Add more cells to a NiMh bike?

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Frolle
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Last seen: 9 years 6 months ago
Joined: Friday, May 11, 2012 - 07:40
Points: 46
Add more cells to a NiMh bike?

Just realized that I got fooled.
The extra “brand new” pack I got with the bike turned out to be pretty lousy.
¾ of the cells was at about 30Ah, and ¼ was swollen and at about 25Ah, except for the two that was shortened and cracked in the bottom… So the replacement pack turned out to be worse than the original one with about 20.000km on it. Looking at the serial numbers the good cells was from one series, and the bad ones from two different series.

As I see it there is two options to increase the range/performance.

Alt. 1 (probably the best)
Add 8 or 9 (maybe more?) cells in the trunk.
+ I have the cells.
+ Increased Voltage = decreased Current = good for the cells/electronics/connections etc.
- Need new firmware for the charger.
- Might affect regenerative braking due to higher system voltage
- I need to bother The Laird once more.

Alt. 2 (probably not so good)
Add 2x AA NiMh cells to every less good cell.
+ No firmware modification needed.
- Time consuming to fix.
- More expensive
- I will probably not do it, since it is more time consuming and expensive.

What do you think?
Is is possible to increase the voltage?
If I ruin regenerative braking a bit, it is no big deal, since I mainly get out on a big road directly for the first 20km.
How high can the charger go? How much will the bike stand?
I think I have seen EQ charge at 148V as highest (154V with original firmware).
102 cells = 148V
102 + 8 = 160V
102 + 9 = 161V
102 + 8 + 8 = 171V

Example, Normal driving I have 127V at 50A (guess) = 6,35kW.
+ 9 cell = 6,35kW at 139V = 45,7A <-- Little happier cells
+ 16 cell = 6,35kW at 148V = 43A <-- A lot more happier cells, less happy electronics…?

And I do not mind filling up the the trunk with batteries since my helmet does not fit there anyway. You know here in Sweden everything is about safety, so the helmets contains twice as much shock absorbing foam as in the rest of the world, thereby they get a lot bigger.

Really bad cells:
IMG_20140309_151855.jpg
.
Yes, the thing about the helmet was a joke.

/ Frolle

R
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Last seen: 3 months 1 week ago
Joined: Thursday, June 18, 2009 - 09:46
Points: 1768
Re: Add more cells to a NiMh bike?

Impressive pictures, poor cells!

My thoughts:


Alt. 1 (probably the best)
Add 8 or 9 (maybe more?) cells in the trunk.

When a bad cell empties and reverses the voltage, in turns into a resistance. It blocks the flow of energy, gets very hot, damaging the nearest cells, and you risk to ignite a fire.
There are 102 cells inside the Vectrix. One cell represents 1% of entire battery capacity, but when it dies to 0.00 volts, it drops the range to only 3-4 miles. That 1% wipes out 85% of the effective capacity of the vectrix!
Adding a string of 9 cells may temporally increase your range, but the swollen cells will continue to collapse at fast pace until they die, reducing the effective capacity of your entire battery to almost nothing.

Alt. 2 (probably not so good)
Add 2x AA NiMh cells to every less good cell.

Same problem. Bad cells will eventually collapse soon. A lot of work for a pair months of good range.

I suggest you find the worst cells of every 8-9 cell string(you can use an Imax B8 RC charger do cycle 9-18 or 27 cells each time), replace them with good cells, and add an external plug to your battery to perform an equalizing charge once per month, at 0,2-0,5A during 2-3 days.

However, if I were you, I would forget about NIMH and install Lithium right now.
Good luck!

Seiermann
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Last seen: 9 years 4 days ago
Joined: Monday, February 6, 2012 - 09:32
Points: 69
Re: Add more cells to a NiMh bike?

Hi Frolle,
as there are many cells on the market I think the best way would be to replace the bad cells. By taking little AA cells ythe capacity would degrease...
I' m selling good cells with 30Ahs (charging/discharging) for 10€/cells, but only in complete bricks. If you need some, pls. send me a PM.
greets
Simon

Frolle
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Last seen: 9 years 6 months ago
Joined: Friday, May 11, 2012 - 07:40
Points: 46
Re: Add more cells to a NiMh bike?

Thanks Seiermann, but I have a lot of cells.
I have used swollen cells previously and they have not cased any problems (yet).
The pack in the picture was the first one I had failing.
I am eager to test the approach with more cells to restore the original performance, or better, with almost no money spent.

R: Yes, it would be nice with lithium, but not until I am out of NiMh-cells. I have driven about 16.000km on one pack that is still in good-enough-shape. I not not agree that once shortened cell wipes out 85% of the capacity. Maybe a single digit % according to my own experience.

Yes, I have used iMax B8s to check every cell.

Does any one know the maximum recommended system voltage?
And can the display show this voltage?

Big-Head-Cop.jpg

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