Why are we using NiMh...really?
 

I started RC in the early 90's, all my radio equipment was on NiCad batteries. As I gradually updated equipment, the NiCads went away and the NiMhs seeped in. At first I thought "great, I can move on to the newer batteries!" But after several years of almost exclusive NiMh use, I don't like them. At all. Compared to NiCads, I see only disadvantages, with NO advantages over NiCad. What I have learned and observed:

1. NiMhs take longer to fully charge....not a lot longer, but longer at any rate.

2. New packs require an incredibly long charge cycle the first time in order to get the best performance out of them.

3. They run down VERY quickly when just sitting.

4. They run down faster in use, even right after a full charge...more frequent charging is required.

Point 3 is really my main area of concern. My time is very limited, my schedule chaotic at times, and the weather in central OK somewhat unpredictable. I may find myself with an hour of two of free time on a sunny evening, but my batteries are too low because I charged them two weeks ago. I can charge a NiCad and pick it up a month later and still see 5+ volts on a 4.8v RX pack under a simulated load.....plenty for a couple of flights. My heli's relatively new NiMh pack was charged less than a month ago and now shows less than 4 volts WITHOUT a load (under a load it's only giving me about 3 volts and gradually dropping...to get the same thing from a NiCad, I would have to leave it on the shelf for months on end).

Overall, NiCads seem far more forgiving and resilient, and more efficient. So why exactly did the industry ditch our trusty NiCads and give us these inferior batteries? Any thoughts? Similar experiences?

Matt

RE: Why are we using NiMh...really?
 

You could switch to low self-discharge NiMH cells, such as Eneloops. They maintain their charge even better than NiCds.

RE: Why are we using NiMh...really?
 

The only advantage to NIMH inmop over nicad is increased capacity.

RE: Why are we using NiMh...really?
 

Why does anyone use NiXX type batteries today/

LiPo have so much more power/weight that they makes NiXX obsolete.

RE: Why are we using NiMh...really?
 

And a flat lipo can be charged in an hour at the most. Many can charge at 5c so12mins if completely flat! <div>
</div><div>Guver- I thought eneloops retain 90% of charge for a year.....</div>

RE: Why are we using NiMh...really?
 

Yea, eneloops do , but not the std NIMH cells. I do use NIMH in my radios cuz it was easy for me to do so. Good capacity too.

RE: Why are we using NiMh...really?
 

The attraction of NiXX is that you can charge them safely without removing them from your plane or transmitter. Some of us still fly glow - we don't need lithium.

RE: Why are we using NiMh...really?
 

Guver you said the advantage of eneloop over (normal) nimh is the bigger capacity.

RE: Why are we using NiMh...really?
 

Think I miss read inmop for eneloop!?

RE: Why are we using NiMh...really?
 

no, the advantage of LSD over std NIMH is charge retention. Advantage of NIMH and LSD over nicad is capacity.

Maybe put this into numbers in an average 4 or 8 cell AA pack.

Nicad 1000 mah
NIMH 2600 mah
LSD 2200 mah
LIPO 2600 mah

RE: Why are we using NiMh...really?
 

I hate NIMH batteries and have had tons of troubles with them. I have nicad packs that are 6 years old that still cycle perfectly. I've never had a NIMH pack last a year. Of course mine suffer from high temps in my storage area and sometimes lack of use, but Nicads beat the h e l l out of them.

I've gone back to Nicads in many cases, plus half my fleet is on Lipolys, but my next step will be to outfit everything I own with A123 batts...

AV8TOR

RE: Why are we using NiMh...really?
 

AV8TOR, Just curious....... do you do anything special to keep your NICADs going for so long?

RE: Why are we using NiMh...really?
 

I've had both NiMh and NiCad that last and perform well for years, all last at least 3 years and most for more than that. I always slow charge however, at about 0.1C. I think that this greatly improves the life (number of charge.discharge cycles) that you get from them. Fast charging is a path to quick deterioration as the added heat usually associated with fast charging accelerates the deterioration of the cells innards. IMHO the Sanyo Eneloops are superior to LiPo's in such application as transmitter batteries as they are longer lasting, less problems to charge (you can charge them safely in place) and are more tolerant to simple errors such as forgetting to turn off and deep discharge. And, yes, NiCad's do have many advantages over NiMh but the NiMh manufacturing techniques are slowly lowering the number of advantages NiCad has over NiMh.

RE: Why are we using NiMh...really?
 

