Re: (ET) Wanted, information on installing Lithium cells in my EGT 200

[John Jeno <jjjeno hotmail com>]

Refer to evtv.me for detailed LIPOFE analysis. 
As to BMS systems as far as I know they do not monitor each cell.  Rather 
they monitor each battery, which is comprised of many cells. So in every 
case you are the BMS in the end. 

Please keep us informed as to you're experiences with this pack. I need to 
lose mass as well. 

Sent from my iPad

On Jun 1, 2013, at 5:31 PM, "David Roden" <etpost drmm net> wrote:

> On 1 Jun 2013 at 16:31, Barry wrote:
> 
>> I am not using a BMS.
> 
> As you probably know, not using a BMS is controversial.   I don't know 
> of 
> any reputable manufacturer of any lithium-battery product - laptop, 
> power 
> tool, road EV, whatever - that doesn't include at least a rudimentary 
> BMS.  
> However, a few EV hobbyists think that BMSes actually make matters 
> worse.  
> Some even go so far as to blame the BMS for the fires in a tiny handful 
> of 
> conversion EVs.  
> 
> From what I can tell, most or all of these folks are, in effect, acting 
> as 
> their own manual BMS.  
> 
> A popular manual approach seems to be "bottom balancing." Please correct 
> me 
> if I'm wrong, but as I understand it, in this method you find the 
> weakest 
> cell in the battery, and then manually adjust all the other cells' state 
> of 
> charge so that all the cells reach flat at about the same time.  This 
> way 
> you can see the big drop in voltage when it's time to quit using the 
> battery.  (If just one cell went flat, you'd be apt to miss that decline 
> in 
> a full-battery voltage monitor, and you don't have a BMS watching every 
> individual cell.)
> 
> Part of this scheme seems to be that you can never charge the battery to 
> full.  The bottom-balancers argue that the percentage of range they give 
> up 
> by doing this is trivial.  This makes some sense, since the weakest cell 
> in 
> the battery is always your limiting factor.
> 
> With this scheme, when you use the EV, you have to carefullly monitor 
> battery voltage.  When it falls to what you consider to be "discharged" 
> voltage, you have to stop using the EV.  
> 
> There's no "wiggle room" here.  You stop immediately, or risk destroying 
> your battery by over-discharge.  Unlike with a good BMS, which monitors 
> individual cells and shuts down battery output as soon as any one goes 
> flat, 
> there's no hardware keeping you from thinking "I'll just drive one more 
> mile, there's a charger in the plaza ahead," or for an ET, "I'll just 
> mow 
> one more strip of grass."  You have to be watchful and disciplined.  As 
> I 
> said, YOU are the BMS.  Your battery's life is in your own hands.
> 
> Of course you hope that your battery monitor gives you plenty of warning 
> before you reach that critical discharge point.
> 
> I'm keenly interested in this because thus far I have only a little 
> experience with lithium secondary batteries in EVs.  I've used only 
> "prefab" 
> units where the battery comes pre-configured, with BMS and charger.  
> I've 
> had excellent results with that setup.  But it tends to be pricey.  It's 
> definitely more expensive than what you did, buying individual cells and 
> configuring your own BMS-less battery.
> 
> I said above that commercial lithum-battery products nearly always have 
> BMSes, but I HAVE seen a few cheap commercial products that don't.  
> 
> For example, I bought a cut-rate, made-in-Taiwan rechargable crank LED 
> flashlight a few years ago, thinking it would be good to keep in the 
> car.  I 
> also got a second one to keep in my computer room, for lost-screw 
> excursions 
> under the desk.
> 
> The car light was first to quit.  It didn't even last a year.  It'll put 
> out 
> light as long as you crank it, but holds no charge at all.  I suspect 
> that 
> summer temperatures in the car killed the battery.
> 
> The computer room light lasted for about 3 years of intermittent use - 
> which 
> from what I've read is about where even a well-cared-for lithium laptop 
> battery starts to decline.  This, though, was a far steeper decline than 
> any 
> laptop battery I've ever used.  The light is essentially useless.  It 
> barely 
> holds any more charge than the car light did.  
> 
> Both of them are sitting on my workbench.  I suspect that these are like 
> ones that I've since read about on the web, and when I open them up 
> (assuming I find the time to do so) I'll find that the manufacturer just 
> dropped in a lithium battery where a NiCd had been in previous models.  
> My 
> guess is they did this to avoid cadmium disposal responsibility (I think 
> there are laws now about this, at least in the EU).  
> 
> If I'm right, this was definitely a high stress lithium test, and no 
> surprise, lithium flunked.
> 
> Don't misunderstand me, I'm not suggesting that your lithium experiment 
> will 
> turn out like my flashlight did!  But I'll be very interested to hear 
> how 
> well your battery is standing up 5 years or so from now.  I'll also be 
> keen 
> to learn whether your battery monitor consistently gave you enough 
> warning 
> to get you back to your charger before the battery hit the danger zone, 
> and -
> if it didn't - whether you were able to resist that "I'll just mow one 
> more 
> strip" temptation, and willingly pushed or towed the tractor back to the 
> garage.  ;-)
> 
> Good luck, and please keep us posted on how this is working out.  I 
> suspect 
> there are others here who might like to try something similar.  
> 
> 
> David Roden - Akron, Ohio, USA
> 
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