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Design Factors for Lithium Batteries Used in Portable Devices: Q&A

Anton Beck
Written by Anton Beck
Posted on October 11, 2019 at 9:31 AM

At the conclusion of our webinar – Design Considerations for Lithium Batteries Used in Portable Devices – 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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Watch the Recording Below:

Question: Is it true that lithium-ion batteries need to be DOT certified before they can be shipped, and doesn't this add cost, as in cost factors, as well?

Answer: Yes, that is absolutely correct. In fact, that a lot of times limits some of the lithium-ion applications. All the lithium-ion batteries do have to go through a UN38.3 test. They need to pass, and a there are a lot of times this will add a few thousand dollars of costs to run all these tests. But in a nutshell for those that still understand UN38.3, it's essentially required because it emulates what a battery could be potentially exposed to during the shipping process. They could care less about how the battery runs or operates or anything like that. They just want to make sure the box doesn't catch fire on a UPS plane. And some of the tests it has, there's essentially tests that they go through. There are altitude simulation tests. If I recall, there's some temperature tests as well. I know they shake and bake it – vibration to emulate a truck driving down the road. They also do altitude tests because let's say a plane loses oxygen at high altitudes. They actually make sure that electrolytes doesn't come out of its cell because that material is extremely flammable and could catch fire.

In the event a package was damaged, they run it through short-circuit tests to make sure fusing is intact, that the battery doesn't overheat or catch fire. So, essentially, they simulate transportation of the battery, somebody damaging the packaging, that sort of thing. So, I'm all for it. I think it's a great addition to keeping everybody safe.

Question: Does anybody still use nickel-metal hydride cells or batteries?

Answer: Yes. For that reason, I just mentioned DOT UN testing, nickel-metal hydride does not need to go through UN testing. There's very, very large packs of some stipulations on that. And if weight is not a factor, because they do weigh quite a bit more than lithium-ion, they can be a much better solution for getting time to market. You can beat your competition using the batteries.

A couple things to keep in mind is not only that they're heavier, but one thing, when lithium-ion came onto the scene I was extremely happy that the charge profile for characteristics are opposite nickel-based chemistries. The reason being, nickel uses constant current, and then you're looking for a little peak on your voltage, and you must have enough current for that peak to be defined enough, and that's how you terminate charge. If you miss it, then the battery starts getting very warm. But if you miss that peak that happens, obviously you must have timers. What's difficult is almost all our applications have lithium-ion batteries being charged while they're being used. Lithium-ion has a very similar charge profile as a lead-acid battery where you're using a constant voltage with current limits. What's nice is as long as that voltage is you don't exceed that max, you can be discharged and charging. Eventually when the load is on, the current to the battery would be very, very low, and if it stays that way then you terminate. You never leak trickle charge on a lithium-based product.

But it's really easy to be able to run your load and charge the same time with lithium based. Nickel-metal hydrides, it's very, very difficult to be able to charge your battery, and there's pulling energy out of the battery at the same time, so that's one major drawback of the nickel-metal hydride batteries.

Check Out Our Battery Pack Enclosure Design Ebook

Question: Adding electronics on a battery, doesn't it cause it to just drain faster?

Answer: Intuitively, you think you slap a whole bunch of circuits on a battery, and you think it's going to be a burden to the cells, and they'll discharge in one day. That's not necessarily true. It depends on the type of electronics you're adding. For instance, if you're putting a battery charger, embedding it into the battery, then it's getting its source of power mainly from the wall brick, the external power, and it's going to be used to charge a battery. But we must be very, very aware of the type of components that we use because when it's not plugged in the wall, we don't want the battery discharging into the circuitry of the battery charger. That would drain the battery quite rapidly.

We've paid close attention to the type of diodes we use for blocking. Standard diodes have really, really nice reverse-blocking current. So those are things we're very cognizant about during the design process. Other areas, sometimes we have to put a processor on board of translators for, let's say, the LEDs don't like the LED function, the way the IC presents it. So, we can essentially read that information and translate it into any type of display. And this is very useful. If you're trying to make a product backwards compatible you must set them on thousands of your original product out in the field. And when we push the button the LEDs look a certain way, and they respond at a certain timing sequence.

We can essentially mimic that by translating what the ICs are telling us, put that in a processor, and then be able to display it the exact same way. They don't realize that's a new generation battery because it looks the same. Little things like that, but when we do that then we also have to put circuitry in so when the button is not pushed and it's inert, that we remove power from those type of processors. Because they have sleep modes, and wake ups. Then the microamp, I think they're down to 1.6 microamps now, and they too can be extremely low.

Question: I am interested in what certifications are required to ship products with lithium batteries around the world.

Answer: This is a multi-level question. Shipping lithium batteries by themselves requires a different certification than if shipping with a product. There are a completely different set of guidelines for shipping a battery within a product.

Some countries require their own designated certification, so there isn’t one global cert that covers all the countries. International Air Transportation Association (IATA) is a very good resource for information, training, and assistance. They provide hazardous goods training, and it’s required for anyone or any organization that manages battery shipping.

Question: What experience does Epec have with batteries over 35 kg?

Answer: Our domestic focus is powering portable devices, but our facility in Asia has substantial experience with larger batteries to include energy storage and backup systems. We are currently manufacturing a battery pack that will power an aircraft that weighs over 60 pounds, but that is the largest one we manufacture domestically.

Question: Does Epec have specifications for G forces in their datasheets? Is there any aircraft standards or specifications that you may recommend for the lithium batteries?

Answer: UN38.3 requires vibration tests, which is called out in the test protocol. G forces higher than that would be called out by the customer. As for the second questions, no, that would be customer driven.

Question: Where can we find more information about charge profiles and information about how to design charging circuits for a given chemistry?

Answer: Reference the cell manufacturer’s design guides. They outline what is required to charge their cells. If you have questions, give us a call.

Question: In order to keep the battery smaller, is it okay to locate the power management system with the electronics of the device? Positives and negatives?

Answer: Sometimes it’s OK. It depends if the battery is not removable by the end user. Fuel gauge accuracy may also suffer if not near the cells. There are a lot of factors. Typically, it requires a discussion with a designer and customer to determine best approach for that specific application.

Question: What are the difficulties in using Li-Ion batteries for intrinsically safe applications?

Answer: Energy and heat. Power needs to be limited and spark prevention is a must by disabling all power to the connectors until firmly seated.

Topics: Battery Packs, Product Design

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