rebelrider.mike
Member
- Joined
- May 25, 2017
- Messages
- 554
We swapped our Christmas tree lights out for LEDs this year. I've lost the patience to replace several bulbs on each string each year. So now I've got many feet of nice green insulated wire, and hundreds of bulbs and sockets to use for whatever.
I've decided to make a thing for my wife that lights up and blinks. Putting them on a battery is a little more complicated than I thought it would be though. The problem was that each bulb is a resistor, and when you put them in parallel, the resistance goes way lower. Because of the 1/R +1/R equation. I started out trying to do a bunch of math to get 25 bulbs in a series and parallel configuration that would use the right Volts and Amps for the battery I wanted. I eventually decided to cheat and put it all in LTSpice, and move things around until I got the results I wanted.
Measuring each bulb's resistance and current under 2-3V gave me all the info I needed to run the simulations. I also decided to use a solid-state blinker for car signals. It's quiet, and there's no worries about the current being too low for it to work. The Voltage range on that is 10-15V, so I had to add a couple resistors so the 16.8V battery would drop down to 15V before it got to the blinker.
The simulation worked out great, and each bank of lights dropped the Voltage by 3V.
The current worked out too. A total of about half an Amp (perfect for a 4s1p battery) and each bulb shows the same current. Just as it would if I were running each on 3V directly.
I got the first bank together and it worked just like the simulation said. Used a bit more current though. 520mA instead of 480mA is close enough though.
Each successive bank of lights I made took another 3V and used the exact same amount of current. Finally got it all hooked up without the blinker, and measured real life current and Voltage before and after the resistors.
Ideally the resistors would have been 3.75 Ohms, but I could only find a combination that would get me 3.9 Ohms. So the Voltage to the blinker will only be 14.85V instead of the full 15V. Again, close enough. I also discovered after adding the blinker, that when the Voltage drops too low, it shuts off and uses no current at all. This will happen before each cell reaches it's maximum discharge.
So here it is running on a desktop power supply with the blinker installed:
Hopefully the gif is animated. Otherwise it'll just be a dark picture, LOL.
So next is to get the battery made, and put the lights in the right configuration without messing up the circuit. And then putting it in a box that looks nice. If I don't get it done by this Christmas, I'll at least be really early for the next one.
I've decided to make a thing for my wife that lights up and blinks. Putting them on a battery is a little more complicated than I thought it would be though. The problem was that each bulb is a resistor, and when you put them in parallel, the resistance goes way lower. Because of the 1/R +1/R equation. I started out trying to do a bunch of math to get 25 bulbs in a series and parallel configuration that would use the right Volts and Amps for the battery I wanted. I eventually decided to cheat and put it all in LTSpice, and move things around until I got the results I wanted.
Measuring each bulb's resistance and current under 2-3V gave me all the info I needed to run the simulations. I also decided to use a solid-state blinker for car signals. It's quiet, and there's no worries about the current being too low for it to work. The Voltage range on that is 10-15V, so I had to add a couple resistors so the 16.8V battery would drop down to 15V before it got to the blinker.
The simulation worked out great, and each bank of lights dropped the Voltage by 3V.
The current worked out too. A total of about half an Amp (perfect for a 4s1p battery) and each bulb shows the same current. Just as it would if I were running each on 3V directly.
I got the first bank together and it worked just like the simulation said. Used a bit more current though. 520mA instead of 480mA is close enough though.
Each successive bank of lights I made took another 3V and used the exact same amount of current. Finally got it all hooked up without the blinker, and measured real life current and Voltage before and after the resistors.
Ideally the resistors would have been 3.75 Ohms, but I could only find a combination that would get me 3.9 Ohms. So the Voltage to the blinker will only be 14.85V instead of the full 15V. Again, close enough. I also discovered after adding the blinker, that when the Voltage drops too low, it shuts off and uses no current at all. This will happen before each cell reaches it's maximum discharge.
So here it is running on a desktop power supply with the blinker installed:
Hopefully the gif is animated. Otherwise it'll just be a dark picture, LOL.
So next is to get the battery made, and put the lights in the right configuration without messing up the circuit. And then putting it in a box that looks nice. If I don't get it done by this Christmas, I'll at least be really early for the next one.