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Discharging batteries into a power bank

Chris Baish

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Can anyone with an Air 3 and the charging hub answer a quick question?

Is it possible to use the charging hub to discharge batteries into a power bank? I'm aware you can use it to charge other devices, but as the hub only has a single USB C that functions as an in and out port, can you set the hub to discharge into the power bank rather than charge from it?

Used to manage my Mini 3 batteries in this way and it was better than waiting for auto discharge to storage level.
 
@Chris Baish yes it should be possible just put one battery into the hub and connect it to the power banks charging port, and see if the lights on the power bank start to flash, to indicate it is being charged
 
@Chris Baish yes it should be possible just put one battery into the hub and connect it to the power banks charging port, and see if the lights on the power bank start to flash, to indicate it is being charged
Thanks very much for your reply.

On the Mini 3 it was clear which way round it would work as the hub had a 'USB out' port. I'm wondering how this hub (with one port as far as I can see from reviews) would determine whether you want it to charge the Air 3 battery with the powerbank, or vice versa?
 
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@Chris Baish i believe the hub is able to tell whether a load, or charge is being requeted ,by what is plugged into it at the time ,thats a so called inteligent part of the hub i guess
 
It could get more complicated if the power bank also has a dual-role USB-C port, leading to inconsistent behaviour across different devices, or even random charge direction.

Some devices may have a setting to toggle the direction. If not available, a hack is to attach two cable adapters to USB type-A, OTG-like for the source. The charge current may be sub-optimal though, as Power-Delivery negotiation between devices can no longer be performed.
1696610640161.png
 
This is the weakest part of the PD spec, and I'll bet it gets addressed in 4.0.

As it stands right now, connecting two dual ports together will randomly pick a source and sink, based on the outcome of a race condition on the CC pin. It might not seem random when using the same two devices and cable, because as race conditions go, it's likely to come out the same over and over again with the same physical devices.

Sometimes this will work out so that the second device plugged in will more often than not acquire the sink role just because of CC pin timing, but it's no guarantee.

So using a power bank to charge another power bank is completely safe, the two devices just may not cooperate and have the one you want to recieve the charge instead act as the charger, frustratingly over and over again.
 
It could get more complicated if the power bank also has a dual-role USB-C port, leading to inconsistent behaviour across different devices, or even random charge direction.

Some devices may have a setting to toggle the direction. If not available, a hack is to attach two cable adapters to USB type-A, OTG-like for the source. The charge current may be sub-optimal though, as Power-Delivery negotiation between devices can no longer be performed.
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Thank you. This is really helpful. I wonder whether it is possible to get adaptors which will work at 65w plus?
 
This is the weakest part of the PD spec, and I'll bet it gets addressed in 4.0.

As it stands right now, connecting two dual ports together will randomly pick a source and sink, based on the outcome of a race condition on the CC pin. It might not seem random when using the same two devices and cable, because as race conditions go, it's likely to come out the same over and over again with the same physical devices.

Sometimes this will work out so that the second device plugged in will more often than not acquire the sink role just because of CC pin timing, but it's no guarantee.

So using a power bank to charge another power bank is completely safe, the two devices just may not cooperate and have the one you want to recieve the charge instead act as the charger, frustratingly over and over again.
Thanks for your detailed reply. This makes sense and, without the technical knowledge behind it, what I thought might be the outcome.

There does seem to be a button on the charging hub, so I wonder whether this serves as a function button to determine whether it's input or output?
 
@Chris Baish ,a full explanation of the charging hub functions can be downloaded direct from the DJI site ,but yes once you have put a battery in the hub and connected up the device you want to charge ,then a quick press of the function button you mentioned is needed to start the process
 
Can anyone with an Air 3 and the charging hub answer a quick question?

Is it possible to use the charging hub to discharge batteries into a power bank? I'm aware you can use it to charge other devices, but as the hub only has a single USB C that functions as an in and out port, can you set the hub to discharge into the power bank rather than charge from it?

Used to manage my Mini 3 batteries in this way and it was better than waiting for auto discharge to storage level.
Just wondering if there is anyone with the Air 3 charging hub and a powerbank who could kindly test this original query before I commit to buying? I know how it functions to charge devices, but nobody has yet been able to confirm definitely whether you can discharge batteries into a powerbank or whether it always defaults to charging the batteries.
 
