Safe Speed Forums

The electricity around here has been chronic. 3 hour power cut last night and the avr light is flashing on the small ups all the time as the voltage is piddle poor at 215 volts!! I'd like some thing that would smooth out the power and have enough in reserve to cope with a long power cut - 4 hours at 1kw

Standard house level UPS would be 12 kva. That's probably more than I need but better to over spec? Anyone got a 4 hours ups and AVR in an easy to install box that would take any electrician minutes and costs as little as possible? Ideally I'd like a 12kva gas generator so I'd just switch over when the mains was manky but they're £4k + vat which is way outside my budget...Might be overkill with my sub 1kw general background usage too.

The other alternative is just to buy lots of little ones and stick them on everything but all the ones I have bought to replace an ancient belkin are useless in comparison. They say they'll last 45 minutes at full load and they last like 15 max at less than full load! Belkin one would go ages - 2 hours early on light load. Used to have my pvr and sky box plugged into it as neither like power cuts. Battery life has reduced now so I think the batteries have had it.

Any bright ideas before I strangle anyone with an E-On truck as they were around here digging in the road when the power went off. Grrr.

One single UPS powered off 6 car batteries in parallel ...

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Is that all??? That's not a lot of batteries

They tend to be in series as it is more efficient and cost effective for the power conversion electronics.

48V is pretty common though a 10KVA might be a couple of hundred and the 100KVA at work is over six hundred.

I reckon your best bet is to go for a 2 - 3 KVA on a dedicated power circuit, you might be able to cobble together some extra capacity using car batteries* as the manufacturer ones tend to be very expensive. APC batteries to give a 4 hour run at a kilowatt would be over £1000 for instance. The other option is to go for a 2KW generator and rig up some kind of timer to power it up after a certain amount of power outage duration. The problem is most generators do not have a clean sinewave output and the ups may refuse to play.

*Some people have tried this, but with marine and other high spec batteries,Google is your friend.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

You are of course correct. Unfortunately, efficiency doesn't go hand in hand with cheapest.


Teabelly, are you sure you need the full 1KW for the 4 hours? What are you trying to keep active?
A string of low energy bulbs and smaller appliances could have a greater cost benefit than a high capacity UPS.
My own UPS is only 600VA and it drives a substantial monitor and a tower, among other things.

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Can you safely put car batteries in parallel?

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

There isn't fully 1kw. Mostly there's about 400-500w going on of generally switched on things that are a pain to switch off. Would be handy to keep the laptop going and wireless router etc. I always allow extra room in these things so that you have more chance of it lasting the time. It is also exceptionally boring in a power cut so being able to carry on as normal and ignore it would be even better. If the heating is running than that can send peaks in usage briefly so it has to be over specced I think just to be on the safe side.

I reckon it can be done. The most important bit is matching the battery voltages before connecting them; the rest sorts itself out (I believe). I'm open to gaining knowledge of any technical concerns.
Even if the voltages are not matched, it's no worse than when using one car to jump-start another.

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

not so much a safety issue, but if you do paralell batteries they should all be the same age, make and capacity. but as has been said, the electronics works better if you use them in series

Also, there is no such thing as a "Deep discharge" battery. if you run them flat you will kill them really quickly!

In serious "Off grid" applications a lead/acid battery is considererd "Discharged" when 20% of its AH capacity has been used. IE if you want the batteries to last more than a couple of dozen cycles you need to ensure that the AH capacity is about 5 times what you actually expect to use! (More is better!)

you would be well into milk float battery territory to power the system that is being discussed.

I have seen controllers that would give UPS type functions on protected circuits that would allow time for a genney to start (or be started manually) to take over from the battery reserve before they discharge. This would allow you to get away with a smaller battery bank.

Such controllers also work "On grid" as battery chargers and will also accept adittional inputs from solar panels etc. Unfortunatly I am not sure where one would get these in the UK without getting screwed over and buying directly from suppliers abroard has its own risks....

