smcras
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Powering Robot with 9V Batteries

Wed Aug 09, 2017 1:23 pm

Hello,

I'm building a tiny two wheeled robot with Raspberry Pi 3. My setup is the following:

Image

I read that connecting +5V and GND directly from L298N to the GPIO pins to power up the Raspberry Pi can damage it if something goes wrong. So I decided to power it through the MicroUSB port.

Unfortunately when I power up my Raspberry Pi through the batteries it reboots every time when setting up WLAN. I assumed that 4x 9V batteries connected in parallel could provide enough current, but I guess it is not enough.

How many 9V batteries do I need? Or do I have to use a different power source?

Any help is appreciated.

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Burngate
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Re: Powering Robot with 9V Batteries

Wed Aug 09, 2017 5:21 pm

Since a bare L298N chip cannot provide 5v, I assume you are referring to a board with a L298N and a regulator on it.
So your Pi is very much at the mercy of what that regulator can provide.
By your description, that regulator can only just supply enough for your Pi without WiFi.

Perhaps you could provide the Pi with 5v from a separate buck convertor.
This will have the advantage of being more efficient (the one on the board is likely to be a linear regulator)

The other thing to bear in mind is that, just because the batteries are 9v, and you've got four in parallel, doesn't mean they'll be able to provide all the current you're asking for. Nor, of course, does it mean they can't!
Looking them up on the manufacturer's website might help.

smcras
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Joined: Wed Aug 09, 2017 12:50 pm

Re: Powering Robot with 9V Batteries

Wed Aug 09, 2017 6:08 pm

Thank you very much for your reply. I honestly do not know much about regulators and did not think that could be the problem here.

I will order a regulator which can provide 5V and 3A and then try it out. I will report, when it works.

pcmanbob
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Re: Powering Robot with 9V Batteries

Wed Aug 09, 2017 9:50 pm

Another consideration is the batteries you are using, you have not said but from the picture it looks like you might be using PP3 or MN1604, I don't think you will power the pi and the motors from 4 of these reliably you might find your pi reboots when you turn your motors on.

I have used 2 x PP3 batteries on one of my projects as a crude ups to power a pi during very short mains fails , and even then the batteries were only good for about 20 mins total I was only covering mains breaks of a few seconds.. The pi used in this case was one of original pi's so there was no wifi and it was only running Jessie lite monitoring a simple switch and pir writing simple switch/ time data to a file with nothing else connected.
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smcras
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Joined: Wed Aug 09, 2017 12:50 pm

Re: Powering Robot with 9V Batteries

Wed Aug 09, 2017 11:11 pm

Thanks for the info.

The batteries are a cheap no name product. The package says "9V E-Block 6LR61" by TOP Craft. I cannot find any infos about these batteries, not even how much capacity they have. So I just ordered a DC-to-DC converter to try it out. They will be delivered in two days.

If your Raspberry Pi could run 20 mins with 2x batteries and the motors can run with only 1x battery, I assumed, that it should work out. I have also seen other robots with Raspberry Pi and 6x 1.5V batteries connected in a row on the internet. I cannot tell which configuration is better, my assumption was that the batteries connected in parallel would have less load. I'm not very investigative when it comes to power supplies. :oops:

pcmanbob
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Re: Powering Robot with 9V Batteries

Wed Aug 09, 2017 11:28 pm

smcras wrote:
Wed Aug 09, 2017 11:11 pm
Thanks for the info.

The batteries are a cheap no name product. The package says "9V E-Block 6LR61" by TOP Craft. I cannot find any infos about these batteries, not even how much capacity they have. So I just ordered a DC-to-DC converter to try it out. They will be delivered in two days.

If your Raspberry Pi could run 20 mins with 2x batteries and the motors can run with only 1x battery, I assumed, that it should work out. I have also seen other robots with Raspberry Pi and 6x 1.5V batteries connected in a row on the internet. I cannot tell which configuration is better, my assumption was that the batteries connected in parallel would have less load. I'm not very investigative when it comes to power supplies. :oops:
Yes that is just another name for the same battery I was talking about, the difference is you are trying to run a pi3 from them and use wifi you have already found a 7805 voltage regulator which can supply about 1A is not able to power your pi, so with a DC-DC buck converter you are going to be drawing around 1.5A to power your pi and the wifi your batteries wont last long, my pi was probably drawing nearer 0.5A and the batteries last 20 min max. if you want a reasonable usage time for your robot look at the 5V rechargeable power banks for powering your pi.
Please only ask questions in the forum I will not answer questions sent to me directly via PM
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OutoftheBOTS
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Re: Powering Robot with 9V Batteries

Thu Aug 10, 2017 7:46 am

I power all my robots via batteries and a step down buck converter like your doing. I always use 2 buck converters, 1 for the electronics and a separate 1 for the motors as the motors when starting and stopping can cause spikes that electronics don't like. I have found that using RC liop batteries to work well as most ar design to be able to out out 50amps (way more than ur every goin to need). I have had trouble using AA batteries not producing enough amps when I try to power too much from them but never had this problem with the RC Lipo ones. hope this helps.

Also I tend to use a RPi Zero W for robotics because of both the lower power use but also the reduced size makes it easy to fit

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OutoftheBOTS
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Re: Powering Robot with 9V Batteries

Thu Aug 10, 2017 8:16 am

Ok I just looked at your post a bit closer and your using the step down regulator that is built into the L298N H-bridge. To my knowledge the 5v regulator used on the L298N BOB that your using uses a 78M05 regulator that has peak current of 0.5amps see http://www.alldatasheet.com/datasheet-p ... 78M05.html.

The buck converter that I usually use to power my RPi is the Mini-360 as it is very small and cheap, most of the BOB come with a adjustable potentiometer that I just adjust to 5v. The manufactures claim it will handle 3amps but anytime I have pushed i that far powering motors it has overheated but it seems to work fine for powering the RPi

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Ronaldlees
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Re: Powering Robot with 9V Batteries

Sat Aug 12, 2017 4:24 pm

Nine volt batteries do not have a very flat discharge curve. The last half of the battery capacity will be at 8 volts or less, and the last quarter will be at 7 volts or less (thereabouts). I use batteries with a flat discharge curve (I think they have the flattest DC of any battery). They are NiMH (Nickel metal hydride) batteries, but they may be too heavy or bulky for your purposes. This battery is not a suggestion for anyone, but they're all I use personally, for all my toys.
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