Cheapest Active Cell Balancer Project

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Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Wed Mar 29, 2017 6:46 pm

Hi all,

I am new here, so, let me know if I am doing anything wrong.

Basically, I think I just successfully designed a non-dissipative active cell balancer using cheap jellybean parts. The cost for all material (excluding labour) is around £3 to balance a 2-cell pack at 1A.

I am actually quite surprised by how simple it is and I wonder why no one is selling it yet.
My design uses closed-loop buck converter topology. It looks almost like this: http://www.flyelectric.ukgateway.net/bal-circuit.htm
But, instead of opamps, it uses half-bridge driver.

The design is analogue based with no microcontroller or any special battery-chip involved. The close-loop is achieved by an LM358.
It is so simple that I am very excited to share it.

At the moment, it is all built on a perfboard and I am currently optimising the quiescent current (quite high actually).
The design is intended to be used while charging (maybe even running?).


The advantages are: low wasted heat, higher current (not tens of milliamps), and, small footprint (almost the same size as 9v battery).



I am planning to open source the design as I think the community will be able to improve it further and benefit from it.

But, before I open source it, I want to sell at least 10 of them (maybe on Tindie?) for around £8 each. The reasons are:

1) To recover my RnD costs (£15)
2) I want to buy a hot air soldering station (£25 on ebay) to assemble it
3) I want to teach myself pcb manufacturing (maybe £15?) and selling hardwares


I am willing to give free three prototype samples to anyone that answer these questions:

1)
Do I need to worry about CE to sell it? I tried to research about it, but, it is difficult for me to understand lawyers' languages.
Breaking this down to simple English would be nice. as IANAL.
I know dealing with battery is dangerous, hence the question.
I will incorporate polyfuses and reverse-polarity protection in 2nd revision for extra safety.

2)
What is the best place for me to sell this as cheap as possible? Is Tindie a good start? Or, is ES is good enough?

3)
As this is my first time manufacturing my own PCB and sell it, any tips? I am planning to use SeeedStudio because of the low price (hopefully lower than £15).
Any suggestions?

4)
Maybe a small review about the prototype.


I am in the UK at the moment, so, the free samples can be posted only to the person that are in the UK (to keep low shipping cost).

I am also interested to see someone else's design (that is <= £3) for me to compare against my design (I can't find any on google search, am I the first?).


Any guidance will be greatly appreciated.

EDIT:
I forgot to mention that, instead of wasting energy in resistors, the design will transfer the charge from strong cell to weak cell.

Thank you. :)
Last edited by AfdhalAtiffTan on Wed Mar 29, 2017 6:50 pm, edited 1 time in total. View post history.
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Re: Cheapest Active Cell Balancer Project

Postby Punx0r » Thu Mar 30, 2017 3:36 am

AfdhalAtiffTan wrote:1)
Do I need to worry about CE to sell it? I tried to research about it, but, it is difficult for me to understand lawyers' languages.
Breaking this down to simple English would be nice. as IANAL.
I know dealing with battery is dangerous, hence the question.


It's highly likely that your product will fall within the scope of at least one EU safety standard and would therefore need to be assessed for CE conformity before it could be placed on the market. However, the chances of it being worth you doing this for the sake of selling a handful of units to a hobby community is slim and the chances of Trading Standards taking noticing your activity and taking action similarly slim.

The main impact in failing to comply with CE marking would be in the unlikely event that your product caused serious damage or injury and the matter reached the courts. It would greatly increase your culpability.
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Thu Mar 30, 2017 1:51 pm

Hi Punx0r,

Punx0r wrote:It's highly likely that your product will fall within the scope of at least one EU safety standard and would therefore need to be assessed for CE conformity before it could be placed on the market. However, the chances of it being worth you doing this for the sake of selling a handful of units to a hobby community is slim and the chances of Trading Standards taking noticing your activity and taking action similarly slim.


I don't think I will be able to sell more than 20 units, so, I will take that as a green light for me.


Punx0r wrote:The main impact in failing to comply with CE marking would be in the unlikely event that your product caused serious damage or injury and the matter reached the courts. It would greatly increase your culpability.


Now that you mentioned it, I will definitely add polyfuses in the final design.



I will be assembling the prototype board to send to you. Give me two weeks to get it done and I will PM you for your address for me to post it.



Thank you so much for your reply!
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Sun Apr 02, 2017 6:36 pm

In case anyone is interested, I am posting my progress on https://hackaday.io/project/20825-low-c ... y-balancer
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Re: Cheapest Active Cell Balancer Project

Postby Vanarian » Mon Apr 03, 2017 1:42 pm

Hi :)

Interesting design ! Do you know what the maximum current will be ? Can it set a max voltage per cell ? I want to make a DIY charging dock for 4x 8S1P 18650 batteries with integrated "bms" for charging. Plug and forget, unplug once full.

