Building a123 packs for dummies.....

[Malcolm]

a 16s8p pack could be built using A123's, What about Batt management system? who should I be talking to for this? Gary Goodrum and Bob Mcree?

Highly recommended reading: http://endless-sphere.com/forums/viewtopic.php?t=2498

Regarding range: I get 15 miles max from my 60V 26Ah lead acid pack. According to the Drain Brain I can actually pull 20Ah from the Hawker batteries if I take things easy.

Replacing my lead acid pack (weight 48 kg) with 20Ah of A123 or LifeBatt cells (weight 15 kg) should give me the same range, thanks to the reduction in weight and the fact that you can actually draw almost the rated capacity from these cells.

With 60Ah of A123 or LifeBatt (weight 45 kg) I should have a real maximum range of 45 miles. The reduced voltage sag of lithium iron would also mean a slightly higher average speed and more lively performance.
Look forward to seeing if my projections hold out when prices come down some

EDIT: Just realised that's a range of 1 mile per kilogram of lithium ion. It won't be linear, of course, but maybe useful as a rough guide.

 

[GreatScott!]

" Why would you want more than 5C? At a 5C discharge rate you're looking at about a 15 minute bike ride. Unless you're trying to set a speed record, you'd be better served by a bike that used perhaps 1.5C. Then you could ride for an hour at least. "

yeah man, well I don't know, all this $hit is confusing me. Whatever will support an alltrax controller that is rated for Max 400amps and set to 300amps or can be set lower. I'm sure it doesn't pull that amperage for long seeing as how I use a 48v 20Ah pack (4 SLA in series). So I suppose when I pin it this pulls high amperages? If I was to ride my bike hard, lets say like on an MX mid size track I can get maybe two solid laps.

can you link to xystersbike ?

"With 60Ah of A123 or LifeBatt (weight 45 kg) I should have a real maximum range of 45 miles. The reduced voltage sag of lithium iron would also mean a slightly higher average speed and more lively performance.
Look forward to seeing if my projections hold out when prices come down some"

Yeah, but is that real world conditions, what sort of hill gradation etc.

 

[Ypedal]

1 C = 1 x the rated AH of your battery

Example :

Your 48v 20ah SLA pack.. at 1 C = 20 amps.

( The thing with SLA is that their capacity is calculated at a slow drain rate.. over 20 hours... and that's C / 20 )

So when you wack the throttle and draw 300 amps ( 300 amps devided by 20 with is your ah in capacity ) .... that's 15-C

So.. at 15C your 20ah pack is dead flat in no time.

Nicd and NiMh canot provide 15C... so you would need 100 ah worth to provide 300 amps..

 

[Malcolm]

Yeah, but is that real world conditions, what sort of hill gradation etc.

Yes, that's real-world, stop-start city riding, averaging around 25 mph, with occasional bursts to 45–50 mph. Not very hilly where I live I though. Like I said, that's taking things easy. If I went flat out that range would probably be cut in half.

 

[J Barrie Wilkinson]

Malcolm,
I seem to remember a good size hill west of Newcastle where Two Ball Lonnen crosses the the road that follows Hadrians Wall. I may not remember correctly, left Tyneside in 1952 at 16, hills always seem steeper when your young.

 

[Malcolm]

Your memory is good J. You're thinking of Westgate Road. All the motorcycle shops are at the bottom of the hill, close to the city and station. The only other real hill is in Byker, to the east of the city.

 

[GreatScott!]

No, they don't last long when the throttle is pinned. But it's hella fun all 2-3 minutes that you get outta of it. I had my bike up to 83kph on road this summer, lasts a few minutes, might put some footage up next season on youtube of drag runs. Electric is hella fast for accel when the battery is fresh, I could probably beat most hi end sports cars in the first 5-10 seconds.

If ridden conservatively I have been gone on rides for about 45 minutes. Goal is, if new batt technology doesn't work out (looking pretty pricy at the moment), will just buy a bunch of SLA's and a few chargers and swap out after a ride. Takes about 2 hours to charge, figure 1/2hr rides, so I would need 4 battery sets and 2 more chargers. That would be continous riding in a 5km radius............with zero outlets left. lol.


Hmmm....I wonder how Zero/electricross does it then, their new bikes use Lipo and I wouldn't imagine they've changed the controller and amperage rates that much.

 

[Malcolm]

Here's a handy little low-voltage battery alarm I found (thanks to jimsky): http://www.rcgroups.com/forums/showthread.php?t=221018
The piezo buzzer sounds when the battery voltage drops below a preset level. It was designed for RC lipo packs, but I figure it's so cheap and simple to build you could make up as many as you need for a pack and just cut your motor when the first one sounds, or keep on going until all the dogs in town are chasing you

It uses an adjustable zener regulator and a logic FET to trigger the buzzer, at a voltage set by R1 and R2. The trigger voltage is calculated as 2.5 x (1 + R1/R2). R1 and R2 should both be above 1K to keep the input current low enough. I've built this on a breadboard and replaced R1 and R2 with a 10K preset potentiometer (with the divider connected to the Zener REF leg). This lets me adjust the trigger voltage from around 3V (for a single cell) to around 9V (for three cells).

The lowest working voltage depends on the piezo buzzer you get. The ones I have work at 3V but aren't very loud at this voltage, so I'll probably use one of these circuits across each two cells. The fewer the number of cells you connect it across, the more sensitive it will be to variations in individual cells (or parallel strings). If one buzzer is always the first to sound it may indicate a weak cell.

R4 is only needed if the battery voltage is higher than the upper limit for the piezo buzzer.

This is just intended as a cheap and cheerful low-voltage warning. Because there are so few components you can just solder them together directly and shrink wrap them with the buzzer. If you want more sophisticated protection I'd definitely recommend following this thread: http://endless-sphere.com/forums/viewtopic.php?t=2498&start=120

 

[GreatScott!]

Just not sure if they are for high amperage.