57w vs 100w charger

[Bad Andy]

Cheers mate -- just for the record - I don't scold.

Fair 'nuff.

I post adding or correcting what I read. I can be wrong as anyone else.

Likewise. My in-depth knowledge of electronics could be an asset, or it could turn out to be a liability. It does make me a lot more cautious about how I treat the information I take in. Battery chemistry is not a directly substitute-able component in Ohm's law and related equations and if it was predictable enough to be so, then we wouldn't need to worry about cell balancing routines.

As to charge rate - as any load - the amp rate is based on its demand unless read short. This does not mean the battery board will have capability to swap CV / CC mode. The DJI charger bangs out 17.5v whatever ....

You mean power supply, LOL... (oh wait, that was N017RW's thing)

When watching my lipo charger display - I see the amp rate declining as expected as the battery level increases. I have as a test set the amp higher - but it never reached that figure - it max'd around 5A, quickly declining as charge continued.

The thought plickens!

So I wonder, is that the pack maxing out its charge rate for a given voltage, or is that a limit designed into the DJI pack's battery management board?

Again, I appreciate the LiPo education.

-Brad

 

[solentlife]

C'mon guys ... no-ones having a go at anyone else. We are all on the same path trying to arrive at a general consensus / agreed conclusion.

If we take all the info and put together - we are all basically same - with just some of the finer points different.

We can bring in experience of circuitry, of LiPo maintenance, LiPo use and charging / discharging. The amalgam of all could provide a better understanding and so benefit anyone who gets to read.

Nigel

 

[solentlife]

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Discharge to low level in progress ... will make second video when ready.

Nigel

 

[solentlife]

OK ...

Here's where I discharge down and then recheck ... and in fact AMPS does go over 5A ... and hits limit of my charger.

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What I find interesting though - the battery shut down on discharge at 13.62V ..... not the 12V I was told by DJI ... I was told that battery is programmed to switch off at 12V (3V per cell) to avoid damage. MIne didn't - it switched off before that and what is generally regarded as lowest safe rested voltage ....

The LiPo chargers will not charge DJI batterys unless switched on - I believe that is because they don't 'ram' 17.5V at them at start ... the charger ramps up voltage as the battery 'fills up' .... but a DJI brick throws 17.5V regardless and that kicks the board to accept charge without switching on.
Because the battery kept shutting of at such low voltage - the charger didn't get enough time to initialise on the battery state, was below 17.5V and therefore connect error.

I put the battery on DJI brick for a minute or so - just to kick the battery up a touch and it then accepted LiPo charger for me to see the amps ...

All interesting stuff !!

Nigel

 

[Bad Andy]

Thanks for the videos and experimentation.

You had the charger set to a max of 8 A and a deeply discharged pack pulled 5.2 A, right? You stated that you hit the limit of the charger but that's not what I'm seeing in the video. And that's still 0.5 short of the capacity of a P3P PSU. Which, seems to imply that either the DJI battery controller does regulate charging current, or the battery is naturally self-limiting (at least for that voltage).

It's probably a good assumption that the DJI battery controller is looking for north of 17 V to "wake up" the electronic connection between the pack's terminals and the battery. It's also interesting that to top off a charged battery pack, you have to turn it on!

Something concerns me about that when using intelligent chargers...

The DJI battery pack's controller board uses semiconductors to control the connection to the blades for charging and for usage, and the LiPo charger's circuit path (because it goes through the pack's controller board instead of directly to the batteries) would be including those semiconductors in its attempts to ascertain pack voltage, internal resistance, etc.

 

[solentlife]

The LiPo charger basically becomes a Power supply with digital readout. Because there is no balance lead connected ... so it cannot do its normal job. You connect it in basic Charge mode.

My charger is 80W ... so lets say 15V will have 5.3A rate ..... because the charger needs to exceed the back voltage of the battery - here at start was about 14.2V ... charger is at about 15V .... therefore it quickly gets a rise on the battery and voltage of charger increases ... amps go down ... so I'm hitting max output ...
I was hoping that discharging to low level - I could use the 80W to get a high ampage ... but didn't allow for needing to jump the battery over 14V. Also DJI reckon discharge can be down to 12v ... which clearly mine would not achieve. It shut off at 13.62V

Topup is mentioned by DJI themselves and is part of their system. If the battery is in the 90's % charge state - plugging in without switching on will not work. DJI tell you to switch on battery first - then plug in and the battery will then be topped up.
It was interesting that to get charging to start from the 13.62V - it needed the DJI charger thumping 17.5V at it !! The LiPo charger couldn't get the battery to stay on to charge until voltage was above 14V.
LiPo chargers - because they adjust the voltage to overcome battery resistance as it charges - means that you need to switch on to do any charge. It makes no different at the top end - as the LiPo charger will be pumping 17.5V at the pack same as DJI unit, so cut-off and board will work as normal.

