Strange behavior of mintyboost

[Vincek]

Hi everyone,

recently I came across this great site and decided to build my own mintyboost. I went for version 1.2 with MAX756 step up converter. After successfully soldering everything, I got 5.02V on the ouptu. So far so good.

Then I plugged my HTC HD2 and the charging status came up and I was pleasantly surprised. But then only problems came - the battery status wasn't increasing at all. I even had the feeling that when using the phone while charging it discharges faster than usually. I checked the voltage at the output of the batteries - around 1,6V (It was 3.2V bofre plugging in the phone and batteries were brand new non-alkaline SONY). The voltage at the output was around 4,2V. I tried new batteries and the same result. The MAX756 is not able to hold 5V under a load even with new batteries. I tried the same now with a GP alkaline batteries and a DURACEL alkaline to be sure it is not the problem of those particular batteries. Same result - OUTPUT voltage dropped immediately to 4,2V. The phone actually charged around 2% (improvement over the shitty batteries), but then charging turned off and again the phone was discharging suspiciously quickly. I base the status of the battery on the phone status indicator which shows battery state in %.

I came to the same result with HT Hero.

I would like to ask you if anyone has used mintyboost with any of those devices. Can this problem be related to the device? I must add that I haven't connected anything to the D+ and D- pins since I assumed there is no protection like with I-Phones and ready to change it later if the phone wouldnt start charging. Can this be the issue? Or is it possible that even the DURACEL alkaline are not able to charge the phone for more than few percent and cause this voltage drop to 4,2V?

I have only few practical experience with such electronics and would like someone to help me and tell me what can cause this behavior, especially the voltage drop on the output.

Thank you very much

[adafruit_support_bill]

What current does your phone need to charge? The Max756 is only capable of about 150mA. Adafruit changed to the LT1302 with version 2.0 to handle the increased current demands of modern smart-phones. http://www.ladyada.net/make/mintyboost/changelog.html

[Vincek]

Thanks for the idea, I am starting to think this might be the issue. I haven't discovered how much current do I need to charge the HD2. But I assumed that with less current it would only take longer time, but would charge up anyway. Maybe the device just expects much more:). However is that normal that the voltage drops this way? can the phone itself pull it down? I measured also the current while charging and it is taking something like 150mA out of the batteries, but seems to be dropping rapidly down to 80mA.

[adafruit_support_bill]

I don't know how the MAX756 handles an overload condition. Best case, it would shut itself down. Worst case, it could damage the chip.

[Vincek]

So if I understand correctly:

if the phone requires more current to charge up than 150mA, it forces the MAX756 to overload? I thought the chip and the circuitry itself decides what current it will provide no matter what the device needs. I am a bit lame in this stuff:).

In that case I am not sure what to do, because based on how long it takes to charge from the original charger (less than 1,5h) it can withdraw as much as 1A.

Will give it a shot with some other booster then.

[adafruit_support_bill]

It is a voltage regulator, not a current regulator. It is trying to keep the output at 5v.

[Oby One]

Hi,
I have the Minty Boost V3.0 built with a 4x battery pack ( 2xserial+2xparallel giving 3.0 volts) and a htc Desire phone.
The mintyboost output is ok and it is 5 volts.

The strange behaviour can be described like this.
The charging strarts ok.. it goes up to 25% then the phone discharges all the way up to 0% then shuts down.
In the morning I find the freshly recharged battery pack completely empty.
I have a brand new 4x Sony Ni-Mh 2500mah that do very well in other devices.
The temperature of the lt1302 chip goes high ...about 55Celsius or 131 degrees Fahrenheit.
As I read from the lt1302 datasheet.. it has a normal working temperature up until 70Celsius so I should be ok....
Please put a faq somewere in the site so people wouldn't have to ask what is the normal working temperature of the V3 mintyboost:
a) in USb charging mode
b) in Ac charging mode ( the two data lines soldered together )
You have to specify this two different working modes because the output on the usb chaging mode is only about 500ma....and in Ac mode about 1000ma ( the drain is much higher and the chip gets much mor hot)

I have attached a few pictures with my minty boost board and its battery pack.
For building the battery pack I have use the instructable guide from here: http://www.instructables.com/id/Double- ... -parallel/
As specified in the guide I have used 2x 1N5817 diodes for the positive line of the battery banks. Unfortunately I didn't have another two around the house for the negative one... but I will buy some today.
I mentioned this because the diodes also get very very hot ... and I don't think this is normal.
Still .. the battery back provides a nice clean 3Volts to the mintyboost..

So what do you think its the problem ? Why my htc desire doesn't get a full charge ? ...and more important why is it discharging so fast when connected to my mintyboost?

[Oby One]

Post two for uploading more pictures

[Oby One]

Post three for uploading more pictures

[Oby One]

A small correction...
I have used 2x 1N5819 diodes.. not 1N5817 ( but this shouln't be a problem since they have very similar specs)
Today I have bought 2 aditional ones... and mounted them on the negative wires...
I only have 2.2 V on the exit of the battery pack instead of 3.0 V
any ideea why ?

[adafruit_support_bill]

I only have 2.2 V on the exit of the battery pack instead of 3.0 V
any ideea why ?

NiMh cells are only 1.2v. (They will be slightly higher for a short time when freshly charged). And there will be a 0.7v drop across a silicon diode.

[Oby One]

Zboing... I didn't take into account that the Schottky diode 1N5819 has such a big voltage drop....
Perhaps this is why they get very hot...
I don't like it ... i loose a lot of power via heat... and I hate bad efficiency .
Can you please recommend me a better diode ?.... one that has a very very small voltage drop ?
Or maybe another schema to use 4x batteries and not use diodes?

[adafruit_support_bill]

Sorry, I missed that they were Schottkys. Those are a little lower, but still about .5v I think.

With NiMH cells, you can actually get away with 4 in series and forget about the diodes entirely. 4x 1.2v = 4.8v which is fine for the MintyBoost. On a fresh charge you might see a shade over 5v, but that will sag quickly under load.

[Oby One]

Please read my post before the pictures.
I didn't use 4xAa with a serial connection to get 4.8 V ...but 2 in series and the two banks in parallel. to get a 2.8 V

Still I need to find a better diode.... that has a very very low voltage drop.

[adafruit_support_bill]

But why in parallel? You will get better boost efficiency with a higher input voltage (within limits of course). And you won't need those energy sapping diodes.