TP820CD under charging.

[Granpappy]

Thanks for your help.

[Grumpy]

The end voltage showed as 12.62V on the AVO and 12.617V on the charger.

Than the battery was fully charged to 4.2V per cell. There certainly is no problem with under charging there, in fact if anything the end voltage is a little high but only by a couple of hundredths of a volt so probably nothing to worry about. As already noted, end voltage is all that matters 'mAh in' may not be accurate.

[Granpappy]

Than the battery was fully charged to 4.2V per cell. There certainly is no problem with under charging there, in fact if anything the end voltage is a little high but only by a couple of hundredths of a volt so probably nothing to worry about. As already noted, end voltage is all that matters 'mAh in' may not be accurate.

With my old charger I would charge up my 5 batteries for the 450 and go out and fly them off. The timer on my transmitter is set to start counting when throttle stick position is at 10% or higher. I would always land before the timer was up and change batteries. The battery voltages would generally be about 11.3 to 11.4 volts after use.

Along comes my new charger and I use the same procedure that I've always used. However, the first thing I noticed was that the battery was starting to flag with the rotor speed down and more collective needed to keep flying. The timer still had another 20 secs to run. I changed batteries thinking the first one was knackered and the same thing happened on the next flight.

I reduced the timer on my transmitter by a minute and flew the rest of the batteries off. when I got home the first two batteries I had used were around the 10.5 volt mark.

So that was the reason for this post and nothing has really explained why this all happened. But thank you for your help.

[Grumpy]

So that was the reason for this post and nothing has really explained why this all happened. But thank you for your help.

The only explanations for that would be that the batteries are getting old and tired and/or you might be flying harder, or maybe using higher headspeed.

If the batteries are at 4.2V per cell then they are 100% fully charged... period. No charger in the world could get more charge into them without exceeding 4.2V, which would be highly dangerous and kill your batteries in no time.

[Granpappy]

Well I did do another little experiment tonight. I charged a battery up but as soon as the charger went into CV mode and the voltage read 12.6 volts I prematurely stopped the charge. I took the battery off the charger and measured the voltage with an AVO which flickered between 12.59V and 12.60V. I then put the battery back on the charger and completed the charge which put another 115ma into the battery before terminating. I took the battery back off the charger and measured 12.6V on the AVO.

[Granpappy]

The point I was making is that a battery can read a particular voltage at rest but the voltage drop when a load is put across it is entirely dependant on how much charge the battery had in the first place. My car battery once read 13 volts at the terminals. When I tried to start the car it dropped to 4 volts because there was no charge in it.

[SGD]

Well I did do another little experiment tonight. I charged a battery up but as soon as the charger went into CV mode and the voltage read 12.6 volts I prematurely stopped the charge. I took the battery off the charger and measured the voltage with an AVO which flickered between 12.59V and 12.60V. I then put the battery back on the charger and completed the charge which put another 115ma into the battery before terminating. I took the battery back off the charger and measured 12.6V on the AVO.

There are a few things going on during the CV part of the cycle that need to be considered.

First if you were to think of the battery as a cardboard box that you need to fill to it's maximum capacity with say sugar cubes. Now the CA part of the charge you just tip the sugar cubes into the box with a bucket until the cubes level with the top of the box. At this point the box looks full at first glance but the sugar cubes are in a random order with spaces around them. Now during the CV part the cubes start to slowly organise themselves into nice neat rows and layers and filling the box more efficiently and as they do so more space becomes available at the top of the box so you can slowly keep adding cubes until the box is neatly filled. (Sorry it's the best analogy I could come up with at this time of day!)

Second thing that's going on is that the battery is being balanced and generally speaking the charger discharges the cells with the highest voltages so mAh keep going in but come out again as heat from the charger. The bigger the differences in condition of the cells that make up the battery the larger these losses can be.

Third is that the older the packs and the higher the internal resistance the harder the charger has to work to push the charge in which again can be displayed in the mAh's out reading.

There may be other factors at play as well but suffice to say that we are trying to understand how to measure how much stuff we can't see that's being stuffed into a bag of chemicals. Much prefer the old simple method Red light = charging Green light = done! let's fly!

[Grumpy]

The point I was making is that a battery can read a particular voltage at rest but the voltage drop when a load is put across it is entirely dependant on how much charge the battery had in the first place. My car battery once read 13 volts at the terminals. When I tried to start the car it dropped to 4 volts because there was no charge in it.

LiPos dont work that way. Th resting voltage very accurately indicates the state of charge of the battery. If it's at 4.2V per cell then it's fully charged. What may have slightly skewed results in you previous experiment when you pulled the battery off early is it takes the battery quite a few minutes to settle down after charging, especially during the high current CC phase of the charge. So if you pulled the battery just as it was going into the CV phase and checked voltage right away it will have been artificially high, it will settle slightly after a few minutes. Bear in mind that 115mAh on a 2200mAh cell is only 5% which would only effect voltage by around 0.05V, that's well within the voltage that a battery 'settles' after charging.

SGD's comment about mAh lost through balancing is also a good one to consider and might explain the apparent differences between what the charger puts in. Some chargers are more efficient at balancing and so will have to drain less from the cells, other chargers might be less efficient and will drain more off. The less efficient balancing charger will have to put more in to make up for what it's draining out. Anyway, the bottom line is it's end voltage that indicates charge state, not how many mAh you think the charger put in.

[Granpappy]

There are a few things going on during the CV part of the cycle that need to be considered.

