Chinese NiMH vs. SAFT cells

I'm trying to come up with a bettery battery pack for my electric bike
conversion and have found huge price differences between 9.0Ah D cells
made in China and those made in Japan or France.
I get more than 10 Ah from the 3 new 12V 12 Ah SLA cells on my bike,
using the 30+ amp full throttle very sparingly. That still only gets me
about 10 miles in a half hour or so with a 40 pound battery. I really
need to get twice that mileage and i don't like having to charge the SLA
immediately after discharge. NiMH cells are the obvious answer, and i'm
trying to determine whether the 9.0 Ah SAFT cell is worth 3x the price
of the 9.0 Ah Chinese battery.
I want to build a 64 cell 40V 18 Ah pack out of 9.0 Ah NiMH D cells. I
need 35A output for several minutes at a time. I can get Chinese cells
rated at 50A for less than $6 and the SAFT cells are about $15. Can it
really be that the SAFT cells will deliver 3x the performance? Anybody
have any experience with this? thanks...
Reply to
bob mcree
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I have not a clue what you talking about.
Batteries Plus has locations all over the country. Everytime I need a battery pack I visit them first. They might not be the least expensive but I have always been satisfyed with their products.
Reply to
SQLit
Then why are you wasting your time and mine responding if you don't understand what I'm talking about? I'm looking for intelligent responses from engineers and others who understand batteries... -bob
Reply to
bob mcree
Guess you missed the referenced experts.
Reply to
SQLit
are you referring to a source of information i missed? i just joined this newsgroup so i don't know what you mean... -bob
Reply to
bob mcree
Generally a little tolerance will get you further on this group which you have just joined. Most will decline to help out bombastic folks !!
Reply to
Rheilly Phoull
you're right rheilly, i just don't understand why anyone would respond to a post that way. i guess i should have offered to explain my post in more detail, though i thought i was pretty clear. nobody else asked for an explanation; i thought SQLit was being sarcastic. i had no intention to be insulting or "bombastic"; i have never been accused of being grandiloquent or pompous and i will try to keep it that way. -bob
Reply to
bob mcree
bob mcree schrieb:
Hello,
I would search for the data sheets of both cells and carefully read and compare them. If I would need 64 cells, I would buy some cells for own tests before I buy 64 cells. But if you want a pack with 40 V and 18 Ah, I would suggest larger cells than D cells. Connecting two D cells in parallel can cause problems.
Good luck
Reply to
Uwe Hercksen
i have read and compared the data sheets of almost all the available cells and the Powerizer cells have the best bang for the buck by far, on paper. i bought 2 cells more than i need and am going to do testing on those 2 before i touch the rest. if the cells do not perform to specification i will return them and i am confident batteryspace will give me a refund. i know i should take more time before buying all the cells but you know how it is when you have a project you get excited about...
i would, but the cost of F cells is more than twice as high, and the D cells on paper will do what i need.
Connecting two D cells in parallel can cause problems.
i intend to have 0.3V 50A Schottky diodes preventing one pack discharging into the other, and my current drain from the two packs in parallel will still be much less than the constant current spec of the individual cells so the bike could run off 1/2 the pack. i will not be charging the cells in parallel, but in banks of 8. I am building an 8 channel delta temp/time charger.
do you forsee any problems i am missing?
Reply to
bob mcree
When i was a teenager we used to use the term "Chinese fire drill" to describe a Keystone Cops type maneuver where we would stop the car and get out one side then run around to get back in the other side, ending up basically where we started. I am reminded of this in my dealings with batteryspace.com.
Every time i think i understand the specification on one of their batteries they change it. They sold me batteries that couldn't work on my ebike and took them back, giving me a refund. Now they have a 10 A/h D cell that they say on their webpage will put out 50A continuous and 100A peak so i bought some. i asked them if it was acceptable to match the cells at 30A and they said that was fine. They said they would ship my cells yesterday, and took my $440. Today they sent me an email saying my order would ship TOMORROW, and that i could only discharge the cells at 10A.
I understand there is a bit of a language problem but this is TOO MUCH. I have let them know that I am going to do extensive unbiased testing on their product and pass the data on to this community, free advertising for which i would expect them to be grateful. I want their cells to work, and I am willing to let them have my services for which i usually charge $100 an hour, for free. Every time i talk with them i get a different story, and i am quickly losing confidence. One day the cells will produce 100A and the next day the same cells can only be discharged at 10A.
If I can't get the straight story from them tomorrow i am going to give up and demand they refund my $440. Their cells sound really good on paper but if they keep changing the spec every day how can i know what they will do? How can they stay in business with this kind of nonsense going on?
I'll let y'all know tomorrow what happens next. it's an interesting, if somewhat frustrat
Reply to
bob mcree
How in the world do you wire 50 amp conductors to D cells? I have no doubt you can get 100 A instantaneously (likely followed by explosion) but 50 amps continously? I think that is much too ask.
bob mcree wrote:
Reply to
**THE-RFI-EMI-GUY**
for 10 years i have been running a 1/10 scale truck that uses sC cells that produce >50A... even the old Sanyo 1400 sC would put out 50A for a couple of minutes and just get warm.
the last rc pack i bought puts out 35A for >450 sec. and it is not at all a top of the line racing pack. this is a sC from GP rated at 3700 mah that puts out over 4 Ah at 35A. some people are using these cells to power ebikes but i don't know what kind of cycle life they are getting. running several strings in parallel is an option some are using, and of course it limits the current drain from each cell. diodes can be used to prevent one string discharging into the other(s)
the peak current drawn by the motor in my rc truck is over 100A and subC sized batteries that can do this have been around for over 10 years.
it is really pretty easy to solder 12 gauge or even larger to batteries, everyone in the rc field has been doing it for 20+ years... the cells i have ordered have spot welded tabs. The Segway uses D cells with spot welded tabs. I was planning on measuring the drop of the tabs with my 4 terminal lab meter and soldering them if resistance seems too high. i really only got batteries with tabs for warranty purposes. i have soldered to hundreds of NiMH batteries and it isn't that hard to do. You just have to scrape off the plating and use Kester 88 flux core solder...
-bob
Reply to
bob mcree

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