# normal initial charge for LI ?



## GizmoEV (Nov 28, 2009)

I think I put something like 14kWh into my set of 40 when I got them. Remember that you are only putting 0.13A average into each 100Ah cell. That is a very slow charge. Mine didn't take 6 days, however. Probably because I was using a 10A charger.

What is the terminal voltage right now? There is very little energy above 3.4V. I did a test where I recorded current and voltage by hand of a 100Ah cell starting at 3.40V and ending at 4.00V and got at most 0.65Ah into it. Because of the way I calculated Ah this number would error on the high side.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> I think I put something like 14kWh into my set of 40 when I got them.


hhmmm, must be a lot of loss at the plug, and surface charge that is not really sinking IN to the cell....



GizmoEV said:


> Remember that you are only putting 0.13A average into each 100Ah cell. That is a very slow charge. Mine didn't take 6 days, however. Probably because I was using a 10A charger.


my power supply is listed at 10a max. started at about 8amps, and is hovering around 5a all day today. 



GizmoEV said:


> What is the terminal voltage right now?


... well, the power supply is set to 3.7v, and still reads 5amps. If I measure across cells, I get values between 3.36 and 3.38 .... before charging they were all around 3.30


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## dtbaker (Jan 5, 2008)

Lemme come at this from a different angle to get a feel for how long I can expect this charge to take. Lets assume my 100ah cells were only 50% charged from factory, which I think is about where they say they are? If each cell is going to need around 50ah, then if I were charging them SINGLEY with the power supply it would take at least 10 hours and maybe more as the rate slows toward end of charge. Am I on track with this?

Then in parallel, it could take 38* 10 hours (minimum)... like TWO WEEKS! ?!

...and the total kWhr that my meter is showing is not really all getting into the cells, so I might see a total of 12 or 15kWhr at the plug to get the 6 or 7 kWhr into the cells. Correct? or, not?

I am thinking it may be worth my time to temp wire in parallel and pump some juice in with my on-board charger until the pack is 'close' to full and seeing a little voltage rise say up to 3.6v per cell, then go back to the parallel to finish and balance to 3.7 or 3.8 for the final top balance? ....

comments?


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## GizmoEV (Nov 28, 2009)

That could work. When I watch my cells voltage after they reach 3.45V they start rising rather fast. This is with a relatively low current like 6A. (Obviously if you were to pump 100A in them the terminal voltage would be a little higher even though SOC wasn't higher.) While are around to watch the cells you could raise your power supply voltage to a higher value to get the current up so it would charge faster.

As for charge efficiency, these LFP cells are quite efficient compared to lead acid. I would think that as the charge rate diminishes that a higher percentage of the energy coming out of the wall is going to be spent on charger cooling and other "waste" energy than what might be lost while charging at a higher rate. As a comparison, with my lead acid pack I could go 4 miles/kWh out of the wall where as with the LFP cells I go 6 miles/kWh.

If you have a BMS which will tell you when a cell reaches a high voltage point you could just hook up all your cells in series and use your bulk charger to get them to that point and then reconnect them in parallel again and finish it off. Just be careful of that top end voltage. It climbs really fast. Remember, after 3.4vpc will only take about 4 minutes to fill them up to 4vpc if you are charging at a 10A rate so if one cell reaches full ahead of the rest you could end up way over charging it. With my Zivan NG1 it only takes about 10 minutes to finish filling my 200Ah pack once the charger switches into constant voltage mode.


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## Overlander23 (Jun 15, 2009)

Hehe... now you're discovering why I went series with my 5kw charger for a bit, and then back to parallel. 

At 3.7v and 10amps you're only talking 37 watts, and as you mention not all of it is getting into the cells. Even though my charger is capable of 5kw, I only had access to 110v so I was only pumping only 2000w into the series pack. That still took several hours... and then two-three more days of paralleling at 3.8v with my 20 amp Mastech. Otherwise, I was looking a two to three weeks of straight paralleling.

If you go the series route, just be sure to check the cells regularly to prevent any one going above 4.0v. Then, either bypass it, or stop the series charge and wire in parallel again. When I did it, there were a handful of cells that hit first. After bypassing the first three, I rewired in parallel and just let it all sit there on the power supply at 3.8v. But 3.7v works, too.... It's really wherever you want them to all line up, as long as it's at or above 3.6v.


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## dtbaker (Jan 5, 2008)

ok, I re-wired cells in series and hooked up the regular charger (elcon 1500), and it ramped up to 11.5 amps and chugged away. I let it go for about 10 minutes while rounding up my multimeter and then started checking cells individual voltages.... which were all over the map.

