Technical Corner: Battery Pack Safety and "Best Practices"

CloneWerks

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Coming into this group from the perspective of an EV car owner and a long time R/C enthusiast I have an extensive background with the care and feeding of various battery systems, especially Lithium Ion (Li-ion) packs.

NOTE: Portions written in italics represent my personal opinion/feelings/observations and should be taken with due consideration.

I mention this again later in the article, but this part is important! ANY PACK THAT IS DEFORMING OR BULGING NEEDS TO BE TAKEN OUTSIDE TO A SAFE, NON-FLAMABLE, LOCATION IMMEDIATELY!

Okay so let's move on;

The first and most basic thing to understand is that there are two basic types of battery packs.

"Unprotected" where the internal cells are just attached in an electrical circuit and there is no form of monitoring or regulation. This style includes most R/C car types, cell phone batteries (the electronics in the phone itself handles the monitoring) and some laptop batteries (also regulated by the laptop itself).

"Protected" where the pack itself has a BMS or Battery Monitoring System inside that controls what happens with the battery and protects it from;
  • Over-Current
  • Over-Charge
  • Over-Discharge
  • Short Circuits
In most eBike battery packs I've see the BMS is also a Balance Charge Monitor because the actual charger that you plug into the wall is usually pretty "stupid" and just provides power.

Any -quality- battery pack should be of the "Protected" type. If a battery pack has one (or more) of the following certifications you can be reasonably confident that it has a robust BMS circuit built in; EN15194:2017, UN38.3, UN-package, UL, CE, FCC, CB, ROHS.

However, problems can still crop up, possibly due to things like a factory defect, or long term damage from the vibrations and/or physical impacts that a bike is constantly subject to during use. It is therefore a wise choice to follow some common guidelines (hereafter referred to as "best practice") to prevent issues.

1) ONLY charge your battery pack in a fireproof location.
I absolutely WILL NOT charge my battery packs "on-bike". I personally recommend that you NEVER charge your packs inside the main living area of your house. In my case both battery and charger go into a large-ish metal toolbox that sits on a ceramic tile (from home depot flooring) outside in my screened-in back porch. I leave the toolbox open so that the charger gets plenty of air circulation. Listen to me, Li-ion fires are no joke [link], you must show a battery pack due respect!

2) Prevent overcharging
The BMS should prevent this from ever happening but why take a chance? Get an inexpensive wall timer and set it to limit charging time. I use this one and set it for about 5 hours, but if you do a search on "plug in countdown timer switch" in amazon you'll get a bazillion options.

3) Prevent over-discharge
Again the BMS should prevent this from ever happening by cutting off your battery power while the pack still has a safe internal charge, but why risk it? If you get down to the last bar on your indicator then stop and charge your battery as soon as you can. Yes I understand you could easily wind up on a long ride with no choice, if so then do what you have to do, just don't make it a regular practice to run so low.

4) Store with a proper charge level
If a Li-ion pack is going to sit idle for an extended period (say more than a week) then it should be charged or discharged until it's at roughly 50%. This will give you a far better battery life than leaving it fully charged and leaving it at a very low charge -will- degrade the battery fairly quickly. If you are leaving it idle for an even longer time, say for the winter months, you should check the charge every month to make sure it's still around 50% as Li-ion batteries self-discharge over time.

5) Inspect the pack regularly for damage or bulging
The pack on an eBike lives a somewhat rugged life and is subject to constant temperature changes, bumping, vibrations, and physical shocks. This makes it very important that you inspect the pack regularly (in my case every time I remove or install it). Check the connectors for any damage, discoloration, or signs that something might have overheated/melted. Check around the connectors for any stress cracks or anything that looks unusual. The same with the body of the pack. MOST IMPORTANTLY watch for ANY signs that the pack is deforming or bulging. ANY PACK THAT IS DEFORMING OR BULGING NEEDS TO BE TAKEN OUTSIDE TO A SAFE, NON-FLAMABLE, LOCATION IMMEDIATELY! If you don't know how to decommission a damaged battery pack (let's be honest, nobody but a professional really does) contact your local fire department (non-emergency number please) and explain the situation and they will assist.

Following these basic guidelines should give your battery pack a long and happy service life and prevent any tragedies from occuring.

EDIT: Adding a new video link to a good battery maintenance overview.
 
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Seems like some well thought out advice. Question.....why do none of the ebike companies make these same points? Don't they have some liability in the game?? Like almost anything....understanding a product is important....can an ebike battery explode or cause a fire....yes.....but so can my propane grill if not used properly. Be aware...be smart....enjoy your ebike and a good steak.
 
