Jump Pack, Charger Pack, Measurements Dont Make Sense

Thread Starter

MrAl

Joined Jun 17, 2014
8,241
Hello,

I was doing some measurements on two Li-ion battery packs.
What i do is first charge them both fully. Then i use one to charge a phone from about 85 percent to 100 percent. Then i drain the phone back down to about 85 percent, then use the other pack to charge the phone.

In both cases the phone takes close to 2 watt hours of energy to charge.
But in both cases the battery packs take about 10 watt hours to recharge back to 100 percent.

This doesnt make much sense because that would mean the battery pack and charge and discharge combined efficiency must be only about 20 percent. That does not match other tests i have done on single cells of different chemistries where the energy in is much closer to the energy out, although those tests do not take into account the charging system losses.

I might do some more tests, but any idea what might be the cause of this?
The two packs are very different types from two different manufacturers and have different internal voltages, where one has close to 15v internal and the other i think is lower but i dont know because i cant measure that one.
 
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KeithWalker

Joined Jul 10, 2017
1,779
How are you measuring how much energy is used to re-charge the Li-ion packs? If you are just recording the time to complete the charge, be aware that a good charger will continue to top up the battery at reduced current when the terminal voltage is reached at full charge current.
 

Thread Starter

MrAl

Joined Jun 17, 2014
8,241
How are you measuring how much energy is used to re-charge the Li-ion packs? If you are just recording the time to complete the charge, be aware that a good charger will continue to top up the battery at reduced current when the terminal voltage is reached at full charge current.
I am using a special USB measuring device that measures ampere hours and watt hours and some other stuff. I have used this device for many measurements and found no real problems with it and it is very handy for keeping an eye on the cell capacity in my cell phone.

I have to add something though to my first post, and that is that the smaller pack tested differently this time with the test i just completed a few minutes ago. The small pack only took about 3 watt hours to recharge while the phone too about 2 wh, so that's much better. Maybe something was strange with the first test.

But the second pack tests 10 watt hours every time. That is a "jump starter" battery pack so the internal Li-ion battery pack is around 15 volts which means when it is charged via USB it has to step up the voltage at least 3 times or more (USB voltage could go down as low as 4.6v when charging something). I am thinking maybe they used a crummy step up converter.

Any other ideas appreciated.
 

Thread Starter

MrAl

Joined Jun 17, 2014
8,241
You are probably right. It does sound as though the step-up converter is not very efficient. Are you using a USB 3 source?
Oh yeah i meant to mention that. I am using a wall wart USB charger that came with the phone, it puts out about 850ma max when charging, and that decreases near the end of charge.

I am going to see if i can determine the truth about that guess about the step up converter by using external measurements. It's too bad there is not an alternate method to charge this thing i could tell right away, but i cant charge it via the "12v" leads because that would lead right to the battery pack and that would mean charging an unknown pack with a charger that may not be suited to that very pack.
There are other packs that allow charging right from a cigar plug too i should have gotten that one.
 

KeithWalker

Joined Jul 10, 2017
1,779
You can do a quick and dirty check by charging the depleted battery with your fancy measuring device on the USB port while measuring the current going to the battery. The ratio of current in to current out should give you some idea of what's going on in in the inverter..
 

Thread Starter

MrAl

Joined Jun 17, 2014
8,241
You can do a quick and dirty check by charging the depleted battery with your fancy measuring device on the USB port while measuring the current going to the battery. The ratio of current in to current out should give you some idea of what's going on in in the inverter..
Oh yeah that would be a great idea, but unfortunately i dont have access to battery current just to battery voltage. The battery pack is enclosed in a case and all i have access to is two "12v" leads (actually as high as 16 volts) that come out of the case that connect what looks like direct to the battery pack inside. I have access to two USB ports for charging my phone but they must have a step down converter inside for them and i hope they were not fool enough to use a linear.

I worried that they might be using a linear for the USB ports so i used the 12v output cigar lighter jack to plug in my own 12v to 5v USB converter and charged the phone with that, and it did not even get luke warm so no loses there. But the pack still took 5 times as much energy to recharge as it did when it delivered energy to the USB converter (and thus the phone).
So since there was no appreciable change, i assume that the step down converter inside is a switcher with reasonable efficiency.

As you say connecting a current meter in series with the battery pack would tell me a lot but i would need to be able to get the case apart and it is very far from obvious how to do that. No screws, no tabs, just a seam all around the outside but no pry holes or anything like that. I think taking it apart would do some serious damage to the case unfortunately or i would do it right now. The case seam is so tight i suspect they may have even used an ultrasonic sealing machine to close up the case so no one could tamper with the inside.