I just purchased a power bank hoping to use when out to recharge A3 batteries. Found that when I plug the charge hub holding my batteries to the power bank USB- C in/out port that can charge up to 100w on the power bank, it is taking charge from the batteries to the power bank and not from the power bank to the batteries. Also I don’t have to hit the function button on the Air3 charging hub either - just starts when I plug it in. I can use the 22w ports that only go out from the power bank which kind of defeats the purpose of wanting a fast charge. I can trick the 100w port by using the adaptor mentioned above by “air4” but it significantly slows the charge (again defeating the purpose). Interested in a solution anyone has where there is a reasonably priced power bank with 100w charging USB-C out only port ($70 or less).
 
I just purchased a power bank hoping to use when out to recharge A3 batteries. Found that when I plug the charge hub holding my batteries to the power bank USB- C in/out port that can charge up to 100w on the power bank, it is taking charge from the batteries to the power bank and not from the power bank to the batteries. Also I don’t have to hit the function button on the Air3 charging hub either - just starts when I plug it in. I can use the 22w ports that only go out from the power bank which kind of defeats the purpose of wanting a fast charge. I can trick the 100w port by using the adaptor mentioned above by “air4” but it significantly slows the charge (again defeating the purpose). Interested in a solution anyone has where there is a reasonably priced power bank with 100w charging USB-C out only port ($70 or less).
Im afraid I dont have a solution for you, but an observation that I have now bought the Air 3 and I have the opposite to what you have. My powerbank will charge the batteries but I can't get it to work so that the batteries will discharge into the powerbank. Wonder what determines this? My powerbank has a 60w maximum output. Happy to share a link to it. It's a few years old.
 
Im afraid I dont have a solution for you, but an observation that I have now bought the Air 3 and I have the opposite to what you have. My powerbank will charge the batteries but I can't get it to work so that the batteries will discharge into the powerbank. Wonder what determines this? My powerbank has a 60w maximum output. Happy to share a link to it. It's a few years old.
Is the port you’re using an in/out port (same port for both in and out)? My 100 watt port is both - others are just out. The in/out port routes the charge from A3 batts to the power bank. Got this for $45 on Prime Days sale, but thinking I’ll be returning it if can’t use to fast charge A3 batts when out.
 

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Is the port you’re using an in/out port (same port for both in and out)? My 100 watt port is both - others are just out. The in/out port routes the charge from A3 batts to the power bank. Got this for $45 on Prime Days sale, but thinking I’ll be returning it if can’t use to fast charge A3 batts when out.
Yes it's a two way USB c PD port which I use to charge the power bank, but it also outputs power too.
 
The concept of charging a power bank with a power bank at first blush seems nonsensical (just use the charged powerbank for whatever the application is).

No one envisioned a multipurpose device like the A3 charge hub.

Surprise surprise, standards committee 😁😁😁
 
The concept of charging a power bank with a power bank at first blush seems nonsensical (just use the charged powerbank for whatever the application is).

No one envisioned a multipurpose device like the A3 charge hub.

Surprise surprise, standards committee 😁😁😁
It's for situations when you charge your drone batteries but for whatever reason don't end up flying. I live in Cornwall and the weather changes every hour. Personally I prefer to bring them back down to storage level quickly rather than waiting for days for the auto discharge. It's a lot easier with a large capacity powerbank to offload the charge into than finding numerous devices that happen to need charging!

This way you can manage the battery charge really effectively.
 
How about connecting a load to the dji battery hub to discharge the dji batteries to 50% for example? There are usb fans or usb lights that would consume power. With multiple drones and batteries, I can easily ran out of other devices to charge.
 
How about connecting a load to the dji battery hub to discharge the dji batteries to 50% for example? There are usb fans or usb lights that would consume power. With multiple drones and batteries, I can easily ran out of other devices to charge.
Sounds good, but how do you know when to stop the discharge so the batteries don’t get ruined? say I put a load on the pack, do the batteries know when to stop output So that they have a storage charge only, or will the load just suck all the juice out of them below the normal lipo storage voltage?
 
Sounds good, but how do you know when to stop the discharge so the batteries don’t get ruined? say I put a load on the pack, do the batteries know when to stop output So that they have a storage charge only, or will the load just suck all the juice out of them below the normal lipo storage voltage?
You just have to keep an eye on it. The charging lights on the battery show the charge level reducing the same as they do when in the drone. I normally stop it when there are two lights on and the third light flashing. Only have one battery in the hub at any time and keep checking it. No way to set the discharge level.
 
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