Total voltage when charging

[CaptainCalm]

So, I've not messed with RC stuff for a few years until today, when my new TRX-4 was delivered.

So I grabbed a few of my old lipo's that I figured should work with the TRX-4. They've been at storage charge for at least the last 3 to 4 years. I picked the following (measured internal resistances from today are in parenthesis):

2 Gens Ace 1800mah 25C 2S [(10ohm, 10ohm), (10ohm, 9ohm)]
1 Gens Ace 2200mah 30C 3S (7ohm, 6ohm, 6ohm)

I've only tried charging one of the 2s packs (that I used for my Carrisma GTB) and the 3s pack (which I used for one of my helicopters and which, incidentally is on charge now).

When charging these two packs, I have noticed something odd and I can't remember if it is "normal". On the 2S pack, I noticed that the charger was reporting a charging voltage of up to 8.58V even though at the same time it was reporting a per cell voltage of 4.20V and 4.20V (when it was reporting 8.4V, it was reporting a per cell charge of 4.13V and 4.13V). As soon as I stopped charging, I put the charger in monitor mode and it reported something like a total voltage as 8.35V and a per cell voltage of 4.17V and 4.18V (instead of 8.58V (4.2V, 4.2V) when charging).

Now I understand the voltage drop after charging, the packs are old and probably need to be replaced. The thing that I don't understand is when charging, the per-cell voltage didn't add up to the charging voltage (e.g. 4.2 x 3 does not equal 8.58V).

Now it has stopped charging, on monitor mode, for the 3S pack, the charger is reporting 12.60V with all three cells at 4.20V. But just before it finished, it was reporting a charging voltage of 12.76V with 4.20V on all three cells (clearing 4.2V x 3 does not equal 12.76V). Is this normal and I just forgot it was normal, or is something strange happening here?

BTW, the charger in question is an iCharger 306B which I got for quickly charging 6S packs for one of my helicopters that have sat gathering dust for the last 6 years (yes I have 6S packs in the garage at storage charge for 6+ years and I'm wondering whether to safely discharge them to 0V and dispose of them or risk seeing if they are "OK").

 

[AC49]

In my experience with 4 different chargers of different brands, I have never seen this. Charging at higher than max voltage will damage the battery and I have yet to see someone recommend doing it.

In every instance that I have ever seen, the voltage on the screen should be (more or less) what your battery is at. Lipo's will drop off after charging of course. This is normal. But the fact that your cell voltages don't line up with your total voltage tells me something isn't quite right in the charger or balancing board. (That would be my guess anyways).
When the charger hits 4.2 per cell it should stop charging, that's how it knows it's full. The fact it's not tells me that it's trusting the per cell value over the total value. Now there could be some kind of voltage drop back looping type thing I've never heard of and someone far smarter than I will be able to explain or come up with.
But my first test would be to find another charger to try it on, and failing that a new balance board if possible. Sorry, I'm not familiar with your specific charger so I don't know if the balance board is build in or not.

 

[Slow Runner]

Old lipos will still last a long time in a crawler...no need to replace. Even high resistance doesn't matter in a crawler.

I'd ignore the total and just concentrate on volts per cell...that's all that matters. If the cells are relatively even, just take it to it's full charge, run the truck and the lipos will relax a little after a few cycles.

 

[Druxus]

Do you have a volt meter so you can get a measurement of the pack and the cells? I have had my charger show wrong values on my total pack before (may have happened 2 times in maybe 7 years) I measured the pack and it was in spec the charger just displayed the wrong Voltage. After powering down the charger and starting it back up everything was back to being right with it.

 

[CaptainCalm]

Thanks all for your input, much appreciated.

AC49, yeah the thing that led me to write the post was concern that the charger could be sending a higher voltage than it should be. I do have a spare balance board somewhere, so I'll dig that out and give it a try. The other thing is, I noticed that moving the cables changed the charging voltage, so it is possible that there is a partial break or perhaps a dry joint somewhere that the charger is compensating for. The thing is though, I don't recall the cable feeling warm, so whatever the cause, it can't be causing too much resistance.

