Alternative Batteries
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Alternative Batteries

by DimiPana on Tue Dec 11, 2012 1:36 am

Hey, hi there, I just purchased this kit with the intention to slightly modify it. But I am hesitant because I am not an engineer, just an DIY electronics amateur/enthusiast.

So can you please tell me -beforehand- if this idea will work, so that I do not do anything stupid and fry this wonderful design?

I want to replace the existing 2 AA batteries with a combination of some brand-new 3.7V Li-ion connected in parallel. Ideally, I would like to end up with a "power pack" that I can charge (without removing the Li-ions) so then I can use the power pack to power/charge my devices. I have a total of four(4) of these Li-ion batteries (about 1000 mAh each) which should approximately add up to a nice 4000 mAh (right or wrong?)

Questions:

1. Is it OK (i.e. safe) to combine these Li-ion batteries in parallel? In this case the mAh will also add up or not?

2. Is it possible to use the same USB port as input AND output? E.g. In this design is the USB port bi-directional so that it can be used for the "power pack" to charge but -also- to be charged? I believe no, so how do I go about using a second connector in order to "charge" the pack?

3. Again, I do not have formal electronics/engineering education, so, is this way out my league? Or, simply put, should I just forget about it and just use the MintyBoost as is?

Sorry if I said/asked anything that from an engineer's perspective is flat out ...stupid, it is not my intention to offend anyone. I am simply trying to use an existing design in a slightly different way to better fit my personal needs.

Anyway, glad to have found this wonderful site/forum, I look forward to your reply.

Thank you!

Dimi Pana
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Re: Alternative Batteries

by adafruit_support_bill on Tue Dec 11, 2012 8:03 am

1. Is it OK (i.e. safe) to combine these Li-ion batteries in parallel? In this case the mAh will also add up or not?

Connecting individual cells in parallel is not recommended. Small variations in cell characteristics can result in unbalanced operation, reduced effective capacity and possible overheating. ' Balanced' packs are available if you need higher capacity. https://www.adafruit.com/products/353

2. Is it possible to use the same USB port as input AND output? E.g. In this design is the USB port bi-directional so that it can be used for the "power pack" to charge but -also- to be charged? I believe no, so how do I go about using a second connector in order to "charge" the pack?

You can't charge via the USB port, but you can just connect your charger output to the battery as in the photo below (That is our solar LiPo charger https://www.adafruit.com/products/390)

3. Again, I do not have formal electronics/engineering education, so, is this way out my league? Or, simply put, should I just forget about it and just use the MintyBoost as is?

The Minty is a great first project, and the modifications you propose are not at all difficult. And if you run into problems, there is always help on the forums! :D

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Re: Alternative Batteries

by DimiPana on Tue Dec 18, 2012 4:22 pm

Thank you for the reply. I did receive the kit (very fast delivery thank you!) and built it with no difficulty. Only mistake, I have to admit, even though I was aware of the 8-pin socket proper orientation, it kept falling out when inverted to solder, so I ended up soldering upside-down (yes, you warned in the instructions) but no worries, I just made sure the IC chip went in the proper way. Other than that a very easy 1st project completed in less than 1hr.

One last thing, I found that it was too easy to allow too much solder to flow creating a blob on the underside of the PCB, I guess I kinda fixed that by working a little faster, and not allowing the gun to stay in contact too long. Well, we learn as we go by our mistakes!

Interestingly enough, I do not get 5V output but 4.96 (!?). However, the charger works fine, it charged everything I connected that I normally charge from my PC's USB source. The IC does not get very warm during the charging cycle, I can barely feel a slight temperature increase (which is good, right?). Also, the voltage output from the 2nd and 3rd USB pins to either outer pin (1st or 4th) shows a constant 1.92 or 1.93 V.

So! What do you think?

Is this a "bad" sign that I do not get between 5 and 5.2V but 0.04V less than 5V? I hope not.

I also used rechargeable batteries that have been constantly used for at least 3-4 months, however they were fully charged and their output was a "healthy" 1.38V before testing with the MintyBoost.

Now, ideally, what I would like to do is find a way to connect the battery charger to the MintyBoost in such a way so that it charges the rechargeables inside. So, I will study the link and picture you provide me and return with questions. I will do my homework first so my questions will be few and to the point.

--

Thank you so much for everything: Great website, great projects, great customer service, great support. You guys are all great at AdaFruit!

Thank you !
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Re: Alternative Batteries

by adafruit_support_bill on Tue Dec 18, 2012 5:39 pm

Is this a "bad" sign that I do not get between 5 and 5.2V but 0.04V less than 5V? I hope not.

0.04v is within 1% of 5v and probably within the measurement accuracy of your meter. If your phone is happy with it, then it is not a problem.
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Re: Alternative Batteries

by DimiPana on Tue Dec 18, 2012 5:48 pm

Yes, it's a cheap-o-mutlimeter from HomeDepot or similar.

And, so far, 3 different smart phones (Samsung, Ericsson, HTC) no complains at all !

Thank you!
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Re: Alternative Batteries

by DimiPana on Thu Jan 10, 2013 2:03 pm

Sorry to bother you again can you please confirm if this is feasible:

--

So far, I am very happy with my MintyBoost (it came handy a few times) I am using it with Duracel rechargeables (2,400 mAh) and I get about 1.5 charges for my 900mAh cellphone battery. I enclosed it in a very interesting oval shape mint box (not Altoids) and I keep it in my car, just in case. I will post pictures shortly!

