iamdarkyoshi's Substantially Less Deadly Powerbank Capacity Tester

[iamdarkyoshi]

So I made this... thing... a while ago.

http://www.eevblog.com/forum/chat/iamdarkyoshi's-highly-dangerous-(but-extremely-simple)-powerbank-capacity-tester/

https://linustechtips.com/main/topic/602435-iamdarkyoshis-highly-dangerous-but-extremely-simple-powerbank-capacity-tester/

 

And then I had an idea. My bench supply counts mAh. Why don't I just discharge the damn powerbank and then charge it with my bench supply? Then I can very precisely measure the capacity without dealing with the output converter circuitry in the powerbank.

 

So here is the setup:

 

I made a very chunky USB lead that can handle over 2A without dropping much voltage. My new powerbank (my white 5 cell one) can charge at over 2A perfectly fine with this cable. I set the voltage to 5v and the current limit to 1.5A. I know this particular powerbank only charges at 1A.

 

So I plug the discharged powerbank into it

 

And I watch the numbers rise.

 

See that value in the bottom right? That is how many mAh I have put in so far. Once the powerbank finishes, I will know its capacity.

 

I could also use this to check my tablet and phone, provided I discharge them first and leave them switched off (as leaving them running will draw power, which would be measured)

 

The powerbank listed here is from BayValleyParts on ebay. The one I bought is out of stock. http://www.ebay.com/itm/131497508451

The bench supply can be found here: http://www.ebay.com/itm/DC-DC-Programmable-Switching-Power-supply-60V-5A-300W-/231579926529

Not sponsored by either of these sellers.

 

Anyway, I should have results in about 10 hours or so...

[Mr.Meerkat]

Looks guld...maybe this won't blow up...

[Mira Yurizaki]

I'm not sure how much trickle charging it'll do or take, but make sure to not take too long getting a reading, otherwise that'll throw your results off.

[You_are_a_cunt]

So, which subscription do you want, @iamdarkyoshi?

Plans start at $29.99/mo

[iamdarkyoshi]

2 hours ago, CUDA_Cores said:

don't know if this is better, but I simply bought an imax B6 and hooked up the +5v usb right into the charger and set it to discharge using the ni-mh cell setting until the output reached zero volts. It works just fine and basically achieves the same result. The charger on it's own can be found pretty cheaply, all you have to do is also pick up a power brick for it.

 

Charger: http://www.ebay.com/itm/IMax-B6-Digital-LCD-Lipo-NiMh-battery-Balance-Charger-TS-/121335752982?hash=item1c402ca916:g:FYcAAOxyi-ZTaJll

 

Power brick: http://www.ebay.com/itm/SKYRC-15V-4A-60W-Power-Supply-Adapter-for-IMAX-B6-mini-B6-Balance-Charger-R4N7-/231951304443?hash=item36016006fb:g:mDAAAOSwciVXP4nQ

 

I've been doing this for awhile and it seems to be pretty accurate.

 

You also have to keep in mind charging the batter and measuring it's capacity that way may not be as accurate because you have to account for the power losses/inefficiencies of the voltage conversion, and the fact the batteries will trickle charge after they are done as @M.Yurizaki said

Well, although these things discharge through a boost connverter, they are charged through a linear regulator. This means that 1A at 5v is still 1A by the time it reaches the cells, and I am counting current, not wattage.

 

Also, you shouldn't trickle charge lithium cells, going over 4.2v is bad. But if you can still push more charge into the batteries without going over 4.2v, then you ARE actually storing more power in the cells.

 

Discharging them however is not the greatest way to judge capacity, as you ARE going through a DC/DC converter. This would be fine if we measured them in watt-hours, but everyone measures their capacity based on what cells were used.

[vanished]

This is a lot simpler, but the one concern I have is to what point to you drain the battery bank?  To be 100% realistic and accurate, I think you should drain it by charging phones until it can no longer do so.  If you use some artificial means to drain it, you may over drain it  (or under) and (in addition to possibly damaging it) you will get an unrealistic portrayal of it's capacity once recharged.

[PineappleHolidays]

the proper way to do this would be a simple CC load at something like 2a

because charging only gives you an approximate estimate ( it's very precise when it's a good bank but will be off when it's a really crappy one )

 

to make a CC load you only need the charged bank, an op amp, big resistor or load, and a mosfet ( and mabe a potentiometer although resistor works fine )

[Coaxialgamer]

But wouldn't you already know the powerbank capacity when you buy it ? I know it's not the most precise way of determining capacity , but it should be close enough ( unless it's a cheap chinese battery in order to find out the real capacity )?

[iamdarkyoshi]

4 hours ago, Ryan_Vickers said:

This is a lot simpler, but the one concern I have is to what point to you drain the battery bank?  To be 100% realistic and accurate, I think you should drain it by charging phones until it can no longer do so.  If you use some artificial means to drain it, you may over drain it  (or under) and (in addition to possibly damaging it) you will get an unrealistic portrayal of it's capacity once recharged.

