Back up electricity

Philip W · Post by **Philip W** » 01 Apr 2008, 09:30

Thinking back to threads about generators etc. The downside with generators is they need petrol/diesel (difficult to store in meaningful quantites) use a lot of the stuff. Are nickable and breakdown....

I think the most likely scenario for the UK will be very expensive electricity and rolling powercuts across the country (to share the load out).

Therefore the supply of electricity will be erratic but not non-existent.

Therefore rather than getting a generator I wonder if the best plan is to get some deep cycle batteries and a inverter. Heavy batteries kept indoors are harder to steal as well as being more discrete than a noisy generator......

Post by **adam2** » 01 Apr 2008, 10:07

I agree, battery backup has much to commend it.
Get the best batteries you can afford, future replacements may be problematic.
Buy a good qaulity fully automatic grid powered battery charger, preferably two in case of failure.
A great range of 12 volt lighting and small appliances are now available and you may therefore find that an invertor is not essiential.
If an invertor is required, consider a spare in case of failure.

For a large or complex battery system it would be well to consult an approved electrician, even small systems are not risk free and I recomend this thread
http://www.powerswitch.org.uk/forum/vie ... php?t=5455

Rmember to stock some very low wattage 12 volt lamps, both to extend battery life and in case you wish to keep a low profile.

If you decide to get a generator as well, then its running hours could be reduced by having a large battery.

Andy Hunt · Post by **Andy Hunt** » 01 Apr 2008, 13:25

Philip W - exactly what I have done.

I have around 900Ah of gel electrolyte deep-cycle batteries. These supply power to one of two ring-mains in my home (I have a separate one for the kitchen which the batteries don't supply).

I use a Powermaster 1.5kW inverter/charger which takes input from the mains, and which feeds it directly through to the ring main whilst charging the batteries at the same time. In a power cut, the inverter/charger has a UPS mode and switches over to the batteries automatically.

Last time we had a power cut it took us about an hour to notice, and then I only twigged when I went out to the shop and everyone else was off.

I have a few PV panels plugged into the system too, so that in summer I can get free leccy. The Powermaster inverter/charger has a built-in solar controller too.

Go for it!!

Philip W · Post by **Philip W** » 01 Apr 2008, 14:04

I had a look on flea bay the other day and can see 300ah ex UPS 12v batteries. They say they will last 10years (but only guarantee them 7 days!) so not sure I trust them. I presume the only way to test this out is to test the voltage, then apply a known load and see how quickly the voltage drops.

Any thoughts/views?

Andy

Did you install the Power Master yourself? Was it reasonably simple? I would describe myself as a competent DIY'er have done house electrics, a solar water system etc.

I like the idea of having a UPS system to stop my solar panels overheating in a powercut situation on a hot day.

Andy Hunt · Post by **Andy Hunt** » 01 Apr 2008, 14:39

Yes I did install it myself, with a bit of help from my partner's dad who is a (retired) electrician.

Pretty straightforward actually, I even read the instructions first (thought I better had really

)

Post by **adam2** » 01 Apr 2008, 14:42

Philip W wrote:I had a look on flea bay the other day and can see 300ah ex UPS 12v batteries. They say they will last 10years (but only guarantee them 7 days!) so not sure I trust them. I presume the only way to test this out is to test the voltage, then apply a known load and see how quickly the voltage drops.

Any thoughts/views?

Andy

Did you install the Power Master yourself? Was it reasonably simple? I would describe myself as a competent DIY'er have done house electrics, a solar water system etc.

I like the idea of having a UPS system to stop my solar panels overheating in a powercut situation on a hot day.

I would be very doubtful of secondhand batteries unless you know the source, or they are virtually free.
To test a battery it should be fully charged, and then test discharged. A simple way of doing this is to use an inverter that cuts out when the battery voltage is to low.
Connect the inverter to the battery, and a suitable load to the inverter, add an analogue electric clock, so that without constant watching you will know for how long it ran.
For a 12 volt 300 A/H battery a suitable load would be about 300 watts, this would be about 30 amps from the battery, which should last about ten hours. Anything over 5 hours might be acceptable for secondhand batteries.
No great accuracy is claimed for this test for the following reasons, the selected test load may not consume exactly the nominal rating, the inverter efficiency is unknown, and will vary during the test, and the clock may not keep good time on inverter power. It is however an indication if batteries are worth re-using.

P.S. the PV modules are not prone to overheating, the risks are overcharging and thus overheating the batteries, and overloading and thus overheating the invertor.
The equipment described above by Andy Hunt incorporates a charge controler to protect the batteries, and is presumably also protected against overloading the inverter.

Andy Hunt · Post by **Andy Hunt** » 01 Apr 2008, 14:53

The inverter is a very clever piece of kit, and has all sorts of protection and control circuits in it (well, a microchip presumably!).

I thought Philip W was talking about a solar hot water system overheating - I must admit, it's good to know that even if there are power cuts in the summer in future, my solar hot water system will still be pumping!

Philip W · Post by **Philip W** » 02 Apr 2008, 09:02

Yup, it's solar water. I have tubes which produce heat in overcast conditions. I understand that PV driven pumps will pump too slowly in those conditions or you need to massively oversize the PV module...

Andy Hunt · Post by **Andy Hunt** » 02 Apr 2008, 10:17

Yes if the PV is directly powering a 12V pump, but in my system the pump is a 240V central heating type Grundfoss pump which is running off the inverter/batteries, so it always has enough power.

Post by **adam2** » 02 Apr 2008, 12:36

Oh I see now, I thought that the OP was concerned that the PV modules could overheat.

Circulating pumps worked direct by a PV module would indeed run very slowly in cloudy conditions, and might stop entriely.
I would consider the use of an oversized PV module for this application as it may be more reliable than relying on a battery.

emordnilap · Post by **emordnilap** » 02 Apr 2008, 14:32

Andy Hunt wrote:I have around 900Ah of gel electrolyte deep-cycle batteries. These supply power to one of two ring-mains in my home (I have a separate one for the kitchen which the batteries don't supply).

I use a Powermaster 1.5kW inverter/charger which takes input from the mains, and which feeds it directly through to the ring main whilst charging the batteries at the same time. In a power cut, the inverter/charger has a UPS mode and switches over to the batteries automatically.

Where d'you get your stuff?

Andy Hunt · Post by **Andy Hunt** » 03 Apr 2008, 12:02

emordnilap wrote:
Andy Hunt wrote:I have around 900Ah of gel electrolyte deep-cycle batteries. These supply power to one of two ring-mains in my home (I have a separate one for the kitchen which the batteries don't supply).

I use a Powermaster 1.5kW inverter/charger which takes input from the mains, and which feeds it directly through to the ring main whilst charging the batteries at the same time. In a power cut, the inverter/charger has a UPS mode and switches over to the batteries automatically.
Where d'you get your stuff?

I got the batteries off a bloke on ebay, a bargain at ?600 for the lot - not sure he's still doing them though, this was ages ago now. Actually I was adding it up, I have 8x90Ah batteries=720Ah not 900Ah.

Got the Powermaster inverter direct from Powermaster:

http://www.powermastersystems.com/Template_000.htm

Got my PV panels from a local company in Chorlton called Energy & Environment.