it must be connected via a 5A FCU, but

240*5=1.2kW, so that's a bigger inverter than I had originally thought.

Also connected to the FCU are the pump, valves, etc. IIRC the pump uses about 40W. When I bought the valves, I didn't realise there were different types, I just bought what was in the screwfix catalogue. Unfortunately, they are spring operated so draw 6W all the time they are on. I wish I had known about motorised on and off ones that only draw current when switching. I will ask the boiler manufacturer, but in the meantime, does anyone know how much current a modern oil-fired condensing boiler draws? Surely it can't be a kilowatt? But then motors have a surge when they are switched on, don't they, so I guess the 5A fuse is to tolerate that?

It would be nice if I could use a (made-up number) 300W inverter with momentary peak output of 1.2kW rather than have to pay for a continuously rated 1.2kW inverter.

I read all the old posts on this group about inverters and generators and see that a break before make changeover switch must be used to protect people working on the line. But for just a boiler I wondered whether I could connect a three pin socket after the FCU and plug the CH electrics into that and have a second three pin socket next to it connected to the inverter. When there's a power cut I could just move the plug from the mains socket to the inverter socket and isolate that way. What do you think?

But then my mind started running away with itself. Being dark was almost as bad as being cold. I wondered whether I could also connect the lights to something. Since lights are on a 5A radial circuit, could you do a similar thing: take the cable from the 5A MCB to a 5A round pin socket and plug the lights into that and have a second round pin socket from the inverter and switch the plugs over in an emergency?

I know one way would be to fit separate emergency lights to each room but SWMBO wouldn't like the aesthetics of two lights per room!

If you had a house with a dozen 100W bulbs, this would be another

1.2kW but if they were CFLs, it might be just 120W, which means you could run them for ten times longer from the same inverter. This is where I get confused because there seems to be so much conflicting advice. It seems there are two issues:

1. do the lights draw high currents when they switch on
2. can they run off less than perfect sine waves?

Does anyone have any definitive answers for the different types of bulbs (filament and CFL mainly).

I was thinking for just CH and lighting an inverter might be sufficient rather than the expense and noise of a generator. But it is tempting to go further and say that it would be nice to run the freezers in a power cut, the TV, the computer... where do you draw the line?

I understand that freezer compressors have a start-up surge that inverters don't like, so I guess that if I want to start powering them, I would need to think about a small generator. I don't want to spend hundreds since (hopefully) these power cuts won't be a regular thing!

We live in a village so there's no mains gas, which means the cooker is electric but I imagine I would need a huge generator for that, so I guess a small camping stove is the only sensible way to make a cup of tea, unless I could run a travel kettle from a small generator?

Thanks very much, and apologies for the long post!

Stephen.

[Adrian]

It's all possible !

Rather than a car battery, look for a caravan 'leisure battery' - which is designed to supply power over a longer period (car beattery is optimised for a short, sharp discharge via the srater motor - and doesn't perform well at lower currents over long periods..

The 5A rating sounds somewhat arbitrary to me - just a 'handy value' - I'd imagine that the actual current is much less than that...

Back at the last house we did a similar thing with a 12v-to-mains invertor run off the car and feeding the c/h system via a long mains extension lead - simply left the car on tickover to keep the battery topped up, and there were no close neighbours to be bothered by it....

Very un-green - but we knew that power was going to be restored later that day......

I guess you have to create a couple of lists of 'must haves' and 'nice to haves' - and measure the actual power requirement for each list (some things may have their consumptions actually marked on them).

Then it's down to how much you want to spend - and how long you anticipate being without power.....

Hope this helps Adrian

[Stephen]

Hello again,

Thanks for the reply. I'm, just wondering do these plug in energy monitors tell you the peak current that something draws when it first switches on or do they just show current in real time? That might be one way to measure the peak requirements?

The old posts about generators talk about connecting neutral and earth to an earth spike and using an RCD on the generator. Does the same apply to inverters?

Thanks.

[Adrian]

Mine (efergy) shows power in real-time - presumably averaged over a few seconds - so it's not going to show switch-on surges...

I never have done - but it was a bit 'spur of the moment' rather than a 'proper' installation...... I'm sure that somebody on here knows the proper answer...

As to switch-on surges - probably the best test is empirical - buy one and give it a try - they're cheap enough....

In our case the c/h system was via a multifuel (wood / coal etc) stove - so all we were switching was the circulating pump and associated valvery

- but the little inverter (150W) was quite happy with it....

Adrian

[Owain]

existing ceiling rose; incorporates a smoke alarm and "An Emergency Light - It activates automatically when mains power fails. To illuminate a safe environment and ensure light is available when required a day and night sensor is incorporated to conserve energy."