The terminals the charger was wired to showed 138v (as expected w/ curve 611), and the charger draw from the wall started dropping from 11.5 as expected. BUT a couple cells were already at 4.0, 4.1, while most of the others were down at 3.55-3.60. So, I unplugged charger before the high cells cooked.

It is now apparent that in addition to my mastech power supply I was planning to use to bring up individual cells on the low side, I will also need a decent, easy, cheap way to drain a little excess off the individual cells that are too high for this initial top-balance. Since there were only a couple high ones, and a lot of low ones, I am thinking it will be way faster to drain a little off the high ones and re-start the pack charger.

Anybody have some great ideas/examples of cheap resistor setup to drain a little juice? Can I just wire up a 100 watt incandescent bulb across an individual cell for a couple minutes to make enough difference?


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## GizmoEV (Nov 28, 2009)

With them all at or above 3.55V it looks like they are all close to being full. I'd hook them up in parallel again and finish them that way. The ones at 4.1V will drop in voltage quicker than the ones at 3.55V. Also, if there is any way you can throttle back your charger you might find that the 4.1V is a little higher than rest voltage. You could hook a lightbulb in series with your charger to limit charge current if you can't do it any other way.


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## dtbaker (Jan 5, 2008)

I found a local electronic supply place that had some big resistors ( 1 ohm x 25 watts for $1.50 ea), so I got two and put them in parallel to use as a 'load' to drain some juice from the high cells.

This is kinda time consuming, I spent a hour taking a first pass cell by cell... to check each cell, drain for a minute on the high ones, go back and see how things recovered.... I should be able to take another pass a series charge to see how things are at the top end. When all cells finish within .01, I'll re-wire in parallel and let the cells auto-balance that last little bit while I work on revising battery racking.


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## dtbaker (Jan 5, 2008)

...getting frustrated w/ lack of success balancing... I went thru the pack several times with my resistor, and discharged the several that were higher than most until they were all 3.34-3.36 . Then, I applied my series charger until the first ones hit 4.1, which was only about 10 minutes. Overnight most have relaxed to 3.34-3.35, but the same ones that were high before are high again at 3.40, 3.42ish

so... is it time to go back to the parallel power supply and trickle it up to 3.70?


d


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## EVfun (Mar 14, 2010)

I'd knock an amp hour out of the high cells, that is about 18 minutes with a 1 ohm resistor, then check the resting voltage the next day and then put them on a series charge for a few minutes and see where they go. 138 volts for a 38 cell pack is only 3.63 volt per cell. At the end there will be some scatter but you should be able to leave them with on charger for an hour after hitting the voltage wall while the current tapers down (naturally, I don't mean walk away during the initial charging.)


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> ...getting frustrated w/ lack of success balancing... I went thru the pack several times with my resistor, and discharged the several that were higher than most until they were all 3.34-3.36 . Then, I applied my series charger until the first ones hit 4.1, which was only about 10 minutes. Overnight most have relaxed to 3.34-3.35, but the same ones that were high before are high again at 3.40, 3.42ish


There is so little energy above that point I'd go parallel and top them up to 3.6-3.7V. It will take a fraction of a second to bring the high ones down to the low ones and so little energy that I doubt that you will even be able to detect any spark on connection. That is less than 0.1V difference between your extreme high and extreme low cell. Unless you have shunting BMS boards and can put them on and throttle back the charging current to below the shunting current in which case I'd do that.

If you stick around you can turn up your bench-top power supply above your cutoff voltage to get it to pump in at its highest current until the terminal voltage is where you want it. Then just taper the voltage back to your target voltage and let the PS finish its job.


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## dtbaker (Jan 5, 2008)

EVfun said:


> I'd knock an amp hour out of the high cells, that is about 18 minutes with a 1 ohm resistor,


hhhmm, maybe I wasn't taking the high ones down enough... they seemed to keep bouncing back almost to where I started. I have two 1 ohm 25 watt resistors in parallel. I guess I will try one more round of balance, another series charge, and then go back to parallel to finish up.


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## dtbaker (Jan 5, 2008)

I was struggling with repeat loading and charging... The high ones I'd let drain for 15-20 minutes at 50 watts. Then when I fired back up the series charge I was seeing a couple hit 3.7 and rise rapidly to 4.0v while the rest were still sucking up juice at 11 amps and sitting at 3.50 v or so. It was getting very time consuming and not seeming much better balanced, so I rewired to parallel and am letting it trickle along unattended with CV=3.70

Unfortunately, it really is just a trickle with bench supply. Only about 3.8 amps with CV=3.70. With 35 watts going to the pack, this could take a LONG time.

