NiMH or NiCad? Charging Your New Battery

NiMH or NiCad? How do I Charge it?

Everybody is curious about NiMH cells. Just as there is a "best" glue for every job in a kit, there is a best battery pack for every application. NICAD technology has been around for a long time and is very highly developed. New larger size NICADs don’t come out very often. However, NiMH is still fairly early in its development. Every few orders I place come in with slightly higher ratings. If you look carefully at most written opinions about NiMH vs NICAD, you will quickly see they almost always are comparing good, well proven FDK(Sanyo)’s to Panasonic. Hydri-Max is Panasonic. Well, to me that is like comparing apples to oranges. 92.2213% of all RC’rs would not consider using anything but a FDK(Sanyo) NICAD for a TX or RX pack. If you would not choose a Panasonic NICAD for your ship, why would you use a Panasonic NiMH pack?

I am sure Panasonic makes a very fine product. But, I feel FDK(Sanyo) has probably "earned" its position with RC’rs for a very good reason. Have you noticed how much they spend advertising to us? Zero! We use them because they have generally proven to be the only wise choice (SR excepted). Currently, the top FDK(Sanyo) AA NiMH is 1650 mAh. The top Panasonic AA NiMH is 1400 mAh. Now, who do you think is at the apex of the technology curve? Simple: FDK(Sanyo) is at the top. Probably they always will be. All my following comments are about FDK(Sanyo) NiMH cells.

Hopefully at this point you will agree that most of the previous press and modeler comment on NiMH is questionable for sure and dated at the very best. Often I will get an email asking me which is better, NICAD or NiMH. Well, there is no answer to that question. It is like asking what is better, apples or fig leaves. If you’re hungry, an apple is pretty good, but if you’re naked, maybe you need a fig leaf. So, which is better depends on the job you are trying to do.

Strengths and weaknesses: There is no such thing as a perfect battery. All chemistries have good and bad points. Most modelers have a reasonable understanding of the personality of NICADs. NiMH has a slightly different personality.

Special considerations for NiMH and NICAD batteries

1. Overnight charge rates must be at Capacity / 10 or less. So, no more than 72 mAh for a 720 AAA pack. This is true of NICAD batteries as well — but a NICAD will tolerate a slightly higher charge rate for a longer period of time without damage.
2. A fast charger must be rated to detect the much shallower peak of NiMH. If you are considering a new charger of any kind, make sure it is NiMH rated. Anything else is a dinosaur! Make sure you invest your money in a tool that will work well into the future. Even if you don’t try NiMH now, you will before too long.
3. Don’t expect them to perform exactly like NICADs in high-drain applications like motor packs. In most cases adding one more cell will allow a similar-weight NiMH pack to outperform a NICAD pack. Those who don’t use the extra cell will be disappointed. For a transmitter, receiver/servo or ignition pack, the drain rate is modest and NiMH compare very favorably to NICADs, often with a slightly higher voltage (we’re talking 1/10’s here) under drain.

NiMH has come a long way in the last two years and is a good choice in my view. I use both NiMH and NICAD packs with great results. I absolutely use what I sell. Most modelers that use my NiMH packs fall into one of two categories. Many want to change out an existing AA NICAD that is 600 or 700 mAh and are replacing it with a "AA" 1650 NiMH of the same size so they no longer have to quick charge it at the field. The largest "A" size NICAD battery you can buy is a 1700 (1400 is the common size). The same A size cell in NiMH is 2700 mAh. This 2700 mAh pack weighs about the same as a sub-C 1300 pack that most everyone has seen. Others are using the "AAA" 720 and 2/3 AAA 280 in 1/2A, HLG, Combat and other space- or weight-critical airplanes. Think of it, a AAA size battery with 720 mAh! That’s outstanding, and weighs the same as the typical 270 mAh 1/2A pack. I’ve used the 720 and 280 packs in my combat ships with from 3 to 5 servos. The 720 gives me the weight advantage of a 1/2A pack (I need all the advantages I can find!) with better capacity than any standard AA pack. The 280 gives me a weight reduction and is what I am currently concentrating on. Matter of fact, one of my good flying friends uses one of my 2700 packs in a 1/3 scale Aircraft International Extra, with 9 JR coreless servos. He has about $4000 in this ship and is one of the most respected pilots in the club. With NiMH, he has a huge capacity reserve and a lightweight pack. He loves hoverbatics!

