| Electronics > Beginners |
| limit current of USB power to 2.5A |
| << < (3/4) > >> |
| Zero999:
If the camera will work from 7V to 24V, connect it to a bench power supply and vary the voltage from 7V to 24V. Does the current change? What voltage results in the least power draw, i.e. P = V×I? Design the boost converter to give that output voltage. Ultimately you can't get power from no where, so if your camera requires more, than the USB port can supply, then you're SoL. If it doesn't need to be operated continuously, then you could charge a battery and power the camera from that, but the average power will still be under what the USB port can provide. |
| Kasper:
--- Quote from: purezerg on August 12, 2019, 06:14:30 am ---1) i have tried with a 12v 3a power supply. it can draw as much as 17w if there are batteries that are not fully charged inside the battery. 2) without any batteries inside. it will draw 9w 3) with full charged batteries, it will also draw 9w. 4) when the camera is active, it will draw 12-14w 5) i do know that 12v @ 0.5A will also work because most macbook pro firewire provides only 0.5a. the powerspike is handled by the batteries. 6) the droop measures as low as 4.91v at the end of 4.5m cable @ 2.5a 7) i dont have a 12v dummy load to measure the efficiency of the boost module. but i do have 2 modules. the good stuff and the cheap stuff. both exceeds 3.0A 8) i have a LMxxx something module that bucks. i tried a 12v3A to 5v. the good module draws as high as 3.2-3.3a. the cheap module draws 3.6a. for those wondering. the camera is a phaseone medium format camera. I am wondering if I do a 1.8ohms 8x 2w parallel circuit. would it work? --- End quote --- I struggled a bit reading your posts. If you describe where the current measurements are happening, it might be a bit clearer. Keeping in mind current in and out of switching regulators is not the same. 1, 2 and 3) Looks like the battery charger was drawing 8W. Could draw more or less depending how full the battery is. 4) camera active: 14W total power 8W + 14W = 22W To limit the current draw, you could try to disable the charger when camera active. You could also control a switching regulator between your power source and the load. Measure the current draw and use that to limit the output of the regulator. When load draws more current than your limit, the voltage to load should decrease. Sounds like load is fine with that, if external power is too weak it takes power from battery instead. To test that, power it with variable voltage supply, adust the voltage and see what happens. |
| Kasper:
--- Quote from: Kasper on August 13, 2019, 12:01:25 am --- --- Quote from: purezerg on August 12, 2019, 06:14:30 am ---1) i have tried with a 12v 3a power supply. it can draw as much as 17w if there are batteries that are not fully charged inside the battery. 2) without any batteries inside. it will draw 9w 3) with full charged batteries, it will also draw 9w. 4) when the camera is active, it will draw 12-14w 5) i do know that 12v @ 0.5A will also work because most macbook pro firewire provides only 0.5a. the powerspike is handled by the batteries. 6) the droop measures as low as 4.91v at the end of 4.5m cable @ 2.5a 7) i dont have a 12v dummy load to measure the efficiency of the boost module. but i do have 2 modules. the good stuff and the cheap stuff. both exceeds 3.0A 8) i have a LMxxx something module that bucks. i tried a 12v3A to 5v. the good module draws as high as 3.2-3.3a. the cheap module draws 3.6a. for those wondering. the camera is a phaseone medium format camera. I am wondering if I do a 1.8ohms 8x 2w parallel circuit. would it work? --- End quote --- I struggled a bit reading your posts. If you describe where the current measurements are happening, it might be a bit clearer. Keeping in mind current in and out of switching regulators is not the same. 1, 2 and 3) Looks like the battery charger was drawing 8W. Could draw more or less depending how full the battery is. 4) camera active: 14W total power 8W + 14W = 22W To limit the current draw, you could try to disable the charger when camera active. You could also control a switching regulator between your power source and the load. Measure the current draw and use that to limit the output of the regulator. When load draws more current than your limit, the voltage to load should decrease. Sounds like load is fine with that, if external power is too weak it takes power from battery instead. To test that, power it with variable voltage supply, adust the voltage and see what happens. --- End quote --- If you try setting external supply voltage to less than battery voltage, measure the current to make sure your battery isn't sending current to your external supply. |
| purezerg:
"total power 8W + 14W = 22W" no no no, that's not what i mean. idle = ~3w charging battery = ~5w camera in operation = ~6w-10w I unfortunately dont have a bench power supply. I'm not as hardcore as you guys. based on what I am gathering from you guys, it's a mission impossible? so far most of the comments are towards giving the camera as much power as it depends. the camera takes power from the battery when capturing the image. but when idle, it uses the extra power to charge the batteries. the whole pet project is the give it more power via the firewire(12v) rails, to charge it when it's idle. |
| purezerg:
--- Quote from: Kasper on August 13, 2019, 12:05:12 am --- --- Quote from: Kasper on August 13, 2019, 12:01:25 am --- --- Quote from: purezerg on August 12, 2019, 06:14:30 am ---1) i have tried with a 12v 3a power supply. it can draw as much as 17w if there are batteries that are not fully charged inside the battery. 2) without any batteries inside. it will draw 9w 3) with full charged batteries, it will also draw 9w. 4) when the camera is active, it will draw 12-14w 5) i do know that 12v @ 0.5A will also work because most macbook pro firewire provides only 0.5a. the powerspike is handled by the batteries. 6) the droop measures as low as 4.91v at the end of 4.5m cable @ 2.5a 7) i dont have a 12v dummy load to measure the efficiency of the boost module. but i do have 2 modules. the good stuff and the cheap stuff. both exceeds 3.0A 8) i have a LMxxx something module that bucks. i tried a 12v3A to 5v. the good module draws as high as 3.2-3.3a. the cheap module draws 3.6a. for those wondering. the camera is a phaseone medium format camera. I am wondering if I do a 1.8ohms 8x 2w parallel circuit. would it work? --- End quote --- I struggled a bit reading your posts. If you describe where the current measurements are happening, it might be a bit clearer. Keeping in mind current in and out of switching regulators is not the same. 1, 2 and 3) Looks like the battery charger was drawing 8W. Could draw more or less depending how full the battery is. 4) camera active: 14W total power 8W + 14W = 22W To limit the current draw, you could try to disable the charger when camera active. You could also control a switching regulator between your power source and the load. Measure the current draw and use that to limit the output of the regulator. When load draws more current than your limit, the voltage to load should decrease. Sounds like load is fine with that, if external power is too weak it takes power from battery instead. To test that, power it with variable voltage supply, adust the voltage and see what happens. --- End quote --- If you try setting external supply voltage to less than battery voltage, measure the current to make sure your battery isn't sending current to your external supply. --- End quote --- i doubt that will happen. ** extra bit of info. the battery is 2 cell @8.4v full charge. the camera has got 2 of these batteries. each battery is basically a 2x NCR18650B. USB BC1.2 is only able to charge 1 of the battery. due to the fact that the USB is able to charge 1 of the battery, i believe there is a gate there to prevent backflow. firewire 12v is able to charge both batteries. firewire spec doesnt have a specific voltage range. i connected the firewire to a macpro and measured the voltage rails and used a clamp to measure the amps. the max was 1a i BELIEVE the camera can handle a wide range of voltage. but wondering further from 11-13v is anyone's guess. |
| Navigation |
| Message Index |
| Next page |
| Previous page |