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Battery Packs for Medical Devices Requirements and Certification - Q&A

Epec Engineered Technologies
Written by Epec Engineered Technologies
Posted on March 9, 2021 at 10:23 AM

At the conclusion of our webinar, Battery Packs for Medical Devices: Requirements and Certification - we had several questions submitted to our presenter, Battery Development Consultant Randy Ibrahim. We compiled these into a readable format on our blog.

Q&A From Our Live Battery Webinar

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Question: It seems like secondary protection circuit is unnecessary expanse when there's a good chance cells will pass anyway. Why add it, and, can you request for it not to be added?

Answer: Absolutely. We’re flexible, and along the manufacturer who's requesting this understands some of the risks. If you exceed the 170-degree before the current interrupt, then you fail the test. But if you're below it, it's great.

But our philosophy, too, is we're not just out to pass tests. Because, that's a one-time event in the grand scheme of your entire product. We want to make sure it's safe also in the field and it passes all these UL and fancy IEC tests. We also want to make sure it's routinely repeatable in the field in case there is a failure. But by all means, and we do it all the time, there's some very cost-sensitive products or volume constraint products. By all means, we can eliminate a lot of that and just rely on high-quality cells that we can supply.

Question: How easy is it in a product developer to access data in the battery? You didn't cover that, and we're kind of curious about how that's done and what type of interface is needed?

Answer: Great question. And in fact, I probably should add that next time. First of all, we use a lot of TI, impedance tracking fuel gauges. We kind of enjoy them. They're very accurate and less work on our side and they interface primarily using I2C or an SMBus.

An SMBus is nothing more than a subset of I2C, and so (it’s) fairly easy to use. But keep in mind some of the fuel gauges, mainly the older ones, have a tendency to have the same address, which is set and you cannot change it. The newer ones can be set it to a different address. But if that's the case, we've gotten around it. For instance, we have an artificial lung customer who uses five batteries in parallel and they can actually talk to all five batteries using a MUX to go out and point to each battery and communicate with them. This extremely easy to do since it is I2C-based. Also, keep in mind since batteries operate slow, there's usually have a 100 kilohertz limit on the bus, even though the bus can operate in megahertz. Batteries don't like going over 100 kilohertz, so keep that in mind. Sometimes you have to have a separate I2C bus separate from what you're currently using.

Question: Why use a TCO when you have a CID in the cell?

Answer: The first thing is redundancy. We like redundancy especially in medical batteries. TCOs, they use temperature, where the CID uses pressure. They go hand in hand; they almost map identically, but it's nice. You can actually set the TCO to a little lower temperature, which would translate into a little lower pressure than with the CID, with a trip at, and therefore a greater chance of being able to pass the test. If you want to [inaudible 00:03:04] CID, that works. And so that goes hand in hand with that first question.

Question: Are secondary protections only used for overcharge?

Answer: Yes. If you look at the primary safety, there's overcharge undercharge cycle, it does a lot of different things over current. The main thing that can cause a fire is overcharge. That's where you can't put any more energy in. They are unlike nickel-metal hydride where they just exert the energy as heat. Well, lithium-ion doesn't have that mechanism built-in, so if you're charged with lithium-ion, it will erupt and cause electrolyte to be exposed, hopefully, to no flame and what have you. And so, yes, it only looks for over-voltage, never looks for under-voltage or anything else. They are strictly for overcharge detection, nothing else.

Question: You mentioned 100-watt hour limit when shipping by air. What exactly does putting two batteries in enclosure, how does it get around this?

Answer: Okay. I did mention, you know, they have to be independent and that was actually, to your point, at the very end of the presentation. And I did mention that you could do that. And if you go back here, I'm going to pump that back here a few slides because this is a good question.

Right down here, if you look closely, let's see, oh, where is it? Right here. I hope you can see my mouse wiggling here, but there's 100-watt hours equals 2 batteries. You can actually package two in and it's totally legal. We actually have a letter stating it's legal to put 200 watt-hour batteries in the same enclosure, as long as there are independent safeties and they're totally independent batteries.

And what we do is we plug them in to the customer's end product, electrically either puts them in parallel or puts them in series, and you get twice the energy because essentially get 200 watt-hours. Keep in mind, we also charge these independently, so each one acts as a separate boundary and it keeps them all nice and balanced over the life of the pack. And so, they truly are independent, but they act as one once they're plugged into the system.

Question: How do we interpret this consensus standard statement by UL per the UL website?

Answer: These standards are some of the original standards that are the most difficult to pass. There has been a move away from the two consensus standards mainly due to the introduction of IEC62133. We believe the consensus standards UL2054 and UL1642 are very relevant. Epec meets and exceeds these stands on many products. All Epec’s medical batteries meet these standards as a minimum. FDA recognizes that batteries that meet these standards have a much greater chance of being safe in a medical application and that it is one less potential issue in premarket medical devices.

Question: Why would I not want to use a super-fast charge (PD) COTS USB power bank for a medical device?

Answer: You most definitely can if traceability is not required for lower-class medical devices. Ensure the device receiving the power can protect itself from any unexpected failure modes with consumer-grade parts, and plan for having backup power in the event anything fails. Avoid supper fast charging whenever possible to get the maximum cycle life from your battery.

Question: For primary cell battery packs, does 30% SOC also apply? How about safety circuits?

Answer: No. The 30% SOC only applies to rechargeable batteries. Safety circuits are normally not needed. However, if there is a chance of a charger being attached or system power feeding back into the battery, then a blocking diode or low-voltage drop block FET is required to prevent reverse current flow that can inadvertently charge the battery.

Question: What about transcutaneous charging in the body?

Answer: We provide wireless charging systems outside of the body. However, a few customers have developed systems using external batteries we developed to charge their internal battery using wireless charging through the skin.

Question: Are you aware of any regulatory requirements, FDA, MDR, specific to building your own battery pack? The battery packs have already been UN38.3 and IEC62133-2 tested, and IEC62133-2 tested.

Answer: Depending on the type of medical device and where it is sold, you might need UL2054. Check with FDA requirements for the medical device as a whole, including battery.

Question: What can you tell us about NRTL certification? Is it required?

Answer: It is required to place a regulatory mark on your product. Europe requires CE marks on products, which covers safety and EMC.

Question: If you have UL 2054 for a product containing lithium batteries, do you need IEC 62133 & UL 1642?

Answer: Those certifications are optional, and all contingent on how you intend to market your product.

Question: What agencies test these standards?

Answer: All the large agencies will test to these standards, UL, CSA, SGS, Intertek, to name a few.

Question: Do they return some of the batteries used for testing after UN38.3?

Answer: They normally do upon request. Be careful only to use them for internal use since they have been subjected to some extreme testing.

Question: Are there any Wh or power limitations that FDA puts when developing a Li-ion battery pack?

Answer: None that we are aware of.

Topics: Battery Packs

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