9C-12C NiMh Battery NEW!!!

safe · Oct 30, 2007

Features and Benefits

(18650 Size)
High quality 4/3 AF size 1.2 V, 4200 mAh rechargeable Nickel Metal Hydride (Ni-MH) battery
High capacity (4200 mAh) and high discharge rate (9C-12C) for super performance
Make your own battery pack in any combination of shape and voltage with easy soldering
Ideally suitable for making mini battery pack for remote controlled (RC) aircraft.
Ultra high capacity, 40% more running time than Ni-Cd battery.
Very long cycle life and Rapid battery charge up
Ideal for building battery pack for laptop, portable DVD etc.
Battery tested based on International Electronic Commission (IEC) standard to ensure capacity, quality and life time.
6 months warranty.

Technical Specifications

Dimension: Height 65 mm, Diameter 18 mm
Weight: 2.2 Oz. or 62.4g
Capacity: 4200 mAh
Voltage: 1.2V
Standard Charge: 15 hours @ 100 mA
Rapid Charge: 1.2 hours @ 1000 mA

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1036

Quantity Discounted Price
1-5 $4.53 (Per Item)
5-20 $4.23 (Per Item)
21-50 $3.93 (Per Item)
51-100 $3.63 (Per Item)
101-500 $3.53 (Per Item)

I think that Tenergy doesn't want to give up and allow LiFePO4 to take over.

This is good for us... brutal competition is a good thing for consumers!

vanilla ice · Oct 30, 2007

I wonder if the C rating is for real. 12c is niiice. Thats gotta be the subC RC technology in there.

A 30s might do nicely for one of those Peukurt buffer packs we were talking about for lead.

Ypedal · Oct 31, 2007

Order 5 and test them. !! report back please !

xyster · Oct 31, 2007

A different form factor, but the specs are on par with sub-C NiMH that have been available for some years now:
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1827

$3.69
High quality Sub C size 4500 mAh Nickel metal hydride (Ni-MH) battery

The folks at rcgroups.com report that the cycle life of high rate NiMH is notoriously poor when actually operated near the drain rate limit -- on the order of dozens of cycles instead of the hundreds of cycles advertised.

Jozzer · Oct 31, 2007

And worst of all, its not easy to manage paralelled NiMh practically...

safe · Oct 31, 2007

Jozzer said:
And worst of all, its not easy to manage paralelled NiMh practically...

Exactly what is difficult about it?

Charging?

Discharging should operate in a pretty straight forward manner...

dermot · Oct 31, 2007

safe said:
Capacity: 4200 mAh
Voltage: 1.2V
Standard Charge: 15 hours @ 100 mA
Rapid Charge: 1.2 hours @ 1000 mA

These numbers don't seem to add up: 4200mAh but only need 1200-1500mAh to charge them fully?

Pretty good technology, you get more energy out than you put in...

More seriously, the relatively low capacity is the real issue - while I have successfully paralleled NiMH (and NiCd also) with unused cells from the same batch direct from the factory, I don't know what long term reliability would be in a tall stack.

I've only done it in short stacks of 8s2p of SubC cells for my radio-controlled duck, Doris. (her cousin, Gertie the radio-controlled goose had enough cargo space to fit F cells)

Brief, occasional outings on the river are rather different to the sort of use seen by batteries in my daily-use e-bike.

I've not seen any guidance from battery manufacturers regarding parallel operation of Nickel chemistry cells, onyone??

safe · Oct 31, 2007

xyster said:
The folks at rcgroups.com report that the cycle life of high rate NiMH is notoriously poor when actually operated near the drain rate limit -- on the order of dozens of cycles instead of the hundreds of cycles advertised.

I wonder how well they perform at moderate drain rates?

If the peak drain rate is something like 10C and you make sure that you never drain faster than 7C you are still able to do a lot of things with these that the "regular" 3C (or flashlight 1C) cannot do.

It seems to me that the goal is to always run "whatever" system you have at some rate that is below it's peak. Peak is "peak" for a reason... when things max out they are running up against some internal limiting factor that is usually a bad thing.

It's like with SLA batteries... if you tried to pull 40 amps @ 36 volts (like on my bike) with something like a 18Ah battery (3) your lifetime is going to be very short. Double that amp hour rating to 38Ah and you get hundreds of cycles and a longer life. After 3100 miles my batteries are still doing well.

