Seeking The "Most Cost Effective" Battery

[TylerDurden]

How would I charge them? Do I have to charge each SLA at a time? or can I buy a special charger to charge them all at the same time? Could I use my existing charger that comes with the bike?

You can use your current charger for two and a car-charger for the third. Other chemistries will need different chargers.

You can get a 36V SLA charger from TNC scooters.

 

[SniperGaulois]

lifepo4 = 1700 cycles = 5+ yrs... nice...

 

[safe]

How would I charge them?

If you mix chemistries you still need separate chargers for each type. If you want to switch from series to parallel to charge (what I do) you need to be able to unplug your batteries and plug them together again in parallel with your charger.

 

[safe]

And I should mention that the Oasis battery (mentioned on at least two other threads) is going to increase the cycle life of SLA from 300 to 1200 cycles.

I have a feeling that in the future the "low end" will be using this kind of battery... it doesn't cost any more (shouldn't anyway) and the extra lifetime means a better return on your investment.

(just to keep this thread "connected" to the lasted news)

 

[needWheels]

Wow I can't believe I just found this thread and I've been trying to calculate the same thing for a couple weeks now.

That NiCD deal is great but since 96 of them give you 36v 7ah for $135 (if they are telling the truth, which we know they are not) how about 36v 6.5ah of NiMh (subc 10C) for ~$165 shipped which I found on another store?

Is there an advantage to using NiCd over NiMh or is the weight savings worth the extra cost?

I have an absolute max budget of $150 for this which is why the limit of 6.5ah bothers me (and it's $15 over budget). 6.5ah of NiMh has to be better than real-world 12ah SLA right?

 

[TylerDurden]

Is there an advantage to using NiCd over NiMh or is the weight savings worth the extra cost?

NiCd lasts and lasts and lasts.... (>2000 cycles)

 

[pwbset]

Hey needwheels... I'm super new to all this, but I can tell you I'm having a blast sucking the life out of a couple Ryobi 18v nicad packs waiting for my main Milwaukee pack to arrive. If you have a max budget of $150 I would look seriously into power tool packs because they are dirt cheap at local "super stores" and easy as pie to charge. I looked into a string of subC nicad cells, but once I thought about all the labor to create it and all the possibilities of shorts from bad connections and the fact that the cheapest 30 cell charger I could find was $70... well... power tools looked a lot better for short range stuff.

Anyway... with 3 Ryobi 18v nicad packs in series (@2.4ah though I never see that) I can go 18mph sustained on a high wound 4011 for about 3-4 miles with light assist. Typically you can find 18v nicad packs for <$30. You could probably get 4 + charger for $150. They charge fast. Depending on your motor, hills involved, range desired etc. you could probably have a lot of fun with that. Here you can see when I had 2 18v packs in my bike.. that was only good for 12.5mph and like 1-2miles on the 4011 though.

 

[Drunkskunk]

Is there an advantage to using NiCd over NiMh or is the weight savings worth the extra cost?
6.5ah of NiMh has to be better than real-world 12ah SLA right?

Nicad has a service life rivaling LiFePO4, But with some drawbacks like the memory effect.
it weighs 30% more than NiMh for the same power output, But NiMh doesn't last nearly as long and costs more. Nicad also keeps charged up for a Long time, were NiMh will discharge its self quickly.

I have a few old items around here that run on Nicad. my Rechargable flashlight is 20 years old, and Its starting to look like I should Maybe replace the Nicads.


As for beating a 12Ah SLA? No, not quite. Close though.You'll get 5 - 6A of usable power from the Nicads, and 6-9Ah from the SLA. SLA have more voltage sag than Nicad, so the total wattage might be closer. But 6.5A of Nicad should weigh 0.25% of the 12A of SLA

 

[NickF23]

Its strange, I've never really experienced the high cycle life of nicd except in low discharge consumer electronics. all the nicd drill batteries I've used last about the same time as the nimh. Does anyone have any direct experience of nicd cells lasting ages on an ebike or similar? I don't trust the "battery university" site as there is so much of the info on it isn't right.

 

[Toorbough ULL-Zeveigh]

Nicad has a service life rivaling LiFePO4, But with some drawbacks like the memory effect.

stop saying that (& I don't mean just you)
While it's technically true that NiCd exhibits memory under a very specific set of tightly controlled circumstances, it is such a miniscule effect in modern NiCd cells that for all intents & purposes it is a non-existent effect to anyone that doesn't work for NASA, plus the effect is recoverable.
It certainly doesn't warrant all the continued press it keeps getting.
If the intent of this forum is to lead the way in disseminating quality info touching upon all things EV then I plead that ES be the place that this urban legend has a stake driven thru it's heart & finally be laid to rest that it don't continue into this new millennium.

Memory has become the scapegoat for any & every kind of failure mode imaginable in a NiCd cell.
In fact the single most common failure mode (of any chemistry) is that of cell reversal of the 'runt' cell in a pack which has gone out of balance (capacity reduction) brought on by exceeding depth of discharge (80% on nickel).
i.e. letting the fun times roll until you've wrung the last electron from the pack until she don't roll no more b4 recharging is the worst possible thing you can do.
Then when the pack dies a premature deth, the prognosis is to write it off as the result of memory.

