Car Battery

eprophet

Hello,

I'm sorry if this has been asked before but I wonder if anyone can help.

Roughly how long can I leave a car standing before the battery goes flat?
I purchased a new battery on the 18th Jan (Bosch S4) but due to a minor operation on my back I been unable to drive since 23rd Jan.

I am wondering if I should start the car I this cold weather and leave it running in the driveway. Or would that just drain the battery quicker?

Thank you for your help.

greyteam1959

Depends on the car really I suppose.
Some cars with complex security devices will use a small amount of power all the time.
Most cars you could leave for many months without the battery going flat.
Would not be helpful just starting it and leaving it running on the driveway.
Would be better just leaving it alone.
Just make sure thing like the interior light are not on !!
I have a car in parked in a parking lot in Spain, it is small Kia.
I leave it for 2 months sometimes without starting it.

rs65

A few weeks should be fine.

It's a good idea to leave it parked in a position that you could get jump leads from another car to its battery if need be.

Wayne3765

mervyn11 wrote: »

Depends on the car really I suppose.
Some cars with complex security devices will use a small amount of power all the time.
Most cars you could leave for many months without the battery going flat.
Would not be helpful just starting it and leaving it running on the driveway.
Would be better just leaving it alone.
Just make sure thing like the interior light are not on !!
I have a car in parked in a parking lot in Spain, it is small Kia.
I leave it for 2 months sometimes without starting it.

Probably depends on where it's parked too , I doubt that Kia would be the same after being parked up for two months in Scotland in the winter.

Strider590

Off the car, 6 months..... On the car maybe a month.

gord115

How about a solar trickle charger,I use one of these for my car when it's stood.Half price too...

http://www.maplin.co.uk/solar-powered-12v-2.4w-battery-trickle-charger-223251

Strider590

gord115 wrote: »

How about a solar trickle charger,I use one of these for my car when it's stood.Half price too...

http://www.maplin.co.uk/solar-powered-12v-2.4w-battery-trickle-charger-223251

Don't waste your money

A standard 4A battery charger will be charging at 50watts and would charge the average battery in around half a day.

A 2.4w (if your lucky on a very sunny day) solar charger would need over 300 hours of blinding sunlight to charge the same battery.

Now taking into account losses (or quiescent current) when the car is not in use, which can be anything up to 200mA (which is funnily enough around 2.5w) + the open circuit discharge rate of a battery. Your solar charger is really doing nothing at all.......

But you can check what it's doing by measuring the voltage at the battery (vbat) and then the voltage from the panel, before the diode (vsol).

(vsol-0.7)-vbat = X

If X is negative, then no charge is coming from the panel.

Joe_Horner

Strider590 wrote: »

Don't waste your money

A standard 4A battery charger will be charging at 50watts and would charge the average battery in around half a day.

A 2.4w (if your lucky on a very sunny day) solar charger would need over 300 hours of blinding sunlight to charge the same battery.

Now taking into account losses (or quiescent current) when the car is not in use, which can be anything up to 200mA (which is funnily enough around 2.5w) + the open circuit discharge rate of a battery. Your solar charger is really doing nothing at all.......

But you can check what it's doing by measuring the voltage at the battery (vbat) and then the voltage from the panel, before the diode (vsol).

(vsol-0.7)-vbat = X

If X is negative, then no charge is coming from the panel.

They're not designed to fully charge a battery in the first place - just to offset the losses of one that's standing, which they do ok. The idea is that any charge at all going into the battery will at least increase the time you can leave it.

For checking whether it's chargiing, it's better either stick an ammeter in line or to measure as you say but the first reading (the battery voltage) needs to be done with the charger disconnected.

Strider590

Joe_Horner wrote: »

For checking whether it's chargiing, it's better either stick an ammeter in line or to measure as you say but the first reading (the battery voltage) needs to be done with the charger disconnected.

Not measuring Amps, just voltage.
You don't actually need to disconnect the charger, the voltage before the diode (which is usually separate to those solar chargers and is there to prevent the battery discharging into the panel) MUST be at least 0.7 volts higher than the battery voltage before any current can flow into the battery..... If not 0.7volts higher then effectively it's the same as having the charger disconnected.

Tis how diode's work

And on that subject, if you use a solar charger without a protection diode, your battery will then discharge more than it charges (and could potentially cause a fire)

gord115

The solar charger has a diode.
I have tested my car voltage with an accurate meter,a week with the solar charger connected and a week without.
After using it I have around 0.8v more.
It does work.
It is not for charging a flat battery though,just for keeping the battery topped up.

mikey72

I've a couple in the motorhome.
They stop the battery discharging, quite well even over winter.
There is no way to check the voltage, the diode is inside the panel, and don't try to put another in it doesn't need it.
If you do want to check it, just use a meter on milliamps as Joe Horner says.

They work best facing straight into the sun, but mine spend most of the time propped up on the dash, and they're still reasonable.
The won't run the lights if you leave them on, but they stop the alarm, and radio flattening the battery over several weeks.