Slow Runner, thanks for your input on not needing to change the batteries for now. I'll keep on using the 2s batteries. I found out last night that the 3s battery doesn't physically fit in the battery tray, or more accurately, I can't close the battery clamp because the battery is too tall. That said, I drove the TRX4 around the house yesterday on the unclamped 3s battery and it was certainly more lively. Perhaps I'll buy a 3s battery that fits it to see what it is like when crawling.

Druxus, that is an excellent idea. Yes, I have a few multi-meters kicking around, I'll dig one out and check the output voltage of the charging cable to see if the charger is misreporting the charging voltage. I'll also check the cell voltages. I did try turning the charger off and back on again when I first noticed the issue, but it still reported the same voltages.

I don't have another charger, so for the moment, I'll not be able to compare the 306B to anything else. I'm hoping that the charger is either misreporting or that there is an issue with one of the cables or balance board. I'll do some testing and report back with anything that I find.

 

[CaptainCalm]

I just started charging one of the 2s packs. The charger was reporting a charging voltage of 7.86V and cell voltages of 3.83V on both cells. I then got the voltmeter and checked the voltage at the charge cable output on the charger and it was reading 7.66V (the screen was still showing 7.86V). So I'm now pretty convinced the charger is just misreading the output voltage, but in practice seems to be doing the right thing.

 

[Slow Runner]

I assume you have a lipo checker to check after a full charge? Then you'll know what's up after it's charged.

I'd stay with 2s on your crawler, unless you like replacing motors. But check motor temps...you might be OK if you don't get carried away. I can get a 40 minute run time off a 2s 5000mah in my Gen 7 and 8 crawler, so even the oldest, most tired lipo will not be challenged. It's all about internal resistance, so the gentle draw of a crawler doesn't even come into play at all.

I have taken some lipos that couldn't cut it in my RC planes and used them in my trucks, where they do just fine.

 

[QuesoDelDiablo]

Sounds like you've basically worked it thoruhg and detemreind that the charger is the issue. I tend to agree with that assesment as it sounds like the most likley scenario.

Your IR values aren't too bad and you said there doesn't seem to be any abnormal heat build up so I don't suspect packs are the issue and you're seeing the same problem across multiple packs so that indicates charger problem to me.

It sounds like the charger is mis-reading/mis-displaying the output voltage but as long as the cell voltage is reading correctly that should govern the charger in terms of peak voltage.

If I was in your shoes I'd use those packs a few times so they go through a few cycles, always monitoring cell voltages to ensure they exceed 4.20V and if the charger doesn't correct itself after a few cycles, toss it. New chargers can be picked up pretty affordably now so it's not worth mucking around with one that's not performing 100% correctly..





*
3S ftw. 2S is only good for club racers imo.

 

[Kingmeow]

Did you really meant Ohm? Or milliohm for the internal resistance? These bigger packs should be in milliohm readings.

Having said that, I doubt it's your charger. Any of the iChargers are very good chargers and I doubt electronics go bad from sitting around and not being used (degrading cheap capacitors not withstanding). And

I have seen and experience this before. It usually happens with very old packs and new packs where the chemistry really hasn't "formed" yet.

What I would do is program your iCharger to do 5 or so cycles for each pack. This means, charge to full then discharge back to storage. That's one cycle. Repeat 4 more times. Your iCharger should have that feature to exercise the pack. This should get it back closer to normal levels.

I think what's really going on here is that they have been stored in storage voltage (a good thing) for quite a long time and they just need to be exercised a few times to "wake" them up.

 

[CaptainCalm]

Thanks for your input everyone.

Kingmeow, good catch, yes I did mean milliohms. I think you might be right about the charger; I've charged one pack more than the others and I noticed that when I was charging it last night yesterday, at the start of charging the charger was reporting a higher total voltage than you'd get by adding the cell voltages together, but as it was coming to the end of the charge, they aligned (8.39V with 4.20V, 4.19V, then 8.40V with 4.20V, 4.20V). It's making me wonder whether the increased voltage that the charger shows is due to some kind of push back (resistance to charging) because they've been in storage charge for so long. I'll cycle the pack in question on the charger a few more times today and see if the voltages align more throughout the final charge cycle. I'll also then compare that to one of the packs that I've only cycled once or twice. My thought is that if it isn't the charger, then the pack that has been cycled at least five times should have better voltage alignment whilst charging than the pack that has only been cycled once. I'll report back with my findings.

