How to regulate charging of NiCd batteries??

[amiklic1]

I got 240 Ah NiCd batteries, but I'm in doubt about charging method.

I'll charge them with wind genny, and now I got charge regulator for lead-acid batteries. It turns on the charging current at approx. 12 V, ant turns off ( turns on the dump load) at 13.8 Volts.

As NiCd batteries are not similar with lead-acid, I can not use it for NiCd batteries.

They show full voltage ( 12V ) for a long period of time, allmost to the end, and then voltage goes down rapidly. That's dangerous as the batteries can be discarged so that the'll be damaged.

How can I determine when the charger should start charging the batteries, and when to stop?

Any info?

[Flux]

Wet NiCd (NiFe) have a totally characteristic and can not be charged with a conventional lead acid charger.

In fact they can not easily be used with a dump load either. You really need some sort of ampere hour meter.

They are normally charged at constant current and you put back about 50% more than you have taken out and assume that they are charged.

I seem to remember from a previous post that they are 7 cells, this doesn't make more than 9V nominal not 12.

They are excellent and very robust but there is a wild variation between full charge and full discharge. This will probably cause you problems if you try to use them with an inverter intended for lead acid.

Flux

[Flux]

That should have said " have a totally different characteristic".

[Flux]

I have found some more data that suggests that they can be floated at 1.4v per cell so you should set your dump load to hold them at that. (9.8v for 7 cells)

They have to be brought back up at a higher voltage every month or so, similar to an equalising charge for lead acid but normally done at constant current.

I can't be sure if this is for NiCd or Nife but the voltages are similar.

Don't let the electrolyte get low, they absorb CO2 from the air and the electrolyte needs changing every few years. Specific gravity gives no indication of state of charge but electrolyte should be changed when it drops to 1.16 ( special hydrometer needed to measure this).

Hope this helps, data is not easy to come by.

Flux

[amiklic1]

OK now!

Here's some fresh info. I found a cousin that is an railway company employee, and lives at the other end of my country. My father connected me with the guy, so he explained me something more about NiCd bat's.

At first, I would like to put some numbers in this.I just turned off my charger, and disconnected it from batteries.

Then I picked up multymeter, and here is what I get:

Total voltage of 7 cells = 9.65 V

One cell voltage = 1.37 to 1.40 V

When I connect a car cigarette lighter to the battery bank ( only large-amperage device I had near), I got voltage drop from 9.65 to 9.45 V. Since I don't know the current in A, it's not a very worthy information.

Now, I plan to get four (4) more cells, so the voltage vould be 1.375 ( average cell voltage) x 10 = 13,75 Volts.

Now, about the cousin's experience. Although I spent many hours of investigating and building different kinds of charge regulators, now that's all useless. He told me that at the train wagons, the batteries are allways connected to the generator, without the regulator of any kind. He told me to simply connect the wind genny and the solar panels to it, and not to be affraid for the batts.

As he also said, it is not bad if the battery voltage drops to allmost zero, because I can then charge them to full, without loosing thew capacity.

For the charging, he told me that I can charge them with 100 Amps for 2.4 hour, or 1 Amp for 240 hours, or any other relation, as it does not matter at all.

It was too nice to listen to be true, but he is in that business for 20 years.

So, few meters of thick wire, and show must go on.

Sorry for possible language mistakes, but I'm only trying to be good in English.

[Flux]

Yes that will be fine if you can get the extra cells, 10 cells is common for 12v, some banks use 9.

Try to regulate your load so that they are not over charged, it will use a lot of water although it probably won't damage them unless the electrolyte drops below the plates.

A dump load at 1.4 v per cell would still be useful unless you can watch the state of charge.

A lot of train dynamos have an almost constant current characteristic and the lights are on often enough to balance the charge.

They should be excellent if you don't have inverters with tight limits on operating voltage.

Flux

[amiklic1]

I think that it would be ok to first measure bank voltage, and then to set the charger to dump load at it.

I mean, if voltage when batteries are fully charged is 12.2 V, then it would be good to set the regulator to dump load at 12.1 volts. On that case the batteries won't ever come in the top-full state of the charge, and would not start to boil.

It'll save some water, what is not as important as not need to worry about state of charge.

[Nando]

NICADs have 1.2 volts/cell and when fully charged may go up to 1 .37 to 1.4 Volts/Cell

Float charge is 1.37 Volts per cell

Discharged cell is 0.9 Volt/cell

Regards

Nando

[ignesandros]

My dos centavos:

NiCADs are almost exclusively sealed cells and don't lose any electrolyte. You want to charge the batteries at a voltage just above its full voltage, at an amperage based on its capacity. Most NiCADs I've seen are designed to charge best at capacity divided by 10 (for me 130-190mA/hr). Since I use packs of 16 cells, I have a fully charged voltage of around 21v. Therefore, I should charge at 22v and 130-190mAh for optimum charge efficiency. I'm impatient, though. I charge at up to 2A (monitoring temperatures constantly). At 240AH (please check this, as this sounds quite high for NiCAD batteries) you could feasibly charge at 10.5v (for 7 cells) and 24A for about 15hrs to charge the batteries completely. Try not to go over C/5 (capacity divided by five) without monitoring temperature. Over prolonged use, NiCAD batteries develop capacitance loss (sometimes called by the misnomer "memory") if you draw most but not all current from them, but not all before charging again. As apposed to lead acid batteries, NiCADs love to go completely dead on occasion. Let the cells go completely dead, charge them completely, then let them die again, and the next charge should be near their actual rated capacity.

I haven't had any experience with NiFe batteries.

-Andrew

[Flux]

These are not sealed cells, they are wet cells almost identical to NiFe and they get through a lot of water in normal use.

They can't be treated like the usual sealed Nicads.

Flux

[steak2k1]

amiklic1,

Is there a chance you can get a digital pic of these batts.  Never seen NiCd liquid filled.  Or do they simply look the same as a lead filled type.

Gonna have to get real friendly with someone at CP Rail..

Thanx,

stk

[amiklic1]

Here is one image I found on the net. I take some pics of my battery bank, and I'll post them into diary about my stuff, but right now I don't have time to do that.

Hope this will be good enough.

[ignesandros]

Well, that's a "Nickel-Iron-Alkaline". I saw a link to a manual for that battery on here a while back. Search for "eddison battery manual".

-Andrew

[amiklic1]

Yews, I know that, but mine looks just like this one. I'll put some pics, maybe even today. I'll try to take the picture of the plate with caracteristics, that is sticked to the battery case.

[ignesandros]

I'd say despite the label "NiCad" on the battery, you should treat it just like a NiFe. I'm sure an unsealed NiCad would behave similarly to a NiFe, anyway.

-Andrew