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Saft NiCad Batteries | 18 comments (18 topical, editorial)
Re: Saft NiCad Batteries (3.00 / 0) (#6)
by Bruce S (bruce(dot)stahl <at>gmail (dot)(com)) on Thu Apr 10th, 2008 at 09:09:23 AM MST
(User Info)

Talk about being lucky!! How do I bribe you for one of those :-)
Where are you located:-)
Okay, batts.
1.)NiCds ae 1.25 standing voltage not the normal 1.5 like Alkalines and Lead-Acid.
So the best thing to do would be like rualmcguyver said, link up 10 of the 20 in series then hook the 2 sets up in parallel.
This will give you a full 72Ahr of usage.
  1. )NiCds, wet or dry can withstand a deeper drain on them than Lead-Acid, so that's also a plus!
  2. ) NiCds are current lovers and need to be charged using a constant current instead of constant voltage like most chargers will do.
  3. ) they'll need to be charged in values of 10, i.e. C/10 is a good value to charge them. C=the total amerage of a string so at 36Ah you'll not want to charge these at more than 3.6Ah for the total string C/20 is better.
  4. ) NiCds like Lead-Acid need to be able to vent, for the same reason, i.e. pressure build up. The lid I see in the back ground is metal and probably okay for previous use, but a plastic one with a bit more room would be better.
The HF PV is a good starter unit, the newer one much better than the old one.
It's max out put is 45 watts on a good day, which is way low for charging this pack fully.
you could have a pack of more than 900 watts total the HF puts out 45 watts total.
That's about 20% which would be okay for mantaining them but possibly not for a good deep charge. Since you're going to be using these once in a while it might be okay, larger unit would better, along with a NiCd specific charger.
There's a ton of charger circuits on the web if you want to build one, even ones specific for solar use.

IF you have a little more money to spend, it would be good to get a real solar controller than the one that comes with the HF set, I did.
I know this is long ;
Hope it helps
Bruce S
 



Re: Saft NiCad Batteries (3.00 / 0) (#11)
by joestue on Sat Apr 12th, 2008 at 06:08:09 AM MST
(User Info)

NiCds love a fast charge. About 1C or half that is good. Read the Wikipedia page about them.

(yes I know this is a storage application and that's impossible)

[ Parent ]



Re: Saft NiCad Batteries (3.00 / 0) (#13)
by Bruce S (bruce(dot)stahl <at>gmail (dot)(com)) on Mon Apr 14th, 2008 at 08:32:54 AM MST
(User Info)

fast Charge! not totaly correct.
They CAN take a fast charge, but you wouldn't want to do that very often. When done this way they get HOT! real HOT! , this would lead to venting and unlike Lead-Acid you can't just add acid back in.
I had at one time a picture on sub-c's that were charged and I forgot to put the temp sensor on them to shut down if they overheated, wasn't pretty.. If its not there I can put it backup.

building with a C10 or even better C20 charge would give the longest use of these and then once in a while hit them with a C1 just to wake up the wiskers :-)
Wikpedia is very good at giving a global overview, but would be best to find an manufacturer and ask for specifics.

Still waiting to hear what Bribe is needed to get one of these:-<>..
Cheers
Bruce S

 

[ Parent ]



Re: Saft NiCad Batteries (3.00 / 0) (#14)
by joestue on Wed Apr 16th, 2008 at 12:09:15 AM MST
(User Info)

The Devil is in the details man!

You should never charge a sub C or D battery that hard because you can't add water.

Correct me if i'm wrong, most of the heat is from the recombination of the O2 and H2 during the charge, since the amount of reconbination is the same whether you charge it fast or slow, (within reason, the increased voltage due to cell resistance will increase gasification), the small chargers just assume that if you keep the temperature down, then the internal cell pressure can't be high enough to vent the cell. With vented cell types, there is an order of magnitude less recombination.

Also, the battery should cool upon charging, until it hits end of charge and the oxygen is consumed in the catalyst.
This is not necessarily the case for all batteries, the internal resistance varies considerably between manufacturers, for instance, some Nicds can discharge 50C, others are rated only 10C or less.
http://www.mpoweruk.com/nicad.htm
www.battcon.com/PapersFinal2005/MeisnerPaper2005.pdf

BTW Nimh chemistry is 66% chemically efficient on charge, and Nicd is ~55% on a 16 hour charge, and ~80% on a fast, ~2 hour charge. Both of which lead acid can beat.

[ Parent ]



Re: Saft NiCad Batteries (3.00 / 0) (#15)
by Bruce S (bruce(dot)stahl <at>gmail (dot)(com)) on Mon Apr 21st, 2008 at 11:45:23 AM MST
(User Info)

Joe;
 I like your numbers. The C/10 or C/20 would give a good long term charge for what he's wanting to do.
Lead Acid batts are good. My main reason for sticking with NiCds are that they can be drained down to having only 20% of their total charge left and be able to recover without a noticeable damage. In fact , they work better when used in this fashion.

When building or designing for NiCds the best way would be to use the negative slope method. NiMh have this slope too, but not as easy to detect.

Cheers
Bruce S

[ Parent ]



Re: Saft NiCad Batteries (3.00 / 0) (#16)
by joestue on Mon Apr 21st, 2008 at 02:41:20 PM MST
(User Info)

I forgot about the 80% discharge part, thanks for catching that.

If you only discharge the first 40%, I bet you could get the efficiency up.
This doesn't apply to NIMH though, speaking of which why do they put these in hybrids?
they should use NiCds.


[ Parent ]



Re: Saft NiCad Batteries (3.00 / 0) (#17)
by Bruce S (bruce(dot)stahl <at>gmail (dot)(com)) on Tue Apr 22nd, 2008 at 03:26:47 PM MST
(User Info)

joestue
The main reason for them using the NiMh is the chemistry. They are way less dangerous. Cadnimum is a very bad thing, and MUST always be handled like the poison it is. Worse than lead paint!!
NiMh also loose their standing charge slower than NiCds do.
But possibly the more important reason is that they only last about 500 cycles before they start wearing out :-)
Lithimum is coming along just fine, once those have been around a bunch more years, they'll be better in the long run.
Price is what keeps them out of my reach.

Cheers
Bruce S

[ Parent ]



Saft NiCad Batteries | 18 comments (18 topical, 0 editorial)

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