Shiftregisters and lightning.
LA6WNA
Posts: 138
in Accessories
Hi all.
Long time since I`ve been writing something here, but I`m reading at the forum almost every day. Thought I could ask you guys if you have som experience with the shiftregisters, 74HC165 and 74HC595. I`m using those registers for inputs and outputs in my Propeller 1 controller for my hydro power station. Been running for about 3 years now, but almost everytime we have thunderstorms and lightning in the area, some of the shiftregisters brake down and has to be replaced.
I`m running the registers at 3,3v. At the 165-registers (inputs), all inputs are pulled up to 3,3v by 10k. Grounding the input = activate the input. All inputs are mainly from the switches in the front of the controller box, abt 0,7m cable.
At the 595-registers (outputs), each output goes to the base of a transistor (via 2k2) that drives the relay.
I`ve also sometimes seen broke transistor and relay coil afther a lightning stroke. But it seems like the registers itself brake down first.
So, my main question is: Do you know about similar shiftregisters (same funktion and layout) that can resist high voltage spikes better than the 74HC165 and 595 ?
I`ve attached the schematic for the project. (expressPCB)
Here is the link to the project: arnevik1.no/Kraftverket.htm
Maybe this is a dumb question at the forum, but I will appreciate some thoughts from you about what to do.
One strange thing; the main board with the Propeller onboard is never ruined by the lightning. It survive every time.
Long time since I`ve been writing something here, but I`m reading at the forum almost every day. Thought I could ask you guys if you have som experience with the shiftregisters, 74HC165 and 74HC595. I`m using those registers for inputs and outputs in my Propeller 1 controller for my hydro power station. Been running for about 3 years now, but almost everytime we have thunderstorms and lightning in the area, some of the shiftregisters brake down and has to be replaced.
I`m running the registers at 3,3v. At the 165-registers (inputs), all inputs are pulled up to 3,3v by 10k. Grounding the input = activate the input. All inputs are mainly from the switches in the front of the controller box, abt 0,7m cable.
At the 595-registers (outputs), each output goes to the base of a transistor (via 2k2) that drives the relay.
I`ve also sometimes seen broke transistor and relay coil afther a lightning stroke. But it seems like the registers itself brake down first.
So, my main question is: Do you know about similar shiftregisters (same funktion and layout) that can resist high voltage spikes better than the 74HC165 and 595 ?
I`ve attached the schematic for the project. (expressPCB)
Here is the link to the project: arnevik1.no/Kraftverket.htm
Maybe this is a dumb question at the forum, but I will appreciate some thoughts from you about what to do.
One strange thing; the main board with the Propeller onboard is never ruined by the lightning. It survive every time.
Comments
Hmm, if you have enough energy to kill multiple parts, it's unlikely any simple swap is going to help.
Serious Gas Discharge Arresters on the power(mains) side can also give a pathway, that is not via your electronics.
What do the relays switch ?
You may need to upgrade those to higher isolation voltages, if the energy is getting across them, as it sounds like it may be.
Or, if you cannot easily upgrade the relays, another way to gain isolation mm, is provide local floating coil power and drive via a Photorelay like TLP241 (5kV rated)
There are '595' variants like STPIC6D595,(/A595/B595/C595) which have 20V rated outputs, but they are open-drain pull downs.
Do you have both HC165 & HC595 failures, and on what pins ?
Also add TVS diode clamps and series R's and ferrite beads, and maybe change to shielded cable ?
Opto isolators can help break signal paths, but you still need to power things somehow...
In extreme discharge cases, I've even seen PCB changes to give a specific ground 'spark gap' type pathway, help diverts the energy from the more delicate stuff....
but best to do that as well as adding that external pathway...
Some relay switches 230v ac contactor coil current and some of them switches 12vDC LED`s etc.
Yes, both of them has failed. No spesific pins. It can differ from time to time. Always input or output pins that fails, never the data or clock pins. Seems like communication with the Prop still runs afther they fails. Just that ruined inputs or outputs don`t respond. I can say that cause I can see the state of all the inputs and the outputs in realtime at the monitor.
I`ve added some TVS diodes at certain Places , but not directly at the in/out pins at the registers. Maybe I should try that..??
Interesting. Maybe the TPIC6595 and 74HC597 are a little better than those I use? My system is also installed in a grounded metall Box. I also have the Power ground well Connected to Earth ground. No ground loops to measure. In the beginning, I didn`t have this connection and I had serious trouble With the communication between the cards. That`s never an issue afther I Connected PWR ground and Earth ground.
My system also runs at 12v battery With a constant charger from mains. Charger is at the type With transformer, so 230v AC and 12v DC are galvanic splitted.
My inputs and outputs Boards With the registers on, are Powered from the main processor Board. 3,3v (same as Prop) Powers the registers and 12v Powers the relays. All daughterboards (input, output, analog, voltage measure) are Connected to main Board through flat ribbon cables at abt 20cm.
Well, I Guess I have to investigate this Things futher on. In the meantime I`ll keep on buy cheap 74HC-registers from China. Anyway, its still meaningfull to hear what others has experied of Lightning / overvoltage troubble.
I am pretty sure the TPICs are quite a bit more rugged than the74HC595's are since they are used to drive solenoids and relay coils directly. Not as sure about the 74HC597's, although being a later design they might be a bit better.
Have to check out those registers that you use. I may build New input and output daughterboards for the system. The P1 Controls the powerstation very well when all Components are up running, so I`ll try some more to get the system as stable as possible. Won`t give up the P1, you know...
There are HEF4094, HEF4021 which are higher voltage, but I cannot find specific ESD ratings on those.
Is it usually the same pins ? ( if your sample size is large enough now
Series resistors on all pins, can help reduce the currents that do flow, usually the inputs can tolerate quite high values, & TVS clamps help too.
Do you have serious arresters on the mains-side, to a solid GND stake ?
However I don't think I've ever bothered to run shift registers over long distances except maybe once I ran a slow I2C over about 100 meters! (many many years ago)
The great thing about RS485 is that it is very simple and you can multidrop over long distances.
One question though. When you had lightning strikes that caused some circuit damage did you make note of the pins, chips, and boards that were damaged? That information may provide a clue as to where to modify the circuit. At the moment the only thing that I can add to the suggestions Peter and JMG made would be to add a good filter to the main power in to the cabinet.
as much capacitance as bandwidth dictates before that. Everything shielded into the box, ideally using
feed-through capacitors so its fully RF-tight.
Goes without saying full RF screening for all logic-level signals - lightning is not forgiving, like welders (in fact
if your circuitry survives close proximity to a welder that's an indication it will be robust to lightning discharge too
(within limits of course)