Selling products with Li-Po batteries inside

[pyrohaz]

Hi all,

I'm looking to use a Li-Po battery for a future product of mine and I'm wondering what the laws are (if any!) on selling products containing these kinds of batteries. I seem to be hearing a fair few stories about them exploding and being a dangerous kind of battery chemistry though if this was the case, surely no products would be equipped with these batteries? Obviously in the circuit design, I'd ensure that the charging current is below the maximum rated and that the battery couldn't be discharged lower than 3v. Along with that, ensuring the battery was mounted somewhere where shock or other physical phenomenon were least effective. What else should be considered with Li-Po batteries?

Thanks,

[sleemanj]

First, watch some videos of lipo fires so you can appreciate what you are dealing with and the importance of doing it right.  If you do it right, there's no problem.  If you do it wrong you can be in for a world of hurt.

Now in no particular order off the top of my head...

1. Ensure the charging system can not overcharge, or charge at too high current
2. Ensure the protection circuit prevents over discharge
3. Ensure that the protection circuit disconnects on over current, especially short circuit
4. Ensure the possibility for short circuit is physically difficult
5. Ensure the cell is physically protected from all damage (especially any puncture of the cell)
6. Monitor cell temperature if you want to add some extra protection, and especially if you are drawing high current think about duty cycles
7. Talk to your shipping handler to see what they need you to do, there may be paperwork and special requirements

[AndyC_772]

Second, state where you're based and the market into which you're selling. There are no "world" standards defining what you need to do to pass each country's local electrical safety regulations.

[pyrohaz]

First, watch some videos of lipo fires so you can appreciate what you are dealing with and the importance of doing it right.  If you do it right, there's no problem.  If you do it wrong you can be in for a world of hurt.

Now in no particular order off the top of my head...

1. Ensure the charging system can not overcharge, or charge at too high current
2. Ensure the protection circuit prevents over discharge
3. Ensure that the protection circuit disconnects on over current, especially short circuit
4. Ensure the possibility for short circuit is physically difficult
5. Ensure the cell is physically protected from all damage (especially any puncture of the cell)
6. Monitor cell temperature if you want to add some extra protection, and especially if you are drawing high current think about duty cycles
7. Talk to your shipping handler to see what they need you to do, there may be paperwork and special requirements

I've designed my power supply to limit undervoltage (down to 3v) but can't think of any easy ways to implement short circuit protection, do you know any methods? The charge current will be much lower than the battery capacity and is based on an MCP73831 IC.

The battery will be kept in an enclosure along with the rest of the electronics made out of 3mm thick plastic, I think somebody would have to purposely try and stab the battery to get to it!

Current draw will be minimal, around 50mA at peak. I'm hoping to get a battery >1000mAh. There is a regulator between the battery and microcontroller so hopefully this adds a small layer of abstraction? How can I increase safety by measuring the battery temperature? In the tests I've done so far, the battery temperature stays below my body temperature (it always feels cold!).

Second, state where you're based and the market into which you're selling. There are no "world" standards defining what you need to do to pass each country's local electrical safety regulations.

I'm based in the UK and would initially like to sell to only the UK

[AndyC_772]

OK, next thing to do is look up which IEC standard applies to the specific type of product you're producing and obtain a copy. That will be the document to which you'll be declaring the product conforms when you apply the CE mark.

Any recognised safety approvals lab should be able to tell you what your obligations in respect of the LVD are.

[sleemanj]

I've designed my power supply to limit undervoltage (down to 3v) but can't think of any easy ways to implement short circuit protection

Use a protected cell (a cell with a protection circuit already built into it), or a separate ready made lithium protection circuit, or build in a protection IC - the DW01 protection IC combined with the FS8205A dual mosfet is a common combination in China for cell protection.

The battery will be kept in an enclosure along with the rest of the electronics made out of 3mm thick plastic, I think somebody would have to purposely try and stab the battery to get to it!

You need to also consider the stuff inside that case, the underside of a through hole PCB being well separated from a typical lipo pack for instance so that solder tails can not pierce the pack.

Using an 18650 cell, or better, a protected 18650 cell, would be my first preference over a typical "bag" type lipo unless the weight or form-factor demanded something smaller.

How can I increase safety by measuring the battery temperature?

For the small current you are drawing, not really going to be an issue, especially if you charge at a nice low current rate.

[pyrohaz]

I've designed my power supply to limit undervoltage (down to 3v) but can't think of any easy ways to implement short circuit protection

Use a protected cell (a cell with a protection circuit already built into it), or a separate ready made lithium protection circuit, or build in a protection IC - the DW01 protection IC combined with the FS8205A dual mosfet is a common combination in China for cell protection.

