Fluctuating mains voltage tripping Shelly 1PM relay (I think)

[Russdl]

We have a Shelly 1PM controlling when our Sunamp charges, normally overnight.

 

On two separate occasions now it's turned itself off due to "overpower consumption detected" (as reported on the Shelly app and by email). I've check the resistance of the Sunamp immersion and it's 18 Ohms. I think that's 'normal'.

 

I checked the mains voltage in the wee small hours when it tripped out, and in the couple of minutes that I was monitoring it the voltage varied between 249.9 - 250.9V (it's now hovering around 248V).

 

The Shelly 1PM trips out at 3500W. If my Googling is correct, when the voltage hits 251V the Watts will exceed 3500 tripping off the Shelly. Does that sound about right?

 

I realise the DNO can pour 216.2 - 253V into the house and as we are right by the sub station we get the upper end of that range.

 

So, to the main question, is there a small voltage regulator out there that can control the voltage to the Sunamp or will I have to get rid of the Shelly?

 

Are there any other solutions?

[dpmiller]

A nice long mains cable that's *just barely* the right capacity might do the job...

[joth]

16A is a large load to thump through a poor little Shelly for sustained periods. I expect it heats up a bit, and that might alter it's over-power detection circuit too. And Shelly has over temperature as well as over voltage protection so even if you stay inside bounds on one the other might flip.

 

Most immersion controllers use a higher rated contactor. You can drive the input to that  from the Shelly.

https://www.screwfix.com/p/british-general-fortress-20a-dp-contactor-no/6654p

 

[Radian]

11 minutes ago, dpmiller said:

A nice long mains cable that's *just barely* the right capacity might do the job...

If it's right on the 3.5kW Sheely trip point, I'd want a 10% reduction in power to make it stick as a fix. That's about 10V drop across 0.75 Ohms, which at 13.3A is a dissipation of 133W. A length of mains cable dissipating that much heat wouldn't be pretty!

You need a different solution like a contactor or SSR.

[SteamyTea]

4 minutes ago, joth said:

Most immersion controllers use a higher rated contactor. You can drive the input to that  from the Shelly.

https://www.screwfix.com/p/british-general-fortress-20a-dp-contactor-no/6654p

 

3 minutes ago, Radian said:

You need a different solution like a contactor or SSR.

Yes, that makes more sense.

 

My cheap timers are rated at 16A, but when I looked inside, there were 20A replays.  Probably why they have lasted at least 13 years now.  They turn on the storage heaters and DHW to limit the E7 window to the last 4 hours.

[joth]

Are you wanting the energy monitoring function from the shelly too?

You could add a Shelly EM clamped on the contactor output side, and replace the 1PM with a basic Shelly 1 if you like. 

[Russdl]

47 minutes ago, dpmiller said:

A nice long mains cable that's *just barely* the right capacity might do the job...

 

Hmmm. Think I'll give that a miss, ta.

 

40 minutes ago, joth said:

16A is a large load to thump through a poor little Shelly for sustained periods. I expect it heats up a bit,

 

I guess it is, but it's been working fine for months, no 'overtemp' shutdowns, just the 'overpower' on a couple of occasions, but I've no idea how hot it gets.

 

I fitted it on a recommend from @PeterW, which I hope I didn't misinterpret?

 

[Russdl]

3 minutes ago, joth said:

Are you wanting the energy monitoring function from the shelly too?

 

I find it very useful, but not at all vital.

 

3 minutes ago, joth said:

You could add a Shelly EM clamped on the contactor output side, and replace the 1PM with a basic Shelly 1 if you like.

 

I don't understand what I'd be changing there as the Shelly 1 and 1PM are identical apart from the 'Power Monitoring' aren't they?

[joth]

14 minutes ago, Russdl said:

 

19 minutes ago, joth said:

You could add a Shelly EM clamped on the contactor output side, and replace the 1PM with a basic Shelly 1 if you like.

