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LiPo Low Voltage discharge cut-off events

by fruitloop on Sun Apr 15, 2012 11:38 am

I have built a Solar Minty Boost charger for my iPhone 4. It consists of

a) 6 V 3.4 W Solar Panel
b) USB / DC / Solar Lithium Ion/Polymer charger - v1.0
c) 3.7 V 2700 mAh LIthium Polymer Battery and
d) MintyBoost Kit - v3.0.

Also included in the circuit is a three way switch and the 2 x AA battery holder that comes with the Minty Boost (so I can alternate between batteries if needed). I can also charge with a 5V 2000mA switching power supply.

All parts discussed are from Adafruit except the three way switch.

I have been experiencing a recurring problem after charging the 2700 mAh LiPo battery to full charge (“green light” on, measured 4.20 V) with either the solar panel or the charger: the iPhone 4 will only partially charge - say from 13% to 46%, at which time the iPhone 4 will indicate it is no longer connected to a charger. When this happens, the LiPo battery shows an extremely low no-load voltage - such as .685V or .740V. For all intents and purposes, the battery looks to have discharged below its shut off voltage of 3.0 V.

If the LiPo battery is charged with the solar panel or the charger for a period as brief as 10 seconds (then disconnected) - the battery will show a no load voltage such as 3.61 V(!) and can then be used to continue charging the iPhone 4 to 100%. Sometimes the charging cycle will stop several times during the process, but can be always be “restarted” as indicated.

Thinking this problem might involve the battery, I ordered a new 3.7 V 2700 mAh battery and fully charged it with the charger. The battery showed a no-load voltage of 4.20V. The iPhone 4 was initially showing a charge of 14%. I left it connected over night. In the morning the iPhone showed a charge of 49% and the LiPo battery showed a no-load voltage of .64V. I connected the charger for 10 seconds (then disconnected it.) The LiPo battery showed a no-load voltage of 3.82 V. I reconnected the iPhone 4 and was able to charge the iPhone 4 to 100%, at which time the LiPo showed a no-load voltage of 3.10V.


Can you suggest what might be causing this or offer any suggestions on how to troubleshoot this further.

Love your stuff. Thanks for your help.
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Re: LiPo Low Voltage discharge cut-off events

by adafruit on Sun Apr 15, 2012 11:46 am

could be the over-current protection is getting activated? its certainly something with the protection circuitry inside
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Re: LiPo Low Voltage discharge cut-off events

by fruitloop on Sun Apr 15, 2012 5:06 pm

So you think the internal over-current circuitry in the liPo battery is probably working correctly during a short-circuit or over-current condition? If the battery is not at fault where would you look next?

I understand that the Minty Boost is set to provide an output of 500 mA at 5 V for the iPhone. I have another Minty Boost kit I could assemble and insert into the circuit if you suspect it could be responsible for an intermittent current overload. Any history of this?

By the way, do you know what level will trigger the over-current protection for the LiPo battery? The spec sheet Adafruit supplies with this 2700 mAh battery shows a Maximum Discharge Current of 2.0C5A. Can you use this to determine the current level that is being exceeded before the protection circuitry activates?

Could this 2700 mAh battery be a tad underpowered to supply a Minty Boost during a full charge of an iPhone 4? I also purchased a 4400 mAh LiIon battery pack from Adafruit, which I could use to replace the 2700 mAh. Please let me know your thoughts.

Thanks for your help.
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Re: LiPo Low Voltage discharge cut-off events

by fruitloop on Mon Apr 16, 2012 8:20 am

By the way, I have erroneously referred to the phone as an iPhone 4, it is an iPhone 4s, if that might matter here.
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Re: LiPo Low Voltage discharge cut-off events

by adafruit_support_bill on Mon Apr 16, 2012 8:59 am

The only way the minty should exceed that max discharge rate of that cell is if there is a short somewhere. You might try swapping batteries and/or minty's to further isolate the problem. If you post pics of the front & back of the minty we can check that out too.
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Re: LiPo Low Voltage discharge cut-off events

by fruitloop on Tue Apr 17, 2012 12:07 am

Thanks for your help.

I have attached some pictures of the solar minty boost circuit and the top and bottom of the Minty Boost. If they are not clear enough, let me know and I will reshoot them with a better camera and better lighting.

I did replace the original 2700 mAh battery once with a new one and got the same problem. If you think this battery is too small to charge an iPhone 4s consistently, I also have a new 4400 mAh Li-Ion battery I could try.

I will build a second Minty Boost and have it available to put into the circuit after I hear back from you.

I should add that the circuits are all attached to the plastic case with 3M double stick mounting tape....

Please let me know your thoughts, and thanks again.
Attachments
photo 4.jpg
Minty Boost bottom view.
photo 4.jpg (233.83 KiB) Viewed 2576 times
photo 3.JPG
Minty Boost top view
photo 3.JPG (767.88 KiB) Viewed 2576 times
photo 2.JPG
Charging an iPhone with case open. Normally the solar panel is unplugged while charging phone.
photo 2.JPG (952.26 KiB) Viewed 2576 times
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Re: LiPo Low Voltage discharge cut-off events

by adafruit_support_bill on Tue Apr 17, 2012 5:31 am

I did replace the original 2700 mAh battery once with a new one and got the same problem.

Is the battery getting warm when you do this?

If you think this battery is too small to charge an iPhone 4s consistently, I also have a new 4400 mAh Li-Ion battery I could try.

It is too small to charge it completely, but I would expect it to work in this configuration. Give the 4400mAh a try.
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Re: LiPo Low Voltage discharge cut-off events

by fruitloop on Tue Apr 17, 2012 8:43 am

No, neither of the 2700 mAh batteries get warm while charging the iPhone 4s.

Okay, I will charge up the 4400 mAh battery today and give that a try this evening.

Thanks.
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Re: LiPo Low Voltage discharge cut-off events

by fruitloop on Thu Apr 26, 2012 9:14 am

It appears that the culprit was the switch I had installed to allow the use of either the 2700 mAh Li-Po battery or AA batteries to charge the iPhone 4s. (The switch was a Radio Shack DPDT Mini Toggle Switch [Catalog #: 275-663] and the problem was most likely caused by either an intermittent internal short or my poorly soldered connections.) I have removed the switch and the option for AA batteries from the circuit.

The Solar Minty Boost is working like a charm, now. I can report that the 6V 3.4 W Solar Panel will easily recharge the 2700 mAh battery in one day with good sunlight and a fully charged 2700 mAh battery will fully charge (95%+) an iPhone 4s in several hours.

I guess the takeaway from this is to "keep it simple".

Thanks again for your help and your great DIY kits.
Attachments
photo 2.JPG
Charger and iPhone
photo 2.JPG (707.56 KiB) Viewed 2483 times
photo 1.jpg
6.4 V 3.4W panel attached to plastic Flambeau storage box
photo 1.jpg (607.22 KiB) Viewed 2483 times
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