Protected 18650 cells in a power bank

Hello! Because electronics isn’t something that i know that much about, then I thought to ask just to be sure.
I have qidian qd184-fc power bank. It has slots big enough for protected 18650 cells but in the picture, it is shown used with non-protected cells. My question is if i have 4 protected cells in parallel configuration in this power bank and if one cell suddenly kicks it’s protection in, what would happen? For example if i drain this power bank and one cell’s protection kicks in before the power bank says 0% ? will there be some kind of fire or huge current break or short circuit… or what else would happen? This may sound like very dumb question but since i have 10 protected 18650 cells laying abouts then I really would like to use them.

Thanks for help!

If one cells PCB kicks in, in parallel nothing bad will happen but you only have 3 cells supplying current and so forth as each cell reaches its PCB trip voltage you would just lose that cell from the supply. If its a low current draw device it should be fine. If its a high current draw device, each time you lose a cell the other cells have to make up for that cell being dropped out. If the voltage sag under the high current load on the other 3 cells reaches the trip voltage they will trip also. If its high current load one cell being weak could trip the whole pack prematurely. The cells will have slight differences and the PCB’s will have slight differences when the will decide to trip. You may not get the exact capacity of all the cells combined but should be close.

Also if you could run a capacity test or a IR test and try to match 4 cells that are close the pack should work better and last longer.

Hello. Doesn’t the cell whose protection has kicked in basically create a short from positive to negative or what exactly does the pcb do? . Thanks for help!

No it doesn’t create a short that cell won’t provide power until its charged again. Wouldn’t be a point in a protected cell if it made the cell short out when it kicks in. Most protected cells kick in at 2.5 volts. Most power banks cut off at 3v under load so the cells will never go into protection unless the power bank is dead for months without recharging. Put some cells in protected or unprotected and use it. Or if your that uncomfortable with cells you can purchase a sealed powerbank with cells already in it they are pretty cheap now adays

With power banks you add your own cells to. The designers have pretty much idiot proofed them. If it says use unprotected cells the charger has protection built in. They don’t want all kinds of lawsuits.

Ideally, the controller board in the power pack itself would do the protecting, so protection on the cells is superfluous.

I wouldn’t worry about it. If the cell’s protection kicks in first, it’s just like unplugging that cell, that’s it.

Thanks for the answers. The uncomfortableness that came with using the cells is just because of always using unprotected cells and not knowing how these protected cells worked exactly. Thanks for clearing this up. I know that using protected cells in a power bank is superfluous but since these cells are highest capacity i have then why not use them.

Use them I have a handful of protected cells. I removed the protection from about 8 of them left 4 on for my wife Wheb she was still new on batteries. The protection comes right off. There are vids on YouTube showing how to remove it. Take off the outer layer and basically rip it out. I just use them now since they don’t go in flash lights anymore I see no need to remove the protection. We have three tomo v8-4 powerbanks thay get used daily. Between them my vape and light used at work and home. It’s not uncommon to have 15 cells a day to charge.

Does your tomo power bank not have the whining noise? High pitched or smth? My tomo t4 sounds horrible when there are any batteries inside. Not really good quality tbh, maybe i just was unlucky but i have heard people saying that tomo power banks are loud in that regard…

I don’t have the t4 yet I just ordered one from gearbest so it’ll take about 6 weeks to get here that’s my average time with them. For 12 dollars hard not to. One of them after two years the USB outputs are worn out from my kids pulling the cables constantly on mine the cable pretty much stays in. But it still works the cable is just loose in there. And my kids broke the charging input on two of them. But it charges slow and I charge the batteries externally. I have the older tomo v8-4 and I can’t say I’ve heard any high pitched whine like with some flashlights on low and medium modes. But the new ones have dual USB inputs and is smaller so I’m guessing it has different electronics inside

Yeah, I got a T4 and M4, charging 2 LGs as I type this, and it’s kinda slow, but no noise.

Forget which is which, this one has the 2 charging-inputs, micro-usb and the other (evil) one.

