drozwood90
Senior Member
Link is bad...
I've been thinking of doing something like this for a while...good ideas!
--Dan
I've been thinking of doing something like this for a while...good ideas!
--Dan
Need some basic Electronics and circuitry help
- Thread starter JohnWPB
- Start date
BraveSirRobbin
Moderator
Hi John;
Here are some “guess-timates” (emphasis on the “guess”) of what I think you can do and the performance you will get. These estimates would be a lot more accurate once the current draw is known for your light with the DC to DC adapter in place (i.e. current actually being drawn from the motorcycle battery).
Here is a guess of the current draw of your light:
The AAA battery has a 0.55 amp hour rating. Let’s assume that the LED light you purchased will last say two hours with fresh batteries installed. Then you can get the amount of current draw by 0.55 / 2 = 0.275 amps. Let’s round this off to a guess of a quarter of an amp (0.250).
You will need an adapter go from 12 volts to 4.5 volts as you stated in your first post. You can get a cheap converter from WayneW’s links above or maybe go to Rat Shack and get this one.
This one has a “self-resetting” fuse so you will not need to purchase an in-line fuse assembly as I previously suggested. You will have to somehow clip/solder/wrap wiring from the battery to the cigarette adapter's studs. Also, make sure you know which wire from the adapter is positive and which is negative as you will need this for connecting to your light.
Of course this adapter will use current and I’m going to throw out a number of 30 percent efficiency or 0.075 amps. This means your total current draw guess is 0.250 plus 0.075 or 0.325 amps (remember this is a guess-timate). For 12 hours of use the light will draw from the battery at a rate of 0.325 * 12 = 3.9 Amp Hours (let’s round this off to 4 amp hours).
Now let’s take an estimate on your charging system:
I looked at motorcycle batteries and most are around the 20 amp hour rating. To be safe and not go under 50% of its capability, let’s use 10 amp hours as the battery supply capability.
This means your battery can supply power to your light/adapter assembly for 10 / 0.325 or 30 hours, which is good because even if I’m off a factor of two in my current draw guess for your light/adapter, you will be under 50% battery draw for a long night of use.
Now you need to of course charge this battery during the daytime. Your solar panel has a current output capability of 0.4 amps. For again, worse case during the short winter days of say only six hours of sunlight, this means that you will supply 0.4 * 6 = 2.4 amp hours back into the battery.
Here is where I’m estimating you may have a problem (in the winter months). You’re drawing from the battery at a rate of 4 amp hours, but only putting in charge at a rate of 2.4 amp hours. Your battery may go dead after a few days of use.
You may need a second solar panel in the winter time. Of course you might want to diode isolate the two solar panels, but I think I’ve gone far enough in this post as the first one seemed to cause you some (unintended) angst!
Anyway hopes this offers some help. The project does seem at least reasonably feasible with the parts you have purchased. You may have to tailor the run time of the light, amp hour rating of the battery, or as mentioned, charge capability into it.
You can see how important it is to actually know the actual current draw from the battery. Once you get this system in place you can easily measure it and fine tune the above calculations!
As always, if you need any help please ask. I also did the above calculations quickly so it would be nice if someone went over my math.
Regards,
BSR
Here are some “guess-timates” (emphasis on the “guess”) of what I think you can do and the performance you will get. These estimates would be a lot more accurate once the current draw is known for your light with the DC to DC adapter in place (i.e. current actually being drawn from the motorcycle battery).
Here is a guess of the current draw of your light:
The AAA battery has a 0.55 amp hour rating. Let’s assume that the LED light you purchased will last say two hours with fresh batteries installed. Then you can get the amount of current draw by 0.55 / 2 = 0.275 amps. Let’s round this off to a guess of a quarter of an amp (0.250).
You will need an adapter go from 12 volts to 4.5 volts as you stated in your first post. You can get a cheap converter from WayneW’s links above or maybe go to Rat Shack and get this one.
