Unhackable and cheap battery pack - Page 1
Forum section: electronics / projects

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 03:23:53 am
content: Hello guys,I am writing you in look for your experience and creativity, since I am out of ideas and out of knowledge (and somewhat frustrated after an engineering review that went bad). From now on I will use "system" to refer to the system that uses the battery pack, and "pack" to the pack itself (batteries + BMS).I need to make acompletely and totally unhackablelithium ion battery pack. I am using and will definitely continue using commercial lithium ion 18650 cells, integrated with its BMS.I need to completely ensure 100% that customers will not have access to the cells themselves to use them, since might pose a safety risk and also not convenient for the the final application. So lets accept that this is a very hard requirement and cannot be negotiated (it happened).So we have several levels of protection: making the system case extremely hard to open, making the electronics of the system difficult to hack, making the pack+system difficult to hack (we have authentication between pack and system) and finally making the pack case difficult to open. But after all these levels, imagine a person that could open the case of the system, take out the pack itself and destroy everything to access the cells. This MUST NOT HAPPEN.No level of electronic safety can avoid a user to destroy our pack and access the cells, and use them for other purpose. So the only option that comes to my mind is POTTING (encapsulating) the whole sh*t. But there is an issue with these:1) Lithium cells expand and contract while charging and discharging, and if this is not considered the cells might catch fire (fail very catastrophically) which MUST not happen.2) A safety mechanism of cells is venting. If the pack is completely potted, then this will be a pressure bomb inside that might promote again a catastrophic failure.3) The energy stored is 70Wh. Is that a too much to consider potting? This is a 4S2P configuration.So, there are two main questions here:a) Does anyone have experience with potting lithium ion batteries? I will very much appreciate and thank a lot any comments, thoughts, suggestions or experience that can share.b) Do you know any other method of making the cells totally unaccessible to the must annoying and malicious of the users? I might be already short of ideas and experience. I have done my google search but have found nothing besides potting.Guys, thank you a lot, really, I will appreciate any feedback.(Do I sound too frustrated? I even waited some hours after that meeting before posting this, since I knew my frustration could come out too much )EDIT: Yes, some users have noted that 100% unhackability is impossible in practical terms. So lets say I am looking for practical solutions. A level of security that makes it a) very difficult to hack in terms of time and tools b) very difficult to replicate massively c) requires high technical skill is probably the level I am looking for.

author: Corporate666
author_rank: Unknown
timestamp: September 27, 2016, 03:35:54 am
content: In my opinion (but I think I am 100% correct), there is no such thing as unhackable, just as there is no such thing as bomb proof or bullet proof.There is only protection to a certain level - never absolute protection. It depends what level the adversary is willing to go to in order to circumvent your security precautions. And the amount of money and time/cost/weight you are willing to spend to stop them.

author: helius
author_rank: Super Contributor
timestamp: September 27, 2016, 03:41:11 am
content: This doesn't make any sense. Why don't you want the cells to be reused? Are you violently opposed to e-waste recycling?

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 03:41:31 am
content: Quote from: blueskull on September 27, 2016, 03:34:20 amI am not sure if I understood, but this is a requirement from my customer (the company I work for) and I have had a real bad time trying to figure this out. I am not trying to take advantage of anything or anyone. (Is that what you meant?)Quote from: Corporate666 on September 27, 2016, 03:35:54 amYou are totally correct, this why it is so hard. So for X amount of money, you can have X level of security, maybe for infinite money you can a ridiculous/not practical level of security. But lets say that if potting was technically feasible, then that is enough level of security (for example, someone with an special "acid" to remove the potting is possible, but definitely is way beyond unlikely, very difficult, low probability to happen, and too expensive for anyone to try....and if anyone does, then we accept it will happen).