Suitable for filament and low-energy lamps

Owain

[Dieseldes]

We have exactly the same situation where we live, except we have a Stanley oil fired range which supplies cooking and CH, the last powercut we had, I had a Aldi 150W invertor in the car extension cable into the house and the wireless router running off it, with laptop on batteries, well you can't do without the world wide web and there is only so many games of 'I Spy' you can play! It did get me to thinking about the Stanley, it uses a single oil burner motor and from what I have seen of other oil central heating systems they they use the same principle and in some cases the same motor!. I checked the spec of mine and when running it consumes max 90 watts which is well within the capability of the cheap invertor. If I include the ch pump at 40W it's only 130 watts combined. If you are planning on using a 300 watt invertor that should work OK even my cheap £14 aldi special should be OK,

Des

[Appelation Controlee]

-------------------8><

I'm pretty sure the Owl that we have does a spot read every six seconds.

[Dave Liquorice]

Perfectly possible. It's already been pointed out that a leisure battery would be better than a car battery as they are designed for deep discharge, car batteries aren't and one deep discharge can kill 'em.

All the bits of kit will have a rating plate, add 'em all up. Our oil bolier is 150W IIRC, 50W for the pump so say 250W all up for the heating. This is probably getteing a bit close to the edge for a cheap 300W invertor and doesn't leave any space for a light or two.

Now do some basic maths on the current at 12v and the size of battery required. 300W output at 95% means 315W input P=VA so that is 26A @ 12v. So to cover your 3 hour outage you need a battery with a capacity of

75A/Hr. I'd go for a 110A/hr battery this should keep you going for quite a while and if you have the capacity on the invertor run the freezer as well. Bearing in mind that the boiler won't be running all the time, I'd also put a jumper and another pair of socks on and operate the boiler manually when it started to feel cold. The freezer would also be OK for 6+ hrs, unplug your boiler plug in the frezzer untill it stops then plug back to boiler.

Think about maintenance of the battery lead acids don't self discharge very quickly but they do if left for a year or so. One of the small solar panels connected across it when not is used should keep it nicely ready for action. Keep an eye on electrolyte levels as well.

What ever you go for it has to work after being idle for possibly a number of years. Routine proper testing under realistic load for several hours is required to ensure that. Just trying a back up system off load for 10 mins every 6 months is *not* a proper test.

That is effectively what I have done except that the 13A plug (with 3A fuse) would be plugged into the extension lead from the small generator outside which would be split to fridges/freezers and a few lights on extensions as well.

I don't like that idea, be far too easy to turn on too many lights. Especially if there are those in the family that only know how to trun lights on and not off.

Up to you! Heating is probably first priority for us as we are exposed and high in a old not particulary well insulated house. 2nd light so you can play board games, cook, be able to move about in relative safety (we have gas lanterns for that, loads of light long run times, bettery lights are poor in comparision). Freezers so you don't have to chuck out and repurchase food, though I expect household insurace may cover the cost of that it is still agro. If you have kids the TV and it's associated set top boxes (DSAT/DTTV, xBox, DVD etc) might be worth considering but that 42" plasma screen is very power hungry. Monopoly doesn't take any power and is a long game to play. B-)

No mains gas here either, for power cut useage we have two ring and grill camping hob and 17kg butance cylinder for it. Stock of cup a soups, bread, pasta tins etc we can eat and drink well for several days, might be a bit repetative after a few days but hey it's decent hot food and drink. Better than cold baked beans on bread (not toast!).

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Stephen saying something like:

I was doing this for real, just a fortnight ago when storm-force winds took out public power supplies around here for 7 hours or so, running my house from a 1kW inverter connected to the vehicle's battery with the engine at fast idle. Mindful of the possibility of overheating the alternator I kept the loads as low as possible, to about 5~600W. I didn't bother running the CH from it, but I've tested it in the past and it ran fine from the inverter, drawing just a couple of hundred watts.

The inverter is a modified sine wave with two 13A sockets and overload protection, quite cheap from ebay. Similar to this one...

one is pure sine wave; if I was buying another one, I think I'd go with this... I understand that freezer compressors have a start-up surge that

What I found was, the fridge would start fine, but knocked the telly out as it did so. The TV being a bit sensitive to the volt drop as the start-up surge robbed it. A couple of times of that happening and the fridge was unplugged.

[meow2222]

CH is very unlikely to consume 1.2kW. Fuse ratings arent chosen that way.

look at the ratings plate

thats how its normally done

lot easier just to use an extension lead. Nothing to install then

you could, but again a single cfl light on an extension lead is easier.

there are ways to make them invisible, and even ways to make them look funky.

and a single 23w cfl would run 5x longer again. Perhaps add a 3w one fot eh bathroom, or a 1w LED on its own battery.

not really. A bit of a surge, but the amount's trivial.

any wave shape and frequency is fine, even dc.

