Downhill Charging on i2

[MJEdelman]

How much benefit is the downhill charging on the i2? When I leave my house it is all up hill and the return is downhill -- so if the trip is split 50/50 between up and down, how many bars will I gain on the return?

I know that there are a lot of variables like speed, terrain, etc.; I am just trying to get an idea of what to expect.

Thanks!

[ryan_walters]

I've gone down hills that take 3-4 min at about 15km/h, and gotten a bar back. Once level, the bar that I got back lasted 2-3km on level ground. If the last 50% of your trip is all downhill, I would think worst case senario, you don't use any batteries.

[polo_pro]

How much benefit is the downhill charging on the i2? When I leave my house it is all up hill and the return is downhill -- so if the trip is split 50/50 between up and down, how many bars will I gain on the return?

I know that there are a lot of variables like speed, terrain, etc.; I am just trying to get an idea of what to expect.

Thanks!

Towing a 150 pound trailer behind my segway, I'd lose a bar or two up some very long hills along PCH. These type of hills were at least half a mile and at least a 6 degree grade. Usually the far side of the hill (also often a half mile or more) would give me back at least a half bar. I found the NiMH accepted a charge (though mainly a surface charge) much better than the Li-Ion batteries.

Keep in mind you have to have pretty cold weather to regenerate batteries on the fly. If the air temperature is 50 degrees and you're keeping up a good clip, your batteries and chasis will most likely be at 70 degrees and ready to optimally regen.

Overall I find that if you're willing to power assist your segway up hills, you can extend your range significantly on NiMH. To the tune of a mile or two extra. The walking alone buys you extra range, but if you carefully manage the regenerated energy then you get a decent distance out if it (even if alot of it is just surface charge). Oh yeah...a headwind is never your friend...nothing worse than that!

ps - One variable I had to struggle with was the trailer "pushing" me down the hill in a jolting fashion. I think the "stuttering" did not allow for proper regeneration on the downhills. But I'm speculating to some degreee.

[bystander]

Towing a 150 pound trailer behind my segway, I'd lose a bar or two up some very long hills along PCH. These type of hills were at least half a mile and at least a 6 degree grade. Usually the far side of the hill (also often a half mile or more) would give me back at least a half bar. I found the NiMH accepted a charge (though mainly a surface charge) much better than the Li-Ion batteries.

Keep in mind you have to have pretty cold weather to regenerate batteries on the fly. If the air temperature is 50 degrees and you're keeping up a good clip, your batteries and chassis will most likely be at 70 degrees and ready to optimally regen.

Overall I find that if you're willing to power assist your segway up hills, you can extend your range significantly on NiMH. To the tune of a mile or two extra. The walking alone buys you extra range, but if you carefully manage the regenerated energy then you get a decent distance out if it (even if a lot of it is just surface charge). Oh yeah...a headwind is never your friend...nothing worse than that!

ps - One variable I had to struggle with was the trailer "pushing" me down the hill in a jolting fashion. I think the "stuttering" did not allow for proper regeneration on the downhills. But I'm speculating to some degree.Um,

1 full bar on gen1 Saphion = approx. 160 wh.
1 full bar on gen1 NiMH = approx. 88 wh.
1 bar on gen2 Saphion = approx. 100 wh.

If I'm not mistaken, polo runs a gen1 when towing, and the OP was asking about an i2.

And since NiMH "bars" are smaller than Saphion "bars", it's easy to see that downhills would seemingly cause NiMH "bars" to go up faster.

Another way to look at it is that a knowledgeable person (JD) posted in this thread (http://forums.segwaychat.com/showthread.php?t=16330) that the PT drivetrain is around 48%-50% efficient on the flat and around 78% on significant hills (see # 8 & # 14). So the 100 wh you burned going up the hill can't give you more than around 60 wh on the same hill on the way down. (assuming the efficiency is similar comparing up slopes to down slopes). And on Shallow hills, 100 wh consumed going up will give back somewhat less than 60 wh when coming down, due to the lower efficiencies involved.

Also, posts # 23 & # 29 point out that a 2.5 to 3 degree downslope is required to gain more energy from the drop than is being consumed to move forward.

[CovRob]

I recall my supplier saying on delivery that the regenerative energy was only about 5% downhill of what was consumed going up ...now he isn't as technical as many on here and I can't be sure of the accuracy, but on the basis of what he said I don't rely on recharging on the move extending my range significantly.