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 03:47:55 am
content: Quote from: helius on September 27, 2016, 03:41:11 amNo sir, not at all. So being clear, the service my customer (the company I am making this for) provides, implies to give "for free" the system. Now, to use the system (a service) the final clients should pay X amount. The usable "thing" is the energy of the batteries, so the final clients will try to get the cells out to avoid paying and still being able to use the cells. This also implies, that since they are unlikely to know the safety risks with the cells, they will probably be seriously injured (fire, explosion because of mishadling). WE (myself and the customer) are not against recycling, but letting any access to the cells is 1) a safety risk and 2) and "commercial" danger.Nonetheless, you are correct that this will not allow recycling the batteries.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 27, 2016, 03:56:46 am
content: Pot it in a flexible rubberlike compound?The easiest way to fix the problem of users disassembling the packs to use the cells inside is to price the packs enough that it would be uneconomical to do so. Maybe ask for a deposit on the pack that can be used towards payments of the service and anything remaining be refunded when the pack is returned?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 27, 2016, 03:58:49 am
content: Take a peek how it's done:http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/140sp1505.pdfon page 6, Physical security.Of course, this is just for information on a chip, the best you can do for a battery is blow a fuse to disable a pouch, but that still leaves the energy in the pack. There's no way short of a fire to drain the energy quickly. Maybe a big bag of baking soda that will be shot explosively into the cell?http://www.dexerials.jp/en/products/c3/sfj0815.htmlSo you'd have a battery that will disable itself if you try to open it with acid or x-ray it ...

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 04:15:31 am
content: Quote from: NiHaoMike on September 27, 2016, 03:56:46 amThanks for reply. I will look at flexible rubberlike compounds, do you have any suggestions? I mean, something designed for lithium ion and their implications.I do not want to sound too unflexible, but having the final client pay something upfront is not an option. To some point, this is a "differentiator" from local competitors.Quote from: Alex Eisenhut on September 27, 2016, 03:58:49 amI will look at your links thoroughly, my first impression is that the first one is something very (electronically) complex, not an issue on that side (lets suppose that) but still you have access to the cells themselves. The second link is one (safety, not "security" ) protection feature we have in the BMS. For it to disable the cells for security, it then should be embedded inside the cell itself... I am not sure if this an option in commercial cells or would require very large number of batteries (>1M, maybe more???) for a manufacturer to do it custom. I will look at both... Thank you.

author: Towger
author_rank: Super Contributor
timestamp: September 27, 2016, 04:34:28 am
content: It this for use in a 3rd world country, where you don't want the user to injure their self extracting the cells or first world where your customer wants to rip off their customers with expensive replacements?If it is 3rd world, I would not pot them, as they are more lightly to have an injury digging out the cells.

author: jitter
author_rank: Frequent Contributor
timestamp: September 27, 2016, 04:46:19 am
content: Quote from: juanfermed on September 27, 2016, 03:41:31 amPractically, that's where you want to go. Technically, you're never going to be 100% sure someone's not going to hack it, nor "damage" themselves in the process.Just as a simple example: I have a few cordless drills, and some of them come with battery packs that are just assembled using screws. Access to and replacements of the cells was easy. There are also some with tightly sealed (noteworthy: Makita) packs that will not yield their insides without destructive disassembly.However, have you taken into account that someone may just find a way to power the device by simply bypassing the (internal) batteries, not even trying to hack them?

author: helius
author_rank: Super Contributor
timestamp: September 27, 2016, 04:56:57 am
content: Quote from: jitter on September 27, 2016, 04:46:19 amThe issue (as I understand it) is not how hard it is to power the device, but how hard it is to draw down the battery.They are selling batteries "on time". Here's a charged battery for $0! Now pay me $1 per Wh extracted.This would clearly make no economic sense in a place with reliable electric power, but in some parts of the world that doesn't exist. But only if the battery pack is an impregnable fortress can the scheme work: otherwise instead of paying, they'll just rip apart the free battery pack and use the energy. I think the reason this scheme seems so unfamiliar is that it is basically impossible and there are no examples of it working. It's DRM for energy.