Seems like some well thought out advice. Question.....why do none of the ebike companies make these same points? Don't they have some liability in the game?? Like almost anything....understanding a product is important....can an ebike battery explode or cause a fire....yes.....but so can my propane grill if not used properly. Be aware...be smart....enjoy your ebike and a good steak.
To be perfectly blunt, it costs them money to take on the liability, write manuals, do warnings. Here in the United States it's worth all that effort because we are so lawsuit-happy but many other places (I'm looking at you China) don't bother with any of it until bad things actually happen and then they play "catch up". You see this a lot in the R/C hobby arena and you also see it a lot in my other favorite thing, high power/high end flashlights (most of which are powered by the exact same 18650 cells that make up a bike battery). You would freak if you saw some of the janky s**t that used to be sold before some standards were put in place and there are still a lot of China/Taiwan/India produced crap 18650's out there that are just sticks of dynamite waiting to go off.
 
This is the label on my Aventon’s battery.

3E902E7F-1B0D-48AC-A9BC-91AC5A730682.jpeg


Should I consider it “Protected”?
Did a Google search on the model number and came up blank, and their website is non-informative on the matter.
 
Are there any stickers on it (UL - underwriters laboratory) or CE mark?
is it the one that looks like this?

2022-09-04 15_07_18-Aventon Battery - Opera.jpg
 
The charger has a UL mark on it, though.

Does that count?

FE322395-D33A-45A0-970D-FF3053A65BC4.jpeg
 
Darn, because the one I showed is a variant production model of the L460 Reention Dorado which I have discovered is a -really good- battery pack.

So it's good that your charger has UL and CE certification. That raises the quality level considerably but still doesn't tell us anything about the battery pack. Given the way eBikes work it pretty much -has- to have a BMC (i.e. be protected) but as to the quality of the BMC board... anyone's guess at this point though Aventon does have a reputation to protect.
 
Darn, because the one I showed is a variant production model of the L460 Reention Dorado which I have discovered is a -really good- battery pack.

So it's good that your charger has UL and CE certification. That raises the quality level considerably but still doesn't tell us anything about the battery pack. Given the way eBikes work it pretty much -has- to have a BMC (i.e. be protected) but as to the quality of the BMC board... anyone's guess at this point though Aventon does have a reputation to protect.

Thx!
 
I've pretty much settled on the fact that my bike will be a bosch mid drive system. Their chargers are certified to UL 1012, and the entire ebike system (battery, charger, drive system and display) are certified to UL 2849. It is important to make sure the entire system is UL certified. I asked another bike manufacturer if they were UL certified and they said they are working on it and plan to have that in place in the future. They were marked off my list.

I have some ekxperience through work with LI ion 18650 cells. The cell itself has built in protection.

Short circuit protection
protection circuit in the anode protecting against overcharge, over discharge, short circuit and overheating
pressure relief valve in the event gasses build up and need relief. (sort of a last protection)

The battery built up of an array of 18650 cells will have it's own protection for external cell to cell and cell to case short circuit protection, usually by physical and mechanical design of the battery preventing short circuit. A key factor is what environmental stresses (loads, vibration, shock etc) the battery is designed to take and still maintain short circuit protection. It's important to not knock them around more than the design allows. The case should be very robust. If for some reason the case becomes compromised the battery should be recycled even if usable.

The charger also has it's own protection circuits to prevent charging over voltage protection, charging over current protection, charging/discharging over temperature protection, reverse polarity protection, short circuit protection, and over voltage and deep discharge protection (getting below 20% charge). Finally some of this same protection needs to be in the drive electronics as well, hence the overall ebike UL certification.

Even with all these protections a failure can occur and I know of one (not an ebike application). I'd guess it was due to physical stress on the battery causing internal cell to cel; short, but I don't know for sure. The system overheated and failed. But other protection measures would have kicked in to prevent fire or explosion, just the system was then unusable.

I never thought about it much until I started researching ebikes. I have several 18v Li ion power tool batteries in the garage where they've always been stored regardless of the temperature extreme cold or hot. I had one battery over the years fail, just wouldn't charge or discharge. I assume a protection mechanism kicked in and I dropped it off at batteries plus for recycling. I have one 40 watt leaf blower with Li ion battery as well. Garage stored. I'll probably get some protective storage bags for these batteries after having done some research.

So after some research any ebike i get will have the battery charger certified to UL 1012 and the entire ebike system certified to UL 2849. So far the only one I know of is a Bosch system.
 
