akaline batteries to charge devices. making a charger/battery pack

I know they make little usb chargers for this, but they can only recharge a phone (fully) once and i like the idea of alkaline batteries being able to pop them out for fresh new ones. Did some fiddling at home with a car charger and 4 C batteries and used the setup to charge my phone. It works great, being just a concept piece, and after buying some parts from radio shack, i should have a good final end product. Here are my expectations:

1. Should have enough power for a 10 charges of a usb device that has a 2000 mAh battery.
2. Capable of charging two to three devices at once.
3. Must use changeable batteries in the pack.

My questions:
1. How do i calculate the number of batteries (Cs or Ds) needed? I know the series has to be 4 long for voltage, but how many parallels for capacity?
2. Do i need to regulate the transfer with a resistor if i use more than on series in parallel?
3. How do i install a battery meter on the pack so i can check how much bat life is left in my portable charger?
4. I can take measurements, but im not sure which ones i need to calculate capacity (mAh vs. mA, Ohms, etc.)

Current setup: 4 C batteries in series. With all new it puts out 6.1 Volts, about 500 mA when charger is plugged in, and voltage dropps to riughly 5.2 to 4.3 while charging depending on how drained the batteries are. 4C batteries in series is good for about 2 full charges right now. D batteries are supposed to be double the capacity.

Thanks!!!!
Ivan.

 

Update: while i am trying to make this battery pack universal, here are the devices currently involved:
Motorola DROID Bionic 1st gen. (1735 mAh battery, 3.8V) charges at: 5.1V, 850mA
Nintendo 3DS (3.7V, 1750 mAh battery) charges at 4.6V, 900mA
Generic usb mini car charger for phone
4 C batteries, Energizer. (6-8 Ah, 1.5V)
Will post pictures when i get home in a few hours.

 

If I understand correctly, you are connecting 4 alkaline batteries in series to the "cigarette lighter" plug end of a USB charger. I'm a little surprised that the charger works with only 6V when it should be expecting 12V, but that's great if it does work.

The battery pack capacity in mAh is determined by taking the number of strings and multiplying by the mAh rating of a single battery.
Example:
C batteries with 7,500 mAH capacity per battery
2 strings of 4 batteries per string
Total pack capacity = 7500x2 = 15,000 mAH

3 strings would give you about 22,500 mAH which would be about right for 10 charges on a 2,000 mAh battery

Whether or not you get the full capacity of the batteries depends on how fast you discharge them. The listed capacity is usually at a C/10 rate, meaning that you would get this capacity if you discharged it over 10 hours. Faster discharges reduce the capacity.

If you are going to connect multiple strings, you should put a diode at the positive end of each string to prevent one string from trying to charge another.

Battery voltage will be an approximate estimate of the remaining battery life. Look up the depth of discharge curve for alkaline batteries. You must me sure the batteries are disconnected from the charger (not under load) when measuring the voltage to get an accurate measurement.

 

Well thought out reply sparky

Ivan......just curious....based on the cost of replacement batteries versus recharging from the grid or car .......you are looking at an expensive recharging method.....no ?

 

Keep in mind that the voltage will typically drop .7 volts across the diodes. This will come into play if you use rechargeable D-cell batteries as they are only 1.2 volts to begin with. You'd then need five in a string to get your 6 volts.

 

How about using a small rechargeable lead-acid battery? It'll be a lot cheaper in the long run.

 

Below I have posted a picture on my mock up conept before i assembled it. just four batteries, a car charger, and some electrical tape is all i used just to see if it could even work. I just cut the car adapter plug off, peeled back the cord, and that was that.

@Sparky31415
your are correct, and thank you for the tips and info.
@PJmax
This is for when a car or wall plug is not viable. I am an Avid out door person, and my dual-sport dirt bike doesn't have a charge port. the conflict with my love for the outdoors is of course my love for gadgets. Also, at airports, Bus rides (I am in the National Guard and we take lots of buses) and other places you simply can't get a plug in. I'd use a small lithium recharger, but like i said they just don't have the capacity for what I end up using. this is the most versatile option I have, and if i drain the battery pack, i don't have to wait for my charger to charge, i can simply plop in another set of batteries. very handy when your out in the forest / field.

