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Old 12-28-2010, 03:51 PM   #1
Ground Loop
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Talking My NiMH -> LiPo battery rebuild for i167. Success!

It's been a while since I posted, and indeed, since I rode my Segway. Hi y'all!

I've purchased six $400 NiMH packs over the years, and continue to disparage the battery design as the weak link in Segway -- certainly from an operating cost standpoint. (If anyone of the 60 NiMH cells falls out of balance and goes bad, the whole pack is junk..) With the batteries discontinued and nothing to lose, I thought I'd try building my own pack. This is the result:



For now, I'm using six $9 3S LiPo batteries, each 2200mAh and nominally 11.1v. It's a fit! The pack is much lighter, and I remove the packs to charge them on a proper balancing charger, but my Segway is road-worthy once again!



Of course, I can't use either of my Segway battery chargers to top off, and a short circuit would burn down the whole show, but at $100 all-up, I'm in business! Most importantly, when one cell fails, I can diagnose & service just that pack without discarding the rest.

With a little more Dremel work and tighter wiring, I think I can fit 5000mAh cells or larger into the same space.

Last edited by Ground Loop; 12-28-2010 at 04:03 PM..
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Old 12-28-2010, 06:08 PM   #2
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Quote:
Originally Posted by Ground Loop View Post
It's been a while since I posted, and indeed, since I rode my Segway. Hi y'all!

I've purchased six $400 NiMH packs over the years, and continue to disparage the battery design as the weak link in Segway -- certainly from an operating cost standpoint. (If anyone of the 60 NiMH cells falls out of balance and goes bad, the whole pack is junk..) With the batteries discontinued and nothing to lose, I thought I'd try building my own pack. This is the result:



For now, I'm using six $9 3S LiPo batteries, each 2200mAh and nominally 11.1v. It's a fit! The pack is much lighter, and I remove the packs to charge them on a proper balancing charger, but my Segway is road-worthy once again!



Of course, I can't use either of my Segway battery chargers to top off, and a short circuit would burn down the whole show, but at $100 all-up, I'm in business! Most importantly, when one cell fails, I can diagnose & service just that pack without discarding the rest.

With a little more Dremel work and tighter wiring, I think I can fit 5000mAh cells or larger into the same space.
Well done! This is a really interesting piece of work! Do post how it performs and what sort of range you are seeing. I cannot remember off the top of my head what the capacity of the standard NiMH and lithium packs is. How big a charger do you need for such a pack? Ideally you need to have an external charging socket on each pack so you can charge without dismantling. While clearly this isn't a perfect solution, given that you cannot fly with the lithium packs anyway, why not go this route, even though it is a bit 'quick and dirty'.

Driving around on my second set of lithiums, now fading into senescence after three years, I definitely agree with you that battery costs are the elephant in the room when considering the running costs of a seg. This may not be the perfect solution but it definitely will move the level of knowledge forward.
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Old 12-28-2010, 11:55 PM   #3
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Nice hack!

How are you limiting the voltage so it doesn't go below less than 3 volts per cell?
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Old 12-29-2010, 12:56 AM   #4
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How does the segway deal with it? I thought there were some cross checking circuits that monitor the battery. Is it satisfied? Does the battery indicator work on the display? What kind of range do you get?

This is a very interesting mod. I realize that you are taking out some of the safety levels, but also are dropping the price hugely. I would not do this for others, but as you are doing it for self, good luck.

Keep us posted.
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Old 12-29-2010, 02:58 PM   #5
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All good points. This is not a fool-proof solution, and has a lot of "manual safety" for now.

The Segway seems satisfied with the battery. (I still have the original 12.0 no-lipo-support software.) I can't see how it would even know. A 11.1v 3S pack has replaced each of the 10S NiMH packs that was there, so the operating voltage is within acceptable range. I kept all of the original NiMH circuitry and temperature sensors. I'll keep an eye on it, but my suspicion is that it will actually be a little bit pessimistic. If it allows NiMH to get down to 1.0 volts per cell (10v a string), then the LiPo is safely within limits, and limiting might kick in a bit early. If it allows 0.8volts per cell (safe for NiMH), then manual intervention is required.

For now, I have a self-contained LiPo monitor (pictured) installed on one or two packs. It will sound an alarm if any cell goes below 3.1v.

Charging is a bit of a hassle, since all 9 cells on each side need to be balanced. I have a Junsi iCharger 3010B with 1000W output, and can charge half the pack (9 cells) in 30 minutes or so (2C), twice per battery pack, four times total.

I have not yet measured range, but I don't expect it to be impressive. The packs are 2200mAh, and I will be limiting discharge to 70% or so. (The NiMH cells were SAFT 4.5Ah) That's still much further than the dead packs got me!

It's all experimental at this point. It would not be expensive ($20 or so) to add pack-monitor/alarms to each battery, so that's likely the next approach, just to make sure no one cell drops below limits.

External taps for charging would be nice, so I don't have to keep taking the screws out.

I also have to tape the 110v AC charging port shut, so nobody carelessly plugs in a power cord and blows up the cells with overvoltage.

Wet weather use is right out, since it's fully open on top.


R/C LiPo batteries have plummeted in recent years. I paid $8.00 each for those 3S packs at HobbyKing.com. 5000mAh packs are available for $22.00 or so, complete with hardcase. If you're willing to hog out most of the battery shell, there is a LOT of room in there. Range might also improve just because the batteries are so much lighter than NiMH. The whole Segway feels lighter. I'll have to measure it.

If anyone knows the pinout/protocol of the battery pins, I sure would like to understand this link better.
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Old 12-29-2010, 03:28 PM   #6
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Here's the link to the $8 LiPo pack:
http://www.hobbyking.com/hobbyking/s...idProduct=6306

The 45A Anderson PowerPole couplers cost half as much as the battery.
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Old 12-29-2010, 05:00 PM   #7
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Quote:
Originally Posted by Ground Loop View Post
Here's the link to the $8 LiPo pack:
http://www.hobbyking.com/hobbyking/s...idProduct=6306

The 45A Anderson PowerPole couplers cost half as much as the battery.
Hobbyking has connectors too you know?
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Old 12-29-2010, 10:10 PM   #8
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Yeah, I know.. I do like the XT60 connectors, but it seems like HK switches to a new connector every year.

I just ordered another 12 Zippy 3S packs, and XT60 pigtails, so the next battery overhaul should go faster.

$67 in shipping.. ouch.
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Old 12-30-2010, 05:30 AM   #9
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That's a bit steep. I've paid quite a bit, but never that much through them!

Maybe you could put a bead of silicon around the outside top of the battery housing to act as a seal?

Have you seen these?

http://www.maxamps.com/Lipo-MV5250-Pack.htm

You could fit a crap load of them in there!

I have a couple, but only because I won them!

Can you post a close up of the main connector and the buss which all the lipo's are connected too?
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Old 12-31-2010, 09:38 AM   #10
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I like the DEKA reference on the inside case of the batteries in the opening photos.
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