Hi All

Wondering if any of you has a similar experience.

My Sonoff pow r2 connected to my borehole pump, literally melted and caught fire. Pic below..

Ive had installed the sonoff about 7 months ago and was working great. Yesterday as the  pump started up, the device caught fire. The borehole pump runs at about 7 amps and about 1600w.

Is this because the borehole pump is a Inductive load? and the pow r2 cannot handle the inductive load?

P.S. i also have another pow r2 controlling my pool pump, should i remove it as the same thing could happen?

Is there any sonoff devices that do support an inductive load?

regards

Iceman

It's hard to say. It burned because something got hot, which usually means there was a high resistance somewhere in the path of the current. Normally I would expect a poor connection where the wires pushed into connectors, or the relay itself burned up (this could happen as repeated switching causes the contacts to carbon up and form a high resistance point).

As you probably know, since you referenced that it is an inductive load, induction motors needs 5 times (sometimes more) the nominal power when they start, so as much as 40A when it starts. Since the POW R2 has a 15A relay, this may well be the problem. If it is, I would expect a disassembly of the unit to confirm this: The relay should be totally melted while other pars further away may be less burnt up. Just from the picture, the terminals themselves looks fairly good, and the hole in the case seems to be right about where the relay is...

But I also see a somewhat bulky 10Ω resistor in that general area, and a fuse. It could be those too...

Edited July 24, 20205 yr by plonkster

It could also be the PCB tracks... then there'd be a hole burnt in the board itself.

Also, I just remembered (a bit slow some days) reading that some earlier 16A POW units were recalled because they could not handle the rated current. The Tasmota site mentions it, and they put something in their firmware so such devices can be used, but with a protection feature enabled:

https://tasmota.github.io/docs/devices/Sonoff-Pow/#self-protection-for-sonoff-pow

Maybe you had one of those.

Check out this thread, similar concerns.

https://powerforum.co.za/topic/3985-2kw-geyser-on-16a-sonoff/

You should use the sonof to close a larger relay or contactor.

upon further investigation, seems as if the neutral wire somehow came loose..

Could this be the cause?

26 minutes ago, DeepBass9 said:

You should use the sonof to close a larger relay or contactor.

Ideally yes, but then the power measurement facility (this is a POW unit) is lost.

Just now, Iiceman said:

upon further investigation, seems as if the neutral wire somehow came loose..

Could this be the cause?

Yes.

Just now, plonkster said:

Yes.

ahh ok cool, cause the neutal wire was not connected to the sonoff and also not burnt/damaged..

that would make sense, thanks Plonkster

3 hours ago, Iiceman said:

ahh ok cool, cause the neutal wire was not connected to the sonoff and also not burnt/damaged..

Mmmh, that is not what I understood. I thought the neutral wire was connected but loose, in other words made a poor connection. Since the neutral wire carries the same current as its live cousin, it is just as susceptible to electrical combustion. I don't see how the pump could have operated if the neutral wire was disconnected. So maybe it has something to do with it... but if it is not burnt, then probably it wasn't the starting cause.

10 hours ago, DeepBass9 said:

You should use the sonof to close a larger relay or contactor.

Anyone have an explanation of how to wire such a setup? Using a Basic Sonoff switch. I take it the relay/contactor replaces the CB?

That is the saddest sonoff i've ever seen

, 

On 2020/07/24 at 2:30 PM, plonkster said:

Mmmh, that is not what I understood. I thought the neutral wire was connected but loose, in other words made a poor connection. Since the neutral wire carries the same current as its live cousin, it is just as susceptible to electrical combustion. I don't see how the pump could have operated if the neutral wire was disconnected. So maybe it has something to do with it... but if it is not burnt, then probably it wasn't the starting cause.

Yes thats correct, sorry i didnt explain properly..

the neutral wire was connected initially, but after the device literally went up in smoke, i noticed the neutral was not connected anymore, and must have come loose at some point.

