No lithium batteries, No supercapacitors: No problem

[nhamilto]

The batteries or supercapacitors in the typical dashcam can be completely eliminated. The whole thing can be powered by the automotive ~14v power system.

non-switched 14v -> 25 minute timer relay module (FRM01 mode 10 or equivalent)-> 5v regulator -> dashcam usb power input

non-switched 14v -> 30 minute timer relay module (FRM01 mode 10 or equivalent)-> 3v regulator -> dashcam internal battery connection


So 30 minutes after ignition power is cut the cam goes into its shutdown routine and x minutes later it is shutdown while retaining the clock etc. on 3v power indefinitely. Of course timers could be adjusted to suit cam firmware and personal preferences.

 

[Kip]

This would still be a problem for vehicles with switched power sources to the dashcam. Once the power is cut, the dashcam, the relay, everything instantly loses power. It will still need a large enough capacitor or battery for the dashcam to save its current file to non-volatile storage. Since a dashcam has to be designed for many different vehicles, they will always need either a battery or capacitor somewhere. It might work if you have access to a constant non-switched live as you say, but, not everyone does. Only supporting vehicles with constant non-switched live in this way would just serve to limit your potential market share. Also, if during an accident, you lose your constant non-switched power, you also lose your footage of said accident unless the camera has its own reserve power (in others words... battery or capacitor).

By the way, aren't capacitors more reliable long term vs relays? I thought relays wore out over time.

 

[jokiin]

The batteries or supercapacitors in the typical dashcam can be completely eliminated. The whole thing can be powered by the automotive ~14v power system.

there are some models that have neither batteries or capacitors, they do need to be hardwired but in the event of an accident where all power is lost you will lose the last file

 

[nhamilto]

Yes this will require a constant power source (fuse tap). The lifetime of a 10A rated relay switching ~1A a few times a day should not be a practical concern.

If the accident is severe enough to destroy the car's power system you are probably dead anyway.

 

[Kip]

If the accident is severe enough to destroy the car's power system you are probably dead anyway.

I wouldn't be so sure. Modern 5-star Euro NCAP rated cars in a bad enough collision could have their engine bays near enough obliterated and the passenger safety cell could remain relatively undamaged. Depending on the rates of deceleration, you could walk away from something bad enough to disconnect your battery or other electrical wires.

Even if you didn't survive, if the evidence and any other party involved did, your family could at least get answers as to what really happened.

Example:

 

[jokiin]

If the accident is severe enough to destroy the car's power system you are probably dead anyway.

you can easily damage a vehicle battery in the engine compartment in an accident without it being a fatal accident, you only need to have cable off to lose power

 

[nhamilto]

So it comes down to the user's desire to record fatal/near fatal crash events. In my mind I consider dashcams to be more for insurance and legal claims.

 

[Nigel]

I wouldn't be so sure. Modern 5-star Euro NCAP rated cars in a bad enough collision could have their engine bays near enough obliterated and the passenger safety cell could remain relatively undamaged. Depending on the rates of deceleration, you could walk away from something bad enough to disconnect your battery or other electrical wires.

That used to be the case, but recent cars have a lot of battery protection so that the battery doesn't disconnect in any survivable crash. The battery is an essential part of the safety system, required for air bag deployment, seat belt tensioner deployment, electronic stability systems, it is even important for steering these days since steering has become electrically assisted, plus part of the NCAP test is that the hazard lights activate in an accident and that the central locking unlocks to give rescuers access. The battery is essential, you will no longer find it placed next to the radiator as the first thing to be crushed.

 

[Kip]

Let's say (hypothetically) you design and manufacture a dashcam with this time delay relay system. You hand them out to your family members as a free gift. One day, one of those who had one of your cameras is killed in a fatal collision. Due to not having a battery or a capacitor, your camera fails to record that event (because somehow, the connection to your camera is severed in the accident). How would you feel?

Even if the vehicle battery is better protected, the camera could come off its mount, windscreen smashed, the camera power cable could come out, be severed, etc.

 

[jokiin]

So it comes down to the user's desire to record fatal/near fatal crash events. In my mind I consider dashcams to be more for insurance and legal claims.

Not sure how you arrived at that conclusion

 

[jokiin]

The battery is essential, you will no longer find it placed next to the radiator as the first thing to be crushed.

