DIY Lipo Discharging

[Julian Murch]

I am considering making a DIY Lipo discharger for 3S batteries using a 12 volt auto bulb.  Presumably the greater the wattage the sooner it will discharge the unit but is there a maximum to avoid damaging it?

[Keith Berriman]

Hi Julian   the only SAFE  way to discharge a LIPO Battery to a safe storage level is with  discharge selected on a Lipo charger 

Opting for a 12 volt bulb to discharge a battery is to take it down to 0 volts for Disposal

even then this has to be watched from a distance incase the battery wants to self destruct its self 

[Don Fry]

43 minutes ago, Keith Berriman said:

Hi Julian   the only SAFE  way to discharge a LIPO Battery to a safe storage level is with  discharge selected on a Lipo charger 

Opting for a 12 volt bulb to discharge a battery is to take it down to 0 volts for Disposal

even then this has to be watched from a distance incase the battery wants to self destruct its self 

Why, it’s a battery, not a hungry bear in the woods. Chuck it in a bucket, with the bulb outside and leave it, to die, outside the house.. A 24 volt lorry bulb is better, can do  up to 6s batteries. A brake light, 24 watt is good. 

Mind I’ve never found a waste site give a monkey if the pack is charged or not. In two languages it goes, that’s why the bin is thick steel, alone, with ventilation.  That is the easy option.

[Simon Chaddock]

Julian

In you original post you don't make it clear if you are trying to discharge for 'storage' or discharging for 'disposal'.

For storage it must be done to a 'storage' voltage which has to be balanced so it is equal for each cell A decent LiPo charger will have this facility.

Discharge for disposal is not so critical. Limiting the amps to a 1C maximum should be safe enough but it will still take some time as the amps will fall away as the cell get fully discharged.

[i12fly]

The charger discharger is just too long winded for me.

If I want to discharge for storage I use an edf model and run it on third to half throttle and monitor it on the checker. Through experience you soon find how low to take it as the battery 'recovers' somewhat after taking off the load.

For scrapping a battery I run it through an indicator bulb, outside in a safe place, it is then well and truly dead.

[MattyB]

Lots of threads on this already - here’s a good one. Tbh there is no need to build your own, you can buy an excellent discharger that will balance and discharge med and small packs for storage for a very low price. You can even use them in parallel to create a really high power discharger for large packs of up to 6S. They even have audio alarms to let you know you once the packs reach the target voltage.

Discharger unit:

http://www.myrcmart.com/rcx-3in1-battery-balancer-discharger-voltage-indicator-150w-discharging-p-4767.html

 

RCGroups thread in how to parallel them up:

https://www.rcgroups.com/forums/showthread.php?2406395-An-effective-variable-load-automatic-LiPo-discharger

 

Edited October 27, 2021 by MattyB

[Julian Murch]

This advice is for storage.  I do have a Skyrc100 balance charger which has a 'storage' setting but that is only to charge up to storage it does not discharge from full.  I also have a 'batguard' but that takes hours to discharge a full battery.  

[Shaun Walsh]

How about one of these

ISDT discharger

or these

ISDT Discharger

Edited October 28, 2021 by Shaun Walsh

[MattyB]

38 minutes ago, Julian Murch said:

This advice is for storage.  I do have a Skyrc100 balance charger which has a 'storage' setting but that is only to charge up to storage it does not discharge from full.  I also have a 'batguard' but that takes hours to discharge a full battery.  

 

In that case the the 3 in 1 discharger unit I linked is a nice fit for you - if you need more discharge power just buy 2 or 3 units and connect them up in parallel as per the RCGroups thread.

 

33 minutes ago, Shaun Walsh said:

How about one of these

ISDT discharger

or these

ISDT Discharger

 

Those are probably fine (ISDT chargers certainly seem to have a good rep in general), but they are a lot more expensive, especially if you need more than 200W discharege power. Admittedly you don't need to make the lamp holder case and do any oldering though (though weirdly I rather enjoyed that part of the project...!)

 

Edited October 28, 2021 by MattyB

[Colin Carpenter]

I use 2 halogen 2 pin lamps in series. Just monitor as you go ! Cheap ! About a quid ! Colin 

[Simon Chaddock]

Ju;ian

According to my reading of the Skyrc100 balance charger V1 manual it has a "storage" function which on page 17 specifically says it balance charges a Lithium battery down or up to a storage voltage per cell, just as does my ImaxB6.    

