GT680W Super-Capacitor (& Stealth) Mod

FWIW, just to be certain, I just went out to my vehicle and ran some tests. The voltage cuts out from the USB cigarette lighter adapter the instant the ignition shuts off. No charge is retained according to my voltmeter/ammeter. The charger has an LED indicator on it that shuts off immediately as well. I can also unplug the GT680W at the camera itself and it will still run for ten seconds after it loses power at the port, so it is clearly running off the super-caps.
 
Last edited:
Usually if left dashcam with supercap for 1-2 horus, then it starts-up 4-5 sec ( @Panorama 2 ), but if left over night, then it takes 6-8 sec to recharge supercaps and another 3-4 sec to start up. Try to leave yours over night and measure difference in time start-up.

So, I've spent several days testing this and thought I would report back with my experience.

For three days in a row I've left the dash cam overnight....generally about 18 hours from parking my vehicle in the early evening around 6PM to starting the vehicle again around noon the next day. Each time, I get the same results. It takes 4 seconds from the time I turn the ignition switch in my truck until the GT680W has booted up and begins to record video. If I drive somewhere, park the vehicle and start it again, let's say a half an hour later it again takes only 4 seconds to boot up and begin recording. It seems to always have a full power right away with no waiting for the supercaps to recharge.

I know there should be some self-discharge from the super-capacitors, so I don't know the explanation or why there would be such a difference with your experience with the Panorama II Niko. Maybe there is something different about the circuitry in the GT680W or maybe the capacitors I used somehow have the ability to hold a stronger charge for a longer period of time. Another possibility is that there might be some difference between how quickly my vehicle (Toyota) provides power to the cigarette lighter circuit after turning the ignition switch than your vehicle.

I will keep checking this to see if there are any changes. Also, one of these days, maybe on the weekend I may be able to leave my vehicle for a longer period without starting it up.
 
Hello. I have a question: do you think that the Mobius Super Capacitor can be used as replacement of the Shadow's GT680W battery?
 
Hello. I have a question: do you think that the Mobius Super Capacitor can be used as replacement of the Shadow's GT680W battery?

Not likely.

The Mobius Super Capacitor module you can buy is made from two 5 farad caps in order for it to be small enough to fit into the case. The super-capacitors I used in the GT680W are 10 farad and therefore have greater energy storage potential.
The 5 farad capacitors probably work in a Mobius because the camera has no LCD screen, speakers, GPS or other energy draining features found in a typical dash cam like the GT680W.
 
Sorry, my bad. Thanks !
 
OK, as mentioned in the other thread regarding a DIY super-cap mod despite an extended period of initial success, after about five weeks I began to run into problems with occasional corrupted files, failure to capture the last file and failure to launch the splash screen and sound the shut-down chime after installing super-caps in my GT680W.

So today at the suggestion of @wrdjr20 I did some testing. I dug out some hook type probes I have for my multi-meter and used them to monitor the voltage at the super-caps for an extended period of time. They power up fairly rapidly but only go to 4.20 volts. The camera powers up normally and begins to record. The voltage then drops slowly to about 4.15 volts and stabilizes but it can drift down to 4.06 volts. I can run the camera and record for extended periods this way. When I then disconnect the camera the voltage begins to drop rapidly and goes down to 2.95 volts and stays there briefly. Then, the voltage begins to recover and increase slowly until it gets to 3.08 volts where it stabilizes again and will eventually creep up to 3.10-3.12 volts where it will stay at that voltage more or less "permanently". At this voltage it will continue to maintain the date, time and other settings. Unlike before, on power down, I no longer get the shut-down chime or logo screen but the LED on the bottom of the camera continues to pulse for 8 seconds.

When I first did this mod I would get readings slightly above 5 volts, maybe 5.2-5.4v at the capacitors, so it "appears" that either something has failed within the caps or they are no longer charging fully.
 
