Charging a balanced Li-Ion pack (solved)

Hello Arduino,

I've been using 4 NiMh AA cells in series to power my project but would like the ability to charge while in use via micro USB just like a mobile phone. I'd like to use a lithium ion pack that contains 3 cells in parallel providing 3.7 v and with a capacity of 6Ah in conjunction with a micro USB charging module. However, I'm unclear as to how I can charge these cells as the micro USB charging modules I've seen warn that they are without balancing features making it unsafe to charge Li/Ions in parallel.

A little about the project:

I need the high current capabilities of multiple cells mostly because there is a thermal printer involved that draws a lot of current. Since most of the devices in the system are 5v, my plan is to regulate the 3.7 v (to prevent from dropping below converter's min voltage) then boost it to 5v with a converter/power supply module. The battery pack has built in protection circuitry.

Battery: 353 Lithium Ion Battery Pack - 3.7V 6600mAh

Charger: Batteries/Holders :: Battery Chargers/Testers :: BAT-C-10 Micro USB Lithium Battery Charger

Power Supply / Boost Converter: PSM-120 DC-DC Step-up power supply module with voltmeter - 3-35V to 3.5-35V

Has anyone had experience with these micro USB chargers? Your help is appreciated!

If the batteries are in parallel, they automatically balance.

Series connections require balancing chargers.

AncientOracular:
I've seen warn that they are without balancing features making it unsafe to charge Li/Ions in parallel.

I need the high current capabilities of multiple cells mostly because there is a thermal printer involved that draws a lot of current.

Has anyone had experience with these micro USB chargers? Your help is appreciated!

It is unsafe to charge individual cells in parallel with that particular charger, however you are using a battery pack which has protection circuitry so it won't be an issue.

How much is a lot of current? that pack can only give continuous current of 6Ah and max 13Ah burst. Moreover your Boost converter module cannot actually handle the 6A advertised current continously , so you need a better one if you actually need 6A.

I have used that charger and it works fine. For you that charger will only charge at 1A which will take a lot of time to charge your battery pack.

Switching to Lithium Manganese cells can give a LOT more current output than this Lithium Cobalt battery pack.

I only need a total of 4.5 A in a maxed out peak current situation, Printer needs no more than 3A. Do you think the converter can handle that? It says 6A max so i figured this should be safe.

Are there any higher current charging modules you recommend for this pack / set up? How long is a long time?

It can handle 3A but it will warm up pretty fast.

There are charging modules with higher current but I suggest you get this adjustable CC CV buck converter that can also charge lithium batteries at 2A or 3A

How long is a long time?

The charger you linked to will take more than 7 hours to fully charge your battery pack. The module I suggested will do it in less than half that time.

Wait a minute. What is your main power source??

because it has to both charge the battery and power your project at the same time. Also the charger module you mentioned is originally built for a single 18650 battery and has an over-Current Protection which will prevent your boost converter from drawing more than 3A which will in turn will cause power shortage.

I was planning on using a mobile charger for the sake of convenience but I guess I'll probably need more current than that to both run and charge simultaneously. I'll need something that can provide 7A continuously (4.5A for operation and 2.5A for charging). Any suggestions?

Can you link me to that converter + charger you mentioned?

Mobile charger can't handle more than 2A if usb 2.0 and 3A if usb 3.0. Although there are dual or triple output models.

The first thing that comes to my mind when I hear high amperage at 5v or 12v is the desktop ATX psu/smps.
There are high amperage power supplies available. Check the site which you first linked. Search for AC to DC 5v in that site.

AncientOracular:
Can you link me to that converter + charger you mentioned?

Which country do you live? do you have ebay or amazon over there?

Canada, so yes we have Amazon, Ebay, etc. Thanks for the help! I'll check around a bit and come back with any questions.

How about this? 658-ADA 5V 10A Switching Power Supply

How would all of these things be wired together? The 3.7v battery pack, 5v PSU, converter/charger, and 5v system circuit?

Yes, Perfect, That power supply can power your project and charge your batteries simultaneously without any problems.

You will have to split the output from the 5V PSU, one will go to the charger and the other will go to your project.
Another separate connection will go from your battery pack to your project with diode protection so that the battery pack will kick in only when the main power source fails or is disconnected and also to protect the batteries from getting over current from the main PSU circumventing the charger.

