SOLAR BUG

[motorspark]

Hi everyone. I'm new around here so don't shout @ me. We're building a small 'garden room' in the garden & we want to use solar energy to power low voltage lighting inside, an analogue radio/cd & possibly a 14" TV. I bought a 75 amp leisure battery from Halfords, a 300w inverter from maplins & 2 £9.99 solar panels also from Maplins. But when I connect it all up the inverter starts to beep @ me & nothing works. Where am I going wrong? I have charged the battery but the actual charger gets very hot to the touch & I'm reluctant to leave it on when I'm out of the house. The battery only gets up to 12.4 v as a result. What should I do?   

[martin]

2 x£9.99 Maplins panels would appear to be the problem! They'll give diddly squat in the way of power. Your battery is about half full, so the moment you put a load on it, the voltage dips below a "safe" level, and the inverter complains!
Best to start backwards.........work out what you need to power, and for how long each day - like this  -one 11w compact fluorescent for three hours - 33w/hrs, divide by 12 to give amp/hrs - just under three amp hrs - your battery is 75amp/hrs, so you should aim to take no more than a tenth of it's capacity per day ~(7.5 amp/hrs)  -so you could run that bulb for around 7-8hrs per day safely.
You will then need to replace that power each day, so you need to size the panel accordingly - a 20w panel (around £70) should comfortably do that in midsummer, in midwinter you'd need around 8x20 watt panels!
Hope that all makes sense - it should give you a rough idea of the sums involved!

[motorspark]

Many thanks for that. I've got 2 of those £9.99 solar panels. Is there any power gain if I attach both to my battery? If this is possible, how do I do it?

[martin]

just looked them up, they quote "125ma" in perfect conditions - so 8 hours will give you 1 amp/hr - in summer, you actually get around 6 times the panel's rating per day, so that would be 750ma/hrs per day - 2 panels give you 1.5 amp/hrs per day (in ideal conditions)
SO, let's presume your battery is half flat - you need to find 40amp/hrs of charge to get it back up - you'll need something like a month of bright sun to do so with those panels!
Just connect the two red clips from the panels to battery positive - the two black ones to negative
Being pragmatic, I'd presume your charger is knackered, so I'd suggest visiting a boot sale, and investing £5 in a "new" one, and recharge that poor battery (the longer it stays flat, the more damage it does!), THEN assume you can take about 1 amp/hr per day safely
(which is not a lot! - your inverter probably eats a third of an amp on standby)

[motorspark]

As the man said, "It's not easy (or cheap) to be green". Maybe I should return the leisure battery to Halfords & get my money back then invest in a CAR battery. Would that be less hassle?

[martin]

you definitely don't want a car battery - their design means that they won't last long at all, you need batteries with some deep cycle abilities - Ivan's 110amp hr jobs at around £50 are a good buy
Unfortunately, salesmen will sell you all sorts of things you don't really need - to have flogged you a 300w inverter with only two tiny pv panels was considerable "overkill" - as previously mentioned, even on standby, they consume rather a lot of current. To run a "normal" small tv off one will probably be using 6-8amps - that would in an hour take your "daily allowance" with a 75 amp/hr battery - and you then need to replace that every day............
There is another way........ditch the inverter, and find a cheap battery b&w tv - you can pick them up for around a fiver at a bootsale, and only draw around an amp! (and do likewise for all the loads - use 12v compact fluorescents etc. - that way, if you cut your "needs" you cut the size of battery and pv panel!)

[Ivan]

As Martin rightly suggests, running 12v dc is a very good idea if you have very little power available to start with.


Ivan

[wyleu]

Your standard plug becomes the car 'cigarette' connector.