Nimh Batteries from Batteryspace.com

Hmm... They say


Standard discharging rate: 13Amp ( Recommended and warrantied)
Highest Discharging rate for continuous running: 40Amp ( high discharging rate will protect battery capacity )


http://crystalyte.com/x5specs.htm -- indicates that the amperage rate at various voltages and wheel sizes would max around 20 amps. Seems like it would be fine.

I found this page by going to http://crystalyte.com/index.html and clicking on the Specs link in the lefthand frame.

- David Heron, http://davidherron.com/

Ric, I've been tinkering around with it more than anything and haven't been riding that bike much. If you head to the Member Vehicles section you'll find a listing for that bike in its current incarnation (Stretch Bicycle). One detail is that bike currently doesn't have a chain so I can't pedal it. Even so I can easily do a 3-4 mile loop with the 2s1p DeWalt pack, using only the battery power to drive the bike. Towards the end of the ride the acceleration suffers a bit.

Yes it's a WE BD36 w/ 35amp controller.

- David Heron, http://davidherron.com/

I'm using the 10ahr (really ~8ahr) D cells . I put them in 2 boxes in parrallel thus I have 60 cells in one box and another 60 in another box for a total of 120 cells (20ahr). These were bought by requesting a bulk quote which cost me just over $3.50 a cell.

Why 2x72v you ask? Well using a single box (72-84v 10ahr) I got voltage drops of 30v at 35A, and determined these batteries cannot deliver more than 1400W (more realistically ~ 1200W). Thus in parallel, the voltage sag is much less and I get 2600W combined at 65vmin and 40A

I also run pretty fast - routinely run over 40 on the flats by the bay (today was 43 coming home) and these batts have now around 300 cycles of abuse and still work fine. I've replaced a few here and there, but even thisD-cell pack works well. Average Ahr to work is 6-7 for 24 miles, and I really fly.
Sustained amps (drainbrain) indicate ~10-12 draw which gets me over 27mph.
So with these F cells, I imagine must be much better than these D cells I'm using, but I avoid any F cells due to their uncertain manufacturing sources (I'm told). D cells are cheap and really work with 72V, but you must stay under 15A sustained or these get very hot.
BTW - the pack is home made of indiv. 60x2 button tops. Probably can send some photos your way.

Also, I must stress, the D cells WILL get hot when charging later on during their lifetime, and the platic wrap WILL come off exposing them as bare metal and cause a very serious short if you're wiring them together without any insulators/isolators.

I should mention I'm running the phoenix racer (503) in a custom welded SS fork. These batts have PLENTY of power. F cells are even better!

Teffo

84V X503 FRONT MOTOR CUSTOM NIMH

All of the larger Batteryspace cells (F, D, C) all have about the same internal resistance. The current ratings only take into account internal heating, not voltage sag and efficiency. None of these cells perform well over ~10A IMHO. If the voltage sags 20% that's 20% of your pack's energy wasted as heat. The Powerizer sub-C cells actually have lower resistance and can deliver 15-20A with decent sag. If you're willing to go through the hoops of dealing with parallel operation it's better to use several parallel strings of cells than one string of large cells.

On my bike I use 20s3p strings of Powerizer sub-C cells mounted in the diamond frame for 24V 9.9AH. I added 4s3p in a little box on the back rack to boost to 28.8V, which makes my Kollmorgan motor happy. This is a light weight setup that gets me to and from work. Voltage sag is ~1.5V at 30A. For longer trips I add another box with 24s2p Powerizer C cells to give another 8AH.

http://mysite.verizon.net/tbrown59/electrobike.htm

Teffo,
What brand of batteries are you using, and where can you get them? What charger(s) do you use?

"the D cells WILL get hot when charging later on during their lifetime"

Hi Teffo,

Thats interesting information, what rate are you charging these cells at?

"Also, I must stress, the D cells WILL get hot when charging later on during their lifetime, and the platic wrap WILL come off exposing them as bare metal"

That's too hot.

I charge with the batteryspace.com 2A 24v chargers and several 1.6A "newer" chargers.

What has happened in the past is when I leave these to charge over the expected 2-3 hour recharge time, I come back after 3.5 hours and the charger is still chugging away. Cells therefore overheat. 2 months ago, to my horror 5 cells went into reversal after the charger did not shut off and I found them vented. Those 5 Cells went to the trash. What I do now, and is my standard workflow, is to never go to sleep until the charger is done. I know from experience 3 hours is max time. At work, I monitor these every 1/2hour.

When these were new, they NEVER even got warm after a charge, but after about 300 cycles, all start to get mildly warm, but not hot to the touch. I will run these till they're gone.

Anyway, I've used these cells over several years and you will eventually have a situation where a cell here or there will get weak, and overcharge, while nearest neighbours are still charging, and the thin plastic will come off.

I believe there's a learning curve with NiMH, and it will be a long time till you're very knowledgeable with your pack.
I can also attest, the older 2A batteryspace chargers are unreliable and need supervision. NEVER leave these charging while you sleep. I have bought 3 of their 1.6A chargers and these are much more reliable. After about 100 cycles, they always shut off.

Remember these are inexpensive cells and their current goes to pits after 10A load. Like I said, 30volt drops at 35A. Run the packs in parallel, and they really shine. If you like 48v with your x503, then run 40cells on each side of the panniers, and I garantee you will like them.

So, like I said, my commute is very long and these cells have never failed me yet. They may not handle high current in 48v, but at 72v, pack capacity is around 1200W. I verified this with drainbrain and keep very detailed graphs. A very good SAFT pack can handle 20A continuous at 72V, and those are excellent for 48v. Not these batteryspace D's - unless you run 2 packs in parallel...

Teffo

84V X503 FRONT MOTOR CUSTOM NIMH

See above post,
Batteryspace.com D cells and Tenergy from ALLBATTERY.COM
Anyone know if their specs are the same?

You guys know of this vendor for batts?
http://www.forsenusa.com/batteries.html

Teffo

84V X503 FRONT MOTOR CUSTOM NIMH

Teffo,

Thats great info. I find first hand reports on nimh batteries few and far between! I think its great that you've managed to get to 300 cycles despite toasting the cells with the dodgy batteryspace chargers. I have a 48 volt 13AH pack . I ordered got my batteries from tmk batteries in China. I think forsen USA also uses them for some of its battery packs.

I've put about 100 cycles on them now and have had no problems or dead cells. The resistance is aproximatly 6 milliohms per cell. So a 48 volt packs sags about 7-8 volts at 30 amps. I'm now using 24 volt bosch drill chargers as it only charges at .9 amps even if it were to overcharge its low enough not to damage the cells badly. It seems to work ok as the cells normally charge on time and only get warm at the end of charge if at all. on discharge they only get warm above 30 amps continous.

I've heard that there are different kinds of nimh cells produced with different resistance. Basically there are 2 kinds, foam and sintered. The foam being higher resistance type which i'm guessing you have. see here:

http://www.electronicproducts.com/ShowPage.asp?SECTION=3700&PRIMID=&FileName=marmol1.mar2001

but even within these two types resistance/discharge rate varies a lot my manufacturer/product line.

I think batteryspace and all battery sell a variety of different resistance d cells. I heard a report on the power-assist forum that some batteryspace d cells were around 7moms/cell and others were higher than this. I guess the best way to find out is to buy a couple / test them and see.