Last edited by a moderator:
Interesting. I am wondering if one of the capacitors is shorted and the other has the entire 4.20 volts across it. In such a case, being way over max rating, it could be leaking some current which would prevent the charge from reaching 5 volts. The easiest way to prove this is measuring the voltage between ground and the copper bridge. If when charged it measures close to 0 volts or close to 4.2 volts then the above is true.

If the voltage measures about 1/2 or 2.1 volts then both capacitors are leaking (damaged) or the regular is having problems charging the capacitors and powering the electronics. Switching back to the battery will tell us which is at fault.

The conditions you are seeing: the voltage dropping rapidly to 2.95 volts then creeping back up to 3.1 volts makes since. It is very unlikely that the display will operate at that low of a voltage. Explains why it shuts down. Same is true of the chime. The processor requires 3.3 volts, may or may not reboot at 2.95 volts. I will have to look at the specs. Whether it reboots or not it may still be able to flash a LED at very low current. It is unlikely that the last file on the micro SD card would be closed resulting in a corrupted file especially if a reboot occurred.

Now I am basing the above thoughts on my working knowledge of embedded controls, without knowledge of how the GT680W's firmware handles brownout resets and the minimum voltage ratings for the processor, display, and supporting chips they are using. But I will see what I can find out.

In the meantime if you could measure the voltage on one capacitor, that may help identify the problem. If not the next step is trying the battery to see if that corrects the problem. If the battery works we still may be able to use capacitors, but they may need to be balanced. We can address that later.
 
Thanks. It will take a day or two to follow up here. You know, I was aware that I could damage the caps by installing the copper bridge so I tried to be very careful about not applying too much heat when I did the solder job. Still, I wonder if I could have damaged one (or both) of them. I made the copper bridge from a copper pipe hanger that I cut with a tin snips and hammered flat on an anvil but I may try this again with just twisting the leads of the caps.
 
This is what I have found so far,
Novatek NT96650 processor: Most chip I/o will operate down to a minimum voltage of 1.62 volts. However the minimum operating voltage for the SD Card I/O is 3.0 volts. So during the time your capacitors are below that, it is unlikely that anything is being written to storage and even if the file is closed then file would likely be corrupted. The speaker output which generates the chime also requires a minimum operating voltage of 3.0 volts which also explains why the shutdown chime does not work. The core logic runs at 1.0 volts so you are not experiencing brownout resets. Explains why the LED continues to flash. Other functions that require a minimum of 3.0 volts are: General I/O interface, MIPI DSI, DLL, Receiver High Speed interface, USB transceiver, ADC, DAC, and Audio Codec. To insure proper function, design specs would never allow it to drop anywhere close to 3.0 volts during operation. Please note: Since the 3.3 volt supply to the chip is being supplied by an voltage regulator powered by the capacitors, it will drop some voltage also. So even when your measuring voltages around 3 volts, the processor is likely seeing less then 2.5 volts, which makes things even worse. It is unclear if the display interface is affected by the voltage drop. The specs say the LCD interface minimum voltage of 1.62 volts. However, The design could use the High Speed interface for some display control functions and that interface will be affected. Also, since I do not know what display is being used, I have unable to determine its minimum operating voltage. But we know it is being affected.
 
Some of this is way above my head but fascinating & enlightening nevertheless as it accounts for why some functions work and some don't. Thanks.
 
@Dashmellow: very neat work. loved the paint job.

regarding your capacitor issue, in your next implementation, you may want to consider the use of balancing resistors to avoid overvoltage issues across each cap while using super caps in series. a voltage rating of 2.7V is dangerously close to the 'theoretically ideal' voltage of 2.5V across each cap in a 5V implementation.

this link is good to read too - Why do ultra capacitors require balancing
 
@Dashmellow: very neat work. loved the paint job.

regarding your capacitor issue, in your next implementation, you may want to consider the use of balancing resistors to avoid overvoltage issues across each cap while using super caps in series. a voltage rating of 2.7V is dangerously close to the 'theoretically ideal' voltage of 2.5V across each cap in a 5V implementation.

this link is good to read too - Why do ultra capacitors require balancing

This is exactly what I was thinking lead to his problem in the first place, not balancing the capacitors. Nice link for those considering installing capacitors in their dashcams.
 
