TP820CD charger


I like new things, and I don't mean in a "Ah shiny" kind of way. I like to learn new things and having new toys is always a good thing ;) Anyhow I have been using my iCharger 208B and 206B chargers for almost 2 years now and have been very happy with them but it just felt like time for something new. So this year I made the decision to get a dual port charger for field charging. But which one? Well that turned out to be simple because as soon as I saw that Thunder Power released their new TP820CD, I knew that was the one for me.


A few specs
Below are some of the more useful specs. The complete specs are available in the manual.

Input voltage range
10.5V-28V
Max input current40A
Max LiPo cell count1-8s per port
Max charge rate
20.0A per port
Max output wattage @ 27V input 
400W per port
Max discharge power
50W per port
Max current drain for balancer
~350mA per cell

First impressions
The first thing I noticed about the 820 was the size and weight of the box. Honestly the box looked too small to contain a dual port charger and accessories, plus it was really heavy for its size. I opened it up to find that it did indeed hold a charger, several accessories and a printed manual. The charger itself was not large compared to the average charger out there but it was considerably bigger than my iChargers. The accessories it shipped with include a balance board and output lead set for each side, and a set of alligator clips ins included for charging off a car battery. 

As far as first impressions go, the TP820CD does quite well. The solid feel and heft of the charger goes a long way to build confidence even before you use it. The input leads are 10awg with a 4mm bullet soldered to each. There are 2 fans in the back of the charger and air vents in the front to facilitate cooling, a straight forward and logical design. I especially like the 4 very sticky rubber feet on the bottom. They do a great job of anchoring the charger to the workbench during use. When powered on, the screen is bright and blue. It is easy to read and a nice size. The buttons feel very nice and solid, and have a satisfying click to them. 

The only initial complaint I had with the 820 is that the unit I received has a decent scuff along the top, back edge, as well as one on the bottom. These scuffs don't detract from the function of the charger but they are noticeable. 

Using the TP820CD hardware
The charger ships with a pair output leads for each port. The leads 12awg and about 8in long. Each has a 4mm bullet soldered onto the one end and bare tinned wires on the other end. The balance board for each port also has an 8in long connection lead. The board feels nice and includes 2s-8s connections for both JST-XH and TP balance connectors. That covers nearly all of the connectors used these days and was a smart choice by TP. The only connector not supported is Polyquest/Hyperion 2s-3s. Of course that is not a problem because the 4s-6s connectors are directly JST-XH compatible and the 2s-3s can easily be modified to work with JST-XH. I really like the placement of the battery connections on the charger, with the main discharge leads on top and the balance leads on the side. They are easy to get at and it makes for a clean look. I did find that plugging in the balance board connection cable can be a bit tough. The new connectors are very tight and I had to sort of wiggle it on there using quite a bit of force the first time, but it is getting easier each time as the connectors loosen up. 

One nice thing about the balance board design is that they have 6s, 7s and 8s JST-XH connectors on them. For those interested, this allows for the parallel connection of 3x 6s packs, one in the 6s port and one in both the 7s and 8s ports (just make sure to align the connector to the negative side of the socket). That one feature is very handy and really adds functionality for me, even if it is not the intended use of the board.

The input leads are made from nice flexible 10awg noodle wire. They are 24in long and have a standard 4mm bullet soldered on the end of each. Unfortunately both wires are just loose, free to flop as they wish. Don't get me wrong, the use of 10awg noodle wire on the inputs is a nice touch but a little heat shrink here and there along the length of the wires would really help them stay together. That is really a minor complaint though, and I simply added the shrink wrap myself. 

My first real complaint with the 820 has to do with the LCD display. The blue LCD is pretty but the polarization is inline with polarized sunglasses, making the screen black anytime you look at it straight on with polarized sunglasses on. Seeing as how I, and most other pilots wear polarized sunglasses, this is a real annoyance. Honestly this is something that should have been taken into account when choosing the LCD for the charger and I am disappointed it was not. But like most complaints, it is more of an annoyance than a deal breaker and I am learning to deal with it. 