[leccyflyer]

19 hours ago, i12fly said:

The charger discharger is just too long winded for me.

If I want to discharge for storage I use an edf model and run it on third to half throttle and monitor it on the checker. Through experience you soon find how low to take it as the battery 'recovers' somewhat after taking off the load.

For scrapping a battery I run it through an indicator bulb, outside in a safe place, it is then well and truly dead.

Spot on - we're each equipped with very efficient dischargers with wings, if you really must discharge your packs. As you said the packs rebound slightly once they come off load - you can connect a battery checker to the balance leads and model the cell voltage during the motor run. It's important to ensure adequate motor cooling and restrain the model properly.

[MattyB]

7 hours ago, Simon Chaddock said:

Ju;ian

According to my reading of the Skyrc100 balance charger V1 manual it has a "storage" function which on page 17 specifically says it balance charges a Lithium battery down or up to a storage voltage per cell, just as does my ImaxB6.    

Yep, looks that way though I suspect it will be a very slow process - the v2 version of that charger only has a max discharge rating of 10W/channel. This is why I never recommend people use the discharging function on chargers unless they have a large leisure battery or similar that can act as a sink; asking your (often fairly expensive) charger to dissipate that energy over long periods of time is bound to shorten the life. For instance the fan will be running constantly during discharge cycles (my iCharger rarely runs the fan on charge cycles, other than when operating at or near peak power).

[MattyB]

7 hours ago, leccyflyer said:

Spot on - we're each equipped with very efficient dischargers with wings, if you really must discharge your packs. As you said the packs rebound slightly once they come off load - you can connect a battery checker to the balance leads and model the cell voltage during the motor run. It's important to ensure adequate motor cooling and restrain the model properly.

Each to their own, but if I arrive home with a set of packs at full charge (which can happen if plans or weather change) and I’m not flying again in the immediate future I find it far quicker and safer to use my 350W discharger, especially with young kids around. There is no need to have to restrain a model or worry about cooling motors or ESCs either.
 

Just connect up, chuck the packs in a liposack and press one button (or 3 if the full 350W is required). There is obviously a tiny possibility of burning your fingers on the bulbs if you’re careless (at full power it will warm a cold room if it’s not that big!), but apart from that it’s very low risk, especially as you can tune the discharge rate. I never go beyond 2C which is a very light load for even an ageing lipo.

Edited October 29, 2021 by MattyB

[leccyflyer]

4 hours ago, MattyB said:

Each to their own, but if I arrive home with a set of packs at full charge (which can happen if plans or weather change) and I’m not flying again in the immediate future I find it far quicker and safer to use my 350W discharger, especially with young kids around. There is no need to have to restrain a model or worry about cooling motors or ESCs either.
 

Just connect up, chuck the packs in a liposack and press one button (or 3 if the full 350W is required). There is obviously a tiny possibility of burning your fingers on the bulbs if you’re careless (at full power it will warm a cold room if it’s not that big!), but apart from that it’s very low risk, especially as you can tune the discharge rate. I never go beyond 2C which is a very light load for even an ageing lipo.

I posted my reply before seeing any details of your home brew discharger, so I'm not referring to that, merely agreeing with i12fly. As you say, to each his own and I don't routinely discharge unused  packs if I'm likely to be flying the next weekend, or even the weekend after.

 

If I know that I won't be flying for a month or so then I'll probably take steps to take unused packs down to 3.85v/cell. For me, the most obvious way to do that is to emulate how those packs would be discharged in use, taking a few minutes each. I don't have any worries in running a model whilst restraining it in a model stand for a few minutes, nor do I have any youngsters about. I'd be more worried about having a heat source sitting on the workbench for hours, discharging multiple packs - I wouldn't want to leave such an apparatus unattended indoors personally.

[Simon Chaddock]

I agree discharging a full battery through a charger can be a long process.

I usually put the battery on 'storage' charge after any flight. If you have judged the flight time correctly to be kind to the battery it should not be far from storage anyway.

In addition the initial cell voltages shown can give an indication of any cell 'weakness' and you know each cell will be taken to exactly the storage voltage.

It works for me. 

[MattyB]

15 hours ago, leccyflyer said:

…I'd be more worried about having a heat source sitting on the workbench for hours, discharging multiple packs - I wouldn't want to leave such an apparatus unattended indoors personally.

