Review: cheap 18650 mobile power bank

… and it wasn’t too much time as I’ve spent some more:)
Reviewing the FM6316CE datasheet & PCB think I’ve isolated its problems root causes; no Output Current limit resistor from chip pin #2 to ground (UPDATE: useless as it doesn’t t lower draw to 1A rated max, so another chip flaw), and FM6316CE itself does not implement the battery undervoltage protection it says it does (no external components control this - it appears an unimplemented chip function).

So is it possible with some DIY, to improve this power bank, or is there a software problem also?

IF I’m correct, low battery cutoff function is absent/faulty in the chip itself & so is not fixable… Other than (the silly notion of) replacing it with a different/working pin-compatible one.

My/our FM6316CE versions look like reference implementations (less the useless OutputCurrent limit resistor - not respected by chip), so IF I’m right any/all devices using this (version of the) chip lack essential/advertised low battery cutoff / undervoltage protection. Hard to imagine but perhaps representative/indicative of lower-tier chip design/development/production houses.

You can maybe limit the output current more by increasing the resistor at the prog pin. If that schematic is correct: Review: cheap 18650 mobile power bank - But then it will probably still over-discharge the battery in terms of capacity (just not in terms of “too high current”)

When measuring my half-broken one (only still charges correctly, output is only at 4V at all times), I measure 36 Ohm from the Prog Pin to GND. Though there is no 36 Ohm Resistor on the board, so maybe it is burned/fused-together at some point inside the chip, but I can’t really say. Maybe someone with a still functioning board could try.

Overall though: I wouldn’t rely on these for critical applications, and would always expect it to start a fire… (I would do the same with the ETA-based ones though…). So don’t leave it on a pile of paper while leaving the house for more than 5 minutes….

Maybe using them with protected cells (short-cut and over-discharge protected) is a viable solution…

Hmmm,
by the way, did anyone search if these ICs are maybe renamed “fake”-versions of high end ICs from for example Texas Instruments, Linear Technology, … ? (catchword “Power Management ICs” I’d say) So maybe one of those chips could in theory be “dropped in” (though probably you wouldn’t waste one of their ICs, but also want to add those few remaining resistors and capacities for a complete high quality design then)

Thanks for the 411 on all of this.

On the ones in bound to me with a FM6313CE circuit I’m going to toss in a DIY protected 18500 cell pull I just slapped up (only made 1 so far as a test.) I made one for use with a 18650 battery carrier & thus did not use tin strips but just plain ole 24~26 gauge wire. Hopefully that will make it somewhat safe to use. I won’t rely on the protection PCB (dissected from an old AW CELL) to prevent overdischarging each time but hopefully it won’t fail on the times that I do need it to work.

Just to be safer -> I won’t gift these away and keep their limited usage for myself.

AZ

Don’t like the phrase but when something sticks in my craw I’m compelled to follow it to the end. So I tried adding the absent Output Current limit resistor from chip pin #2 to ground, to try to reduce the max current to 1A chip can safely handle. FM6316CE spec says it configures the output current limit from 2.5A - 0.5A using range 10k - 100k to ground. Found adding any such resistor raised the max current, the lower the resistance the higher the allowed draw (e.g. 10k resulted in about 2.2A draw into IPad). Tried 10k, 22k, 47k & 100k - all had bad effect of raising max current draw BUT also resulted in the BLUE LED lighting dimly during discharge - going off when batt dropped to about 2.6V (but not stopping drain/draw).

So I’m finally & fully done with this:) My research & testing suggests at least 2 faults in this FM6316CE chip itself, e.g. deviating from its published spec, neither battery low voltage cut-off OR current draw limiting (to <= its 1A rated max) are implemented properly or at all.

This seems to leave 2 possible uses for these FM6316CE-based units, with the only(?) cells that may fit - unprotected ones, charging batteries OR discharging them to proper storage charge (monitoring w/DMM to 3.6v –3.7v) then removing them. DIY hacker types could have fun adding a $2 Mini DC voltage meter + momentary switch for monitoring and just make sure they don’t charge things that draw too much.

Again an HKJ-reviewed “ENB USB Power Bank 2×18650”/battery box is what I’ll be using.

bluey - WRT your broken one measuring “36 Ohm from the Prog Pin to GND” must be toasted - my “working” ones measure more proper 1.4k.

Thanks for the update CFcubed. Your efforts to test and report on these units are much appreciated. Also your efforts to see if the issues could be fixed. Your tips on how to identify the bad units in Post 53 should be handy. I have come across 2 chargers (one black and one blue) that have the bad chip, but are configured differently.

Here are a few pictures. First on is like your to show how to identify from the top. Has 2 resistor perpendicular to tail wire and different led and other components configuration. Mouse over zooms in to the 2 resistors.

Bottom. Looks like dchomak's black unit.

Before I forget. Welcome to the forum Cfcubed!

So far, BIC is telling me they can not refund for the bad units.