The battery will be kept in an enclosure along with the rest of the electronics made out of 3mm thick plastic, I think somebody would have to purposely try and stab the battery to get to it!

You need to also consider the stuff inside that case, the underside of a through hole PCB being well separated from a typical lipo pack for instance so that solder tails can not pierce the pack.

Using an 18650 cell, or better, a protected 18650 cell, would be my first preference over a typical "bag" type lipo unless the weight or form-factor demanded something smaller.

How can I increase safety by measuring the battery temperature?

For the small current you are drawing, not really going to be an issue, especially if you charge at a nice low current rate.

After further internet research, it turns out Olimex sells LiPo batteries with what looks like integrated safety mechanisms (https://www.olimex.com/Products/Power/BATTERY-LIPO1400mAh/), it says it has overcharge and short circuit protection which seems great! Would a battery like this be considered safe in my application? Talking of which, to make it much easier for you to understand what I'm asking, I'm designing a desktop synthesizer (quite like the Shruthi - http://mutable-instruments.net/shruthi1) which I'm wanting to be battery powered. The case will be acrylic (hence the previous comment about stabbing through the plastic!).

What protective advantages does a 18650 cell have over a standard "bag" cell? Also, the charger IC I'm using only supports up to a maximum current of 500mA, to which I'll probably use slightly less to ensure the IC doesn't get too warm (along with good ground plane heatsinking!). IIRC, the maximum "safe" charging current for a LiPo is 1C, if I'm using a current of say 454mA (easily set by just using a 2.2k resistor, within the range of the MCP73831 charge resistor impedance), will this give a safe margin from the maximum "safe" current of 1.4A?

Thanks for all the help by the way! I'd rather get this stuff right from the start then have some scary explosive li-po's on my hands, along with some law suits!

[sacherjj]

Most supplied batteries come with a small protection board that bridges the welding the tabs from the pack to PCB for wire soldering.  This also includes a protection IC that stops overcharge, undercharge, shorts, etc.  This may be different on small capacity, but we are dealing with 6-30 Wh cells.  I would NEVER integrate Lithium in a product without a protection circuit, unless there was a reason that couldn't be bypassed.  Protection circuits are often left out of RC power packs, because they limit max current draw.

You may also want to look at alternate chemistry, depending on service life you want.  We are using LiFePO4 cells, these have lower voltages and about 30% less energy density, but will equal LiCo cells in 12-18 months, and be functional in 5 years, when LiCo are 2 years dead.  All your circuity must be 2.8V capable, or you need a boost circuit to get to 3.3V (LiFePO4 is 2.9-3.6V with 3.2 nominal.)

There are fixed cells in AA and AAA formats that include protection circuitry and allows the customer to replace them.  14500 (AA) and 10440 (AAA).  Although 10440 are not that common.  I use an unprotected AAA cell in my everyday carry flashlight, because I can switch to high power mode for 60 seconds or so with the LED in it for a nice beam when I need the power.

[sleemanj]

Yes that cell is a protected cell, you can see the circuit board on top.  Just don't mistake protection for charge control, ideally your protection circuit should never get triggered at all, it's a "failsafe".

What protective advantages does a 18650 cell have over a standard "bag" cell? Also, the charger IC I'm using only supports up to a maximum current of 500mA

An 18650 is metal shelled, so more resilient to impact damage.  However if it's fully enclosed and secured inside that enclosure then a protected bag type is fine.

I think generally 0.5C is regarded as a "safe" rate for charging in so far as lipo goes.

[AndyC_772]

Please don't be too distracted by well-intentioned practical advice; the requirements you NEED to meet if you're selling your product commercially are in the IEC safety regulations.

You mention, for example, that your case is acrylic. Is it 94V-0 flammability rated, and would it meet the requirements of a fire enclosure?

[pyrohaz]

Please don't be too distracted by well-intentioned practical advice; the requirements you NEED to meet if you're selling your product commercially are in the IEC safety regulations.

You mention, for example, that your case is acrylic. Is it 94V-0 flammability rated, and would it meet the requirements of a fire enclosure?

That is a very good point! Perspex seems to have a flammability rating of HB which is < V-0. I assume this means I can't make the enclosure out of perspex though how do other manufacturers achieve this? Could I use some form of shielding on the inside to help with this matter?

Yes that cell is a protected cell, you can see the circuit board on top.  Just don't mistake protection for charge control, ideally your protection circuit should never get triggered at all, it's a "failsafe".