You might be surprised to learn that not everyone owns new cars

 

[Nigel]

You might be surprised to learn that not everyone owns new cars

, I wasn't thinking about Oz when I wrote that!

Actually, my car has the battery directly behind a headlight, so close it needs removing to change the bulbs, which probably puts it more at risk than the radiator, but it was designed before NCAP which is very unusual for a car currently on UK roads.

 

[jokiin]

I have one car that has the battery behind the headlight also, can't imagine it standing up to too much of a hit

 

[russ331]

... recent cars have a lot of battery protection so that the battery doesn't disconnect in any survivable crash.

This 2015 car has a pyrotechnic device on the negative terminal to disconnect the battery in a collision.

When my girlfriend had an accident in her 2011 Honda, the impact did not trigger the airbag, but did disable the electrical system.

A dashcam without an internal battery or capacitor, to save the file being recorded when an accident occurs, isn't fit for purpose.

 

[Nigel]

This 2015 car has a pyrotechnic device on the negative terminal to disconnect the battery in a collision.

When my girlfriend had an accident in her 2011 Honda, the impact did not trigger the airbag, but did disable the electrical system.

A dashcam without an internal battery or capacitor, to save the file being recorded when an accident occurs, isn't fit for purpose.

That is effectively a fuse which disconnects the starter motor and alternator in the event of a short circuit in those cables. It is also a way for BMW to make money out of your crash since a replacement is not cheap!

Since the alternator and starter motor cables go through the engine compartment they are likely to be damaged in an accident and are capable of carrying a huge current capable of starting a fire it is important to disconnect them. However it will not disconnect the safety systems, hazard lights, dashcam power or mobile phone power for emergency calls.

I think it may be necessary in a BMW due to the use of magnesium in the engine components, ignite that with a good powerful spark and you get a fire which is impossible to put out! However it also protects the power to the safety critical systems.

 

[nhamilto]

So for modern cars this is a viable idea just tap into the hazard light fuse. If you are stuck with an outdated car use a lithium/supercap backed dashcam.

And no the fusible link on your BMW is not a "pyrotechnic device" it is just a large electrical fuse.

 

[Nigel]

So for modern cars this is a viable idea just tap into the hazard light fuse. If you are stuck with an outdated car use a lithium/supercap backed dashcam.

And no the fusible link on your BMW is not a "pyrotechnic device" it is just a large electrical fuse.

I think a super cap is still sensible, and should be getting more practical as the chips become more power efficient and are fitted with better power control circuits.

Using the hazard light fuse would be unwise since the hazard lights are located in the areas most likely to be hit so are quite likely to experience a short circuit and blow their fuse, if you use a fuse tap on the hazard light fuse then make sure you insert it the correct way around to tap in before the hazard light fuse instead of after.

The biggest problem of not having a battery or super cap is that there is no way to turn the camera off without corrupting a file, except by pressing the power button, if you install a battery protection device and it turns the power off then a file will get corrupted, possibly the card format will get corrupted.

BMW do use explosives in the fuses for the starter motor and alternator, but they are just hi-tech fuses, plus the cables are shielded so that those cables can not produce sparks in the engine compartment. On older cars those cables have no fuse due to the amount of power they carry so a short circuit in them takes out the entire electrical system.

 

[nhamilto]

The additional fuse in a properly installed fuse tap is in parallel. There is no before or after. The hazard light fuse and the dashcam fuse are completely independent. A blown hazard fuse has no effect on the dashcam circuit.

Camera fuse is purple and the hazard fuse is blue in the pic.

 

[Nigel]

The additional fuse in a properly installed fuse tap is in parallel. There is no before or after. The hazard light fuse and the dashcam fuse are completely independent. A blown hazard fuse has no effect on the dashcam circuit.

Camera fuse is purple and the hazard fuse is blue in the pic.

View attachment 23586

That is an improperly installed fuse tap since it allows you to draw more power from the source than it was designed for if both circuits are loaded to the rating of their fuses. However if placed the correct way around then a short in the hazard circuit would take out both circuits.

 

[normm]

That is an improperly installed fuse tap since it allows you to draw more power from the source than it was designed for if both circuits are loaded to the rating of their fuses. However if placed the correct way around then a short in the hazard circuit would take out both circuits.

Looks fine to me. 14V fed to each individual fuse. If placed the other way around as you suggest, the 14V would flow through the hazard fuse before then being fed into the cam fuse. Now THAT could cause problems.