Using the TP820CD menus and options
My first task was to learn my way through the menus and options on the 820. I quickly discovered that the 820 is a pretty simply charger in terms of the menus and options. Here is a basic program flow chart I put together.


I honestly found the 820 very simple to use once I learned my way around it. Here are some of my personal likes and dislikes
  • The large LCD allows for the display of lots of info on each screen. That makes for very few screens, and that is nice. I also think the way the charger works is very intuitive. 
  • I really like the way it uses presets. I am sure this is not the only charger that does it this way but it is the first I have used. All you do is press "Enter" at the charge screen and then use + or - to cycle through them. Each one simply remembers the last settings used. There is no saving or retrieving of presets. It's a very simple and effective way to do things, and I like it. 
  • The charger automatically limits the charge rate to reflect the power supply settings and current input voltage. That is a nice touch, as it helps inform the user what the maximum charge rate before they begin charging. 
  • Some of the options are tailored to the battery type selected in the charge screen. This could lead to some confusion as to where to find specific settings but it does make for a less cluttered set of program screens. 
  • This is a personal thing but I don't like is having to tell the charger the capacity of the pack you plan to charge. I understand that it is a safety measure but it makes for an extra step when setting the charge settings. If you are always charging at 1C this would not be a problem because it automatically sets the charge rate to the capacity, but I almost never charge at 1C and so I have to set the capacity and then set the charge rate. Of course the presets solve this by allowing you to set it once and then recall it whenever you want but I still don't like it. 
Charging a pack
It's finally time to get to it, actually charging a pack. Plug in the charger and turn on the power supply. The charger boots up and defaults to the last used charge screen. Connect the pack to the correct output. Press "Enter" and the memory # will blink. Press "+" or "-" to select the memory you want and if it is set properly, just hold "Enter" and the charge cycle will begin. Or if the setting are not correct, press "Enter" to advance to each setting. Once correct hold "Enter" to start charging. The following it what I see when charging my 6s packs.


The current ramps up quickly and holds very close to the value selected. Pressing "+" once shows the cell voltages. Pressing it again will take you to other screens showing internal temp, input voltage and more. Pressing the "Port" button at any time will switch the display to the other port's screen. During the charge cycle, the charge phase is always displayed. It starts out as "CC" for constant current and can change to "EB" for extended balancing if additional balancing is required, or "CV" for constant voltage. That is something I am very fond of, as it can be very handy to be able to quickly look at the charger and know what phase it is in. When the charge cycle is complete, it plays a tune and shows the "Battery Charge Complete" screen. Press "Enter" to go to the charge screen where the completed charge data is shown. Press "Enter" again to clear the screen and go back to the charge screen, ready to charge another pack. 

Other modes
Since this is a charger, its primary use will be to charge batteries. That doesn't mean it will not do other things though. I don't want to go into the other modes in any great detail, but below are a few things I have found.
  • I decided to try storage discharging a 6s 2700 lipo on each channel at its max discharge rate of 2A (50W per port). The charger started out at 2A and things carried along for about 5min. At that point the internal temp reached 134F and it switched to a screen stating the "Over Temperature Please Wait ... 134F" and it began cooling down. The temp dropped until it reached 104F and then it went back to work discharging. I found out that the highest I could go without the charger overheating was 1.2A per port (about 30W per port). I did find that I could discharge at the max 50W when only using one port. The charger showed a temp of about 122F. This was done in my office which sits at about 68F.
  • The TP820CD will measure both battery and cell IR, or internal resistance. It seems to work pretty well and the numbers line up fairly close to my iChargers. I did run into a problem when try to check the IR on A123 packs though. This led me to find out that they charger applies a charging load to the pack during the IR check. That load is roughly 8.5A. When checking the IR on a lipo, it only takes the charger a split second to determine the values. But when checking the IR of an A123 pack, it take anywhere from 3sec to 30sec or more. During that whole time the charging load is held and this can be potentially damaging to certain packs. For example my LiFePO4 pack never returned a reading and I finally unplugged it after 30-40sec. The pack states a max charge rate of 4A and it was being charged at 8.5A. The pack got fairly warm during the event and I hope no damage was done. I will not be checking the IR on any A123 pack again. 


