I have a large Hexcopter with six ESCs (electronic speed controllers) supplied by a 12S LiPo battery - nominal voltage is 48v.

The battery connects with paralleled XT60 and XT90 connectors rated at 60A and 90A.

Due to the size of the capacitors on the ESCs the inrush current causes heavy contact sparking when the battery is attached, to the point where the connector surfaces are eroded and are difficult to fit together. The maximum rated working current for one ESC is 80A. Under full power the aircraft draws 150A @48v from the batteries. The capacitors are 2x 1000uF 100v on each ESC.

How can I suppress or reduce the spark effect when first connected? Would a 200A contactor be a good option (12 or 24v coil)?

 

A contactor would be one step better but one for 200a DC will be fairly large.
If you can get one, a DC rated with arc suppression would be best.

I think I have disconnect somewhere from a DC railway locomotive!
Max.

 

For something like this a pre-charge circuit is normally used. Some sort of circuit (or a manual jumper-set) places a low value resistor in a series connection across the high current contacts until the DC line capacitors have charged up sufficiently to stop most of the arcing from a dead line connection. With two connectors for DC power it should be easy to make a pre-charge series jumper for one connector before the second one is plugged it. You can then remove the series pre-charge jumper from the first connection and plug it in directly.

http://myelectriclifan.blogspot.com/2010/06/pre-charge-resistors.html

 

Put a 10 ohm resistor in series with the battery.
Put a simple toggle switch across the resistor.
Plug it up and after a few seconds throw the switch to bypass the resistor.

 

If he can find a 200 amp toggle switch that would work.

 

.... A resistor dissipates battery current as heat. The step input from the connection of the battery would have a high frequency content. Make an inductor coil out of some #12 solid wire ... maybe 10 turns or so. ...

The transient is only momentary .. difficult to guess what the exact numbers are.

 

Can't you bring all six on line sequentially?
Max.

 

.... A resistor dissipates battery current. The step input from the connection of the battery would have a high frequency content. Make an inductor coil out of some #12 solid wire ... maybe 10 turns or so. ...

12 gauge wire? Not a good idea for a permanent connection, it's good for maybe 40 amps in a chassis and a useful sized inductor of the proper sized wiring would be huge and heavy.

 

Ok
Second idea. Pre-charge the caps. Avoid high current arc.


9 volt rectangular batteries!

Put 5 in series. 45 volts. MAX current less than 200 mA if you dis count alkaline types. Tiny spark when you connect it. Wait about 10 to 15 seconds. Pop it off and snap on big battery

Bob's your uncle son.

 

Great replies - thank you all. Precharging makes a great deal of sense in this situation.

So the plan is now to build a simple timer circuit:
a) connect battery to the circuit which uses a 200A 1000V DC NO contactor with a back EMF coil diode
b) a first stage timer (1/2 556 monostable) begins when the battery is connected and a tact switch is touched
c) the timer drives the base of a small bipolar to deliver a precharge to the ESC circuits via a 100R 10W for T1 seconds
d) the first stage timer also trips a second stage timer (2/2 556 monostable latched) which is set for T1 + a few seconds
d) the first stage timer expires and turns off the precharge transistor
e) the second stage timer latches high driving the base of the solenoid transistor until the power is removed or a switch disables the contactor coil, de-energising the high power circuit

This device must be "reliable" in the sense that it should be literally plug&play. e.g:
Attach battery to UAV. Press NO power on tact. Wait 10 seconds. Power enabled. Press NC power off tact. Contactor disabled. Rinse & repeat.

I'll post the results. (project 209 on the HunnyDo list)

 

BTW Digikey contactors of this size are around $150. Alibaba, eBay etc show prices around $25-35. for lightweight miniature devices.

 

If he can find a 200 amp toggle switch that would work.

Well actually it does not work for long. The switch I used for testing was a knife (blade) switch. It welded together very quickly.

 

Ok
Second idea. Pre-charge the caps. Avoid high current arc.


9 volt rectangular batteries!

Put 5 in series. 45 volts. MAX current less than 200 mA if you dis count alkaline types. Tiny spark when you connect it. Wait about 10 to 15 seconds. Pop it off and snap on big battery

Bob's your uncle son.

That is also a good option for a separate precharger. Inexpensive and an easy DIY for others with this problem. I'm looking for something more industrial as part of a commercial UAV flight system.

 

For plug and play, any dummy can do it, kind of operation.
Use the resistor.
No expensive parts. No destructive arc damage. Minimal weight. Can be built into a battery pack quickly and easily. No moving parts to fail or break down.
Piggy back another identical connector to the currently used battery connector.
Color code them somehow. GREEN has resistor - hook up first. RED is straight battery hook up after green is disconnected.
Plug your UAV into the green plug wait ten seconds. Plug the UAV into red plug and fly.
Same effect as the separate charging from 9 volt batteries, but built onto the operative battery pack.

 

Maybe an inrush surge limiter such as this:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMuqZeNK75brDxRgT1KUh2F442dhAcr/Sdo=

I can't find one good for more than 50 amps, however.

 

^ ... place 3 or 4 in parallel.