Completely discharging most types of batteries will shorten their life drastically. Check the recommended discharge level for the battery chemistry you are using and try not to go beyond that.
Completely discharging most types of batteries will shorten their life drastically. Check the recommended discharge level for the battery chemistry you are using and try not to go beyond that.
+1
Just read some blogs on various RC sites and they all strongly recommend to never take a LiPo below 20% of its Capacity. They use low cost battery monitors to prevent over discharge. Another method they use is to take an open circuit voltage reading of the battery immediately after use and if each cell is at 3.7 to 3.74 volts then it has reached its recommended discharge point. Taking a LiPo down to 3.0 volts will severely shorten its useful life. Fully discharging a LiPo will destroy it.
As for charging, the going recommendation (if not outright firm rule) is to never push more than 1C of current into the battery to prevent severe overheating. 1C just means if the battery capacity is 2200 mAh then you have to limit the charge current to no more than 2200 milli-Amps.
Today is going to be a non-solar charge day here, the open circuit reading should not get any higher than 2.75V. I found another Tenergy battery which had a reading of .0025V, so I am going to hook it up and leave it on the whole solar charge day, just to see what a trickle charge can accomplish with the battery, if anything.
Since I am going to be using the 2.95V mark as the start battery charging point, or no usage point, I wonder how I should be getting that value? It seems like you have to stop the usage process in order to get the real charge state of the battery pack. I wonder how the laptops to that, let you know that you are about to shutdown because of low battery state? I guess one way is to calculate the known current usage value and add that to the battery reading. Which leads to another problem solution, how to I get a real open circuit voltage reading while I have a battery connected for a charge session? Just a couple things to think about.
During this week I was observing the light conditions on my window sill, and it looks like, even on a cloudy day, I could probably get a battery charged up, starting from a 3.5V level. Because the light conditions are varied, this being fall going into winter, I will probably have to start with one battery and then add batteries as the light conditions improve.
So, I am thinking that maybe I need something like an H-Bridge set up where I can have one battery online and then via software bring another battery online. I was also looking at the servo ports on the Activity Board, I wonder if that could be used in some way to bring online batteries to be charged. If I feed the open circuit juice via the barrel connection, then I have some pins (servo ports) available to activate a connection, or am I all wet on this concept? There are only certain light conditions where I could have more than one battery online to charge, I really need some kind of switching scenario.
Tomorrow I will be getting my battery holders, so I will be able to set up a couple of batteries and see how many I can put online and still get a decent charge.
Yesterday was a very good indicator for the possible uses of my window sill solar array charge station. I am calling yesterdays charge day as typical, meaning a little bit of overcast, a little bit of partly cloudy, a little bit of mostly sunny, ...
I put online a 3.7V battery that had a start value of 3.59V, started at 8:30AM and took it off line at 4:00PM, the battery charged state was 3.67V. So, after an all day session with mixed light conditions, it was able to achieve an .08V charge. This leads me to believe that the best usage of this setup is, is to use the solar array in use while the battery pack is also in use. Hopefully at the best solar charge conditions it might be able to top off the batteries and in other conditions it will supplement the current use.
I will probably test this out tomorrow using a couple of freshly charged batteries, with a battery charger, have them linked in series and plugged into the Activity Board plus it will be plugged into the solar array. This test should give an indication as to how well the batteries hold up with a supplemental input from a solar array.
Yesterday I wired in two battery holders, barrel plug cable, and two leads from the solar charger. The light conditions were overcast for the whole charging day, with the exception of a brief ten minute appearance of some indirect sun.
The battery holders, you get what you pay for. I purchased them from an ebay site, making the assumption that they are to work as expected. First, the battery contacts, the negative side, because it has a spring, that is not a problem, it is the positive side that is the problem. The contact part does not make contact with the battery. The Tenergy battery has a flat recessed contact surface, these battery holders have no chance of making any contact. After I made some modifications, it finally worked as expected. The other problem is battery holder wires, they are so thin, it looks like it has three hair like strands of wire, you will have lots of fun trying to strip them.
The actual test day ended after four hours when I had an internal error shut down of the RPi, and in this case, the Activity board also. Not sure what happened to cause the problem. After calculating the amps being produced by the combination of the batteries and the solar array output, it would be just a little less than two amps. The RPi can handle that, but now I am not sure about the Activity Board.
