Strange behavior of mintyboost

[adafruit_support_bill]

What is the output voltage of the MintyBoost in "zone B"?
What is the current draw in "zone B"?

[oby_one]

What is the output voltage of the MintyBoost in "zone B"?
What is the current draw in "zone B"?

I just measure it now and the output voltage of mintyboost is 4 Volts...
As for the current draw the phone will constantly require 500ma.
If you ask me to actually measure the current.... then I can't help you .. as I wasn't yet able to make my multimeter measure any amps...

[adafruit_support_bill]

the output voltage of mintyboost is 4 Volts...

The voltage is sagging because the phone is pulling more than the MintyBoost can supply.
How do you have your 4 NiMH cells connected? Series or parallel? As discussed earlier, conecting them in series will give you a higher input voltage that will allow the MintyBoost to operate more efficiently.

[oby_one]

In this moment I am really upset

*I have read successful stories about charging Htc Desire here on this forum with just 2x batteries.
*It is also advertised on your site:
New In Version 3: Provides 500mA @ 5V, tested and designed to work with all the latest iGadgets including the latest iPhones and iPods, etc., improved efficiency for high-drain devices, works much better with LiPoly battery mods
* My device is on your compatibility list :
Minty Boost compatibility webpage

After all this you tell me: "The voltage is sagging because the phone is pulling more than the MintyBoost can supply."
Aaaaarghhhh

I don't like this attitude... you told me that here on this forum I will find support for your products... yet since I started building it.... I have done all the debugging myself and received no useful advice.
Even though I struggle to post in a very clear way, with a wealth of information.. nobody really reads my posts if they are longer than 5 lines.
I post my questions in a specific, clear way (1. 2. 3. ) but I receive an answer to only one question ....or none at all.

I understand you are not forced to answer my questions, or help me in anyway...but since adafruit helped others in solving their problems I expect the same.
I totally understand if you are tired or busy... but when you answer me please do it with all your heart and do a complete and good answer.

Yours angry ,
Oby

[oby_one]

the output voltage of mintyboost is 4 Volts...

The voltage is sagging because the phone is pulling more than the MintyBoost can supply.
How do you have your 4 NiMH cells connected? Series or parallel? As discussed earlier, conecting them in series will give you a higher input voltage that will allow the MintyBoost to operate more efficiently.

As I have already stated a few times before.. I am using a 4x battery pack in which the batteries are 2x in series and the 2 banks in parallel ....giving a nice and steady 3 volts.

I have read again the specs of this lt1302 chip...and the max voltage is 8Volts so I will rewire the battery pack to allow the batteries to stay in series... giving 5Volts

Until then ..something else is bugging me:

Please tell me why is it so inefficient ?????
I have 4 x (1.25 V x 2500 mAH ) =12.5 Watt.Hrs available in that pack. and yet I am only able to charge my phone 50% ?????
Why ?
Again please tell me why is it so inefficient ?????

[adafruit_support_bill]

I have done all the debugging myself and received no useful advice.

If you look back over the posts you will find that you were given useful advice but chose not to follow it. Despite what you may have read on the internet, NiMH cells in a 2Sx2P configuration is not a good match for your phone.

Again please tell me why is it so inefficient ?????

If you read the documentation online for the MintyBoost and/or the chip, you will see that the conversion efficiency of the device improves with higher input voltages and plummets dramatically when the current demand is too high. Your 4 NiMH in 2Sx2P configuration gives you an input voltage of 2.4 volts which has a peak efficiency well under 100 mA and is already on the steep downward slope of the chart at 500 mA. That is why I have been suggesting a 3S or 4S configuration.

(Scroll down about 2/3 to see the efficiency chart)
http://www.ladyada.net/make/mintyboost/process.html

[oby_one]

I am now rewiring the battery pack for a 4x serial connection.

Just out of curiosity I wanna find out the efficiency of mintyboost in this configuration

In the battery pack I have 4 x (1.25 V x 2500 mAH ) =12.5 Watt.Hrs while in my phone battery I have 3.7V*1400=5.18 Watt.Hrs
Because I only got 50% charge I will calculate the efficiency like this:
12.5 * x=5.180/2
x=2.59/12.5=0.207
So I was in the range of 20% efficiency ????

It seems WAY too low......
I mean .... all the other guys.. have just two batteries and they should have this problem also...
Right?

[adafruit_support_bill]

I mean .... all the other guys.. have just two batteries and they should have this problem also...

1) Which two batteries?
2) What phone?
3) And for how long?

Your graph shows that your phone did charge for a 3 hours with two NiMH cells.

But if you look at the efficiency chart, your starting point with those cells at 500 mA is just over the edge of a cliff with an efficiency of less than 80% and dropping fast. With a strong current demand and some battery fatigue, the input voltage will go down and the efficiency will plummet even faster. To be honest, I am surprised that it went 3 hours.

Alkalines have a higher starting voltage, so you would have started a bit back from the edge of that cliff. But the voltage of alkalines decreases steadily during discharge. It's hard to say where the crossover point would be compared with NiMH.

In any case, it is clear that your phone does not like it when the output voltage drops substantially. This is addressed in the documentation. See "When to stop charging": http://www.ladyada.net/make/mintyboost/manual.html

[oby_one]

I mean .... all the other guys.. have just two batteries and they should have this problem also...

1) Which two batteries?
2) What phone?
3) And for how long?

1) any two AA batteries ( the default mintyboost comes with an altoid can that can house just 2x batteries)
2) htc desire could be one example... but there are many other new phones with similar specs and similar power requirements.
3) for how long what?