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 04:58:15 am
content: ******************Practically, that's where you want to go. Technically, you're never going to be 100% sure someone's not going to hack it, nor "damage" themselves in the process.Just as a simple example: I have a few cordless drills, and some of them come with battery packs that are just assembled using screws. Access to and replacements of the cells was easy. There are also some with tightly sealed (noteworthy: Makita) packs that will not yield their insides without destructive disassembly.However, have you taken into account that someone may just find a way to power the device by simply bypassing the (internal) batteries, not even trying to hack them?******************Well, I agree on what you said. The difference here is that you already payed for the cordless drills, and it is your money what you loose (or win) if you crack open the battery pack. For my customer, he is the one absorbing the cost of other a) destroying b) hacking the pack. So the damage goes to my customer, not to their final client. I am explaining this to give you context.The second scenario you propose would not happen since a) it needs authentication with the batteries in order to work (suppose that the system is already very unhackable, to not drift on the topic) and b) the value is in the energy stored in the batteries, since this is what they use, not in the system making use of the batteries (which is want they want to bypass).Quote from: Towger on September 27, 2016, 04:34:28 amWell, this is for any world in which a person does not want to pay for the service, but still wants to leverage the advantages the services provides. And definitely no, my customer does not want to rip off expensive replacement, my customer is the owner of the systems and any replacement is payed out of his own pocket...that is why the topic includes "cheap" battery pack, even though I am not making the "cheap" characteristic the main point of the topic.

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 05:12:51 am
content: Quote from: helius on September 27, 2016, 04:56:57 amYes! It is very unfamiliar to me!! hahaha (crying inside).An example is what Telecoms usually experience: a lot of battery theft in their backup plants. They are trying to provide a large customer base of a reliable service (cellphone) but a lot of people steal batteries in their plants. This have to be payed by the Telecoms, so basically they want to stop theft by making batteries "not steal-able". Something somewhat similar happens to me. I am not trying to prohibit access to a resource, but only protecting that what makes it possible the access to that resource, in order to keep it accessible. Not sure if that makes sense haha.....

author: helius
author_rank: Super Contributor
timestamp: September 27, 2016, 05:12:54 am
content: Here's my idea. If you cover the cells in potting compound, it will be okay until someone discovers where to drill to make contact with the tabs on the end of each cell series. I would approach it from a tamper-detection perspective. Can you detect that the pack is being attacked, and then blow fuses that are inside the 18650s? I think some types contain thermal fuses.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 27, 2016, 05:13:19 am
content: This is made more difficult by your need (desire?) to use standard cells. Can I suggest that you may get a partial solution if you make the standard cells unusable as standard cells after recovery from your packs.An example of how to do this follows. Bond a component to the ends of the cells which provides the continuity to the cells, that is disrupted by the mechanical forces of removing the case. This might take the form of two ceramic disks lightly bonded together. These disks would have a spiderlike set of traces from a center contact, vias at the end of the legs, and with the spider leg vias in physical contact between the two disks. The outer disk would be on a friable substrate, something that disintigrates when triggered mechanically (think of breaking the tail off of a Prince Rupert drop). Carefully placed holes in the disks would protect the venting capability inherent in the cell.When disassembled the result would be a cell of the same diameter as a normal cell, slightly longer length and all of the normal safety features of these cells. But hard or impossible to use because the electrical contact is distributed over multiple small contacts in non-standard position with little or no area for soldering or physical contact. Each contact would be unable to sustain normal contact from the battery.A determined hacker could remove the bonded end pieces, but if done appropriately it would be a lot of work and with less than perfect yield. Or they could design a custom battery holder that would render these cells usable, but since it would have to provide precision location and orientation, it would also be a difficult and expensive proposition.