Would I blow things up if I hooked up the series charger, that would kick out 11amps, and watch it like a hawk? Or, would I accomplish the same thing by cranking up the power supply to its max CA (10amps) and watch the cells manually while they are in parallel, and back down to CV when I start seeing cells up around 3.55-3.60?


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## rwaudio (May 22, 2008)

dtbaker said:


> I was struggling with repeat loading and charging... *The high ones I'd let drain for 15-20 minutes at 50 watts. *Then when I fired back up the series charge I was seeing a couple hit 3.7 and rise rapidly to 4.0v while the rest were still sucking up juice at 11 amps and sitting at 3.50 v or so. It was getting very time consuming and not seeming much better balanced, so I rewired to parallel and am letting it trickle along unattended with CV=3.70
> 
> Unfortunately, it really is just a trickle with bench supply. Only about 3.8 amps with CV=3.70. With 35 watts going to the pack, this could take a LONG time.
> 
> Would I blow things up if I hooked up the series charger, that would kick out 11amps, and watch it like a hawk? Or, would I accomplish the same thing by cranking up the power supply to its max CA (10amps) and watch the cells manually while they are in parallel, and back down to CV when I start seeing cells up around 3.55-3.60?


When you are draining the cells, I assume you are using the pair of parallel 1 ohm resistors. I'm taking a stab that the voltage under load is 3.3 to 3.4V, if that's the case you are only drawing 6.6 to 6.8Amps which works out to ~22-23watts not 50watts. (that's good for the resistors though)

As for attaching the series charger, I think your asking to blow something up then, best case the charger thinks it's a short circuit condition and turns off. It's just not going to work down to that voltage, I'm sure there is an output range on it somewhere.

I've been using some of these http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380195053685&ssPageName=STRK:MEWAX:IT
in parallel adjusted upto 3.65V to charge some headways I'm testing. I put 4 dc/dc converters in parallel to charge 6-12 parallel 10AH headways and they charge pretty quick. It would be easy to parallel more for even higher currents. I use a 48v 60A power supply to power the dc/dc converters but any good size 36-75V supply would work.


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## dtbaker (Jan 5, 2008)

ok, I will continue to be patient in parallel.... sigh.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> Or, would I accomplish the same thing by cranking up the power supply to its max CA (10amps) and watch the cells manually while they are in parallel, and back down to CV when I start seeing cells up around 3.55-3.60?


That is what I suggested the other day. It is also what I did when I was testing out a single cell so doing that on your paralleled pack it would be even easier because the voltage won't move that fast.


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## dtbaker (Jan 5, 2008)

FINALLY, amps are dropping and pack is looking almost full in parallel. maybe just a couple more days.....


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## dtbaker (Jan 5, 2008)

whoo hoo! amps dropped to Zero.... so parallel pack charge is done. I will unhook power supply, and let them sit in parallel for probably a day while I work on other stuff.....

I am tempted to re-wire in series on the bench, apply a load to drain a little, and then use my series charger to make SURE they finish re-charge in balance before I have them all wired up in the car. Am I being too fearful? Is it worth the hour to rewire on the bench and verify charge balance, or am I being overly chicken?


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## dtbaker (Jan 5, 2008)

pack is relaxing a little, and still within .01v across all cells. yay.

I had set the power supply to 3.8v, which 'finished' at 3.83-3.84 according to my multimeter. A little above where I hope my series charger will take things (3.65) if all goes well. I decided to go a little above to purposely get to the steeper part of the curve to nail down the balance as closer than where the curve is flatter.

I left things in parallel for about 24 hours now, and cells have relaxed to 3.73-3.74. I won't be working on anything today, so plan to leave in parallel for a while longer.

still debating on whether it is worth some piece of mind to take the time to wire in series, load the system to bleed a little, and use the series charger to verify that they remain in balance and hit the finish at the same time....


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## EVfun (Mar 14, 2010)

How many hours in parallel did it finally take? Did you get an idea of how many amp hours they ended up taking?


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## dtbaker (Jan 5, 2008)

EVfun said:


> How many hours in parallel did it finally take? Did you get an idea of how many amp hours they ended up taking?


well, I spent a lot of time in the middle re-wiring to serial and attempting to use the regular charger to dump a bunch of juice in, then manually bleeding the high cells with the resistors... in retrospect, that was not very effective and I may have finished sooner just leaving it in parallel from the beginning, or taken a first pass in series from the start to get close to done before switching to parallel.

My pack is 38 * 100ah cells, and when I started they were all showing about 3.2, plus or minus .05... but this is a really flat part of the curve, so they could have been anywhere. Most of what i read indicated that on average they came from factory 'about' 50% DOD, so I was counting on putting at least 5 or 6kWHr in before getting close to the end.