.........

1) ONLY charge your battery pack in a fireproof location.
I absolutely WILL NOT charge my battery packs "on-bike". I personally recommend that you NEVER charge your packs inside the main living area of your house. In my case both battery and charger go into a large-ish metal toolbox that sits on a ceramic tile (from home depot flooring) outside in my screened-in back porch. I leave the toolbox open so that the charger gets plenty of air circulation. Listen to me, Li-ion fires are no joke [link], you must show a battery pack due respect!

2) Prevent overcharging
The BMS should prevent this from ever happening but why take a chance? Get an inexpensive wall timer and set it to limit charging time. I use this one and set it for about 5 hours, but if you do a search on "plug in countdown timer switch" in amazon you'll get a bazillion options.

5) Inspect the pack regularly for damage or bulging
The pack on an eBike lives a somewhat rugged life and is subject to constant temperature changes, bumping, vibrations, and physical shocks. This makes it very important that you inspect the pack regularly (in my case every time I remove or install it). Check the connectors for any damage, discoloration, or signs that something might have overheated/melted. Check around the connectors for any stress cracks or anything that looks unusual. The same with the body of the pack. MOST IMPORTANTLY watch for ANY signs that the pack is deforming or bulging. ANY PACK THAT IS DEFORMING OR BULGING NEEDS TO BE TAKEN OUTSIDE TO A SAFE, NON-FLAMABLE, LOCATION IMMEDIATELY! If you don't know how to decommission a damaged battery pack (let's be honest, nobody but a professional really does) contact your local fire department (non-emergency number please) and explain the situation and they will assist.

......

Cloneworks, All,
Took bits n pieces from Clonework's post. I have some questions about ebike battery best practices. Keep in mind that our one and only ebike at the moment is an Aventon Pace 500.2

1. Before reading this, I was thinking charging in-bike might be best, because it's kind of up and away from things. But now I'm going to look for a better place, probably in the basement. But for in-bike charging, might it be possible to have some type of fireproof wrap where a few wraps of the fireproof blanket around the battery/ frame would help prevent the spread if it bursts into flames for some reason? For off-bike charging, I'd like to find a big metal box, but nothing comes to mind yet.

2. About over-charging, instead of being timer based, isn't the best solution a charger that stops when the charge gets to say 80% (like my laptop battery is setup to do)? In another thread I had asked about this and was pointed to a charger made by Bafang. I feel like this whole charge time thing is hit or miss because you may be starting from a different point each day. Seems like charging to a particular % charge would be a lot better. No?

5. About inspecting the pack for damage, with the Aventon 500.2 battery pack I can't see a thing on what's happening on the inside. Is there some other way to do a health check on it?

And finally, I'm trying to figure out the best way to use a mechanical timer outlet that we just got a few days ago (that has the little tabs you can push down or pull up). Let's say the bike is at 25% after the last rider at 7pm. And the next planned use is at 9am the following morning. For that scenario I was thinking we would setup the charger to not do anything for 1 hour (to allow the battery to cool), then charge for say 15 minutes (that's the shortest interval our timer can do) to bring it closer to a reasonable storage charge, then turn off again, and then turn on the charger again for about 3 hours starting at 6am. That way instead of sitting all night at 25% or at 100%, it will at least have a little more charge for storage and then be charged ready to go at 9am. Thoughts? Overthinking it maybe ?

Thanks in advance for whoever replies.
 
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Nice of you to make that post. I also do R/C trucks, planes and drones sometimes, and am a regulatory electrical engineer for a tool company by day. I'd like to clarify a couple of points that you made:

