TP820CD under charging.

[Granpappy]

Hi there,

I recently bought a Thunder Power charger TP820CD and I have a small issue with it. Whilst charging Lipo's it will move on to the constant voltage phase once 4.2V per cell has been reached but it will terminate the charge once the charge current goes below 0.35 amps.

My old Graupner Duo would charge down to 0.1 amps before it terminated the charge. I reckon it's costing me about 30 secs flight time on a 3S 2200mah lipo on my 450. I cant find any way to adjust the shut off current when charging Lipo's on this particular charger. Does anyone have any ideas?

Cheers.

[1chris]

Get a bigger battery

[SGD]

What's the cell voltages reading when it's finished charging?

[Granpappy]

4.2 Volts.

[SGD]

I no longer have a 450 but if I remember correctly the flight time was about 5 min (just basic hovering flight). And as I always tried to end the flight with 20% battery capacity left of a 2200mAh pack. Given these basic figures it's easy to calculate a rough estimate of how much battery capacity 30sec of flight take.

2200mAh - 20% = 1760mAh for a 5 min flight

So 1760/10 = 176mAh for a 30 sec

I know this is only a very rough calculation but even so I doubt that any charger will come close to adding an extra 176mAh without increasing the end voltage even if it was charging at a very low amperage. So you may want to look elsewhere for your missing capacity.

The only things that I can suggest are first you check that your TP charger is running the latest firmware. Details can be found here: Software for TP820CD

Second suggestion is that either your old or new charger may need calibrating. (A link to the instructions are in the above link)

And finally check the lipo "Charge End Voltage" setting in your charger, which is adjustable. Instructions and warnings on doing this can be found on page 25 of your user manual under the heading SETTING DATA (SETTINGS) MODE.

[Granpappy]

I no longer have a 450 but if I remember correctly the flight time was about 5 min (just basic hovering flight). And as I always tried to end the flight with 20% battery capacity left of a 2200mAh pack. Given these basic figures it's easy to calculate a rough estimate of how much battery capacity 30sec of flight take.

2200mAh - 20% = 1760mAh for a 5 min flight

So 1760/10 = 176mAh for a 30 sec

I know this is only a very rough calculation but even so I doubt that any charger will come close to adding an extra 176mAh without increasing the end voltage even if it was charging at a very low amperage. So you may want to look elsewhere for your missing capacity.

The only things that I can suggest are first you check that your TP charger is running the latest firmware. Details can be found here: Software for TP820CD

Second suggestion is that either your old or new charger may need calibrating. (A link to the instructions are in the above link)

And finally check the lipo "Charge End Voltage" setting in your charger, which is adjustable. Instructions and warnings on doing this can be found on page 25 of your user manual under the heading SETTING DATA (SETTINGS) MODE.

Thanks for the help Stew. However Charge End Voltage is correct, TP is running latest firmware and the chargers are accurate to the best of my knowledge.

Adding another 176mah will not increase the end voltage on Lipo's in constant voltage mode. The chemistry is different to NiCd, Nimh in the way it reacts to charge. In CV mode the charger should terminate the charge when the input current is down to 1/10th of the current capacity. On my charger it should actually terminate at 220mah current, but it's terminating higher than that hence the original question. I'm starting to think that you can't actually alter this figure on the charger because it seems to be (wrongly) set in the firmware. I was wondering whether anyone had a solution for it. I am definitely losing flight time with this charger.

[Mike Sanders]

Don't look at it as losing flight time. Consider it as looking after your batteries by not overcharging them. They will last a lot longer, particularly if you don't discharge them too much.

If you are bothered about losing 30 seconds of flight time, buy a few extra packs, they are cheap enough!

[Granpappy]

Don't look at it as losing flight time. Consider it as looking after your batteries by not overcharging them. They will last a lot longer, particularly if you don't discharge them too much.

If you are bothered about losing 30 seconds of flight time, buy a few extra packs, they are cheap enough!

I can't over charge them. They are being undercharged which means after running the potential exists for them to be more discharged then I would like. Sure batteries are cheap enough but the charger was expensive and I would rather it do what it is supposed to do rather then buy more batteries.

[Granpappy]

Get a bigger battery

I did consider the battery from my golf trolley but it wouldn't fit.

[1chris]

ok .......just a suggestion, nobody else seems to of come up with a satisfactory answer, just seemed a bit of a picky question, what difference in the cold light of day does loosing 30 seconds of flight time make?

I don't think a golf trolly battery would fit in a model helicopter thats all most a sillier suggestion than worrying about loosing 30 seconds of flight time.....................

[SGD]

Thanks for the help Stew. However Charge End Voltage is correct, TP is running latest firmware and the chargers are accurate to the best of my knowledge.