@Justin Smith
I may consider this depending on the capacity I can find, and the size I can find. I want to be able to fit it in a cargo pocket.

 

Here are the numbers I have gathered:
V = I * R correct? Volts I is current, R is resistance

these were my notes during testing:
Data:

Cellphone:
Battery: 3.8 Volts
1735 mAh Minimum.
Charger: 5.1 Volts
850 mA

Nintendo 3DS
Battery: 3.7 Volts
1750 mAh
Charger: 4.6V
900 mA

V = I * R (V = Volts I = Current (watts or amps) R = Resistance

Cellphone:
Resistance on Charger: 6 Ohms

Nintendo 3DS:
Resistance on Charger: 5.112 Ohms

Testing: stripped Car charger, two wire. Attached 4 C batteries end to end (6 Volt system) and attached to phone. Charging symbol displayed. 22:05 battery was at 5%. Battery pack was at 6.12 Volts, 5.1 Amps BAT+ to BAT-
*after 2 hours:
While charging: 4.4V, 500 - 550mA
While not charging (battery pack): 5.2V, 3600mA from BAT+ to BAT-

Note: phone will not accept 5 battery series. An over voltage regulator prevents this.

Would four parallels of this battery series quadruple capacity without raising resistance? Current pack: 6 Volts ~ 6 Ah. R = V/I
R = 4.4V / 550mA

I've read that D batteries are meant for a higher discharge, about 600 mAh, would that be correct? that would make them better suited for the current that is flowing while the charger is plugged in, thus giving me more battery life, right? THats my biggets concern. I want to use a battery that can be bought at a gas station taht is suitable for this task. I used these sites to gather by data, but The internet is full of misinformation, so I want to check and hear ideas.
Battery Capacity
BatteryStuff Articles | Understanding Series and Parallel Battery Configurations
Ohm's law - Wikipedia, the free encyclopedia

Also, I want to put a guage on the pack that will tell me with an LED how much power is left in the pack before I'm out (green, amber, red) and am curious how I would add that to the final product. I plan to get real battery holders (from radioshack or somewhere else) and find a suitable case to enclose everything in. What should I look for in a case, and if you know what would make a good waterproof case (waterproof as in batteries enclsoed seperate of the cords so I could plug in under my coat in the rain or something). I want to make this a literal go ANYWHERE battery pack. also, whats the best padding to sue the protect batteries from being dropped if the charge pack was dropped? thanks guys!
*the 4 C batteries by themselves gave me about 2 charges, so I am thinking I need a battery that can handle a higher draw than the Cs.*

 

Why don't you try a 6v battery for an emergency light? They are smaller than a 1 pound brick of cheese and for lighting they keep the lights on usually a half hour at least your charger should last much longer on one

 

As long as each string has the same number of batteries, you can add strings to increase capacity. 2 strings have 2x the capacity of one string..

D cells could charge at 600 mA and still be at a c/20 rate or lower which should maximize battery capacity. Multiple strings would lower the rate at which each string discharged. I suspect that if you added a second string of C batteries to your current deign you'd also drop below the c/20 rate for each string.

There are a number of ways to do the battery charge indicator. One way is to set up a network of Zener diodes that will stop conducting at voltage levels that correspond to certain depths of discharge. Those diodes would control transistors that turn on/off power to the LEDs. There might also be a speciality IC that does these things. It's all much too detailed to explain in a post, but I'm sure that a google search will turn up some schematics.

 

Thank you very much! I rigged up two strings of D battereis and am currently charging the phone from complete dead to full, as a test timer. I had to put a diode in (1n4004 i believe, found it in an ancient AC adaptor) to keep the current flowing, otherwise, i think the Ds and their capacity were holding to high of a voltage. I put the diode on the negative side, between the cord black and the battery holder black cords. We'll see how the batteries faired after a full charge (voltage measurement).

On another note, I am VERY puzzled by one thing: I can not wire in a simple USB female plug to the batteries and get a charge. I've read voltage on the female plug once it's wired in, its perfectly fine, but for some reason when i plug my USB to Micro USB cord into the batteries and phone, it will NOT charge. it won't recognize it or something...