The battery charge state at the barrel plug was 7.91V, as soon as I started the program, the ADC was showing 7.3V, since I do not know how to figure in an amp value, not sure what the amp reading would have been. The individual battery charge readings were 3.91V and 3.99V before the test, and after the test, the readings were 3.59V and 2.99V. I am not sure why the big difference, unless the one battery was getting a bigger solar charge than the other. If that is the case, than solar charging batteries in series may not be an efficient use of the solar charge.
Lots of questions need to be looked into, and appropriate modifications will have to be designed in. This does not seem like it will be a week long experiment, this just might keep me busy until next spring.:-) Today I will be doing another testing session using two UltraFire batteries with a start reading of 4.01V on both. Maybe the battery itself has to be looked into.
For those of you following this thread, Parallax has reduced the price on there Solar Panel Kit to $125.99, not sure if this reflects 10% off thing that just started or if that means you get to knock off 10% off the $125.99 price, plus free shipping? I take it that this will last until after the holiday.
I was just starting to look into the next step with the solar stuff, most of the other resellers are offering units that are 12V, and the unit that Parallax offers is 6V. Now do I consider putting a system together that will be based on 3.7V Li-ion batteries(Parallax Solar), something in the 6V - 9V batteries(other 12V systems), or power some 12V device(s)(other resellers 12V systems). The only problem that I have is the actual assembly of the Parallax kit, there is lots of soldering, and if you mess up then...
Not sure which way I will go on this, but I guess I have a few days to figure things out, 3.7V Li-ion batteries or 12V stuff, decisions, decisions. Somebody give me a nudge in the right direction.
For a fixed installation I would go with a 12V system using lead acid batteries to keep the cost down. For the solar panels I would use a single panel or multiple series connected panels that provide 15V or more so I could use a switching regulator to match the panel output to the battery charging voltage. Maybe not as efficient as an MPPT charger but close and much lower cost.
I do not want to make changes to my roof, so that kind of fixed system is out, not even sure about a mini-solar farm in my backyard, either.:-) I have noticed that there are mobile solar arrays for outdoor use, like for RVs, and just unfold on the ground stuff, they also run in the 12V range, not sure if linking up two units to get 24V to charge up 12V batteries would work out. I did notice that on ebay the price for 18650 2400mAh 3.7V batteries, the price is starting to come down, not sure what the price will be in a couple of years from now would be. Also I keep thinking about yesterdays test and the results from charging two 3.7V batteries in series.
And yet I still keep thinking about all that soldering for the Parallax solar kit, my confidence is very low in that area...
This little experiment is still alive and well. Since I was not getting the performance that I expected with the nine panel array, I added the last panel that I have, now it is a ten panel array. To my surprise, by increasing it to 1.1 Amp array, it seems to be a little more responsive to charging at the lower voltage levels with minimal light conditions. I added four of my battery holders and wired them up to be 7.4VDC output using four 3.7VDC li-ion batteries. So I am getting closer to a minimal portable solar panel experimentation board.
The next thing I have to do is create something that will prevent the batteries from an over charge. I guess I have an option of using a 5V regulator, but I was thinking about what the benefits of using a zener diode would be, aren't they supposed to have some kind of turn off at a specific voltage feature?
I still have room for maybe two or three panels, so I am keeping that option open, but I do want to stay within my budget for this experiment, I am very close to going over.
Once that certain voltage is reached, it very quickly conducts and prevents further increase in voltage by consuming power. While conducting, if too much current is supplied then the zenor will overheat and permanently go short-circuit. If a very large amount of current is supplied then it will explode and go open-circuit.
Voltage regulators use a zenor internally as their reference.
Comments
+1
Just read some blogs on various RC sites and they all strongly recommend to never take a LiPo below 20% of its Capacity. They use low cost battery monitors to prevent over discharge. Another method they use is to take an open circuit voltage reading of the battery immediately after use and if each cell is at 3.7 to 3.74 volts then it has reached its recommended discharge point. Taking a LiPo down to 3.0 volts will severely shorten its useful life. Fully discharging a LiPo will destroy it.
As for charging, the going recommendation (if not outright firm rule) is to never push more than 1C of current into the battery to prevent severe overheating. 1C just means if the battery capacity is 2200 mAh then you have to limit the charge current to no more than 2200 milli-Amps.
