Sparks

A couple of days ago Kevin Ross emailed me to ask about spark suppression when connecting a 6s battery. I said that I would show him how I did it when we were next at the field. However, I had a bit of time and decided to improve my system.

A little background for those unfamiliar with higher voltage electrics...when you connect your battery to the speed controller you get a massive surge of current as the battery charges the capacitors on the back of the controller. This creates a spark and the following video shows a typical spark...the spark is the click you hear when the second connection is made.

The next clip shows how I use a resistor to suppress the spark. The resistor plugs into a 2mm female bullet soldered into the negative wire of the speed controller. The positive connection is made and then a crocodile clip joins the negative prior to the 4mm bullets being connected. The resistor limits the flow of current and allows the capacitor to charge slowly and reduces the spark to virtually nothing...there is no click when the crocodile clip is connected.

The problem with this method is that you need to remember to bring the resistor. The solution is to build resistors into your connectors. Hobbyking do this with their XC90 plugs.

hobbyking.com/en_us/xt90-s-anti-spark-connector-2pairs-bag.html

There are a couple of problems with these. Firstly, they are not that commonly used and take up a lot of space (they are BIG). Secondly, the resistor is on the battery side of the system, so you'll need to add a connector to every one of your batteries, even if it already comes with an XC90. Spark suppressing XC60's would be nice and maybe HK are planning this for the future.

Jeti also produce a spark suppressing connector for 5.5mm bullets...but at quite a hefty price.

www.dumfries-model-flying.com/connectors...nnectors-jeti-hacker

So I decided to have a go at making my own version of the Jeti 5.5mm spark suppressing connector.

First image shows a regular 5.5 mm bullet alongside a 2mm ring cut from the end of another bullet and a disc of copper clad circuit board. This has a 6mm hole drilled in it and a diameter of 9mm.

Second image shows the bullet, the disc and the ring soldered together on a 5.5mm drill bit to keep it all lined up.

Last image here shows the new connector removed from the drill bit

I've then filed four slots trough the copper clad board and solder so that I can join the 5.5mm bullet to the ring using surface mount resistors.

First two images show slots and the third image shows own of the resistors soldered in place. Pencil shows how small and fiddly it is to solder these in place.

I'm using 4 resistors because I already had a stock of 120 ohm resistors and 4 of them in parallel give a resistance of 30 ohm. This will allow a current of about 1 amp from a 6s lipo.

Last image shows the connector soldered and heat shrinked to the negative of my speed controller

And here's a video of the new connector in use. There is no spark at all - very pleased.



This controller is particularly 'sparky' and after a couple of connections using the new spark suppressing bullet I go back to the old connectors (the red ones). Each spark is worse than the one before and the final one ruins the connector. Images show charred male and female connectors after just 4 connections

Advantage of this connector over the HK XC90's is that just one connector is needed per model. I can buy new batteries and not need to change the connectors assuming they have 5.5mm bullets already, which they often do.