QuesoDelDiablo, yeah I monitored the packs with respect to temperature and voltage and they are fine. I am starting to see corrected values from the charger, so I'm wondering if Kingmeow is right and that it is somehow related to the packs having been at storage charge for so long. I don't quite get where the charger is getting the higher voltage value from given that it's sending the correct output voltage. I'm guessing that it's detecting some kind of loading whilst charging the battery and is reflecting that as a voltage delta that it's adding to the displayed charging voltage. At the moment, I'm cycling one of the packs a few times to see if I get better voltage alignment.

Slow Runner, the charger has a monitor mode where it will tell me the total pack voltage and the cell voltages, it then has another mode where it will tell me the internal resistances. The charged pack shows as 8.40V total, with 4.20V per cell. I've verified the total voltage (but not cell voltage) using a multimeter and it checks out. So it looks like the charger is only displaying an incorrect value when charging. On the battery pack front, I must admit, I put a 2s pack back in the crawler yesterday and I think I prefer the extra low-speed control it provides vs 3s. So as you advise, I think I'll stick with 2s for crawling, but might go for 3s when on a trail. I'll keep my existing 2s batteries going until either they puff or the IR gets too high... not sure what too high is though at the moment for a crawler.

 

[Slow Runner]

Capt. you should invest in a little lipo checker. Hitec makes a good one. Great for checking voltage without having to use the charger. Great for a quick lipo check when outside.

I time my runs, and then have a baseline. I know almost exactly how long each truck will run before it hits storage charge. I'll do a quick voltage check to be sure.

 

[Kingmeow]

Kingmeow, good catch, yes I did mean milliohms. I think you might be right about the charger; I've charged one pack more than the others and I noticed that when I was charging it last night yesterday, at the start of charging the charger was reporting a higher total voltage than you'd get by adding the cell voltages together, but as it was coming to the end of the charge, they aligned (8.39V with 4.20V, 4.19V, then 8.40V with 4.20V, 4.20V). It's making me wonder whether the increased voltage that the charger shows is due to some kind of push back (resistance to charging) because they've been in storage charge for so long. I'll cycle the pack in question on the charger a few more times today and see if the voltages align more throughout the final charge cycle. I'll also then compare that to one of the packs that I've only cycled once or twice. My thought is that if it isn't the charger, then the pack that has been cycled at least five times should have better voltage alignment whilst charging than the pack that has only been cycled once. I'll report back with my findings.

Ding, ding ding, we have a winner!

BTW, you probably know this but never charge lipos unattended. You don't have to stare at them all the while but at least be in the same room where they are charging.

Having said that and where I'm going with this is that although the numbers may be slightly off (I think they will align once cycled a few times), just use the packs. They are Gens Ace so they are very good and you are using them in gravity-independent vehicles. I'm primarily an airplane guy but I've also done helis like you (6S, 500 size) so we are more anal about batteries as it's critical we keep the airplanes in the air. A battery failure would be a very BAD thing. For a crawler, not so much. :mrgreen:

 

[Slow Runner]

lol....in a crawler, you may never notice a bad lipo until it just doesn't take a charge anymore...

In a heli, that lipo better be in top shape!

 

[CaptainCalm]

Capt. you should invest in a little lipo checker. Hitec makes a good one. Great for checking voltage without having to use the charger. Great for a quick lipo check when outside.

I time my runs, and then have a baseline. I know almost exactly how long each truck will run before it hits storage charge. I'll do a quick voltage check to be sure.

That's a good call, I'll certainly invest in one.

 

[CaptainCalm]

BTW, you probably know this but never charge lipos unattended. You don't have to stare at them all the while but at least be in the same room where they are charging.