Testing the TP820CD
Below are several tests I ran in order to learn various things about the TP820CD.

Maximum output on 12V
I used a pair of 6s 2600mAh packs on each output and used my 2C preset of 10.4A. I then started the charge on both ports and used my watt meter to gather numbers. The charger showed a 8.52A charge rate on both ports. Connecting up the watt meter inline on each port showed nearly the same numbers of 9.1A and 23.1V, equating to 210.2W per for a total charger output of 420.4W.

Next I used adjusted the power distribution to show a 90/10 split, then checked the outputs again. The charger showed 10.95A on port #1 and 1.75A on port #2. Connecting up the watt meter on port #1 showed 11.4A and 23.3V. That equates to 266W. I did not measure port #2 but the result is far from the 420W output attained using a 50/50 power distribution. 

Maximum output on 24V
Same as the 12V test except I set the charger to the max output for 6s on 24V, which happened to be 17.6A. The charger showed a 15.21A charge rate on both ports. Connecting my watt meter inline on each port showed nearly the same numbers of 15.9A and 23.7V, equating to 376.8W per port for a total charger output of 753.6W.

Charger efficiency when charging 6s packs on 12V and 24V
On 12V with both ports charging at max output, 420.4W, my watt meter showed that the charger was drawing 42.2A on 12.1V, equating to 510.6W. That equates to an efficiency of 82.3%.

On 24V with both ports charging at max output, 753.6W, the watt meter showed that the charger was drawing 33.8A on 24.2V, equating to 818.0W. That equates to an efficiency of 92.1%. 

Faster than other chargers?
Both the promotional material and the manual make the claim that the 820 is that it is faster than its competitors chargers, even those with more output potential. Here is one example found in on page 5 of the manual.

"Popular examples of the powerful charging capabilities of the TP820CD are the ability to charge two 5S 5000mAh batteries, one on each port simultaneously at rates up to 4C, or two 6S 5000mAh batteries at rates more than 3.5C, to have a complete 10S or 12S 5000mAh battery setup charged in as little as 15 minutes or less time. That’s even faster than single port chargers rated at higher current and wattage output, without the need for cumbersome parallel charging and an even more powerful power supply, and without giving up the added convenience and flexibility that independent dual port charge, discharge and cycling functionality offers."

Of course this sort of statement catches my interest. Just how are they managing to support it? Well I decided to do a few tests and find out. My first comparison would be against my iCharger 206B. I planned to use my paired 6s 2600mAh Voltz flight packs for the test. Since each of the 2 packs used in each flight pack is exactly the same age, have the same number of cycles and have seen exactly the same use, they are perfectly suited for such a test. The packs were storage charged in parallel on the 820 and then split up to be charged, one on each charger. The cell voltage measurements were done with my CellLog using the most accurate method I have at my disposal (shift the balance plug down to read each cell on the CellLog's cell 1 measurement).

Test 1: Charging at 1C (TP820CD stock settings vs. iCharger 206B stock settings)
Charger    Total Time
Total mAhTime in CVCells
TP820CD28:25
1188~3min4.176, 4.174, 4.166, 4.171, 4.165, 4.179
iCharger 206B43:041357~15min4.204, 4.203, 4.199, 4.199, 4.199, 4.204

These results were much different than I expected. Both chargers reached the CV phase within 1-2min of each other but both handled the CV phase much differently. The 820 fairly rapidly lowered the charge current and finished. The 206B spent a great deal of time lowering the charge current and balancing the cells. The results show the differences in the end voltages as well as the additional mAh consumed by the 206B during the lengthy balancing. In this case the 820 was much faster but the resultant charge shows less voltage as well as being less accurate, a trade-off most will happily accept. 