 

I don't understand what I'd be changing there as the Shelly 1 and 1PM are identical apart from the 'Power Monitoring' aren't they?

 

Yes, I think the Shelly 1 is a lot cheaper though so my comment was more if you had another use for the 1PM you can swap it out and replace with the cheaper unit.

 

 

17 minutes ago, Russdl said:

1 hour ago, joth said:

16A is a large load to thump through a poor little Shelly for sustained periods. I expect it heats up a bit,

 

I guess it is, but it's been working fine for months, no 'overtemp' shutdowns, just the 'overpower' on a couple of occasions, but I've no idea how hot it gets.

 

 

The extended time working makes this sound more likely. A relay has a mechanical switch that degrades over time (especially if turning on and off under high load) and as it wears it creates more resistance which will result in higher operating temperature. Also it will become more liable to electrical arcing which might trip the overpower component.

 

Another idea is open up the Shelly and see if the relay is replaceable, maybe with a higher rated one, but personally I'd always be a bit nervous running it exactly at its limit.

 

 

[Russdl]

@joth I think I'm getting it. Just for clarity, the Shelly replaced the timer in a fused, timed, spur.

 

The relay in the Sunamp controller which is downstream of the Shelly is doing the 'heavy lifting' as I see (and hear) it.  Does that change things?

[PeterW]

Sounds like your voltage / current is pushing the limits here - what does the power monitor show on the Shelly as max consumed power ..?

[Russdl]

@PeterW

 

This is a ‘normal’ days charging:

 

 

Below is Saturday, I woke up early to find that the Shelly had tripped off for ‘over power protection’ every time I turned it back on (via the app) the kW’s increased rapidly from 3.1 to 3.5 at which point it tripped off. The same happened a bit later in the day until it finally stayed on to complete the charge:

 

 

it’s back on now, supply voltage is 248.6V and the Shelly is registering 3.4kWh

[tonyshouse]

I would report the high voltage to the DNO 

 

have had problems on both solar and hydro and both DNO tapped down the voltage on their transformers 

[Russdl]

3 minutes ago, tonyshouse said:

 

I would report the high voltage to the DNO

 

I did that a while ago as my PV was occasionally tripping out and the advice was that a high mains voltage may be causing it.
 

DNO did a week long survey which showed it was high but within limits, the limit being 253V. They told me that if they wound it down for me there would be problems with low voltage at the other end of the line. In a nutshell, I think I’m stuck with the high voltage. 

[joth]

4 hours ago, Russdl said:

it’s back on now, supply voltage is 248.6V and the Shelly is registering 3.4kWh

Partway through there you jumped from talking about kW to kWh. Which do you mean?

 

The line graphs don't help explain much as they are (non accumulating) kWh against time which is mathematically befuddled

 

[SteamyTea]

1 minute ago, joth said:

The line graphs don't help explain much as they are (non accumulating) kWh against time which is mathematically befuddled

CUMSUM is needed.

@pocster claims it is terrific fun.

[Russdl]

58 minutes ago, joth said:

Partway through there you jumped from talking about kW to kWh. Which do you mean?

 

I think I meant kW. 

 

My understanding of the line graphs is that you can see how much power was being consumed at a point in time  and underneath the x axis it shows how much power was consumed in total. 

[Temp]

Not sure if this is relevant but others have had similar issue even with no load. Firmware change mentioned. 

 

https://www.shelly-support.eu/forum/index.php?thread/4446-shelly-plug-overpower-issue-without-load/

 

 

[Russdl]

@Temp thanks very much

for Posting that, much appreciated. 
 

My issue differs to the majority of those posted in that mine has tripped under load, and the firmware is up to date.
 

I’m fairly confident that my issue is caused by my high incoming mains voltage, so I’ll either have to junk the Shelly or get a big old drum of cable as suggested by @dpmiller

 

Neither option appeals!