Unique issue That I think can be solved with a capacitor.

Thread Starter

hank75

Joined Mar 22, 2019
16
Hi, I'm Henry and new to the forum, I am an automotive technician
Some may think this should be in the automotive thread, but I think I'll get better results here.
So, I installed a dash cam that is basically a bigger rear-view mirror, this:
https://www.amazon.ca/TOGUARD-Waterproof-170°Wide-G-Sensor-Detection/dp/B07DN8Q8Q6
It is powered by a USB that runs off the cars ACC plug(cig lighter), so 12-14 volts to (usb) A 5 volts converter.
It only runs while the ACC socket is powered, and the dash cam shuts down when acc socket is unpowered
What happens is when the dash cam initially turns on, there is a display in the mirror glass of what the cam is recording, then after 30 seconds that image turns off so you can use the rear-view as its intended for.
My 2017 Ford Escape is wired so the acc sockets are always powered on, so the cam would never shut down.
I bought a USB hardwire kit that only is only powered with key on, and it works great: This:
https://www.amazon.ca/SHISHUO-Dash-Cam-Hardwire-Kit/dp/B07FD3TTVN/ref=sr_1_5?keywords=usb+to+12+volt+kit&qid=1553553104&s=electronics&sr=1-5
So here's my problem;
My vehicle has a feature called Auto Start/Stop, basically when you stop with your foot on the brake pedal and vehicle is in gear( waiting at a stop light) the engine shuts off and will remain off until you lift your foot from the brake pedal or put it in park, then the engine automatically restarts and away you go.
What's happening is there must be a momentary voltage drop in the fuse panel when the engine auto re-starts and what happens is the recording image pops back on the display for the 30 seconds which is annoying and blocks my rear-view for that time.Bare in mind the cam is not actually performing a couple restart, just image pops up on the mirror.
It will not do this if I use the provided ACC plug, but I want to use the hardwire kit I installed so I don't have to keep unplugging and plugging in that ACC plug, I bought the hardwire kit so it is a " set it and forget it"
Would a capacitor in-line with the 12 volt feed hold the voltage momentarily while the vehicle re-starts? I know something greater than 15 volts is needed but, What rating of cap would you use?
Thanks
 
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Yaakov

Joined Jan 27, 2019
1,547
A capacitor could be a good solution. To decide what value you need, you'll have to work out the current draw of the USB power supply and the time of the sag. You could guess at it, and try some things, but if you can make some current measurements, you can do a better job.
 

paulktreg

Joined Jun 2, 2008
771
It sounds feasible but I am by no means an expert.

The only problem I for see is the capacitor across (not in-line) the 12V feed to the camera is still going to be discharged by the rest of the cars systems but you could try installing a diode as well to stop this happening. This would reduce the supply to the camera by 0.6V which may or may not be a problem?

You could try a 1N4004 in series with the positive camera supply followed by a 4700uF 25V electrolytic capacitor across the supply.
 

Thread Starter

hank75

Joined Mar 22, 2019
16
It sounds feasible but I am by no means an expert.

The only problem I for see is the capacitor across (not in-line) the 12V feed to the camera is still going to be discharged by the rest of the cars systems but you could try installing a diode as well to stop this happening. This would reduce the supply to the camera by 0.6V which may or may not be a problem?

You could try a 1N4004 in series with the positive camera supply followed by a 4700uF 25V electrolytic capacitor across the supply.
something like this paulktreg?
circuit.png circuit.png circuit.png circuit.png circuit.png
 

MrSoftware

Joined Oct 29, 2013
1,571
Yes you have the right idea, though you may have to add more capacitance depending on how much current the camera draws. 4700uF is a reasonable starting point.
 

Thread Starter

hank75

Joined Mar 22, 2019
16
Thanks all, I think I will go with a little more capacitance as it will do no harm and the system is actually running a front and rear camera simultaneously.
I think it will be a matter of trial and error,
I’ll update after some trials
 

WBahn

Joined Mar 31, 2012
24,709
It sounds feasible but I am by no means an expert.

The only problem I for see is the capacitor across (not in-line) the 12V feed to the camera is still going to be discharged by the rest of the cars systems but you could try installing a diode as well to stop this happening. This would reduce the supply to the camera by 0.6V which may or may not be a problem?

You could try a 1N4004 in series with the positive camera supply followed by a 4700uF 25V electrolytic capacitor across the supply.
The diode shouldn't drop the 5 V output of the converter unless it drops the input voltage below the minimum input voltage for the converter, which should idealy be able to go well below 12 V to account for weak batteries.
 

Thread Starter

hank75

Joined Mar 22, 2019
16
The diode shouldn't drop the 5 V output of the converter unless it drops the input voltage below the minimum input voltage for the converter, which should idealy be able to go well below 12 V to account for weak batteries.
Very true
 

oz93666

Joined Sep 7, 2010
669
4700uF seems rather small ...