I guess i could look around the web for a teardown that might help, but i doubt i'll find one.
I have taken things apart that were never made to be taken part and in such a way that i could get it back together, but often it isnt pretty. The electric can opener i took apart recently i had to cut apart with a Dremel tool as there was just no other way. I got it back together but the case shows a jagged cut mark all along the edge of the back of the unit. Works like a charm now though :)
 

KeithWalker

Joined Jul 10, 2017
1,779
I know what you mean. I have a number of repaired devices around the house with rather ugly seams on them now.
All I can suggest is that you borrow a DC clamp-on milliammeter or try to make one yourself with a hall-effect device.
 

Thread Starter

MrAl

Joined Jun 17, 2014
8,241
I know what you mean. I have a number of repaired devices around the house with rather ugly seams on them now.
All I can suggest is that you borrow a DC clamp-on milliammeter or try to make one yourself with a hall-effect device.

Well i dont even have access to the wiring inside.

Here is a diagram showing what i am up against.
Nothing inside the red box is accessible only that which is outside.
Note that it would not be a good idea to charge using the 12v high current output because i dont really know what is inside, this is just what might be inside.
So the only means to charge it is through the left hand side USB input port and i can measure the current going into that no problem but i have no access to the output of the step up converter, and there must be a step up converter of some kind.
 

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Thread Starter

MrAl

Joined Jun 17, 2014
8,241
You don't have too much choice! I guess you will just have to live with it until you get something better.
Yeah i was thinking about returning it i have time yet, but i did another test now too.

I found that the pack also takes QC 3.0 charging so i connected a USB QC 3.0 charger to the only input port which is a USB C connector. The voltage went right up to 12v on the input because the pack will allow that even though it is still over the USB. The current went to about 1.4 amps.
So that is now charging at 16.8 watts instead of about 7.5 watts which is at least twice the power, but more significantly the voltage to what must be the step up charger inside the unit is 12v instead of 5v which should be better for the step up converter to handle. Step up converters often are more efficient when the input voltage is higher.

But unfortunately wouldnt ya know it, it did not make much difference. If any difference it might have went from 20 percent efficient to 25 percent efficient, which means that for 16.8 watts going in only 4.2 watts was being used to recharge the pack and so that also means that 12.6 watts is being wasted as heat. That is very very sad for a modern piece of power equipment especially in a day and age when we are supposed to design power equipment that does not waste energy due to the ongoing problems with the power grid infrastructure. It did come from China though where they may not care much about that. The heat can be felt near the end of the pack where the USB connectors are located it gets significantly warm.

Although this is certainly not the main point, cost wise it isnt that expensive to run. To fully charge a 20 ampere hour battery at 16 volts at 100 percent efficiency from completely drained requires 0.320 kilowatt hours of energy. At 25 percent efficiency it takes 1.28 kilowatt hours. That's a lot more but still not much overall maybe around 10 to 20 cents USD. But if everyone did this at the same time, it would be a significant power draw from the grid. That's why the gov wanted higher efficiency wall warts for one.

So in the end it sucks but as long as it works for the intended use i guess it is just one of those things we have to accept. Some manufacturers just dont care about efficiency and it's relationship to the US power grid health. You know what is strange though, even back in the 1980's when i worked in the industry we were shooting for 90 percent efficiency, so who in China didnt get the meno :)

Now if i could find out what exactly is inside, what the pack is made up of, i may be able to charge it using my own charger design. If the pack had self protection it may work. I guess it would still be a risk though as there must be at least 4 cells (or packs of cells) in series which means i would be charging multiply series connected Li-ion cells in series, which i dont like to do without adequate monitoring circuitry for each cell or each parallel connected cell pack.

As another side issue, not only does the pack get significantly warm the QC 3.0 charger also gets very very warm. That indicates low efficiency too. Based on that i would guess that the entire charging process is around 10 to 15 percent efficient. That's completely nuts.
 
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Thread Starter

MrAl

Joined Jun 17, 2014
8,241
A quick little update....

I contacted the manufacturer/seller and they said that they dont specify that kind of thing the only thing they specify is that it will jump start a car.

The thing is though, it works so well to charge a cell phone or other device that either allows high current 5v at up to 3 amps or actual QC 3.0 (up to 12v at 1.5 amps) that it is nice to be able to charge these other devices too iff needed so it would be really good if the charging efficiency was higher.
But i did check some other charging devices like wall warts even the modern ones and it seems that even they might be lacking.greatly. No wonder we have such a problem with the grid in the USA with manufacturers basically not paying attention to that issue. IT will just get worse as electric vehicles become more widely sold as people with have to recharge their vehicles at regular intervals so imagine how many cars around the country could be charging all at the same time.. I might start another thread on this issue as it is a growing concern.

So i call this sad engineering, it's not necessarily bad, but it lacks responsibility. In today's world we can design power supplies that are 90 percent efficient it only makes sense now to do that with all modern equipment.
There is finally also some serious thought in upper government about improving infrastructure which includes the power grid(s). I think there are two main power grids and some secondary ones. Texas for example has or at least had it's own, i dont know if that changed after the recent problems down there due to the storm.
 
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