Weight is the biggest reason so many pilots switched to Nimh. As you go up in capacity, the weight difference can become substantial. Not mentioned yet in this thread though is my favorite flight pack battery, the LiFe. It is even lighter than a Nimh, has very little self-discharge, can be fast charged, can put out more current without dropping voltage than any Nixx technology, and is a little cheaper. The only downsides I see is that you have to buy a charger that can work with them and you have to run a balancing lead to wherever your charge port is.

RE: Why are we using NiMh...really?
 

By the time NiMH tech reaches a point where I would do away with my NiCDs, the Li tech (or something new) will have reached a point where i will just bypass NiMH altogether. Until then, I will stick with my trusty NiCDs!

RE: Why are we using NiMh...really?
 

I think Rodney has it. Peak detect just does not work well with NiMH. The peak voltage inflection is tiny, and add to that the batteries in a pack may not all peak at the same time. Chargers will sometimes miss the peak and cook the pack. Charging NiMH at C/10 or less using a timed charge is the way to go in my opinion.

So far my Eneloops are holding up well. Three years and counting. And their self discharge rate is practically zero.

RE: Why are we using NiMh...really?
 

Just go lipo and you won't have the issues you are having with NIMH.

RE: Why are we using NiMh...really?
 

Rechargeable batteries are rated by energy density, which is specified by Watt-hours per kilogram.

The energy density for NiCd cell is rated at 45 Wh/Kg.

The energy density for NiMh cell is rated 70 Wh/Kg.

This is the reason why NiMh batteries seeped in.

RE: Why are we using NiMh...really?
 

Weight!!!

RE: Why are we using NiMh...really?
 

And if you forget an leave your transmitter on they are toast. They must be charged on a balancing charger to get maximum life. If Eneloops don't fill your Tx need you need another hobby.

RE: Why are we using NiMh...really?
 

Life is the way to go for rx packs. $10-20 packs $30$chargers. Sold a set of A123 that hadn't been chsrged for 6 months. Guy asked me to charge them at the field. So he could fly right now. They took 56 and 52 ma respectively. Talk about low self discharge!

And with tx a lipo does great. If I were to run one down $10 get' s me back in business. I use eneloops elsewhere at home but some $30+ eneloop packs are just a scam versus the lithium tech.<br type="_moz" />

RE: Why are we using NiMh...really?
 

The O.P. was talking about RX batteries, not TX batteries.

Anything other than LiPo in the air is a complete waiste because of weight.

Besides, a LiPo in your TX only needs charging about 4 time a year versus NiCads at about 2 per month if not weekly.
And if you are not old and forgetfull, you will turn your TX off everytime.

RE: Why are we using NiMh...really?
 

Easy for anyone to leave a TX on.

For Rx power nothing beats life. Leave it fully charged for months and go fly. Charge in your plane with no worries about burning down your garage or house. No regulator needed. 1000+ charges. Flat discharge curve so your surfaces feel the same at the very end of your flight as the very beginning. No need to worry about storage charge or storing planes/batteries in a hot place and damaging your lipo. Leave a switch on by accident and just charge the battery, Lipo would be toast.

I buy HK lifep04 1100 ma/h packs for $3.55 and 2500 ma/h packs for $8.45. 11 packs in use with the oldest going on 3 years and no issues yet. I balance charge thru my switch with a FMA Multi 4 and I like simple.

RE: Why are we using NiMh...really?
 

I agree with you, got rid of all my NiMh about three years ago after all the same problems, for me main one is they don't hold a charge for long. Still using all Nicads for receiver packs and eneloops for my transmitter. However, picked up a DX8 for my indoor electric planes and it came with I believe a NiMH pack and it seems to work well, I do recharge it slowly though. It will get warm with the factory tx charger the radio came with so I take it out of the tx but leave it hooked up to the radio to recharge. I also am wanting to go all A123 someday but with 16 planes it is a big step for me. Also I was concerned about how to monitor how much charge remained in the 123 batteries but I hear they are coming up with ways to solve that problem. The Nicad reciever packs still are available from some online vendors but if that comes to an end will have to upgrade someday.

RE: Why are we using NiMh...really?
 

you can also go with lithium ion's, very similar to the polymers but dont need the balancing and not as dangerous as the polymers. they are light weight, fast at charging, more voltage, long lasting. the only draw back if you want to call it that, is they recommend you replace them every two years. small price to pay. i have charged mine forever with no supervision. you can go to fromeco.org and get all the info on them and they are great people to deal with. they will answer any questions you have.