AA Nihm's

How do you store and manage your electricity?
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Plagiarise
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AA Nihm's

Post by Plagiarise »

Hello all, complete noob here. I was just wondering if like a thousand AA Nihm's would be a viable option to power an EV. They go for around $1 on ebay and am sure even less in bulk. They could be stacked in different ways to conserve space and balance weight. (obviously very time consuming)
It was like that when I got here!

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acmotor
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AA Nihm's

Post by acmotor »

Yep, it has been done and it works.
The thousands of battery connections mean a lot of work though.

If you consider the required battery capacity of say 10 to 20 kWh for a vehicle, then looking at the volts and Ah rating you get a feel for what is involved.

Consider a 120V system and 12kWh capacity with peak power of 48kW.
You would need 100Ah capacity with peak current of 400A.
If you had AA cells of 2Ah you would need 50 cells in parallel x 100 cells high (for 120V). That makes 5000 cells.
(I think the tesla runs 7000 small format lithium cells)
The NiMH cells require less battery managment than lithiums however there is still a need to keep track of the voltages on the 100 cells high.
I would arrange the battery pack as 50 x 120V strings in parallel with some way of monitoring each string current to confirm that there is load sharing whilst still monitoring the 100 cell voltages high.
NiMH are tollerant of low current overcharge, however they suffer (as most batteries do) by over discharege or reverse charge.

This probably sums up the disadvantage of building a battery pack from small cells..... the vast amount of V and A monitoring. However it can be and is done.

Do buy batteries with pre-fitted solder tabs.

iMiEV MY12     110,230km in pure Electric and loving it !

Plagiarise
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AA Nihm's

Post by Plagiarise »

That's a lot of batteries... some are 2.5Ah so that would bring the number to 4000, but that's still a hell of a lot. The Tesla has over 6000 lithium but they are a bit bigger and I'm guessing have a higher capacity.... but it gets 350km which is amazing (I watched a stupid promo on youtube which said it was only good for a second or third car because of the limited distance...wtf... who drives more than that it a day??? That would be my first car, with a second (ice) for uber long holiday trips). Sorry getting of topic. Ok, like I said before I am a total noob, but very excited about the idea of an electric car. I would like to build a car capable of 100km/h and 100km range (I live in Perth hills about 35km from city), would the figures you quoted be capable of that?
It was like that when I got here!

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acmotor
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AA Nihm's

Post by acmotor »

There is a lot of info on the net about energy requirements.
There is a spreadsheet on the waeva.asn.au site that may help.

Just roughly,
1000kg vehicle to cruise at 100kph may require 10-15kW
to get up Greenmount (5deg) 30kW
to accelerate 0-100 in 10 sec 60kW
to travel 100km at 300Wh/km = 30kWh of battery pack stop/start/hills

So look for a 30kWh battery pack with 60kW peak discharge rate as a starting point. This is the top end of present battery technology.
LiIon, Lipo, Zebra Ni/NaCl etc. Between $10k and $25k.





iMiEV MY12     110,230km in pure Electric and loving it !

zeva
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AA Nihm's

Post by zeva »

About a year ago I looked at using NiMH and had a good chat with the experts on EVDL about the idea. In short, it doesn't work very well..

The main problem is that nickel battery chemistries, when being charged, reach a peak voltage then actually start to drop in voltage. This is fine when charging single strings of cells - you just get the charger to stop putting charge in when it detects the pack voltage has stopped increasing - but problems come up with cells in parallel. No two cells are identical, so when charging in parallel one cell reaches its peak first. Its voltage starts to drop, so it starts to accept more and more of the charge current. In worst case scenarios, the cells its in parallel with will start discharging into that cell, which quickly overheats.

The pack might work OK initially with brand new, closely matched cells - and using a charger with amp-hour counter to make sure you never go past the peak voltage.. but as the pack gets older the cells will drift further apart, and eventually things will start blowing up!

As a side note, did you know there's no technical reason why large capacity NiMH batteries can't be made? Unfortunately Chevron Texaco own the patents (through subsidiary company Cobasys) and won't let anyone produce cells larger than 14Ah. Since you can't easily parallel them, it basically precludes use in EVs. (At the time they purchased the patents from Ovonics, Panasonic was making 100Ah NiMHs for Toyota's Rav4 EV.. then they got sued by Cobasys. Since then there hasn't been a single commercial EV using NiMHs; Cobasys are basically patent-shelving the technology Image such a travesty..)

At any rate, Lithiums are here now and are superior to NiMH in almost every respect (other than cost.. for now!)

PS: Here's one EV that did use NiMHs, though it's not exactly a daily driver:
http://www.dwra.net/whitelightning.htm

PPS: Where abouts in the hills are you Plagiarise? I'm in Maida Vale.
Ian Hooper
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"Never doubt that the work of a small group of thoughtful, committed citizens can change the world." - Margaret Mead
http://www.zeva.com.au

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acmotor
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AA Nihm's

Post by acmotor »

Ian, correct, thus my comment about arranging the pack as 50 x 120V strings with indiviual current monitor.
NiMH are still very viable and I would not rule them out.

BTW Lipo will pass Lithium Ion wet cells very soon.
iMiEV MY12     110,230km in pure Electric and loving it !

Plagiarise
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AA Nihm's

Post by Plagiarise »

I'm in Parkerville. I was looking into Nihm and found some companies who do pack (like for remote control cars and stuff, but some big enough for electric bikes and mopeds)so I was thinking seen as they make them, for a large enough order, perhaps they would do much bigger packs like 100 batteries. However I am a bit tight and would not be keen (and my wife would kill me) spending a lot to only have it blow up. Acmotor, I looked at the links on waeva site a couple of weeks ago. I think they might be in German, cause I don't understand a damn thing. I don't know much (or perhaps anything) about electricity and there is way to much info for a noob like me to even know what I'm looking at. One of my friends is an electronics engineer and if I go ahead with an EV I will be seeking his help. The lithium's are way to expensive. I was hoping for something better than lead without having to spend a fortune. Thanks for input, it is very useful.
It was like that when I got here!

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