Since I am going to be using the 2.95V mark as the start battery charging point, or no usage point, I wonder how I should be getting that value? It seems like you have to stop the usage process in order to get the real charge state of the battery pack. I wonder how the laptops to that, let you know that you are about to shutdown because of low battery state? I guess one way is to calculate the known current usage value and add that to the battery reading. Which leads to another problem solution, how to I get a real open circuit voltage reading while I have a battery connected for a charge session? Just a couple things to think about.
Ray
So, I am thinking that maybe I need something like an H-Bridge set up where I can have one battery online and then via software bring another battery online. I was also looking at the servo ports on the Activity Board, I wonder if that could be used in some way to bring online batteries to be charged. If I feed the open circuit juice via the barrel connection, then I have some pins (servo ports) available to activate a connection, or am I all wet on this concept? There are only certain light conditions where I could have more than one battery online to charge, I really need some kind of switching scenario.
Tomorrow I will be getting my battery holders, so I will be able to set up a couple of batteries and see how many I can put online and still get a decent charge.
Ray
I put online a 3.7V battery that had a start value of 3.59V, started at 8:30AM and took it off line at 4:00PM, the battery charged state was 3.67V. So, after an all day session with mixed light conditions, it was able to achieve an .08V charge. This leads me to believe that the best usage of this setup is, is to use the solar array in use while the battery pack is also in use. Hopefully at the best solar charge conditions it might be able to top off the batteries and in other conditions it will supplement the current use.
I will probably test this out tomorrow using a couple of freshly charged batteries, with a battery charger, have them linked in series and plugged into the Activity Board plus it will be plugged into the solar array. This test should give an indication as to how well the batteries hold up with a supplemental input from a solar array.
Ray
The battery holders, you get what you pay for. I purchased them from an ebay site, making the assumption that they are to work as expected. First, the battery contacts, the negative side, because it has a spring, that is not a problem, it is the positive side that is the problem. The contact part does not make contact with the battery. The Tenergy battery has a flat recessed contact surface, these battery holders have no chance of making any contact. After I made some modifications, it finally worked as expected. The other problem is battery holder wires, they are so thin, it looks like it has three hair like strands of wire, you will have lots of fun trying to strip them.
The actual test day ended after four hours when I had an internal error shut down of the RPi, and in this case, the Activity board also. Not sure what happened to cause the problem. After calculating the amps being produced by the combination of the batteries and the solar array output, it would be just a little less than two amps. The RPi can handle that, but now I am not sure about the Activity Board.
The battery charge state at the barrel plug was 7.91V, as soon as I started the program, the ADC was showing 7.3V, since I do not know how to figure in an amp value, not sure what the amp reading would have been. The individual battery charge readings were 3.91V and 3.99V before the test, and after the test, the readings were 3.59V and 2.99V. I am not sure why the big difference, unless the one battery was getting a bigger solar charge than the other. If that is the case, than solar charging batteries in series may not be an efficient use of the solar charge.
Lots of questions need to be looked into, and appropriate modifications will have to be designed in. This does not seem like it will be a week long experiment, this just might keep me busy until next spring.:-) Today I will be doing another testing session using two UltraFire batteries with a start reading of 4.01V on both. Maybe the battery itself has to be looked into.
Ray
I was just starting to look into the next step with the solar stuff, most of the other resellers are offering units that are 12V, and the unit that Parallax offers is 6V. Now do I consider putting a system together that will be based on 3.7V Li-ion batteries(Parallax Solar), something in the 6V - 9V batteries(other 12V systems), or power some 12V device(s)(other resellers 12V systems). The only problem that I have is the actual assembly of the Parallax kit, there is lots of soldering, and if you mess up then...
Not sure which way I will go on this, but I guess I have a few days to figure things out, 3.7V Li-ion batteries or 12V stuff, decisions, decisions. Somebody give me a nudge in the right direction.
Ray
And yet I still keep thinking about all that soldering for the Parallax solar kit, my confidence is very low in that area...
Ray
The next thing I have to do is create something that will prevent the batteries from an over charge. I guess I have an option of using a 5V regulator, but I was thinking about what the benefits of using a zener diode would be, aren't they supposed to have some kind of turn off at a specific voltage feature?
I still have room for maybe two or three panels, so I am keeping that option open, but I do want to stay within my budget for this experiment, I am very close to going over.
Ray
Once that certain voltage is reached, it very quickly conducts and prevents further increase in voltage by consuming power. While conducting, if too much current is supplied then the zenor will overheat and permanently go short-circuit. If a very large amount of current is supplied then it will explode and go open-circuit.
Voltage regulators use a zenor internally as their reference.