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How can I test this circuit???

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thebigbasicq

New Member
I have built this circuit with the following modifications:
1. I have used 200V zeners instead of the 400V(1N5117) zeners.
2. I have used a bead type 100uH inductor.

I am using a 6V 250mA solar panel. The MAX639 IC is a regulator IC. All resistors are 1/4 watt.

Now, how can I test this circuit. Whether it is working or not???

I don't want to connect Ni-Cd cells(infact i haven't bought them yet). I connected my multimeter accross the output terminals but it simply shows 0Volts? Meanwhile solar panel is supplying 6V to the circuit!

Here is the datasheet of MAX639. It too contains the same circuit.
http://pdfserv.maxim-ic.com/arpdf/AppNotes/A0809.pdf
 

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evoke

New Member
test it on a sunny day. when the sun is shinning hard get a multimeter and connect it in series where the + and - of where you are going to have your batteries. it should tell you if you have enough votltage and current to charge up your batteries
 

thebigbasicq

New Member
Well...

I connected the input terminals to a 6V regulated powersupply and checked the ouput at the output terminals. They registered 0V so i rechecked the circuits for flaws, broken connections, incorrect wiring etc. and found nothing wrong with it.
 

evoke

New Member
hook the 6v regulated power supply to the solar panel itself and see how much volts are coming out of it. connected it in series with the solar.

what is the current and voltage
 

Scubasteve

New Member
evoke said:
hook the 6v regulated power supply to the solar panel itself and see how much volts are coming out of it. connected it in series with the solar.

what is the current and voltage
Don't do this :p

Check the circuit over again, something must be wrong. Perhaps if you load the circuit with a resistor that will behave like your batteries, you will get a reading. I am pretty sure with it open, you should have voltage present.

Steve
 

thebigbasicq

New Member
Well...

I finally got this dumb circuit to work. The regulator IC works but it holds the output at 0.8V. That is no matter what the input voltage(above 2V) it holds the output at 0.8V that is how I know it works. Why is this so??? The output voltage must be above 1.5V or greater if I have to charge any Ni-Cd cell. Also if I connect a resistor(about 2k) in series with the zener(i.e. one which is connected between pins 4 and 5) I get the ouput which is little less than the input voltage(around 1-2V) but it varies directly with the input voltage i.e. the IC no longer regulates the voltage.

Thanx
 

thebigbasicq

New Member
Ok...

Now I replaced the zeners. Somebody told me that zeners should not exist in that circuit at all. He too suggested me to put Schottky diodes. I didn't have them at hand so I put normal silicon diodes(1N4148). It works but the circuit is still not regulating the out put. When the light level increases the output voltage increases and... So what do i do now???
 

Scubasteve

New Member
I read the description a few times from different places, and they all are quite clear that it is a zener diode. They do not say anything about why it is a zener diode, they just say it is an odd part.

I am not really sure how this circuit works.. I suggest you print out the actual datasheet (not that appnote) and understand its internal function. This will give you an insight on how it should work.

Goodluck,

Steve
 

Chippie

Member
Solar panels can supply a limited amount of power, the more current that is sourced from it the lower the output voltage........

This is the basis upon which the circuit works. The presence of the MAX is to charge the nicad batteries as quickly as possible but at the same time maximising the useful energy provided by the solar panel, it does this by
regulating the input voltage as opposed to the output volts....

If you refer to the app notes, you will see the performance curve for the solar cell, all will be apparent then , I hope 8)
 

thebigbasicq

New Member
I got it working but in a funny way...

I had 1N4148 silicon diodes on hand so I put them in instead of the zeners. The circuit worked but I don't know how to interpret the result. That is the output is visible on the multimeter only when I remove the diode at the output so I removed the silicon diode.

For test purposes first I read the output on the multimeter. It was around 6V. I connected 2, 1.5V dry cells to the output terminals and again read the output it was just above 3V. Now I cut off the sunlight a little bit and observed that the output still remained at exactly the same voltage i.e. the IC is regulating the voltage.

But I do not understand that why doesn't the circuit work without the 1N4148 diode at the output. I think it is to prevent the backflow of the current in the circuit from the charged cells.

CHIPPIE could you please explain me what you did a little bit more clearly. I understood what u posted but not very clearly. :oops:
 

Chippie

Member
Ok no problem....

Before we start, let me just say, the post I made earlier was just my interpretation of what is supposed to happen.... :)


So, how can I help? Which bit do you not understand ?


The MAX 639 is a "control" chip. It appears to control the charging of some nicad batteries in this case, using a solar panel. The solar panel can only output so much voltage and current.......In order to maximise those attributes, to charge the nicads, it regulates the amount of power that the solar panel can provide.......As you draw current from the panel the voltage drops...So in order to make full use of the available power the MAX chip will draw as much power it can without the voltage falling too far......This I have determined from the graphs provided in the application document in the link you posted.......

HTH Chip
 

thebigbasicq

New Member
Ok, I bought Ni-Cd cells finally...

Ok, I bought 2 panasonic Ni-Cd rechargeable cells(pencil cells, 1.25V, 650mAH each). I connected them across the output and kept the solar panel in sunlight(its bright and sunny today). How do I know whether the cells are charging?
 
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