Passthrough charging of power banks

No.

See THIS POST for more information on the topic.

Does "thermal runaway (chemical combustion)" mean explosion?

If I do not mind if itshorten the lifespan of the bank's cells and prematurely reduce its charging capacity, can I use a normal powerbank for my purpose?
 
Thermal runaway = VERY nasty. Fire/sparks at 1200F+ degrees, hydrogen flouride gas which one lung-full can cripple you forever, and not easily extinguished. You don't take chances with LiIon, though when used correctly they have a huge amount of energy available at relatively low costs which is why most powerbanks use them.

Phil
 
Let say I am using a 20000mAh power bank and it supply power for dash cam for more than 24 hours then it will be empty.
When the power bank still has its own internal power and the car charger is on (engine on) at the same time, does the dash cam draw the power from power bank or does it draw power from the car?

My connection
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Does "thermal runaway (chemical combustion)" mean explosion?

If I do not mind if itshorten the lifespan of the bank's cells and prematurely reduce its charging capacity, can I use a normal powerbank for my purpose?

Since you've asked the exact same question for a second time I will give you the exact same answer for the second time. No.

Charging a lithium-ion battery bank at the same time it is discharging is an unwise idea, period!

The same factors are at work that will shorten the lifespan of the battery bank if you do this are the SAME ones that can create the conditions for it to catch fire or even explode. You cannot simply rationalize that you can tolerate a shorter lifespan for the device without accepting the fact that it also might eventually catch fire in the process. If you abuse lithium-ion batteries you don't get to pick and choose which problem you might encounter.

Despite all the evidence here on the pages of DCT, including in this very thread going back two years now people keep asking if pass through charging is viable and then when they hear an answer they don't like they insist that somehow they can do it anyway as if the laws of physics or electro-chemistry do not apply to them.

Powerbanks were never designed to be permanent uninterruptible power supplies for dash cams. They are designed for occasional back-up charging of smartphones and tablets or to temporarily power certain other devices.

While I provided a link to a previous detailed explanation of why lithium-ion batteries are placed under severe stress if they are charged and discharged at the same time I will repeat the explanation here in brief:

When the batteries are charged, electricity drives lithium ions from the cathode, across an ion-filled electrolyte fluid, and into the anode, which is made of stacks of graphite where it stores this energy until it is later released as electrons to power your device. As the battery drains, the lithium ions migrate from the anode back towards the cathode. So, if you try to charge the battery at the same time you are discharging it you are forcing ions to travel in opposite directions through the electrolyte at the SAME time and this causes much stress (and heat) within the cells. This stress eventually causes some of the lithium ions in the electrolyte to form metallic lithium (called plating) which is flammable and burns at a very high temperature. While some lithium plating is normal and is part of the aging process of a lithium cell, accelerating this process by placing the cell under undue stress causes problems and compromises safety. This rapid build-up of metallic lithium can under certain circumstances eventually cause a direct short circuit within the battery or it can merely become a source of fuel for a fire caused when the electrolyte chemistry overheats. Once this stress caused overheating process starts it can create a situation where the increase in temperature can change the conditions in such a way that causes yet a further increase in temperature in a chain reaction often leading to a full fledged fire that ignites the metallic lithium that has been forming. What can happen then is that hot volatile gases are released when the battery swells and finally bursts. Once the battery cell bursts these hot gases and burning lithium metal very suddenly come into contact with oxygen and this leads to a catastrophic result. That is what is meant by the term "thermal runaway" in regard to lithium-ion batteries.

Does "thermal runaway (chemical combustion)" mean explosion?

A "thermal runaway" as described above causes a fire that can't easily be stopped until all the fuel is used up. Usually, that will mean just a fire like in all those Samsung Galaxy Note 7 that were in the news recently after catching fire when their batteries failed. However, smartphones and dash cameras use a form of lithium-ion battery called a lithium-polymer which is basically a lithium battery in a foil wrapper. If these foil wrapped batteries have a problem most of the time they will simply swell up. If they burst and catch fire the expanding gases can easily escape.

Powerbanks are not the same. They are usually made with individual 18650 lithium-ion battery cells. A typical 20,000 mAh powerbank uses eight 25o0 mAh 18650 cells. These are sealed metal cylinders in the traditional shape of a typical alkaline cell. Unlike the foil pouched lithium-polymer battery you will find in a typical dash cam or smart phone these 18650 cells are not able to expand and release hot gases during a thermal runway and when enough pressure builds up inside them they can indeed explode. Of course, this will all be happening to the battery cells inside the sealed housing of the power bank thus compounding matters. Think hand grenade.

There are still other reasons not to charge while discharging. Isidor Buchmann, the battery scientist behind Battery University explains: "A portable device must be turned off during charge. This allows the battery to reach the set threshold voltage unhindered, and enables terminating charge on low current. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low. A battery may be fully charged, but the prevailing conditions prompt a continued charge. This causes undue battery stress and compromises safety."

Aside from the fact that charging a bank of lithium batteries at the same time as they are discharging is a demonstrably poor idea there are also other very important reasons not to engage in this practice.

For one thing, lithium-ion power banks were never designed to be permanently installed in an automotive environment where they are subject to constant vibration and shock that inherently causes stress to the cells in the unit just by itself without even any charging or discharging going on.

Then factor in @blink that you live in Singapore, a tropical climate that is always hot and humid. Heat is probably one of the most stressful things that can happen to lithium batteries, especially in the oven-like temperatures inside a car in a hot climate. So, if you permanently keep a powerbank connected to a charging circuit while it is at the same time discharging - which is something it was never ever designed to do and you do so inside the hot, vibrating, shock prone environment of an automobile, you are asking for trouble.