The newer one is the t4 with the two input slots. The specs say 1.2 amp charging. I’m not sure if it’s 1.2 total or 1.2 per input the description isn’t clear on that. The older one (evil) has the single input and only accepts 1 amp charging. Using 4 ncr b charging at 250mah takes overnight and still not done sometimes. If you charge one or two batteries it’s not to horrible. But I purchased them as powerbanks not as chargers. The batteries go into my opus for charging. Occasionally I’ll plug mine in as I sleep with my phone plugged in. Since it can charge and discharge simultaneously. When they are on sale for 10 to 12 dollars it’s to good to pass up. (at least for me)
I want powerbanks I can change the cells in as needed and not need to wait for one to charge back up. My wife uses it all day on her phone. With two young kids 18 months and 4(special needs) she can’t just put her phone on a wallwart charger. And my daughter usually has one plugged into her tablet and carries it around. Tablet has horrible battery life even on the lowest brightness setting. The Amazon tablet she lost had awesome battery life. Would go 4 5 hours on a single charge. The rca voyager 3 has the worst battery life I’ve seen on a device. Within a hour on lowest brightness no location or Bluetooth or anything on is dead in under a hour But it is the cheapest one available 40 to 50. The Amazon one was over 100

Naw, I meant the one with 2 charging inputs has 1 micro-usb, and 1 evil one, “lighting” or whatever it is.

Was wondering why my cable wouldn’t go into that slot, flipping it one way then the other, then back again, ’til I looked at the damned thing with a light to see it wasn’t micro-usb at all!

Urg… :confounded:

Is it that new type c USB input? My wife had one phone for a short while with the USB c input and the phone actually started smoking from the input with the factory supplied cable. Never again. Well supposedly all phones over the next decade are going to the USB c the cable goes in either way there is no wrong way to put it in. Supposedly thry can handle more power and transfer data faster then the micro b cables. And they sell adapters to turn your micro b cable to USB c

Oh, joy. Yet Another Standard…

Dunno if this is c or lightning or whatever.


Cells properly set in parallel self-balance without delay. Power delivery self-balances too because as the faster discharging cells (lower internal resistance) drop voltage faster and this causes a balancing pull current transfer from the higher internal resistance cells to the momentarily lower volted low IR ones. This happens fast.

Setting different cells in parallel can offer advantages due to combination of cell characteristics. I once succesfully built a 2S2P drill battery with LiitoKala INR26650-50A and TrustFire IMR14500 teams. The much smaller high discharge cell allowed starting currents close to 50% higher.

For cells with much different discharge profile curves care must be taken because cells only cycle 1:1 for full charge-discharge cycles. Cycling 90% to 50% versus 50% to 10% can have very different actual cycling impact depending on cell types: higher voltage ones may deliver most of their capacity before the low voltage units hit 40%, for example. Extrapolation of discharge curves is a wise advice.

Cheers ^:)

If the current load is high one weak cell will cause all the other cells to work harder and possibly cause degradation from the extra current strain and heat with the pack having a lower capacity because one cell cut out early. Cells in parallel is basically one big cell with all there capacity’s added together. If one cell is 1000mah and 3 are 2000mah you basically have 7000mah 3.7v li-ion. If all 4 where 2000mah then you would have a 8000mah pack. With a PCB circuit installed in every cell, there could be differences between when the PCB trips for each cell regardless of what voltage it’s suppose to trip at. In a high current load these variances between cells and PCB’s matter. Not so much on low current loads.
Trying to get 4 cells that are close insures they will try to all work together and help each other in high current loads, the hard working cells don’t want a lazy cell in the bunch. RC guys have known this for years, they buy 50 or more cells at a time to match maybe 10 to be there race ready pack.
If the current draw is low the pack would still suffer slightly from one weak cell but no where nearly as bad as if the current load was high.
Every cordless tool pack I have ever had that went bad, always had one cell that was the cause. Threw it away and recycled the rest of the cells.