Hi. I am currently working on a project that includes a 12v gel cell battery. I also want to be able to charge it through a wallwart or a solar panel in the future. To do that I am trying to regulate the max voltage through 2 6.8Zv zener diodes (according to the datasheet). The circuit looks like this (I am using 1N5235 instead 1N5235B):
The voltage between A and ground is supposed to be around 13.3V (13.4V wallwart measured by my multimeter) to a max of 13.6V if the source is higher (for a solar panel).
The problem is that after putting all parts together on my breadboard, the voltage measured by my multimeter is around 10.4V.
What should I do? Should I trust multisim and the datasheets and just stick to the circuit plan? Should I start trying different diodes combination so I reach the desired 13.6V? Should I buy better diodes? [smiley=undecided.gif]
At least for voltage I think it is ok. A fairly new AA is measured between 1.49 and 1.50V.
The voltage across each diodes were 4,91 and 4,85.
The voltage on the other side of the resistor is 13.93
The voltage of the wallwart changed to 14.27V.
I dont know if I am doing it wrong or what but when the multimeter is set to 10A I get between 0 and 0.01A, if I set it to 200A it fluctuates between 0 and 0.1A (I open the circuit and close it using the probes as they were a single wire).
Please dont laugh at my ignorance but what do you mean by the zener being string out of the circuit?
Try this. I would make a heat sink for the regulator and I would use the protection diodes mentioned in the data sheet for the LM317T http://shdesigns.org/gcellchg.html
This is good information from Cadex who has a rather amazing charging and rejuvenation technology. Their equipment would recover 90 percent of the NiMh cell phone batteries we used their equipment on. Lithium ion batteries did not fare as well but after reprogramming the equipment per their tech support I was getting about 60 percent recovery. That is to rated capacity. We'd pitch anything that would not reach that level or had any over temperature reading.
Of note is that off brand lithium ion batteries consistently failed capacity and a few would go into meltdown by the test and in some cases damaged the charger. Examination showed that the internal safety circuit was LYING to the charger in the phone and to the Cadex device. I don't consider that Cadex fault. OEM batteries never did this but then I don't recall running Sony batteries as I'm still alive. ;D
So for a 6.8V zenner this is way off. It look to me like you have got the wrong diodes as your meter seems to give sensible readings for the other voltages.
Try this. I would make a heat sink for the regulator and I would use the protection diodes mentioned in the data sheet for the LM317T Gell-Cell Charger
The problem with that circuit is that even if it is ok for a 18V solar panel, it is not good for my 13V - 14V wallwart since the input must be at least 15V.
That's why I am trying to regulate voltage through zener instead of using a common voltage regulator.
http://www.batteryuniversity.com/
This is good information from Cadex who has a rather amazing charging and rejuvenation technology. Their equipment would recover 90 percent of the NiMh cell phone batteries we used their equipment on. Lithium ion batteries did not fare as well but after reprogramming the equipment per their tech support I was getting about 60 percent recovery. That is to rated capacity. We'd pitch anything that would not reach that level or had any over temperature reading.
Of note is that off brand lithium ion batteries consistently failed capacity and a few would go into meltdown by the test and in some cases damaged the charger. Examination showed that the internal safety circuit was LYING to the charger in the phone and to the Cadex device. I don't consider that Cadex fault. OEM batteries never did this but then I don't recall running Sony batteries as I'm still alive. Grin
Thanks for the link. Useful info.
The voltage across each diodes were 4,91 and 4,85
So for a 6.8V zenner this is way off. It look to me like you have got the wrong diodes as your meter seems to give sensible readings for the other voltages.
I can read clearly on the diodes 1N5235. Is it possible that my diodes are that bad quality?
What do you see if you use something like a 1K resistor and just one diode at a time? That would directly measure the Zener voltage of each diode.
Using a 1K resistor (973ohm according to my multimeter) I get 5.88V across the diode, 13.20V including the resistor and 13.66V from the wallwart alone.
What about the other Zener diode? Sounds like you have bad Zeners.
I measured all my 1N5235 diodes, 3 1N4001 and 2 1N4004.
The zener voltage were 5.83V, 5.88V, 5.88V, 5.78V and 5.82V.
For the same diodes I measured their voltage drop and they were all 0.79V.
For the 1N4001 the voltages were 0.56V, 0.65V, 0.63V.
And finally for the 1N4004 both were 0.67V.
I am really confused. For the rectifiers gettting between 0.63V and 0.67V seems normal (the one with 0.56V seems to be bad). The same thing goes for the 0.79V on the zeners.
I am starting to think I have to test each zener to get the 13.6V
The zener voltage were 5.83V, 5.88V, 5.88V, 5.78V and 5.82V.
Looking at your datasheet, this is actually within specifications (+/-20%) for your 6.8V zeners. I'm also inclined to believe they will be far off the mark since the manufacturer offer 10% and 5% versions as well. When tested during manufacturing, anything significantly off will fall into the 20% bin.
The voltage across each diodes were 4,91 and 4,85.
This however is outside specifications unless zener current and/or temperature deviate significantly from 20mA/25C respectively. You may want to repeat the single zener experiment with a different resistor (e.g. 500 or 2k) to see how zener voltage will change with varying zener current.
Another issue that may influence your readings is if your wallwart has significant mains ripple. You would need a scope to check this, but you could also try to measure zener voltage with your meter set to AC to get an indication.
If accurate zener voltage is critical to your project, you may have to look at reference grade zeners. They are however quite expensive.
A low cost zener alternative could be the BZX55 type with a zener voltage close to 5V (4V7 or 5V1). Around 5V, they're typically quite accurate and with a near neutral temperature coefficient.
The zener voltage were 5.83V, 5.88V, 5.88V, 5.78V and 5.82V.
Looking at your datasheet, this is actually within specifications (+/-20%) for your 6.8V zeners. I'm also inclined to believe they will be far off the mark since the manufacturer offer 10% and 5% versions as well. When tested during manufacturing, anything significantly off will fall into the 20% bin.
The voltage across each diodes were 4,91 and 4,85.
This however is outside specifications unless zener current and/or temperature deviate significantly from 20mA/25C respectively. You may want to repeat the single zener experiment with a different resistor (e.g. 500 or 2k) to see how zener voltage will change with varying zener current.
Another issue that may influence your readings is if your wallwart has significant mains ripple. You would need a scope to check this, but you could also try to measure zener voltage with your meter set to AC to get an indication.
If accurate zener voltage is critical to your project, you may have to look at reference grade zeners. They are however quite expensive.
A low cost zener alternative could be the BZX55 type with a zener voltage close to 5V (4V7 or 5V1). Around 5V, they're typically quite accurate and with a near neutral temperature coefficient.
I think I'll just have to get to the desired 13.6V by trying different diodes combination.
So the fight between datasheets vs multimeter is winned by the multimeter with a knock-out on the last round.