Blowing Lemons

[alexc]

Hi Guys,

I wonder if you can help me.... I've managed to blow 2 Lemon RXs in the past few days.... The first one that blew I though I had just shorted on a piece of metal on the bot, however when I plugged the replacement one in, it blew straight away too and it deffo wasn't anywhere near anything that could short it.

After thinking about this, I realise this has happened after I fully charged my 4C Lipo for the 1st time ever, I guess previous times I've just charged it to approx 90% (maybe not even 90% - i was concerned about setting it on fire), but this time I decided to fully charge it.

After blowing the 2nd Lemon, I started checking and discovered that the battery is actually giving out 16.8v so I guess that's what caused them to blow as the listed operating range is only 3.4 to 8.4v...... but I had also assumed that the ESCs (the Botbitz 30a ESCs) would only put out a 5v supply to the Rx, not the full 16.8v, but when I checked this tonight I discovered it's 16.8v at the Rx too. Is this the correct behaviour from the ESCs? and if so, how do you guys prevent fully charged 4C Lipos blowing the RXs?

Any advise would be greatly appreciated.

Cheers,

Alex

[daveimi]

I've done the same thing, cut one of the power lines to the lemon. The signal cable from esc to rx is three cables, positive, negative and signal. You have two lots of power going to the lemon and it blows. i did the same thing, wasn't until i posted that someone mentioned it. Wish i had known to be honest, at the time there was nothing in the literature of the esc that mentioned this.

[alexc]

Thanks Dave, I'll defo snip the +ve & -ve cables from one of the ESCs going forward, but when I plugged in the replacement Lemon tonight, I only connected one ESC (just in case that was the issue) and it blew the second I switched the power on. It was at that point I decided to dig out the voltmeter and see what the power was at different points.

I've been looking at the specs of the ESC tonight on the BotBitz website and it says.....

Voltage: 6V to 24V
Amperage: 30A
Dimensions: 50mm x 30mm x 10mm
Weight: 15g
BEC: 5v @ 1A (Switch Mode)

I'm guessing the BEC is the signal cable, so does anyone know if there is anything wrong with these ESCs as they are passing the full 16v down the signal cable?

Cheers,

Alex

[daveimi]

Oh right, erm not sure then. Yeah, be careful what you cut, hopefully someone can jump in here as it's a while since i did it. i can't remember whether it's positive or negative that needs to be cut as the signal cable uses one as a comparative for the signal. I had a load of this sort of trouble using two separate speedo's so moved to one big duel controller and haven't looked back.

[RogueTwoRobots]

Generally when plugging two ESCs into a receiver that both have BECs, I just remove the +ve wire from one of the connectors and tape it up out of harm's way. As the specs state, they should only be supplying 5V down the wires to the receiver so if you're getting 16.8V at it, there may be a problem with the ESC, but that sort of fault isn't a common occurrence as far as I'm aware. Have you got/are you able to get a picture of the way you've got it all connected, just to see if we can spot anything untoward?

[alexc]

Hi Jamie... I have done a diagram (figured this would be clearer than a picture)....

Robot_Wiring.jpg

I don't think this will be a wiring problem though, as it's been wired up like this for several months and has been fine (although still best to check there isn't some fault in my logic), and all connectors are XT60 so unlikely to have been plugged up incorrectly after the battery charge.

Cheers,

Alex

[Pinski1]

Both BotBitz in that picture are supplying ~5V to the LemonRX, this could cause it to blow up. Ideally you'd remove the red wire from one of the ESCs so it's only getting power from one.