This one has a “self-resetting” fuse so you will not need to purchase an in-line fuse assembly as I previously suggested. You will have to somehow clip/solder/wrap wiring from the battery to the cigarette adapter's studs. Also, make sure you know which wire from the adapter is positive and which is negative as you will need this for connecting to your light.
Of course this adapter will use current and I’m going to throw out a number of 30 percent efficiency or 0.075 amps. This means your total current draw guess is 0.250 plus 0.075 or 0.325 amps (remember this is a guess-timate). For 12 hours of use the light will draw from the battery at a rate of 0.325 * 12 = 3.9 Amp Hours (let’s round this off to 4 amp hours).
Now let’s take an estimate on your charging system:
I looked at motorcycle batteries and most are around the 20 amp hour rating. To be safe and not go under 50% of its capability, let’s use 10 amp hours as the battery supply capability.
This means your battery can supply power to your light/adapter assembly for 10 / 0.325 or 30 hours, which is good because even if I’m off a factor of two in my current draw guess for your light/adapter, you will be under 50% battery draw for a long night of use.
Now you need to of course charge this battery during the daytime. Your solar panel has a current output capability of 0.4 amps. For again, worse case during the short winter days of say only six hours of sunlight, this means that you will supply 0.4 * 6 = 2.4 amp hours back into the battery.
Here is where I’m estimating you may have a problem (in the winter months). You’re drawing from the battery at a rate of 4 amp hours, but only putting in charge at a rate of 2.4 amp hours. Your battery may go dead after a few days of use.
You may need a second solar panel in the winter time. Of course you might want to diode isolate the two solar panels, but I think I’ve gone far enough in this post as the first one seemed to cause you some (unintended) angst!
Anyway hopes this offers some help. The project does seem at least reasonably feasible with the parts you have purchased. You may have to tailor the run time of the light, amp hour rating of the battery, or as mentioned, charge capability into it.
You can see how important it is to actually know the actual current draw from the battery. Once you get this system in place you can easily measure it and fine tune the above calculations!
As always, if you need any help please ask. I also did the above calculations quickly so it would be nice if someone went over my math.
Regards,
BSR
I just did a quick speed read of the thread (coffee break) and I did not see the mention of a low battery cutoff. If you shut down before the battery is deep discharged the battery should recover fully the next day.
I am suggesting this because John mentioned midnight would be enough so why drain the battery all of the way down and need a larger solar cell.
Just a thought.
I am suggesting this because John mentioned midnight would be enough so why drain the battery all of the way down and need a larger solar cell.
Just a thought.
BraveSirRobbin
Moderator
Remember though that I cut the amp hour calculation of the battery in half to prevent this (avoid discharging below 50% capacity).
Since this was not a agm (glass mat) type I was extra conservative.BSR, Thanks that post was much easier to wrap my head around
I received the light a couple days ago, and I must say it is pretty darn bright! Taking the light apart, it is all nicely packaged onto one small board, with all the circuitry and LED's mounted to it. This is gonna be a breeze to mount into the outdoor housing I mentioned earlier.
I am going to use a 12c to 4.5v like the one you mentioned above. I will get it all hooked up here in the coming days (After this hurricane passes!) and give it a test run to see how it all works.
On a side note, there really is not much of a decrease in sunlight in "winter" here in South Florida, so that should not play too much of a part. I actually got a pretty nasty sun burn while putting up the Christmas lights on the roof and palm trees last December
Thanks for all the help and advice from everyone!
I received the light a couple days ago, and I must say it is pretty darn bright! Taking the light apart, it is all nicely packaged onto one small board, with all the circuitry and LED's mounted to it. This is gonna be a breeze to mount into the outdoor housing I mentioned earlier.
I am going to use a 12c to 4.5v like the one you mentioned above. I will get it all hooked up here in the coming days (After this hurricane passes!) and give it a test run to see how it all works.
On a side note, there really is not much of a decrease in sunlight in "winter" here in South Florida, so that should not play too much of a part. I actually got a pretty nasty sun burn while putting up the Christmas lights on the roof and palm trees last December
Thanks for all the help and advice from everyone!
tmbrown97
Senior Member
so, just to play devil's advocate here...