What protective advantages does a 18650 cell have over a standard "bag" cell? Also, the charger IC I'm using only supports up to a maximum current of 500mA

An 18650 is metal shelled, so more resilient to impact damage.  However if it's fully enclosed and secured inside that enclosure then a protected bag type is fine.

I think generally 0.5C is regarded as a "safe" rate for charging in so far as lipo goes.

Thats good to hear at least, thank you for your input!

[pyrohaz]

Please don't be too distracted by well-intentioned practical advice; the requirements you NEED to meet if you're selling your product commercially are in the IEC safety regulations.

You mention, for example, that your case is acrylic. Is it 94V-0 flammability rated, and would it meet the requirements of a fire enclosure?

As a further question too, looking at the wiki list of IEC standards (http://en.wikipedia.org/wiki/List_of_IEC_standards), where would my product sit? I would've thought IEC 60065 as I would class it as a piece of audio electronic equipment though it could also be classed under IEC 60268 potentially as a piece of sound system equipment? Unless of course this only classes hi-fi equipment?

[AndyC_772]

HB is Horizontal Burning. I don't know for sure, but I wouldn't expect it to be adequate if there's a potentially flammable battery inside your product. If you have the choice of a metal or 94V-0 rated plastic enclosure instead, then you could save yourself some time, trouble and (ultimately) cost by using one from the outset.

One of the more difficult parts of meeting the necessary safety standard is working out which one actually applied to your product. I don't know what your product is, so I can't advise - and in any case, if you're going to get it formally tested for CE compliance, the lab you use should be able to tell you which one they would test against. It may well be that if there's more than one that looks applicable, the different standards will all prescribe many of the same technical requirements anyway.

You'll save yourself a lot of grief if you take some professional advice from an accredited test centre early on, I promise!

[London Lad]

Study how to properly charge a Li-Po cell. Its not just current regulation.

You need to constant current charge at a max of 1C until the cell reaches 4.2 volts and then switch to constant voltage until the current draw is less than 3% of the rated cell capacity. Then terminate the charge, do not trickle.

[Stonent]

Another option would just be leave the battery out and design it around a commonly available cell phone or camera battery.
Original Galaxy S GT-i9000 batteries are pretty commonly available.  Batteries for older Nokia phones are common as well.

You might also be able to find a battery distributor that will drop ship the battery to the customer when the order is processed.

[Neilm]

If I remember correctly, Li-Ion and Li-Po batteries are classed as hazardous goods, and have to conform to a UN transportation standard. This has recently changed and I am not too sure of the changes. I believe that the standard for secondary cells is IEC60133 - the batteries will also have to meet this standard AS WELL as the UN standard.

[pyrohaz]

Wow what a drag! I never knew that designing a product containing li-po batteries would be such a chore. How do normal manufacturers get away with it?!

HB is Horizontal Burning. I don't know for sure, but I wouldn't expect it to be adequate if there's a potentially flammable battery inside your product. If you have the choice of a metal or 94V-0 rated plastic enclosure instead, then you could save yourself some time, trouble and (ultimately) cost by using one from the outset.

One of the more difficult parts of meeting the necessary safety standard is working out which one actually applied to your product. I don't know what your product is, so I can't advise - and in any case, if you're going to get it formally tested for CE compliance, the lab you use should be able to tell you which one they would test against. It may well be that if there's more than one that looks applicable, the different standards will all prescribe many of the same technical requirements anyway.

You'll save yourself a lot of grief if you take some professional advice from an accredited test centre early on, I promise!

I most definitely think that getting some professional advice on this subject would be wise! I'll hopefully be doing so in the relatively near future.

Study how to properly charge a Li-Po cell. Its not just current regulation.

You need to constant current charge at a max of 1C until the cell reaches 4.2 volts and then switch to constant voltage until the current draw is less than 3% of the rated cell capacity. Then terminate the charge, do not trickle.

I do understand the basics of LiPo charging, fortunately the charging IC takes care of all that for me!

Another option would just be leave the battery out and design it around a commonly available cell phone or camera battery.
Original Galaxy S GT-i9000 batteries are pretty commonly available.  Batteries for older Nokia phones are common as well.

You might also be able to find a battery distributor that will drop ship the battery to the customer when the order is processed.

Yeh that would be cool! How could I PCB mount a standardized battery?

If I remember correctly, Li-Ion and Li-Po batteries are classed as hazardous goods, and have to conform to a UN transportation standard. This has recently changed and I am not too sure of the changes. I believe that the standard for secondary cells is IEC60133 - the batteries will also have to meet this standard AS WELL as the UN standard.

I agree, there seems to have been a lot of things against LiPos in the UK news laters (plane crashes caused by lipos etc.). If they're deemed this dangerous, how have they become so mainstream and why hasn't my mobile phone exploded in my pocket yet?

