Solar Panel Car Battery chargers - any good?

Alfrescodave

My wife's car is often not used for a couple of weeks and even though the battery is fairly new, its sometimes not able to start the car because of lack of volts. This situation is not helped by the fact that she only drives short distances.If I remember, I take the car out for a run to charge it up.

I've seen solar powered car battery chargers which trickle charge the battery via the cigarette lighter. Does anyone use such a charger ? and what are the best ones - 1 w / 1.5w / 2w or what ?

B00st

You need to check that the cigarette lighter is actually active when the ignition is switched off.

You also have to be careful when using a trickle charger for long periods as they can slowly cause the battery to dry and fail. Far better to use a proper maintenance charger which monitors the battery's condition and applies charge as appropriate.

Strider590

One of those solar chargers isn't going to help you.

Even at 2 watts and assuming maximum sunlight, you'll be charging at 0.15 Amps or 150mA.... This simply isn't enough.... The car charges itself at 4 Amps when it's running so for every hour of running the car to charge the battery, you'd need 26 hours of solar power..... Now the standard rate of discharge would mean whatever you gain in the day, you'd more or less lose at night.

savemoney

Your better of with a charger that does trickle charge thsi one you can charge even with battery connected and even do it through some cigarette lighter sockets

http://www.amazon.co.uk/Ctek-CTE-XS4003-Multi-Battery-Charger/dp/B003B344NC/ref=sr_1_1?ie=UTF8&s=automotive&qid=1293843683&sr=8-1

Hammyman

A 2W solar charger will take a few hundred hours to fully charge up a battery - 500 hrs to charge up an 80Ah battery. Currently thats 50 days of daylight at this time of year.

forgotmyname

They are OK to keep the battery topped up when not in use, ie a leisure battery but a modern car with
voltage sensing and alarm/immobiliser may draw more power than one of those panels can supply.

Buy a decent charger and give it a topup charge every now and then.

exup

they're really meant for when the car is not used for a long period of time - like you went away on holiday - some of the people in my owners club have them and they do work OK though.

Strider590

^^ Placebo effect

If you want results, get one or two of the big 20watt+ mother's fitted to your garage roof

Tomflute

I have got a Maplins 4W solar panel charger. They are NOT for charging flat batteries but are useful for keeping charged batteries close to full charge. They generally have a plug for the interior socket that is fused but if when you take the key out and this socket is dissconected then you need to use a direct croc clip lead to the battery. WARNING!! ,if you do this make sure there is a fuse in this lead as close to the battery as possible,if not you will need to add one (i took the 500ma fuse out of the other plug lead and used that) .Anything added straight from the battery without a fuse is DANGEROUS!!. If this lead or the panel develops a short a fully charged car battery will deliver in excess of 400 Amps and the lead insulation will melt and can start a fire (your whole car could go up!!).
This said mine delivers 100ma + in sun, 30ma = in bright cloud, 24 ma in dark cloud tailing off to just a few ma in evening daylight. The drain on my locked alarmed car is a constant 16ma, so especially in summer it should keep a car charged or at least prolong considerably the tme it will take for a flat battery. If you get say a 15W it will deliver more charge but could overcharge the battery so would need a charge regulator. 1W is too low , 4W to 5W seems about right.

Strider590

Tomflute wrote: »

I have got a Maplins 4W solar panel charger. They are NOT for charging flat batteries but are useful for keeping charged batteries close to full charge. They generally have a plug for the interior socket that is fused but if when you take the key out and this socket is dissconected then you need to use a direct croc clip lead to the battery. WARNING!! ,if you do this make sure there is a fuse in this lead as close to the battery as possible,if not you will need to add one (i took the 500ma fuse out of the other plug lead and used that) .Anything added straight from the battery without a fuse is DANGEROUS!!. If this lead or the panel develops a short a fully charged car battery will deliver in excess of 400 Amps and the lead insulation will melt and can start a fire (your whole car could go up!!).
This said mine delivers 100ma + in sun, 30ma = in bright cloud, 24 ma in dark cloud tailing off to just a few ma in evening daylight. The drain on my locked alarmed car is a constant 16ma, so especially in summer it should keep a car charged or at least prolong considerably the tme it will take for a flat battery. If you get say a 15W it will deliver more charge but could overcharge the battery so would need a charge regulator. 1W is too low , 4W to 5W seems about right.

100ma wouldn't even cover the quiescent current draw from devices such as the alarm and ECU (in standby).
The maximum allowable quiescent current draw for cars on the ignition off condition is currently in the region of 200ma and most modern cars are right up on that limit.

Yes ok, so it's replacing some of that loss and in theory prolonging the time it would take to drain the battery if left for a long period.

But there's a problem (and im doing some project work with solar cell nimh battery charging right now), with the protection diode in place, the panel must be producing 0.63volts above the battery voltage in order to forward bias the diode and allow current to flow into the battery.
So with a normal car battery being fully charged at an open circuit 12.9volts, your cell has to be producing at least at 13.5v (open circuit) before it can even start to charge the battery.

Ideally it needs to be kicking out something like 14.5volts.

marlot

Batteries self discharge, at about 1% a day. So 2W isn't going to even keep up with that, let alone the alarm, etc. Absolute waste of money.

If you can plug into the mains, you're far better off with a CTEK xs300 (or the very cheap aldi or lidl alternatives which come up from time to time)