I've never left a lipo charging unattended, I'm too scared of what could happen. I saw a friend's lipo's catch fire on charge one time when I was at the track with my Carisma GTB, - it was pretty scary. He'd damaged it in a crash whilst in a race but figured he'd try charging it anyway (not the brightest idea but he knew that and did it anyway). Nice to see your reminder though.

Having said that and where I'm going with this is that although the numbers may be slightly off (I think they will align once cycled a few times), just use the packs. They are Gens Ace so they are very good and you are using them in gravity-independent vehicles. I'm primarily an airplane guy but I've also done helis like you (6S, 500 size) so we are more anal about batteries as it's critical we keep the airplanes in the air. A battery failure would be a very BAD thing. For a crawler, not so much. :mrgreen:

Yeah my favourite helicopter that I have is a Gaui X5. One of the 6s packs for that I experienced a voltage drop about 20 seconds into the flight (like dropping from 6s to 5s). So I landed it immediately and ran it with a different pack and all was fine. Put the prior pack back in and within about 15 seconds the voltage drop came back so I retired the pack. Curiously though, on the meter, it was reading the correct voltage and the internal resistances were all good, so I'm not sure what was going on there but didn't want to take any chances.

 

[Kingmeow]

Yeah my favourite helicopter that I have is a Gaui X5. One of the 6s packs for that I experienced a voltage drop about 20 seconds into the flight (like dropping from 6s to 5s). So I landed it immediately and ran it with a different pack and all was fine. Put the prior pack back in and within about 15 seconds the voltage drop came back so I retired the pack. Curiously though, on the meter, it was reading the correct voltage and the internal resistances were all good, so I'm not sure what was going on there but didn't want to take any chances.

I had a MSH Protos. I bet you might have felt something in your underwear when that battery sagged and that few seconds felt like an eternity! :lmao:

That pack probably got too old and the chemistry couldn't sustain the current that the motor is asking for. You should have seen higher IR readings but sometimes you just can't explain it. Good that you retired it rather than risking a multi $100 heli!

 

[CaptainCalm]

The MSH Protos is a nice machine . Yeah, I had a definite panic, the voltage drop was instant and caused the heli to drop in the air a little until I corrected the elevator. For a fraction of a second, I thought the power was going to die completely - I had no idea what the problem was. Thankfully I was hovering at the time - I normally follow a practice with that heli (because of how dangerous it could be and also the cost of repair) that when I first take off, I hover it for around 10 seconds making some simple movements (like checking each axis) before switching flight mode ready for 3D flight. I'd just switched flight mode causing the rotors to spin at 100% throttle and was just about to fly off and have some fun when the voltage drop happened. The heli was about 15ft off the ground at this point and still hovering, so after a quick elevator adjustment, I hit throttlehold and landed it via autorotation - at least that way I couldn't be surprised by further unexpected drops in power whilst landing.

The scariest flight that I'd had with that heli though was when the transmitter turned off and then immediately back on again mid-flight. I was using my Spectrum DX7s at the time, and having completed one stall turn I'd brought it down at speed to follow a parabola into another stall turn, I was about 3/4ths of the way through the parabola when the transmitter turned off and back on again. The helicopter had enough momentum that it's trajectory hadn't changed much from what I'd intended, but if the transmitter had taken much more time to switch back on, the heli would have run out of momentum and started to drop out the sky! That one called for the most direct landing I've ever made. After landing and unplugging the lipo from the heli, I shook the transmitter and it stayed on absolutely fine. But after that I didn't trust it and figured it was a good excuse to buy the transmitter I'd always wanted, a Futaba T14SG and new Futaba receivers for my helicopters. I kept the DX7s for some of the little indoor heli's like the blade nano. Whilst flying one of those the DX7 once again, turned off and back on again. This time when I shook it, it turned off and back on again. So I did what I should have done the first time it ever happened - I took the battery cover off to find that the battery lead wasn't properly seated in the in the battery connector on the receiver - the only thing wrong with it was pilot error!