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 05:38:14 am
content: Quote from: helius on September 27, 2016, 05:12:54 amThat is an interesting suggestion, thanks. I will look at it, I just hope to find something that can be blown "on demand", lets say, by an external signal. If not, which I think might be the case, having a resistor heat a lot up to triggering the thermal fuse might work. Or draw a huge current to trigger an internal current limiting device. This will required the internal device to be a one-time only.Thanks.Quote from: CatalinaWOW on September 27, 2016, 05:13:19 amQuite an interesting approach, thank you. I will get on this as well and see what options I have. In the meantime, to answer your question: It is a need to use the standard cells, unluckily. I am not emphasizing on cost, but these is the cheapest format you can find lithium cells given specifications. If you have any suggestion using other packaging types I am more than willing to hear.

author: juanfermed
author_rank: Regular Contributor
timestamp: September 27, 2016, 06:00:00 am
content: Quote from: blueskull on September 27, 2016, 05:46:30 amThanks. Yes, safety + security (using potting??) is the question. And safety is an issue, though final clients are damaging my systems, I cannot pose any danger to them (so no pyrotechnic charge to set things on fire).I already edited the first post, to make it clear what "level" of security is "good enough". Yes, with enough time, tools and skills it might be opened, but probably too difficult to be attractive.

author: janekm
author_rank: Unknown
timestamp: September 27, 2016, 06:52:07 am
content: Any approach that involves potting or otherwise messing with the batteries is potentially very dangerous. For example, under certain conditions the cells need to vent excess gas, if they are sealed inside potting compound an explosion could occur. Testing for all these kinds of conditions would be very difficult.I would consider an approach similar to printer cartridges, you have a chip inside the battery pack that tracks usage and disables the pack when it is "empty". Still difficult to secure (as can be seen with the printer cartridges, where these kinds of systems are usually defeated after some time) but it avoids a lot of the safety issues involved in trying to prevent physical replacement of the batteries.You can add a means of tamper detection (for example a thin wire wrapped around the pack that erases the keys in the security chip if cut, in fact you could simply keep the keys in volatile memory) to discourage disassembly of the pack.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 27, 2016, 08:02:13 am
content: If you're using standard cells, there will always be a way to get at them, and mechanical protection is all you can do, which will be expensive. Potting, with a vent path, combined with some sort of internal switch or discharger is probably about all you can do.If you're really serious you'd need to put something inside the cell so that accessing it inherently destroys the cell somehow - maybe chemically?

author: zl2wrw
author_rank: Regular Contributor
timestamp: September 27, 2016, 08:25:05 am
content: Quote from: juanfermed on September 27, 2016, 03:47:55 amI'd say that your customer's business model is seriously flawedI get the impression that you do not want your battery system to turn out like the CueCat (remember those? - a free giveaway barcode scanner that was re-purposed by hackers instead of being used for its intended purpose of scanning codes in advertisements) - problem is, everyone on this forum should know by now that hackers are gonna hack!If you want to "rent" batteries (instead of selling batteries outright), and prevent your end users from damaging them, then what you can do is charge the end user a bond, and if the end user does not return the battery (or brings it back damaged), then you get to keep the bond.Honestly, it's probably easier to jump into bed with a finance company and sell the batteries outright on "hire purchase" terms to the end users (then it doesn't matter if they hack or recycle the batteries, and collecting payment is the finance company's problem).An anecdote from a long time ago, a New Zealand company produced a remote controlled relay product, where remote control was achieved by sending messages via the telephone company's paging network. they jumped in bed with a large computer company, which provided an 0900 (premium rate telephone) front end user interface, and of course put them in a position to "clip the ticket" every time a customer flipped a relay...The competitor's product was very similar, except that it just had a normal pager connection (out of the box, the telephone co would let you send numeric pages from a normal phone for less than what it cost to call the other company's 0900) and the customer could port it to a pager plan if they wanted.Guess who's product was successful in the marketplace? (not the one where the middleman was clipping the ticket every time it was used)