This is a similar problem to that encountered by people who have large sound rigs in their cars , for a split second their amplifier may draw too much for their battery , so they have a capacitor across it .....

They are super capacitors , this one is 5 Farads! ... ( one farad =1 million uF) this one is a thousand times more powerful than the one suggested 4700uF

The unit below is a supper capacitor module designed for car use 2F ,15V ... Only 6 pounds inc. delivery... https://www.ebay.co.uk/itm/10F-3V-Super-Capacitor-Module-Pack-2F-15V-Car-Audio-Electrical-Stabilizer-DIY/264009044754?hash=item3d782a5312:g:e3sAAOSwv7pb1CAc

Having one of these across your battery will also extend battery life ... help with the high current needed to start engine.



There are many different sizes on eBay , apparently they ....

"1. Raise the engine power to make the throttle response more brisk and sensitive.

2, to improve the low-speed driving car phenomenon, so that shifting more smoothly.

4. Spark plugs that provide power evenly to the cylinders make the engine work more smoothly.

5, to reduce the phenomenon of idling jitter, making it more stable.

6, to reduce clutter and improve the sound quality of the car audio system.

7, protect the battery and the original car electrical circuit system, reduce its load and extend the service life.

8, shorten the car engine startup time.

1. Reduced load on the generator circuit system:
The ignition voltage of the engine is stabilized, the spark plug ignition current is enhanced, the torque output is more abundant, and the throttle response is quick and quick. When a super capacitor rectifying regulator is not installed, the current generated by the generator directly reaches the battery and is ......"

https://www.ebay.co.uk/itm/16V-20F-Ultracapacitor-Engine-Battery-Starter-Booster-Car-Super-Capacitor-new/302873768157?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=20140122125356&meid=b8deb05b934847bba5e3faf6c4977b0f&pid=100005&rk=5&rkt=12&mehot=pp&sd=264009044754&itm=302873768157&_trksid=p2047675.c100005.m1851
 
Last edited:

WBahn

Joined Mar 31, 2012
24,709
The amount of power drawn by "a large sound rig" is on a completely different scale than the power drawn by a USB-powered back-up camera.
 

cmartinez

Joined Jan 17, 2007
6,469
Thanks all, I think I will go with a little more capacitance as it will do no harm and the system is actually running a front and rear camera simultaneously.
I think it will be a matter of trial and error,
I’ll update after some trials
If it's any help, I had exactly the same problem with different electronic equipment that I installed in a car, and I solved it in exactly the same way, using a very large cap preceded by I diode. And I'd seriously consider crutschow's suggestion of using a schottky diode for this application.
 

oz93666

Joined Sep 7, 2010
669
The amount of power drawn by "a large sound rig" is on a completely different scale than the power drawn by a USB-powered back-up camera.
Certainly ... but the audio high demand is for less than 1 sec ... I think TS mentioned 30secs ...

there's no disadvantage to using a high value capacitor ... they're ridiculously cheap and have many other advantages as listed above.
 

WBahn

Joined Mar 31, 2012
24,709
Certainly ... but the audio high demand is for less than 1 sec ... I think TS mentioned 30secs ...

there's no disadvantage to using a high value capacitor ... they're ridiculously cheap and have many other advantages as listed above.
The 30 seconds is how long the camera image is displayed in the rearview mirror after it is powered up.

The engine starts almost instantly -- it has to otherwise it couldn't be used this way. Imagine if you are at a stop light and there was even a two or three second delay between the time you let off the brake and stepped on the accelerator and when the car started to move. These systems are typically design to have the engine restarted and ready to go in under half a second, the goal being that the restart begins as soon as you release the brake and is finished by the time your foot presses the accelerator.
 
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oz93666

Joined Sep 7, 2010
669
The 30 seconds is how long the camera image is displayed in the rearview mirror after the engine starts.

The engine starts almost instantly -- it has to otherwise it couldn't be used this way. Imagine if you are at a stop light and there was even a two or three second delay between the time you let of the brake and stepped on the accelerator and when the car started to move. These systems are typically design to have the engine restarted and ready to go in under half a second, the goal being that the restart begins as soon as you release the brake and is finished by the time your foot presses the accelerator.
I initially just scanned though post 1 .... having just read it all now , I get the picture ... this car is constantly starting and stopping , cranking the engine (100's Amps) many times a day .....

This makes it even more imperative to get a super capacitor across the battery , to ensure a decent battery life ... I would get a big one .. these capacitors last virtually forever......

I'd be willing to bet a cost analysis would show stop/start cars cost more to run ... minimal saving of fuel , against reduced battery life , wear on starter motor etc ...Of course emitions are reduced
 

Thread Starter

hank75

Joined Mar 22, 2019
16
Any vehicle that uses the start/stop technology always use AGM (Absorbent Glass Mat) battery’s which are more characteristic of a deep cycle battery and yes a more robust starter.
I’ll have to brush up on my diode knowledge
to understand the differences.Any reference’s here would be helpful, but I will search.
 