These might be worth trying... the fact that I could assemble my #003 bikes pack for around $107 if I wanted to is really nice. Doing the minimum pack would mean pulling 7C all the time. I'd probably double that so that the drain rate drops to less than 4C. For cells that are supposed to handle 10C that should result in a decent life.

At this price it's not that much more than SLA's... 8)

safe · Oct 31, 2007

dermot said:
I've not seen any guidance from battery manufacturers regarding parallel operation of Nickel chemistry cells, onyone??

I know you aren't supposed to charge in parallel. Each charging string need to be isolated into it's series string. So the ideal way to charge these is to divide you pack into units of 12V each and then use a separate 12V charger per string. You could also divide by 24V or 36V, but the main thing is to only charge in series.

Discharge should not be a problem...

Jozzer · Oct 31, 2007

Discharging no, But being able to isolate all the strings means either big switches or lots of plugs to disconnect each string before charging. Either way, not a great "turnkey" solution..

safe · Oct 31, 2007

Jozzer said:
Discharging no, But being able to isolate all the strings means either big switches or lots of plugs to disconnect each string before charging. Either way, not a great "turnkey" solution..

I use three connectors to charge or ride already so from my perspective I don't mind. Xyster probably holds the record here for most chargers with something like 10 or so (?). The more chargers you use (or if you can use a balancer) the more precise the charge can be done and the better use you get from your pack.

All it takes is one bad cell and the whole pack is reduced to it's level.

This still makes the strongest argument for "free cells" because you can get in and get really technical on a cell by cell basis and be able to identify problems early on.

For the ordinary user that doesn't know about the technology all this precision would be a waste. The typical user just let's the pack fall into decline and then replaces it and never knows why.

But your point is valid... for mass production purposes the "high precision" approach is a non-starter...

TylerDurden · Oct 31, 2007

dermot said:
I've only done it in short stacks of 8s2p of SubC cells for my radio-controlled duck, Doris. (her cousin, Gertie the radio-controlled goose had enough cargo space to fit F cells)

No SLA swan??

:lol:

Ypedal · Oct 31, 2007

SLA would turn the swan into a submarine !! :lol:

safe · Oct 31, 2007

I'm wating for a Lead Zeppelin...

oatnet · Oct 31, 2007

Tenergy: I built a few packs with the Tenergy "3500mah" NiMh sub C cells. Best I ever got out of them at a .2c drain rate (CBA-II) was 1700mah, less than half their rated capacity. I will never use another Tenergy product.

Parallel NiMh strings: The last pack I built from the "3500mah" subCs was (4) 36v strings (1p36s). Each string is charged by a separate charger, but they were very difficult to balance. One string would heat up before the others, heating them up and ending their charge cycle prematurely. Although the chargers were identical, each one charged a string to a different point. With a 30a load (2c+ based on rated ah, 6c delivered ah) I could pretty routinely get @5ah out of what should have been a 14ah pack, but by charging them to cutoff (yeah I know, cycle life) 5-6 times and rotating the chargers each time, I could squeeze a few more ah from the pack. All in all, way too much hassle to get a good charge from them, and way too heavy for a mere 5ah.

-JD

safe · Oct 31, 2007

oatnet said:
Tenergy: I built a few packs with the Tenergy "3500mah" NiMh sub C cells. Best I ever got out of them at a .2c drain rate (CBA-II) was 1700mah, less than half their rated capacity. I will never use another Tenergy product.

Which type were you using?

The blue one are rated as 1C "at best"... they are for flashlights and stuff like that.

vanilla ice · Oct 31, 2007

But he was draining them at 0.2c.

The price on 5 of the 7.2v 4500 subC packs is about the same as 30 pieces of the 18650 cellls. I'd rather get the 5 packs and have less wiring hassels and a good selection of chargers. But if what oatnet says is true, nevermind on that idea.

CGameProgrammer · Oct 31, 2007

Well it sure sounds like these cells are pure garbage. As someone mentioned, they even say you can charge it in 1.2 hours at 1 amp, so right there they admit the capacity is 1.2 Ah!

xyster · Oct 31, 2007

vanilla ice said:
But he was draining them at 0.2c.