Test 2: Charging at 3C (TP820CD stock settings vs. iCharger 206B set to "Balance Fast" (I/5))
ChargerTotal TimeTotal mAhCells
TP820CD11:261072 4.174, 4.174, 4.170, 4.174, 4.170, 4.178
iCharger 206B21:0511854.199, 4.199, 4.194, 4.199, 4.198, 4.204

After the first test, I could better guess what the results of a faster charge would be and I was not off by too far. The 820 once again finishes the charge cycle much more quickly. I was watching the charger when it finished on this test and I noted it finished exactly when the charge current dropped to .78A or 1/10th of the initial 7.8A charge rate. By contrast, the 206B hovered around 1A for nearly 10min while it topped off the cells and balanced them. Again the results show the differences in the two approaches, with the 206B doing a better job of getting all cells to 4.2V but at a cost of neatly 10min more charge time of the 820. 

Now to for 2 more tests but this time against a Hyperion 720i Duo3. Test 3 is using the same Voltz packs as the first 2 tests, while test 4 uses my well used and abused Turnigy Nano-Tech 2650mAh 6s 25C packs. 


Test 3: Charging at 2C (TP820CD stock settings vs. Hyperion 720i Duo3 stock settings)
ChargerTotal TimeTotal mAhCells
TP820CD14:3410754.185, 4.184, .4.179, 4.184, 4.179, 4.189
Hyperion SDuo318.4311364.194, 4.194, 4,189, 4,194, 4,194, 4,194

Like the iCharger, the Hyperion charger spends more time in the CV phase and the resulting charged pack shows slightly higher voltages, as well as slightly better balanced cells. 

Test 4: Charging Nano-Tech packs at 1C (TP820CD stock settings vs. Hyperion 720i Duo3 stock settings)
ChargerTotal TimeTotal mAhCells
TP820CD30:2712164.137, 4.160, 4.131, 4.140, 4.161, 4.172
Hyperion SDuo339:4813824.174, 4,174, 4,174, 4,176, 4,183, 4.179

This test turned out to be a little more interesting. Both chargers came up well short of 4.20V per cell but the 820 came up really short. Like I said these packs are old and tired, not that they were high end to start with, so the lower voltages and poor cell balancing is not too surprising. What is surprising is how differently the two chargers charged the packs. I may do a 5th test comparing the 820 to the iCharger again but with the Nano-Tech packs to see how the iCharger handles them.

Testing conclusions
What do I take away from these tests? Well the output of the charger is right about what I would expect. TP states you need a 27V power supply to get the full 400W per port and that sees about right from my tests. Efficiency wise, the 820 does very well when the input and output voltages are close but drops a bit more than I would have expected as they diverge. It turns out the TP820CD definitely charges packs more quickly than 2 of its competitors but not without giving something up. It accomplishes this "faster charging" by terminating the charge cycle as quickly as possible, but that means falling short of 4.20V per cell and giving up some precision on balancing. The resulting charged packs are still charged but are a few % less charged than they might be on other chargers. This is a trade-off I happily accept, as I believe many users will, but for some this will not sit well and may be a deal breaker.

Final thoughts and conclusion 
First off I have been using the 820 for a few weeks now and I like it. Aside from the A123 IR check problem, it has performed perfectly. I really like the small size, simple design and layout. The large blue back-lit screen is nice, even with the polarization issue, and I find it easy to navigate through the charger. My only complaints are the screen polarization issue and the lack of certain features like regen. discharge. TP has promised that they are working on the firmware, so we may still see those features in the future. In the end, I feel the TP820CD is an excellent charger, if not one of the best available. Good work Thunder Power. 


Updates and notes

I will post up updates and new info as I find it.