I see that you use 14S recycled pack so it must be working right ? What max charging level do you usually set ?

I'd love to test this if it can meet my needs. If it can bear high enough current I know a handful guys who'd be interested too for a "battery integrated" solution on their e-boards.
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Wed Apr 05, 2017 3:17 pm

Hi :D


Vanarian wrote:
Do you know what the maximum current will be ?


The maximum current is set by the chip (around ~3A), but I want to limit it to 1A for safety reasons.


Vanarian wrote:
Can it set a max voltage per cell ?


This is a simple active balancer, the max voltage is always half of 2S cells (it will auto adjust). For example, if you have 2S cells staying at 9V, the max voltage per cell will be 4.5v.
In other words, the max cell voltage is set by the full pack voltage, e.g. 8.4v for 4.2v or 8.0v for 4.0v, etc.

Vanarian wrote:
I want to make a DIY charging dock for 4x 8S1P 18650 batteries with integrated "bms" for charging. Plug and forget, unplug once full.


The good thing about my design is that, instead of monitoring each cell's voltage, you can just monitor full pack voltage (in your case 33.6V), and the balancer will force all to be 4.2V.
i.e. no need to monitor 8 voltages, just one is enough.


Vanarian wrote:
I see that you use 14S recycled pack so it must be working right ? What max charging level do you usually set ?


No, it is an ongoing project. I usually charge at 4.1v, but it is difficult to maintain with a passive balancer. Recycled cells are very capacity-inconsistent, this is why I started this project.

Vanarian wrote:
I'd love to test this if it can meet my needs. If it can bear high enough current I know a handful guys who'd be interested too for a "battery integrated" solution on their e-boards.


That is awesome! Once I fully optimise it, I will send a free board for you to test and review. Hopefully it will be useful for e-boards too. :)
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Re: Cheapest Active Cell Balancer Project

Postby Vanarian » Sat Apr 08, 2017 8:34 am

Hi, that's great thank you! ;)

OK so basically the balancer splits equally in 2 based on charger voltage input? That's good feature too!

Two more questions :
- how could we help you?
- how is it plugged? Is it like - charger - > balancer-> batteries or charger - > batteries - > balancer?
Last edited by Vanarian on Sat Apr 08, 2017 9:07 am, edited 1 time in total. View post history.
I needed to turn Air Gear stuff into reality so I am making this!
-+Electric inline skates - no remote control - weight / angle sensor - hub motors - one frame for all wheels sizes between 80/125mm - from 3.2 to 12 KW :mrgreen:

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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Tue Apr 11, 2017 4:29 pm

Hi :)

Vanarian wrote:OK so basically the balancer splits equally in 2 based on charger voltage input? That's good feature too!


That is the plan. ;) I designed it that way so that i don't have to measure individual cell voltage, this simplifies monitoring.
Feel free to suggest any features. :mrgreen:


Vanarian wrote:Two more questions :
- how could we help you?
- how is it plugged? Is it like - charger - > balancer-> batteries or charger - > batteries - > balancer?


At the moment, I am working on optimising the close-loop stability. I post most of my progress on hackaday if you are interested.

In terms of help:
-I might need some advice on the questions in my first post.
-Contribute by improving the circuit that I posted on hackaday
-Provide reviews for the prototype that I will send for free (and hopefully suggest some improvements)



The final application will look somewhat like this:

[charger] --> [battery] <-- [balancer]

The battery can be charged normally, but with the balancer hooked, it will force all cells to have equal voltage.
Without the balancer, the cell voltage is determined by its capacity, i.e. high-capacity cell will gain voltage slower than the weaker cell.
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Re: Cheapest Active Cell Balancer Project

Postby sn0wchyld » Tue Apr 11, 2017 6:53 pm

interesting project. I presume your using a isolated buck converter between the cells? Does it have any kind of 'deadband' where if the cells are within x% of each other, it stops trying to equalize them?
Seems as if you could technically charge up just 1 cell in any given series string, and this would distribute the energy among the whole pack... Not the most efficient or quick way of doing it though hahah.
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Wed Apr 12, 2017 4:01 pm

Hi,


sn0wchyld wrote:interesting project.


Thanks :)

sn0wchyld wrote:I presume your using a isolated buck converter between the cells?


No, I use a synchronous buck topology.

sn0wchyld wrote:Does it have any kind of 'deadband' where if the cells are within x% of each other, it stops trying to equalize them?


It has no deadband at the moment. It will never stop equalising as long as the total voltage is above 5V.
I plan to add auto shutdown later.

sn0wchyld wrote:Seems as if you could technically charge up just 1 cell in any given series string, and this would distribute the energy among the whole pack...