 

[Kingmeow]

Oh man! Definitely an underwear changing moment! :mrgreen:

I also have a DX7S but I use it for Horizon's BNF planes. All my helis were Futaba (8FG, their prime radio before the 14SG came out <-- nice radio BTW!) controlled with not a single incident. With the Spektrum? I've had brown outs and cut outs and a few crashes because all of a sudden the plane lost signal even though the DX7S was on (at least from a quick glimpse). Luckily I was only flying a small UMX Pitts (plane-in-a-box) and they are light weight and I was flying over grass so no damage.

I sent the Tx in to Horizon for check up and told them I had cut outs a few times. Yeah, you guessed it, nothing wrong with your transmitter sir. :roll: From that point on I never trust my DX7S to anything serious. I'm not sure if I can even trust anything Spektrum, including crawlers. :lmao: I'm using a Flysky GT-5.

BTW, when it first happened the first thing I checked was the battery connection on the Tx. Nice and tight.

 

[CaptainCalm]

You know what, when I was writing "the only thing wrong with it was pilot error", I was thinking to myself, that I seem to remember the same issue happening after I reseated the tx battery connector when flying my Blade 130X (resulting in a crash). But then I started to doubt my memory gave the DX7s the benefit of the doubt, hence why I wrote what I wrote. But reading your post has got me wondering again whether that particular 130X crash truly was after I'd reseated the battery connector. To be fair, I've crashed that 130X countless times trying out new stuff (or sometimes just due to me being a muppet - I went through a lot of spares! ), but the reason why that specific crash sticks in my mind is because I was convinced it wasn't my fault and thought I'd already fixed seating of the battery connector.

Like you, I have never had the slightest issue with my Futaba TX/RX's and I've been really pleased with them. For RC cars I have the Futaba 3PL, but I can't use it with the TRX-4 because it doesn't have enough channels. I did think about changing it for a Futaba with more channels when I have a little more cash to spend, but can't find one with a wheel on it that has more than 4 channels, or at least if I could I expect it would be more than I'd want to spend. Gotta say though, that Flysky GT-5 you have looks perfect and great value for money!

Back on the battery charger front, the voltages aren't aligning as well as I'd like; on the same pack, sometimes, it's better than others (it changes over the cycle), a couple of times I've seen perfect alignment whilst charging, but then the next charge of the same pack, it's out again - I'll note that each time I've charged a pack, I've disconnected it, used it in the TRX-4 and then connected it back to the charger to either storage charge it or charge it for use again. Although the charger has the option, I've not used the charge/discharge cycle option. I might get a new pack and see how closely that aligns, but I'm thinking it's probably more likely the charger than the packs at the moment. I have noticed that turning the charge cable banana plugs in the charger's output connectors affects the displayed voltage by up to 150mV, so maybe there is some connector corrosion in the charger. The cable looks perfect, but I haven't checked the connector on the charger. I'm going to check for breaks in the cable and after that, I might take it apart to take a look. If all else fails, I'll think about getting a new charger (kind of reluctant until I know it's definitely an issue with the charger that can't be easily resolved).

 

[nightcrawler48]

I'll keep my existing 2s batteries going until either they puff or the IR gets too high... not sure what too high is though at the moment for a crawler.

It shouldn't matter what you are using the Lipo for. IR is a condition within the battery and has little to do with whether it is used for surface or air. Having said that, batteries used for boats and air, where full throttle is more common, will show their age quicker than those used in crawlers.

A brand new battery should have an individual cell IR of between 2 and 6 milliohms. Any higher and request warranty from the manufacturer. After some use, the IR should settle in to a range of 6 to 12 milliohms. Eventually, with age or abuse, or both, IR starts to creep up. 12 to 20 milliohms is still okay but it's best to keep an eye on the battery and check the IR after each use. Anything over 20 milliohms and I'm looking for a replacement battery.

Cell IR will also let you know if one cell has a problem. I've checked IR for people where one cell is as high as 60 milliohm, or more, and the other cells are below 20.

Without an IR tester, another indicator of a battery in poor condition is runtime. All things being equal, you will notice the runtime getting shorter as the battery condition degrades.