Toshiba SCiB 24V 4.2Ah performance

krazykat

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Hello,

I am new to E-bikes. AndI am looking at a Schwinn Tailwind. This is a new bike but have concerns about the battery which has probably been in storage for some time. My question arises from the fact that the bike does not seem to be performing up to specs and the battery seems to be acting a bit odd.
The stated range is 20 miles. I am able to get about 16 miles on a flat gravel trail using the mid-range setting and peddling steadily with little effort.
The battery, a Toshiba SCiB 24V 4.2Ah, has 4 led lights, which when fully charged show 4 lights. After I have ridden about 9 miles it still shows 3 lights and after another 5 miles or so it shows 2 lights, then within the next mile or so it fails completely showing a dead battery. The manual warns against completely discharging the battery but this happens so fast as to be unpredictable . Is this proper battery behavior? Could it have been stored incorrectly?

Any help would be much appreciated,

John
 
If you really have a 24V 4.2Ah battery pack, I am surprised you get anywhere near 16 miles on a charge. That would be a 100.8 Wh battery pack. At a range of 16 miles, you would only be using 6.3 Wh/mile which if true is an excellent number.

According to nycewheels (http://www.nycewheels.com/schwinn-tailwind-electric-bike.html) their Schwinn Tailwind actually has a 29.4V 10Ah battery pack. That would be 294 Wh or 18.375 Wh/mile for 16 miles of range which is much more reasonable. To get 20 miles range out of this pack, you would need to limit your power consumption to 14.7 Wh/mile. This can be accomplished by pedaling more and/or going slower.

You don't mention what speed you were going. Speed can have a huge impact on range. My first ebike (SLA battery pack) was getting about 25 Wh/mile at around 20 mph (light pedal assist). I expect to get that to about 20 Wh/mile at around 20 mph with my second ebike (lithium ion battery pack) with a bit more pedaling. Going 25 mph would probably mean 30-35 Wh/mile for my bike. Going 15 mph would probably mean 15-20 Wh/mile.

The way the led lights are behaving doesn't really surprise me. They are going to be based on the voltage of the battery pack, which isn't completely linear. There is a sharp drop off near the end of the discharge curve.

You really should get a CA (Cycle Analyst) or at least a watt meter to monitor your power consumption and get a better idea of how your battery is behaving.
 
Sounds normal to me.
It is impossible to believe manufacturers range estimates, and 4.2Ah is a very tiny battery .
 
I have the same bike and have the same issues with the battery. Has anyone heard of replacement batteries being available? Or the battery getting refurbished?
Thanks! jodall
 
Those cells are Lithium Titanate, which are typically regarded as both the safest and highest cycle-capabilities of any lithium battery. (no SEI layer to break-down)

If those packs are dying, it's likely due to an improperly designed BMS that is functioning as a battery murdering system rather than management system. I know they are able to be disassembled, I would open one up and measure cell voltages, I suspect the issue is related to imbalance rather than worn out cells, and the imbalance can likely be corrected manually with a little power supply and/or a lightbulb.
 
That's a cool cell characteristic, but 64>90Wh/Kg gravimetric energy density (at cell level for Toshiba's LTO cells) significantly handicap's it against NCA chemistry on a pretty important characteristic for EVs.

NCA
li_7(2).jpg

LTO
li_8(1).jpg


graph source: http://batteryuniversity.com/learn/article/types_of_lithium_ion
 
You've swapped your labels on those diagrams.

Also, just as a friendly FYI, that site is notorious for outdated or bad data. Note the graph at the bottom of the page... lol
 
Yeah, I noticed that error and swapped the labels back the right way just before you posted :lol:

I'm aware of Battery University's dubious information credibility, but they were the only source I could find of those neat graphs in JPEG form (which they themselves referenced from BCG research's PDF publication published in 2010). In any case, the energy density figures I calculated are directly from Toshiba published figures.

As a comparison with the Panasonic 3.1Ah/3.6V NCR-18650A (NCA chemistry) that has a cell level gravimetric density of 245Wh/kg and significantly better cycle life than most other competing chemistrys with such high energy density's, my point is that LTO is much better suited to stationary applications - like grid stiffening - than in EV use where the relative weight penalty is just not competitive at the moment.
 
Yes, I absolutely agree. If conventional ~2v/cell LTO is ever going to have it's day in the sun, it's likely to be stationary applications. I would love to have a few kWh of LTO battery for home storage, I think it's my all time favorite for that application.
 
Backing up to post one. 16 miles from a 4 ah pack is not bad. The led's are not the greatest way to measure it, but the gradual winking out of the lights seems to indicate a gradual loss of voltage. Not a ride 2 miles then wham it's dead like a damaged battery would do.

Sounds like a good bike to me, the battery good enough for minimal assist. Getting 3/4 of advertised range is exceptionally good. But that may be that you pedal well.
 
Where I live it's hilly so I only get 11-12 miles.

I have a failed battery I'm trying to fix - does anyone have a schematic of the battery management circuit?
 
I have a Schwinn Tailwind and have not charged the battery for a few months. When I hook it up to the charger, it tries to charge but goes back to green in about a minute. I read not charging it can kill the battery. I can't find any replacement batteries out there on the web - does anyone know if they are available anymore?
 
Thanks to all of you who contributed to answering my original question. It was answered to my satisfaction and beyond. I have had the bike for a year now and am very happy with it.
Now I have a problem; I took the bike in for it’s yearly maintenance and it looks as though someone in the shop dropped the battery. A slight ding in one corner and a rattle that was not present prior to me taking it in. That battery seems to have lost about thirty percent of its normal cruising range. Does this make sense Is it something that could be fixed? It would help if I knew how to talk to the folks at Len’s Cycles about the issue.

Thanks again,

John
 
http://www.endless-sphere.com/forums/viewtopic.php?f=1&t=63158&p=944704#p944802
amberwolf said:
Unless there are parallled cells in there and some of them are now disconnected from the rest of the pack, and/or damaged from impact, it wouldn't make sense for range to drop like that.

However, is it possible they could have accidentally swapped your pack for someone else's, that has the ding on it and also is older or aging faster?
 
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