solar charger for 12v car/leisure battery

[Stephen]

Hello,

I posted this on he camping group but I've had no replies. perhaps they are all on holiday?

I was advised (on uk diy) that a leisure battery might discharge if left unused for some time and I was told that a solar charger would top-up the charge and prevent this. What size solar panel would I need? Does the output of the panel have to be a certain ration of the capacity of the battery? If so, what's the magic formula?

BTW can you recommend a good make of leisure battery and any good suppliers?

Thanks, Stephen.

[Chris J Dixon]

You would probably get a few opinions on uk.rec.caravanning

Chris

[Dave Plowman (News)]

The rate of self discharge of a lead acid battery is very low - I've expect it still to be healthy after the seasonal break in use. And a charge with an ordinary charger before use will be fine. Solar units are very expensive for what they are - and not reliable in the UK climate. Get a Lidl charger when they come up again - about 12 quid and small enough to fit in the pocket.

[Harry Bloomfield]

Stephen presented the following explanation :

There is no magic formula. It needs to be large enough to more than cover the self discharge, plus any loads such as alarms multiplied by 2 or maybe even 3 during the shorter and darker days of winter.

Likely a 5w or better unit would take care of the self discharge of a

110amp/hour leisure battery, but don't expect it to recharge the battery from flat.

Cheaper and arguably better would be the use of an intelligent charger' at least every month or two, assuming the battery has no loads to support between charges. Aldi/Lidl have had these chargers on special offer several times for around £10 and they really are well worth buying and highly recommended. With one of these you can either top the charge up regularly, or simply leave it connected to the charger for the entire winter.

Getting back to the solar charger...

sell a variety of these, but if you get one make sure it is a controlled output type rather than one which simply keeps on charging irrespective of need. Over charging is as damaging as under charging, or leaving a battery to go flat.

[dennis]

They have a 12W panel for £50 ATM.

[Al]

Any chandlers should have a good range of solar chargers too. Not aware of any specific newsgroups though. GIYF.

Al.

[geoff]

In message , Stephen writes

or out to lunch ...

Just go and buy the one Maplins have on offer at the moment

Solar chargers depend on light falling on the cells - otherwise more or less known as sunshine

we live in the UK - go figure

[geoff]

In message , "dennis@home" writes

You only want to blow the bloody doors off den you dick

£12 should suffice

[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've been using a cheapy 5W panel I got off ebay two years ago and it's been topping up an 80Ah battery quite happily for most of that time. Peak current from it is around 300mA during sunny days and dips to almost buggerall on really horrible overcast winter days - 17mA or so. Overall it works rather well and I'd buy another one as the need arose.

[Dave Liquorice]

I have one of those on the genset battery. Last time I started the genny= (a month or so ago) there was no problem. Panel sits behind a north faci= ng window so doesn't generate an awful lot of juice and would put 50% more =

into the battery if it didn't have 50% duty cycle flashing LED...

Lead Acid batteries have very low self discharge rates. 40%/year accordi= ng to:

an 80A/hr battery 40% is 32A/hr over a year (8760hrs) =3D 3mA =3D 0.0=

4W. So even a 1.5W panel is more than capable (even taking into account dark an= d cloud) of maintaining quite a decent sized battery.

[Dave Plowman (News)]

Wonder how much current such a device *draws* from the battery in low light conditions when not charging? It must be something.

[gazz]

The li-po batteries i use to fly my model planes have a 2% self discharge per year, and they are working on getting that better!!!

[Dave Liquorice]

Most have at least a protection diode so the reverse leakage of a silicon rectifier diode, few tens of nano amps?

[T i m]

I have 2 x 5w panels in the South facing workshop windows connected via a charge controller / switch to the backup workshop lights.

Seems to be working ok on a 10Ah gel motorcycle type battery (that I had spare).

The charge controller is only there as a light switch and to protect against over-discharging the battery. As an aside it also has a couple of multi state LED's to indicate charge and battery status.

It's surprising how 'dull' a day can be yet the charge indicator can still shows green.

Cheers, T i m

p.s. I had one of the 1.5W panels permanently connected on the dash of my old Sierra Estate and that helped keep the battery up (at least against any self discharge).

[Harry Bloomfield]

Dave Liquorice submitted this idea :

Almost no leakage at all. Likely most of the leakage will be leakage from the skin oils left on the wires and devices as the unit was assembled.

Having said that - the mains charger which keeps my motorcycles battery topped up (on permanent charge), has a fatal flaw in its design. If connected to the battery, but not plugged into the mains it flattened the battery via its charge status display. Long power cut, or mcb trip =flat battery.

[Mark]

Optimate?

[Harry Bloomfield]

Mark was thinking very hard :

Yes and three times replaced under guarantee due to the first two failing within weeks of delivery. The present one seems to be hanging in there, two years use so far, but still not a good design.

[Mark]

I was always told they were the "rolls royce" m/c battery charger. I've recently bought one too!

[Andy Dingley]

Several of my friends have independently reported Optimates as killing their m/c batteries

[Huge]

several years.