WBahn

Joined Mar 31, 2012
24,709
I initially just scanned though post 1 .... having just read it all now , I get the picture ... this car is constantly starting and stopping , cranking the engine (100's Amps) many times a day .....

This makes it even more imperative to get a super capacitor across the battery , to ensure a decent battery life ... I would get a big one .. these capacitors last virtually forever......

I'd be willing to bet a cost analysis would show stop/start cars cost more to run ... minimal saving of fuel , against reduced battery life , wear on starter motor etc ...Of course emitions are reduced
Depending on conditions, they save roughly 2% to as much as about 15% in fuel, with 10% seeming to be pretty common if you aren't running the A/C. A lot of it depends on if you are in a lot traffic where you sit at lights (or otherwise in traffic) for a long time. That saves more. But if you are in warm weather and are running the A/C, then you save a lot less because they will detect that the cabin temperature is climbing (since the A/C system doesn't have much effective thermal mass) and will restart the engine early and usually will not stop it again until it detects that your speed got above some threshold. The same is true if you creep forward at the light, so there is a significant driver-behavior dependence involved, too. Cold whether isn't as much of an issue because there is a lot more thermal mass involved in the heating system.

The car itself is significantly different than a similar model without the stop and go feature. The starter is specifically designed for the additional duty, the engine itself is designed with different components, such as bearings, to make starting a warmed-up engine easier and less wearing. As an aside, starting a fully-warmed up engine that has just been shut off is usually very easy even on a regular-ole vehicle; all of my vehicles, including The Beast with its 460 c.i.d. engine, will start with just a tap of the starter (well under a quarter second), and the lowest number of miles on any of those engines is 127k. The batteries are deep-cycle batteries and the electrical system is designed to deal with the loss of alternator output for extended periods of time. I would not be at all surprised if there aren't already supercaps there as part of doing so.

But the TS is asking about keeping his backup camera from resetting, and that isn't going to require a 5 F supercap.

Oh, and don't infer that I am a fan of start/stop technology. From my perspective, it is just one more thing that is likely to make a car end up in the repair shop on a regular basis, particularly since I don't baby my vehicles -- they work hard and get put away wet.
 

oz93666

Joined Sep 7, 2010
669
To summarize this can either be fixed by having a big capacitor across the battery (Farad size) .. or a smaller capacitor (47000uF) at the appliance ... With the capacitor at the appliance , the resistance of the wires between appliance and battery should should isolate appliance slightly , keeping the voltage at appliance higher, during starting . ... Since the cost of 47000uF is very close to that of 2F , because of the other advantages a big capacitor seems sensible .....

I've been searching stop start cars ..... "According to Argonne National Laboratory, a 2-litre car will use around 0.7 litres per hour with zero load." ..... when moving the same car consumes about 10 liters per 100Km traveled

So if on a 100km journey you spend 1 hour stationary ... and that's totally still , not crawling along in a traffic jam ..... then stop start will save only about 5% (not 7% since some is lost in restarting inefficiencies ) .... Who spends 1 Hr stopped at traffic lights ??? ... a more realistic figure would be 3 minutes for an averaged 100km journey ... Zero for motorway journeys

in the most densest city perhaps 12 mins halted at lights per 100km traveled ...that's a 1% saving in gas...

Of course manufacturers selling these cars will exaggerate the benefits.
 
Last edited:

Yaakov

Joined Jan 27, 2019
1,547
To summarize this can either be fixed by having a big capacitor across the battery (Farad size) .. or a smaller capacitor (47000uF) at the appliance ... With the capacitor at the appliance , the resistance of the wires between appliance and battery should should isolate appliance slightly , keeping the voltage at appliance higher, during starting . ... Since the cost of 47000uF is very close to that of 2F , because of the other advantages a big capacitor seems sensible .....

I've been searching stop start cars ..... "According to Argonne National Laboratory, a 2-litre car will use around 0.7 litres per hour with zero load." ..... when moving the same car consumes about 10 liters per 100Km traveled

So if on a 100km journey you spend 1 hour stationary ... and that's totally still , not crawling along in a traffic jam ..... then stop start will save only about 5% (not 7% since some is lost in restarting inefficiencies ) .... Who spends 1 Hr stopped at traffic lights ??? ... a more realistic figure would be 3 minutes for an averaged 100km journey ... Zero for motorway journeys

in the most densest city perhaps 12 mins halted at lights per 100km traveled ...that's a 1% saving in gas...

Of course manufacturers selling these cars will exaggerate the benefits.
My X5 has autostop as well as autohold. Not only does it make driving more pleasant, if all cars in cities reduced emissions 5% it would be a if benefit. It really requires a modern engine in good condition, and it’s smart—if the engine is too cold, it doesn’t try. I find it quite nice.
 
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