Feather battery charger too slow

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Jeremy97469
 
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Feather battery charger too slow

Post by Jeremy97469 »

I have several of the various Feather boards and ordered the M4 Express and M0 Radio today. They are all great for projects especially the battery powered ones. I do have one complaint though which is the low battery charge current. With the 6,600mAh battery pack, it takes several days to fully charge the battery. Is there a good way to charge the battery faster without having to disconnect the battery from the feather? Preferably, a way that still allows the feather USB port to be used for programming purposes.

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Franklin97355
 
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Re: Feather battery charger too slow

Post by Franklin97355 »

Are you always using the Feather on the USB or just when you want to charge? How long does it have to be on battery before recharge and, how many other devices do you have connected?

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Jeremy97469
 
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Re: Feather battery charger too slow

Post by Jeremy97469 »

The USB will mainly be used for charging, but sometimes the program will need to be updated.

My current project needs to have enough battery capacity to run for up to 36 hours on the battery before recharging. It will have the Feather M0 RFM69HCW board and the Adafruit ADXL343 + ADT7410 Sensor FeatherWing. I am putting it together for a friend who doesn’t want to be messing around with the hardware, just wants to be able to plug in the USB cable to recharge, and then run it on battery for up to 36 hours. The battery size required is unknown and the transmitter usage rate will vary depending on the accelerometer data.

For my usual usage, it runs as a clock on battery power until the battery dies. I want it running as long as possible on the battery and minimize the charge time. The device location doesn’t have power so I have to charge it in a different location. When charging, it is not doing its job. Ideally, it would recharge overnight with the 6,600 mAh battery pack.

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sj_remington
 
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Re: Feather battery charger too slow

Post by sj_remington »

According to the manufacturer's data sheet, the MCP73831 charger IC rate is 500 mA maximum. Glancing at the schematic, the charge rate is currently set to 100 mA by the 10K programming resistor.

If you replace that 10K with a 2K resistor, the charge time should be somewhat more than 6600 mAh/500 mA = 13 h, for a completely exhausted cell.

Presumably you are monitoring the cell voltage, and shutting off the board before the cell voltage drops below about 3.2V. If not, the cell will be quickly destroyed.

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michaelmeissner
 
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Re: Feather battery charger too slow

Post by michaelmeissner »

When I started looking at feathers I noticed the 100mA limit for charging. I am not an EE or product designer, but I would have to imagine it possibly a combination of two things:
  • The smaller lipo batteries can't be charged with too much current. If they went with a higher capacity charger, it would force people to use 1000mA batteries or higher. In fact, a lot of the chargers limit the output to 100mA to allow for these batteries. There are some chargers with switches to allow you to change the current used for charging batteries.
  • At the time the feathers were designed, chargers with higher charging capacity might not have been available or that they would be too costly to use in the feather. Even if it was cheap enough, the decision not to use it may have been the desire to allow the smaller batteries to be used. I suspect the large li-po batteries may not have been sold at time when feathers were initially designed.
There are other chargers with higher currents. Typically these would have their own USB plug. You would use the charger USB plug to recharge the battery, and connect the output of the charger to a JST cord to connect to the feather. You likely would need to ensure that both USB plugs aren't used at the same time, and maybe unplug the battery/charger from the feather if a USB cable is connected.

Adafruit has the PowerBoost 1000C that charges at 5v/1A, but given it is a booster, you likely loose some of the power by the boosting circuitry. I don't know if you can eliminate the boost and just get the raw battery power. Unfortunately, it does not seem to be available at the current time. Off the top of my head, I don't remember if there is an Adafruit lipo charger that can do higher than 5v/1A.

I've used the Seeed Lipo Rider Plus (available at digikey). It advertises that it can use up to 5v/2A of power to charge the battery. Like the PowerBoost 1000C, it boosts current to 5v, but it has a pinout for the raw battery output. At present, I have only used it for boosting current, so I don't know if hooking up the battery output to a JST cable and hooking it to a feather would be safe if you provide USB power to the feather. I would likely just disconnect the battery when I'm programming the feather.

Do remember what I said at the top of this post. I am not an EE (I am a computer programmer). I don't know if hooking up a battery/charger in this fashion might meet all safety guidelines.

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Jeremy97469
 
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Re: Feather battery charger too slow

Post by Jeremy97469 »

I appreciate your responses. The suggestion to change the charger resistor sounds like the best option and I would like more information if possible. Does anyone know the charge program resistor location and size (2010?)?

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sj_remington
 
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Re: Feather battery charger too slow

Post by sj_remington »

The PCB design files are posted. You said you had "several" Feathers -- the part might be in different places on different boards.

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