I was trying to say that if I have this problem with 4x batteries ... all the other persons in this world who are using mintyboost powered by just two batteries ....must have similar problems like mine.
By similar problems I mean they don't get a complete charge(probably less than 25%) ... and have a very low efficiency.

Your graph shows that your phone did charge for a 3 hours with two NiMH cells.

My graph doesn't show the number of batteries used to charge the mintyboost. It only shows the level of my phone battery vs time.
I have never ever said that I used 2x batteries.... in ALL my posts I clearly stated that I use 4x NiMh
This is just one example of how much attention you are paying to my posts.

In any case, it is clear that your phone does not like it when the output voltage drops substantially.

No phone likes more than 10% deviation from the main voltage requirement.
Can you give me an example of a phone that will like a substantially voltage drop ?..
I guess not!

This is addressed in the documentation. See "When to stop charging":

You realize that when I am off road.... on the mountain ... the last thing in the world that I wanna do is measure from 5 to 5 minutes... the output voltage of my mintyboost.
It's impossible to ask a normal user to disconnect the mintyboost when the output voltage drops ....
Nobody will stay to monitor it every 5 minutes... so nobody will know when to disconnect it on time.
The lt1302 chip should know when it is not able to meet the requirements and shut itself off...


What troubles me is why the phone is discharging rapidly after the mintyboost batteries are worn out.
You remember the Zone B and D from the last picture? this shouldn't happen.
Here is a quote from the mintyboost assembly manual :

Next is the schottky diode D1. This diode is part of the boost converter. Essentially it is used to make sure energy is transfered in only one direction-from the batteries to the USB port.

So why does it drain power from my phone ?

[oby_one]

thanks... very clear

[oby_one]

So ...
I rewired the cables to have 4x batteries in series.
I measured the output of battery pack and it was ok... but the output of the mintyboost was about 5.4 Volts....
The phone accepted this <10% deviation and started to charge....
As you can see in the attached graph the new wiring delivered a good 55% percent and then it stated to discharge again.
I was expected to go around 85% efficiency this time...and to get at least one good charge as the math suggested.

Still I got the same 20% efficiency.... getting only 5% more charge then the previous 2xseries+2xparallel connection.

*What could be the problem ?

[oby_one]

I thought to try another set of batteries..... so I went and bought a normal 1.5Volts 4xpack.
The output of mintyboost is a little over 6 Volts.... and the phone won't accept the charge.
This was the main reason I stated to use 2xseries+2xparallel in the first place.....
It seems that I can't use 2xseries+2xparalell because of 20% efficiency.....I can't use batteries higher then Ni-mh because the phone will not accept the charge...as the voltage is not regulated above 5V... so I am stuck

So what do I do now?

[adafruit_support_bill]

The previous test started with a little more than a 30% charge. This test started at 0%. Charge rates are not always linear at the extremes, so it is not clear that we can compare these curves directly.

We also don't know what the actual current draw is. We have been assuming 500 mA, but have not actually measured it. If it were 500mA, the MintyBoost would have delivered 1500 mAh to the phone in the first three hours. That alone should be enough for more than a 50% charge on your 1400 maH phone battery. But, as yeoj4151 has said, the phone may think that it is connected to a wall charger and be discharging at the same time you are trying to charge it. In that case, you would have to account for the discharge rate of the phone.

So what do I do now?

• You could carry an extra pack and charge in 3 hour shifts with one of the batttery configurations you have tested so far.
  You could look into using C cells (nearly the same energy density as AA, but without the need for diodes)
  You could look into Lithium cells.
  You could investigate other charging alternatives. What you are looking for may well be beyond the capabilities of this device.

[oby_one]

The last test did not start at 0%. we are being deceived because the phone shut down at 30% while trying to empty it.
The super-bright led from the camera blitz consumes a lot of power so when I turned it on .... it put the battery for a short period of time beyond its capabilities, the phone sense that the voltage has dropped below a certain level and shut down the phone.
But the battery wasn't at 0% ...it was at least 20%

But, as yeoj4151 has said, the phone may think that it is connected to a wall charger

Nope.
The phone is telling me that is has an uSB charger.. so it knows exactly what current to draw.
Trust me on this... because I have made many tests.

Now here comes the funny part

You could carry an extra pack and charge in 3 hour shifts with one of the batttery configurations you have tested so far.

I have taken your suggestion with great amusement
I can already imagine myself caring 1Kg ( 2.2Lbs) of batteries with me on my mountain trips...
I can perhaps share the load between my friends.. and do combinations... like everyone carry 1kg for one hour.. or 500grams for 30 minutes.. or each member of my team should carry some of the batteries...
Funny .. very funny

You could look into Lithium cells.

I will ...but I am sure that I will have the same efficiency problem.

You could investigate other charging alternatives

Like carry one wind turbine.. or a nuclear power plant ?

What you are looking for may well be beyond the capabilities of this device.

How should I treat your affirmation ?
It is said on Minty Boost compatibility webpage that my device is supported. Now it's not ?

I would expect a more professional approach... in which adafruit is trying to investigate why the mintyboost doesn't fulfill it's specs.
Once again I quote from your site: New In Version 3: Provides 500mA @ 5V, tested .....

If the mintyboost was giving out 500ma and 5Volts... I wouldn't have a problem. Trust me the usb from my computer is giving exactly 5V and 500ma ...and my phone doesn't have a problem with that.
The second problem would be the very very low 20% efficiency.

So how about we try to seek out the problems of my device?