The other biggie in small consumer cells particularly that gets the automatic memory label is separator puncture from dentrite growth which is specific to NiCd that forms when sitting on trickle charge for an extended period of time, anything over a month without a discharge.
The puncture results in even higher than normal self discharge so that the cell is down to zero volts within a couple of days.
It's typically flat when you go to use it, then you say "but I just charged it & only used it once!!", you can always count of someone to perk up, "yep, dat dere's de memory", cuz to the end user it appears like a reduction in capacity so it's hard to convince someone it's not memory.
A good NiCd or NiMH should *never* read zero volts, even after it's been sitting discharged for months.
It may not have any discharge capacity left to power a load but there should always be enuf to get a voltmeter reading around one volt open circuit even a year later if the cell is healthy.
You can still get some useful life out of a cell with a separator failure but you have to drain it straight away off the charger.
Dentrite formation is so common cuz NiCds do self discharge rather quickly even normallly so it's tempting to leave the battery on charge continuously so that they're ready to go at all times, but it's best to remove them from the charger after 24 hours & top them up just b4 you need them which is difficult to plan for a lot of times.

There are other failure modes as well but in my experience these two are the most common by far probably responsible for 99% (WAG) of the ded NiCds out there & are not reversible, therefore they are not memory, yet they don't get anywhere near the mention to the extent that memory does that I have seen to educate people of what's really going on here.
You have to charge a battery like you were voting, early & often & nickel batts like to be exercised with an occasional deep discharge (not more than 80% tho) to keep them limber & I've gotten 10 years out of AA NiCd by observing these precautions acting as a human BMS.

So can we part company with the memory boogeyman pls?
Thank you for your cooperation.

 

[Link]

LOL, I was gonna say something similar.

Short version: You probably have never encountered memory effect and you probably never will. :wink:

 

[Toorbough ULL-Zeveigh]

I'd go so far as to say there's no probably about it & you absolutely never will.

 

[Larry]

Hey Pwbset,

How are you attaching the wiring to those Ryobi packs? I can't figure out how that would easily be done.

 

[safe]

Does anyone have any direct experience of nicd cells lasting ages on an ebike or similar?

Not yet... but my next two bikes will use high discharge SubC NiCads so I'll be focusing on them for the forseeable future. I bought 288 raw 2.4 Ah SubC cells for $360 or $1.25 each.

 

[MitchJi]

Hi Safe,

Michael Barkley experimented with combining Lead Acid and LiFePO4 documented here (the quote below is one excerpt):
http://www.flickr.com/photos/mbarkley/s ... 514650280/

HYBRID BATTERY EXPERIMENT BELOW:
Lithium battery experiment photos:

12/20/07
Building 6.4vdc 20ah lithium battery modules , to be wired parallel across each 6volt golfcart battery, which power the '94 Mitsubishi Eclipse EV.

Hoping to eliminate most of the voltage sag on the main battery bank of 78vdc, during acceleration periods. Which would help with vehicle performance, abit on range, and maybe extend the life of the golfcart batteries.

Right now, 4 modules are installed, one on each of the last 4 golf cart batteries in the battery pack. Will be monitoring the performance of the 4 hybrid's as compared to the remaining standard GC batteries in the string.

 

[needWheels]

So what are the things to be concerned about with using NiMh and ebikes?
Does minimum safe voltage apply to NiMh or do they recover? How about temperature?

Only thing I remember reading about NiMh is that you have to watch the temperature on charging.
And I think they can be left drained without damage?

Would I get a real 7ah out of NiMh sub-c vs the "fake" 7ah of SLA?

NiMh still works out to half the cost of LiFePo4 the way I calculate it, so what's the catch?
I can live with the 4-5 extra pounds of weight.

 

[Link]

Not much. NiMH's proven tech. Probably shouldn't go under like 0.7-8V/cell with NiMH, but I dunno. They aren't affected nearly as badly as SLA by temperature, I think

Temp doesn't really have to be watched if you have a negative delta based charger. I'd try not to let them self-discharge too far.

Yes, you should really get 7Ah out of them. They don't suffer Peukert like SLA does.

Half the cost over lifetime or outset? I haven't seen any decent NiMH cells that were all that much cheaper per Whr than LiFeP04, unless you're "comparing" something like Tenergy to A123.

 

[needWheels]

I've read enough to know Tenergy is absolute junk but I did manage to find some other high C, sub-c, in the form of RC 7.2v packs, that I believe are oem GP which has a decent enough reputation.

Since you are saying I would get a real 7ah from 7ah of them
(if they are true enough to their rating) that makes it far more desirable than SLA.

Since my bike is my workhorse, I dislike the idea of 8x5.5=44 pounds of lead to get decent speed/range.
I've carried 25 pounds of cat liter + 8 pounds of cat food + 6 x 4.25 = 25.5 pounds of soda some weeks!
I bet I'll snap the rear axle if I tried that with lead batteries as well.

But similar power with NiMh would be around 15 pounds if my math is right.

Can anyone find me a low cost NiMh charger that could charge several RC packs safely in parallel or maybe I should just get several simple cube chargers (that are cpu controlled).

 

[MitchJi]

Hi,

If you are looking for inexpensive NiMH cells you might consider looking for a used Prius pack:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=4605&start=0&st=0&sk=t&sd=a
http://www.diyelectriccar.com/forums/showthread.php?t=13605

 

[johnws6]

These also look to be a choice for the most cost effective battery. http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=89

I myself have had luck searching the surplus bins for good quality nicads. My last score was 350 1/2 D 2.5 ah SAFT nicad cells that i purchased at 43 cents per battery. They were never used , after a few cycles they came back to full capacity and have worked since then. Just have to shop for the deals and you will find them i guess.

 

[pwbset]

Hey Pwbset,

How are you attaching the wiring to those Ryobi packs? I can't figure out how that would easily be done.

Well I had a flashlight, rotory drill and vacuum that were all dead so I took them apart and used the little connector clips that were in the tools. The batteries fit them nice and snug. I'm almost hoping some other tool goes tits up so I can try 72v!

 

[needWheels]

Safe, have you recieved those NiCd sub-c's yet and what do you think of their quality?

I am just about ready to jump on board with that.

I noticed they also make a 48v 40 cell NiCd charger for $50 shipped. Does anything lower cost exist?