Fortunately, these types of fires and explosions are relatively rare but they do indeed happen on a regular enough basis to be of concern and this is the risk one is taking. Exploding lithium-ion battery cells have caused severe burns, loss of limbs, eyesight, and even deaths. Exploding or burning lithium-ion batteries have caused cars to burn up and houses to burn down.

So, I'll once again repeat your question along with my answer:

"Can I use a normal powerbank for my purpose?"

"No".
 
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Thanks Dashmellow. Very detailed answer.

I guess the only way to keep the dash cam turned on for 24 hours is after the engine is turned off, unplug the cable from car charger and plug the cable into the powerbank. When I turn on the engine, unplug the car charger cable from the powerbank and plug the cable into the car charger.

Is there any swtich/hub that I can keep my cables connected forever and just flick the switch button to "use power from car charger" or "use power from powerbank" to decide where to draw power?

The only real uninterruptible power supplies for dash cams method, is it to connect dash cam to the car internal battery?
 
I use two 20,000 mAh power banks to run four cameras when I am away from my vehicle. They will run for many, many hours. I bring them inside when I get home and after I let them rest for awhile and adjust to room temperature I recharge them and they are good for the next day. I paid about 20 dollars or so USD for each of these banks and they are both approximately two years old and working perfectly. If I wanted to run my cameras for longer than I do now I would simply buy extra power banks and swap the drained down ones for freshly charged ones and charge the drained down ones later when I get home.
 
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I use two 20,000 mAh power banks to run four cameras when I am away from my vehicle. They will run for many, many hours. I bring them inside when I get home and after I let them rest for awhile and adjust to room temperature and then recharge them and they are good for the next day. I paid about 20 dollars or so USD for each of these banks and they are both approximately two years old and working perfectly. If I wanted to run my cameras for longer than I do now I would simply buy extra power banks and swap the drained down ones for freshly charged ones and charged the drained down ones later when I get home.

You only use power bank and do not use car charger at all?

4 cameras, so I guess there 2 side doors have cameras too? Mounted to the side windows?

Are all powerbanks the same? What to choose?

It seems like there are 2 kinds

1 Normal kind with "battery" inside
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2 Slim kind http://www.mi.com/sg/pb5000/
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I use 12v USB chargers when I am driving and power banks when I park my vehicle and leave it. Sometimes I will simply leave the cameras plugged into the power banks instead of plugging and unplugging.

My four cameras are front, rear and sides and this gives me overlapped 360 coverage around my vehicle.

I've had excellent luck with generic Chinese power banks but there a dozens on the market and you need to be careful about what you buy. Seek out companies that have a web site with good contact information and that offer a decent warranty. Also, be aware that some power banks are counterfeits of name brands like MI.

I kind of like the PowerAdd brand and own one of their 20,000 mAh models.

Edit; PowerAdd sells a 32,000 mAh power bank that will run your camera for many, many hours before needing a recharge. https://www.ipoweradd.com/collectio...ah-battery-charger-for-laptop-and-cell-phones
 
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Does any powerbank have some beeping sound when it is going to empty. I mean I might not remember to check if the dash cam have power everyday, I might just leave it connected to the powerbank and forget about it until the powerbank is empty.
 
I'm not aware of any with that feature. I think if you get into the habit of using a powerbank everyday you would learn not to forget about it until it is out of power. BTW, if at all possible it is best not to let powerbanks drain down all the way but instead keep them topped off as much as possible. Like I mentioned earlier, if I were using them the way you intend I would have two or more banks and rotate them into and out of service on a regular basis keeping a fully charged one ready to go when needed.
 
Would powerbank explode because it is inside a hot car, the temperature inside a car is very hot (when no one is in the car, engine off).
 
Nobody said there's no way to run your cams continuously without worrying about the car starting battery; only that you can't do it with LiIon or powerbanks. A dual-battery setup with charge isolation like RV's use will do exactly what you want but it's not plug-and-play. And it can be done with a wet-cell deep cycle battery, a sealed lead acid battery(this would be my choice), or an AGM battery that can be mounted almost anywhere there is space for it. These batteries are much larger and heavier but are available in many capacities.

This is in the realm of a good DIY'er or you can get a RV mechanic to do it. Lowest DIY cost would be around $150 using scrounged wiring components and a DIY battery mount, but when done you'd have 12V to the cams for 8+ hours with the engine off. That can be extended to as many days as you have battery capacity (and money/space) for. Nothing to remember or do except checking the added battery occasionally and if done well totally safe. Not as simple as powerbanks but can be done- just not with LiIon involved.

Phil
 
Would powerbank explode because it is inside a hot car, the temperature inside a car is very hot (when no one is in the car, engine off).

Normally no. Hot interior temps such as a car sees parked in the summer will reduce the lifespan of LiIon batteries but only in extreme cases would I be concerned about safety. The quality of the cells and charger are the critical parts of LiIon safety (though not the only parts) and the best cells generally fail less catastrophically than 'venting with flame' like you see on the youtube vids. But there's always going to be a tiny percentage of catastrophic LiIon failures due to unseen manufacturing issues and also failures in safe use and charging. Just keep the powerbank out of direct sunlight and you should be OK anywhere save for a desert environment.

With good equipment and proper care, you're far more likely to be struck by lightning than to experience thermal runaway or venting with flames using LiIon. With low quality stuff anywhere in the mix or improper care the risks increase greatly.

Phil
 
With good equipment and proper care, you're far more likely to be struck by lightning than to experience thermal runaway or venting with flames using LiIon. With low quality stuff anywhere in the mix or improper care the risks increase greatly.

Phil

Is there some way to determine if a power bank is high quality?

Anker, Aukey, Mi powerbanks are they high quality?
 
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