[bystander]

I recall my supplier saying on delivery that the regenerative energy was only about 5% downhill of what was consumed going up ...now he isn't as technical as many on here and I can't be sure of the accuracy, but on the basis of what he said I don't rely on recharging on the move extending my range significantly.It's been mentioned that regen recovery depends on the amount of slope, speeds, and riding technique. At higher speeds, shallower inclines, and with more aggressive start/stops, 5% could be an accurate estimate.

By the way, when we're talking about a closed circuit course (that is, returning to the same elevation that one started from), range is not being extended, we're just losing less because a fraction of the energy is being recovered during the downhill portions.

If your PT can go 20 miles on a full charge on a flat course, you will find that it can only go a fraction of that if it is all uphill, depending on payload weight and the elevation gain.

Let's say you find a long hill and determine that you can go 12 miles one way (up) on a full charge.

If you get someone to give you and your PT a ride home, recharge it, and try the hill again, but this time stop at the 6 mile point, and glide back down to the start point, you will have traveled 12 miles, just like the previous trip.

However, this time there will still be some energy in your batteries for a few more miles of travel. If the PT were 100% efficient at regenerating charge, you would have 8 miles of range on the flat left. If the PT were 5 % efficient, you would only have 4 /10ths of a mile left.

On the other hand, on non-closed-circuit courses, when the start point is uphill of the destination, then we can talk about truly extending range, because the net elevation loss contributes extra energy for the trip. In this case, a heavier payload can give more distance, provided that the slope is steep enough.

[ryan_walters]

Also, posts # 23 & # 29 point out that a 2.5 to 3 degree downslope is required to gain more energy from the drop than is being consumed to move forward.

Sounds about right.

I have noticed that one hill, when going up, is just shy of flat face kicking in. I get 19-20km/h if I ride the speed limiter. When going back down the same hill, I can hear that the motors are on average, not braking, and also not really 'driving'. Pretty much at the break even point. I would imagine that going down this is is using very close to zero power, ignoring the power used to spin the motors at the same speed as the wheels. And of course power used to keep you balanced. Any hill steeper than that, ie one where flat face kicks in going up, and coming down, there will probably be some regenerative charging. Anything less, and you'll probably use power going down it. I'd also wager that the slower you go down a hill, the more benefit you'll get out of it, asuming it's steep enough in the first place.

[Llarry]

Hills? Huh? I don't get it... (I live in the Phoenix area...)

Actually, a couple of weeks ago I got to glide on a paved trail in Scottsdale and after heading up part of a climb, when I turned back I did actually see a small gain from the descent...

[KSagal]

Going downhill can surely charge the batteries. Long ago, I was told that the maximum that can effectivly be absorbed by the NiMH batteries was about 3 to 6 miles per hour back... In other words, if the hill is steep enough that you would glide down at 12 miles per hour, and you restrict to 6 to 9 mph, you would put energy into the batteries.

You could leanback to 3 mph, but would not put more into the batteries.

I suspect that you could get about 3 mph of regenerative power into the NiMHs and more, maybe closer to 6 mph into LiIons.

I believe this has been discussed many times before...

It is worthwhile to try to glide uphill on the full batteries, and downhill on empty ones, as the less charge in the battery, the more receptive it is to regenerative charging...

[polo_pro]

Going downhill can surely charge the batteries. Long ago, I was told that the maximum that can effectivly be absorbed by the NiMH batteries was about 3 to 6 miles per hour back... In other words, if the hill is steep enough that you would glide down at 12 miles per hour, and you restrict to 6 to 9 mph, you would put energy into the batteries.

Sounds about right based on my real life experiences. I've done some 3000 foot descents! But I only got 3 or so miles back despite the empty batteries being fully charged.

[David Long]

It is worthwhile to try to glide uphill on the full batteries, and downhill on empty ones, as the less charge in the battery, the more receptive it is to regenerative charging...

So someone who lives up on top of a hill won't see as much recharge as one who lives at the base of the hill and visits the top? ;-)

[KSagal]

So someone who lives up on top of a hill won't see as much recharge as one who lives at the base of the hill and visits the top? ;-)


This is basicly correct. I believe that there is not likely to be even energy extended in ascending and decending, but your suggestion is right. If you start at in the valley with full batteries, glide uphill in the beginning, and downhill at the end, you should go a bit further than the same hills if you start at the top, glide down and then back up at the end of the glide.