Smoked my Receiver with external BEC

[ChemEng]

OK, so this isn't for an Arrma vehicle, but this forum is so much better than the "other" one, i thought i would try posting it here, especially since it is more of a general electrical question...

anyway, i replaced a servo in one of my cars and decided to run it on an external BEC so i could get more power out of it. I wired it up as per the diagram below, and it let the magic smoke out of the receiver. What did i do wrong?

EDIT: this car uses 2 x 4s batteries in series. I wired the castle BEC up to 1 of them (because it only works up to 6s). I plugged that battery in first, powering the BEC. The smoke didn't come out until I connected the second battery.

(Purple is signal, Red is +, Black is -)

 

[Engineer]

Per Castle’s wiring diagram you should remove the red wire from the ESC going to the receiver since the BEC is supplying the power:


Edit: if you need more than a 25V input you may have to use their Pro BEC

 

[ChemEng]

So I was trying to power the receiver with the ESC at 6V and then power the servo with the external BEC at 8V since the receiver can't handle 8V.

 

[1coopgt]

Sorry I don't understand why you would add a BEC into the system when your ESC has a bec.

 

[ChemEng]

Sorry I don't understand why you would add a BEC into the system when your ESC has a bec.

Because I want to run the servo at 8 V to get more power out of it. The Reciever can only take 6 V.

 

[KingKeif]

Because I want to run the servo at 8 V to get more power out of it. The Reciever can only take 6 V.

This.

 

[SrC]

Is the servo rated for 8v? Not that it matters for your issue. Just asking. Think its ovekill though. Your call.
Rx, have a voltage limit. Your wiring wasn't correct. Needed to isolate the Rx from the CC BEC. Signal wire only at the Rx. Like posted above.
What is the max Rx voltage for that Trax RX??? Again not that it matters 100% at this point. just have to ask yourself, what the benefits are of an Aux BEC.
If your Servo needs 8v to run significantly better as intended for optimum torque and speed, then it is what it is.

2 4s packs in series is essentially doubling the volts. If you want to get fancy with a separate BEC, best served to have a separate Lipo dedicated for it. You went this far already....

 

[TriggerHappy]

I would get a esc with 7.4v before i would add a external bec-more wires and sumthing else to go wrong with.

 

[SrC]

Yeah HV servos approaching 8.4 volts are not commonly used. At least for bashing. Crawler rigs are usually done this way with a a separate BEC. And Nitros as well.
Get a servo that will match the max BEC volts of your ESC. Best.
Is that servo runnable at 7.2/7.4 volts ESC BEC??? U May just be fine with that.
In case you haven't, You absolutely need the CC programmer to adjust all the parameters of that CC BEC.
You just cant use that CC BEC without the programmer. The default values are preset. And cant be adjusted without one. I believe they are set very low out the box. Food for thought.

 

[ChemEng]

Yeah HV servos approaching 8.4 volts are not commonly used. At least for bashing. Crawler rigs are usually done this way with a a separate BEC. And Nitros as well.
Get a servo that will match the max BEC volts of your ESC. Best.
Is that servo runnable at 7.2/7.4 volts ESC BEC??? U May just be fine with that.
In case you haven't, You absolutely need the CC programmer to adjust all the parameters of that CC BEC.
You just cant use that CC BEC without the programmer. The default values are preset. And cant be adjusted without one. I believe they are set very low out the box. Food for thought.

the stock receiver is only rated for 6 V

sure, it will work at 6V, but the savox SB2290 has over 60% more torque at 8.4 V than it does at 6 V. I am turning some pretty big tires, so i want all the torque i can get. (and i do have the programmer)

Specifications:

• Torque @ 6v - 40.0kg/555.5oz-in
• Torque @ 7.4v - 50.0kg/694.4oz-in
• Torque @ 8.4v - 65.0kg/902.7oz-in

Is the servo rated for 8v? Not that it matters for your issue. Just asking. Think its ovekill though. Your call.
Rx, have a voltage limit. Your wiring wasn't correct. Needed to isolate the Rx from the CC BEC. Signal wire only at the Rx. Like posted above.
What is the max Rx voltage for that Trax RX??? Again not that it matters 100% at this point. just have to ask yourself, what the benefits are of an Aux BEC.
If your Servo needs 8v to run significantly better as intended for optimum torque and speed, then it is what it is.

So the servo only needs the signal wire connected to the receiver if i power it externally?

2 4s packs in series is essentially doubling the volts. If you want to get fancy with a separate BEC, best served to have a separate Lipo dedicated for it. You went this far already....

I wired the BEC in parallel across one battery, so it will only see the voltage of one 4S, not both combined... (this part is apparently the only part of the setup that was correct).