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"The road to a police state is paved with public safety legislation"

You are correct that it is best to have a bit of overload margin on your UPS sizing even though this results in a small efficiency drop. A modern UPS will run at over 90% efficiency at near full load and if you run a 1KVA unit at 50% load (500W say) you will see a minimum battery power requirement of, say, 600W.

Most medium power UPS will be 24V or 48V DC (it's easier to comply with the Low Voltage Directive). Current loadings at 600W would be 25A or 12.5A respectively.

As you can see, you will not need a big battery array to provide this current for 1 hour. I suggest a nominally 40Ah size for the 24V system or 20Ah for the 48V. Car batteries are unsuitable for UPS use and will give a short life. You need deep cycle lead acid batteries which are a bit more expensive but will last, say, 5 years on float charge.

You can parallel lead acid batteries to give longer run time but you will need a bigger charger to recover them reasonably quickly. You run the risk that if one battery develops a short then the parallel connected batteries will also "go down" (sometimes catastrophically).

If you had a 40Ah battery then, to recharge fully in 16hrs you would need a minimum 4A charger.

I hope this helps.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

That's very helpful, thank you.

The easier solution would be to use a few smaller UPS with standard electric sockets but they don't seem to be made any more. Belkin used to do them and several of those around would do most of it apart from the boiler pump. Just having one on the boiler would be very useful as in sub zero it is a pain when you can't have hot water or heating.

I know what you mean about the little UPSs being useless for more than a few minutes. We have one (same reasons as you!) and it won't power the pc and monitor for anything like as long as it says on the tin!

Have you considered an inverter? That's what caravaners and yotties tend to use.

http://www.caravantechnology.com/Power- ... 4Qod3GH6ng

You feed them 12 (or 24) volts and they give you 240V back.

Only thing to beware of is that they (like generators) tend not to produce a pure sinewave output, which can upset some electronic equipment. You can buy pure sinewave ones but they're a lot more expensive:

http://www.caravantechnology.com/%2F100 ... r-P36.aspx

You can get some stonkingly big ones (at a price!) - my boss runs a four ring electric cooker off one on his boat!

Might be worth buying several smaller ones rather than one big one. You can then have a battery for each and size them according to the needs of the equipment they're powering. For example, the central heating boiler (but possibly not any electronics in its timer or controller) could maybe manage with a modified sinewave inverter - and lights certainly could. A telly, on the other hand, might need a pure sinewave one. I regularly run a laptop from a cheap 150W modified sinewave inverter and have never had a problem with it.

You could also get some 12V "Leisure" batteries. As Dusty says, lead-acid batteries don't like being deeply discharged - car batteries especially so. There are, however, different designs of lead-acid battery that can tolerate it better. "Leisure" batteries are the next cheapest alternative. I use them and they last about 5 years or so. I abuse mine a bit by starting a small diesel engine from them (unlike car batteries, they can tolerate deeper levels of discharge, but they don't like supplying high currents (like starter motors) even for short bursts. As with most things, you get what you pay for! You could also try "traction" batteries - which are generally more expensive and tolerate even deeper levels of discharge and for longer. I have a few electric wheelchair batteries that are gel-filled and have been run down to about 25% charge repeatedly over the last year and still seem to come back for more!

I imagine that in the next 5 years, people will start buying electric cars and using them in the way you suggest - to even out peaks and troughs in domestic demand. In effect, you just use the car's battery (typically 20-50 kWh!!) as a big reservoir. (Not sure what happens when you're getting to the end of a long power outage and you want to use your car all of a sudden though!

I think the real purpose of small UPS units is to allow you to shut down in the proper way without corrupting data rather than actually going on working.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

I checked the box on the trust one. It said 'up to' 45 minutes and in tiny writing 'depending on load'. I'm sure I bought it for 45 minutes on full load! I'm fairly certain that's what it said in the product description but I can't remember where I bought it from. I usually put the computer to sleep so that it should last for ages without having to reboot. I also use one to keep the pvr going as it is very annoying to lose a recording as it trashes it totally even if it was nearly at the end.

