DIY altoids USB charger won't charge sufficently

[rice923]

So I've built the ever popular altoids charger, except in a setup that i haven't quite found on the internet yet. I went for a 2 AA setup with a DC to USB step-up board. I have attached pics below to demonstrate the equipment used, along with the schematic.

I used the following parts:
1) 2 AA battery holder from RadioShack
2) SPDT submini slide switch from Radioshack
3) DC to USB step-up with variable output voltage
4) Various types of AA cells

Everything seems to be working except one detail: the contraption won't charge my smartphone (Samsung Galaxy Nexus if it matters). The best result I've had was a 20% charge on a fresh set of alkaline batteries. On my rechargeable NiMh batteries, I got about a 5% charge. However, after the phone fails to receive any more juice, I test the "spent" cells on an SMD flashlight, and they are actually still running well.

What am I missing? The only other thing I haven't really tried is to mess with the USB step-up settings. The item came as preset for 5V output. I'm not even sure how to adjust anything properly on it, and I'm not willing to ruin my phone to try my luck. If you look at the pic, there is a small brass knob on the blue box located on the step-up board. The brass knob appears to be adjustable for something.

Any insight as to what's causing the insufficient charge?

Note: I am using "current widget" on my phone to see what kind of voltage the charger is delivering to the phone. On both a wall charger and my DIY charger, there have been an average of 3.9V being recorded by the widget.

 

[Raven Luni]

- Use a proper meter to measure things and not your phone.
- Check the current output of the converter as well as the voltage. Compare it with a standard charger.

 

[(*steve*)]

The voltage required from the batteries to keep the inverter running may be high enough that it stops well before the batteries do.

What are the specs on the inverter?

 

[BobK]

Have a look a this:

http://data.energizer.com/PDFs/l91.pdf

At 1A discharge rate, the capacity of an AA cell is only 1000maH. You are going to need a 2A discharge rate to raise it up to 5V at 1A, and the capacity will go down, to maybe 750maH. 750maH at 3V is 2250mWH. Your cell battery is 3.7V so at that voltage you will get about 600maH at the very best of charge out of your AA cells. What is the rating of your cell battery? Likely something like 1200 or 1500maH?, so your charger is performing about as I would predict it should.

Bob

 

[rice923]

The voltage required from the batteries to keep the inverter running may be high enough that it stops well before the batteries do.

What are the specs on the inverter?

The specs are:
pecifications:

Input voltage: DC 0.9 - 6.0V
Output Voltage: DC 3.3-9.0V (adjustable, O/P Voltage > I/P Voltage by 3v, the default is 5V when delivery)
Output current: Rated current 800mA (when input in 2.8-3v), max up to 1000mA.,
Output Mode: Standard USB
Minimum Voltage difference: 3V
Conversion efficiency: Up to 94% (O/P voltage higher, the higher the efficiency)
Potentiometer adjustment direction: Clockwise (increase), counterclockwise (decrease)
Output ripple: 50mV (MAX)
Operating temperature: Industrial grade (-40 ℃ to 85 ℃)
Full load temperature rise: 20 ℃
Quiescent Current: 130uA
Load regulation:± 1%
Voltage regulation:± 0.5%

Raven: I don't have access to any multimeters, hence I had to do what I could (use the phone's software).

BobK: The alkalines did not have any indication of mAh ratings on the label, and I could not find anything from Google that matches the cells I used. The Rechargeable NiMh were 1600 mAh and 2100 mAh. This project was also inspired by Minty Boost, which also used two AA cells (and reviews for the MintyBoost indicates much better results).

Not sure if tweaking the potentiometer would help anything, but it's the only thing I haven't tried at this point.

PS. Thanks for the input so far guys. I was hoping to write a comprehensive tutorial on this, but it's not looking that useful at the moment.

 

[CocaCola]

What BobK said...

And further emphasized by this specification you posted...

Output current: Rated current 800mA (when input in 2.8-3v), max up to 1000mA.,

Your batteries will puke below that 2.8V-3V threshold in no time flat trying to supply [email protected] out... Once the output current that is rated at a max of 1000mA under perfect conditions falls bellow a certain required threshold (with current smart phones that want 1000-2000mA to charge) the phone likely just gives up as it simply is not getting the current it wants to charge, and thus stops charging... I would hazard a guess that this is in or about the 500mA area, off the top of my head based on my limited hands on testing...

