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150W Discharger - Printable Version

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150W Discharger - disoriented - 11-11-2014

I tend to crash or suffer miscellaneous mechanical mishaps only on days when I've brought lots of charged lipos to the field. That leaves me with a sackful of charged batteries, and nothing but the puny 20 watt discharging capacity of my iCharger 206B to bring them all back down to storage (3.85V/cell) level.

It takes around an hour to discharge a 3S 2200mAh pack in that manner. Last Saturday I had 17 such packs with me. I went through 6 before my Trex 450 developed a strange tail wobble, which put an end to heli fun for the day.

Now, squeezing 11 hours of discharging into 6 hours before bedtime poses some serious logistical difficulties. Even worse, the only way the charger can bleed off all that energy is to heat itself up, and let its 40mm fan whirr itself to oblivion. It's slightly abusive to the charger, and that has always made me uneasy.

(With the iCharger line it's possible to add an external power resistor, but there are drawbacks which are "beyond the scope of this article".)

Enter the 150W $20 discharger from RCX:

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

It uses three 50W halogen globes to handle discharging duties, which means a full 3S2200 pack is back down to storage voltage in minutes - about as long as it takes to fly it.

Here is what it looks like in action:

   

Needless to say, I forgot to take a photo during the pretty stage when the lights were all aglow Smile

The unit came with a Deans plug. Being an XT60 aficionado, I decided to unsolder the Deans plug and replace it with an XT60 on a pigtail. This photo shows the location where the Deans plug was originally soldered:

   

Overall, I'm very pleased with this discharger, and I'd recommend it to anyone whose OCD makes it impossible to leave lipos charged overnight.

It's quite an accurate 2S-6S battery checker too. I verified its voltage readouts against a lab-grade instrument. It was always within 0.01V, which is very good.

RE: 150W Discharger - symowallo - 12-11-2014

Looks really useful, I wonder if you could discharge in parallel? Ie. using a parallel charging board, in order to discharge a bunch of lipo's at the same time, in parallel.

Saves having to disconnect and connect up the next battery each time.

RE: 150W Discharger - disoriented - 12-11-2014

Sure, parallel discharging is fine. I do it all the time. The usual "parallel" caveats apply:

- cells being hooked up in parallel should be at similar (dis)charge levels. Ideally, no more than 0.1V difference.

- cell count MUST always be the same. (Attempting parallel hookup of say a 3S pack with another that's 4S will result in wicked currents and quite possibly a fire. It must be either all 3S or all 4S, but never a mix.)

- capacity is irrelevant. It's fine to hook up a 3S22000 with a bunch of 3S500 packs, or any mix thereof.

The discharger will only "see" one battery, whose total capacity will be the sum of the individual packs.

RE: 150W Discharger - smuzz - 13-11-2014

Nice bit of research and reporting there Andre!

RE: 150W Discharger - disoriented - 13-11-2014

Thanks Steve. I enjoy battery management. It's like a hobby-within-a-hobby.

RE: 150W Discharger - Flying fisho - 13-11-2014

Does this discharger have the ability to fully discharge a battery to a level that the battery can be legally disposed of in a domestic garbage bin?

RE: 150W Discharger - symowallo - 14-11-2014

(13-11-2014, 06:12 PM)Flying fisho Wrote:  Does this discharger have the ability to fully discharge a battery to a level that the battery can be legally disposed of in a domestic garbage bin?
That is a good point, as it would be very handy. I had to use the "salt water in a bucket trick" this week on a suspect battery.

RE: 150W Discharger - helijeli - 15-11-2014

I have a 12V soldering iron that I soldered a XT60 plug onto the end so I can power it from 3S packs (Could be a chicken & egg scenario here! - obvious used another iron!). (You can also buy these irons from Hobbyking). Effectively makes it cordless and means you could use it at the field.
This is a good way to totally discharge a pack - just leave it plugged in till the Lipo is totally dead. If its a 25W iron, at 12V supply, it draws around (Power = Volt X Current), 25\12 = 2amps, so a 2.2 Lipo would be drained in a little over an hour. When actually using the iron in a normal fashion and wanting to be kind to the Lipo, I have a battery monitor hanging off the balance lead to audibly (& Led display), warn me when the battery is getting low.
My mild OCD also niggles at me when having fully charged Lipos lying about. I currently am consciously aware of 2 charged ones sitting in the metal Cash box I store them in (in the back Fridge). I don't stress too much however - I know they'll get used the following weekend; I wouldn't leave them charged indefinitely, but as long as you store them in the Fridge, minimal damage is being done.
Basically. the theory is:
This is roughly how much storage capacity you permanently lose:
Fully Charged: ambient temp (25deg) - 20% per\year, just above 0 deg (fridge) - 6% per\yr.
Storage Charge: ambient - 4%, Fridge - 2 % per\yr
Temperature has the biggest impact, so as long as you store them in the fridge (don't freeze!), you'll find your Lipo life significantly improved. There are other factor too. You can significantly increase the number of charge\discharge cycles from several hundred to double or more if you don't fully charge to 4.2V\Cell - say 4.1V & don't discharge below 40%. Not very practical though as chargers are designed for 4.2V and most people want max flight times. I do however tend to land around the 40% mark - next charge cycle is quicker also and you're at the storage level if you happen to be finished for the day. Anyway lots of info online about Lipo theory if you're interested.
Funny, I think I looked into all this when I acquired my 4 $50 each 6S, 3.3 Lipos for my 550 Heli and wanted to look after them. Theyre over 3 years old now and I haven't noticed any significant loss in capacity yet. Still landing after 6 or so minutes with 40% capacity left.