Leisure batteries sound sensible. Tempted to fill the garage with them

http://www.justgenerators.co.uk/pages/product210.htm This is the generator I was looking at and dreaming about. Don't know how long it takes to start up so some kind of battery arrangement would probably also be needed to allow a seemless transition.

A fully charged battey is 13.8 volts and I know it would mean losing 0.6V, (or better still use germanium diodes @ 0.3V drop), and some useful power but I can see nothing wrong with using a diode on each battery to isolate them. (Something heavy duty; not a 1N4148 )

That way you can use any 12 volt batteries you have knocking around in parallel. I can do the CCT for that one Where's Pete317?

Edit: I don’t know about you Claire but those 12V inverters we both have aren’t as good as I'd hoped. They work okay but when I used one to power my 32” TV, which I know consumes 94 Watts, I found I was lucky to get 15 minutes from a fully charged heavy duty motorbike battery. I also found the buzz you get from them a little annoying so I had to turn the volume up, which ironically will reduce the time of course.

I can’t remember the rating of the battery but it just seemed quite poor to me at the time but I guess a car one would have given me over an hour. The maths to work it out is easy enough..

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

There is a farmer near Hawkshead who does on site arc welding with a trailer full of batteries... ANY site!

I know they came from the railway network - via the Chloride Co. near Manchester.

They were used as back up on signaling and automatic barrier equipment.
They change them regularly apparently - and Chloride are big UPS providers thee days!
Botach...?

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Time to take responsibility for our actions.. and don't be afraid of speaking out!

I'm surprised the 32 inch survived.
The 94 watt on sine wave 50hz would be about 150 watt on a modified sinewave inverter, which is what most of the cheaper ones are. The power supply on the tv would have been a switched-mode one....which are designed to run on 50 hz sinewave (ish). It would run hotter than usual.
With the price differential between gas (about 6.6p/kwh on the first tariff and less than half that on the second tariff (BG)) it would be cheaper in the long run to go for a gas ic engine and combined heat and power....and sell the excess to the grid !

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The world runs on oil, period. No other substance can compete when it comes to energy density, flexibility, ease of handling, ease of transportation. If oil didn’t exist we would have to invent it.”

56 years after it was decided it was needed, the Bedford Bypass is nearing completion. The last single carriageway length of it.We have the most photogenic mayor though, always being photographed doing nothing

Gee, thanks Tone

The trouble with putting batteries in parallel is that the strongest and/or freshest battery(ies) tend to contribute the lion's share, although diode voltage drop (which tends to increase with current) does tend to even out the load to a certain extent.
All in all, unless you really want to use a mishmash of batteries, it's much simpler and cheaper to put them in series rather than in parallel - the only real problem with this is that one duff battery tends to kill the system.

BTW if you want a low voltage drop with reasonable cost, it's best to use a Schottky diode.

BTW2 What's wrong with a 1N4148? Put a few thousand in parallel and you can push a fair amount of current

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

This kind of thing turns up, though you take a risk on the batteries of course.

http://cgi.ebay.co.uk/APC-Smart-UPS-RT-7500VA-230V-SURT7500XLI-AP9619-Card-/300502504760?pt=UK_Computing_Networking_SM&hash=item45f7585538
http://cgi.ebay.co.uk/APC-Smart-UPS-RT-192V-Battery-Pack-SURT192XLBP-4-bats-/300502509213?pt=UK_Computing_Networking_SM&hash=item45f758669d

The problem is a largish UPS will pull a certain amount of power just to run itself so at lower loads the total efficiency will be lower. The extra battery pack on this still only gives you a couple of hours running at 1kw.

You might be better going for a smaller UPS and something like this http://www.hartindustrialtools.co.uk/acatalog/EU20i.html

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

I used to scrounge the diodes and thyristors out of washing machines when I was a kid

Very handy for making light units for my mates mobile disco.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May