DX8 voltage sensor+6hv+CC Bec pro+ incorrect wiring =BANG !!!

[Snaaakeey]

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[FONT=Tahoma]Just thought I'd share this interesting little tit bit of knowledge I have just found out. This is defiantly something anyone using a Castle Creation BEC pro in a 12s (2x 6s in series) setup needs to read.[/FONT]
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[FONT=Tahoma]So this is what happened.....[/FONT]
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[FONT=Tahoma]I have a 6hv with the standard gear on it. 2x 6s batteries in series, a hobbywing platinum pro 70a ESC, A CC BEC pro and now a TM1000 telemetry unit with voltage, temp and RPM sensors connected through an AR7600 Rx. I connected the voltage sensor across the esc (50v).Plugged in the 1st battery pack and all was well. The Tx was reading 25v. Plugged the 2nd battery in and woof!!! The smell of fried cable filled the shed (or the Wendy house as my wife likes to call it!).[/FONT]
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[FONT=Tahoma]The post mortem reviled the neutral cable of the voltage sensor had fried along with the neutral on the data cable between the TM1000 (telemeter unit) and AR7600(Rx). So a short had occurred but how and how it had passed through the TM1000. Surly the sensor side (At 50v) and the power/data side (at 6v) must be separated and that wouldn't explain the short anyway so what was going on? The TM1000 still worked as well as all the other components like gyro servos esc so no damage as the small cables had acted as a fuse before anything else went up!.[/FONT]
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[FONT=Tahoma]Rang up horizon Hobby for advice. John was very helpful and couldn't see a problem from our telephone conversation so he got me to send it back. 2 days later and a conversation over the phone brought no answers and the tm1000 was assumed to be at fault. I received a new unit with all wires and connectors! Great service![/FONT]
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[FONT=Tahoma]So what did it turn out to be! Well the CC BEC Pro was known for letting go on 12s systems even though it was rated for 50v+ so to get round this you connect the BEC across one battery only. This gives the BEC 25v only and ensures the BEC can handle it easily (pretty much a standard setup in the 6hv with a BEC pro). Now silly me had connected the BEC pro's neutral between the packs and the phase to the phase of pack 1. It has worked faultlessly for 6 months. Now I have found out that this was a big no no. The BEC pro was getting 25v across pack 1 but because it's neutral was connected in between the two 6s batteries it was seeing the top 25v of the total 50v. The BECs neutral was at 25v and its positive was at 50v. The BEC pro (via Google) has no regulator on its neutral so 25v on the input side = 25v on the output side to the AR7600!!!!! Why my electronics have been fine till now I don't know. Telemetry says I have 7v on the Rx. How the short managed to go through the BECs 25v neutral through the Rx without doing any damage onto the TM1000 and then jump across to the voltage sensor neutral ( which was connected to the ESC neutral that goes back to the battery pack 2 neutral so is effectively 0v) I don’t know. The weak point seems to be the TM1000 and I assume it has electrical black magic like one way resistor gates or some such trickery that failed when the Rx neutral connection to the TM1000 became 25v live! [/FONT]
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[FONT=Tahoma]I have now moved the BEC connections around so the positive is connected between the battery packs and the neutral is on the negative of pack 2. All is well and all is working.[/FONT]
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[FONT=Tahoma]I'm sure there are lots of guys and girls on here with a better understanding of this field so any ideas and theories are welcome. I find these types of threads interesting as they can get some good discussion going![/FONT]
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[FONT=Tahoma]To round this post off anyone using a Castle Creations BEC Pro and a 12s (2x6s) setup and are splitting the packs voltage to the BEC beware! Make sure your BEC pro phase (red) is connected between the packs or you’ll have a high voltage neutral to your BEC and on into your Rx I suspect the RPM sensor would also short in this case as it also sees high voltage from the 3 phase motor wires. [/FONT]
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[FONT=Tahoma]Well I hope that made sense and Cheers for taking the time to read it![/FONT]
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[maderdog_1024]

you need a hitec aurora 9 in your life mate.

Using 2 6s packs you would take a feed from one of them 22.2v and connect to the SBC pins on the optima7 or 9 receiver, and then connect the CC BEC pro to the battery pins.
The TX will see the 22.2v and you can set low battery alarms etc accordingly! simples!

if you required extra telemetry functions there after, then you would connect telemetry box to RX, battery functions are standard on Hitec.

[bigpops]

[url]http://www.rctoys.com/pdf/cc_bec_multi-cell_iInstallation.pdf[/url]

I think I saw a video about this from Finless too once where he points out how the direct short happens. I've had a look, but can't find it fight now or I'd post a link.

It's a very easy mistake to make, and one I'd totally forgotten about myself until I read this post.