author: TerraHertz
author_rank: Super Contributor
timestamp: September 27, 2016, 10:04:17 am
content: The usual way companies make monopoly money from selling battery packs, is to ensure the buyer can't simply replace the individual cells when they wear out. Instead has to buy a whole new battery pack with all its management electronics and custom moldings. Effectively this is a restriction on how many times the user can put powerintothe battery, for the price they paid. Most laptop battery packs are like this, with the casing glued shut and so flimsy that breaking it open involves actually wrecking it, beyond reuseability.The OP's case (billing to draw poweroutof the battery) doesn't seem very likely. For one thing, what user is going to find the power from individual bare cells useful, without the management electronics? Very few cycles before the batteries are killed by overdischarge, overcharge, etc.Also it's hard to imagine a scenario where battery electrical power is so precious it justifies such security measures.I can't help but suspect someone isn't being told the truth here.Sounds more like a battery pack being used as a security control on some high value system, where it's desired to prevent anyone from removingthen replacingthe cells in the pack.What's the bet the actual use case is unethical?Edit to add: I thought of a use case that might fit OP's description. Stand-alone solar electrical systems for remote homes, in which the battery bank has a 'power used' meter, and this is used to bill the homeowner for his power consumption. It's not hard to imagine some government of an under developed country thinking this might be a good way to raise money.

author: Zero999
author_rank: Super Contributor
timestamp: September 27, 2016, 10:33:26 am
content: Quote from: juanfermed on September 27, 2016, 05:12:51 amThe difference is the Telecoms companies is their battery backup plants are on their own property and can be reasonably well secured with alarms, CCTV and locks. Your customer's product will be in the hands of their clients and they can do whatever they like with them.Quote from: zl2wrw on September 27, 2016, 08:25:05 amI agree. It's a flawed business model. Your customer is better off selling the batteries to their clients. Giving them to their clients for free is just asking for them to hack it. There's no way to stop it and when you consider the amount of extra money spent on security then it's not cost effective.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 27, 2016, 10:44:58 am
content: Quote from: TerraHertz on September 27, 2016, 10:04:17 amI agree; I think we need more information about what this product is, and what the business model is behind it.Right now, it sounds as though the 'product' is just the power from a battery. That sounds really odd to me, so there must be more to it than that.As a rule I always enquire about exactly how any product I'm asked to design will be used. More often than not it's essential to know this anyway, so I can be sure that whatever I come up with is actually fit for purpose. Products that have been designed 'blind' to a specification without context, rarely work well for anyone involved, in my experience.If a product needs to be kept confidential, then a public forum isn't the place to ask anything about it at all. If it doesn't, then go into enough detail to allow smart, experienced people to solve the real problem.

author: Ian.M
author_rank: Super Contributor
timestamp: September 27, 2016, 11:37:23 am
content: Maybe Sodium Sulphur, if its a stationary or semi-stationary application?If you do get the cells out of their insulated and thermally maintained pack, few end users would have the technology to maintain them at working temperature to get usable power out of them. Another possibility would be fuel cells, specificallyflow batterieswhich are useless without the control system to manage puming the electrode fluids through them.However the phenomena of stealing infrastucture metals to recycle is yet another reason your client's business model is fatally flawed. If there is significant value in the packs raw materials, a ghetto industry of stealing them for sale to unscrupulous recyclers will soon develop. If pack replacement is free, there is insufficient incentive for the end users to protect their 'property' against such theft, or they may even sell them to the recyclers themselves and claim they were stolen. The only way your client's business model can work is if they employ goon squads of heavies that an organised crime family would be ashamed to associate with, to do asset protection, collections and client 'support'!