 

[rice923]

What BobK said...

And further emphasized by this specification you posted...

Your batteries will puke below that 2.8V-3V threshold in no time flat trying to supply [email protected] out... Once the output current that is rated at a max of 1000mA under perfect conditions falls bellow a certain required threshold (with current smart phones that want 1000-2000mA to charge) the phone likely just gives up as it simply is not getting the current it wants to charge, and thus stops charging... I would hazard a guess that this is in or about the 500mA area, off the top of my head based on my limited hands on testing...

According to the transformer of my factory supplied phone charger, the output is rated at 1A (or 1000 mA). The specs of the converter also mention an 800mA output when there is a 3V power source, which is available from the two alkaline cells.

Assuming my converter is not pulling enough current from the cells, would a different board with the following specs get the job done?

Non-isolated DC-DC Step up module
Input voltage: DC 1 - 5V
Output Voltage: DC 5.1 - 5.2V
Output current: Rated current 1A , max up to1.5mA.,
Output Mode: Standard USB
Switching Frequency: 500KHZ
Output ripple: 30mV(Max) 20M bandwidth (Input 4V Outout 5.1V 1A)
Minimum Voltage difference: 3V
Conversion efficiency: Up to 96% (O/P voltage higher, the higher the efficiency)
Under voltage direction: Input voltage less than 2.7V, LED direction off
Quiescent Current: 130uA
Load regulation:± 1%
Voltage regulation:± 0.5%
Dynamic Response Speed : 5% 200uS
No short-circuit protection
No reversal protection

Note: I am very new to electronics, so please correct my language where applicable.

Edit: Also, If I can add another cell in series to the power source (4.5V total on alkaline or 3.6V total on rechargeables), would I get a more complete charge as desired?

 

[CocaCola]

According to the transformer of my factory supplied phone charger, the output is rated at 1A (or 1000 mA).

Yes, but that is a constant rating, it doesn't drop over time...

The specs of the converter also mention an 800mA output when there is a 3V power source, which is available from the two alkaline cells.

Only for a short time, please consult a drain curve (if you use this link look at the first graph) of the batteries you are using, the average AA battery drained at 2A (see Bob's post) will only be at 1.4-1.5V for about give or take a few minutes... It will fall down to below 1V after about 15-30 minutes... So after give or take 3-5 minutes of charging your alkaline batteries are likely well bellow the 2.8-3.0V threshold to supply the boost converter and it starts to puke on the output...

NiMh is even worse since they start at 1.2V a cell, thus you only have about 2.4 from the start and the boost converter is already puking...

Assuming my converter is not pulling enough current from the cells, would a different board with the following specs get the job done?

It's not a matter of the converter not pulling enough, it's the fact that the batteries can't supply that much...

If you look at Lady Ada's Minty boost you will see that she is only outputting 5V @ 500mA... This lower output gives the batteries a fighting chance, but I still believe her numbers on potential battery charge are a little optimistic... Also many new smartphones will complain about such a low charging current, or will cease to charge at all with that level of current... Or worse they will strain the charging circuit trying to pull more and cause a fault...

***EDIT***

Yes, adding more batteries both in parallel or series (lots of configurations, some better than others) will increase your ability to charge...

 

[(*steve*)]

Assuming my converter is not pulling enough current from the cells, would a different board with the following specs get the job done?

More/larger batteries.

Edit: Also, If I can add another cell in series to the power source (4.5V total on alkaline or 3.6V total on rechargeables), would I get a more complete charge as desired?

Almost certainly.

You may even get away with 4 rechargeables in series. Just make sure the battery voltage does not exceed 5.5V (if the input voltage to a buck regulator exceeds the desired output voltage, the regulator loses control -- it can't reduce it)

 

[rice923]

More/larger batteries.



Almost certainly.

