Two bad cells ruin entire Segway Battery.

[Ground Loop]

After a year of occasional use, I'm getting the dreaded Red Sad Face of Doom. With an overnight charge, my HT will go only a few hundred feet before showing the Red Face and eventually forcing a shutdown. One battery is letting me down. :(

As we know, each battery pack contains two blocks of 30 battery cells, wired in series for 36 volts. After "conditioning" both batteries with the wall-lean discharge and recharge, then riding until the red face, I removed the batteries from the HT and put them on my analyzer.

This puts a constant 1/2 Amp load on each "half" of the batteries, essentially testing the four blocks separately. The result looks like this:

http://www.trix.com/GroundLoop/segway-batteries.gif
The green, magenta, and blue traces represent three "normal" discharge curves. At half an amp, the batteries held over 36v for 3.5 hours.

The red curve shows my problem child.. it couldn't hold 36v from the start. It appears two cells out of the 30 are not contributing to the voltage, while the rest of them actually have a normal capacity curve.

For two lousy cells, I have to throw out a $295 battery pack! That's just wasteful and frustrating. There's really no reason the Segway batteries couldn't have been built as 30-cell packs, four total, even if it means bolting two of them together. At the very least, I wish they weren't so sealed and unmaintainable. I'd love to repair just the two failed cells.

I should point out that a constant-current graph isn't an exact model of the HT discharge, of course. For range, the "area under the curve" is a better indication of the total power available. The normal discharge in an operating HT with my weight on it is closer to 2A with spikes going much higher. So a steady 1/2A discharge should be very flattering to the batteries.

[bystander]

Great data. Much appreciated for posting this.

I do agree fundamentally with your conclusions about it being a shame that the NiMH cells can't be serviced. It certainly does seem wasteful.

However,

What the data doesn't show is whether all the other cells are good for another two years, or if you have one hundred eighteen ticking timebombs on your hands.

Imagine the cells were designed to be serviceable. Is it possible the revised design would be more costly and bulky? Is it possible that their might be a higher possibility that moisture could intrude and affect long-term pack life? Is it possible that they would be more temperature sensitive due to the extra bulkiness caused by the complication of the pack to be user serviceable?

If you could replace the two bad cells, how long until a few more go bad? And when do you find out? In the middle of a glide? How much time, money and inconvenience do you pour into a damaged pack until you realize it's time to write it off and just get a new one?

I don't mean to be too critical here, and I apologize if I sound like a Segway LLC apologist.

I guess I am considering the idea that it was determined by the designers that once a few cells go bad, the rest can follow in a short enough time to make partial replacement impractical for a device reputed to be so safe and convenient.

---

On the other hand, I would be very interested to find out how quickly the rest of the cells follow the first two. You probably recall the previous thread (http://www.segwaychat.com/forum/topic.asp?TOPIC_ID=10133) where W9GFO shared his experiences with reworking a diminished pack. A series of holes were drilled near the edge and sub-banks of 10 cells were tested. Cuts were made in strategic locations and a sub-bank was replaced. End result - a working pack.

But,

How waterproof is it now? How long does it last until another rework is required? Was the original conclusion about the pack design made by the designers justified?

I don't know if we will ever really know about that last question.

I know when the time comes and my NiMH packs die, I will be sorely tempted to repair them and see how long they can last. If I have the free time to do it at that time, I will probably try. I may have bought a set of Saphions by then, but in my (current) view, Saphion availability is too low and cost too much to abandon the NiMH right now.

I do plan on ordering Saphion packs once dealers have them in stock. Unfortunately it is unknown whether this will happen in July or December. Perhaps, in time, keeping NiMH packs going won't seem worthwhile.

Of course, I would like to get Saphions now. But I realize the longer it takes for the Saphions to become a separately stocked item, the more new HTs get sold, and the more fellow gliders there will be. And that might be worth waiting for.

[Ground Loop]

You raise a good point -- that failing cells may be accompanied by more aged cells in the pack preparing to fail soon.

In my limited experience with NiCd and NiMH batteries for R/C projects, this isn't always the case. Sometimes you just get a bad apple in the pack, and the rest from the same batch can have lifetimes several times longer.

In fact, from looking at the discharge curve, you can usually spot exactly that -- a cell that is on its last legs will "drop out" just before the big knee at the end of the charge. Over the next several cycles, the "drop out" will happen sooner and sooner.

As soon as one weak cell dies early, it is effectively getting a "Reverse Charge" for the whole remainder of the run! The cells are wired in series, so the continued current will be flowing backwards through the one dead cell.

If I see a discharge curve with a "stair-stepped" dropoff at the end, that's usually a sign that the pack is worn out. The cells are no longer at the same capacity, and the steps will just get wider because of it.

