Finding details on current drawn

[John Nixon]

Hello all
I have zero experience of dash cams. A friend has problems with vandalism whilst parked, and wants a dashcam fitted, preferably via lighter socket. Could be on for hours at a time, so need to find out current drawn. Reviews seen so far seem vague about such details. Also don't know which sort for this purpose. Any advice gratefully received

 

[dash riposki]

You're looking at .30 t0 .50 Amps and up. The lower amperage draw will be a cam without a screen.

 

[Ralph2]

Could be on for hours at a time, so need to find out current drawn. Reviews seen so far seem vague about such details.

Far too many variable to be able to predict how long before the battery is dead. Most cameras draw very little.. but over time will deplete the battery to the point it will not start the car. There are gadgets available that will shut the camera off at a predetermined voltage.. others run their cameras off a separate power supply. Like leaving a dome light on.. hard to predict how long before the battery is flat.

 

[russ331]

I have zero experience of dash cams. A friend...

Welcome to DCT. What is your friend's budget?

 

[John Nixon]

Thanks to all three of you - this seems to be a very helpful, friendly forum. I think I now have a good idea about battery capacity - shall tell her to visit the car every few hours and run the engine for a few minutes - only has a vandalism problem during working daytime.
russ331 - good question - I should have thought to include that. She wants to spend quite a bit less than £100, but doesn't have a clear limit in mind.

 

[russ331]

Please note that what she wants to do isn't viable on a day as hot as today in the UK. Aside from that I suggest something like the A119, DDPai Mini 2, Mobius, etc, powered by a, say, 10000mAh USB Power Bank when parked, so no need to worry about depleting the car battery.

 

[dash riposki]

Sometimes cranking an engine up, and running it a few minutes every few hours doesn't do much for the battery charge.
I'd probably lean toward the power bank, also.

 

[Ralph2]

Sometimes cranking an engine up, and running it a few minutes every few hours doesn't do much for the battery charge.
I'd probably lean toward the power bank, also.

Offhand.. I would think the power draw on the battery to start the car once is equivalent to "many" hours of camera use. Unless you drive the car (thus keeping the engine running faster than idle) you are not replenishing battery very much..if at all.

 

[SawMaster]

Almost all of todays cars have nearly full or better alternator output at idle. The computers balk at low voltages so they have to, or the car could quit. This also allows for a smaller battery since it has less work to do. Not good for recording while parked since you can use only 30% of the car bettery before damage begins. Just use a powerbank and problem is solved.

Phil

 

[Paul Schmehl]

This subject fascinates me, so I did some digging. I found this site that lets you play around with the numbers. http://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.htm

So, my dash cam is protected by a 1 A fuse. Taking that as the absolute maximum draw, at 5 V that's 5 Watts of power. 5 Watts at 12 V is .416 amps. So what @dash riposki said is correct.

This site has a calculator for battery drain. http://www.gizmology.net/batteries.htm Car batteries are typically rated in cold cranking amps (starting power) not amp hours (deep cycle), but a typical small car battery has about 45 aH capacity. Plugging those numbers into the formula shows a 20% discharge in 24 hours or about .833 % discharge per hour. According to this chart - http://modernsurvivalblog.com/alternative-energy/battery-state-of-charge-chart/ - a 20% discharge of a 12 V battery would result in a battery voltage of 12.5 volts. Some protection systems will cut off power to the camera at 12 v or slightly higher (12.1 or 12.2) That's about a 50% discharge.

So, if a car is used every day, allowing the battery to recharge to 100%, you would not need protection against discharging.

Of course all of this is subject to the variabilities of your particular setup, the current draw, the state of your battery and a thousand other variables. So take it all with a grain of salt.

 

[lacibaci]

I use this for all kinds of USB power troubleshooting:

 

[Nigel]

Offhand.. I would think the power draw on the battery to start the car once is equivalent to "many" hours of camera use. Unless you drive the car (thus keeping the engine running faster than idle) you are not replenishing battery very much..if at all.

I've calculated 1 start = around 17 minutes recording on one camera, or if like me you have front and rear cameras then that is only 8 minutes 30 seconds. Camera uses about 2W, starter motor uses 1KW, but only for 2 seconds, after about 2 seconds the starter motor is up to speed so wont use as much even if it takes longer for the engine to start, I think most engines start in less than 2 seconds.