Yes, that is how it will work.

sn0wchyld wrote: Not the most efficient or quick way of doing it though hahah.


It is better than using bleeder resistors ;)
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Re: Cheapest Active Cell Balancer Project

Postby Vanarian » Sat Apr 22, 2017 8:23 am

Hi,

Just checked your Hackaday page, good work keep it up! :wink:

I receive a batch of new cells on Monday, can't really wait to try it out on them.

Edit : just forgot, since you don't want to sell a lot of them I assume that you will sell them not as a company but as a private person; hence your sales may remain in the "personal goods" sales category. In that case selling your units as private won't strain you with any certification duties because you are not a professional selling a commercial product.
You need to check how many goods people are allowed to sell in UK before reaching the "professional activity" category though. Hope this helps a bit :)
Last edited by Vanarian on Sat Apr 22, 2017 8:37 am, edited 1 time in total. View post history.
I needed to turn Air Gear stuff into reality so I am making this!
-+Electric inline skates - no remote control - weight / angle sensor - hub motors - one frame for all wheels sizes between 80/125mm - from 3.2 to 12 KW :mrgreen:

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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Sat Apr 22, 2017 9:53 pm

Hi Vanarian,

Thanks for checking the logs, I appreciate it.

At the moment, I got the balancing tolerance down to lower than 0.3%, that is just under 10mV for 4.2V li-ion cells.

Yes, I don't plan to sell many of them as I am still in a uni, I worry I can't time manage myself.

Your cells arrived on Monday? That will be exciting! :)
I think I am ready to send the prototype version to you (built on a perfboard), I hope I can build it fast enough.

If you want a proper manufactured PCB (with safety features included -- overcurrent/reverse-voltage), I can't make it until the end of next month because I have to wait for my student allowance to finance it.

And yes, thank you for your advice, it surely helps! :D
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Re: Cheapest Active Cell Balancer Project

Postby Vanarian » Sun Apr 23, 2017 10:20 am

I feel you there it's harsh for us students to support projects!

I'd gladly help out though, since I was planning to offer at least to pay for shipping (I'm in France :P) I send you a PM.
I needed to turn Air Gear stuff into reality so I am making this!
-+Electric inline skates - no remote control - weight / angle sensor - hub motors - one frame for all wheels sizes between 80/125mm - from 3.2 to 12 KW :mrgreen:

Rollo Ergo Sum!
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Re: Cheapest Active Cell Balancer Project

Postby Offroader » Sun Apr 23, 2017 2:12 pm

Quick question, could you really trust that this is working to balance the cells if you have no feedback on the voltages?
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Re: Cheapest Active Cell Balancer Project

Postby miffi » Mon Apr 24, 2017 9:39 am

This is a nice project you have going. When you are ready, I will take a few balancers off your hands.
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Mon Apr 24, 2017 4:58 pm

Offroader wrote:Quick question, could you really trust that this is working to balance the cells if you have no feedback on the voltages?


It depends on how you define a feedback.
If you looked at my hackaday log, you will see that it does have a feedback at the output node.
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Mon Apr 24, 2017 4:59 pm

miffi wrote:This is a nice project you have going. When you are ready, I will take a few balancers off your hands.


Thank you for the support! :)
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Mon Apr 24, 2017 5:05 pm

Vanarian wrote:I feel you there it's harsh for us students to support projects!

I'd gladly help out though since I was planning to offer at least to pay for shipping (I'm in France :P) I send you a PM.


Students in da house woot woot :lol: :lol:

I will check with the local post office, hopefully you don't have to pay for the shipping. :)
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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Mon Jun 12, 2017 7:38 pm

Hi all,

I finally got the chance to learn KiCad to redraw the final schematic of the project.
I decided to open source it because I can't manufacture it myself as I am in a financially challenged situation.

I also posted one of the boards to @Vanarian for a review, unfortunately, it was lost during shipping and the board doesn't reach to him.

Anyways, here is the final circuit: http://www.afdhalatifftan.com/2017/06/l ... ancer.html

Hopefully, this will benefit the community. :)
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Re: Cheapest Active Cell Balancer Project

Postby Vanarian » Tue Jun 13, 2017 5:08 am

Cheer up ! I'm a bit mad after my postal country services, was really looking forward to give you feedback too.

In any case that's a great share and as soon as I can I'll make test units for review ; hope more people here will adopt it :) I'll forward your link to the french DIYer community too.
I needed to turn Air Gear stuff into reality so I am making this!
-+Electric inline skates - no remote control - weight / angle sensor - hub motors - one frame for all wheels sizes between 80/125mm - from 3.2 to 12 KW :mrgreen:

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Re: Cheapest Active Cell Balancer Project

Postby AfdhalAtiffTan » Tue Jun 13, 2017 12:58 pm

Thank you Chris :)
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