charging NiCd from solar cells

[mettam]

I have 3 Solar Cells connected in series the + is attached to a diode and the diode is connected to the + of the Nicd battery, the - of the solar cell is connected to the - of the battery (see attached photo to see what I did.)
Can someone tell me if I have attached the battery the correct way to the solar cells for charging.

Justin.

 

[audioguru]

Your wiring is correct and the battery should charge if the solar panels can supply a total of 6.3V at 60mA.

 

[mettam]

Your wiring is correct and the battery should charge if the solar panels can supply a total of 6.3V at 60mA.

The Cells each are 2V at 200mA, considering they are connected in series of 3 does this mean they are supplying 6V at 600mA ?

Would you know what my NiCd should read once fully charged ?

If I look at 4 AA batteries they are about 6V and 1.500A. I'm not sure about how to read the Amps on my multimeter, I think it is telling me 1.5A. Could this be correct ?

Should these 4 AA NiCd batteries once fully charged read roughly the same Amp as 4 AA Duracell ?

 

[audioguru]

The Cells each are 2V at 200mA, considering they are connected in series of 3 does this mean they are supplying 6V at 600mA ?

Of course not. Voltages add in series, currents add in parallel. It will be 6V at 200mA at noon on the equator on a bright sunny day with the solar cells pointing directly at the sun. The voltage and current will be less in all other conditions so the Ni-Cads might not fully charge.

Would you know what my NiCd should read once fully charged ?

My old Ni-Cads were 600mA/hr and measured 1.45V each when fully charged and still on the charger. My new 2500mA/hr Ni-MH cells last more than 4 times longer.

If I look at 4 AA batteries they are about 6V and 1.500A. I'm not sure about how to read the Amps on my multimeter, I think it is telling me 1.5A. Could this be correct ?

You are not supposed to short a battery with a multimeter. You are only measuring how much current the wires can or cannot handle (the wires might catch on fire).

Should these 4 AA NiCd batteries once fully charged read roughly the same Amp as 4 AA Duracell ?

No. Removed from the charger their voltage will quickly fall to about 1.25V each.

 

[Oznog]

The voltage tells you little about the state-of-charge. State of charge is not a simple thing to determine on NiMH. In fact, the voltage initially increases while charging, though only slightly, and near the time where it reaches full charge it actually decreases for a brief time.

It gets rougher with solar cells because the current is not consistent. You may get 200ma at first, but later in the day you have only 50mA. With the drop in current, the battery voltage will go down. Likewise, a fully charged cell that was at 1.25v under a cloud may be suddenly exposed to 200mA as the sun comes back. It may take awhile for the battery voltage to rise again.

You may have problems with overcharging, because those look like fairly small batteries. 200mA could be enough to dry them out if left on too long after fully charged. But then again this probably isn't going to be a setup used for a really long time.

 

[hawk2eye]

re-chargeable batteries

I have 3 Solar Cells connected in series the + is attached to a diode and the diode is connected to the + of the Nicd battery, the - of the solar cell is connected to the - of the battery (see attached photo to see what I did.)
Can someone tell me if I have attached the battery the correct way to the solar cells for charging.

Justin.

++++++++++++++++++++++++++++++++++++
I would add:
The charged voltage , unloaded battery is a useless indication of the capability of the battery.

A good test would be to load the a recharged battery
with 10% of maximum capacity for 20 seconds while monitoring the battery voltage. A fully charged NiCd battery is not in good condition if its voltage drops by
10%.

hawk2eye

 

[bananasiong]

Hi,
Can this solar panel charge NiMH batteries?
Can they be charged and used simultaneously?

Thanks

 

[audioguru]

Hi,
Can this solar panel charge NiMH batteries?
Can they be charged and used simultaneously?

The battery is 1.45V x 4= 5.8V when fully charged. The diode adds 0.7V for a total voltage needed of 6.5V. The solar cells are only 6V so the battery will never fully charge.

The solar cells meet their spec for only 1 hour per day when it is sunny at noon.

It will take many days to partially charge the battery when it doesn't have a load. The battery will go dead if there is a load, because the voltage and current from the solar cells aren't enough.

 

[bananasiong]

The battery will go dead if there is a load, because the voltage and current from the solar cells aren't enough.

I thought, when there is no load, the batteries will be charged by the solar panel? Why the batteries will go dead? The voltage and current from the solar cells aren't enough for what??

 

[audioguru]

I thought, when there is no load, the batteries will be charged by the solar panel?

Never enough charging voltage, very low average charging current. After many days of sunny weather the battery will never fully charge.

Why the batteries will go dead? The voltage and current from the solar cells aren't enough for what??

You need to calculate how much load. For running a watch maybe? What about during bad weather when the solar cells won't have much output?

 

[bananasiong]

I'll use it to run a DC motor.
Three things are connected in parallel: Solar panel, rechargeable batteries (Ni-MH) and load (DC motor). I'll start with the fully charged batteries, the DC motor is powered by the batteries, then the solar panel keeps on charging to the batteries. Is this possible? I've never tried them out, I'm still planning.

 

[audioguru]

Do the math.
Is the average solar cell current more than the motor's current? I doubt it.

 

[bananasiong]

Of course no, but why do we need to concern this??? The motor is not running all the time, then the batteries will be charged when it is not running.

 

[audioguru]

The solar cells are in bright direct sunlight only at noon on a sunny day. They will charge the battery for only 1 hour each day! You could make a moving platform point the solar cells at the sun as it moves, then maybe the battery will charge 3 hours each day.
You don't say how much current the motor uses, you don't say how long you want it to run each day.

 

[bananasiong]

You don't say how much current the motor uses, you don't say how long you want it to run each day.

I have not decided yet. The motor is a toy car motor. I just want to know whether it can be charged or not when it is running. It is not fully depends on solar energy. Maybe without solar cell, it can run 1 hour continuously, with the solar cell, maybe extra 5 minutes?

 

[audioguru]

I have a little fan that uses two AAA cells. It draws nearly 1A!
Ni-MH rechargable cells have a capacity of 750ma/hrs and power it at full speed for about half an hour then slower and slower for the next half an hour.
I have a real plug-in charger for them.

I bought a 12V/150mA solar panel on sale. Through a window at noon I got 6V at 50mA. With the window open I got 13V but it dropped when it was loaded, 9V at 80mA max. I am in Canada, not on the equator, the sun was about 20 degrees from vertical. It is very critical to the aim at the sun.

 

[bananasiong]

Is the 12V/150mA expensive? Is it rated maximum voltage and current that afford to supply?

 

[audioguru]

Is the 12V/150mA expensive?

Pretty cheap. I paid $10.00 Canadian. The sun is too far away and keeps moving.

 

[bananasiong]

I've found one, 4.5V/80mA, if i charge 4 AA Ni-MH, they won't be full right?
If the solar panel is used indoor, energy source from the light. How low is the current & voltage be?

 

[audioguru]

I've found one, 4.5V/80mA, if i charge 4 AA Ni-MH, they won't be full right?

No. Ni-MH cells need 1.4V each to be fully charged. Four of them plus a series diode to block discharge at night equals a charging voltage of 6.3V. Your solar panel is only 4.5V.

If the solar panel is used indoor, energy source from the light. How low is the current & voltage be?

I don't know your light. Candles?
If it is outside then it will supply 80mA for 1 hour per day at noon when the weather is sunny. The AA Ni-MH cells are rated at 2500mA/hrs and need 3500mA/hrs to fully charge, so it will take about 3500/80= 44 days to fully charge 2 cells in series.