Connected a external BEC, magic smoke happened.

Texan45

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Hello all,

I have a almost 2 week old Arrma Kraton and the servo went out last week. I bought a Savox 1230
and a external bec to go with it based on other threads on here. I hooked everything up, running the power leads from the BEC to the positive and negative of one of the battery leads. Removed the red wire from the esc to the receiver and plugged everything back into the receiver, making sure wires were correct. Plugged bec into channel 3. I plugged in the battery without the BEC leads in first and the black (ground) wire from the ESC to the Receiver started smoking and melted. Something else might of smoked up too, but couldn’t tell where it was coming from. Was the error in plugging in the battery lead without the bec power connected to it? Should I have plugged in the lead with the soldered BEC leads first? Do both battery leads need a bec power and ground? I removed the BEC lead from the receiver, plugged the red wire back into the esc to receiver, plugged the new servo back into channel 1 and everything still works, from what I can tell.
Hoping someone will chime in as to what I did wrong. Thank you! Chris in Canyon Lake.
 

olds97_lss

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Should you only use the signal wire from the esc to the receiver and not use the black/red wires at all from the esc? I think that's how I did mine on my castle sct sv3 esc in my stampede as that esc only puts out 5V and I wanted 6v. With it wired properly, I can't imagine it matters when you plug what in, it's just a matter of wiring things right and having the BEC set to the correct output voltage.

Now I can't remember how I wired it... and it's a pain getting everything in the receiver box or I'd pop it off and look... I just used a cheap 6A $12 generic BEC I got off ebay.
 

Texan45

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I think that would be a good place to start, running a signal only wire, pulling the black and red going to ESC. I read something about a ground loop, still don’t fully grasp the concept, other posts on inter web said to leave the ground wire in because all electronics needed a ground. I’ll try again tomorrow with only the signal wire. Good news is everything’s replaceable if it goes up in flames. Thank you for the idea olds97_lss.
 

olds97_lss

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I'm thinking of swapping my servo out of my stampede this week, so will have to crack open the receiver case to do that anyway. My traxxas servo has a lot of slop and with the awful stampede steering linkage geometry, a little slop anywhere is too much slop. If I do, I'll try to remember to take a photo of how I have it wired. It was my first BEC in 20 years of RC... so I was kind of guessing a bit as well. Whatever I ended up with works though.
 

Texan45

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A photo would be awesome. I’m holding off reconnecting the bec until I find out/receive some more info. Ran the savox 1230 off the esc bec and it seemed to do ok. Kraton is partly disassembled for installation of HR servo mount, HR Bellcrank/servosaver, HR Servo arm and link, and backflip tires, arriving tomorrow. The Kraton is on of the best 500 dollars I’ve ever spent. Always brings a smile to my face. Anyone who sees it run, says “wow, that thing is fast”, and thats on 4s!
Going to try 6s in the near future, read that SMC batteries are good.
 

olds97_lss

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I'm kind of waiting for similar parts for my stampede. I ordered an all aluminum steering bellcranks/saver/ackerman bar. Figured I'd replace the servo at the same time... I think have a spare hitec 5985 laying around. Total overkill for a stampede... but it's what I got... I think.
 

2fast4u

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Hello all,

I have a almost 2 week old Arrma Kraton and the servo went out last week. I bought a Savox 1230
and a external bec to go with it based on other threads on here. I hooked everything up, running the power leads from the BEC to the positive and negative of one of the battery leads. Removed the red wire from the esc to the receiver and plugged everything back into the receiver, making sure wires were correct. Plugged bec into channel 3. I plugged in the battery without the BEC leads in first and the black (ground) wire from the ESC to the Receiver started smoking and melted. Something else might of smoked up too, but couldn’t tell where it was coming from. Was the error in plugging in the battery lead without the bec power connected to it? Should I have plugged in the lead with the soldered BEC leads first? Do both battery leads need a bec power and ground? I removed the BEC lead from the receiver, plugged the red wire back into the esc to receiver, plugged the new servo back into channel 1 and everything still works, from what I can tell.
Hoping someone will chime in as to what I did wrong. Thank you! Chris in Canyon Lake.

Sounds like polarity was reversed.
 

Texan45

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64254AB8-A92B-49BB-83CD-56AC261AA3F8.jpeg So maybe this is the error, I connected the positive wire of the bec to the long positive of the battery connector and the negative from bec to short “u” side negative? Of same xt90.
Does the negative need to go to the long negative lead? I’m totally baffled why the U connects to the negative on one xt90 and the positive on the other xt90? Is there a better place to solder in my bec?
 

2fast4u

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View attachment 20485 So maybe this is the error, I connected the positive wire of the bec to the long positive of the battery connector and the negative from bec to short “u” side negative? Of same xt90.
Does the negative need to go to the long negative lead? I’m totally baffled why the U connects to the negative on one xt90 and the positive on the other xt90? Is there a better place to solder in my bec?

Yes it is the error. It's because you have two batteries in series, not parallel You are connected to the positive side of each.
 

olds97_lss

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To me, I think your fine with how you have it wired. If you go positive on the one your red is wired to and negative of the other xt90 the other battery connects to, then your BEC is going to have to throttle down 25.2V on full charge.

The "jumper" wire is so you can have 2 3S lipo's to simulate having 1 6S lipo. When you wire packs in series like that, you add the voltage of each pack and retain the capacity of one pack. If you wired in parallel, then you would double the capacity, but have the voltage of a single pack total.

Wired the way your BEC is wired, it should be seeing a single 3S voltage (11.1V nominal, 12.6V fully charged). I would think that's how you would want to wire it when dealing with packs in series.

FYI, I did use the black and signal wire from my castle ESC into the receiver. Only the red wire was removed from the connector and taped off so it didn't touch stuff.

2018-0717-Stampede-BECWiring.jpg
 

Texan45

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Thank y’all very much for all the help! Parts came in, did some rewiring , and now she’s running better than ever.
 

DoNoHarm

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View attachment 20485 So maybe this is the error, I connected the positive wire of the bec to the long positive of the battery connector and the negative from bec to short “u” side negative? Of same xt90.
Does the negative need to go to the long negative lead? I’m totally baffled why the U connects to the negative on one xt90 and the positive on the other xt90? Is there a better place to solder in my bec?
SMH made the same mistake in my e revo. That’s why the negative esc to receiver lead got torched... SMH. Do NOT wire your bec like that! Make sure to use the long positive and the long negative wire.... I used the jumper wire as the negative and the same thing happened to me as the OP.


My esc-to-receiver Black wire completely snapped off because it got torched so bad, so I hope that ground isn’t needed... I rewired my BEC to the correct spots and now I’m waiting on a receiver.
 
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