How to discharge portable Lion battery packs to 30% quickly

Thread Starter

Eldon00

Joined Mar 9, 2017
3
Hello, new here and have a question. With the regulations on air transportation of Lion battery packs changing, I'm looking for a way to discharge shipments of 100-3000 units quickly to the required 30% charge prior to shipping. Has somebody come across this already? Is there a machine that does this? A machine that can be built to do this quickly? Thank you all for your help in advance.
 

drc_567

Joined Dec 29, 2008
1,134
Apart from doing a specific analysis, one way would be to fabricate light bulb sockets with clip leads, using an appropriate light bulb. Then time several units to determine an appropriate 'on' period.
This method would insure that an excessive current would not damage the batteries, due to overheating.

If you are talking about the 18650 cylindrical lithium-ion battery, then you might have to employ a battery holder for each individual battery. ... depends on the particular battery you are talking about.

Given sufficient lead time, an array of probes could be constructed, such that a platform of probe tip pairs is lowered and raised onto a group of batteries at specified times, with load resistances on each pair of probes.
 
Last edited:

wayneh

Joined Sep 9, 2010
17,153
That's pretty much what I was thinking of also , except I think you'll want to avoid clips and leads by using some sort of socket in which to load the battery cells or packs.

I second the lightbulb approach because of the visual feedback, self-limiting load, and the natural ability to disperse the heat.

I was wondering how you would monitor the state of charge, but @drc_567 has the solution: Don't. You should be able to run the discharge for a known period of time that guarantees the battery is drawn down from 100% to 30%. It's possible the brightness of the bulb would confirm the lowered state of charge.

You'll want to follow whatever method the authorities will use to validate that your depleted batteries actually comply with the regulation. There's probably a very detailed test procedure. Run your discharge device so that very few (or zero) cells survive to be non-compliant.
 

Thread Starter

Eldon00

Joined Mar 9, 2017
3
Ok, I built several of the light bulb rigs. Simple 6V automotive bulb connected to a USB plug to ease in use. The issue I'm having is that the bulb only seems to work on some of the battery packs. I picked the 6V bulb as it is closest to the 5V of the battery packs. Why would it not work on all units. It's only about 40% of the models that it has worked on. Some 1A and Some 2A outputs so I don't see a pattern.
 

wayneh

Joined Sep 9, 2010
17,153
The only thing I can think of other than a bad connection or a dead battery, is a smart battery that can limit its discharge to only 100mA unless the load can negotiate for a higher current. Do you have something you experiment with, like an iPhone? Do you measure a good voltage from these batteries using a multimeter?
 

drc_567

Joined Dec 29, 2008
1,134
... sometimes sockets have issues involving efficient contact between the bulb center contact/tip and the corresponding socket contact. ... Use a meter to check for continuity. Sometimes there is a central spring-like part that fails to make contact. ... easily fixed.
 

Thread Starter

Eldon00

Joined Mar 9, 2017
3
... sometimes sockets have issues involving efficient contact between the bulb center contact/tip and the corresponding socket contact. ... Use a meter to check for continuity. Sometimes there is a central spring-like part that fails to make contact. ... easily fixed.
I can plug it into 5 battery packs and only 2 will work without moving anything, I have another device that reads the volts and amps that passes through and as soon as i connect the light bulb it shuts off as if there is no current. unplug that and connect to another battery pack and everything works fine. it's very bizarre that it is only occurring sometimes and not others.
 

ian field

Joined Oct 27, 2012
6,539
Apart from doing a specific analysis, one way would be to fabricate light bulb sockets with clip leads, using an appropriate light bulb. Then time several units to determine an appropriate 'on' period.
This method would insure that an excessive current would not damage the batteries, due to overheating.

If you are talking about the 18650 cylindrical lithium-ion battery, then you might have to employ a battery holder for each individual battery. ... depends on the particular battery you are talking about.

Given sufficient lead time, an array of probes could be constructed, such that a platform of probe tip pairs is lowered and raised onto a group of batteries at specified times, with load resistances on each pair of probes.
For test discharging various battery types; I often use bulbs - but they radiate much more IR than resistors and it isn't impossible to set fire to things. Resistors are more manageable, and cooling fans actually accomplish something useful if needs be.

Is there any correlation between the minimum allowable terminal voltage per cell and the required % of charge?
 

Dodgydave

Joined Jun 22, 2012
10,027
I would use a constant current load, the reason for the batteries not giving power out is the internal monitoring circuit is shutting the battery off, at it's minimum voltage.
 
Last edited:

wayneh

Joined Sep 9, 2010
17,153
... as soon as i connect the light bulb it shuts off as if there is no current
... the reason for the batteries not giving power out is the internal monitoring circuit is shutting the battery off, at it's minimum voltage.
Asked and answered.

I don't know the rules, but I suppose a battery that shuts itself off to prevent excessive discharge must be below the charge level you need to achieve? Otherwise that required level is unachievable.
 

ian field

Joined Oct 27, 2012
6,539
from my point of view there is no machine, who can do this
Just out of curiosity - how is it possible for the carrier to determine the state of charge?

If the undervoltage shutdown has kicked in, that should be good enough for anyone, It can't cause a fire by heating an external short, and its unlikely there's enough energy in any cell to cause an "event".
 
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