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I have a system which consists of 2 12V DC motors(0.65 A on max load) and 1 RPi 2 model B. I want this system to be plug free. I have Li-Ion batteries to power up motors. I use a L298N module to drive motors. This module also can give a 5V output. Here is where the problem appears.

If I use this output for my RPi, RPi shows lightning symbol time to time and shuts itself down if I open things like chromium on it.

I have these options.

  • I can use this cable to increase cable quality, since I am using a random cable atm. But I don't know if it will really help.
  • Use a step down module to directly feed RPi from Li-Ion batteries.
  • Using a powerbank to directly feed RPi.

Which options is better?

(Batteries - 5x Li-Ion 3.7-4.2 V - 2100 mAh each. I use 3x atm)

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    \$\begingroup\$ The power symbol appears when the GPU detects a too low supply voltage. This is because of too long, too thin supply cable. You put +5V in, and get <4.5V when the current peaks. So, first thing to change is that cable. \$\endgroup\$ – Janka Mar 25 '17 at 13:45
  • \$\begingroup\$ You did not say which version of RPi you are using... Look here for the minimum current you need, and make some measurements of the voltage to check what Janka suggested \$\endgroup\$ – frarugi87 Mar 25 '17 at 17:46
  • \$\begingroup\$ I actually said at start( pi 2 model b) but thanks for the link. It made things more clear. \$\endgroup\$ – bcan Mar 25 '17 at 17:57
  • \$\begingroup\$ Ok, time to go to sleep then... -.- Sorry, I definitely missed that.. \$\endgroup\$ – frarugi87 Mar 25 '17 at 18:11
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The L298N module doesn't say how much current it can supply at 5V, but based on the components visible on the board, I would guess that it's no more than 1A, probably less. The RPi requires up to 2A at times.

You need to get a beefier regulator (step-down module) that can handle the peak demands of the RPi.

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  • \$\begingroup\$ I have this as a step down module. Will it be enough? (only difference is my step-down has JM64RP instead of JM38RP on its LM2596) Also dividing Ampere between step down and motor driver can be a problem? aliexpress.com/item/… \$\endgroup\$ – bcan Mar 25 '17 at 14:07
  • \$\begingroup\$ It should be enough. Connecting it to the battery along with the motor driver should not be a problem. The input current of the step down module should be no more than 0.5A @ 20V. ... Or 0.85A @ 12V, since you just changed your question. \$\endgroup\$ – Dave Tweed Mar 25 '17 at 14:16
  • \$\begingroup\$ Yep I forgot to add that point but still dividing makes me worry. Will it take enough Ampere or limit/overcharge itself because of this? : en.wikipedia.org/wiki/Current_divider Motors will take 1.2A max. \$\endgroup\$ – bcan Mar 25 '17 at 14:25
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    \$\begingroup\$ The battery is a voltage source, not a current source. There is no problem as long as the total current doesn't exceed the maximum discharge rate of the battery. 1.2A + 0.8A = about 2.0A, which should be fine for cells rated at 2100 mAh (i.e., about 1C). \$\endgroup\$ – Dave Tweed Mar 25 '17 at 14:29
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    \$\begingroup\$ The module is a regulator, which means that it its output voltage will remain stable (+/-2.5%) over a wide range of input voltages (up to 40V). All of this information is in the page you linked to. There is also a minimum input voltage that depends on the output voltage that you select. Curiously, the LM2596 data sheet doesn't talk about this other than to say that the saturation voltage of the internal switch is about 1.5V max. This would imply that the minimum input for a 5V output would be 6.5V. \$\endgroup\$ – Dave Tweed Mar 25 '17 at 15:39
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The instruction that comes with raspberry pie says " external power supply rated at 5v, and a minimum current of 2A" when you are using the driver module regulated output, it gives you a maximum of 5 volts and 1Amps depending on the regulator it uses. for example regulator 7805 gives only 0.5 amps and that is not enough so I recommend you to use another regulator for your raspberry pie board like lm2576 which i suppose gives 3 amps of current. or you can just use 2 separated power sources one for your motors and their drivers one for the rasp. just remember your rasp needs 2A current to run properly

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