 

[3d-rc.myshopify.com]

The ext bec didn't need to be contacted to the reciver at all. All you needed was the reciver wire connection to the servo

 

[ChemEng]

Well a new reciever from Traxxas is $55 with shipping, but a DumboRC radio and reciever combo is <$50 and it will run on up to 10V (and I can get it delivered tomorrow).

This way I can run my castle ESC at 8V and dump the external BEC.

So my Xmaxx will have exactly zero traxxas electronics now. Good riddance.

 

[3d-rc.myshopify.com]

Well a new reciever from Traxxas is $55 with shipping, but a DumboRC radio and reciever combo is <$50 and it will run on up to 10V (and I can get it delivered tomorrow).

This way I can run my castle ESC at 8V and dump the external BEC.

So my Xmaxx will have exactly zero traxxas electronics now. Good riddance.

I can save you some money I have extra Traxxas receivers I will just give you it if you pay for shipping

 

[ChemEng]

I can save you some money I have extra Traxxas receivers I will just give you it if you pay for shipping

Thanks for the offer, this is why arrma forum is so great, it has the most helpful and generous people I have ever found on a forum - actually probably better than real life.

(I haven't even recieved a reply to my post in the traxxas forum yet)

But I think this thread has helped show me that I was going about solving my problem in the wrong way. Instead of trying to run multiple voltages, complicating my setup, I should just make my esc, reciever and servo match. The reciever was the odd man out, the weak link, so I will replace it with something more suitable.

 

[SrC]

That Traxxas Rx max volts at 6v is junk. So dated. One reason Trx makes their own BEC for this reason. They rather give you old Rx tech out the box and have you need to buy their propietary $optional$ BEC crap. Instead of a better Rx. They can make more $$ this way. The whole stupid Trx Eco stuff. They suck you in slowly.
Most any cheap Rx these days can go well over 6volts for modern Servo considerations and Higher volt ESC BEC's.
Get rid of that Trx Radio crap. Just me.
I think any servo capable of 7.2 or 7.4v is standard these days. And some Rx's can handle well over 8v. and more these days.

 

[ChemEng]

That Traxxas Rx max volts at 6v is junk. So dated. One reason Trx makes their own BEC for this reason. They rather give you old Rx tech out the box and have you need to buy their propietary $optional$ BEC crap. Instead of a better Rx. They can make more $$ this way. The whole stupid Trx Eco stuff. They suck you in slowly.
Most any cheap Rx these days can go well over 6volts for modern Servo considerations and Higher volt ESC BEC's.
Get rid of that Trx Radio crap. Just me.
I think any servo capable of 7.2 or 7.4v is standard these days. And some Rx's can handle well over 8v. and more these days.

agreed, i actually really like the x-maxx, but the electronics were junk.

the dumboRC radio/receiver combo i ordered is only $42 for the set and it'll handle 4.8 - 10 V. I think the non-gyro receivers are only $15 or so.

I actually run the Nobel NB4 radio in my trucks, but this x-maxx is my son's truck. It needs a separate radio so we can drive at the same time otherwise i would just get another NB4 receiver. My son is only 7 so he tends to be hard on radios, he isn't ready for a $200 radio yet (although he does pretty well with the x-maxx w/castle 2028 800kv setup. pretty proud of him for that, some adults couldn't handle it).

 

[SrC]

Yeah my son wants the NB4 Also. Like dad's.
I may consider getting him a RL RC6GS. (he speed runs the Infr) He is finally at an age (12 yo) where he is fussy about caring for his Radios after breaking RTR radios, many from just tossing them, breaking the wheels treating it like its an X-Box controller. And he has broken a few of those too.
He now doesn't even like to place his radio on the ground. When checking his rig out in the field, asks me to hold it for him. I told him to just ly it flat on the grass and it wont' tip over and break the wheel.

 

[ChemEng]

Yeah my son wants the NB4 Also. Like dad's.
I may consider getting him a RL RC6GS. (he speed runs the Infr) He is finally at an age (12 yo) where he is fussy about caring for his Radios after breaking RTR radios, many from just tossing them, breaking the wheels treating it like its an X-Box controller. And he has broken a few of those too.
He now doesn't even like to place his radio on the ground. When checking his rig out in the field, asks me to hold it for him. I told him to just ly it flat on the grass and it wont' tip over and break the wheel.

That's awesome. I hope my kids stay into it with me. Lots of learning opportunities and life lessons to be had with RC.

Last time we went out crawling, my son used his radio like a claw to climb up a steep hill, wheel side down. Took some work to get it to self center after that, it has a nice gritty feel to it now.

 

[SrC]

Crawlers are fun.

 

[ChemEng]

FYI, i actually had a good post on the traxxas forum... one guy posted this diagram, its exactly what i did wrong... Hopefully someone will find this post in the future and NOT fry their receiver (i connected the BEC to the battery as per the "NEVER DO THIS" on the bottom left and i can confirm that "you will boost the ground voltage in a disastrous way"):