How to build your own automatic and programmable 6S discharger

[gbrockway]

To answer this question. Are there any devices that can emit energy, in large amounts, that is not heat?
I think a battery, flywheel, air compressor, etc. would be about the only thing. Store the energy for later. Then you are moving it. Not using it up.
My PowerLab 8 can charge a Battery with the energy from discharging the Lipo. The PowerLab 8 can discharge at 1,000 watts. The issue is you need a battery that is low enough to take the charge.
To make this yourself you would have to limit the current somehow.

[CyprusDave]

The Powerlab 8 can discharge at 100 watts internally, ie in a way similar to Raf's device. It can discharge externally at 1000 watts by using the lipo being discharged to power the charger to charge a battery (external regenerative discharge). Then you have another battery to discharge

[redbird300]

Originally Posted by redbird300

1. The general idea:

....I am not talking about regenerative discharge into a car battery here, as this involves even more work to hook it all up. It allows for high currents, but I looked for another solution.....

[redbird300]

Andrew, the strongest high power LEDs take 3 Watts at most, producing around 120 lumen each, but only when properly cooled, they are usually delivered on their own mandatory heatsink, or they would be destroyed in seconds. To achieve a 100 Watts of discharging power you would need like 33 of these LEDs, and they really don’t come cheap. The Luxeon 3 Watt LED sells for around 10 euro a piece down here, heat sink included.

To be honest, I don’t know of any fairly compact, silent and non-heat producing method which involves no moving parts to dissipate these amounts of energy. I would have tried it otherwise. Even looked into Peltier elements, which is basically an electronic heat pump, and stuff like that.

About your dilemma: I would choose to charge the packs a little faster, instead of having them laying around fully charged for a long time, at least that way you’re following the manufacturers guidelines. At condition that your packs allow a 2C charge rate, but most of them do allow that nowadays.

[mnwizard]

Wow! Outstanding work Raf!

[sutty]

Thanks Raf, that was the advice I was looking for, and that is what I will do from now on. I'll wait until 1 hour before I plan to fly, and then charge them all up at 2C, which they can indeed accept. I have two chargers, each with two channels, so that will do four batteries in less than half an hour, as from storage to fully charged at 2C should in theory only be about 15-20 minutes, right? So including balance time about half an hour max. I can then repeat for my other four batteries, giving me all 8 of my batteries in around an hour. Doesn't sound too bad, and is probably manageable.

Cheers

Sutty

[jperkosk]

Personally after spending a few hours trying to research the subject I decided that the information supporting the claim that the LiPos need to be discharged to storage level is inconclusive, so I will continue storing them fully charged, just making sure they're not laying around in a hot place.

Mind you, my biggest LiPos are 3S 2200mAh, so if I shorten their life span it won't cost me arm and leg...

The bottom line is I'm unwilling to wait for a battery whenever I can get a half an hour flight time on a moment's notice, In my opinion they should be waiting for me, not the other way around

[redbird300]

Originally Posted by jperkosk

Personally after spending a few hours trying to research the subject I decided that the information supporting the claim that the LiPos need to be discharged to storage level is inconclusive, so I will continue storing them fully charged, just making sure they're not laying around in a hot place.

Mind you, my biggest LiPos are 3S 2200mAh, so if I shorten their life span it won't cost me arm and leg...

The bottom line is I'm unwilling to wait for a battery whenever I can get a half an hour flight time on a moment's notice, In my opinion they should be waiting for me, not the other way around

Found this on Wikipedia, perhaps that risk of delamination might be a reason why manufacturers advise us not to keep them fully charged ? If you think about it well, it's their own fault, they should make the casing stronger, like these RC car type of batteries that we never use in our helis. But that adds weight, I guess.

Cells sold today as polymer batteries are pouch cells. Unlike lithium-ion cylindrical cells, which have a rigid metal case, pouch cells have a flexible, foil-type (polymer laminate) case. In cylindrical cells, the rigid case presses the electrodes and the separator onto each other; whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.
Since individual pouch cells have no strong metal casing, by themselves they are over 20% lighter than equivalent cylindrical cells. However, all Li-Ion cells expand at high levels of SOC; if uncontained, this may result in delamination, and reduction of reliability and cycle life; the case of cylindrical cells provides that containment, while pouch cells, by themselves, are not contained. Therefore, to achieve the rated performance, a battery composed of pouch cells must include an overall, strong, external casing to retain its shape.

http://en.wikipedia.org/wiki/Lithium...attery#Storage

[jperkosk]

That's the effect we know as "puffing", isn't it? So far the only time my Lipos slightly puffed was when I left them too close to a window on a very warm and sunny day back home, and that didn't reduce their apparent capacity at all.
So I moved the storage place to always shaded area in the heli room, I do the same in all kinds of hotels when I travel, and never saw this puffing again

[redbird300]

And what to think about this quote ?

In a nutshell, the lithium batteries have 3 components which make them work. A cathode, made out of either lithium, manganese, and oxygen, or lithium, cobalt, and oxygen, an anode made out of lithium and carbon held in a semi-liquid state, and a separator between the two made of a special polymer soaked with a conductive electrolyte. A chemical reaction between the cathode, anode, and electrolyte causes electrons to flow, giving us electricity.