I started from the beginning in parallel, which was limited to about 8 amps at 4.0v by my power supply... I got impatient after the kill-a-watt meter on the wall showed 10 kWhr after several days, but I suspect that with the losses in the power supply I was actually pretty close to done because after I messed around re-wiring to serial and using the regular charge I was seeing the high cells headed past 4.0 rapidly. I wasted a lot of time changing the cells between parallel, serial, and back... it takes almost an hour each time!

so.... not having an accurate measure of actual amp-hr going into the batteries, I cannot really answer how many ah it took. I can guess that if I had left it in parallel on my mastech power supply at 3.80v, it probably would have shown about 12kWhr consumed at the wall skipping the messing around I did in the middle. I suspect probably only loaded a total of 5 or 6 kWhr into the cells, which makes sense considering the max capacity is around 12kWhr.

If I were going to do another pack from scratch, I think I would wire in series to dump in juice at a decent rate for a while and start watching carefully after no more than 40% of pack capacity shows as going in from the wall.... which means checking every 15 minutes max, or just re-wire to parallel with a power supply and be patient. 

so, if I had left it parallel from the beginning, it probably would have taken... about 100 hours, or more, since amps going in slow down toward the end. A good solid week, and probably more.


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## Elithion (Oct 6, 2009)

First of all, let me say that it was a pleasure following your progress and seeing you doing everything right!



dtbaker said:


> cells have relaxed to 3.73-3.74.


You're done. That's as good or better balancing than most BMSs on the market could do.



dtbaker said:


> still debating on whether it is worth some piece of mind to take the time to wire in series, load the system to bleed a little, and use the series charger to verify that they remain in balance and hit the finish at the same time....


Don't bother: your BMS will do that for you. You'll be able to do your verification by looking at the cell voltages reported by your BMS (assuming your BMS reports voltages).

Davide


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## dtbaker (Jan 5, 2008)

Elithion said:


> You'll be able to do your verification by looking at the cell voltages reported by your BMS



this is where I deviate from what you would probably want to see in that I plan not to install a BMS. At most I would install a loom to enable manual cell checks periodically.

I initially was considering installing a 16ga paired wire loom from a central location to every cell to allow manual balancing 'in situ'. After much reading and pondering, and considering that 38 strands of paired wire is a chunk of copper about an inch in diameter, I am itching to put the car back together without any loom at all, and just check manually periodically.

what I would REALLY like is a 'set-and-forget' charger that would just shut down when the FIRST cell hits a set voltage.... as cheaply as possible. If no balancing were intended over the cell monitor wires, I'd only need one per cell plus one, and they'd only need to be skinny little 24ga ethernet cables.


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## EVfun (Mar 14, 2010)

dtbaker said:


> I left things in parallel for about 24 hours now, and cells have relaxed to 3.73-3.74. I won't be working on anything today, so plan to leave in parallel for a while longer.


You are seeing 3.73 volts on the cells after they have been sitting off charge for a day or more? I do like the plan to leave them in parallel.

No cell in my TS pack has ever rested that high! My pack has not been balanced, every cell read 3.30 volts when received and the cell level boards would alert me and stop charging if any cell goes outside the range of 2.5-4.1 volts. They can shunt up to 600 ma over 3.65 volts. One cell was manually knocked down 0.8 amp hour because it kept creeping to 3.79 volts while the rest where just 3.61 volts. I only charge to 3.65 volts per cell plus hold that voltage for 1 hour (40 cell pack, 146 volts.) The current has not dropped to zero, but it appears to be under 1 amp. My typical resting voltage the morning after charging is 3.35 volts.


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## dtbaker (Jan 5, 2008)

EVfun said:


> You are seeing 3.73 volts on the cells after they have been sitting off charge for a day or more? I do like the plan to leave them in parallel.


...yes, they were all 3.73-3.74 this morning, and all 3.72-3.73 after another 8 hours sitting. The absolute value may be off a little considering I have a low-end digital multi-meter that is not calibrated to any lab controlled value, but the repeatability and the whole pack only .01 apart seems good.



EVfun said:


> No cell in my TS pack has ever rested that high!


surprises me a little too. I thought they would rest somewhere between 3.45 and 3.6. However the final charge was to 3.8 and was at a very slow rate in parallel so that might allow a fuller charge than the typical series charge?

anyway, I am just leaving them sit in series for at least till tomorrow.