In the four packs above, you can see the cliff is still steep, and there aren't any visible steps. (There might be one forming at the end of the blue one, but it's still the best overall)

In short, the red discharge curve is still pretty strong. It really is just those two cells that are completely failed, while the others are as good as my other three packs.

I fully expect that my own repair attempts will leave the pack less sealed and more fragile, but for $300, I can continue to avoid deep puddles.

[Ground Loop]

For anyone curious, here is the full charge required to bring all four up from the discharge. Since the HT would never let all four batteries get this low, I thought it was interesting to see that it needed about 700 WattHours of power to top them off. You can clearly see the four phases of the charge cycle here:

http://www.trix.com/GroundLoop/full-charge.gif

[dgbint]

Hi

I think that there's another quite important factor regarding cells and replacements.

A complete assembly, as currently used has the electricals welded together, thus the chance of an electrical disconnect is almost zero.

If there were replaceable cells or blocks of cells, how would they be connected ?
In a vibrating environment like an HT, any user connection would have a higher failure rate.

What would happen to an HT, if it lost power for 1/2 a second ?
It's more critical than your walkman skipping a track or two.

If you could choose between a whole pack and a segmented pack but a less reliable machine, what would you choose ?

Michael

[Mr. Protocol]

I've quoted Doug Field's answer to my question regarding rebuilding battery packs, in which he said it basically wasn't worth it, and anyway they spot-weld the things together. However, I failed to mention that at the very end, sort of as a coda, he said, "[it might be worth rebuilding a pack] if there are only one or two dead cells or something."

So, if the rest of the pack looks like the cells might last long enough to make the effort worth it, I say go ahead and solder in replacement cells. At the worst they'll shake loose and you'll be no worse off. At best you might epoxy them in place or something so that the shaking won't put stress on the solder joint, and get yourself a nice new(ish) pack.

[W9GFO]

quote:Originally posted by Mr. Protocol

At best you might epoxy them in place or something so that the shaking won't put stress on the solder joint, and get yourself a nice new(ish) pack.


The design of the case makes it easy to immobilize the cells. I use hot melt glue to secure them - there's no where for the cells to go...

Rich H

The Un-Official Segway Battery FAQ
http://www.spinfoot.com/SegwayBatteryFAQ.html

[terryp]

A great product for this sort of thing is E6000, the industrial version of Shoe Goo.

Segway - What's holding you up?

[W9GFO]

The thing is, when it comes time to remove the cells, all you need is a heat gun. The glue that Segway uses is some form of hot melt glue that softens with heat. Otherwise removing the cells undamaged would be next to impossible.

Rich H

The Un-Official Segway Battery FAQ
http://www.spinfoot.com/SegwayBatteryFAQ.html

[Ground Loop]

I thought that by cycling the batteries a few times I might revive the weak cells, but it appears I've actually made the problem much worse. I now have three cells dropping out early in the discharge.

This graph shows the good half of the pack (green) versus the failed half (red) from a full charge. You can see three "steps" on the red curve early on. I don't understand the jagged rising part of the curve, but my power load is not constant under 33v so it may be confusing things. The important thing to note is the three drop-outs within the first hour, versus the smooth curve of the good pack.

I haven't measured it yet, but I believe the HT sounds the red alert when any one pack drops below around 36v or so.

http://www.trix.com/GroundLoop/really-bad.gif

[bystander]

One hundred and seventeen ticking timebombs...

Could have been worse, the third cell could have failed after you located & replaced the first two and resealed the pack.

Groundloop, It must be really frustrating to be going through this. I know if one of my packs died on my HT as early as you indicate yours did, I would be really grumpy right now.

At least let me thank you for pointing out a few of the problems some of the rest of us may eventually experience and showing everyone the details.

[Stan671]

Very, very intersting graph, GroundLoop. I believe this is the same thing that has happened to one of my original batteries - a bad cell or two is bringing down the whole pack.

Stan Dobrowski

[clr22182]

Great data. Much appreciated for posting this.

I do agree fundamentally with your conclusions about it being a shame that the NiMH cells can't be serviced. It certainly does seem wasteful.

However,

What the data doesn't show is whether all the other cells are good for another two years, or if you have one hundred eighteen ticking timebombs on your hands.

Imagine the cells were designed to be serviceable. Is it possible the revised design would be more costly and bulky? Is it possible that their might be a higher possibility that moisture could intrude and affect long-term pack life? Is it possible that they would be more temperature sensitive due to the extra bulkiness caused by the complication of the pack to be user serviceable?

If you could replace the two bad cells, how long until a few more go bad? And when do you find out? In the middle of a glide? How much time, money and inconvenience do you pour into a damaged pack until you realize it's time to write it off and just get a new one?

I don't mean to be too critical here, and I apologize if I sound like a Segway LLC apologist.

