Friday, 19 May 2017

Getting Started on the PRC-350 LiPo Pack

The 4S LiPo pack was received with a clear marking that it was shipped at 30% and should be brought to a storage charge level as soon as possible, so I decided to day to at the very least get the main connections sorted so I could do this.

The battery case originally had just a single tag for each connection, however as I want to add additional facilities to this build, I opted to use a pair for each terminal. A short length of figure 8 DC cable is attached to one side.

The main cables of the battery attach to the pair of tags on the other side. This is very heavy gauge wire and required a lot of heat! All connections are sleeved for insulation. In addition the screws will later be covered with hot melt glue to ensure there is nowhere to short out! Likewise, the inside of the alloy case will be lined with an insulating sheet.

With both main cables attached, I could put the battery on charge.

While this was charging to safe storage level, I started work on the cutouts in the battery case for the external balance connector, low voltage alarm module etc. The usual combination of drilling and filing required here, along with the usual stabbed fingers! First to be cut was the hole for the 9way D type connector that will serve as the external balance charging port, and the 'loop through' for the low voltage monitor.

The wiring involved isnt complex, but it is quite fiddly. Now, ive noticed some constructors seem to have a fear of heat-shrink! But, there really is no excuse for not sleeving connections properly - especially when they are attached to a device that can give several hundreds of amps short circuit current!

 I did choose however to remove the pins on the voltage monitor board and solder directly to it. One track was damaged to ive wired straight to the input resistors. Below shows the monitoring and balance charging wiring in place and under test on the battery. A 9-way D plug is wired for 'loop-through' connection, this plug will be attached when the battery is in use and the alarm and monitoring facility is required (or briefly when in storage to check the condition)

With the wiring done, all apart that is from the external balance charging cable, the D socket could be secured to the case. Ive provided a 2.1mm DC Jack socket for an external 15V output. This will have an internal fuse attached! The part cutout is the start of the 'window' for the monitor boards LED display. Not shown, as I dont have it yet, is the USB output, which will be wired from the same fuse via a switch. The switch mounting position I will decide later.

It is remarkably tricky tightening nuts and soldering wires at the bottom of a small closed tin!

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