As long as the unused packs are all of the same cell count (which they generally tend to be; it’s rare that I take planes to the patch that require any more than 2 different sizes of pack) I can discharge them outside to storage in ~20-25 mins, not hours. I generally do that whilst tidying stuff away on arriving home. Alternatively I just discharge in whatever room I need to be in as the discharger is very small and light and requires no other power supply. I carefully check cell voltages and IR each time I connect so the risk of something going wrong whilst discharging at such low currents is very, very low, but if it did the setup would always be in the same room on a tray so I could whisk it out of the house as needed.

Edited October 29, 2021 by MattyB

[Simon Clark]

For electric flight, I charge the batteries at the field as I need them. At the end of a day's flying I often have one or two batteries charged that i will not fly that day - then I discharge to storage on my iCharger 4010 duo in about ten minutes (whilst I pack everything else away). 

 

However, if flying i.c. I also use Lipos for RX packs, ignition batteries, glow batteries and engine starters so i can have quite a few batteries left at the end of the day in need of discharging to storage voltage. For these I simply plug in one of these to each and leave on the bench until done.:

 

https://www.droneauthority.co.uk/products/vifly-storesafe-discharger?_pos=3&_sid=c81844101&_ss=r

 

It might take a few hours for some, but the heat generated is very low so perfectly safe to leave.

 

Simon

 

[Julian Murch]

To answer the post from Matty B,  page 17 of my manual relates to pb lead-acid battery use. The unit is T100 if the 'T' makes a difference.  There is a sticker on the box relating to Schumacher racing with a UK phone number so I contacted them.  I was told that the unit will only charge up to a storage level so it has to be below that level already.

 

Just to go back to my original post if using some form of bulb to drain the Lipo is there a maximum wattage advised.

[Martin Harris - Moderator]

First consideration is (essentially) watts = heat. The higher wattage, the more heat is generated so ensure it can be dissipated safely. 
 

Your battery will also determine the discharge rate. 1 or 2C won’t do a lot of damage but remember there are a finite number of charge/discharge cycles for any battery so charge management is better than unnecessary discharges. 

[John Lee]

Remember Murphy's Law. 

 

If you just use a bulb it is guaranteed that at the most inconvenient time in the future your attention will be diverted, your Lipo will discharge past the point of no return & it will be ruined.

[i12fly]

5 hours ago, John Lee said:

Remember Murphy's Law. 

 

If you just use a bulb it is guaranteed that at the most inconvenient time in the future your attention will be diverted, your Lipo will discharge past the point of no return & it will be ruined.

That's why I only use a bulb when the battery is to be scrapped. A bulb is not really suitable for partial discharge IMO.

On the few occasions I need to  go to 'storage', as I was saying, I use an edf model, keeps fingers etc pretty safe. At low to medium throttle it only takes a few minutes, I sit with it for 'safety' and discharge to about 70% charged. Maybe this storage level shortens the life a bit but I haven't noticed and the topping up doesn't take long then either. Over winter when likely to leave the batteries in store for a fair while I store at 30-40%.

Last winter due to 'a few side issues' I forgot some and left a few 3s2200 at 80-90% for 4 months. Fortunately no puffing or noticeable loss of power, guess I was lucky.

[leccyflyer]

You mean that they didn't instantly puff up on Day Four? You WERE lucky! ?

[MattyB]

8 hours ago, John Lee said:

Remember Murphy's Law. 

 

If you just use a bulb it is guaranteed that at the most inconvenient time in the future your attention will be diverted, your Lipo will discharge past the point of no return & it will be ruined.

Completely agree - there is just too much risk of killing a pack without some control circuitry to ensure you never get near to or  go below the critical 3V/cell at which damage occurs.

Edited October 30, 2021 by MattyB

[Don Fry]

Very small point, but I’ve just replaced the cabin bulb on my boat.

It was a 4 watt instrument panel bulb, filament bulb, useless light output.

The new bulb, 4 watts, LED,  gives bright office light levels. Cost minimal.

 

But the point is, the bulb, does not care what the input voltage is. I think it states, 6 to 30 volts. I reckon other wattages exist. They would flatten most batteries we use.

BUT AGAIN, if you wish to dispose of an old battery, the disposal site does not care if it’s flat or not. They have disposal systems.