The price on 5 of the 7.2v 4500 subC packs is about the same as 30 pieces of the 18650 cellls. I'd rather get the 5 packs and have less wiring hassels and a good selection of chargers. But if what oatnet says is true, nevermind on that idea.

From what I know of both, I'd choose lithium 18650s hands down...as I did. Being able to parallel lithium (like lead) for charge and discharge is a huge advantage in practice.

vanilla ice · Oct 31, 2007

What I meant was out of the two nimh options I would choose the premade subC packs over the 4200mah 18650 cells. The form factor of the 1.2v 4200mah nihms in the original post is 18650 if I'm not mistaken. Price works out about the same as the RC packs.

safe · Nov 1, 2007

Information is (cheaper) Power

If you were to take these batteries and push them to their full 10C and EXPECT that amperage all the time you will be very disappointed with your results. The reason is that like all batteries they decay with cycle life and so if you want to get longer usage (better economy) you need to design from the beginning a system that uses about HALF of the capacity.

Look at the charts...

If you were to design your pack so that it used 5C then you get a decent voltage performance for about 10 minutes. (assuming you are only using one series string... obviously you would parallel several strings for more range)

Now... the next thing to think about is your "life cycle cost". If you want your machine to be running strong at 600 cycles you need to set your peak current so that it is ONLY 50% of it's initial capacity. So let's run some numbers:

Baseline machine for the example:

36 volt
30 amp current limit

Flawed Approach:

30 cells produces 36 volts and an initial peak current of 3.5 * 10C = 35 amps

...but after 600 cycles you get only 75% of your initial capacity so the ability of the batteries to produce current drops to 35 * 0.75 = 26 amps.

Your machine can no longer perform as designed...

Correct Approach:

60 cells produces 36 volts and an initial peak current of 2 * 3.5 * 10C = 70 amps

...but after 600 cycles you get only 75% of your initial capacity so the ability of the batteries to produce current drops to 2 * 35 * 0.75 = 52 amps.

Your machine can still perform within your needs...

The moral of the story is that as you add range (adding more parallel strings) you extend the life of the pack. However, there's a limit to how much extra range will help because at some point the rate of cycle life pack decline is steep enough that the argument for more range no longer applies. There is a "sweet spot" of just enough batteries verses too much (too expensive) in order to satisfiy the minimum current demands of your bike. Knowing the "sweet spot" will give you the cheapest battery over the full life cycle.

vanilla ice · Nov 1, 2007

Yeah but Oat said he discharged at 0.2c and still got less than half the rated capacity. No spreadsheets going to make that ok.

xyster · Nov 1, 2007

I find your argument rather academic, Safe, because better lithium cells are no more expensive.

I could buy an old, beater Chevy for $2000 and ask how I might fix it up so that it runs reliably. Or I could buy an old, beater Honda for $2000 that already reliably performs adequately. Unless I just like fixing things as a hobby, why should I bother exploring the former?

I think you just like fixing things as a hobby .... not a value judgement, just an observation.

safe · Nov 1, 2007

vanilla ice said:
Yeah but Oat said he discharged at 0.2c and still got less than half the rated capacity. No spreadsheets going to make that ok.

How old were the cells? It's possible that he got some bad cells. The Tenergy brand is huge and I'd be surprised if they deviated so dramatically from the specs at the point of initial sale. He also never replied which color code he used and they vary a great deal between cell types.

The blue ones are strictly for things like flashlights...

safe · Nov 1, 2007

xyster said:
I find your argument rather academic, Safe, because better lithium cells are no more expensive.

The Li-ion are cheap, but then you have to do the whole BMS thing. Also, the Li-ions only make sense if you are willing to buy $500 or more. (the 1C rating requires a big initial investment) For someone who just wants a pack for $200 that can pull 36V 30 amps for 600 cycles the high discharge 10C cells are more economical. LiFePO is still expensive.

Try to build a Li-ion pack for 36V 30 amps and you need a lot of Li-ion cells.

Xyster... try running your "cheapest price scenerio" for a Li-ion 36V 30 amp pack... include all the chargers, BMS, etc...

The whole point is being cheap, cheap, cheap...

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