  • You talk about bulging packs, however this mostly is not applicable to eBike batteries so far. eBike batteries are using regular Li-Ion cylindrical cells like you might find in power tools or electric cars. They don't bulge, you'll know they're reaching end-of-life by other means. The R/C batteries you're thinking of are lithium-ion polymer. Or, we call them "pouch cells" in the industry. They don't have any built-in housing except the foil used to house the chemicals. We use them in R/C because their weight is low and their energy density is very high, but they are more volatile than cylindrical cells.
  • Regarding certifications, you should know that CE (and UKCA) are mostly self-declared compliances. The use of the mark is not regulated or confirmed, except in case legal action. Compare that to UL, which has ongoing inspections to confirm the product continues to be built to the relevant standard(s). If you see a battery pack, charger or eBike with ONLY the CE marking on it, don't put much stock in it. The manufacturer only has to show compliance in case of legal action, and a lot of these mushroom Chinese manufacturers will just shut down the business, move down the block and open a new business rather than deal with that.
  • EN15194:2017 - This is a European eBike safety standard. If there is a 3rd party certification mark associated with it.
  • UN38.3 - This is a US standard for shipping of batteries. It covers things like dropping and crushing the packs and packaging, but would not necessarily mean anything to us, as we are not usually shipping them once we get them.
  • UN-package - There are certain standards for how batteries may be shipped; these would not apply to us except when we ship battery packs.
  • UL - UL is the original safety certifcation company. I worked for them for 21 years. They not only evaluate products to the standards, but also they WRITE the standards, often at the request of government. For example, they wrote one or more standards as a result of all the hoverboard fires several years ago. UL is the gold standard certification mark in my opinion. They're not just "selling marks" like a lot of their competition seem to do. (Intertek/ETL, etc.)
  • FCC - This regards EMC and is not related to safety, except that the products must accept interference without causing something dangers to happen and must not emit harmful interference that could affect something else. (like pacemakers)
  • CB - This is a certification structure that requires 3rd party approval, and it will be backed up by a 3rd party mark. So it's better than CE alone without a 3rd party mark.
  • ROHS - (Restriction of Hazardous Substances) This is just controlling what substances go into the product. Certain chemicals are not allowed, because they poison us or our environment. It's not a safety standard or anything.
Here is some info I wrote for another forum after looking into the standards used for eBike batteries and electrical systems:

I found that there are a LOT that goes into safety certifications on an eBike: Bike system, battery and charger are all separate. Tests they do on the bike:
  • Input: make sure the input current drawn doesn't exceed ratings
  • Temperature: make sure that component temperatures don't exceed their specs. (which is easy to do, if components are under-spec'd or under-cooled)
  • Isolation Resistance: measure the resistance of electric insulation to make sure it's adequate
  • Dielectric Strength: test the electrical insulation with a high voltage to make sure it's adequate; doesn't arc
  • Humidity Conditioning: Same as Dielectric, but after a humidity soak. (humidity can penetrate certain materials and reduce the insulation properties)
  • Abnormal Conditions:
    • Overcharging
    • Component Faults
    • Blocked Ventilation
    • Locked rotor: Lock the motor up and confirm no fire, explosion, concentration of flammable gas, etc.
    • Running Overload: gradually overload the motor and confirm no fire, etc.
    • Battery short circuit
    • Imbalanced charging: This is an important one. There are dozens of cells in the pack they go out of balance over time and then when the charger charges to the same pack voltage, it means that the other cells in the pack are overcharged as a result of the tired cells not reaching their full voltage.
    • Shock: (kind of an impact test)
    • Thermal cycling: Confirming nothing bad happens when the bike is moved from a cold environment and back
  • Impact
  • Mold Stress: Makes sure the molded parts don't distort and expose anything that should be enclosed under hot conditions
  • Flexing: checking wire harnesses to make sure they're rugged & reliable
  • Ingress protection (IP testing) for dust and moisture; make sure safety-critical electrical spacings aren't effected
  • Vibration: Checking the effects of shipping. You'd be surprised how many components will shake off a board in this test. Usually big capacitors and inductors that aren't glued down
  • Strain Relief: Check that if a cord or harness is pulled, it can protect the electrical connections from the strain
  • Startup Assistance Mode: confirms max 6 kph (3.7 mph) in walk mode and that it self-cancels if the button is released

The battery cells have to be certified on their own. Then, they are certified in the pack and again in a certified bike.

The chargers have their own requirements.

This is a big expense, but they really do make the bikes safer.

I remember when cheap Chinese hoverboards were burning houses down. The US government approached UL and asked them to write a standard so they could require it. Now that eBikes/batteries are burning down shops in NYC, there is a standard for electrical systems for eBikes (UL 2849) as well as for the battery packs for use in light electric vehicles (UL 2271).

Any questions, just ask.
 
Props to @Smaug for clearing up a lot of questionable information. I would say, at-present, the only certification worth anything is a UL compliance certification, and unfortunately we're seeing fakes of that as well by the aforementioned 'mushroom' companies.

However it seems UL is aggressively pursuing those fakers. I just checked a known offender and they have removed all mention of UL anything on their site (formerly it was on the front page, claiming they were the only UL approved battery of X amp-hours in the marketplace.

