Thanks, it was just to know if you had data, it’s not that important to be honest.
I actually have the same setup as you mention and your wiring looks exactly like mine
The COB light will have a specified current draw. The Lithium battery has a specified capacity. Battery capacity divided by COB current draw = how long it will run before the battery is fully discharged.
Also, the COB will have a voltage specification. It’ll light up brighter if you exceed that limit, but it will also quickly lead to LED failures in the COB. And LEDs have a minimum forward voltage that’s required to make them light up. So as you reduce the voltage to fade the LEDs down, you’ll get to a voltage where the LEDs shut off even though the voltage hasn’t gotten all the way to 0V. The better way to modulate LED brightness is with a Pulse Width Modulated (PWM) signal that changes the duty cycle from 0% to 100%, which will guarantee the LED dims smoothly all the way to full off from full on.
And lastly, Lithium batteries are prone to catching fire if they are over-charged or over-discharged. Batteries can be had that are just the bare cells, and with a BMS built in. It’s critically important that you use a Lithium battery pack with a built in “BMS” (Battery Management System) or you are risking a battery fire.
If I understand properly, it could last around 7h?
But, I see that the LED is rated for 5V whereas the battery generates 7.4V. Does this mean that it will potentially damage the LED if we open the potentiometer to 100%?
No. The Cyberbrick batteries are protected. But you can buy batteries from many, many other places besides BBL. They may look the same but that’s no guarantee. So understanding there’s a difference in LiPo battery types is important.
Yes, 800mAh divided by a COB that’s drawing 110mA = 800 Milliamp-hours/110milliamp = 7.27 hours.
Yes, if you are powering the COB with a 7.4V battery, and it’s only rated for 5V, you will burn it out. It is drawing more than 110mA when you run it at a higher voltage. Possibly quite a bit more. Unlike a purely resistive load like an incandescent bulb, LED current draw as a function of voltage is highly non-linear. A small increase in operating voltage can produce a large increase in the current being drawn. So at the >5V operating voltage the COBs are drawing more than 110mA, probably quite a bit more. Which gets them hotter than they’re supposed to get, which leads to them failing.
Keep in mind, LiPo cells go from 3.0V (discharged) to 4.2V (charged). A fully charged 2 cell LiPo battery is 8.4V. The “7.4V” rating is the half-discharged specification.
So your 5V COB is running on 8.4V on a freshly charged battery. That’s way too high.
The Cyberbrick must have a spare 5V regulated voltage output you can use instead of going direct from the battery to the COB. (I don’t have a Cyberbrick, but I am an electrical engineer).
You have to watch it when you use a potentiometer on circuits that pull any kind of current. I’d bet you’re ok but I2R can cause problems in the potentiometer. Generally ok at high R but al lower R, I can go up and heating goes up with the square of current. Just something for folks to be aware of.
Even though it’s rated for a maximum voltage of 7.4V, we can’t expect it to lower the voltage to 5V on the Channels I guess. We would be better with 3 standard AA batteries or maybe another rechargeable battery like the one in that kit: Rechargeable Power Kit | Bambu Lab US Store ?
Yeah. That PDB is just straight-through wiring. Whatever voltage goes in is the voltage that comes out. It’s maximum voltage rating is meaningless. It’ll easily go to much higher voltages. The Max Current rating is the one that matters. Pull more than that, maybe burn out traces on the board.
Yeah, that Rechargeable Power Kit is the right solution. The board you can see on the webpage has the BMS features to protect a “bare naked” LiPo battery cell, which is also pictured. But you could use any one-cell LiPo with the board. Once you have the board, you’re not limited to the 500mAh cell that comes with it.
Alternately, for people who have some soldering skills, a “5V Boost/Buck voltage regulator” (A google for those words will reveal many options - I’m partial to parts from Pololu) can be had at low cost (and a little soldering) to regulate the Cyberbrick LiPo down to 5V for the LEDs.
I’m trying to build a model for that anyone can build, without any soldering skill.
When I look for other types of batteries on amazon, strangely enough I only find batteries that have a voltage of 3.7V. I guess that with those batteries, the light will just not be as strong as it can be with a 5v power supply.
I cannot find anything that would allow a standard user to connect the 7V battery to power the light
Not only are the connectors incompatible with what is provided by MakerSupply in their kits, but often there aren’t any and a soldering iron is required.
Then, you need a potentiometer to confirm that the dial they added was turned correctly, and hopefully, you do not accidentally knock it.
Then, the end user has to do all this and source the correct part from their local country.
Maybe you can answer a few questions then: how come we don’t find 5V batteries on the market, it’s whether 7v or 3.7? Would it be possible for Bambulab to get 5V batteries? Is what we are trying to achieve so abnormal (to power the COB with a battery)?
