Barrier to current - Page 1
Forum section: electronics / beginners

author: msknight
author_rank: Regular Contributor
timestamp: May 27, 2020, 10:45:53 am
content: I have a "light" powered by solar power. It's actually a bit more complex than this, as it was designed for use in Africa and also uses the USB port to charge mobile phones, etc. I'm in the UK, in a poor light area and the solar panels only produce good power when the sun comes around to their side of the building.The device has two issues ... which I have to stress are issues for me, and me only. The device wasn't deigned for my use case, and the manufacturer has been very accommodating to me. I'm not mentioning the product or company because they've been superb in their communication and assistance.The first one is that daylight is enough to turn it on, but the balance of average non-direct daylight (14mA at about 4.7V) is lower than the unit needs to run, so for a good portion of the day it is actually draining its own battery. It can drop about 10% of its charge during this period. (it turns itself on when the voltage hits about 4.7v)In the evening, when the sun is in a direct position, the voltage rises to about 5.1v and produces over 200mA, which is enough to reclaim the 10% lost, and give another 20% on top of that.I can put a circuit in-line between the solar panels and the device, but I can't alter the device itself.I don't believe that inserting a voltage barrier is going to help; it's too fine a line. I also believe that creating a mA barrier (so that current is only passed when it increases beyond, say, 50mA) will help... part of this is because inserting a capacitor would result in an on-off sequence which would not help... because of issue number 2.The unit has flash memory, which is written to whenever the unit is switched off. It's rated to 20,000 write cycles which, on-off once or twice a day, would last years. However, when pulsed on-off many times during a day, would really hit the flash.I believe my best way forward is to provide a barrier to current, at 50mA, but to do it in a fashion where it is not pulsing on and off, and for that barrier itself (if it needs it) to be powered by the solar power being input. However, I've got no idea how to do this.Any pointers please?

author: Syntax Error
author_rank: Frequent Contributor
timestamp: May 27, 2020, 10:58:40 am
content: A high power schottky diode?A link to the manufacturer's datasheet or website?

author: mikerj
author_rank: Super Contributor
timestamp: May 27, 2020, 11:04:33 am
content: Quote from: msknight on May 27, 2020, 10:45:53 amIf you are measuring 50mA, then current is already flowing. You can't gate a current based on measuring some minimum amount of current since the circuit has to be closed in order to measure it.A simple block diagram of the system and the proposed changes would help here e.g. are you asking to have the solar panel switched to into a dummy load and measure the current into that?

author: msknight
author_rank: Regular Contributor
timestamp: May 27, 2020, 11:06:12 am
content: That would be preferable Mikerj ... at less than 50mA, dump the current into a dummy load... once it reaches 50mA, feed it to the device.