Minder protection against lightning

Hi guys,

I need some additional info regarding the protection circuitry on the Minder.
We had quite a couple of lightning strikes lately and resultant damage to the systems.
Now we have a client who is trying to blame the product.
According to me the AC side should be ok seeing that it has the PSU in-line.
If the telephone side has a decent surge protector in-line would that be sufficient, and what protection is on-board? I suspect this to be the achilles heel.
I also would like to know what protection the inputs have on-board. What additional protection can be put on the inputs.
This particular system has irrigation valves connected to the outputs, and I suspect that the lightning entered through here. Any suggestions here?

Thanks
Hein

 

Lighting protection is always very difficult thing to do and get right.

Typical design parameter for lighting strike are allowance for about 50 kV at 50 kA, for about 50 us. Dats a tall order.

To get compliance tests to pass for telephone products always mean some kindof lightening / surge protection has to be on telephone lines inputs. So this is probably not place of entry for lightening.

Surge protection on mains is not always installed in any product. Is a good idea to add your own external surge protector. You can buy these in lots of retail outlets and electrronics stores and they cost only a few pesos.

Your problem is probably from the irrigation control. When lightening strikes the ground the big currents cause big voltage differentials to appear in the ground. Tis induces currents into buried cables (even cables buried inside steel pipes can be affected - I heard of co-ax ethernet systems being blown up by lightening strikes).

You probably need to add some MOVs or similar high voltage / breakdown device to those input. There are lots of device from different makers that will do a good job.