How long will a battery last?

Dirkster

hi there,

I have a mondeo Mk4 and have installed a dash cam which automatically starts when it has power and stops when the power is cut off.

On the mondeo though the 12V power stays active for 15mins after the car has been locked and starts fresh anytime the car has been unlocked. My question is, would this be much of a drain on the battery? taking it that it'll record for 15mins every time the car is locked or if I go to get something from the car it'll be another 15mins recording again. Do you think this would have any significant impact on the car battery?

Also, anyone recommend a good iphone 4 cradle for the car which charges when its placed in it?

L1011

What's the power requirements of the dash cam? Without that, the question is unanswerable.

mickdw

Would there not be another location to take the power from - somewhere that immediately goes off with the key?

crosstownk

What's the power consumption of the dash cam? I doubt it's anything to be concerned about.

Dirkster

crosstownk wrote: »

What's the power consumption of the dash cam? I doubt it's anything to be concerned about.

Its 5V and 1.5 amps.

firefly08

The dash cam is hardly going to be more than 10 watts I'd say.

Here's a typical one that runs on 250ma, 3 watts.

Your battery is probably rated for at least 40aH (in other words it can supply 40 amps for 1 hour). So even if your dash cam used 1 amp (12 watts, which is very unlikely) it would still take 40 hours to drain the battery completely.

That said, you wouldn't have to completely drain the battery to render the car unstartable, but 15 with a little dash cam is going to be fine.

Dirkster

mickdw wrote: »

Would there not be another location to take the power from - somewhere that immediately goes off with the key?

Ya there would be but I'm no auto electrician so it was handy to rig up a socket multiplier and hide all the wiring. That was me peaking at my electrical skills

Dirkster

firefly08 wrote: »

The dash cam is hardly going to be more than 10 watts I'd say.

Here's a typical one that runs on 250ma, 3 watts.

Your battery is probably rated for at least 40aH (in other words it can supply 40 amps for 1 hour). So even if your dash cam used 1 amp (12 watts, which is very unlikely) it would still take 40 hours to drain the battery completely.

That said, you wouldn't have to completely drain the battery to render the car unstartable, but 15 with a little dash cam is going to be fine.

Thanks, that sums it up nicely!

firefly08

Its 5V and 1.5 amps.

Yikes, guess I have to eat my words about 1 amp being unlikely...just saw your post about the power rating there. :o

1.5 amps is probably ok but if that's at 5v and it's running off your 12v supply then the rest of the energy is presumably getting wasted?

The dash cam is hardly going to be more than 10 watts I'd say.

Here's a typical one that runs on 250ma, 3 watts.

Your battery is probably rated for at least 40aH (in other words it can supply 40 amps for 1 hour). So even if your dash cam used 1 amp (12 watts, which is very unlikely) it would still take 40 hours to drain the battery completely.

That said, you wouldn't have to completely drain the battery to render the car unstartable, but 15 with a little dash cam is going to be fine.

Dirkster

firefly08 wrote: »

Yikes, guess I have to eat my words about 1 amp being unlikely...just saw your post about the power rating there. :o

1.5 amps is probably ok but if that's at 5v and it's running off your 12v supply then the rest of the energy is presumably getting wasted?

It's linked to the cigarette charger so not sure, would it draw down the 12V and essentially waste 7V through the adapter?

firefly08

It's linked to the cigarette charger so not sure, would it draw down the 12V and essentially waste 7V through the adapter?

Yep exactly - if it runs on 5v internally then I'd guess it probably has a 5v regulator which draws the same current as it outputs. So the actual power consumption is 1.5 amps @ 12v which is 16 watts. Since the device is using 7 watts, 9 watts is being dissipated as heat.

I still think you'll be ok though.

crosstownk

If your in any way still apprehensive, just put an inline switch on one of the wires from the cigar lighter and switch it off manually.

L1011

I would imagine it has a switch mode transformer, rather than dissapting any energy as heat. Cheap phone chargers will do that, proper devices have transformers.

Dirkster

crosstownk wrote: »

If your in any way still apprehensive, just put an inline switch on one of the wires from the cigar lighter and switch it off manually.

Ya I was thinking this alrite but couldn't see any handy around. To be honest, I got a bit impatient with it. I think I'll get some scotch locks and a multimeter and cut out the cigarette lighter element of it. Just have to make sure I dont cut anything important!

firefly08

I would imagine it has a switch mode transformer, rather than dissapting any energy as heat. Cheap phone chargers will do that, proper devices have transformers.

Cool...am I right in thinking that this would mean since you have 7 watts coming out, you'd have 7 watts going in, which at 12 volts would mean there's only 583 milliamps being drawn from the battery?

L1011

firefly08 wrote: »

Cool...am I right in thinking that this would mean since you have 7 watts coming out, you'd have 7 watts going in, which at 12 volts would mean there's only 583 milliamps being drawn from the battery?

There will be some loss in the transformer, but basically yes.

Where To

My neighbour has the same battery in his 94 astra from new.




Hasn't started it since 97 though. . . .

Dirkster

MYOB wrote: »

There will be some loss in the transformer, but basically yes.

What constitutes a decent one? got it off amazon for £20 and seems well made.