However standard batteries don't charge very fast so it can easily take 10 minutes to put the power to start the engine back into the battery before you can start putting power for the camera into the battery. Better to start the engine once a day and go for a decent drive.

Normally, if you start the engine and leave it idle for a few minutes, it will charge the battery at double speed for the first few minutes. The issue with not charging at idle was solved sometime in the 1960s when we started using alternators instead of dynamos to generate the electrical power.

 

[SawMaster]

There's a lot of 90's and early 00's cars designed for the battery to do some of the work at idle if a lot of current was being used, you can spot them by watching their headlights dim slightly when they stop .Some GM cars were notorious for this as it greatly shortened battery life if you did a lot of city driving at night. Aftermarket manufacturers sold a regulator that gave higher voltage to compensate which cured that issue. I had to do that for mine; battery life went from 1-2 years to 5+ years using the same mid-grade battery. I've heard of similar with some European and Asian cars of this period. Older cars had smaller alternators still, and their much larger batteries masked the deficiency. GM refused to admit there was a problem so they wouldn't have to fix millions of cars, and since it wasn't a safety-related item no recalls were issued

And an alternator cant charge at 'double speed', it can only give what is rated at or close to that. As a lead-acid battery (along with most battery technologies) reaches a higher state of charge it's internal resistance also rises which causes more of the charging current to become heat instead of becoming stored energy, so less charge happens in a given time. Thus the initial charge does go faster, but the alternator or car has nothing to do with it- it's inherent in the battery. The same effect happens when charging a battery from house current. The higher the charging rate is, the more the internal resistance increases exponentially. That's why a long slow 1-2A charge can 'revitalize' a battery that a car's alternator can't charge sufficiently; you're overcoming more of the now lower resistance. Ask any used car dealer and they'll tell you it works long enough to sell the car even if they don't know why it works

Lead-acid starting batteries are not designed for long duration loads, they're best at short high current loads like a car starter. Deep-cycle lead-acid batteries are the polar opposite so while either will work in any role, using them for what they weren't designed for will greatly shorten their service life. Some 'marine' batteries are advertised as good for both jobs but actually aren't all that good at either. It's always best to use things as they were designed for which is why so many use powerbanks for their cams when parked. That doesn't mean it can't be done; my last van sustained a Mobius running full-time for 4 1/2 days on a 4+ year old starting battery without any noticeable lack of starting power. It was a huge battery compared to today's cars, there was room for 2 sizes bigger than the factory battery and I used it all, which is why it worked for me. I wouldn't even try that with a new car

Phil

 

[Nigel]

And an alternator cant charge at 'double speed', it can only give what is rated at or close to that...

For the first few minutes after starting, mine charges the battery at 14.2V and then drops to 13.6V. How quickly the battery actually charges will depend on it's state of charge and the actual voltage is affected by the amount of power being used by lights etc but simplifying things greatly, it does charge at double speed for the first few minutes.

 

[dash riposki]

don't forget the somewhat modest amp draw of other electronic stuff in the car, clocks, etc.

A lot of the German cars shipped to the US on boats have a small solar charger sitting on the dash to keep the battery topped up during the several week journey, and probably a few weeks sitting outside in the ports. I can't imagine they get much sun sitting in the ship, which is like a steel parking garage inside.

 

[John Nixon]

Well, returned today to find a load of helpful posts. Thank you all soooo... much. This is an impressive forum site. Thank you all, and I believe I now have all the info I need to help the lady in question.
Kind regards
John

 

[Lola]

Look into a "Vico Power Plus " it is a new electronic piece of equipment that enables one to automatically cut off battery drain after a certain amount of time plus other cool things associated with controlling ones battery and dash cams.
Pier28 sells them and is very knowledgeable about their functions. I believe he has a video of the unit on his website explaining things. Just do a search on Google for Pier28.

 

[lacibaci]

don't forget the somewhat modest amp draw of other electronic stuff in the car, clocks, etc.

A lot of the German cars shipped to the US on boats have a small solar charger sitting on the dash to keep the battery topped up during the several week journey, and probably a few weeks sitting outside in the ports. I can't imagine they get much sun sitting in the ship, which is like a steel parking garage inside.

You mean like this one:

This was in my 2003 Jetta. Still works.