Overcharging and timers were mentioned above, along with a question on the best method. The answer is to spend the time to learn how long it takes to add 1 volt to your pack's capacity, and then use the countdown timer and a little math (everyone has a calculator on their phone) to shut the charger off at the right time. Sure you also want to get a charger that charges to less than 100%. But also back that up with another layer of protection by setting a cutoff timer to physically cut the power before it is even possible to create an overcharge condition.

I know my charger adds 1.2v per hour on my pack when in Constant Current (bulk charge) mode. Thats when it is putting out all of its rated amps, before it starts to slow down as it nears the voltage target I set. So if I have a 52v pack (I do), I have depleted the pack to 50.5v, and I want to charge to 80% which is 55.4v, 55.4-50.5 = 4.9 volts needed. 4.9/1.2 = about 4 hours. Since the charger will slow down at the latter portion of the charge, I can probably kick that time up to 4.5 hours to arrive at roughly 55.4. Or just go 4 hours, err on the low side and give it a bump for a half hour just before my next ride. Either way, the cutoff timer will kill the power completely before anything bad can even get close to happening... so long as I do my part and use my brain.

I've had enough of the cheap timers, too. They're a weakness in a system that is a fail-safe for a process that can be catastrophic if it fails.

 
The discussion(s) should be ongoing as Owner Education as the eBike/eMobility space continues to evlove.


CLICK HERE UL's e-BIKE PRODUCT STANDARDS/POSITION OVERVIEW

CLICK HERE SGS PRODUCTION TESTING AGENCY AS 1ST OSHA APPROVED NRTL eBIKES

There are "Product Standards" - such as UL - then there is Production Testing (using a 3rd party such as SGS as a NRTL).

You are seeing more of "SGS Certified" from Asian manufacturers in their more recent product bylines - however the "doughnut hole" with that is when they state "SGS Certified" the question becomes "SGS Certified to what Standard" ?to what standard?"
 
The discussion(s) should be ongoing as Owner Education as the eBike/eMobility space continues to evlove.


CLICK HERE UL's e-BIKE PRODUCT STANDARDS/POSITION OVERVIEW

CLICK HERE SGS PRODUCTION TESTING AGENCY AS 1ST OSHA APPROVED NRTL eBIKES
How interesting that SGS became a NRTL in this category before the authors of the standard! (UL) UL should have had a leg-up...
https://www.sgs.com/en-us/news/2022/03/expansion-of-nrtl-testing-capability-for-emobility-devices
There are "Product Standards" - such as UL - then there is Production Testing (using a 3rd party such as SGS as a NRTL).
Yep, and of course UL is a NRTL too. They split into two companies: UL Inc., who writes standards (and is not-for-profit) and now UL Solutions, who is the NRTL. (and is for-profit, but not publicly traded)

You are seeing more of "SGS Certified" from Asian manufacturers in their more recent product bylines - however the "doughnut hole" with that is when they state "SGS Certified" the question becomes "SGS Certified to what Standard" ?to what standard?"
I'm about 90% certain that my battery pack on my Aventon has the SGS mark and also cites which UL standard was used. Some unscrupulous NRTLs proudly put their mark on a product, but when some digging is done, we find out the wrong standard was used, to avoid some pesky requirements, so you make an excellent point.
 
Thank you hsdrggr for your post last summer recommending the charger sold by Shenzhen Hengji Power Electronics Co. (model HGJI-1608). I have been using the device extensively for both 48V as well as 52V batteries (which include the 3-pin GX16 charging port). By allowing me to observe in real time the charge amperage as well as the battery voltage I am able to routinely stop the process when the 80% full charge state is reached and hopefully prolong the life of the battery.

hsdrggr

 
Thank you hsdrggr for your post last summer recommending the charger sold by Shenzhen Hengji Power Electronics Co. (model HGJI-1608). I have been using the device extensively for both 48V as well as 52V batteries (which include the 3-pin GX16 charging port). By allowing me to observe in real time the charge amperage as well as the battery voltage I am able to routinely stop the process when the 80% full charge state is reached and hopefully prolong the life of the battery.

hsdrggr

I bought one too, and I like it.

One note of caution on it: It is really an adjustable output power supply, rather than a purpose-built battery charger, even though it seems to have set points corresponding to common battery voltages.

The difference is that a purpose-built lithium battery charger will stop charging once the charge current gets to a certain low level. (maybe 200 mA) But this little power supply will just keep charging and charging. (as much as the voltage limit allows) For this reason, I use it only through a mechanical timer, which will cut the power after a certain set period of time.

You'll notice this with the OEM chargers; which usually have a bi-color LED to indicate what the output is doing. Typically, green = standby (not charging) and red = charging.
 
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