The typical cause of puffiness is either age, or abuse (or a combo of the two.) As the cells are used, the anode naturally degrades, producing oxygen and leaving the Lithium and other element in a useless state. In addition, as usage goes along, the cathode slowly starts to produce metallic lithium. The oxygen produced by the anode bonds to the metallic lithium produced by the cathode, again limiting cell usability, and creating lithium "rust." However, the anode produces oxygen faster then the cathode produces metallic lithium for it to bond to. This means that the oxygen has nowhere to go, and pressurizes the cell, making it puff out.

BTW Jerry, almost all my packs start puffing near the end of their lifecycle, no matter what brand. So I guess what's mentioned above could make sense ?

[sutty]

I just completed a test where I took 2 of my 450 batteries from storage to fully charged in 27 minutes. This means I will be able to get from 0 to all 8 batteries charged, within an hour, if I already have them at storage charge before I begin. Perfect result, and as predicted, so I think this is the way to go.

Not sure if the jury is still out on this or not Jerry, everything I had read to this point had been that it is detrimental to keep them fully charged, so I will use this approach from now on. I feel sure it isn't going to do them any harm.

Cheers

Sutty

[jperkosk]

Originally Posted by redbird300

BTW Jerry, almost all my packs start puffing near the end of their lifecycle, no matter what brand. So I guess what's mentioned above could make sense ?

Yes it rings true. I'm not enough of a chemist to confirm or contradict any of this, but it all refers to normal life-cycle deterioration, it says nothing of permanent negative effects of storing the battery fully charged. Your experience seems to confirm this. Basically, Lipos will deteriorate at the end of the life-cycle no matter what and they will puff.

Originally Posted by sutty

Not sure if the jury is still out on this or not Jerry, everything I had read to this point had been that it is detrimental to keep them fully charged, so I will use this approach from now on. I feel sure it isn't going to do them any harm.

My point Sut is that what I do know is that Lipos have a limited lifetime measured in charging cycles, and that in fact holds true no matter what battery type. There are chemical processes involved in charging-discharging that make the battery deteriorate over the time. So within normal use limits the Lipo will take maybe 500 80% charge-discharge cycle, or 1000 40% charge-discharge cycles before it has deteriorated, right?

So my feeling is that deliberately discharging your Lipo to 50% is taking away a half charge-discharge cycle out of its lifetime, and I haven't found (or experienced) any evidence that storing them @ 100% actually harms them.

My current thinking based on what I found so far:

1. If you expose charged Lipos to heat the self-discharge rate goes way up really quick, to the point that it can get dangerous to the battery's health and in extreme cases, even to the surroundings. At lower voltage the discharge current will be less likely to damage the battery even if stored improperly.
2. Because of polymer (read plastic) cell containers the batteries are way more susceptible to mechanical damage compared to metal encased batteries of most other types. Shipping/transporting them fully charged is a much bigger safety risk, there is much more energy that a damaged battery will release. I bet you everyone would be recommending a 0% storage level if it weren't for a known fact that the Lipo doesn't survive these discharge levels.
3. So based on 1 & 2 above I think if you make sure you store your Lipos @ <25°C (not a very difficult task), and treat them gently while handling (difficult in crash, though ) they will actually give you more flying time when stored (properly) @ 100%, and you can keep them ready-to-go as an extra benefit . The whole "storage level recommendation" smells a lot like a strictly safety related issue rather than something aimed at maximizing your battery lifetime. Nobody sued any manufacturer yet for getting 300 cycles rather than 500 out of their Lipos, did they? On the other hand, it the battery bursts in flames... You get the picture.

Now, this is strictly my opinion based on the absence of any valid evidence to the contrary, which may or may not be correct. I haven't done any scientifically valid trials to validate my opinion, and I take no responsibility if your battery bursts in flames because you followed my line of thinking rather than manufacturer's recommendation .

For my part, however, unless the real evidence emerges, I will store my batteries 100% charged, ready to fly on a moment's notice, making sure they sit in their metal box on a shelf where they'll never get hit by a direct sunlight far away from the edge so they can't accidentally be knocked down .

Does it make sense to anyone, or I'm completely out my mind here?

[CyprusDave]

Jerry, IMHO it all makes sense. Particularly, I think you have a very valid point about which is more damaging - leaving fully charged, or increasing the charge cycles by discharging when not used.

Your point that all batteries have a finite life measured in charging cycles is very valid, probably about the only thing that's not in dispute

[sutty]

Agreed, I had been aware that by discharging them to 50%, if I failed to fly, meant that I was creating an additional part cycle, and that concerned me too. It felt like I was just wasting one of my cycles, which of course I was. However my understanding had always been that it was worse to leave them fully charged.

