Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

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wrenson
 
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Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

Post by wrenson »

I just purchased the Adafruit Micro-Lipo Charger for LiPoly Batt with USB Type C Jack (Product ID: 4410) and the 2500 mAh 3.7v lipo battery.

I misunderstood the product description and thought that this board's breakout pins provide a steady 5v with a lipo battery attached. The pins only seem to provide 5v when connected to a USB cable, which negates the need for a battery. The only other power I seem to have access to on the board is directly from the battery, which varies depending on the charge level

I'm trying to power several LEDs in a diorama, and they're sensitive enough to voltage and current that the battery's fluctuating voltage due to discharging could cause the LEDs to experience overvoltage when the battery is full and dim significantly when the battery is low, but not dead. I'm not entirely sure whether I would calculate which resistors to use based on 3.7v or 4.2v and how I could protect the LEDs. They're quite difficult to replace without damaging the model kits. The LEDs recommended forward voltage varies between 1.8-2.2v or 2.8-3.3v depending on the color (all 20mA). I have about 20 LEDs set in the dio already, and I was planning on installing more.

Does anyone have any advice on what I could add to this project to provide a steady power source to my LEDs?

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michaelmeissner
 
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Re: Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

Post by michaelmeissner »

The verter (https://www.adafruit.com/product/2190) will do what you want. If you are only going to use lipo batteries and not anything higher than 5 volts, look into the Power Boost charger 500 (https://www.adafruit.com/product/1944).

An alternative if the verter and power boost 500 sells out again is to get the Seeed 'LIPO RIDER PLUS (CHARGER/BOOSTER)' that you can find over at digikey.

A much simpler alternative might be to switch from using lipo batteries to USB power bank batteries and just plug your microprocessor into USB power. Note, depending on how much power your processor draws, some power banks have a nasty habit of turning off if the microprocessor doesn't consume enough energy like a cell phone would while recharging. You would have to charge the power bank directly instead of plugging USB into the microprocessor to charge it.

Another alternative is to use AA rechargeable batteries in a 4 pack. Don't have the batteries attached if your microprocessor is connected to USB and it wants to recharge your batteries. To recharge it, you just have to remove the batteries and use a normal NiMH charger.

Don't use non-rechargeable batteries, since they start out with a higher voltage (1.5 volts instead of 1.2 volts), but over time the voltage goes down. Thus a 4 pack of AA's would be 6 volts, but as they get expended, they would go under your LEDs threshold.

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wrenson
 
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Re: Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

Post by wrenson »

Would adding a buck converter like the LM3671 with with the boards and battery I've already bought? I haven't applied resistors to the LEDs yet, so 3.3 or 5v would suit my needs. Also, they sell that buck converter at my local Micro Center.

I'm concerned that using removable batteries would require flipping the diorama upside down to get to the cells, which would damage the diorama.

A powerbank could work, but I'd have to deal with a button switch to turn on the bank and another to turn on/off the LEDs. There's no microcontroller; the LEDs are powered directly by the power source. So the LEDs would either run long enough to drain the powerbank or I'd need to deal with two switches.

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wrenson
 
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Re: Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

Post by wrenson »

Also, on the buck converter, what am I supposed to wire the EN pin to on that buck converter? It says to use it, but it's not specific. Do I run a wire from the battery to V in and also EN?

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michaelmeissner
 
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Re: Powering LEDs in a Diorama with Micro-Lipo Charger and Batt?

Post by michaelmeissner »

Generally you need to look at the datasheet for your particular boost/buck converter. Usually if the EN pin isn't connected, it means the converter will do the conversion. If you connect EN to ground (typically) it shuts off the conversion, and if you connect it to the power, it enables it (but again check the data sheet). So you can use this as a button to turn on/off the power.

Note converters can run hot to the touch, so you might want to try it out before mounting it, and mount it in a location where the heat won't melt other things.

For small number of LEDs that are only lit for 1/2 hour or so, it may not matter, but if you are doing larger displays, you need to figure out how much power the LEDs will consume, whether the converter can convert that much power over a period of time, whether the battery can supply that much power at any one time, and how long the battery will last. You don't necessarily need to do extensive calculations and such, but it is helpful to have a general idea ahead of time (otherwise you might wind up buying several batteries and converters until you get to the right size, and/or you might buy way too big of a battery system that you don't need.

And when you are designing the diorama, consider designing it in such a way that you can either recharge batteries and/or replace them without turning the thing upside down.

And with a diorama, perhaps you use can A/C power, and plug in a USB wall wort and use a USB cable to connect to the display.

FWIW, I do this steampunk camera setup that I've been tinkering with for over 10 years, and in the last design, I finally got around to designing it to have enough power (2 batteries in the camera, and an external power supply), and if the power runs out that I can easily change the external battery, rather than disassembling the whole assembly, take out the camera, replace the batteries, and put everything back. In this, my power needs are much higher (something on the order of 30-40 watts of power for a 10-12 hour run), but the principal is the same, design your unit so that you can easily replace and/or recharge the batteries unless you only need a small amount of battery power. And it can be a process where you iterate over time.

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