Coax Cables on Phantom Vision 2+ ESC Boards Power Leads

[Sierra Aviator]

Does anyone know the purpose of the power leads to the ESC boards being made of coax? Do they provide any EMF protection, or are the coax cables just used as some kind of cost saving measure?

I'd like to replace mine with regular wire and Dean's connectors, to make testing and changing them out a lot easier and field friendly. But I have my doubts about making this mod not knowing why the coax is there to begin with.

 

[Sierra Aviator]

Does anyone know what kind of coax cables those are?

 

[Sierra Aviator]

Does *anyone else* know what kind of coax those esc power leads are?

 

[SteveMann]

I thought it kind of odd to use coax, but maybe they had a few thousand feet on hand? It looks like RG 58. You can get it at many places. Since you don't say in your profile where you are located, I can't make any recommendations where to get some. Make sure you do not use solid center conductor coax. Personally I would have used a very flexible multicore power wire from a hobby shop (made specifically for powering ESC's) and add my own shielding and cover it with heat shrink. Coax was never designed for DC power, so you won't find any DC specs for it. I did find a paper on using coax as a DC power cable (here) and here's what they say about RG58 cable:

"For example, coaxial cable RG-58, Belden part number 8240 has a AWG20 center conductor and a PE dielectric with a melting temperature of 120C per the table above. The Wire Parameter Calculatorreports a single wire ampacity for a 200C rated wire at 70C ambient temperature of 6.15A. If the maximum operating ambient temperature is 40C, then the consolidated ampacity adjustment factor calculates to 0.78. The ampacity of RG-58 at 40C operating ambient temperature is 0.78 * 6.15A = 4.82A."
​

So, by their math, 5 or 6 Amps is all that you can reliably send through a piece of RG58 cable.

 

[yorlik]

Not very helpful response so I erased it.

 

[Sierra Aviator]

I thought it kind of odd to use coax, but maybe they had a few thousand feet on hand? It looks like RG 58. You can get it at many places... Since you don't say in your profile where you are located, I can't make any recommendations where to get some. Make sure you do not use solid center conductor coax...

Thanks for the info Steve.

 

[mad in nc]

believe it is thinner than RG-58 (maybe Thinax?), and being a run of only ~1- 1.5 inch long it will handle more current than 5A.... worse case it would fuse but the dielectric insulator would handle a hell of a lot more than 5A or even 50A before it broke down....

............ and the center conductor is used, along with the braided metallic shield.

BTW pic copied from other forum that shows pic is from a vendor but the same as my V3 ESC...

 

[burlbark]

The insulator in the esc power leads is pathetic and melts at low temp. If you are not careful working with them it easily bridges into a direct short.
I can see no reason other than package size and cost savings to use the wire they elected to use.

Jeremy

 

[Sierra Aviator]

The insulator in the esc power leads is pathetic and melts at low temp. If you are not careful working with them it easily bridges into a direct short.
I can see no reason other than package size and cost savings to use the wire they elected to use.

Jeremy

Yep that's what started all this. I took the leads off at 650F and melted some insulation. If you're not real careful the insulation melts before the solder does.

It's not like any coax I've ever worked before. I think it's crap but don't want to take any unnecessary chances here. According to some of the literature I've read these power leads do need to be shielded to prevent emf from interfering with some of the other components.

Reusing these melted leads carries some risk, so does replacing it. Not sure which way to go.

 

[Sierra Aviator]

Not very helpful response so I erased it.

No worries, you echoed some of the concerns I have about this.

Hopefully some good similar sized shielded cable will work as a replacement. Will keep y'all posted how this works out for me.

 

[mad in nc]

good challenge.... insulator is probably the same for all of the RG cables as the high temp rating is only referred to the outer jacket....

good luck!

 

[yorlik]

I deleted my first but I think you need to realize there is a very good reason they used coax cable!

The 4-7amps that feed each ESC thru those coax cables are connected directly to the output FET power devices and motor. They are PWM switching. The PWM noise is ABSOLUTELY HORRENDOUS AND FLOWS RIGHT BACK DOWN THAT FEED LINE TO THE BATTERY.

Each one of those feedlines is so full of PWMM noise that, even with a the coax approach, you could likely place an oscilliscope probe right next to the outside of one and whatch the noise that is still getting out.

This noise is very broad frequency and if you try to replace those coax cables with any thing less than very well shielded supply line, you will most likely kill any GPS capability, probably screw up both the wifi and the 5ghz RC control sigs.

Interupt the feedline with any kind of connector and you will allow MORE noise to get out.

That cable is likely a VERY HIGHLY engineered part of the phantom and any changes to it will probably cause failure to other electronics on the unit.