Solar panel to charge a car battery

[Happy Hunter]

Anyone know of the spec's of a solar panel that could charge a 12v car battery from flat?

I've bought a 'trickle' charger which does state 'not to be used to re-charge a flat battery' and guess what - it does what it says on the box

I assume it doesn't produce enought amps ?

website link etc where I can get one in the uk?

thanks

HH

[fishertrop]

So long as your PV panel produces the right voltage (usually just over 12v) and has any current at all it will charge a (not wrecked) battery from flat.

The notice on the product you read probably should say "will take a VERY long time to charge a battery from flat".

Every battery has its own specification - if you can find out data on your battery it will say exactly what voltage is optimal and also how long it will take to charge with a given current.

I've used one of these to charge a poor condition ex-car battery:
http://www.maplin.co.uk/Module.aspx?Mod ... 6&doy=21m6

It can takes WEEKS to charge a big flat battery with such a panel - hence they call it "trickle charge".

What do you want it for (the battery and panel) ?

If it's just an experiment (which can be very useful) then just charge the flat battery from the mains and use the panel to finish it off or keep it topped up.

If you plan to use the battery for anything meaningful then you probably need more charging power - weeks between resue is probably not what you had in mind!

Car batteries, esp knackered one, are RUBBISH for home power use by the way - but ok for experiements...

[Happy Hunter]

So long as your PV panel produces the right voltage (usually just over 12v) and has any current at all it will charge a (not wrecked) battery from flat.

The notice on the product you read probably should say "will take a VERY long time to charge a battery from flat".

It can takes WEEKS to charge a big flat battery with such a panel - hence they call it "trickle charge".

correct! I have had in connected to the (flat) battery for about 3 weeks and it's made little difference (the dash lights didn't come on at all before but now they light up but there is no way it will turn over the starter motor

What do you want it for (the battery and panel) ?

The battery IS for my car but I'm interested in solar power for the house too, to try to reduce dependency on mains electric.

If you plan to use the battery for anything meaningful then you probably need more charging power - weeks between resue is probably not what you had in mind!

Yeah, I'm going to but a mains charger or get a friend to charge it in their car (by swapping over once theirs is started!)

Car batteries, esp knackered one, are RUBBISH for home power use by the way - but ok for experiements..

What would be needed for serious use (like lights etc) - I've heard people getting hold of old submarine batteries! I haven't got the space unfortunately!

thanks for the help

HH

[fishertrop]

What would be needed for serious use (like lights etc) - I've heard people getting hold of old submarine batteries! I haven't got the space unfortunately!

The number ONE thing you need to do in a home power exercise is reduce your demand significantly.

For lighting, you might be better off with non-mains, non-12v, battery powered lights - there are many 6v (or similar) self contained rechargeable lamps and lights.

Similarly things like radios and walkmans are better with just regular nicads and a solar charger.

For proper work, such as cooking, you will need serious battery power and serious PV to charge them.

A small electric grill might take 30mins to cook a medium sized meal - it'll probably take 1kw steady for the whole time, which is 500w/hr.

To provide this from a system that won't die after one use, you'll need several big batteries - 50a @ 12v for 30mins is a lot of energy, and you need to keep your battery bank from discharging too far (else it will be damaged) so you need more battery capacity than the ultimate numbers.

Industrial batteries like those used in fork trucks, and of course the famous sub batteries, are great for home power systems but they can cost a LOT and need room, ventilation and maintenance.

In the example I gave, one hot meal per day using 1kw for 30mins would need a big enough PV system to put that energy back in the system in 24hrs, so you can use it each day.

The average house in the UK uses about 10kw/h per day - which is an absolutely HUGE amount of power.

Getting by on much less power is the first thing we need to do, and is a must if you want home-power.

PS: It sounds like your battery is charging SLOWLY, maybe it'll take months! Angling the PV panel directly towards the sun can make a lot of difference...

[revdode]

Generally PV batteries are referred to as Deep Cycle batteries, most are fairly similar to car batteries in principle but the construction is optimised for big discharge/charge cycles. Modern car batteries on the other hand are seldom discharged and are continuously charged in use.