Adding another 176mah will not increase the end voltage on Lipo's in constant voltage mode. The chemistry is different to NiCd, Nimh in the way it reacts to charge. In CV mode the charger should terminate the charge when the input current is down to 1/10th of the current capacity. On my charger it should actually terminate at 220mah current, but it's terminating higher than that hence the original question. I'm starting to think that you can't actually alter this figure on the charger because it seems to be (wrongly) set in the firmware. I was wondering whether anyone had a solution for it. I am definitely losing flight time with this charger.

I was trying to compare your two chargers and their setup when I was asking about the Charge End Voltage and calibration and I was looking for differences that might explain the apparent loose of charge capacity. But if we don't know how accurately both are calibrated then the rest is just a bit of guess work as the Charge End Voltage is just a number that could be higher or lower than expected.. The ability to calibrate chargers has been included by the manufacturers as they can and do go out of calibration and need to be reset occasionally.

With the CV section at the end of the charge cycle the charger looks at the difference between the end voltage set within the charger and the pack resting voltage. To do this the charging voltage is held constant at the max pack voltage but current continues to flow because there is still a difference between the charge and pack resting voltages. As the pack resting voltage rises, the difference will become less and less until they are very close. During this phase the charge current will drop and when the two voltage are within a very narrow predetermined band the charge cycle is deemed to be over.
It's at this point in the CV charging that you're saying that your Graupner Duo can add another 176mAh or 10% of your packs capacity over and above that of the TP charger without changing the voltage, correct?

A very simple test can be carried out to check the new charger against the old and that would be to cycle charge some packs on the new TP charger one at a time, make a note of the total voltage, cell values and total mAh in. If you have a standalone battery checker then check the pack with that as well. Now put the fully charged packs on charge on the Graupner, again one at a time, and if your theory is correct then every pack will accept around another 10% or 176mAh in the case of you 2200mAh packs without an increase in the pack voltage.

[heliboys]

I've got 2 TP820CD chargers, charging 2 6s 5000mah packs at 2·5c charge rate, I have noticed that most of the time they cut off at 0·20amps and sometimes slightly higher, they have even been checked straight after being charged on a battery checker and the cells are 98-99% charged.

[Grumpy]

So what voltage are the cells at when they actually leave the charger?

If they are in the 4.16-4.2v range then to all intents and purposes they are fully charged. Roughly every 0.01V (one hundredth of a Volt) below 4.2V is 1% of battery capacity, so if the batteries were at 4.16V per cell on all cells that's a 'loss' of about 4% over their maximum attainable charge. 4% capacity is about 12 seconds flying time (assuming a full charge gives you 5 minutes), so not really enough to get too excited about.

To lose 30 seconds flight time would mean that the cells were only at about 4.1V coming off the charger, which would certainly indicate something very wrong with the charger's settings.

[Granpappy]

Well I've just done a complete test using both chargers and the results are odd.

I started with an Align 3s 2200mah battery. Starting voltage showed as 11.56V on the AVO (Multimeter) and 11.589V on the new TP charger.

I charged the battery on the TP charger at 1C. It took 35:42 mins and pumped in 1029ma. The end voltage showed as 12.62V on the AVO and 12.617V on the charger.

I then put the charged battery on the old GP charger and it showed 12.67V and would not charge the battery any further.

I then discharged the battery on Storage setting on the new TP charger at a discharge rate of 3 amps. It took 21:13 mins and took out 889ma. The end voltage showed 11.62V on the AVO and 11.629V on the charger.

I then let the battery settle for 3 hours. After 3 hours the battery voltage showed 11.62V on the AVO and 11.65V on the old GP charger.

I charged the battery on the old GP charger at 1C. It took 43:15 mins and pumped in 1017ma. The end voltage showed as 12.54V on the AVO and 12.60V on the charger.

I then discharged the battery again on storage setting on the new TP charger at a rate of 3 amps. it took 23:22 mins and took out 978ma. The end voltage showed 11.61V on the AVO and 11.617V on the charger.

The old GP charger needs calibrating but it's putting in more charge than the new charger even though the end voltage is below 12.6V for the battery.

[SGD]

The only important figures to concerned about when charging are the end voltages of the pack and the individual cells.

The mAh numbers are a little irrelevant especially if compare across different chargers as these are arrived at through calculations done within the chargers firmware algorithm which will be written slightly differently for each make of charger. If you were to take any two makes of charger there would be some variation in the mAh figures but the figure would be more closely matched on a single charger.

In the end as long as the end voltage is at the maximum permitted and the cells are well balanced then the battery is as full as it can be regardless of mAh in.