Hello all, I installed a new hot water system over the weekend which has a pair of temp monitoring ports. Keen to see what it was doing I grabbed one of the four new emontx3.4's I have here waiting to go into my work and do 3 phase monitoring to log the temps temporarily. I modified emonTxV3_4_RFM12B_DiscreteSampling so it would output the two DS18B20 sensors and powered the emon from 3 x AA batteries. It took me about 30 mins back and forth to get my code working, but once it was ready to go I noticed when I powered up the emon the red LED would simply stay on and not proceed past the POST phase in the debugging output. Thinking it may have been a problem with my code, I reloaded the original code and tried that with the same result. As it was late and I wanted to head to bed, I grabbed another emontx3.4 I had here, loaded in my modified code for the multiple temp inputs and it worked. Sweet, the other one's a problem for the morning I thought.
Well it worked for about 5 hours and then stopped transmitting. I hit reset on the unit and it hung at the red LED post sequence again. I did some debugging and it locks up at the rf12_initialize line. On closer inspection of my RFM12B module I noticed a pair of smt capacitors had literally blown off the board. I then had a look at the other one which died last night and it had the same caps failed in the same manner. I haven't looked over the schematics yet but I'm at a loss as to how this could happen. The only thing which *might* be relevant is when programming the board I left the batteries in when I plugged in the UART module. I've plugged in my 3rd unit and changed JP2 to open just in case that had anything to do with it which I doubt.
Any ideas? I've had a pair for emontx3.2's in service for months running 4 temp inputs with the code modified in the same manner without a single issue so I'm at a bit of a loss as to why these ones have failed. The pic attached tells the story...
Re: RFM12B capacitors blown on emontx3.4
What is the actual voltage on the 3.3 V supply?
Re: RFM12B capacitors blown on emontx3.4
Hi Brad,
Very sorry to hear your having trouble. Sounds like you have a faulty unit. Contact us at support@openenergymonitor.zendesk.com and we'll sort out a replacement. Please send the faulty unit back to us for inspection / repair. Very sorry for the hassle.
Re: RFM12B capacitors blown on emontx3.4
Hi Glyn,
I can understand striking an odd fault like this with one unit, but two? Possibly a component issue for the batch perhaps. Good news is the 3rd one which I installed this morning has been running without fault for over 12 hours now, the only thing I did different with this one was open JP2 which I can't see having any effect.
I've just taken a measurement of the 3.3v and 5v rails on both of the failed units:
I also took a voltage measurement across what's left of the pads on the two failed units. I read 3.3v across the pads where the rightmost capacitor on each one should be and 0v across the pads for the leftmost cap. These voltages are identical whether the unit is being powered by battery, the TTL to UART adaptor or with both connected at once. In addition to this, I also performed these tests with 2 x DS18B20 probes connected to be sure I was replicating the scenario under which the fault occurred with no change in observed voltages. I don't understand the cause of the failure based on the fact the voltages are in check, I'm pretty sure those SMT caps aren't polarized...
Given how cost prohibitive is is for us to ship aboard here in Australia (we get royally reamed) I would be happy to order the correct SMT components from Farnell/element14 and replace them myself if that's an option. If it is, could you please advise what values they are? Thanks.
Re: RFM12B capacitors blown on emontx3.4
I'm not sure how this could have happened, it could possibly be a physical issue where the capacitors have got knocked in transit. I'm not what the values of the capacitors are, one of the is 4.7nF according to this post http://jeelabs.org/2011/01/27/ook-reception-with-rfm12b-2/
How about initially I try sending you four capacitors salvaged from faulty units here in the lab to see if this fixes the problem?
Please email the support email address above to open a support ticket to make sure this gets resolved, forum posts often drop off my radar!
Re: RFM12B capacitors blown on emontx3.4
Hmm - that is catastrophic module abuse ! Scrap them - most unlikely only the caps were affected - they are caps, only accidentally surge protection diodes!.
To blow an SMD cap off like that, there was a major energy pulse on Vcc and/or GND.
I strongly suggest you review how this could have happened - it looks like a "mains" event to me....
Re: RFM12B capacitors blown on emontx3.4
Glyn - I'll create a support ticket now, I can imagine trying to manage support via the forum would be a nightmare, hence the reason you put systems in place like Zendesk :) -- I'm happy to fit those caps, when you send them please label them accordingly!
Emjay - these particular emon's have never been powered from an AC adaptor (yet), they were brand new out of the box, then only connected to the USB to UART adaptor for programming, then powered from 3 x AAA batteries (I didn't have any AA's handy at the time). When I saw the damage I was at a loss as to how it could have possibly happened with such meager power supplies! If I get the opportunity I'll borrow my macro lens back from my friend and take a *real* photo. There's none of the usual "let the magic smoke out" artifacts around the components, the damage looks physical yet I can't see how it could have happened as they were purchased as assembled units inside the extruded case. They were opened for inserting batteries and connecting the temp senders and reassembled. On close inspection the remainder of both boards are perfect; I'm at a loss as to how it could have happened.