NiMH advice
 

Hey everybody, two questions about NiMH packs that seem like they should be really basic, but I can't seem to find answers.

First, how do you know when it's time to recharge? Without really knowing how much battery I needed, I ended up with a 5000mAh 7.2V battery for my SCX10II. It seems to last forever. I've measured voltage after several runs and it doesn't change much. I've read that you don't want to recharge NiMH if it's too close to full, because chargers are looking for a characteristic voltage drop near full charge, and if the voltage isn't low enough when you start, they never see the pattern, at which point they run way too long, overheating and over charging the battery. On the other hand, I don't want to just run it until it quits - I'd like to charge up frequently enough to know I can finish a hike with it before leaving the house.

So, can I measure voltage and get anything meaningful from that? Or do I just have to get spare batteries and run one all the way down before switching?

The other question is about heat during charging. When I first got the battery, I charged it right away, and it was pretty hot at the end of the cycle! I've run it quite a bit for the last week or so, and finally the voltage had dropped enough (reading 7.3V, down from a peak of around 8.05-8.10) that I decided to charge it. Again it came out very hot. This time I measured, and it was 150F! That's hotter than I expected. Most articles I've read say that there's not too much heat when charging properly, although I found one article that said 130-140F at the end is ok.

What do you all think is acceptable heat from a pack at the end of charging?

Almost forgot to mention, I'm using a brand new Spektrum S150, charging at 5A rate. I've read that charging up to 1C is good for NiMH and that charging too slow can actually cause problems where the charger doesn't recognize the end of the cycle. I originally bought a Tenergy TB6B, but it was DOA, and weeks later they still haven't sent me a replacement. I'm pretty peeved right now. Anyway, got the cheaper, simpler S150 just so I could finally start playing!

Re: NiMH advice
 

I have not used NiMH batteries since I was a teenager :shock:

I unfortunately am too old to remember anything about NiMH. I am just curious why you did not go with a Lipo battery?

Re: NiMH advice
 

That's a fair question. To be honest, the main reason was to humor my wife, who's heard all the horror stories about Lipo fires and explosions. She really didn't want Lipo here if it wasn't necessary.

Besides that, I wasn't sure I needed the extra voltage and power Lipo would offer, so I figured maybe I wouldn't miss it. Since this is my first RC vehicle (other than an RC plane disaster over 20 years ago,) I don't know what I'm missing. I'm pretty impressed with what I can do in terms of crawling as is.

Re: NiMH advice
 

OK I can see that. Maybe you can show your wife a lipo charging bag and tell her the battery will always be stored and charged in that bag.

https://www.horizonhobby.com/li-po-c...-small-dyn1400

That NiMH will work and put many smiles on your face. You don't need a Lipo, I was just curious as they have been around for so long now. Just some information from this site about Lipo vs NiMH.

http://www.rccrawler.com/forum/redca...e-vs-nimh.html

Your first RC vehicle other than an RC plane disaster over 20 years ago :lmao::lmao::lmao::lmao:

Sorry, it made me laugh as an RC airplane is one of the last RCs I would try out as a first RC. I fly planes too so that made me laugh.

Re: NiMH advice
 

In retrospect, you're obviously right, but as a kid in junior high, I didn't know any better, and neither did my dad. I loved planes and drums, that was it. No other vehicles, and no other instruments. Drums worked out, but planes failed miserably.

The day of our first flight attempt I checked everything a dozen times, all controls were good, etc... but the plane was one that recommended you throw it to get it started, so I was manning the controls and my dad threw it. I'd swear we both did everything right, but somehow the plane immediately did this weird climbing corkscrew into an inverted nose dive. The flight couldn't have lasted more than a few seconds, and the plane was thoroughly destroyed!

For a while I made half hearted attempts to repair what was left of the plane, but I gave up pretty quickly. I still love the idea of flying (tons of fun with MS FSX and X Plane, where crashes don't cost you anything!) but haven't tried any RC planes since.

My new truck is far more forgiving. I've already flipped it more times than I can count!

Re: NiMH advice
 

I did some digging and I am not finding any clear answer to your question. Hopefully a member here uses them or remembers the ins and outs of using them to answer your questions.

As for how long it will run. I'll say it will really depend on how you are running it. If you are really crawling and or going at a walking pace it will last much longer than if you were ripping it around at full throttle. With that said it is not a bad idea to have an extra charged battery on hand if you are away from home. I always have more than one for any rig, some share them, but I always have more than one battery on hand.

For the heat, what you described sounds like it may be too hot at the end of the charge. I did see that it should be warm but what you describe sounds like it is far past warm.

Maybe you'll give flying planes a shot again. A lot has changed in 20 years. If you get yourself a flight simulator for RC planes like Real Flight you can practice on your computer. That is how I taught myself. Get a small Micro from Horizon as they are cheap and you won't feel horrible if you crash practicing.