So, if you have a ship that could benefit from a lighter pack, or if the space you have available won’t carry a high enough capacity NICAD, or if you just want to get away from having to quick charge at the field and want to up your capacity a great deal, give NiMH a try. It is excellent, RC-worthy technology. That in itself makes it an interesting choice. I think you will like it.

“Will my standard wall charger charge it?”

Here is how you calculate charge times for NICAD and NiMH packs: (mAh Capacity × 1.4) / Charger mAh = Charge time in hours. For a little safety margin you might replace the 1.4 figure with 1.6.

So, a 1650 TX pack would work like this: 1650 × 1.4 = 2310. Then 2310 / 50 mAh = 46.2 hours. If the answer is less than 14 hours, then the charge rate is too high to be left unattended, or too high to be used without proper peak detection.

Keep in mind, you won’t be running down a 1650 TX pack in a day of flying! So, you will only charge it from dead one time most likely. Most cyclers have a 120 charge setting. This is a better overnight rate for this pack: 2310/120 = 19.25 hours. But your 50 mAh wall charger will work just fine as long as you keep the pack full and allow enough time to charge.

“What fast chargers do you recommend?”

I suggest the SIRIUS Chargers or the Ace Super Smart Charge. Either charger is of excellent quality and will properly detect NiMH cells as well as NICAD. I sell the Ace Super Smart Charge for $70. Runs off your 12V field box battery, will charge two packs from 4 to 8 cells simultaneously. One side of the Ace SSC does 4 and 5 cell packs and the other does 4–8 cell packs.

As of this time (10/19/2000) there are no Hitec chargers that properly detect NiMH packs.

“Can I use my RC Car pack charger to charge this TX or RX pack?”

Some RC electric car people who move into RC Airplanes or Gas Cars or Gas Boats want to use their car motor pack chargers on their TX and RX packs. Almost without exception, the use of an RC Car battery charger to charge any TX or RX pack is a terrible idea. You will incinerate your packs. These type chargers are made to charge very large (sub-C) high charge/discharge rated cells — not delicate AA cells. Remember, your TX and RX packs are very important. If one of your packs fails from your abuse, the airplane won’t just stop, and a gas car or boat won’t just quit racing ahead. It will crash! How often does an electric RC car pack get flaky and need replaced? Pretty often. If you use one of those chargers on your TX and RX pack, which is very tiny compared to your RC car packs, the abuse will be even more severe. Kind of like Mike Tyson against a 6th grader. Your TX and RX packs will fail at a faster rate than your car motor packs did. Can you afford to destroy a model with even great regularity? A charge rate of Capacity × 2 is the maximum that should ever be considered for any RX or TX pack, and then ONLY with proper peak detection — preferably Slope or Delta Peak detection. I use the Ace Super Smart Charge and much less of a charge rate.

"Yea, but shouldn’t it be ok with my Super Wiz-Bang XLT Charger?" NO! Invest in the right equipment for the job so you don’t have a bad day with your model or hurt anybody. You might get away with it for a little while, but pretty soon you are going to crash. I hope nobody gets hit with your airplane or boat that you were pinching pennies on. Besides, I have always found penny pinchers spend 2 or 3X as much in the end. How much are your models worth? My strong opinion on this matter comes from a desire to see the sport grow without black eyes from accidents that could be avoided, and to see all succeed. For the good of us all, try to be safe by doing things right.

“What is the highest rate I can charge a NiMH pack with proper peak detection?”

Though all manufacturers recommend a maximum charge rate of C × 1, I have had good luck up to C × 2. Above C×2 is strongly discouraged. Any charging is ultimately up to you and in your control and consideration. Just remember, the higher the charge rate, the higher the risk to the pack. C/10 is considered the safest charge rate for NiMH or NICAD packs.

“What are some examples of good NiMH motor packs?”

Speed 480 or Twin 280 and below: The RRC-1000 is an awesome cell that replaces the 600AE and 500AR in most normal applications. It is the exact same size so no worries about fitting it in. As long as your load is 12 amps or less I know you’ll prefer this cell over your 600AE. You’ll find the discharge curve is very, very flat — she’ll pull hard until you’re down to the last 20% of the pack. In this regard, it is a standout, head and shoulders above the 600AE. For most applications, you want to order 8 or 9 cell RRC1000 packs. Available in popular shapes, and yes, there has been lots of good feedback on them.

The AA 1650 works well too but is too heavy for most Speed 400 applications. I’ve had good reports and it’s popular in the Zagi 400X. But remember, the Zagi has lots of wing area and tolerates a few ounces extra weight well.

