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Battery components

A project log for Pengu Q1 quadruped

A low budget quadruped with dynamically generated free gait

Pengu MCPengu MC 01/30/2015 at 09:513 Comments

Components for the battery pack came in today. There's:

- 2 li-ion batteries, 3.7v 1200 mAh

- usb li-ion battery charger board (not pictured, TP4056)

- DC-DC converter board (LM2596S)

- current sensor board (ACS712)

I'll make a 7.4V battery and use the converter to step the voltage down to 5V to power the servos. The current sensor is going on the battery leads so I can track the power consumption. It outputs an analog voltage so I'll use an attiny to read that and put it on the I2C bus.

I'm not sure if the batteries have enough capacity to provide a decent amount of running time for the robot but we'll find out. At least the current sensor will give some insight into the actual power consumption of the robot.

Discussions

de∫hipu wrote 01/30/2015 at 11:20 point

I can run my robots (using 12 similar 9g servos) on a 350mAh 2S LiPo pack for about 20 minutes (less if they move about vigorously), so I think you should be fine with 1200mAh. One thing to look at is the C rating, telling you how much current you can draw. But with 1200mAh even with 1C you have 1.2A, which should be enough.

How do you plan to charge them? That charger you have is for 1S batteries, and you want to connect yours in series effectively making a 2S pack. Are you just going to use that charger as an external charger, and unplug the batteries for charging?

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Pengu MC wrote 02/02/2015 at 07:12 point

Nice, so mine should run at least 20 min then :)


For now i'll just take them out to charge them separately. I'll try to make a
switching circuit later that would switch the batteries to paralel for
charging, but I expect a lot of problems in there since I don't want to
use relays but I also can't have any voltage drop (from a transistor for
instance) beyond the charger board...

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de∫hipu wrote 02/02/2015 at 09:31 point

Yeah, it's difficult. There are chips for charging 2S lipos out there, but unfortunately no ready modules. Plus, you have to balance them too, to make sure they have similar internal resistance, otherwise they have pretty bad performance.

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