I guess I am considering the idea that it was determined by the designers that once a few cells go bad, the rest can follow in a short enough time to make partial replacement impractical for a device reputed to be so safe and convenient.

---

On the other hand, I would be very interested to find out how quickly the rest of the cells follow the first two. You probably recall the previous thread (http://www.segwaychat.com/forum/topic.asp?TOPIC_ID=10133) where W9GFO shared his experiences with reworking a diminished pack. A series of holes were drilled near the edge and sub-banks of 10 cells were tested. Cuts were made in strategic locations and a sub-bank was replaced. End result - a working pack.

But,

How waterproof is it now? How long does it last until another rework is required? Was the original conclusion about the pack design made by the designers justified?

I don't know if we will ever really know about that last question.

I know when the time comes and my NiMH packs die, I will be sorely tempted to repair them and see how long they can last. If I have the free time to do it at that time, I will probably try. I may have bought a set of Saphions by then, but in my (current) view, Saphion availability is too low and cost too much to abandon the NiMH right now.

I do plan on ordering Saphion packs once dealers have them in stock. Unfortunately it is unknown whether this will happen in July or December. Perhaps, in time, keeping NiMH packs going won't seem worthwhile.

Of course, I would like to get Saphions now. But I realize the longer it takes for the Saphions to become a separately stocked item, the more new HTs get sold, and the more fellow gliders there will be. And that might be worth waiting for.
Good morning,
The NIMH battery packs can be opened safely. I have done it. It is a little difficult to describe so please be patient. Here's how. Place the battery on a solid surface and prevent it from moving side to side with whatever is handy. Use a sharp utility knife with new blade. On the surface that shows the plug attachment choose to insert the tip of the knife just inside the perimeter of the case sides (about 1/8th inch from the edge and only about 1/16th to 1/8th inch deep. If necessary use some fingernail polish to mark the blade so that you won't allow the tip to penetrate deeper than 1/16 or 1/8th inch. You only want to cut through the plastic and not allow the It is very important to be especially careful about the depth of the knife tip along the long FLAT side of the case because this is where the circuit board is located. The circuit board mnust not be damaged opening the case. Use a small hammer tapping the handle of the utility knife to push the blade along the perimeter of the panel you trying to cut. Cut the entire perimeter of the top of the case in this fashion and then pry it out with a small thin screwdriver. The areas of the top that are joined to the screw holes in my case "popped" loose the welds and voila the entire case was open and I was staring at the two 30 cell packs and the circuit board! There are numerous NIMH sub C batteries with tabs available on the net up to 4500 ma but the most cost effective ones are the 4200ma cells. I haven't done anything with my batteries yet but am very interested in your test equipment. Please let me know more about it and how it can be obtained or constructed so that I may test this battery pack. You may reply to clr22182(at)verizon.net.
Thank you,
Charles L. Rogers

[hellphish]

Good instructions, do you mind if I copy this into the segwaywiki?

BTW, you replied to a thread that was two years old. You would be better off putting this information into a new thread.

[joe]

@clr22182: A picture says more than thousand words, so please ... ;)

--
Johannes

[JohnG]

The thinking behind the sealed battery packs is multi-fold and makes sense from a large scale manufacturing point of view (perhaps not as much from the "hobbyist" point of view). Moisture and vibration are two factors the engineers spent a lot of time to minimize *any* infiltration into anything that could cause a short or malfunction.

So, sure, they could've done it, but they also assumed most battery packs would fail as a unit (e.g., if 2 or 3 cells are going now, another 2 or 3 will likely be going soon) given the QA on individual cells. It also would've added to the cost for the rest of us to go from a nice sealed pack to one that could be opened and readily serviced by Joe Handyman *safely* without also disturbing the electronics contained therein. Probably would've been a lot more headaches from an engineering and manufacturing process than it was worth.

John

[jgbackes]

It would be nice if someone would take some photos of the process of opening the battery and replacing the cells.

The newer cells have much better chemistry. I remember reading for the same size a newer NMHi cell has almost twice (3000 vs. 5000) mah as I recall.

www.all-battery.com (http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=892)

[Sharkie]

It would be nice if someone would take some photos of the process of opening the battery and replacing the cells.

The newer cells have much better chemistry. I remember reading for the same size a newer NMHi cell has almost twice (3000 vs. 5000) mah as I recall.

Sure, they're available, but can you imagine spending about $10.00 each for 240 cells????? It makes a set of lithiums look like quite a bargain!

Jim

[jgbackes]

A 240 cell order is $3.83 per cell. $919, is much cheaper than li-ion. And much better performance than the original NM-hi. Also you don't have to upgrade the software!

If anyone has some NM-hi batteries that are toast, I'd be happy to take them off your hands to do a complete project workup.