I am baffled. and clues? should I take this to the computer forums for this issue?

Charger setup is like this: Batteries > cord > device > diode > batteries.

 

After my phone reached 80%, it stopeed charging. I pulled the phone off the charger and gave the batteries a sit for about am inute, and then tested their voltage: 5.5V. I plugged the phone back in, no dice. stopped charging. I removed the diode and plugged the phone back in and the phone started charging again. So with the initial charge, the voltage (6.4V on new D batteries) is too much, but after 80% of a charge, the diode needs to be removed because at that point, the voltage is being dropped too much for the USBs tolerances.

New plan: step up the voltage off the two packs, install a NTE1951 Voltage Regulator, and that should clear up things.

My problem is I don't know what to do to step up the voltage without adding more batteries. It is already heavy enough, and it's size is about as big as I want to get.

QUESTION: What would I use to step up the voltage from 6v to 12v? preferably a small circuit board or something. Also, where to get parts?

 

Braether suggested earlier If it's v. size and weight you're becoming concerned about, what about 9V batteries?

 

I'm at 6v now, and the batteries are much easier the acquire than a 6v emergency light battery. like i said, i want to be able to replace them from a gas station if i need to when traveling on my dirt bike or bus trips in the National Guard.

9v batteries have more voltage, but the amp hours are pitiful, they have no capacity.

seeing as how I will have to go to a regulator anyways, its time do put a circuit board on this thing, I jsut don't know what to use in a circuit that can convert the voltage up ( i know it will dampen the current a little). I know of diodes, regulators, resistors, capacitors....but I'm not finding much info on what converts voltage up or how.

 

That may be true of 9V alkaline batteries, but have you looked at 9V lithium-ion batteries?

Since you'll be using this thing over and over, what if you used rechargeable batteries in it. I'm thinking now of the 1.5V rechargeable lithium-ion batteries that are packed into the batteries for cordless tools.

 

Here is my problem with rechargable batteries in this battery pack: I don't want to have to wait for my charger to charge up to charge my phone.

This charger is for trips. I don't want to pack the battery charger to charge the batteries for my battery charger(after I drain them the first time). This pack will be used once a month, sometimes twice. I'm willing to spend the money on disposables for one weekend a month.

I want the batteries to be easily available. Short of packing around extra batteries, spare batteries, a charging platform in case all of them get drained, im left with one option: purchase them on the Go. This is also why I want a high capacity, so that I most likely won't be buying too many. I want to be able to charge my devices, toss the batteries that are dead out, and throw in fully charged ones if i need to do more charging, and I will not have the carrying room for spare batteries.

as a small infintesmal factor: I'm a duracell fan, so I don't mind helping keeping their Alkaline branch of business going.

My issue is not the type of battery, I've settled on what kind I need and will work, and the quantity I can afford to have in this system. I know - switching over to two 6v emergency lights would be easier for getting the voltage i want. switching to a car battery would give me amazing voltabe and capacity - it owuld flat out be ideal.

But the device isn't about attaining a result. its about a product. D batteries are easily acquired, easily changed, and easily handled. They are small enough, with the right amount of capacity and rated discharge rate for my needs, and so in the end they suit my goals best.

Where I have hit a wall in this project: USB has a tolerance of 4.75 to 5.5 volts actively running through the system, depending on the device it can be slightly more tolerable. I need to make the output voltage consistent (current can fluctuate) and to do that I need to go up (to a minimum of 8) in Voltage, so that I can use a regulator to bring it back down, because a regulator requires higher voltage input to reduce it on the output (unless there is a way to provide consistent stepped-up voltage, then that would work well but I've yet to find anything like that).

​"Why not just add more batteries?" ​ answer is: weight and size. the device, with two 4-D battery holders back to back, is as large as I can go. its just right to be shoved in a cargo pocket (although heavy) for a short walk or whatnot.

​"Why not put all your batteries in series for 12 volts?"​ Capacity. I need two parallels

the last factor is this: the regulator ( 7805 +5V, or NTE1951 +5V) will have to go on a circuit. might as well just put more than the regulator and a few capacitors on the circuit to make it worth while, so I will use the circuit board (as it will take less space) to do the work of the voltage regulation for me. Or so I am going to attempt.

