Li po low volt cut off

[craig_colliass]

Li po low volt cut off Li po 11.1v,2200 m/amp,

6.1.1.4.
The robot must be fitted with both an under voltage cut-out set at or higher than
the battery manufacturers recommendation that will prevent the batteries from
becoming damaged due to over discharge.


I'm looking for a cut off for Seraph can anyone help?

[grant_ploughbot]

Re: Li po low volt cut off

Hi Craig, the current Lipo rules were written a while back, when the people wrtting the rules had no experience with lipo's or as to what was readily available.
You can not buy an off the shelf low voltage cut off that will cut throttle to 50 percent (as we need in robot's). It's not a safety issue over discharging, but will permanently effect the life span of the packs if you do.

I recommend using a fuse directly inline with you Lipo, thats rated under that of the batteries maximum discharge.
I will not pass a tech-check with a featherweight using these batteries without a sensible fuse inline.
You can however buy Low voltage alarms. I use one in PloughBot that turns on a red LED when the battery is getting flat, and allows me to know when I should take it easy.

[craig_colliass]

Re: Li po low volt cut off

thanks Grant
I have the alarm and will try to fit it without blowing the thing up, the pack is a 11.1v 2200ma 25c unit 55amp continuous and 77amp maximum do you have a preferred fuse type for this?

[grant_ploughbot]

Re: Li po low volt cut off

Are you just using two drive motor's like drills or similar?
If so, I would try a 30-40A fuse inline (standard automotive fuses). Wayne uses the same size lipo in Basher with drill motor's using a 30A fuse and has never had a problem.
Wiring in your robot will play a bigger part of tech-checking than in general, so it's worth making sure all your connections are good and no wire chaffing.

[craig_colliass]

Re: Li po low volt cut off

Seraph uses two 150w 12v motors they are going to draw 12.5A each so i would probably need 60A fuse to be on the safe side.

[Metal Demons]

Re: Li po low volt cut off

Hmm, time to find myself a 400A fuse I guess for when I go lipo... :twisted:

[Mouldy]

Re: Li po low volt cut off

Id use a fuse.. but these look interesting if your running less then 6s

http://www.dimensionengineering.com/CellShield.htm

[geeza]

Re: Li po low volt cut off

CellShield is intended for aircraft with 0-100% style one direction only throttle. A future product will be aimed at cars.

So probably not suitable for a robot at the moment.