On another note, getting batteries delivered seems to be a complete chore too nowadays, extra postage restrictions etc.

Do LiFePO4 batteries have these same sanctions imposed upon them?

[AndyC_772]

Wow what a drag! I never knew that designing a product containing li-po batteries would be such a chore. How do normal manufacturers get away with it?!

"Normal manufacturers" hire professional engineers, either full time or on a contract basis, and they have EMC and safety testing carried out as a normal, routine part of the development process.

It's partly about having an R&D budget that can pay for the development and testing, but mostly about having the knowledge and experience to know what hoops need jumping through and how to avoid problems further down the line. Guiding people through the process, and designing products with EMC and safety approval testing in mind, is how I make a living.

[sacherjj]

Do LiFePO4 batteries have these same sanctions imposed upon them?

Yes.  While they are moderate safer chemistry, they have higher power density (meaning they can produce more current) than LiCo in short circuit. 

Yeh that would be cool! How could I PCB mount a standardized battery?

Most commercially available batteries have blades or spring terminals that are soldered on the board for connection.  This generally relies on an accurate enclosure design.  Getting into custom mold design for injection molding gets expensive. 

[Stonent]

Do LiFePO4 batteries have these same sanctions imposed upon them?

Yes.  While they are moderate safer chemistry, they have higher power density (meaning they can produce more current) than LiCo in short circuit. 

Yeh that would be cool! How could I PCB mount a standardized battery?

Most commercially available batteries have blades or spring terminals that are soldered on the board for connection.  This generally relies on an accurate enclosure design.  Getting into custom mold design for injection molding gets expensive.

Here's an option for the battery mounting.

http://hackaday.com/2014/07/16/finally-an-easy-to-make-holder-for-lithium-ion-batteries/

[Rick Law]

Couple of thing not talked about so far:  Availability and insurance.

(1)
I know you said LiPo, but some suggested 18650 cells and you've shown interest.  Panasonic wont even sell 18650 cells except to certain (licensed?) pack makers.  As I understand, many if not most 18650's out there are repack used laptop batteries.  LiPo or LiIon, make sure it is available in the area and cost in the volume you need.  Given the shipping restrictions, you should also put that into consideration that they cannot be air-shipped to many places in the world.

(2)
I think if you have a large amount of LiPo in a warehouse or the factory floor, you should also make sure your insurance is ok with it.

[amyk]

You can get real Panasonic, Sanyo, Samsung, etc. 18650s, just not direct from the manufacturer. There are other distributors that sell them some with protection circuits added. I'm also seconding the 18650 recommendation, because unless you need the thinness of a LiPo, 18650s are much more common and if you are worried about safety issues you can ship the product without the battery and have them be bought and installed by the user. This is the case for many torches, for example. Otherwise using an existing lipo standard like Nokia/Samsung mobile batteries would also be a good choice - they come with their own protection and a thermistor to measure their temperature.

As for the safety, I think many of the fears are overhyped - remember that there are probably over a billion of these batteries in use every day in things like laptops and smartphones, and yet we hear at most around a dozen of them doing any significant damage in a year. They can catch fire and burn, but need a lot of provocation to do so.

[mikeselectricstuff]

Here's an option for the battery mounting.

http://hackaday.com/2014/07/16/finally-an-easy-to-make-holder-for-lithium-ion-batteries/

..which is completely hopeless and will not be reliable - you need a spring contact so each pin has individual compliance.
There are plenty of battery contacts available, though most are for contacting parallel to the plane of the PCB.
e.g. these


Some Nokia batteries, e.g. BP-6MT and a few others have internal spring contacts that just need a flat blade to connect to.

 

[AndyC_772]

As for the safety, I think many of the fears are overhyped - remember that there are probably over a billion of these batteries in use every day in things like laptops and smartphones, and yet we hear at most around a dozen of them doing any significant damage in a year. They can catch fire and burn, but need a lot of provocation to do so.

This is a very good point. We do hear of battery fires, and each one can, if we're not careful, reinforce an idea that each one is an incendiary device waiting to go off.

To do so ignores the quantitative evidence, though. If you sell a million batteries, chances are you'll have sold a thousand to people who are unlucky, and at least a few hundred to people who are incredibly stupid. One or two will end up in the hands of people who are both - but very few of even these ever actually catch fire. That's why it's newsworthy when they do.

However, being unlucky and/or an idiot still doesn't justify having your house burned down, and that's why there are mandatory safety standards which have to be followed. A test certificate showing that your product was designed according to the relevant standards won't stop you ending up in court if one of your products causes (or is alleged to have caused) a fire, but it's a good defence against a negligence claim. With a test report, you'll be looking at a claim on your professional indemnity insurance and some time wasted. Without one, the consequences could be a lot worse.