Every article I have read about battery care suggests keeping them at 50%. Perhaps this is now a kind of folklore but the original reasons why this came into being may well be for the reasons you described, i.e. don't keep them flat, as they could then easily decay below their safe discharge level, which is known to cause problems, so that seems reasonable, and don't keep them full because they are more dangerous, and more likely to suffer damage due to high temperatures, again seems reasonable.

As you say, I don't know either if I have ever read how keeping them fully charged actually causes cell degredation, apart from where high temperatures are involved, which as you rightly say is fairly easy to avoid.

The only evidence I personally had, if you can call it that, was that I left all my little batteries for the mCX and mSR fully charged. When I came to use them a few months later they were nowhere near as good as they used to be. Temperatures had not been excessive, since as you are no doubt aware 20 C is a hot summers day for us here in the UK, lol. Not hard evidence I know, as these little batteries are not the best quality, etc, and may well have degraded, just as significantly, if they had just been sitting there at 50% the whole time.

Still, the new plan avoids all those 'possible' problems, since I won't be charging them unless I am going to use them. I can cope with an hours delay.

Cheers

Sutty

[jperkosk]

Funny that you mention mSR batteries, Sut, I have noticed the same effect...
But they never puffed, did they? And with eFlight charger you have no option other than either leave them empty or fully charged, so I think you're correct on the second part as well: they're just crappy.

Safety concerns are very legitimate, and I'm not about to disagree with anyone who discharges his Lipos to storage level for safety reasons, this is especially true for those scary 6S (and bigger) packs.

It just doesn't jive with me that the manufacturers are trying to scare us into safer behavior by presenting false claims related to battery lifespan, which I think is what's happening on the subject. No real conspiracy here , just a case of choosing legally easier path, that's all.

[sutty]

No they didn't, so crappy it is.

Cheers

Sut

[redbird300]

While I'm waiting for some parts, I started to work a bit on the housing of the electronics, it will probably look like this:

Balance and main connectors for the pack at the left side (hey, I'm lefthanded ), and at the top the banana connectors for the resistors on the heatsinks, which will be at the right. These connectors are not necessary, but if ever something would go wrong, I could simply pull hem out in a second. Or if I would ever decide to change the resistors or heatsinks...whatever, lol.

A push button to start discharging, and that ugly light bulb has been replaced by a small red LED. Still wondering if it's worth to build an amp meter on the front, above the Cell-Log, or not. Well, I have the room for it, but can always do it later. Need to add some labels, and it will be OK.

[chansen1953]

hi Raf,

Well
I have built my 6s discharger,, and it sort if works.. I have a few questions..
1. my batts usually start off with about 4.15v average per cell when fully charged
2. after flying for my 5m30s , I land and they are at about 3.8V average..
3. so what voltage should I set the cell-log -discharger at... ??

is it ok to just leave the batteries at the 3.8V level till my next charge.... which is in fact very close to the recommended "storage" level ??

I guess the discharger can be used to take a fully charged battery to the 3.8v storage level if you know you will definitley not be using them for in the next 7 days or more ?

btw.. for some reason, the discharger will not automatically start -- no matter which way I set the cell-log alarm -- either NO or NC ,,,
I have the resistive load across the "NO" contacts, and unless I short the +ve alarm wire to the -ve pole, the relay wont trip... its as if the ALM port is not working.. !!
any ideas ??

[EatMorePizza]

amazing raf. I cant wait to get back home and try one. As an enthusiastic electronics kit builder this will be great to try.

I just hope hobbyking wont start selling your creation.

[redbird300]

Originally Posted by chansen1953

hi Raf,

Well
I have built my 6s discharger,, and it sort if works.. I have a few questions..
1. my batts usually start off with about 4.15v average per cell when fully charged
2. after flying for my 5m30s , I land and they are at about 3.8V average..
3. so what voltage should I set the cell-log -discharger at... ??

is it ok to just leave the batteries at the 3.8V level till my next charge.... which is in fact very close to the recommended "storage" level ??

I guess the discharger can be used to take a fully charged battery to the 3.8v storage level if you know you will definitley not be using them for in the next 7 days or more ?

btw.. for some reason, the discharger will not automatically start -- no matter which way I set the cell-log alarm -- either NO or NC ,,,
I have the resistive load across the "NO" contacts, and unless I short the +ve alarm wire to the -ve pole, the relay wont trip... its as if the ALM port is not working.. !!
any ideas ??

Yes Chris, anywhere between 3.7 and almost 4 Volts will be OK. That's exactly what I do: fly and let the batteries sit there until the next charge, without doing anything with them. The discharger is indeed only ment to discharge full packs. Set the Cell-Log at around 3.8 - 3.85 Volts in that case, but as said, this isn't critical at all.

I don't know if I understand your problem completely, but start by checking the wiring, andf next ALL the settings in the Cell-Log: there are menus to set values and how it should operate, but also a menu to simply activate it ! Sounds like it is not active ? So please tell me all the settings, refer to the manual, some menus are hard to find. Don't mess with the alarm wires, the alarm output is not protected, and can be blown up, ask me about it, lol. If that doesn't help, get back and we will check a few more things.

Oh, and we want some pics, or I will refuse to help you any further !