From your story your dad put too much force in his throw of the plane most likely. For hand launch you throttle up to full while holding it and then toss it into the air and a slight incline with a bit elevator. Too hard of a throw or too much elevator and you get the results you experienced. At least your dad did not hold onto the plane too long and throw it into the dirt. I've seen that! :lmao:

Re: NiMH advice
 

my rc airplane exsperiance was vary simmiler lol only i took off from the ground then crashed it
any way lol
almost every battery powered anything these days use lipo batterys laptops cell phones outdoor solor patio lights even toy grade rc cars use them lipos are in just about everything
using a lipo is no more dangous than taking a shower ill bet there are more people dieing from sliping in the tub than there are lipos catching fire
what about driving a 1:1 car they catch fire all the time but people still drive them
i dont know anyone who charges there cell phone in a lipo safe when was the last time you removed your laptop battery from the laptop for storage
ive never had a lipo catch fire i have had them punctured on the trail ive over heated them till they poped ive over charged them ive drained them to 0 volts then charged them ive even fast charged them to the point were the battery poped and vented out no fire
theres always a little risk and for that reason i never leave my batterys unatended while charging theres always a chance they could go up
you can tell when a lipo is going bad and once you notice it going just toss it to be safe i store all my bad puffy packs in a lipo safe untill i can recycle them and still never had one pop off

but lipos arent the end all be all your nimh pack is still a good battery but you realy should discharge it to 1 or 2 volts then fully charge it nimh have battery memory so evetualy it will have issues and wont hold a charge vary long even though the v9lts are good that dosent mean you cant charge it from the 7 volts just every 5 or so packs drain it all the way fown and recharge it all th3 way up on trickle charge then you4 good for a few more cycles ive herd it sayed many times a nimh pack isent charging if it isent warm as long as you can hold the pack its not to hot
i know a guy who would charge directly off of a car battery just cliped it on and when the battery got to hot to touch he would take it off and run it usaly took about 5 min he sead it never got to full charge because there was no trickle charge at the end to top it off all the way but hay it worked and was fast the good thing abo7ut the nimh is you can abuse the hay out of them and the worst your gona do is kill the battery

Re: NiMH advice
 

This discussion is kind of interesting to me. I have been playing with the RC ground vehicles for years and I recently have started thinking about RC flying. There is an active RC air field about 20 minutes from the house and they offer free flying lessons. I might need to take them up on that.

Re: NiMH advice
 

It's been a while since I used HiMH batteries so most of this is from memory, which probably isn't too good.

The voltage drop as you use the battery does similar things to what lipos will do. Somewhere below 7.0 volts you will notice the max speed dropping and maybe the servo slow to turn. If you have lights hooked up on the RC, they will start to blink/flash when you're on the throttle and steering at the same time. That's when a fresh battery is useful.

As far as charging, can't say I ever checked the battery temp after charging but do know it could be pretty warm to the touch. I do remember I could set my charger to do a discharge to some recommended voltage before it would start charging. This kind of confirms what ferp was saying about discharging the battery occasionally. I don't think it was as low as 1 or 2 volts though. If your charger can do the discharge/charge cycle then you would be able to charge the battery after each run and know you're at full capacity for the next run.

Also, if I remember correctly, NiMH batteries will lose about 1% of their charge per day so if you haven't used them for a while, check the voltage and maybe top the charge up before you head out.

May be all wrong on this but might encourage others to post corrections if I have screwed up. :)

Re: NiMH advice
 

As far as your battery getting hot at the end of a charge, that's kinda normal.
Even with all the technology of these new chargers, they don't really shut off as soon as they should with niMh batteries. They rely on voltage dropping a certain amount for the shut off point, and by then, the battery is pretty hot.
Best advice I can give is as the battery is getting near full charge, start feeling the battery for temperature. As soon as you feel it starting to get warm, shut down the charger.
5000 mah will last you a long time in a crawler. Could last up to an hour and half or longer. As soon as you see it has reduced power, stop and change the battery.
If you don't get a full run and the battery still has plenty of life, consider making up a discharge unit. A discharge unit could be something as simple as a couple of older style automotive lights (1158 come to mind) wired in series. Plug the battery in and watch for the lights to start dimming, then unplug.

Re: NiMH advice
 

I’ve run my 5000mAh NiMh packs in rigs a bit. I’ve gotten over 2 hours runtime, easily. They all get charged on cheap Prolux Peak Chargers at 2amps with no problems. I find these do better than the B6 variant chargers I have. They do get stupidly hot sometimes. Especially on the 5000’s. Don’t let this worry you too much. I’ll be worried if they get difficult to handle after the charge...

You will notice that you will loose power drastically and that is when you will know. Even before the NiMh cutoff steps in on the esc.

Don’t be to worried about the charge cycle on them. Just don’t peak/charge them if they are not drained enough. I’ve got 4x 3300 packs that gets taken with when we go away with the Tamiya bashers. They get rotated on the charger non stop sometimes. Run one flat while one is on 4a peak charge in the car. They’ve been going for 3 years. You cannot do this with a lipo. And lipos don’t fit in the Tamiyas without modification...