Speed 280 and below: For loads at or below 6 amps the 720 cell works great. 7 cells for an MG-1, 7 or 8 cells for a GWS ICS motor or Speed 280 motor. At or below 6 amps, using packs with 1 extra cell, the 720 will beat the 270/350 NICAD in any application you have — also great for the GWS motor line. I’ve heard many like this pack in a flat 7 shape for the Pico/Cub/Lite Stick for outdoors. It’s awesome with 7 cells on the MG-1 motor. The AAA 720 cell weighs just slightly less than the 270 or 350 NICAD.

RRC300 Cell: This cell is great for loads at or below 4.5 amps. YES, you can use it on a Speed 280 but it is most generally used on motor sizes below this. This is a very popular cell in packs of 7 or 8 for the GWS ICS motors; due to the reduced weight these ships fly much better on this pack. Generally, anywhere you’d use a 110 NICAD the RRC300 will do a great job. Without a doubt, this NiMH cell will outperform the 110 NICAD in any motor application you have at 3 amps or less, and in some applications up to 4.5 amps. I’ve even used it at 6 amps with careful throttle control. The RRC300 weighs about the same as the 110 NICAD. You still need to add one additional cell. The RRC300 is not a FDK(Sanyo) cell but still of high quality. FDK(Sanyo) does not make a cell in the 2/3AAA size range at this time.

RRC120 Cell: This cell is well liked in applications up to 1 amp. Some like it up to 1.4 amps. The DC17-17, when propped within this cell’s range, is very happy for example.

“What charger can I use to get an appropriate C/10 charge rate for overnight charging my odd-sized pack?”

Without a doubt, the ACE Super Digipulse is an excellent choice for small to medium sized packs. With it you get 6 charge ports. Each charge port can be programmed anywhere from 10 to 150 mAh. Digital readout and simple keyboard entry make it a modern high quality tool. It is a great overnight charger for 100 mAh to 2000 mAh packs. There is no peak detection as it is intended to be used for overnight or trickle charge rates. It charges continuously at the rate you set it at. $85

For an even wider mAh output setting, the ACE Super DDVC is the way to go. It has 2 ports that can be programmed from 5 mAh to 500 mAh. Great for overnight rates on 50 mAh cells all the way up to 5000 mAh or larger packs. Digital readout makes it a modern high quality tool. It charges continuously at the rate you set it at. $85

You will find many other manufacturers charge a great deal for a NiMH pack. With Radical RC, you get the brand cell you want, FDK(Sanyo), at a price that beats the off-brand cell. It is my view that NICADs will always be with us, but over time more and more people will be converting to NiMH. FDK(Sanyo) is producing fewer and fewer NICADs and more and more NiMH cells. So, it is happening already. Even if you don’t decide to try NiMH now, make sure all your future charger purchases have this capability. You won’t be sorry you planned ahead.

If after reading this long-winded article you still have a question, feel free to ask it. I will add the answer to this page.

Happy Flying All!
Dave

Your New Battery Pack

Here are the basics for getting the best out of your new battery packs.

If you take a new pack and put it on a Delta Peak or Peak detect charger or any other kind of NiMH-rated fast charger, it will not be filled up. I don’t care what the instructions say. I’m sure they say to never charge a new un-conditioned battery on them. If they do not tell you not to charge new packs on them, then they are wrong. The voltage curve is measured and calculated by these chargers in order to predict the peak. The voltage curve is not normal on a brand new pack. It needs one slow conditioning charge before the curve becomes stable. Try as you may, you can’t fill up a new battery on one of these chargers. After its first C/10 charge, it will work fine.

We’ve had many customers write us saying "I’ve cycled this pack 3 times now and it has not come up anywhere near where its rating is." I remind them to put one slow overnight charge on the pack; they always write back and say "You were right! It cycles perfect now." So, we’ve been there many times. Don’t suffer the frustration of trying to fast charge a new pack if you want the best out of it. After its initial break-in charge you can fast charge all you like. In fact, this is almost all I do with my personal packs.

Any TX or RX pack should never be charged above C×2 at any time in its life. These are mission-critical packs, and Capacity × 2 is as high as you want to go for the best reliable life out of the cells. Never under any circumstances charge a NiMH pack above C×2 — not even a motor pack. Always use a NiMH-rated charger for either kind of battery. The NICAD-only "peak detect" chargers are dinosaurs, and put a pack into a state of deep overcharge before they have figured out that the pack is full.

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