Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: ursine on February 07, 2011, 02:45:14 PM

Title: Lipo hard cutoff
Post by: ursine on February 07, 2011, 02:45:14 PM

I'm using a lipo to power the wireless router and ethernet board on my robot. I'd like to use a hard cutoff to save the lipo from over discharge. Most of what I see is for RC applications and are soft cutoff and work in conjunction with the ESC to lower or pulse the output. Not a good idea for the electronics. Is there a way to modify it for a hard cutoff or is there an equivalent circuit that's not too involved? I could probably use an arduino for this but that's overkill.

Thanks,

Dave

Title: Re: Lipo hard cutoff
Post by: Soeren on February 07, 2011, 08:47:48 PM

Quote from: ursine on February 07, 2011, 02:45:14 PM

Is there a way to modify it for a hard cutoff or is there an equivalent circuit that's not too involved? I could probably use an arduino for this but that's overkill.

A comparator driving a relay through a transistor, or just a power MOSFET (depending on voltages) should suffice - If a dual comparator is used, you could have a warning LED to tell you that you're close to empty, with only a slightly larger layout.

At what voltage do you want it to cut?

Title: Re: Lipo hard cutoff
Post by: ursine on February 08, 2011, 04:33:42 PM

It's a 3 cell Lipo so for drawing no lower than 3v per cell would be 9 volts cutoff. Can you point me in the direction of a circuit diagram that would work?

Thanks,

Dave

Title: Re: Lipo hard cutoff
Post by: newInRobotics on February 08, 2011, 04:51:01 PM

This (http://www.rcgroups.com/forums/attachment.php?attachmentid=210702) might help I believe.

It makes a sound when pack drops to 3V/cell.
Piezo can be easily replaced by an led for silent alarm.
Or relay to implement hard cutoff.

Title: Re: Lipo hard cutoff
Post by: ursine on February 08, 2011, 07:00:36 PM

Thanks a bunch. That should work fine...now to Digikey.

Dave

Title: Re: Lipo hard cutoff
Post by: TrickyNekro on February 09, 2011, 08:35:55 AM

Although not good documented and having some errors... See my tutorial on this here...

http://www.societyofrobots.com/member_tutorials/node/302 (http://www.societyofrobots.com/member_tutorials/node/302)

It comes also as a first result if you google search LiPo protection ;-)

Title: Re: Lipo hard cutoff
Post by: newInRobotics on February 09, 2011, 08:56:02 AM

Quote from: TrickyNekro on February 09, 2011, 08:35:55 AM

Although not good documented and having some errors... See my tutorial on this here...

http://www.societyofrobots.com/member_tutorials/node/302 (http://www.societyofrobots.com/member_tutorials/node/302)

It comes also as a first result if you google search LiPo protection ;-)

I am working on LiPo charger atm (actually gathering enough knowledge to build it (big thanks to Soeren)). At the moment I need some guidance on how to detect when battery is fully charged. I've made same drawings according to my understanding of how it works. Could You please have a look and point out mistakes.
This is my thread. (http://www.societyofrobots.com/robotforum/index.php?topic=13150.msg98095#msg98095)