I just used one of the 2 "bad chargers" that I mentioned in the above post to charge a couple phones to see where it would cut off. Halfway through discharging the second phone, it stopped charging. It flashed the blue led when it cut off. My wife quickly disconnected it before I got a chance to check the voltage. I did check the voltage within one minute of it cutting off. The cell was at 3.3x volts.

The charger was definitely running hotter than seems appropriate. I had the lid off. I think it would have been too warm with the lid on. I didn't check temperature or current while it charged. I will try another run sometime this week and report back.

I don't know if good units also get hot discharging. I think I will pot mine with the first recipe from here anyway.

Good additional data esp. the nice photos, so looks like there may be several variants of this thing. IMO most/all(?) of the research/testing WRT FM6316CE-based ones should still hold…. E.g. think any FM6316CE-based ones that cease charge prior to nearly or fully discharging cell (e.g. to below 2.2v) are only doing so because the device being charged is ceasing charge due to low USB voltage.

Good point. I don't know why this one stopped yesterday. It would be nice to know the cell voltage under load just prior to it stopping. I'll try to capture more info next time. Maybe tomorrow.

I dug around a bit, and didn’t find any flat 4 18650 usb chargers less than this, in qty 1, but I did get a flat 2 x 18650 usb charger for a few bucks, and is on the way. I think there were some triangular 3s, and square 4s between $4 and $10 but the shapes weren’t interesting to me.

This may be a decent power bank for the price?

Received a blue one today from BIC. FM6316CE inside. It overcharges - I stopped when charging voltage was 4.4v, the battery measured 4.3v. It likely would go further. When I reinserted the battery something shorted and I saw smoke coming out the charger.
I’m glad I’ve ordered only one unit.

Now that I have that ENB 2x18650 that HKJ reviewed ($12 or so delivered) in hand & tested I offer this simple summary comparing to the FM6316CE-based ones:

The 2-cell ENB above is working very well as per HKJ’s review. Will say though that it seems better to use 2 reasonably matched cells in it. I found that although it does a nice job individually charging differing cells (e.g. both to 4.1Xv) it doesn’t discharge differing cells down to same voltage. But its still a safe/conservative cut-off voltage regardless, e.g. when it shutdown/ceased charging my iPod 2 the new green cell was at 3.5v and the old/differing purple cell at 2.9v when they were coupled. Also it takes a good long while to recharge the cells. But like it a lot - Thanks again HKJ!

You overpaid it for 50%, but still, u now have a decent power bank :stuck_out_tongue: http://www.buyincoins.com/item/25240.html

FYI - One of my white units has a bad chip as pictured in post #53’s 1st picture. :frowning:

Time the crack open the white units I closed up before the bad chips were discovered (better have a look at those boards. I have no clue what’s in them.) This should be fun. These things are closed up like tanks… :~

Yeah…sad that the chips suck…they are decently designed cases, close up really tight.

Ah well…I ordered some other charger and will retire these for sure, sucks these could have been pretty good little rigs

- The units’ (likely) cold solder joints on battery tab & spring can loosen when taking these all apart, be prepared to have to re-touch their solder joints.

- Again you don’t have to dissect them to confirm they’ve a “bad” design for charging your devices, you could check how it charges each device and avoid use for known high-draw ones (e.g. IPad 2). E.G. with power bank open during charging; 1) feel if USB jack is “too hot”, 2) use pack checking if battery voltage gets below 2.6v. IF you confirm/assure that ALL devices that would charged with it don’t pull > 1A (gets too hot) AND don’t pull battery below 2.6v, it may be OK to use.

  • I found not too hard to open using a small, thin blade putty knife in combo w/a thin blade screwdriver & knowing where the tabs were. The plastic sides give.

BTW my FM6316CE-based two are going in the trash. Not worth the hassle or risk, need at least 2x18650 to do any decent charging anyway.

FYI - In order to easily remove a closed case -> I carefully dremeled a hole in the back lid in order for me. Held in a bench vise with a rag & one usable hand this was still relatively easy.

It’s hard to see in this picture but the white bank with the bad chip is a lighter(newer?) shade of white then the white banks with the good chip. Perhaps this signifies that the bad chips were used in a new batch where there is a slight variation in the plastic used?

(it’s the 1st one on the left.)

here’s a pic of the white bank w/ the bad chip

Man, my batch order contained ~80% of the ones with bad chips. It seems the is much protection PCB soldering onto 18500 cells in my future (I might not even have enough of these.)

Anyway -> for the banks which I will keep for personal use I am contempting whether or not I want to make a notch in the lid (before closing) in order for future cell removal.

On the ones intended for gifts -> I haven’t decided if I want to do this. + Using protected cells in the “bad” chipped ones only partially addresses one of it’s downfalls. I would not use high drain devices on the such as tablets. I fear the drain will be too high for some of the components. Unless one had already ordered these I would recommend getting a different type of power bank. What a hassle.

Heck I might not even gift the ones I have here if the “good” banks still turn out to be junk in repeated usage. I’ll think it over before giving these out.