As much as I love a good project, is the intent to save money here by using solar? Cuz I'm guessing the overall investment in hardware will actually be more than running the light for 6 hours/day for the next 10 years...
Not to say I've never spent $1,000 to save $50...
Another approach too, is to order a battery that's 4.5 volts, and step down the charging circuit instead - at least that way you're more likely to waste your charging power through heat loss, and optimize the battery consumption specifically for the light.
Also given the low current draw of those lights, off a little 4.5 volt battery like this: http://www.bfmbatterysales.com/index.asp?P...94&src=nxtg I would think the light would run for a month without even charging the battery! Of course, there's many more people here who could do the actual calculation and confirm that...
As much as I love a good project, is the intent to save money here by using solar? Cuz I'm guessing the overall investment in hardware will actually be more than running the light for 6 hours/day for the next 10 years...
Not to say I've never spent $1,000 to save $50...
Another approach too, is to order a battery that's 4.5 volts, and step down the charging circuit instead - at least that way you're more likely to waste your charging power through heat loss, and optimize the battery consumption specifically for the light.
Also given the low current draw of those lights, off a little 4.5 volt battery like this: http://www.bfmbatterysales.com/index.asp?P...94&src=nxtg I would think the light would run for a month without even charging the battery! Of course, there's many more people here who could do the actual calculation and confirm that...
Well the investment was not much at all around $40 or so, as I had the battery here, and the light was only $9. On top of that, it was far cheaper than any of the solar lights that I had found at the big box stores and online. Even then the ones I found were pretty wimpy like the Malibu's and such. (Really dim) This light is BRIGHT to say the least. So all in all it was cheaper, no need to run wires from an outlet to the location, and is far brighter, and the LED's will last a lifetime. Far better than any of the "ready made" options I found.
So far I have it running off a 12v to 4.5v cigarette lighter adapter (One from an old phone I had here in a drawer & taken apart putting the circuit board in the light housing) and it is working perfectly. Its a matter of time to see if the battery eventually drains, or if it maintains whats needed with the charging it does in the day time. I think it is going to be ok, as I hooked up the solar panel to the light with the 4.5v stepdown (minus the battery), and it powers the light directly. So, that in mind, the solar cell is providing enough direct current to run the light, thus the cell is proably providing a little excess power. That being the case, I am almost certain that the panel is enough to keep the battery fully charged by the time the sun goes down each night.
In time, I may add a couple panels here and there, and a larger battery to power other exterior lighting... I'll just see how it goes for now
So far I have it running off a 12v to 4.5v cigarette lighter adapter (One from an old phone I had here in a drawer & taken apart putting the circuit board in the light housing) and it is working perfectly. Its a matter of time to see if the battery eventually drains, or if it maintains whats needed with the charging it does in the day time. I think it is going to be ok, as I hooked up the solar panel to the light with the 4.5v stepdown (minus the battery), and it powers the light directly. So, that in mind, the solar cell is providing enough direct current to run the light, thus the cell is proably providing a little excess power. That being the case, I am almost certain that the panel is enough to keep the battery fully charged by the time the sun goes down each night.
In time, I may add a couple panels here and there, and a larger battery to power other exterior lighting... I'll just see how it goes for now
BraveSirRobbin
Moderator
Can you see how much current it is drawing from the 12 battery with a meter?
mustangcoupe
Senior Member
Looking at your meter it has a max 200mA setting or a 10A setting.... your calculations show 250mA I believe... so you'd blow the 200mA fuse on that setting. Set the meter to the 10A setting (I it looks white or grey. ) connect your probes to the 10A plug and the Com plug then disconnect the positive wire and connect the meter probe to the battery, and the other meter probe to the wire.(put it in series with the light....) this will complete the circuit and current will flow through the meter allowing the meter to measure the current. because you are on 10 A I do not know how sensitive the meter will be.
hth,