You may even get away with 4 rechargeables in series. Just make sure the battery voltage does not exceed 5.5V (if the input voltage to a buck regulator exceeds the desired output voltage, the regulator loses control -- it can't reduce it)

I plan on doing 3 AAs in series to give a greater voltage output. Reason being I want this whole setup to fit comfortably inside an Altoids tin (with a short micro usb cable also tucked inside).

I will probably head out to pick up a 4 AA holder at radioshack and hack it into a 3 AA holder in series. Hopefully that will work and I can have a charger to bring to Vegas

Thanks all for the input so far. It has been very constructive and I will report back about any updates. Also, please feel free to comment on anything else about the project thus far.

 

[BobK]

If you want to know what it will really take to get a full charge, we need to know the rating of your cell battery. You have not given us that. I suspect that 2 AA does not even have the energy to give a full charge under ANY circumstances.

My 10 year old dinosaur flip-phone has a battery rated at 3.7V 1700maH. That translates to 6920mWH. Two AA cells have (at best) 3V * 2000maH = 6000mWH. So they could not charge my cell phone battery in a perfect world. In the real world, it would be diffcult to get them to give it a 1/2 charge.

Bob

 

[rice923]

If you want to know what it will really take to get a full charge, we need to know the rating of your cell battery. You have not given us that. I suspect that 2 AA does not even have the energy to give a full charge under ANY circumstances.

My 10 year old dinosaur flip-phone has a battery rated at 3.7V 1700maH. That translates to 6920mWH. Two AA cells have (at best) 3V * 2000maH = 6000mWH. So they could not charge my cell phone battery in a perfect world. In the real world, it would be diffcult to get them to give it a 1/2 charge.

Bob

My phone's battery is 3.7V 1750 mAh.

I'm switching to a 3 AA in series (probably tmr if I have the time). I plan on using the charger with alkalines (1.5v 2000 mAh each cell) or rechargeables (1.2v 1600mAh each cell). I'm not sure how to calculate how much of a charge I can yield from those particular battery choices. Please do tell

BTW, is there a "thanks" button in this forum? The other forum that I frequent (XDA-developers) has a little "thanks" button under each person's post to give thanks.

 

[CocaCola]

I'm not sure how to calculate how much of a charge I can yield from those particular battery choices. Please do tell

Lucky for you it's easy at the core BUT there are LOTS of other variables that will alter the 'perfect' world math, these numbers we can only fudge unless we really want to get into some fancy simulation equations...

You have a 3.7V @ 1750mAH battery, so you take the Voltage 3.7V and multiply it by the Amps 1750mAH and you will get a Watt Hour value...

In this case for your battery you take, 3.7V x 1750mAH = 6475mWH...

Now we do the same for your 'charging' batteries...

3 AA alkalines = 4.5 x 2000 = 9000mWH
3 AA rechargeable = 3.6 x 1600 = 5760mWH

BUT, we live in the real world where energy is lost in conversion and where you will never totally sap every bit out of a battery... Also battery mA ratings are hyped up and factored with LOW drain numbers, when you have a high drain the batteries will puke much sooner...

With that said as Bob hinted in your design you can probably knock off about 50% (possibly more) off the top of your expected battery output in this case in loses or sub-par performance due to excess high current drain...

So now you have 3 AA alkalines realistically providing about 4500mWH, while your 3 AA rechargeables are probably in the 2880mWH area... Your phone battery requires 6475mWH, so once again we do some simple math...

4500 divided by 6475 = about 69% charge capacity
2800 divided by 6475 = about 43% charge capacity

 

[BobK]

To reinforce what C.C. is saying. If you look at the datasheet I posted earlier for the Energizer alkaline AA cell (which is going to be as good as you will get), it is listed at 2000maH at 50ma discharge rate, 1000maH at 1A discharge rate. With 3 cells the discarge rate while charging will be close to this 1 A rating. This is why C.C used 4500 as the energy of the cells, rather than the 9000 that you would get a 50ma (but it would take over 35 hours to charge your phone, if it would even charge at that rate.)

Bob

 

[rice923]

Wow... Thank you Bob and CC for all the informative posts. I'll need to check out those links after finals this week. In the meantime, gotta study for my physiology final.

Thanks again and I'll be sure to report back once the build is complete.