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Do You Really Need Lithium or Will Nickel Metal Hydride Suffice - Q&A

Anton Beck
Written by Anton Beck
Posted on June 17, 2020 at 9:23 AM

At the conclusion of our webinar, Do You Really Need Lithium or Will Nickel Metal Hydride Suffice, we had several questions submitted to our presenter, Randy Ibrahim, Battery Development Consultant at Epec. We have compiled these questions into a readable format on our blog.

Q&A From Our Live Battery Webinar

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Watch the Recording Below:

Learn the Pros & Cons of Nickel Over Lithium Based Batteries

Question: I noticed in the section about how nickel-metal hydride batteries can be smart batteries. Does this mean I need a BMS in my nickel-metal hydride battery? I just saw a lot of electronics on your slide.

Answer: That's actually a very good question. A BMS, for those that don't know what that means, that's a battery management system, and a lot of times, that's grouped into any electronics in the battery. It could be safety circuits; it could be fuel gauging. That's what the BMS is. And so, the electronic circuits to help control your battery. So, the answer is no, you don't need it. And a lot if it, you can just have the fuel gauging portion; you don't need to have the safety portion in there. So, it can be very, very simplified in nature. You can restrict all of that, so definitely you do not need it in there, but we would want, if you want fuel gauging, the capacity and run-time on your battery, we can just put only the fuel gauged portion in.

Question: I heard nickel-metal hydrides still needs to be shipped the full Class 9 hazmat sometimes. Is this true?

Answer: The answer here is one that I think a lot of people can benefit from, and that is actually true. If you exceed 100 kilograms, which is over 220 pounds worth of battery... think about that for a second, that's a lot of battery. If you exceed that, you do have to go full hazmat, full Class 9. You can't get around that. But for our talk here, it's rare that we ever see batteries that size, or we're shipping them all together at 220 pounds worth.

Question: Can nickel-metal hydride batteries catch fire like lithium-ion?

Answer: The office next to mine caught fire, sprinklers went on, fire department came out, and had to evacuate the building. There was a substantial amount of damage. What happened there is one of the engineers left the batteries charging overnight, and they had the settings on the charger. It was a large whole bank of batteries, and they had the charger setting incorrect, the wrong voltage. So, they kept pumping energy in, and the batteries did catch fire. The shrink wrap just melted, and gases came out. The whole area caught fire, and the office did, too. So, you do have to be careful. Lead-acid batteries can catch fire if you use them enough. So, you really need to be cautious of how you handle these. They are much less volatile in nature. They're not like a blowtorch when they go off, but they definitely can catch fire, so that's definitely something to consider and be aware of, especially with your environment when you're testing these, to make sure there's no flammable materials in your lab.

Question: I heard adding a safety circuit similar to lithium-ion is good for nickel-metal hydride batteries. If so, why is that?

Answer: Yes, actually we've done that. It's interesting because even though you can go down to a 0% charge, the nickel-metal hydride battery, if it just naturally goes down to that 0% charge because it's sitting on a shelf and you don't have a load on them, that's fine. There's going to be no harm whatsoever to that battery. You do want to bring them up slowly regardless in charge. You don't want to hit at full charge. You want to nurse them back a little bit before to a minimum voltage before you hit them with a little faster charge. But with safety circuits, which we've done, we don't really monitor the cells like lithium-ion, but we will actually look at the overall pack voltage because you really don't need to get down to that level of detail and add all the unnecessary cost. But we have put in circuits where, let's say we have a really heavy load, and we're just driving the heck out of this battery and it's getting close to minimum voltage for the cell. In order to avoid that cell reversal, we do put safety circuits in to disconnect the battery when we hit minimum voltage. That way none of the cells ever can get into reversed polarity, which is extremely important in any chemistry, not just nickel-metal hydride. So, where that really comes in handy is when you do have high currents and really heavy loads, and you're driving these batteries hard. It's very good to have. It's a nice level of safety to prolong product life, and your battery will last much, much longer by doing that. It's very rare that we do this, as most applications have very light loads and it's kind of worthless, but definitely worthwhile considering under certain applications.

Question: What is the abbreviation for lithium-ion batteries? Is it Li-Ion or Li-ion (IEEE 1881)? What is industry standard?

Answer: Good question. Both are used in the battery industry.

Question: Is it lithium titanate or lithium titanite?

Answer: Lithium titanate ("LTO", Li4Ti5O12) Please see the difference here: https://wikidiff.com/titanite/titanate.

Question: Is there a way to explaining charge=c/1hr formula?

Answer: A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 amp-hrs., this equates to a discharge current of 100 amps.

Question: Aren't there NiMH batteries that have low self-discharge such as the Sanyo Eneloop, which has a 6-month shelf life?

Answer: Sanyo Eneloop cells are the lowest self-discharge cells on the market, and they are a very good cell. They are often rebranded by other manufactures. Unfortunately, all higher capacity cells, which are commonly used/required in larger batteries, still suffer from high self-discharge rates.

Question: How strict are IEC regulations for NiMH? Do NiMH require on cell protection as Li-ion do, or you can afford to have that on the motherboard of the device?

Answer: IEC and UL regulations look primarily at the shock and fire hazard of the batteries, mainly high-voltage batteries and batteries that have or are in elevated temperatures. NiMH batteries need very little protection. Usually a simple resettable fuse is embedded within the battery to prevent high currents in the event the output wires are shorted. This protection needs to be on the battery, which is the source of the energy, and not on the host motherboard. This is especially important if replacement batteries are ever shipped separately.

Question: Looking to replace alkaline cells in an undersea application. Temperature effects are important. Self-discharge is important.

Answer: Sanyo Eneloop NiMH are the lowest self-discharge cells on the market. If exchanging batteries in this undersea application is difficult or costly, Li-Ion should be considered. Also, consider using energy harvesting to recharge the batteries if there it has ocean currents/movement available. This could potentially give you a lifetime power source with no maintenance.

Question: What are the fuel gauging options for embedded solutions that only require a single-cell NiMH battery?

Answer: There are no direct options that we are aware of since the cell voltage can drop down to 1V at the end of charge.

Question: The fuel-gauge IC that I've found require a minimum battery voltage that is only possible with mutli-cell NiMH solutions.

Answer: Correct. TI, Linear Technology, and Maxim all require a higher voltage.

Question: Are there any recommendations to monitor the capacity with a ready-to-apply solution without involving much of the host processor?

Answer: There is no easy solution that we know of. You can achieve some accuracy if you can accurately measure cell voltage, current, and temperature, but the overhead might be too much. If your load is very light, and if you only care about being able to shut things down in an organized manner before losing power, you can look at the rate of voltage fall. The voltage will fall off faster at the end of useful energy. If this is detected and you are not drawing too much current, your system can close up its open operations before the voltage drops to 1V. Keep in mind as you reduce the current load, the voltage will rebound some, so hysteresis is important.

Topics: Battery Packs

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