Hi there,

I am doing a project where I am going to charge a 12V 6 Amp Nimh Battery with a Solar Panel. my Solar panel is 20W 18V rating so it can provide max of 1.1 Amp.

I was thinking of using LT1510 IC (LT1510 datasheet) in order to charge my battery with constant current configuration. So now here I don't understand, can LT1510 maintain the constant current even though the Solar Panel is not delivering enough Amp's? I can understand if we are plugging in our wall socket then there is a constant volt and Amp's coming out but in case of the Solar panel the amp's is varying depending upon the intensity of the sun light.

So, for eg. I configure LT1510 with 800mA constant Current configuration, So now if the Panel is only providing for like 300mA then can LT1510 still maintain 800mA at the output? If yes how can I know the minimum amp rating in the i/p of the LT1510 at which it can maintain 800mA. I am imagine if the Solar is only providing like 50mA in the evening then for sure LT1510 will not be able to maintain 800mA, so what will happen in this case? will there be zero current?

I am looking forward to hearing from anyone who has any idea about this

 

can LT1510 maintain the constant current even though the Solar Panel is not delivering enough Amp's?

No. The 'constant' current will droop once the power demand exceeds the power available from the panel.

 

When the panel drops below 7 volts the under voltage lockout in the chip will shut it off.

 

I know you only asked about charging the battery, but generally the real goal is to power some useful load. The battery just provides short term storage for the energy collected during peak sunlight, and smoothing it out over the darker times. It's a means to an end.

Just about every such project we see here is unrealistic about the sizing of the panel for the load. So take no offense when I ask, what are you hoping to power with this arrangement?

 

Thank you for your reply and no offense taken
I am trying to charge my 6Amp battery to drive 4 Leds of (3Watt each).

But I still don't understand if I can maintain the constant charging current (using LT1510) even if the panel is not providing enough current. I am afraid if I don't provide constant current to the Battery then I am going to break it

Let me know if you have any suggestions

 

I am afraid if I don't provide constant current to the Battery then I am going to break it

Providing less current won't break it. How are you determining the end-of-charge state?

 

Battery is 6Ah. How long are LED's on? 20 W panel is probably good for about 15W for average conditions. 4 LED's with drivers , about 15 W. Battery then is just transferring day energy to night energy?

 

I know providing less current wont damage the battery, the thing I am afraid is the current from the panel is varying and if I feed that varying current (if its varying with high number) to the battery then it might get damage. So this is why I want to stabilize the o/p current. About the end of charge state I haven't decided but I am thinking of using a comparator.

 

Hello Bernard,
Design is actually for 5 hours, so its 60W/hr. battery charges at the day time discharge through the leds at the night. But now I am not really concern about this the thing I am focusing about is for charging the battery. I am doing some simulation in LtSpice using LT1510.

 

I know providing less current wont damage the battery, the thing I am afraid is the current from the panel is varying and if I feed that varying current (if its varying with high number) to the battery then it might get damage.

That's what your regulator is doing - preventing an over-current situation that would damage the battery. The battery won't care if charging sags when the panel is in the dark, although you may want to prevent it from being drawn down too far. That's very bad for batteries.

 

They are hard to charge correctly. You might want to give this a read.

http://www.powerstream.com/NiMH.htm

Is 18 volts the open circuit voltage of your solar panel? I suspect it is if it is a 12 volt panel.

 

you mean I need to think for under voltage protection? Yes I did think of this but still don't have much idea about. Can you refer me to some links which will help me to understand this and to design it as well.

 

Yes, you want to prevent dropping below a set voltage. There are recent threads here on auto-shutoff strategies.

 

You could join the fun, on this page, " Need help to light up 8 LEDs---", OP, jenovauh. 12V Jell cell battery, 10W panel & 200 mAs worth of LEDs.
Can you tell how many cells are in your battery? 9 or 10 " C" maybe?

 

There are 10 cells in the battery and the data sheet of the battery says it require 18V to charge. It's a 12V battery why does it need 18V rather than just 15-16V to charge it?

 

Looks like 18V could shove a bunch of amps thru the battery, 6 to 10A? The solar panel, SP, might charge at 1/10th C to 1/7 C, where to stop, maybe @ 1.41 V/ cell, & or a slight temp rise.
Did the data sheet offer any other inf?

 

Thanks for your reply.
here is the data sheet of the batttery, in the data sheet it says it is a Li-ion battery but also a Nimh battery. So its kind of confusing. It also mentions about the min (380mA) and max (1600mA) charging current.

I did some simulation in LtSpice using LT1510 IC, with different charging current. If you are interested I would love to share it here.

 

enertech really screwed up, partial specs. on two different batteries. Since you counted 10 cells, it is a Ni-MH? Battery just has 2 connectors?