So, we're past batteries. How do you jump DC voltage? Inductor? Transformer? a special sub-circuit? I need a new lead to investigate, I've hit dead ends on nearly everything i can think of to google.

 

What's wrong with using a receptacle or your car's cigarette lighter?

 

Where I am at:
Capacity - Check
Voltage - Working, not Ideal
mA current - Check
USB - still not working, but that's on the phone side of things. separate task.

What I still Need:
How to step up DC Voltage
Where is it best to acquire parts for making a circuit
Basics of setting up a circuit


So, the closest thing I have found to what I'm trying to do:
MintyBoost

this is two AAs doing the same thing I am trying to do. Why don't I just build this and attach my batteries to it? It's discharge rate is only 200 mA. Not what my goal is. However, he does manage to step voltage up and then regulate it back down. I just can't exactly decipher how he did it, and what he used / how it was implemented.

I'll attach his schematic for his circuit below. Is there a possible way to modify his circuit so that it can output a higher Ameperage? how would I set it up for a different voltage if I still wanted to stick with my 6v setup?

also, how in the bloody hell do you read these things?!

 

This is a device for the OP to take along on his adventures on his dirt bike.

 

Dirt bike.......I thought it was an ATV ...


That circuit is a boost type circuit and it's output is based on how much current that IC chip can handle. As you've found out it's very low.

You don't get something from nothing. In other words....you can't put in low voltage and low current and get higher voltage and current from it.

 

I forgot the part about the bus trips when I was replying to Justin.

 

Rather than trying to build a boost converter, I'd recommend looking for a very low dropout regulator like http://www.onsemi.com/pub_link/Colla...NCP57152-D.PDF
Data sheets will generally have reference circuit designs that you can use to regulate the voltage.
You can learn most common electronics symbols and how to read schematics at many places on the Internet, such as Tutorial - How to Read a Schematic
As for acquiring parts, RadioShack will have some basic stuff but if you want the biggest selection, you'll have to mail order from places like Allied Electronics and Newark. Fry's also carries some stuff, at least a bit more than RadioShack.

 

Sparky, i can't thank you enough! 350mV dropout, thats insanely low, and will work great. And with your other info i should be able to start the circuit design. I'll post back in a couple of days, maybe you or someone else could proof it? And then it would be on to final production. Thank you again!

 

Been trying to disect the data sheet from that chip sparky sent me. The LT1618.

I'm lost.
"FB (Pin 1/Pin 1): Feedback Pin. Set the output voltage by
selecting values for R1 and R2 (see Figure 1):
R1 = R2((Vout / 1.263V)-1)

ISN (Pin 2/Pin 2): Current Sense (–) Pin. The inverting
input to the current sense amplifier.

ISP (Pin 3/Pin 3): Current Sense (+) Pin. The noninverting
input to the current sense amplifier.

IADJ (Pin 4/Pin 4): Current Sense Adjust Pin. A DC voltage
applied to this pin will reduce the current sense voltage. If
this adjustment is not needed, tie this pin to ground.

GND (Pin 5/Pin 5): Ground Pin. Tie this pin directly to local
ground plane.

NC (Pin 6/NA): No Connection for MS Package.

SW (NA/Pin 6): Switch Pin for DD Package. Connect this
pin to Pin 7.

SW (Pin 7/Pin 7): Switch Pin. This is the collector of the
internal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.

VIN (Pin 8/Pin 8): Input Supply Pin. Bypass this pin with
a capacitor to ground as close to the device as possible.

SHDN (Pin 9/Pin 9): Shutdown Pin. Tie this pin higher
than 1V to turn on the LT1618; tie below 0.3V to turn it off.

VC (Pin 10/Pin 10): Compensation Pin for Error Amplifier.
Connect a series RC from this pin to ground. Typical values
are 2kΩ and 10nF.

Exposed Pad (NA/Pin 11): The Exposed Pad on the DD
package is GND and must be soldered to the PCB GND for
optimum thermal performance."

FB PIN 1
SO if I want 5V out, R2 = 2.9588 ..but 2.9588 what? Ohms for resistance? volts? Amps? I understand math, but electronics add a whole new level to it, please help me understand this...