Some details on deep cycle PV batteries are here available under products/batteries on the beco solar website

http://www.becosolar.com/

I've been playing with a small 12V portable charger cell, which I charge from a 15W panel through a homebrew charge controller (lidl and ebay and the net respectively) this is turn is used to charge all the AA 2300mAh MiMh cells I can get my hands on. Stacking up the losses this makes little sense but keeps me amused and keeps my daughters toys fed.

I don't know how long the portable charger will last used like this, I guess It'll be fun finding out though. So far despite a less than optimal position and fairly poor conditions it's working.

[Happy Hunter]

The number ONE thing you need to do in a home power exercise is reduce your demand significantly.

Yes, definately. My flat is awful, it is an old school house conversion and has terrible insulation. In winter we use so much energy just keeping the place warm. All energy use it electricity - no gas or oil. I would like to see if I could get some water heated by solar as we have access to the roof so I could place cells there.

For lighting, you might be better off with non-mains, non-12v, battery powered lights - there are many 6v (or similar) self contained rechargeable lamps and lights.

Similarly things like radios and walkmans are better with just regular nicads and a solar charger.

I think I'll start looking at recharging nicads from solar. This seems a good place to start 'playing'

Industrial batteries like those used in fork trucks, and of course the famous sub batteries, are great for home power systems but they can cost a LOT and need room, ventilation and maintenance.

Interesting. I'll have to wait until we move out to the country and have a space where I can try this!

In the example I gave, one hot meal per day using 1kw for 30mins would need a big enough PV system to put that energy back in the system in 24hrs, so you can use it each day.

Which in the winter will not be alot of sunlight..

PS: It sounds like your battery is charging SLOWLY, maybe it'll take months! Angling the PV panel directly towards the sun can make a lot of difference...

yes I had the cell in the sunroof (under the glass) I think the glass is slightly tinted and so was restricting the available sunlight.

thanks for the info, very interesting.

HH

[AllanH]

Interesting thread.
I had been thinking of getting a solar panel & just connecting it up to a car or bike battery to power an electric water distiller, light or other appliances for use in an emergency. It seems this isn't practical now (I'd probably need an inverter too but I'm not sure about this).
Does anyone have a rough idea of prices of deep cycle batteries?

I'm not thinking of getting the full solar panels on the roof (couldn't afford it anyway), though a solar panel to heat the water may be possible, but just a panel I could put outside in the sunshine to charge a battery that I could bring inside & use to power 'essential' items rather than the whole house. Anyone have any suggestions or thoughts on this. Is it even possible without an inverter?

Thanks

AllanH

[mikepepler]

I've been doing a lot on solar+batteries on my MSc.

I recently bought a 10 solar panel, 10amp charge controller (room for future expansion...) and a 7ah gel-cell lead acid battery. I've also got 5 LED spotlamps, which have a cluster of about 30 white LEDs in each of them. Very bright! The panel certainly charges the battery, I'd guess a few days of bright sun from empty to full, though I've not tested it fully yet. I got all the kit from here: http://www.cps-solar.co.uk/uk2shop.htm
It's all unbranded, but it's cheap and it works.

Regarding batteries, if you drain a car battery flat between charges it may last as few as 3 cycles if it's cheap. You must only discharge it to about 80% of it's capacity. This is why I bought a charge controller - it prevents overcharging by limiting the voltage, but also has an output connection, and prevents over-discharge - which is what will really knacker the battery. Also beware of voltage levels. Wet cells should be charged to 14.4V, but gel cells only need 14.1V - overcharging will cause damage, but if your panel is low power you might get away with it. Expensive charge controllers have a switch to select the battery type.

Gel-cell batteries are much better than "wet" cells (car batteries) for deep cycle. On ebay you can get batteries from fork-lift trucks and golf carts which are deep cycle and very high capacity. My little battery is only sufficient for running the LEDs really, but that's all I wanted it for.

Be warned though, thinking long-term, that a properly sized battery for your demand with a decent charge controller will still only last about 5 years of daily cycling. Not a problem now, but something to bear in mind for a post-peak system...

If anyone's got any particular questions, give me a shout and I'll see what I can dig out of my course notes...