Nigel

 

[Bad Andy]

So even though you set an 8 Amp max, your charger (along with the serially connected cells) is the limiting factor for charging current. OK.

Question remains, how does that LiPo charger as a power supply in basic charge mode know when the charge is complete? Or if it does not, then how do you know?

 

[jephoto]

WOW .... money to burn !!

Why not have a look at this one that charges 3 flight batterys and the RC simultaneously without sequencing ...

4in1 Battery Charger Adapter Quick-Charge For DJI Phantom 3 & Remote Controller | eBay

Cost about $40 .....

I have one from Amazon .. slightly higher priced but still well under the price of the DJI single unit !

Nigel

I've got one like this. The case is blue. Been very happy with it too. Between the 3 battery leads on it plus my 2 -100w DJI chargers I can charge 5 batteries and the controller at once. In about 70-80 min.
Which is excellent when I've had a full day of flying at multiple locations and have to be ready for more the next morning...

 

[solentlife]

So even though you set an 8 Amp max, your charger (along with the serially connected cells) is the limiting factor for charging current. OK.

Question remains, how does that LiPo charger as a power supply in basic charge mode know when the charge is complete? Or if it does not, then how do you know?

It acts like a basic power supply regulated to the max amps / voltage (S) you set. Once the voltage hits the max and is stable - it stops charging.
It will do that for any LiPo / battery ... it uses user settings to determine when to stop. It also still has its safety functions active - if a short or event occurs that it detects outside of safe parameters - it will automatically shut off power. That gives you double protection ... charger shutting off (which DJI brick does not) and the battery board terminating charge.

Nigel

 

[Bad Andy]

It acts like a basic power supply regulated to the max amps / voltage (S) you set. Once the voltage hits the max and is stable - it stops charging.
It will do that for any LiPo / battery ... it uses user settings to determine when to stop. It also still has its safety functions active - if a short or event occurs that it detects outside of safe parameters - it will automatically shut off power. That gives you double protection ... charger shutting off (which DJI brick does not) and the battery board terminating charge.

OK, so when connected to the external prongs on a DJI pack, that charger will either stop when the pack's circuitry stops, or when the charger sees that max/stable voltage it's looking for.

Is there a way to set the max voltage?

Here's why I'm asking...

The DJI pack's prongs are obviously not a direct connection to the battery. There are semiconductors governing that connection. There will be a voltage drop across those semiconductors. I'm not sure what kind of semiconductors, so I don't know the drop. But I wonder if and how that gets accounted for with a LiPo charger.

The good news is that from the charger's POV that drop is effectively divided by the number of batteries so the effect may not be so severe. But it's going to make the charger see a slightly smaller voltage from the battery than what it's looking for. That may also change the current delivery, if the charger compensates.

It would be interesting to measure differences in potential between the exterior prongs and the wires going to the batteries, throughout the charging cycle.

 

[solentlife]

Andy - you are working this up into some mega item ...

The charger is set to Lithium High Voltage ... LiHv and 4S charge mode .. That sets the charger to stop at 17.4V - which matches the battery circuit board.

In fact what happens is the batterys board cuts off just before the charger ... if working ... if not then charger does it.

The fact that board is fitted to battery leads makes no difference to charger.

Nigel

 

[Bad Andy]

I'm not making a "mega item" out of anything, Nigel.

Neither of us have seen a schematic diagram of the circuit boards in a DJI pack. Neither of us know its electrical characteristics.

The pack's board may introduce a voltage drop.

How much?

What is the impact to charging from a smart charger that is looking for a particular voltage?

If the pack's board cuts off first, probably nothing. I think it is telling that the pack cuts off first. The charger may not be seeing the target voltage due to the pack's board.

It remains an unknown.

 

[solentlife]

The charger displays the voltage and it agrees with terminating level.

It really is simple. It works !

Nigel