SegwayChat - View Single Post - My NiMH -> LiPo battery rebuild for i167. Success!

Ground Loop · 02-27-2011, 12:33 AM

I made another one, and I like this one best:

I left the middle strip 'mohawk' of plastic intact this time, to retain the battery connector and add some structural rigidity.

Now I'm all matched batteries (twelve 3S batteries), XT60 connectors, and cleaner wiring.

I also got a chance to run the Segway under more conditions with just LiPo power. First, the full performance envelope is available. With my resuscitated NiMH batteries, they would sag under load and get the straight-face slowdown.

I also added some battery monitoring of my own to track performance in motion.

I rode the Segway with a young passenger to bring it to 200lbs load, up and down hills at full speed and around the block. I measured a peak draw from each battery of 129 Watts. That works out to 11.4 Amps at peak load.

I made a second ride with 170lbs load and worked it as hard as I could. Rapid starts, rapid stops, full-speed turns, inclines, etc. The highest I could hit was 192 Watts, 17.5 Amps.

Overall, this puts the whole battery array at 2300 Watts peak.

As most of you predicted, battery cutoff became an issue. The Segway went to blinking-red when the packs reached 11.0 Volts. At this point, I had used only 0.58 Ah out of 2.2 Ah of capacity, so that's way too early.

None of the 3S batteries dipped below 10.97 volts at any time. (They're rated for 45A or so, so this is a cakewalk). Temperatures stayed slightly above ambient.

So what does all this data show? I believe the batteries are well-matched to this application, operating well within both average and peak load demands.
However, 11v per array is clearly the "zero bars" cutoff for the NiMH Battery monitor, so I'm going to have to experiment with added cells.

Next I will try 3S+4S+3S and see if the segway is monitoring each 10-NiMH string individually, or the one-of-four assembly as a whole. Based on the complex monitoring circuitry, I suspect it will not fall for this, but who knows.

If I had it to do over again, I would go with 4S (14.8v) packs all around. At 45v peak, that's still within the 'float' charge you might find on 30S NiMH, so I doubt it would fry anything. Anyone experiment in this direction? Does anyone know the resting voltage of the Segway/Valence Lithium packs?

02-27-2011, 12:33 AM	#24
Ground Loop Member Join Date: Dec 2003 Location: San Diego, California, USA. Posts: 517	I made another one, and I like this one best: I left the middle strip 'mohawk' of plastic intact this time, to retain the battery connector and add some structural rigidity. Now I'm all matched batteries (twelve 3S batteries), XT60 connectors, and cleaner wiring. I also got a chance to run the Segway under more conditions with just LiPo power. First, the full performance envelope is available. With my resuscitated NiMH batteries, they would sag under load and get the straight-face slowdown. I also added some battery monitoring of my own to track performance in motion. I rode the Segway with a young passenger to bring it to 200lbs load, up and down hills at full speed and around the block. I measured a peak draw from each battery of 129 Watts. That works out to 11.4 Amps at peak load. I made a second ride with 170lbs load and worked it as hard as I could. Rapid starts, rapid stops, full-speed turns, inclines, etc. The highest I could hit was 192 Watts, 17.5 Amps. Overall, this puts the whole battery array at 2300 Watts peak. As most of you predicted, battery cutoff became an issue. The Segway went to blinking-red when the packs reached 11.0 Volts. At this point, I had used only 0.58 Ah out of 2.2 Ah of capacity, so that's way too early. None of the 3S batteries dipped below 10.97 volts at any time. (They're rated for 45A or so, so this is a cakewalk). Temperatures stayed slightly above ambient. So what does all this data show? I believe the batteries are well-matched to this application, operating well within both average and peak load demands. However, 11v per array is clearly the "zero bars" cutoff for the NiMH Battery monitor, so I'm going to have to experiment with added cells. Next I will try 3S+4S+3S and see if the segway is monitoring each 10-NiMH string individually, or the one-of-four assembly as a whole. Based on the complex monitoring circuitry, I suspect it will not fall for this, but who knows. If I had it to do over again, I would go with 4S (14.8v) packs all around. At 45v peak, that's still within the 'float' charge you might find on 30S NiMH, so I doubt it would fry anything. Anyone experiment in this direction? Does anyone know the resting voltage of the Segway/Valence Lithium packs?