(Now, here comes the important question)

Is there a way to recharge the Minty Boost, without removing the batteries, by connecting the output of a wall-wart Ni-Mh charger to the red(+) and black(-) points on the pcb?

I am thinking that if do that I will be essentially providing (external) power to the Minty Boost and at the same time charging current to the batteries. Yes? Or ...NOT so fast mister!?

Is this going to be OK? Will the batteries still charge since the Minty Boost has a very low "internal" consumption when not in use? And to take this a bit farther, what will happen (in regards to both the batteries and the Minty Boost) if (at the same time) I try to use the Minty Boost to charge a device? Can I potentially destroy the circuit this way?

The more I think about this, it would be great if the Minty Boost can be slightly modified to -somehow- accept an external connection from a power source. This way, Ni-Mh batteries can stay in until they need to be replaced. Actually, if a solar panel charger is used, the Minty Boost becomes a really mobile power pack.

--

Again, I am not an engineer, I am coming from a purely "what if" perspective. Hopefully I am making some sense and not a fool of my self. :oops:

Thank you for your feedback, always appreciated!
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Re: Alternative Batteries

by adafruit_support_bill on Thu Jan 10, 2013 2:11 pm

The (potential) problem with recharging the batteries in place is that the charger needs to know the charge-state of the cells to control the charging cycle. Different chargers have different ways of implementing this. Depending on your charger, the extra MintyLoad may confuse it enough to disrupt the charge cycle and possibly even damage the cells.

One way to avoid this is to disconnect the batteries while recharging. Some users wired an SPDT (single-pole double-throw) switch in-line with the positive lead of the batteries. That way you can switch between the charger and the Minty.
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Re: Alternative Batteries

by DimiPana on Thu Jan 10, 2013 3:42 pm

Thank you so much for your prompt response, you guys are amazing!

--

So, yes, to be 100% on the safe side, the wall wart/solar charger output can be connect to the circuit's + and - points and charge the batteries in-place, but ONLY if there is a SPDT switch to isolate the Minty Boost input from the battery.

I have attached a picture of a SPDT . The switch has points L1, L2 and Com . Minty Boost, Battery Pack and External Charger have positive (+) and minus (-) points. Obviously some cables have to be disconnected and re-wired. Can you please describe how to make the new connections?

--

How about the scenario where a solar panel is used ? It's the same idea right?

So, now: Do you guys have available for sale the parts I need to accomplish this?

I beleive what I need is:

1. Wall wart charger for NiMh .

2. Solar panel charger

3. SPDT switch (the smaller the better).

4. Anything else required or recommended for this project.

--

Again, thank you for the feedback.
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SPDT.jpeg
SPDT.jpeg (3.27 KiB) Viewed 1992 times
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Re: Alternative Batteries

by adafruit_support_bill on Thu Jan 10, 2013 5:07 pm

If you are going to go the wall-power + solar route, you should seriously consider using a liPo cell instead of the rechargeable AA's. Then you can use our Solar LiPo charger which is specifically designed for "load sharing" so it can charge the cell and power a load at the same time. No manual switch needed. And it has a DC & USB input as well, so you can power it from a wall-wart or your PC too. :D
https://www.adafruit.com/products/390
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Re: Alternative Batteries

by Supreme_D on Mon Jan 14, 2013 5:05 am

adafruit_support wrote:you should seriously consider using a liPo cell instead of the rechargeable AA's

I know it may sound stupid, but what will be the fundamental difference in use between liPo battery and regular rechargeable AAs? In compatibility?
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Re: Alternative Batteries

by adafruit_support_bill on Mon Jan 14, 2013 6:49 am

Compared with NiMH (Rechargeable AAs) LiPo has a higher energy density, so it packs more power into the same space. But you can't use them interchangeably. LiPo cells are typically 3.7v vs 1.2v for NiMH. And the charge cycles are different, so they need different chargers.
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Re: Alternative Batteries

by Supreme_D on Tue Jan 15, 2013 3:01 am

adafruit_support wrote:Compared with NiMH (Rechargeable AAs) LiPo has a higher energy density, so it packs more power into the same space. But you can't use them interchangeably. LiPo cells are typically 3.7v vs 1.2v for NiMH. And the charge cycles are different, so they need different chargers.

Now I see, thanks for the explanation!
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Re: Alternative Batteries

by DimiPana on Tue Jan 15, 2013 5:54 pm

Hello -

I was browsing the various LiPo batteries you have available for sale and realized that there is a high capacity battery pack consisted of three cells wired in parallel using a special "balancing circuit".

I was wondering, since this balancing circuit appears to be the only safe/practical way to wire in parallel many LiPo batteries, is it possible to find/purchase/make such a circuit?

I have a number of unused LiPo I would love to combine, is it possible though?.

Thank you again!
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Re: Alternative Batteries

by adafruit_support_bill on Tue Jan 15, 2013 6:21 pm

Circuit designs are available on the web. But LiPo charging in general should be approached with great caution. Improperly charged cells can fail rather explosively.
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Re: Alternative Batteries

by DimiPana on Tue Jan 15, 2013 9:00 pm

Absolutely! I am glad I asked about LiPo charging in the beginning of this thread, I had no idea how dangerous this can be.

So, from your response I take it that I cannot purchase such a (balancing) circuit here at adafruit and I should rather look on the web.

Thank you!
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