Tabbed C-Cell Batteries (http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1334)

I just re-read the post above, if there are two 30 cell packs in each battery, you only need 120 cells to fill both batteries, so that's more like $460. Not bad if you ask me.

[PeteInLongBeach]

It would be nice if someone would take some photos of the process of opening the battery and replacing the cells.

The newer cells have much better chemistry. I remember reading for the same size a newer NMHi cell has almost twice (3000 vs. 5000) mah as I recall.

www.all-battery.com (http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=892)
I assume these would provide better range? If so, any guess how much farther?

[polo_pro]

A 240 cell order is $3.83 per cell. $919, is much cheaper than li-ion. And much better performance than the original NM-hi. Also you don't have to upgrade the software!

If anyone has some NM-hi batteries that are toast, I'd be happy to take them off your hands to do a complete project workup.

Tabbed C-Cell Batteries (http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1334)

I just re-read the post above, if there are two 30 cell packs in each battery, you only need 120 cells to fill both batteries, so that's more like $460. Not bad if you ask me.

Check your private messages on this forum. I can route you to a few dealers who'd love to get rid of their pile of NiMH doorstops.

[jgbackes]

I assume these would provide better range? If so, any guess how much farther?

Well, 3000/5000 = 12/x = 20. So assuming everything is equal, 20 miles.

[hellphish]

...But I realize the longer it takes for the Saphions to become a separately stocked item, the more new HTs get sold, and the more fellow gliders there will be...

And the more expensive those Saphions will be ;) ;) (going by current trends)

[bystander]

...But I realize the longer it takes for the Saphions to become a separately stocked item, the more new HTs get sold, and the more fellow gliders there will be...

And the more expensive those Saphions will be ;) ;) (going by current trends)

LOL, you realize I wrote that over two years ago, before dealers could sell Saphions w/o selling a PT, and a special appointment was necessary for the necessary firmware upgrade?

Yes, the batteries are supposed to get cheaper as time goes on, and it looks like they set the initial price too low to realize that trend.

But just think how bad Dean Kamen feels. According to this quote (http://www.autofieldguide.com/articles/020204.html) (back in 2002):

Speaking of the Segway, Kamen said, “A big benefit will be that it will eventually dramatically reduce the cost of building the Ibot because the quantities”—of things like motors, sensors, batteries, and processors—“will get so high.”

The sales of consumer-level PTs (called HTs two years ago) were supposed to increase production and lower the cost of components that would be used in both the PT and the Ibot. Since the PT has yet to take off, those Ibots never realized their volume parts reduction.

I feel sorrier for the people that need the use of an Ibot and will never be able to afford it, than for we PT owners who grouse about the cost of replacement batteries.

[hellphish]

LOL you're right, I didn't even notice this was an ancient thread.

[GlidingAlan]

Ground Loop,

I'm an R/C pilot as well and I have many NiCads, NiMH, L-Ions and Lipo's and charging equipment. I have spare Segway packs and would like to analyze which are the best so I'd be interested how you did your analysis so I could duplicate it. Please let me know!

Thanks,
GlidingAlan

[bentbiker]

Ground Loop,

I'm an R/C pilot as well and I have many NiCads, NiMH, L-Ions and Lipo's and charging equipment. I have spare Segway packs and would like to analyze which are the best so I'd be interested how you did your analysis so I could duplicate it. Please let me know!

Thanks,
GlidingAlan
Alan,

I don't know if you noticed, but Ground Loop hasn't logged into this site since January according to his user profile page. He could be reading without logging in, but I wouldn't bet on a quick response. He has elected not to receive emails from members, so that is not an option -- unless another member knows him and could advise him of your interest.

[polo_pro]

Ground Loop,

I'm an R/C pilot as well and I have many NiCads, NiMH, L-Ions and Lipo's and charging equipment. I have spare Segway packs and would like to analyze which are the best so I'd be interested how you did your analysis so I could duplicate it. Please let me know!

Thanks,
GlidingAlan

There are other R/C pilot/gliders here on SC. They'll probably contact you if you stay active on this forum and keep asking about this topic.

[ryan_walters]

Ground Loop,

I'm an R/C pilot as well and I have many NiCads, NiMH, L-Ions and Lipo's and charging equipment. I have spare Segway packs and would like to analyze which are the best so I'd be interested how you did your analysis so I could duplicate it. Please let me know!

Thanks,
GlidingAlan

I am an RC guy too. As far as battery testing / charging, etc, I have two Thunder Power 1010 chargers, one Triton, and two Diamond super turbo chargers. For analysis (discharging), I use the CBA (computer battery anylizer) by West Mountain Radio. It will not handle the total voltage of a segway battery though, either NiMh or LiIon. It would let you run cycles on different 'sets' of NiMh cells in the pack to help determine which set contains weak / bad cells.