1 hour ago, Iiceman said:

noticed the neutral was not connected anymore

Well, I'm not a fire inspector and I don't know how possible it is anyway, but I would look at where it is the most melted, the most burnt, and try to see where it started. To my naked eye it seems to have started around the relay/fuse area (red arrow), that area seems more charred up than the wire connections (yellow circle). I can even see some clean copper on the blackest of those connections... which I would not expect if that part got very hot.

Just checked mine and it doesnt look like the pow R2 is fused. Judging by the position of burns its power supply input resistor. Perhaps it wasnt the loads fault..

@Weasel mine is the same as yours . No fuse

14 minutes ago, Chris Louw said:

@Weasel mine is the same as yours . No fuse

Maybe the 10Ω resistor doubles as a fuse.

I'm not kidding... this sort of thing is done to save a buck...

Look online, a while ago some people reviewed a Weller soldering station and went a bit ape about no fuse (like the old ones had), and Weller wasn't particularly worried... it's apparently perfectly safe to let the transformer's primary winding take the hit.

Oh yeah fair enough.  Its common practice non servicable "fuse" hehe. Nothing really too wrong with that imho. But a fuse fails reliably by contrast. My assumption earlier was that the first pows were fused? That would have been on the load side not to the power supply section. Just interesting. Im keen on testing mine, wondering what higher voltages would do to that because ive seen some horrible grid voltages here lately. 

If i had to guess the failure reason its either power supply isolation fail making the supply circuit over draw or most commonly and already discussed a loose connection. I dont like the push pin terminals, thats why i use the ferrules here. Gimme screws pls

Good afternoon all,

I would like to hook up a spare sonoff basic switch that I have got to by 1.5kw borehole, I have looked in vain for an ac relay capable of handling the draw of the borehole with no luck(I am in Zim hence the issue).

An electrician suggested I add an auxiliary contactor to the existing borehole contactor and use the sonoff to control the auxiliary which in turn controls the main contactor. I am not an electrician and the guys here are pretty basic but it did sound like it might be feasible however I wasn't going to go that route without getting some advise first hence me poaching on this post!

Please let me know if this is a stupid idea! Thank you

1 hour ago, Dougiedanger said:

add an auxiliary contactor to the existing borehole contactor and use the sonoff to control the auxiliary which in turn controls the main contactor

That is what the AC relay does, so yes this will work. 

A contactor is just a heavy-duty relay with higher current ratings (more used in electric motors)
As long as the power required to switch the contactor is within the limits of the Sonoff (plus some margin) you will be fine.
 

21 hours ago, Louisvdw said:

As long as the power required to switch the contactor is within the limits of the Sonoff (plus some margin) you will be fine.

Thanks Louis, is there a way of checking in advance of installation what that power required would be?

 

45 minutes ago, Dougiedanger said:

what that power required would be

That would be in the specs of the contactor. Look for something referring to the switching current. 

Had a sonoff running my pool pump... until the capacitor on the pool pump died... 10A relay, 15A breaker... no flames though, only killed the relay. Getting the dead relay out isn't difficult and replacing it with a big solid state relay is easy enough... makes the wiring a bit weird but it takes the sonoff out of the path of the current so probably the safer way round. (Also the bigger SSRs have a metal back for a heat sink... if you're really worried)

On 2020/07/28 at 7:20 PM, ___ said:

Maybe the 10Ω resistor doubles as a fuse.

I'm not kidding... this sort of thing is done to save a buck...

Look online, a while ago some people reviewed a Weller soldering station and went a bit ape about no fuse (like the old ones had), and Weller wasn't particularly worried... it's apparently perfectly safe to let the transformer's primary winding take the hit.

Yeh I think you are right my pow r2 just stop working and when I open it mine is also without fuse but I see that risistance is totally burned out . 

Can you do me a favour I want to know the value and type of that risistance so I can easily buy from the market.