author: LaserSteve
author_rank: Super Contributor
timestamp: September 27, 2016, 02:17:41 pm
content: As some one who had to work with high energy Li Packs for a defense project that later was also sold to the civilian and first responder markets, I would really, really, really evaluate what you intend to do carefully. It needs bulletproof long term testing, if you do it at all. Ours had to be certified for air freight transport, and be nearly indestructible. World wide, there are a host of regulations on these batteries, including evaluation of wrapping the cells with ANYTHING. Thermal issues prevail during charging, and many batteries come with a "protector" circuit board in/on each cell.My employer at the time, a small company, finally settled on a stock pack made by a power tool company, and obtained that companies permission to use their interface and mounting scheme, as well as permission to purchase the packs from their distributers. It made life so much easier for world wide distribution. Permission was granted more or less for patriotic reasons after a serious hold harmless was executed. There are vendors who sell generic packs, you might look at that as well.The Mil side of the project was provided with a Mil spec battery made by a division of A123.Only thing that came to my mind was hand gluing a thin isostatic pressed alumina sleeve to the outside of the battery, and I have DOUBTS about doing that, as these cells can expand during normal operations as they age or are stressed.. Pure Alumina would at least crack. Potting, well, perhaps is insane. Especially if it ever blocked a cell vent. Use of any other material for the sleeve would be doubtful as well. Issues come to my mind on what happens when you pot welded battery straps, as well. If there is ever a catastrophic shorting failure, your potting material is right up against a prime ignition source with no air gaps.Go to a prismatic cell and a snap together case that is thermal or ultrasonic welded. Then safety test the unit over and over at an approved battery test lab. Note the lab will want 15-30 packs for testing, minimum. Welded current carrying straps can go a long way to prevent casual reuse.We went with the A123 style chemistry because you can shoot the cell with a nail-gun and at worse, have massive amounts of steam discharge, but in most cases, no fire.I really think you need to rethink your scheme, including transport and third party testing of the finished item. Hire a battery consultant.Steve

author: Bicurico
author_rank: Super Contributor
timestamp: September 27, 2016, 05:01:18 pm
content: My idea: if the product/service is profitable enough, then I would just fit the battery in a metallic case that is locked. The device itself should contain a GSM module (cheapest and easiest: Arduino + GSM900 module = less than 20 US$). It will monitor if the metallic battery case has been tampered. The same wire that gets energy will monitor 2-3 switches. If they open, a SMS is sent to the manufacturer. The contract will have a clause that any tamper attempt results in an expensive fee. Problem solved: manufacturer knows who is messing with the battery and a contract states what will happen in such case.I would not try to overly protect the battery, as it will result in:a) eventual security issues (Samsung Galaxy Note 7 shows impressively what can go wrong)b) people hacking it anywayc) more difficult maintenanced) increased production coste) non-ecological wasteRegards,Vitor

author: PointyOintment
author_rank: Frequent Contributor
timestamp: September 27, 2016, 08:32:08 pm
content: I have no technical suggestions, but I will suggest a slightly different business model. Your client gives his customers the battery packs for free, but he gives them out empty. He then charges his customers for the service of charging them (to whatever level the customers want). If, as you've implied, there is no other place the customers can get their batteries charged, this should result in there being no incentive for the customers to disassemble the packs.

author: Ian.M
author_rank: Super Contributor
timestamp: September 27, 2016, 09:39:00 pm
content: There's always *someone* who's got some hacked together means of generating electrical power.Unless you make it difficult and dangerous to recharge hacked packs they *will* get diverted to unofficial uses.

author: KL27x
author_rank: Super Contributor
timestamp: September 27, 2016, 10:06:45 pm
content: You could shop around for cells with 18650 cells with built-in safety fuse? And electronics which (safely, haha) blow the fuse if the case is tampered with by shorting cells? Build case, first, then activate the system from an external port (not ICSP, which can be hacked, but just a simple I/O or I2C or something which cannot deactivate the system or which must receive correct 16 bit code to deactivate... wrong code = blown fuses. Maintenance can be done using the keycode. Say closing the case makes a connection that isn't accessible/jumperable from the outside. And opening it causes instant cell death.The battery must cutoff while there's enough juice to blow the fuses, still. And until recharged, T-minus X weeks until self-destruct sequence initiates!Of course the safety aspect is the biggest concern. The fuse is intended for emergency backup to proper cell usage, CYA laywer speak this and that and so forth. If your client has sufficient budget for this project, perhaps talking to some li ion cell manufacturer can get this done with all the i's dotted. All we're talking about is a properly rated/spec'd fuse contained within the cell, and they already do that on many of these cells. Such that the fuse is guaranteed to blow before cell can overheat to point of self-ignition, given minimum current from short circuit... which should be child's play, really. I mean, that's what they're already designed to do. You could find supplier that will provide this specification and do in house testing of samples out of each batch, to ensure it conforms.