I just plug LED strings into them. The ones I test DO have overdischarge protection (completely disconnects the cell)

 

The bananas don't though. Just have to watch them for when they start flashing between bright and dim.

 

Anyway the test is in on the BayValleyParts 10Ah battery bank:

 

Thats close enough to 10Ah that I would consider it a TRUTHFULLY rated powerbank from ebay! And I got it for 7 bucks! On sale though. They can be had for less than 15 bucks normally.

[vanished]

1 minute ago, iamdarkyoshi said:

I just plug LED strings into them. The ones I test DO have overdischarge protection (completely disconnects the cell)

 

The bananas don't though. Just have to watch them for when they start flashing between bright and dim.

 

Anyway the test is in on the BayValleyParts 10Ah battery bank:

 

Thats close enough to 10Ah that I would consider it a TRUTHFULLY rated powerbank from ebay! And I got it for 7 bucks! On sale though. They can be had for less than 15 bucks normally.

The trick with cheap batteries from disreputable distributors though is the lifespan.  They may actually seem to be close to rated capacity at first but how fast does that disappear?

[iamdarkyoshi]

1 minute ago, Ryan_Vickers said:

The trick with cheap batteries from disreputable distributors though is the lifespan.  They may actually seem to be close to rated capacity at first but how fast does that disappear?

Dunno. They aren't top brand cells, but they at least weren't nabbed out of something else like my big pink sausage powerbank. This one uses new cells

[Huntsman]

This sparks a series of questions in my head... which process is more efficient? Charging or discharging? Thus, which methods of measurement would show a more accurate value? Also, there should be somewhat of a hysteresis curve... what would it look like?

 

A power bank's capacity is not really defined by how much is the cell's capacity but how much it can put out...hmm....

[.spider.]

I'd say in the best case you are 20% off with that method

[vanished]

On 5/31/2016 at 3:00 AM, Huntsman said:

This sparks a series of questions in my head... which process is more efficient? Charging or discharging? Thus, which methods of measurement would show a more accurate value? Also, there should be somewhat of a hysteresis curve... what would it look like?

 

A power bank's capacity is not really defined by how much is the cell's capacity but how much it can put out...hmm....

Well assuming the rate at which the battery loses the ability to hold a charge is not noticeable after a single use, the amount of energy drained has to match the amount that goes back in, or you're gonna have problems

[iamdarkyoshi]

11 hours ago, Ryan_Vickers said:

Well assuming the rate at which the battery loses the ability to hold a charge is not noticeable after a single use, the amount of energy drained has to match the amount that goes back in, or you're gonna have problems

When discharging, some energy is lost in heating up the cells. They are being drained fairly fast.

 

But powerbanks seem to always be rated at the cells' capacity, without any extra circuitry.

[vanished]

23 minutes ago, iamdarkyoshi said:

When discharging, some energy is lost in heating up the cells. They are being drained fairly fast.

 

But powerbanks seem to always be rated at the cells' capacity, without any extra circuitry.

But even if that's a parasitic loss, it's realistic.  No point measuring them in an ideal scenario if they will undergo that inefficiency when actually charging a phone.  Measure them how they will be used!

[Mr.Meerkat]

Am I the only one who hates when these companies uses shitty battery like cells instead of actual flat square/rectangular cells? It annoys me as all it does is scream "this battery bank is cheaply made and uses shitty cells" (the battery like cells are usually lower quality than square cells...or that's what I found out) and it makes them soooo much bulkier...

[iamdarkyoshi]

2 hours ago, Mr.Meerkat said:

Am I the only one who hates when these companies uses shitty battery like cells instead of actual flat square/rectangular cells? It annoys me as all it does is scream "this battery bank is cheaply made and uses shitty cells" (the battery like cells are usually lower quality than square cells...or that's what I found out) and it makes them soooo much bulkier...

I have had plenty of issues with lipo cells. They are pretty damn fragile compared to cylindrical cells, and they can also be made cheaply. Have you ever dealt with a cheap knockoff phone battery?

[Mr.Meerkat]

4 minutes ago, iamdarkyoshi said:

I have had plenty of issues with lipo cells. They are pretty damn fragile compared to cylindrical cells, and they can also be made cheaply. Have you ever dealt with a cheap knockoff phone battery?

Meh, still prefer lipo cells over cylindrical cells battery banks as they can be sooooo much slimmer (which is more important than bulkiness  in my opinion)  for example, the 10k mAh battery bank I have is only slightly thicker than my z3 compact (about 2mm thicker) with it being a tad bigger than a iphone 6. Plus it charges my phone 3 full times and around 40-65% on the fourth charge, pretty sure that's close enough to the 10,000 mAh manufacturer stated spec .

 

Also for you actual question, yes I have dealt with issues on lipo cells, used to be a radio controlled enthusiast so I've dealt with plenty of 6 cell lipos and what ever  (still have my lipo smart charger actually but sold everything else ).