[pyrohaz]

Do LiFePO4 batteries have these same sanctions imposed upon them?

Yes.  While they are moderate safer chemistry, they have higher power density (meaning they can produce more current) than LiCo in short circuit. 

Yeh that would be cool! How could I PCB mount a standardized battery?

One of the reasons I was wanting to stick to standard "bag" li-po batteries was so I could stick them to the inside of the enclosure using those sticky foam pads (http://goo.gl/WSq0v1) though I bet they'd go up in flames in seconds! I'm still trying to get my head around standard manufacturers and how they assembly battery packs. For example, this product here (http://goo.gl/n1Hw2P) is manufactured from wood and contains a 3.7v 1000mah battery (assuming lithium based due to the voltage), surely wood doesn't have a suitable UL rating? I know UL is for plastic so what is the wood equivalent?

As for the safety, I think many of the fears are overhyped - remember that there are probably over a billion of these batteries in use every day in things like laptops and smartphones, and yet we hear at most around a dozen of them doing any significant damage in a year. They can catch fire and burn, but need a lot of provocation to do so.

This is a very good point. We do hear of battery fires, and each one can, if we're not careful, reinforce an idea that each one is an incendiary device waiting to go off.

To do so ignores the quantitative evidence, though. If you sell a million batteries, chances are you'll have sold a thousand to people who are unlucky, and at least a few hundred to people who are incredibly stupid. One or two will end up in the hands of people who are both - but very few of even these ever actually catch fire. That's why it's newsworthy when they do.

However, being unlucky and/or an idiot still doesn't justify having your house burned down, and that's why there are mandatory safety standards which have to be followed. A test certificate showing that your product was designed according to the relevant standards won't stop you ending up in court if one of your products causes (or is alleged to have caused) a fire, but it's a good defence against a negligence claim. With a test report, you'll be looking at a claim on your professional indemnity insurance and some time wasted. Without one, the consequences could be a lot worse.

Most commercially available batteries have blades or spring terminals that are soldered on the board for connection.  This generally relies on an accurate enclosure design.  Getting into custom mold design for injection molding gets expensive.

Agreed, its a rare occurrence in todays news, there was some speculation on some previous aeroplane fires (I was watching a Panorama on the recent Malaysian airlines crash - Not the very recent Ukraine one!).

I'd definitely go through a full testing regime before bringing my product to market for that sole case. For the potentially small profit of the product, it would be a complete shame to have to shell out a ton of money due to one of my products spontaneously combusting in someones hands.

Couple of thing not talked about so far:  Availability and insurance.

(1)
I know you said LiPo, but some suggested 18650 cells and you've shown interest.  Panasonic wont even sell 18650 cells except to certain (licensed?) pack makers.  As I understand, many if not most 18650's out there are repack used laptop batteries.  LiPo or LiIon, make sure it is available in the area and cost in the volume you need.  Given the shipping restrictions, you should also put that into consideration that they cannot be air-shipped to many places in the world.

(2)
I think if you have a large amount of LiPo in a warehouse or the factory floor, you should also make sure your insurance is ok with it.

I'm not large enough to warrant a warehouse for of LiPo's just yet but i'll definitely keep that in mine for the future! I would preferably prefer to use a flat LiPo as they're a lot easier to mount than their cylindrical counterparts. However if using an 18650 style battery would increase the safety and decrease the amount of testing required, I feel that it would be a suitable change.

You can get real Panasonic, Sanyo, Samsung, etc. 18650s, just not direct from the manufacturer. There are other distributors that sell them some with protection circuits added. I'm also seconding the 18650 recommendation, because unless you need the thinness of a LiPo, 18650s are much more common and if you are worried about safety issues you can ship the product without the battery and have them be bought and installed by the user. This is the case for many torches, for example. Otherwise using an existing lipo standard like Nokia/Samsung mobile batteries would also be a good choice - they come with their own protection and a thermistor to measure their temperature.

As for the safety, I think many of the fears are overhyped - remember that there are probably over a billion of these batteries in use every day in things like laptops and smartphones, and yet we hear at most around a dozen of them doing any significant damage in a year. They can catch fire and burn, but need a lot of provocation to do so.

I suppose this could be a good shout with the whole shipping the battery separately but I don't see any other companies really doing this, you mention torches but I can't think of any other examples, most standard mobile phones and laptop seem to ship with their batteries albeit unconnected initially. Could it be the fact that the battery is unconnected which simplifies some of the safety issues?