Converting to LiPo Power

Submitted by JonnyAlpha on Thu, 12/28/2017 - 14:06

Forums:

Hi;

What is the best way to convert the MonsterBorg to LiPo batteries?
I tend to use XT60 connectors on my LiPos so that they are interchangeable between my Robots. The version of UltraBorg supplied with the MonsterBorg looks to be soldered to the battery lid that is fitted with a PP3 connector. So, to fit a LiPo, rather that making up an XT60 to PP3 adaptor with the ThunderBorg Battery Lid still fitted, could I simply connect the V+ and Gnd from the LiPo to the ThunderBorg V+ and Gnd Connector that sits between M1 and M2 (+ and -) Like this:
https://www.piborg.org/image/data/PIBORG/blog/ThunderBorg/ThunderBorg-mo...

If connected in this way I guess I will need a separate on / off switch. WIll the voltage LED still operate?

Thanks

piborg's picture

piborg

Fri, 12/29/2017 - 12:02

That is how I would suggest connecting the battery.

You are correct that the power switch on the ThunderBorg lid will not work connected that way, so you will want the separate on/off switch on the positive wire like in the picture.

The LEDs will still work fine this way and show the battery voltage when not used for something else. The battery monitoring range voltages and the script battery voltages should be changed to match the LiPo chosen as follows:

Monitoring minimum voltage = S number × 3.0
Monitoring maximum voltage = S number × 4.2
Script voltageIn values = S number × 3.7

As an example a 4S LiPo this gives us these values:

Monitoring minimum voltage = 4 × 3.0 = 12.0
Monitoring maximum voltage = 4 × 4.2 = 16.8
Script voltageIn values = 4 × 3.7 = 14.8

With these values the battery monitoring will show a constant red when the battery needs to be recharged. As this is the absolute minimum a LiPo should be used at you can increase the minimum a little to indicate the battery needs charging a bit earlier :)

JonnyAlpha

Fri, 01/19/2018 - 10:28

Following your excellent response I have successfully tested a LiPo (I only had a spare 3S knocking around) without anything else connected it worked fine.
Quick question on wiring.
I need to order some wire to connect a 4S 14.8v but I am not sure what AWG In need. To work this out I guess I need to know the stall current from one of the motors and x that by 4 (4WD)?
Can anyone help?

piborg's picture

piborg

Fri, 01/19/2018 - 17:53

At the rated 12 V the motors have an approximate stall current of 2.4 A.

I would recommend adding an extra 1 A for the DC/DC and to allow some headroom.
This would give a total worst-case current of:

2.4 A × 4 + 1 A = 10.6 A

General operating current for the motors is much lower, about 0.15 A each no load and something around 0.3 - 0.6 A each when driving with the standard MonsterBorg weight depending on terrain / steering.

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