battery question??

[ecgoeken]

i have a 36V 500W ebike and right now I am using a 36V 13.5Ah SLA battery.  This pack is incredibly heavy!  im looking for a way to shed the weight.  I was looking for some good deals on batteries (if anyone has any other suggestions, that would be great) and came across this on ebay.  http://cgi.ebay.com/10-D-10000mAh-NiMH-Rechargeable-Batteries-with-Tabs_W0QQitemZ330158063379QQihZ014QQcategoryZ40975QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247  does anyone have an opinion on whether or not this will be a good upgrade from what I already have or if these will even work?  I was planning on putting 30 of these in a series.  the math works out to be 36V 10Ah.  but im not sure if using this many smaller voltage batteries is a good idea or not.  any thoughts?

[Electrobent]

The choke point is how much current you can draw from them at once.  I have the 36V BLDC 500W motor and after I melted the SLAs that came with I ordered a 39.6 10MAH NIMH pack from battery space.  While they assured me that this would be adequate, the pack grew very hot and started to get hot when charging.  I ordered another pack and put them in parallel.  That was about a year ago and there was a 1.5V difference in the two packs then and there still is now. 

It works very well now and I probably have 10 times the range I need carrying 66 D cells around.

If I were doing it now, I'd buy the LiFePO pack from Golden Motor unless someone said it was sh!t.  You can suck 20 amps out of a 10 AH LiFePO pack and not bake it--not so with NiMH. 

[philf]

That's an interesting post...

I've purchased two sets of the very same batteries from "all-battery" in the last two months, and the price wasn't as favourable as it is in this eBay listing.  I think I know why...

The first set of cells I received were excellent.  The power delivery was indiscernable from the SLA batteries I had been using before.  This enticed me to go back at them for another set.

I can tell you in no uncertain terms that the second batch I received were nothing like the first.  Not only were they physically different (the first set had flat positive terminals and insulated tabs, where the second set looked like regular flashlight batteries with tabs welded on), but the power delivery is not the same.  They do the job, but their performance under high current drain falls REALLY short of the first set.  Not only that, but the welds on the tabs are inferior.  You can rip the tabs off the positive terminal with little effort.

I'm wondering if this is why all-battery is dumping "27 sets" of these things on eBay.  Interestingly, the batteries they are showing come loosely boxed in packages of 8.  The first (superior) set I got were shrink wrapped in sets of 4.  Clearly from different sources, despite the common heat shrink wrapper.

Ack.  This is easier...  Here - pictures help...



The one on the left was what came with the first order (I was impressed with these).  The one on the right I'm not as happy with, and this appears to be the same cell they're selling on eBay.  As you can see, the tab on the positive terminal is missing.  Fondly remembering the late Steve Irwin, I can only say (in my best mock Aussie accent), "I barely touched the beggar, and it came ROIGHT off"...

[ahend]

I have no experience with the 10AH NiMH “D” cells, but I was running a 14AH “F” cell NiMH pack which worked very well. My commute would pull up to 25 amps at times for short periods without any excess heat. The pack never got hot (warm, yes) during charging or use. There was enough energy in a full charge to make a round trip of 23 miles (37km), on mostly flat, paved terrain. In fairness I need to mention that I pedal like a mad man to hasten to commute. The weight of the pack was around 14lbs (6.4kg).

Because I provided no shock barrier between my pack and the rack it was tightly strapped to, a rather abused corner cell shorted internally during a rough patch of my commute and the whole thing discharged through it. Alas, it is no more. I am not at all unhappy with the performance of the NiMH pack. It was cost effective, fairly light weight, and delivered the goods when I asked for them. If I would have taken better care of it, it would still be taking care of me.

I currently have an order in for the Golden Motor LiFePO4. If you can justify the cost, it truly seems to be the chemistry to have.

[ecgoeken]

thanks for the suggestions.  so I guess the concern with these types of batteries is the current pull.  its about $180 to get 36V 10Ah from these d cells, which is enticing.  but if they're going to overheat then maybe its not even worth the $180.  I looked at the F cells mentioned above and they look great but almost double the price ($340) for a 36V 14Ah.  for that it seems I could get 60 of the D cells for a 36V 20Ah battery.  but again I am concerned with the durability of these D cells under the power demands of a 500W motor.  price wise I am inclined to go with the D cells, but performace wise I am inclined to go with the F cells.  does this seem like a reasonable claim? (maybe I am just looking for an excuse to buy the cheaper batteries:-) any more suggestions on which type of battery to go with?  I really want to get rid of the 35 pounds of lead strapped to the back of my bike!

[Electrobent]

and you are going to need a charger or two--only charge in series--not parallel.

How about the 10ah 36V LiFePO4 pack from GM with charger for $389?

Or I sell you my NiMH packs and chargers and I'll by the LiFePO4 packs   ??