Why not Nicad?

[Parker]

Nicads are looked good to me right now. What I read on ebike.ca got me looking in to them.
I'm on SLA's now and am not ready to spring for lithium yet tho pings ebay packs are a little tempting.
The weight of nicads is half of lead - 25% less capacity of NMHi. But the thing that really impresses me is
the number of cycles. 1000 vs 600 on NMhi. I also like that you can drain them down and not worry about it as
much. I read that the memory effect is not significant. Sorry I don't have links - don't remember what I read where. The toxic thing is not good but recycling happens and my purchase with not stop the move to lithium anyway.
So what is not to recommend about nickel as a good mid level battery?

 

[Link]

Considering nickle based chemistries are effectively the ONLY mid level batteries, I'd say nothing.

I like the slightly more energy dense NiMHs, but if NiCds will do what you need them too, then by all means use them.

 

[safe]

SubC NiMh

I've looked at this issue a lot.

The Nicads do have long life, but they tend to be down on the power for their weight and the price is "so-so" for what you get. "D" cells have this bizarre legal problem that doesn't allow the high "C" rates that you can get with the SubC cells. SubC NiMH can deliver up to 10C and are pretty cheap.

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1827

$3.69 in volumes above 100...

It all depends on your design goals. For me I'm looking to spend very little and have high peak amps. As far as "most bang for your buck" I'm seeing the SubC NiMh as the best option, but the lifecycle's aren't that great.

Everything seems temporary right now as prices and technology are in a state of constant disruption...

 

[Ypedal]

Nicads are good, reliable and tested over the years.

If you use your bike on a daily basis, then they rule.. but if you ride once a week or less they self-discharge ( just like NIMH.. ) considerable self discharge ...

Skip nimh, go with nicad if the choice is up in the air. not as fragile.

Edit : Also.. i suggest the F cells vs strings of subC.. makes charging easier.

 

[andrew]

safe:

"D" cells have this bizarre legal problem that doesn't allow the high "C" rates that you can get with the SubC cells.

I haven't heard of that. Any details? I thought it was merely an issue of design. The subC cells are popular for high-rate applications like power tools, while the D cells may be more popular for applications requiring more capacity at a lower rate.

There are some SAFT NiCads here: Septechnologies

I'm considering the D 5500 mah cells possibly as a range-extender pack. At least it would be pretty cheap to experiment, and these SAFT cells would be much less of a risk then the cheapo chinese cells.

 

[Electricdirtbiker]

Nicads are a very robust and proven technology. Mostly only the sub c size cells are offered in high c output ratings, but the amp hour ratings are modest for ev work. The D and F sizes are light on the c output ratings. A solution would be to parallel up several series packs before riding. Unparallel them before charging. I don't know much about leaving them stored paralled but they don't charge properly when in parallel.

 

[recumbent]

I've used NICAD's for about 8 years on my 36 volt Heiny system, and have nothing but good things to say about them...EXCEPT, they heat-up significantly when driven hard. Thermister in the battery pack made my system pulsate heavily when hot, and when you get home and want to use your bike the next hour? Forgetabout it, your walkin buddy.
The batteries are too hot to charge because the intelligent system wants your bats to cool down before it charges, takes a couple hours cooldown sometimes.

But this could be with other "D" size cells for all i know.

 

[Ypedal]

Most Ni cells do that.. nimh and nicad.

Best to let them cool after a good charge as well.

 

[Parker]

Thank you. That settles it. As my bike is a daily rider and my main transportation I am not as concerned
about getting the best performance, peak amps and C rate, as long as its decent to good. I'm more concerned about cost,
effeciancy and I really like that they are not as fragile. And with the longevity the cost is even better than it first appears.
ebikes.ca seems to be the only place selling premade packs. So they will restock at some point or I'll start reading the battery pack building treads... How hard can it be? Actually the real question is how time consuming it will be. Don't answer that, it's just retorical at this point. I'll read the treads and ask questions if I can't figure it after that.

 

[Ben]

Silly question, but do nicads require a BMS?

 

[Parker]

That's a good question. I'm guessing no but I don't really know....

 

[Ypedal]

Nope.. not that they could not make good use of one.. but they don't need it.

Ni cells self ballance by trickle charge ( low rate charge ) and can safely over-charge to an extent.

 

[Parker]

I was just reading the duck tape lipo pack thread and there is even more
good stuff about Nicads over there. Apparently Nicads are possibly the ONLY
battery chemistry that does not degrade from deep discharge cycles.

I work with cordless power tools, mostly drills, at work at a cabinet shop and no one
replaces the batteries. The cycles just get shorter and shorter till the whole
drill just gets thrown away. I think I should push for Nicads there
as well. Maybe it's cheaper to buy a whole new drill though. mmm

 

[D-Man]

I've experienced some weird nicad symptoms. For instance, take an older dustbuster. Turn it on and it runs fast then slows down quickly; then it starts to speed back up as it is being recharged but its not! I'd imagine this is the "memory effect." Now these batterys are older but I've seen this problem more then once. This is why I really wouldn't want nicads in an ebike. Plus it would be a pain to have to cycle a big battery to get good performance if not being used every day. But, if you live in cold climate, they say these are what you want.

 

[fechter]

The main problem I see with NiCd is the capacity issue. Large sizes, as pointed out earlier, do not perform well at high discharge rates. Even then, about the largest size you can get is around 8Ahr. Sub-C sized cells have good high rate discharge performance, and are the most economical size. You need to parallel multiple strings of cells to get enough capacity, which tends to be problematic for charging. You cannot charge NiCd cells in parallel. Each series string needs to be isolated and charged independently. This can be done, and it's not as difficult as a LiFePO4 BMS. Multiple chargers, one for each string, is the best approach.