This is exactly what I was thinking lead to his problem in the first place, not balancing the capacitors. Nice link for those considering installing capacitors in their dashcams.

@Dashmellow: very neat work. loved the paint job.

regarding your capacitor issue, in your next implementation, you may want to consider the use of balancing resistors to avoid overvoltage issues across each cap while using super caps in series. a voltage rating of 2.7V is dangerously close to the 'theoretically ideal' voltage of 2.5V across each cap in a 5V implementation.

this link is good to read too - Why do ultra capacitors require balancing

Thank you both for your feedback. As I mentioned earlier in this thread, I know a thing or two but am not an electronics guy as much as I am a tinkerer willing to experiment and try things. Things don't always work as well as hoped or planned but it's fun and I learn new things.

Thanks for the link. The resistors make sense to me from the little I've read so far and I will study it further. If I understand from what you are saying, it looks like overvoltage led to partial failure of the super-caps which would explain the initial success. Is this what you are suggesting?

BTW, I was partially inspired to try this because of the super-caps I put in my Mobius cameras that have worked so well. The ready made super-cap module you can buy has no resistors, although as I understand it, some accommodations have been included in the firmware.
 
Last edited:
In order to avoid an unbalanced condition the capacitors in the kit are measured and matched, capacitance wise, resulting in balanced capacitors. Equal capacitance means equal voltage drop. Manufacturers can do this because they have large supplies.
 
yes dashmellow you understood correctly. our guess is over voltage issues led to the failure of one of your caps.

i've not looked into the mobius implementation but some of the dash cams seem to have a 3 wire connection module to the LiPo battery - i'm guessing this is to derive a dual voltage supply from a single battery. sometimes this too involves a balanced resistor implementation - maybe this worked as a kind of a balanced resistor bridge for the super caps. or maybe you got plain lucky with the mobius caps and got yourself an 'accidentally' matched pair of caps with close enough tolerances (ESR & leakage current wise) :)
 
Thanks again. Well.....back to the ol' drawing board, I guess.
FWIW, the Mobius battery and Supercap modules are a two wire affair. Most people are reporting positive experiences installing caps in the Mobius.
 
This does not mean you can't use capacitors, you just need two balance resistors. We can help
With the selection. I plan on installing them on my GT680W soon once I'm sure it is fully functional. I've only had it a day now.

I would recommend the you test it with the battery first to eliminate and issues the capacitors might have caused. It's unlikely but it is always good to start with a verified functional unit before making any modifications.
 
Thanks so much! I have other more pressing fish to fry at the moment, so I may have to put this project on the back burner for a brief time but am very interested in exploring this further, especially with some knowledgable help.
 
OK, so I've been reading up a bit on balancing ultra-caps and trying to stretch my limited understanding of electronics. At this point, my question is, how do I determine the type and value of resistors to install? Some of the reading @outofthebox referred me to seems to indicate I don't have the appropriate equipment to properly measure ultracap discharge. My modest priced multi-meter certainly isn't up to the task.

I think for now, when I get some time I will re-install a battery and see how the camera is working. If the camera works but I am ultimately unable to go with new super-caps I am considering remote mounting a battery to get it away from the hottest place on my windshield.
 
@Dashmellow, do you have replacement capacitors and do you have a data sheet?
If so, can you tell me the leakage current?
If not, can you tell me where you purchased them from and a part number?
Then I will see if I can get the data sheet.

The simple approch is to select resistor values that allow 10 times the leakage current.
Purchase some 1% resistors, use an ohm meter to select two that are closely matched.
Breadboard the circuit, for temporary testing, before installing in the camera .
Apply 5volts and measure the voltage drop across each capacitor to make sure they are idenical .
If not we can swap is a slightly higher resistor to raise the voltage, or lower resistor to lower the voltage to balance the voltage.

This should be good enough for this application. I can step you through this process.
The first step is determining the leakage current and calculating the resistor values.

@outofthebox, if you have any suggestions to add, please do so.
 
Back
Top