Theres no way you want to run 1kW of filaments off a battery! Its cfl, linear fl or led.

yup

things stay frozen for many hours with no power

how often are these power cuts, how long do they last? I doubt its worth doing most of the things you suggest here, but thats your decision. Easier would be to get a few battery powered LED lights or a portable gas lamp for lighting, and a candle driven food warmer for tea, and leave it at that. Eating sandwiches and waiting for the tea is hardly the most rigorous hardship once a year.

forget it - unless you really live in the middle of nowhere and expect power cuts to last for days.

or use a candle or candle powered food warmer. Yes, its very slow.

no

Perspective is the place to start. Have you nothing better to do with the time and money? Can you not cope with minimal lighting levels for a few hours per year? These systems have their uses, but most of us dont need them.

[dennis]

It says it illuminates a 3.6 sq meter room so it would be OK in a small toilet but not much more. I assume it means 3.6 meter sq.

[Stephen]

I hadn't appreciated that the boiler has a duty cycle, that's a good point; the battery will last longer than I had thought.

If I have done the maths right, you are rating the freezer at just over 200W?

I had forgot these appliances had label on! I've just got on my hands and knees and our freezer says something about being 140W, 13A fuse, picture of a square wave, 240W. I'm not sure why it says both 140W and

240W, nor the significance of the wave picture? If it is only 240W, why the 13A fuse? I guess that's because of the surge current; it must be pretty big. I suppose that like the boiler, a freezer is not running continuously, so it's all about diversity?

But does this mean you have to go outside and bring lights in? What are they, site lights? Isn't that a hassle having trailing leads everywhere?

Would that depend on your choice of lights? I know some here hate CFLs, but if you were completely CFL, it might work?

Can these be used indoors? I wondered about one of these but I'm sure I read somewhere they were for outdoor use only.

I know that gas heaters have been criticised here because they cause condensation and need fresh air. I suppose a gas light using much less gas these things become less of a concern? Do gas appliances set off your battery-backed up smoke alarms though?

Thanks again.

[Stephen]

But it's a DIY group and we want to justify buying an inverter ;)

[Stephen]

I had a look at the link but I couldn't see the emergency light. Does it power the bulb at low power or does the pendant glow?

[Stephen]

A travel kettle is 240v 850W, so why not?

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Stephen saying something like:

No reason at all why not. Purely resistive load and just make sure you don't use all the gen output up on the kettle.

[Dave Liquorice]

Define "small generator"...

The generators used at work "small" would be 50kW...

The little 2 stroke jobbies are about 600 to 750W. Probably survive for the time taken by a couple of mugs of water, might be pushing it for a 3l kettle full though. B-) Wouldn't be able to power anything else at the same time though.

[Owain]

I thought it would power the bulb, but not sure

Owain

[Dave Liquorice]

You might be misreading what I wrote. Almost any freezer will be OK without any power at all for 6+hrs, provided you don't open it. It would just need a boost of cold every so often.

I'm not sure about the square wave, duty cycle? 140W mean 240W running? That doesn't feel right though at 3.36kw/hr day.

Probably the motor is starting underload so will pull quite a surge. When thinking about the rating of gensets to power motors the rule of thumb is

2 to 3 times the running rating of a motor is required to start it.

Electric lights would be way down the list as we use gas lanterns... They would be normal table lamps from bedside cabinets or else where.

I'd have to go out and fire up the generator and run the lead from it into the house.

It's gets quite complicated if you want to use the house wiring when the power has gone. You can't reley on the supply earth still being earth so you need to provide your own, and tie the "neutral" side of the genset to that. Not to mention ensuring fail safe isolation between your gen/house wiring and the supply. And the possibilty of someone forgetting that you are on a 2kW generator and clicking on the 3kW kettle...

Extensions are the "simple" way out and can be manged safely with a bit of thought. Running temporay cables safely is a major part of my job, so it's second nature. I must admit to being horrified at the way most people handle and run cables.

Probably I just don't like the idea of the house wiring being live when the rest is dead. You also have the earthing implications to think about.

What is the difference between it and a mains gas hob? Provided you have some where stable and safe to put it. Ours sits over the rings of the elctric hob quite nicely.

True enough every kg of gas burnt produces a litre of water. We also have a portable gas fire as backup. I guess in a hermetically sealed, heavly insulated modern box, the bit of extra moisture might be a problem (have they banned having opening windows yet?) but it's not in a 17th C farmhouse...

Nope, only if you burn the toast like a normal gas grill. The combustion products are mainly CO2 and water.

[meow2222]

Literally speaking you can, its just not a solution I could imagine recommending. All that kit, hassle, cost, time, trouble, storge space... there are so much easier ways.

NT