You will be perfectly fine for a long time with them. Till you fit a lipo. There is a big power difference but if you just trail with the rig, NiMh is perfect and easy to use.


This is what I use:
https://uploads.tapatalk-cdn.com/202...41f0fb7d6d.jpg

Another thing I do when I know I’m not going to use the packs for a while is charge them all and pack them away. But if I’m going to be messing with them on and off I’ll just leave them and peak them whenever the power drops to useless. This is always before the cutoff kicks in.


Sent from my iPhone using Tapatalk

Re: NiMH advice
 

I've been flying RC planes for over 30 years. If you're thinking about getting into RC and want to have almost guaranteed success, get one of these:


https://www.horizonhobby.com/apprent...tter-p-efl3700

The plane has multiple safety aspects that are perfect for someone new to flying RC but those safeties can be turned off as you're skills progress.

I watched a 90 year old Vietnam pilot who's never flown RC in his life fly one of those around for about 15 minutes and never once got remotely close to being out of control.

What ever your do, take your own suggestion and go to local RC club and get instruction. While the Apprentice is incredible, you still need some basic flight instruction and a safety review.

Re: NiMH advice
 

I use only NiMH batteries to this day. I had a heli with a LiPO a few years back catch fire and burn a hole in my carpet, so I'm pretty well set on NiMH batteries. Being that I have a family and oafish nature, NiMH is my destiny.

There's several reasons I prefer NiMH: 1) a heavy battery mounted low and front of a crawler rig adds stability 2) they're very safe regardless of abuse 3) no low voltage cut equates to long run time. 4) store them charged and they're always ready to go

Regarding heat and charging, I follow general rules-of-thumb;
1 amperes per 1K mAh rating of the battery (1A to charge a 1000mAh battery, 3A to charge a 3000nAh battery, 5A to charge a 5000mAh battery, etc).
Above all, heat is detrimental to most electronic components. Hot to the touch will take several cycles away from the battery's life. Warm to the touch will lessen the severity. Luke-warm makes for a happy efficient battery.

Re: NiMH advice
 

It's nice to hear from someone who's still using them!

So, it sounds like you're recommending the standard "1C" charging rate, which is what I've been doing. It's a 5000mAh battery and I'm charging at 5A. Does your charger do a good job at stopping before the pack gets hot, or do you have to monitor the charging process and just manually stop it when things start getting hot?

I'm starting to think that my Spektrum S150 charger just isn't good at detecting charge completion and that it's overcharging. I think maybe a need a different charger.

It's too bad Tenergy still hasn't done anything about the DOA charger they sent me several weeks ago. I'm trying to give them the benefit of the doubt since COVID-19 is having a big impact on all sorts of businesses, but the fact that I paid them $70 for something that never worked for even a moment, and they're doing nothing to fix that, is very disappointing. I thought they were supposed to be a reputable brand, and so far this has been an abysmal experience. If they ever send me a working replacement, maybe it will be better at charging NiMH batteries than the Spektrum.

Re: NiMH advice
 

I use peak chargers, but they do not have any "C" adjustability. At peak charge batteries are warm to the touch, perhaps 105*F, which is the max temp I am comfortable with. If the batteries get hot enough to shrink the shrink wrap encompassing them, it is most certainly too hot. I also charge on a hard tile surface so the charger and battery get good airflow. The tile helps to wick away some of the heat from the battery as well.

Given the low price of battery packs, it is advisable to buy several and rotate them to avoid heat damage from heavy back-to-back use.

Regarding Tenergy, we'll likely have to be patient. Many businesses have limited personnel to acheive social distancing. Do contact them again to assure your request does not fall on deaf ears.

Re: NiMH advice
 

A while back I ran across a yt video from rc girl reviewing a htrc t240 duo charger so I ordered it along with temp sensors from bang good and took over two weeks. I only run NiMH now because of my 4yo grandson. I have 12 5000mah packs and he can run through a few of them in his 4wd sct. The charger works really well, even has a bar graph to show when the voltage drops off and will shut off maybe a minute after. Back in the day we called it peak detection. We typically get an hour run time with the redcat and scx10ii crawlers.

Sent from my SM-G920V using Tapatalk

Re: NiMH advice
 

Hey everybody, I just realized that I forgot to update this thread. Tenergy did eventually respond and send a replacement charger, and the new one works beautifully. It took about 6 weeks from my original complaint to the day they said they'd replace it. Normally I'd consider that ridiculous, but with COVID-19, I can understand the delays.

Anyway, the point is that they did come through and I'm happy with the charger now! Right out of the box, it does a better job of charging the NiMH battery without getting quite so hot. It still gets warmer than I'd like, but I think I can change the delta-V threshold and/or change my max mAh limit in order to reduce that heat even farther. I love how configurable this charger is!

Re: NiMH advice
 

Glad to hear they did right by you and thanks for letting us know. Too often we never hear about the positive results and it helps when deciding who will get some of your hard earned cash down the road. "thumbsup"