vmsguy

OK...

I bought a P-38 just recently and I'm going to convert it to electric.

I've got the setup figured out.

Per nacelle:
Axi 4130/16 motor
80 Amp High Volt ESC
8s2p Thunder Power Pro-Lite 4200mAh batteries
14x8 or 15x8 prop.

I am worried about safely handling this aircraft. I do NOT want to plug in that much battery without an arming switch.

I know it's hard finding one toggle switch that could handle the amperage.

But I think I could take 2 or even 3 switches and wire them in parallel? If any on switch is on, power would flow.. But if all were on, then the load would be spread amongst all switches..

Thoughts???

Questions???

hdpartman

My Feedback: (35)

No Switch is required or will work the way you want. [link=http://www.maxxprod.com/mpi/mpi-21_files/6970%20c.jpg] CLICK [/link]Go to this site and look at the bottom of the page.


Good Luck, Al

DaveFlynn

I've been thinking about this for a while. This circuit switches the battery power to the ESC when the Rx power is switched. No more sparks when you plug in the battery.

http://www.oxfordvue.com/ESC_Power_Switch.pdf

Let me know how it works if you build one.

tIANci

I use what Al suggested, its nice ... I don't need to leave my TX on all the time esp. on planes where access is via the wings.

jesse1919

The current would not split equally in parallel switches due to small differences in resistance in the switches and wires leading to them - not recommended.

The Sermos plug looks good but use at least 12GA wire for that pack. I would add a ESC capacitor charging toggle switch and resistor.

The circuit is interesting but why P channel FETs - N-channel are lower RDSon?

DaveFlynn

Using 3 standard P-Ch MOSFETs in parallel the on resistance is 0.007 Ohm and can switch 150 amps. At 36 volts and 25 amps no heat sync is required. Unless you have full opto-isolation it is safer to switch the positive side. If you're sure you have no other ground path then you could flip the circuit over and use N-Ch FETs. I didn't because I use the flight pack with 2 BEC's that are always on. I finally built the circuit, it works.

P-40: 9S1P 2100mAh, CC HV-45, eLogger, Glow Emulator (current limit device), KMS5331/10 250RPM/V, 2 x XBEC-1, 7 x HS-5645 servos and MOSFET switch thing.
I'm not sure if the data logger would work if I switched the low side, it connects across the ESC.

whitecrest

You could accomplish the same thing by using a single-throw, multiple-pole switch and wiring the redundant poles in parallel to reduce the overall contact resistance. Since you will be mechanically switching only the current needed to charge the filter capacitor in the ESC and not the full motor current, you can use a switch with a lower current rating per contact that is a more convenient size. I have read several accounts of fliers using such an arrangement in high-current installations with no problems. I definitely agree with your desire for some type of arming scheme. Good luck with the configuration you choose.

-pkh-

My Feedback: (2)

Small differences in resistance means small differences in current through each switch, so that is not a problem. With MOS devices, you won't get thermal runaway - as they heat up, they increase resistance and will conduct less current.

cyclops2

Nothing is better or safer than a HUGE knife blade switch.

Actually at the weight of the completed plane, a set of Sermos heavy duty plugs is your safest & most reliable switch possible. It could be mounted anywhere a simple door could open for access. Keep it simple and safe. Disconnect the battery. Always.

Rich

DaveFlynn

Having melted various electro-mechanical parts, I tend to trust the electronics more.

jesse1919

Dave - I see. I thought you had an opto. Cool.

pkh - OK what I meant was all the resistances involved are very small (the switch contacts and the wires branching off to the switches) so you can't assume the current splits exactly equally unless you're careful how you wire them. I wish I could just draw it out here. Anyway, it will work, just don't use (3) 20A switches for 60A total. I guess that's pretty obvious.

The current charging up the ESC filter cap is a big spike for a few ms. A switch will arc just like plugs do. That's why I was thinking about a small toggle switch and precharge resistor in parallel with the switch/ plug. BUT the question is always will you re-kit the plane before the switch wears out?

cyclops2

The repeated arc when connecting BIG planes will eventually cause pitting on 1 of the contact surfaces. That will lead to a hot spot & burning out of the surface. Which could cause Melting of any plastic housings. Then the VERY FATAL short circuit between the + & - of the battery.
KABOOM goes the lipo in the plane while flying.

The smaller pre - connecting contact, is the only sure way to stop KABOOM.

rwh100

Here is a complete design for a very capable MOSFET semiconductor on/off switch that can be built DYI and used with LiPos from 2s to 8s. Rated for 50 A continuous and 180 A peak.

Check it out!