Electronics > Beginners
How to build a simple volatge buffer
Adhith:
--- Quote from: Kleinstein on June 05, 2018, 08:08:38 pm ---With a battery pack, it is probably OK to use just one inductor, I don't think there is common mode filtering required.
The slightly odd point is having a separate buck/boost stage and a LED driver. If the led driver is also switched mode, they might interact and a good led driver should work with the voltage range from the Li cells. So the best way would be to make the LED driver to work directly from the cells.
--- End quote ---
Yes I have thought about directly connecting the LED driver to the BMS, but the problem is that the LED driver is capable of input from 5v to 28v so I guess it could be used to drive any LED strip rated form 5V to 28V and thus no restriction or regulation at 12V. So I guess the 16.8V battery pack could damage the 12V strips.
Kleinstein:
The easy type of LED driver would need an input voltage that is higher than the LED strip nominal voltage. So for a 12 V LED strip the driver would need something like 12.5 V - 28 V. It might still work with 12 V. So one should check the details on the LED driver. A 12 V LED stip might be 3 LEDs of maximum 4 V in series and thus more like 11 V actual voltage.
So the 4S (thus 12-16.x V) pack should be likely OK and no need for an extra voltage converter. One might loose a little of capacitance at the low voltage end, but not really much and it comes with less stress to the cells.
Adhith:
--- Quote from: Kleinstein on June 06, 2018, 04:06:43 pm ---The easy type of LED driver would need an input voltage that is higher than the LED strip nominal voltage. So for a 12 V LED strip the driver would need something like 12.5 V - 28 V. It might still work with 12 V. So one should check the details on the LED driver. A 12 V LED stip might be 3 LEDs of maximum 4 V in series and thus more like 11 V actual voltage.
So the 4S (thus 12-16.x V) pack should be likely OK and no need for an extra voltage converter. One might loose a little of capacitance at the low voltage end, but not really much and it comes with less stress to the cells.
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OK I understood that Sir. but I have a doubt. What about the additional voltage above the 12V?? does it get dissipated in the LED strip resistors and heats than the normal limit??
Kleinstein:
It depends on the LED strip and the driver. The usual LED drivers give out an defined current (e.g. 350 mA). So the voltage over the LED strip will be whatever it takes to get that current, but not more than available.
For the LED strips, there are 2 types: some with a series resistor that can be operated at constant voltage and those made for constant current drive. If there is a series resistor in the LED chain, it will get hot if the LEDs are lit.
So you have to get and understand the manuals / data-sheets for both the driver and the LED strip, or at least have a look at the circuit / description. Depending on the LED chain the best way is either a constant voltage regulator or a constant current regulator (e.g. the LED driver), but not both.
capt bullshot:
--- Quote from: Adhith on June 06, 2018, 03:59:45 pm ---Thank you again for your reply. Yeah I have understood. updated the circuit diagram and has been attached with this post.
Since the BMS is now damaged and I'm waiting for the new one that have been purchsed, I cant currently charge the pack. I'll let you know about the progress as soon I get the new one.
Also one thing that I would like to ask is that, does adding this filter have any trouble in driving the buck/boost when powered from a DC adapter??
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I've mentioned to put two capacitors on each side of the inductor, four in total. Each one ceramic and one electrolytic in parallel.
No, there shouldn't be any problems running this filter from an DC adaptor.
I'm still believing that a discharged battery caused your root problem, so I'd recommend to try again with a fully charged battery and without the filter when you get your new BMS. Anyway, if you want to ensure your LED strip supply doesn't exceed 12V, a step-down regulator will do the job, no buck-boost required. This is because you shouldn't discharge your cells below 3.3V in normal (low current) use, this leaves 13.2V at the battery when it is assumed empty.
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