author: Ian.M
author_rank: Super Contributor
timestamp: September 27, 2016, 10:20:18 pm
content: Another idea. Use LiPO pouch cells and a vented sheet steel enclosure with the cells bonded to it and the proprietary electronics sandwiched in the middle. Design it so opening the enclosure after assembly rips the pouches letting the electrolyte dry out and rendering them useless. Of course ripping open a pouch cell isn't particularly safe, but the odds are against it catching fire if no ignition sources are present.

author: m98
author_rank: Frequent Contributor
timestamp: September 28, 2016, 07:41:13 am
content: Ok, this is just ridiculous. But hey, why not use a hard epoxy potting compound mixed with aramid fibers, steel wires and wolfram carbide balls?

author: KL27x
author_rank: Super Contributor
timestamp: September 28, 2016, 09:02:07 am
content: Hammer and chisel?

author: juanfermed
author_rank: Regular Contributor
timestamp: October 30, 2016, 09:26:18 pm
content: Hey all,So just wanted to give you an update on this subject. After reviewing several options we had to make this thing "unhackable" together with cost, manufacturing process associated and risks, it was decided that the best we could go for was a hard plastic with ultrasound welding. No potting no autodestruction. In this sense the final safety measures are encryption and authentication, and as good as ultrasound welding is from the mechanical perspective. So now I have been going further with this technique and talking with our battery supplier on how this can get done.Thank you all for your input and recommendations. As mike said, since we are using commercial 18650 cells, there is really not very much to do.

author: juanfermed
author_rank: Regular Contributor
timestamp: November 04, 2016, 03:06:32 am
content: Hello guys,One thing I forgot to mention, and that I think can save sometime to anyone in a situation similar to me with this topic, is the following:http://blog.epectec.com/custom-battery-pack-potting-process?utm_campaign=Blog+Posts&utm_source=hs_email&utm_medium=email&utm_content=36913787&_hsenc=p2ANqtz-8xs1HLkNzh0HZguF3QWFR7G5791UWkeNVBZMNJgdRF6Ul-xcffZWMfI1dY__vk9tPLTkaRJ5mFIgiUKAIKgVVIF903EpshU0QJrcOjigvIZDlIrN4&_hsmi=36914148It seems this US company, EPEC, does have a battery potting process designed specifically for Lithium Ion Batteries and battery packs. When I tried to contact them they said they could not help me, so unluckily I can go no further on details of their process considerations for potting batteries.I hope this is useful at some point.

author: mariush
author_rank: Super Contributor
timestamp: November 04, 2016, 03:38:09 am
content: Like other people said... blow up fuses to disable them permanently.You could put the battery cells in some kind of thin plastic container to have some air around the batteries to allow venting or whatever else you want, then wrap your container in some kind of mesh made by thin insulated wires .. for example have 2 or 4 such thin long wires interwoven over the container and then maybe have a thin layer of potting material glue this mesh to the plastic container (so that when someone wants to remove the potting compound they'd break the thin wires as well)Since you know the length of each individual wire and their resistance you could have a controller inside the battery pack constantly measure the resistance of those wires ... if someone tries to break the mesh to get to the inside batteries the resistance of those wires would change and your controller can blow the fuse and disable the battery.Have some eeprom chip or some 1-wire chip inside products to pair battery to products, if someone tries to use battery outside product without authentification your controller inside the battery pack could disable output using some mosfet..