First if you were to think of the battery as a cardboard box that you need to fill to it's maximum capacity with say sugar cubes. Now the CA part of the charge you just tip the sugar cubes into the box with a bucket until the cubes level with the top of the box. At this point the box looks full at first glance but the sugar cubes are in a random order with spaces around them. Now during the CV part the cubes start to slowly organise themselves into nice neat rows and layers and filling the box more efficiently and as they do so more space becomes available at the top of the box so you can slowly keep adding cubes until the box is neatly filled. (Sorry it's the best analogy I could come up with at this time of day!)

Second thing that's going on is that the battery is being balanced and generally speaking the charger discharges the cells with the highest voltages so mAh keep going in but come out again as heat from the charger. The bigger the differences in condition of the cells that make up the battery the larger these losses can be.

Third is that the older the packs and the higher the internal resistance the harder the charger has to work to push the charge in which again can be displayed in the mAh's out reading.

There may be other factors at play as well but suffice to say that we are trying to understand how to measure how much stuff we can't see that's being stuffed into a bag of chemicals. Much prefer the old simple method Red light = charging Green light = done! let's fly!

I love that analogy. :-)

So basically the battery can be at 4.2 volts per cell before it has started sorting out the sugar lumps. i agree with this and it defeats the statement that when the cells are at 4.2 volts then they are fully charged.

So therefore my problem is that my old charger is better at sorting out the sugar lumps then my new charger. This brings me back to my original question:- 'Is there anything I can do about it?'

[Granpappy]

The only explanations for that would be that the batteries are getting old and tired and/or you might be flying harder, or maybe using higher headspeed.

The only thing that has changed is the charger.

[SGD]

So basically the battery can be at 4.2 volts per cell before it has started sorting out the sugar lumps. i agree with this and it defeats the statement that when the cells are at 4.2 volts then they are fully charged.

So therefore my problem is that my old charger is better at sorting out the sugar lumps then my new charger. This brings me back to my original question:- 'Is there anything I can do about it?'

I'm sorry I don't mean to be rude but it appears to me that you are cherry picking snippets of replies and using them in isolation in an attempt to prove your original theory regarding your GP charger.

The point regarding the charge end voltage 4.2V reading as opposed to the initial 4.2 reading has been covered a few times. You yourself have pulled a battery of the charger as soon as it hit the initial 4.2V value but if you had checked the pack voltage every few minutes for 10 or 15 mins you would see the voltage reduce over that period. Plus when the pack hits the initial 4.2V the individual cell are at their most out of balance with probable only only one cell actually reading 4.2V. The out of balance cells will, to a very small amount, balance themselves which will reduce the overall pack voltage very slightly during this period.

And on the subject of charge end voltage the 4.2V is a coarse reading as the chargers generally work to three decimal places or more and if you look at you TP manual, pages 25-26 you will see this on the subject.

For LiPo batteries, and LiIon batteries with a nominal voltage of 3.7V per cell (and full charge voltage of 4.2V per cell), you can set the charge end voltage up to 4.24V per cell. And although the maximum recommended charge end voltage per cell is 4.235V, due to slight variations in the components and calibration of each charger, resistance of charge leads and cells/batteries, ambient conditions and more, it is possible that when the value is set to 4.24V it will not actually exceed 4.235V per cell when checked with a calibrated Digital Volt Meter (DVM).

And as Grumpy has already stated: 115mAh on a 2200mAh cell is only 5% which would only effect voltage by around 0.05V, that's well within the voltage that a battery 'settles' after charging.

[Granpappy]

I'm sorry I don't mean to be rude but it appears to me that you are cherry picking snippets of replies and using them in isolation in an attempt to prove your original theory regarding your GP charger.

Well, I'm extracting what I consider to be relevant information that supports the cold hard fact that my older charger gives me longer flight times on my batteries. I'm not trying to win any arguments and I appreciate all the theory relating to battery charging and battery chargers. But what I'm being told is that I'm wrong and that what I'm describing as the physical problem isn't actually happening.

Well the problem as described does happen, I'm getting shorter flight times, and was just hoping that there might be some resolution to it. If there is no resolution then I will just have to live with it.

[1chris]

I could see this thread was going to deteriorate lol..... at the end of the day it is just a "toy" helicopter.... who cares, go out fly it and enjoy yourself

[SGD]

Well, I'm extracting what I consider to be relevant information that supports the cold hard fact that my older charger gives me longer flight times on my batteries. I'm not trying to win any arguments and I appreciate all the theory relating to battery charging and battery chargers. But what I'm being told is that I'm wrong and that what I'm describing as the physical problem isn't actually happening.

Well the problem as described does happen, I'm getting shorter flight times, and was just hoping that there might be some resolution to it. If there is no resolution then I will just have to live with it.

I can fully understand your desire to understand the differences your experiencing with your chargers but unless you can ensure that both chargers are certifiably calibrated perfectly and have exactly the same settings it's virtually impossible to identify any potential differences.

We have been explaining at, length, how and where even the smallest differences can have an accumulative effect and influence the resultant end charge. One such small difference has been identified by Grumpy in that a small variation of 0.05V in the end voltage can alter the end charge capacity by as much as 100mAh which alone would be a big chunk of your missing 30sec flight time.

[SGD]

I could see this thread was going to deteriorate lol..... at the end of the day it is just a "toy" helicopter.... who cares, go out fly it and enjoy yourself

Some of us enjoy understanding the science that goes into letting us play with our toys nearly as much as the playtime itself! I know it's not for everyone but each to their own.