How to extend battery life with portable battery?

Knowledge Base
1

Hey Hello Robot team and community!

We want to use Stretch for experiments that take more than 2 consecutive hours (up to 8-10 hours in a day) and thus need longer battery life on the robot.

What’s the best way to accomplish this?
Should we plug the robot into a portable battery with the same 12V supply as the the NOCO GENIUS10 battery that ships with it?
Or should we plug the NOCO GENIUS10 battery itself into a portable battery?

Could you please recommend the best way forward?

Thanks,
Theo

2

Hi Theo, thanks for posting this question to the forum so others can learn as well!

We haven’t tested using external battery packs so caution should be taken. Batteries can store a lot of energy and therefore present a potential danger. Engineering a new battery pack is beyond what we can do here, so please use caution and expertise. I do know that one customer has added a battery pack but I don’t know the details.

A few background items to guide your design work:

  • A bank of SLA batteries can create large currents if they are not at the same voltage level. They may discharge and charge at different rates depending on their size, age, etc.
  • The NOCO charger doesn’t do load balancing of the battery bank. In practice we haven’t seen this be an issue for the two batteries inside of Stretch (albeit it may reduce the battery lifetime).
  • The Pimu board on Stretch fuses the battery inputs to 8A. I’d recommend fusing your battery pack as well.

The circuit below shows the battery connectors and charger connector wiring, where a fused 8A B12V powers the robot.

Stretch_Power_In
Stretch_Power_In1174×609 11.7 KB

I hope this helps get you started.
–Aaron

3

Thanks for your quick response @aedsinger!

I’m a bit confused, likely because I’m very ignorant about how batteries work.

If we use the NOCO GENIUS10 battery to interface between an additional portable battery and the robot, does this pose a risk for the robot?

We were thinking of plugging the NOCO GENIUS10 battery into something like this or this. Would you expect this to work? Or pose a risk for the robot?

4

Ah, I now understand what you are proposing. You will power the AC plug of the NOCO battery charger using one of these devices.

This should not pose a risk to the robot. However it isn’t clear how much added runtime you would gain

  • You’ll be converting from DC LiPo battery -->AC–>DC charge voltage → 12V SLA battery → Robot Load. This will be inefficient

  • Batteries can’t really charge and discharge at the same time. Thus the 12V AGM mode of the charger works well when the robot is powered off but confuses the charger when the robot is on.

  • The robot doesn’t have ‘smart logic’ to both charge the battery and power its load simultaneously. Placing the NOCO in Supply Mode approximates this (though likely reduces the battery life). I’d recommend trying this mode.

Let us know how it goes.

5

Thanks! We’ll try it out and post our experience here