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## GizmoEV (Nov 28, 2009)

When I charged my cells to 4.00vpc and let the current taper to zero they would sit in the 3.7+v for quite a while. I decided not to stress them so much and have been charging them to 3.5vpc. So far they haven't been "wandering around" at the end of charge. Also, since you aren't going with a BMS I would recommend not charging above 3.5-3.6vpc and definitely stay away from the bottom end of the pack where you stand a good chance of reversing a cell while under load.

It would be great if you took regular cell voltage readings at about 1 month or so intervals to track any variation. You might decide that the monthly readings are not necessary after a while. I quickly decided to quit my weekly and then bi-weekly readings and have gone to just monthly readings. I do have a BMS but they don't shunt until 4.00vpc and warn me at 2.93vpc on the low end.

I would recommend watching the video linked to on this blog posting: http://jackrickard.blogspot.com/2010/12/what-he-said-what-i-said.html

Here is a quote from the blog about the professor giving the talk:

"Jay Whitacre received his Phd in Materials Science in 1999 at
University of Michigan Ann Arbor - so he's a lot smarter than I am. He
worked for Jet Propulsion Laboratory 2000-2007 mostly on lithium
battery projects. Today, he is an assistant professor in Materials
Science at Carnegie Mellon university. He's also head of Whitacre
Research Group which studies functional materials for electrochemical
storage."

After this you might decide you only need something like Lee Hart's Batt-Bridge circuit ( http://www.evdl.org/pages/battbridge.html) to monitor for a cell going out of line.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> ...since you aren't going with a BMS I would recommend not charging above 3.5-3.6vpc and definitely stay away from the bottom end of the pack


My charger is set such that the average cell voltage *should* be 3.65v average at finish... fairly conservative if cells are balanced close enough. I do plan to check periodically, probably more at first, and hopefully less often if things don't drift.


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## dtbaker (Jan 5, 2008)

after another night just sitting in parallel, about half are 3.71, rest are 3.72... probably all the same within the error range of my cheap multimeter.


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## Overlander23 (Jun 15, 2009)

Interesting... my TS160s charged to 3.8v rest at 3.4v... I'd like to get my Elcon reset to a 3.65v final charge, though...


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## dtbaker (Jan 5, 2008)

they are down to 3.67-3.68 now.... still sitting untouched, in parallel. perhaps happier with the very slow parallel charge that the typical quicker charge in series? maybe did a better job moving available Li and filling ALL spots?

which charge curve is your elcon set to? I had them set mine to finish at 3.65 average.


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## Overlander23 (Jun 15, 2009)

My PFC5000 is on algorithm #312, which basically finishes at 3.8v, but stops CC at 3.6v... I've balanced at 3.8v. In addition, supposedly the finishing current (anything above 3.6v, the L3-phase in their charge profile) can be user selected... my selection maxes current during the phase to Ah/50. That's pretty low. The current as the charge approaches 3.8v drops to Ah/100.

As long as it stops the big power from flowing at 3.6v I should be fine. I'll see what happens before sending it back for a different profile.


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## dtbaker (Jan 5, 2008)

Overlander23 said:


> My PFC5000 is on algorithm #312,


supposedly, once the max pack voltage is set, the algoryths are user selectable/changable using some button under the sticker... but I dunno. I had mine set using curve #611, which finishes at 3.65


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> I would recommend watching the video linked to on this blog posting: http://jackrickard.blogspot.com/2010/12/what-he-said-what-i-said.html
> 
> Here is a quote from the blog about the professor giving the talk:
> 
> ...


OK I've looked everywhere, where is this video? Did they take it down? The link loads but I can't find ANY video.


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## Overlander23 (Jun 15, 2009)

ElectriCar said:


> OK I've looked everywhere, where is this video? Did they take it down? The link loads but I can't find ANY video.



http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387


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## ElectriCar (Jun 15, 2008)

Thanks Overlander. *The video is I'd say a must view* if you're concerned about the health and safety of your high dollar pack of lithium. Lead is pretty forgiving but these boys you MUST know what you're doing or you're going to waste some serious dough!


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## dtbaker (Jan 5, 2008)

Overlander23 said:


> I'll see what happens before sending it back for a different profile.



for a different profile (with same nominal pack voltage) you are supposed to be able to set with the button under the sticker...

and yes, the video is worth the hour to watch just to get a little better understanding of what is going on. Although, not much time spent on the real issues We are concerned with regarding the reality of series packs staying balanced, or going out, and any 'real' guidelines regarding real life management of a multi-cell pack other than the broad generalization that cell-level BMS won't be affordable in a mass market regardless of engineering preferences.

The video helped me feel a little more comfortable with my personal approach with top-balance since I will not be installing an active BMS.


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