Another problem is to run high voltages, you need a crapload of cells in series due to the low cell voltage. This is OK, but during discharge, it would be very easy to overdischrarge and reverse a cell, causing permanent damage. In Nimh hybrid cars, they monitor the voltage of small groups of cells to protect against cell reversal with a kind of BMS. Most bikers do not use such a system, but with long strings, it would be a very good idea.

I'm using some NiCd batteries in a hedge trimmer that were sitting around on a shelf for 18 years and they work fine. NiCd has an extremely long calendar life if stored in a discharged state.

 

[Ypedal]

The whole memory effect has been blown way out of proportion.

The best text i've found after oodles of reading explained that nicad cells that are drained at a low rate, and are stopped at a given voltage level over a long numbr of cycles.. will develop a dip on a discharge graph at that voltage.. this can make some sensitive electronic devices shut down before the cells are fully drained..

Using nicads on Ebikes will not be a problem in this way as the high currents and varying discharge cut-off points are nothing like sensitive digital cameras etc...

Like most batteries, hot cells dish out amps better than cold cells.. and fire up a cold pack and it will heat up within no time and this is likely what you see with the vaccum nicad sceanario above.

 

[Link]

The whole memory effect has been blown way out of proportion.

The best text i've found after oodles of reading explained that nicad cells that are drained at a low rate, and are stopped at a given voltage level over a long numbr of cycles.. will develop a dip on a discharge graph at that voltage.. this can make some sensitive electronic devices shut down before the cells are fully drained.

I heard it was the chargers. Back when they were using crappy timer-based chargers, filling it up without it being completely dead meant it got overcharged.

I've used NICAD's for about 8 years on my 36 volt Heiny system

You dirty, dirty boy.

 

[PJD]

Agreed, nearly all of this "memory" stuff is just a urban myth that arose because people were overcharging their partially discharged cells with cheap timer chargers.

Geosynchronous communication and weather satellites use Nicads to provide power for the hour or so each day when the sun is behind the earth. The cells get repeated shallow discharges - and would be good candidates for the memory effect if it existed. Nonetheless, the batteries last a decade of more because they use a very good battery charging management system.

 

[PJD]

But as far as the "legal" limitations on the c-rate for "D" and larger NiCd cells, could this be a like the Chevron/Cobasys sleazy anti-competition patent licensing -type thing? Would there still be patents out there for NiCd chemistry?

 

[TylerDurden]

Not an urban myth. The memory issue exists, but is often confused with other NiCd issues. Stationary uses like orbiters easily avoid the problem.

http://www.battcon.com/PapersFinal2003/McDowallPaperFINAL2003.pdf

 

[D-Man]

All I know is that my dustbuster vacuum is inside the house so the batteries are at room temperature. As Ypedal indicated, maybe when the nicad batterys gets older, it has to be somewhat hot to work right. But you still wonder how this happens to an older battery. Like I said, if your not using it often with complete discharges, it will play games with you like this. If you just top it off all the time, it still does it. It may have something do to with not being in a discharged state all the time before you use it. But you can't expect to store and use a dustbuster like that. I do have a connector on it so I can charge it with a powersupply. It is somewhat amusing to watch the thing wind up slowly to warp speed on its own.

 

[docnjoj]

My wifes bike has had 30 cell, 4.5 amp Sanyos on it for the last 5 years or so. She uses it 3-4 times a week. Recently, it showed some degredation and now only D/Cs to 3.5 ah. I added 4 cells and it helped, but we finally went with the Ping pack as a replacement. It weighs half (9+ lbs) compared to the Nicads for 2X the Ah. Nicads are very reliable and consistant, but like all Batts, they will wear out. She is very light on the throttle, averaging 2-3 ah per 10 miles.
Doc

 

[andrew]

I think it is hard to find a rechargeable (secondary) battery commercially available that will last as long in terms of shelf life. I have some old NiCad AAs that I took out of something's battery pack. They may be over 15 years old and still hold a reasonable amount of charge. I also have some C cells that I use for flashlight batteries, and they are probably at least 10 years old. I've used some Radio Shock sub-C packs which had very high output power and probably the speced capacity, after being ~8 years old. I have some D cells for flashlight batteries that are probably over 12 years old.

Although they are not a great flashlight battery due to self-discharge, I can just pop them in a charger for a few minutes if they die. They maintain a high voltage right until they go flat.

I think NiMh degrade faster, and also don't have as flat a discharge curve.

It's important to store them with some charge. I think storing them completely discharged can possibly cause them to leak electrolyte and degrade quickly.

 

[monster]

I've used NICAD's for about 8 years on my 36 volt Heiny system, and have nothing but good things to say about them...EXCEPT, they heat-up significantly when driven hard. Thermister in the battery pack made my system pulsate heavily when hot, and when you get home and want to use your bike the next hour? Forgetabout it, your walkin buddy.
The batteries are too hot to charge because the intelligent system wants your bats to cool down before it charges, takes a couple hours cooldown sometimes.

i found that you can charge them when hot and they will actually cool down. its only the end of charge, and discharge that makes the batterys heat up. so its probably ok to charge nicds when hot.

 

[fitek]

Is all-battery.com a good place to buy these cells? I'm balking at the cost of a 48v ping pack (~450 plus nearly $100 shipping for 10ah). I'd rather get 40 of the 10ah D cells at all-battery.com. There are also some 7Ah NiCad D cells for $5 at batteryjunction.com. For total cheap assness, 2.6Ah AAs are 1.41 each. I guess I'd need about 120 of these to equal the NiCad D cells, but I'm not sure I want to solder so many batteries together.