Hello everyone,
I’m exploring ways to extend the battery runtime of my Stretch robot.
I was wondering if it is feasible to mount an external 12 V LiFePO₄ battery pack on top of the robot and feed power through the charge port. The idea would be to use a DC-DC converter to provide regulated output, similar to how the NOCO charger operates in Supply mode.
According to the NOCO charger documentation, the Supply mode outputs 13.6 V. So my questions are:
- If I feed power through the charge port, should I target 13.6 V (as in NOCO Supply mode), or would 12.0 V also be acceptable?
- What precautions are recommended (e.g., current limits, inline fuses, or back-feed protection for the internal SLA batteries)?
- Would using this method while the robot is powered on pose any risks to the charging circuitry?
Any guidance or experience with extending battery time in this way would be greatly appreciated.
Hi @seongwoncho,
Few things to note the NOCO charger in supply mode is not a traditional regulator it is a constant current source.
A traditional voltage regulator regulates voltage, it tries to keep the same constant voltage output with different current demands. If you were to connect a DCDC regulator to the battery it would damage the regulator
The NOCO charger in Supply mode actually adjusts voltage output based on current demand, this is why it works well to charge the battery as the battery is low and you plug in the NOCO charger the voltage on the output will adjust as the current demand on the battery decreases from 10A to eventually 0A.
As for connecting a LiFePO4 battery pack to the charge port we strongly do not recommend this see below:
If the LiFePO4 battery is at full charge state and the batteries in your robot is low or damaged, the LiFePO4 pack will try to dump as much current as it can to the the SLA batteries to bring it up to the same voltage level. This will blow the fuses on the robot
Even if you were to get the voltage levels at the same point before use, since the capacity and discharge profile of both batteries would be significantly different you run the risk of over discharging the SLA batteries, meaning that terminal voltage of the system could be at 12V but this would be due to the LiFePO4 battery forcing the voltage at 12V but the true capacity of the SLA batteries would get extremely low and cause sulfation and permanent capacity loss
As mentioned before the safer option we have seen some groups do is purchase an external power pack that provides an AC 120V where you can way you can plug in the NOCO charger into it while in 12V supply mode. its not ideal and very bulky but would be the safest option
Hope this answers some of your questions
Hi Visaacan,
Thank you for the explanation. I agree that using an AC power station with the NOCO charger in Supply mode is the best option.