Blue flash plugging in LiPo?

[tomatwalden]

In a related thread to my earlier post about soldering advice for EC5's ... So I bit the bullet, bought some "practice" cable before having a go at soldering EC5 connectors onto both a 6S LiPO and my ESC.

So plugged it in tonight - shaking like a frigging leaf as a 22V 6S LiPo isn't something that fills me with a warm fuzzy feeling ...

The AR6210 light came on (so, power being delivered somewhere at least!) although the 3GX wasn't showing any signs of life ...

The thing that freaks me out though is that every time I tried plugging the battery in, I could see a momentary blue flash inside the black side of the connector. It's only for a split second, but it's there.

Is this normal!? (I think not!) - I guess I've f***ed up with my soldering, but then, the male->female connection of the EC5 isn't a bit that is actually soldered. Could it be a bad solder joint in the "cup" that the cable goes in to?

[xygax]

It could be that you have soldered the connection and its not actually soldered but sort of hanging together because of the flux. Unplug it all and then pull each cable in turn hard if its soldered properly it wont budge if not it may fall apart in your hand... better a bird in the hand than a birs in the bush because of a bad connection

Steve

[Si_B]

A flash between the physical points where the connectors touch is okay, if its flashing somewhere else........don't use it till you've checked your wiring. EC5's are a bugger to solder which is why I use other types of connector. Any pics of your handy work ??

[Rob Barnes]

When plugging hv connectors together you always get a blue spark ! You wait till you plug 48 volts together with a 12s set up you get a massive crack too lol !

[tomatwalden]

I gave the connectors a real good tug before I pushed them into the blue plastic sleeve. Both seemed pretty much rock solid.

I found this thread on HF that seems to imply the blue spark is normal? : BIG spark when Lipo pack get connected to the ESC ?! - HeliFreak

Is it just a factor of the larger packs !?

T

[tomatwalden]

A flash between the physical points where the connectors touch is okay, if its flashing somewhere else........don't use it till you've checked your wiring. EC5's are a bugger to solder which is why I use other types of connector. Any pics of your handy work ??

Unfortunately not now that the plugs are in the blue plastic holder. I can't really tell if the flash is where the male/female make contact (which I assume is ok), or where I've soldered the connectors from the ESC. I guess if it was the latter, they'd be a constant arc rather than a flash?

I'll try to get somebody more knowledgeable than me to check it tomorrow ...

[highlightshadow]

Its why some of the ESC's come with anti-spark ... i get nothing plugging into my 12S YGE with EC5 but on my Trex with align ESC at 6S i do get a small flash.

[Si_B]

What was your soldering technique. Did you use a flux? Was everything tinned before you bought the wire and the connector together?

[cjcj1949]

When you connect up the battery to the esc you are connecting to a large capacitor. The volts on the capacitor just before connecting are zero and this looks like a short circuit to the battery. The battery then pumps out a very large current as it looks like a capacitor as well. A very large current flows and a high voltage is produced. If you make a good connection once and don't break it you should avoid a flash, but this is difficult to do. There are ways around this if it bothers you. Basically you need to charge up the capacitor in the esc more slowly before making the full battery connection. One way is to use a resistor to make the initial contact. This is easy to do but needs an extra connector. I doubt if this high current is doing the capacitors any good. The better the lipos the greater the possible harm. Jeti have connectors for around £5 that do this for you. Purple Power use to advise using a resistor.

[Vikki]

No high voltage is produced, it's a capacitor not an inductor

CJ is right, though, in that an empty capacitor itself requires to be charged to do its job but unlike a battery it can charge in the blink of an eye.

When you connect the battey the current is very high and that causes the blue flash (sometimes you'll hear a little 'crack' as well). In a few microseconds the voltage across the capacitor rises and the current drops until the capacitor is at supply voltage and only leakage current flows. This is perfectly normal.

The way to reduce the flash is to add an inductor to the path. The inductor will try to resist the rapid change and slug the amount of current being drawn from the battery (had a similar problem I had to cure once but that was with 44,000uF worth of capacitance). Instead of the current spike lasting a few microseconds the inductor will stretch it to about 200 milliseconds and the flash will not be present. But:

You really don't need to worry about it, the capacitance is small and the flash is small and at these levels is perfectly normal. Don't worry about it.

[tomatwalden]

What was your soldering technique. Did you use a flux? Was everything tinned before you bought the wire and the connector together?

Technique - well, amateurish! :-) Otherwise, yes and yes - flux used, solder is 40/60 lead with flux core and everything tinned beforehand ...

Seems from other posts that flash is normal? Now just got to work out why my 3GX isn't springing into life ....

T

[cjcj1949]

I think there is a high voltage produced. The di/dt is very large and the inductance of the wire is enough to generate very high volts from V= Ldi/dt. I don't know of a way of producing a spark without high voltage. Limiting the current with a resistor is easier than an inductor. The ripple current rating of the esc caps is probably being exceeded, especially as the current is largely undefined during the initial connection.

[heathy]

Its why some of the ESC's come with anti-spark ... i get nothing plugging into my 12S YGE with EC5 but on my Trex with align ESC at 6S i do get a small flash.

S

YGE have anti sparks built in.. Tom you going to phoenix tomorrow? Sounds normal by the way

[tomatwalden]

S

YGE have anti sparks built in.. Tom you going to phoenix tomorrow? Sounds normal by the way

Was there today - lovely afternoon, just ross, mark and myself (and pete of course). Might try and swing by briefly tomorrow, but unlikely. Have got 3GX powered up now but having nightmare with dx6i settings ...

Mark's 130x tail servo died, and mine ejected a tail blade .... ho hum ....

[Vikki]

In this instance contact spark is due to high current. Not enough inductance in wire. Think arc welder. Welds by high current not high voltage.

if you use a resistor you need to short it at some point to allow full current to flow. Not so with an inductor.

Arup horizontal fire curtain: I used a high Watt resistor in path to 88,000uF worth of capacitance. Two seconds later the PLC closed a power relay to bypass it. That level of capacitance being charged just blasts fuses to bits.

Coopers Emergency Power unit kept welding relays out to multiple curtains, four curtains each with a 10,000uF capacitor adds up. No option to fit a timer, resistor and bypass relay. Answer was to use an inductor to slug the CURRENT spike. Once the current stops changing the inductor behaves like a wire.

I've been there and had to deal with it, ok! It was a technique mentioned but not required. At this level all you get a bit of pitting on the connector where the two parts initially touch.