RE: 150W Discharger - disoriented - 15-11-2014

(13-11-2014, 06:12 PM)Flying fisho Wrote:  Does this discharger have the ability to fully discharge a battery to a level that the battery can be legally disposed of in a domestic garbage bin?

I checked just now - the minimum setting for the "discharge" mode is 2.00V/cell. While that's basically 99% empty for a lipo, it's not quite totally discharged, and I'd personally be taking other measures to bring it all the way down to zero.

The discharger's own electronics are powered by the pack it's discharging, which is I think the reason its limit is 2.00V.

John's soldering iron trick, or any automotive 12V globe should be fine for fully discharging a 3S battery. A mains-powered charger can do it too.
(14-11-2014, 01:35 PM)symowallo Wrote:  That is a good point, as it would be very handy. I had to use the "salt water in a bucket trick" this week on a suspect battery.

I believe the salt bath method is no longer recommended. As I understand it, the reason is that the tabs to which the leads are soldered can corrode and lose contact before the cell is fully discharged. That leads to a dangerous situation. The battery is electrically dead as far as any circuit or cell checker is concerned, but the lithium polymer medium is still very much full of life and ready to burn if punctured or compressed (like in a garbage truck!).

For disposal, the battery should be discharged down to absolute zero, and then disposed of in the trash. Lipos are relatively environmentally friendly, as far as garbage goes, unlike the cadmium in NiCd cells.
(15-11-2014, 11:16 AM)helijeli Wrote:  This is roughly how much storage capacity you permanently lose:
Fully Charged: ambient temp (25deg) - 20% per\year, just above 0 deg (fridge) - 6% per\yr.
Storage Charge: ambient - 4%, Fridge - 2 % per\yr

I'm certainly no expert, but I believe the main problem with leaving lipos charged is not so much the loss of capacity, but rather the increase in internal resistance.

A lipo is kinda happy to sit long-term anywhere between 3.70 and 4.00V/cell. Resting voltages below that range lead to permanent damage. Whenever the pack is above 4.00V/cell, internal resistance is inexorably increasing.

IR is bad because it makes the battery heat up during current delivery. An ideal battery would have zero IR, in which case it's capable of sustaining infinite current. As IR climbs, power being dissipated by the battery itself rises, and the battery heats up. At around 58 degrees Celsius, the cell starts to vent (puff).

To put it another way, long-term storage of fully charged lipos does not significantly reduce their capacity, but it increases the IR, which is the same thing as saying the C-rating gets lower and lower.

RE: 150W Discharger - riblit - 23-11-2014

It looks like its based on the balancers that are all over eBay, with the addition of the board with the connections to the halogen globes and the battery.

Andre, can you read the details on the three ICs on that board?

John

RE: 150W Discharger - disoriented - 26-11-2014

(23-11-2014, 05:10 PM)riblit Wrote:  It looks like its based on the balancers that are all over eBay, with the addition of the board with the connections to the halogen globes and the battery.

Andre, can you read the details on the three ICs on that board?

John

Hi John, it's a snap lock housing, unfortunately, and I could not pry it open last night. No doubt I'll drop it on a corner soon enough Smile

Yes, you're quite right - externally it is identical to the copy-of-a-copy balancer/discharger which everyone sells, including HK. The only visible difference is the extra connector which leads to the board that drives the globes.

It is significantly more precise than my HK unit (I've got one of those too, bought say three years ago). Voltage readings on the 150W discharger appear instantaneously, which I rather like, as opposed to the HK product that takes 5-10s to show a stabilized reading.

The Junsi cellpro is the worst that I know of in that regard. Very precise and full of features, but near half a minute has elapsed by the time it has finished playing tunes and showing me its splash screen. I just want to know the voltage! No time for pleasantries Wink