ISN PIN 2 - i need to know what inverting and non inverting are, and how current Sense works.
I apologize if i am sounding like i want someone to just outright do the circuit for me....but I'm way more new to this than I thought. Just trying to get enough info to push forwards. Please, I would appreciate the help. I'm understanding what symbols mean what on a circuit diagram, just not how they flow through this one to generate an output.
I need to build a parts list for the circuit board this month. And if a perfect reference for what my end goal should be is needed, I'm basically trying to build one of these with a disposable battery:

HyperJuice Plug

I don't want to shell out $160 for a portable charging station.

Final output desired: 4.8 - 5.2 V constant, 700 mAh - 1 Ah.
current input : 2 sets of 4 D batteries ( 4.8 to 6.8 V depending on battery life)
Considering this input: 2 sets of 5 D batteries (6 - 8.5 V depending on battery life)

the below pictured charger is 2 sets of D batteries, directly wired to a car charger I cut off at the 12v converter. It worked, but for the first charge (when the batteries are pumping out the higher voltage) I have to use a diode to drop the voltage in the system. after the first charge I can remove the diode, and get about 5-7 more charges out of it before the voltage gets too low (hence considering adding one more battery to each parallel). It works great, but rewiring in a diode everytime I change batteries is going to be a pain, and also I know these batteries have more juice, I just can't get to it without more voltage, so I need to add another battery each parallel, and that means I need the regulator. SO I'm almost there. Final stages. This thing worked great! I can't wait to finish it.

 

Electronics is a fun and exciting hobby. Semiconductors have changed immensely since I started in this field back around back around 1970.

I was looking at that chip you've picked out. It's a tough one to work with as it's surface mount technology. Your questions are answerable but I have a few of my own.

Actually I just re-read your previous post and some of my questions were answered.


Current is an important question because that chip can only dissipate so many watts in heat. Part of the design circuitry is a heatsink to extract heat from the chip. I think I read it may deliver 1A max. I guess that is possible but that means heat to get rid of.

Let me give it some thought.

You actually have enough voltage to supply to your devices. You really need a low loss close tolerance regulator. Something that will work close to the regulated voltage. Normally with a regulator circuit you would need several volts over the output. You don't have that cushion.

 

Thanks, i would really appreciate the help. Annual training starts at the end of the month, and i will be out in the field for 3+ weeks before i see a wall outlet again. I know solar chargers are an option, but i prefer batteries.

 

I've been looking at the MintyBoost pretty heavily, and considering hooking my battery setup to that. having 4 parallels of D batteries (total of 8 batteries) looks like it would work, rather than using just two AAs.

MintyBoost User manual - Choosing batteries
MintyBoost Kit [v3.0] ID: 14 - $19.50 : Adafruit Industries, Unique & fun DIY electronics and kits

would this work? should I jsut buy their kit and wire my own power supply in?

 

It would work but it looks like it's limited to 500ma. of output.

 

500mA is better than the 200mA of the minyboost 2.0. It may take forever to charge something at 500mA, but it looks like it gets the most from the batteries. I'll order it and at least give it a shot. There are a lot of modifications that can be made to thr mintyboost as well, as much i did try to avoid it. Like you originally told me, you can't get something from nothing.

 

I don't mean to beat a dead horse by plugging rechargeables since the OP has ruled them out, but I'd like to share my results with anyone else following this discussion since there's nothing i can find related on this diy site.

My 24 AA pack fully charges my power-hungry (3200 mAh 3.8v) razr maxx 3 times.
Without any diodes, resistors, boost circuitry, or any voltage regulation, it provides a steady 4.8 - 5.2 volts for about 8 hours. I haven't measured the amperage draw but it does charge the phone a bit more quickly than does the 850 mA wall supply.

i was inspired by the minty boost concept and did some experimenting with a boost converter and my 24 AAs arranged in different voltages, and i found that with the pack wired this way (6 strings of 4 directly through micro USB plug end), it provides the most usable charge for my device.

I use [Product name redacted] which are low-self-discharge and are advertised to have a 2000 mAh capacity.