I’m still a little confused about how to wire these together. I attached a schematic indicating what I understand by your description. Please let me know if this is what you meant.

AncientOracular:
I was planning on using a mobile charger for the sake of convenience but I guess I'll probably need more current than that to both run and charge simultaneously.

Why? Does the printer draw current continuously?

aarg:
Why? Does the printer draw current continuously?

As I understand it, it requires a spike in current to heat the tip when printing. If it were to print, for 20 seconds let's say, I'm not sure if that would technically count as continuous current draw or just a series of spikes, thereby requiring lower continuous current capabilities.

AncientOracular:
I’m still a little confused about how to wire these together. I attached a schematic indicating what I understand by your description. Please let me know if this is what you meant.

I’ve done some modifications and uploaded a file so that you can get a better idea.

You forgot the boost converter, and also you must add another diode to the output of the psu and connect it to the boost converter instead of directly to the load. - Why? - because you don’t want the battery output to backfeed the charger or the psu. Also the diode drops ~0.7 volts so all the diodes in circuit must be before the boost converter.

If you use a schottky diode the voltage drop will be less.

Awesome, thank you! I thought you were recommending a module that boosts and charges, that's why I only had the charger depicted and also why I was confused about wiring in general. What charger and booster do you suggest?

AncientOracular:
I thought you were recommending a module that boosts and charges, that's why I only had the charger depicted and also why I was confused about wiring in general. What charger and booster do you suggest?

Nope, the module I showed you was a buck converter that can also charge Li-ion batteries.

The boost converter you linked has a serious problem. It will struggle and be erratic below an input voltage of 4V. You can clearly see it in this video. This is a common problem for most high power boost converters. Another problem is that switching boost converters draws a lot of current to boost voltage.

My suggestion is that you pick a high voltage battery pack (like the ones used by drones) and then use a high power buck converter to drop the voltage to 5V. This will be much more efficient and doesn't draw that much current from your batteries as compared to your first setup. This way you also don't have to buy a high current 5V psu, you can simply use a 19V laptop psu or the more common 12V wall warts which almost everybody has a spare lying around in their homes.

Update-
I did some search and found these

RC LiPo battery pack.

It costs 10$ less than the one you linked. Also has a continous discharge current of above 90A whereas your battery pack was 6A. This battery is at 11.1V so it can be easily stepped-down to 5V.

Also the new one is 35Whr compared to your 24Whr one, so you will get more run time out of it.

Before you go and buy anything, I also want you to know that there are other options available too.

You can also use a 12V SMF battery along with it's own special wall charger with trickle charge function.

Actually how long do you to power your project on batteries? I forgot to ask you this in the first place. :slight_smile:

Noobian:
Actually how long do you to power your project on batteries? I forgot to ask you this in the first place. :slight_smile:

The longer the battery life the better, with no minimum run time in mind. The solution with longest life span, highest efficiency and cost effectiveness is ideal. What would be the advantage of using the SMF battery?

I see what you mean about the boost converter being a poor choice but I’m not seeing 12v PSUs that give more than 2A. Is it common to find these wall warts that give higher current?

AncientOracular:
The longer the battery life the better, with no minimum run time in mind. The solution with longest life span, highest efficiency and cost effectiveness is ideal. What would be the advantage of using the SMF battery?

I see what you mean about the boost converter being a poor choice but I'm not seeing 12v PSUs that give more than 2A. Is it common to find these wall warts that give higher current?

You can have a room full of truck batteries or Tesla Powerwalls and run your project for years :smiley:
but that's not the point , Like for example if your project is portable then you also have to take weight of the battery and space taken by it too. Which itself is a major deciding factor that leads to choosing the right battery.

The advantage of an SMF battery is that it's damn cheap. For 10$ you can get an 80Whr battery.(12V 7Ah)
The disadvantage of an SMF battery is that it too damn heavy. That 10$ battery can weigh like a dumbbell.

There are 12V wall warts that give more than 2A, but the thing is that you don't need 12V PSU's that give more than 2A because you can simply use 2 of them. One to charge that Li-Po battery pack and another one powers your project. :slight_smile:

Now if your project will not ever leave your desk, then this guy will be the ideal choice. Since it's cost effective and gives a decent amount of backup. The most interesting part is that you don't have to worry about converters or batteries or stuff anymore . You can simply run your project using a wall wart. As an added feature you can also plug in other small appliances to get battery backup.