Hello folks

So we have a little airbnb cottage we rent out. It's got an extension cord in there that is connect to our small 1000w inverter. We have tried to tell our guests please not to plug heaters or hair dryers into the extension cord as our inverter shits itself each time. 

Im worried it soon might just call it a. Day on us and then we are all screwed. 

In saying this is there a device where one can set a max wattage (say 600w or 1000w) and then shuts off when it hits that. Itss gotta be quick enough before my very quick inverter notices something. 

It's a real pain having to drive home to turn on and off my inverter each time.

I have home assistant. 

No I don't have the money to buy a bigger inverter. 

 

Many thanks 🤙 

Edited June 13, 20233 yr by sunset1

A 3A or 5A circuit breaker on the that Extension cord could be a safeguard of sorts. 
https://leroymerlin.co.za/acdc-circuit-breaker-1-pole-c-curve-4-5ka-3a

1 hour ago, sunset1 said:

Itss gotta be quick enough before my very quick inverter notices something. 

The problem with a breaker is that the inverter needs to ramp up the output to the max before the breaker will kick out, leaving it revving in the red and then suddenly the load disappears. Surely this is not good for the inverter as that energy needs to go somewhere. One of these days it will convert that energy into the magic smoke that makes the inverter work.

I would say you are probably better off just putting the lights and the WIFI on this backed up circuit. If you can see where you go and have wifi then loadshedding isn't that bad

 

37 minutes ago, iiznh said:

The problem with a breaker is that the inverter needs to ramp up the output to the max before the breaker will kick out, leaving it revving in the red and then suddenly the load disappears. Surely this is not good for the inverter as that energy needs to go somewhere. One of these days it will convert that energy into the magic smoke that makes the inverter work.

I would say you are probably better off just putting the lights and the WIFI on this backed up circuit. If you can see where you go and have wifi then loadshedding isn't that bad

 

Use a dedicated socket with dedicated 3 pin plugs so nothing else would be abled to be plugged in. You get the sockets in surface mount so no chasing necessary.

 

Edited June 13, 20233 yr by TaliaB

On 2023/06/13 at 9:56 PM, iiznh said:

The problem with a breaker is that the inverter needs to ramp up the output to the max before the breaker will kick out, leaving it revving in the red and then suddenly the load disappears. Surely this is not good for the inverter as that energy needs to go somewhere. One of these days it will convert that energy into the magic smoke that makes the inverter work.

I would say you are probably better off just putting the lights and the WIFI on this backed up circuit. If you can see where you go and have wifi then loadshedding isn't that bad

 

Is this not the same thing as just turning an appliance off? 

4 minutes ago, sunset1 said:

Is this not the same thing as just turning an appliance off?

Not if the load is 2KW and your inverter is rated at 1KW, it will probably overload for a couple of miliseconds till the protection kicks in.

The heat generated in those couple of milliseconds could cause the weakest mosfet to blow, leading to a cascade effect. 

With cheap inverters there is no telling how much abuse it will take. 

On 2023/06/13 at 9:56 PM, iiznh said:

The problem with a breaker is that the inverter needs to ramp up the output to the max before the breaker will kick out, leaving it revving in the red and then suddenly the load disappears. Surely this is not good for the inverter as that energy needs to go somewhere. One of these days it will convert that energy into the magic smoke that makes the inverter work.

I would say you are probably better off just putting the lights and the WIFI on this backed up circuit. If you can see where you go and have wifi then loadshedding isn't that bad

 

Surely the breaker will trip the load  before it reaches the inverter? Thank you 

17 minutes ago, sunset1 said:

Surely the breaker will trip the load  before it reaches the inverter? Thank you 

A breaker is a electro-mechanical device, meaning a high current needs to flow (for a certain amount of time) first before it can action a mechanical movement that will disconnect the contact point. Current is instant whereas the breaker will have several (hundreds) of milliseconds before the current is interrupted. So it is impossible for the breaker to trip before the load reaches the inverter. 

25 minutes ago, iiznh said:

A breaker is a electro-mechanical device, meaning a high current needs to flow (for a certain amount of time) first before it can action a mechanical movement that will disconnect the contact point. Current is instant whereas the breaker will have several (hundreds) of milliseconds before the current is interrupted. So it is impossible for the breaker to trip before the load reaches the inverter. 

Thanks for the info. 

Sheesh wondering how I can solve this issue. 

The thing is the inverter is simply on an extension cord so that the guests can also plug the cellphones and laptops into during load shedding. 

I'd like to offer them this service without blowing up my inverter. 

I can go the red plug route but they need regular sockets for their devices. 

 

36 minutes ago, sunset1 said:

Thanks for the info. 

Sheesh wondering how I can solve this issue. 

The thing is the inverter is simply on an extension cord so that the guests can also plug the cellphones and laptops into during load shedding. 

I'd like to offer them this service without blowing up my inverter. 

I can go the red plug route but they need regular sockets for their devices. 

 

You can also use fuses as they blow much faster than an circuit breaker. Keep a few spare. At the 3-5A level you can use 5x20mm fuses as well at R2 a pop. Much cheaper than replacing an inverter. 

8 minutes ago, Scorp007 said:

You can also use fuses as they blow much faster than an circuit breaker. Keep a few spare. At the 3-5A level you can use 5x20mm fuses as well at R2 a pop. Much cheaper than replacing an inverter. 

Thanks! lol yeah a lot cheaper! 

Will be doing this. 

2 hours ago, sunset1 said:

I can go the red plug route but they need regular sockets for their devices.

You could suppy the apartment with dedicated plugs (or a dedicated multipug) as well as dedicated power cables that can connect to for example a laptop charger.

https://www.geewiz.co.za/power-leads/23397-8m-dedicated-clover-power-cord.html?sfdr_ptcid=2961_617_13189049&sfdr_hash=0a8c3f5a8fc0176042bd7ca8dd1fe9d1&gclid=CjwKCAjwkLCkBhA9EiwAka9QRnKF8FnxZxH9aDEpbHfHx3m_ZzqsViKAodrxLaF266o6sgFJtGpF0hoCIswQAvD_BwE

Or the figure of 8 type cable for that matter.

 

With maybe a USB charging hub like this one, where you swap the 2-prong pug for a dedicated red plug. Basically this

https://www.takealot.com/5-port-usb-adapter-20w-4a-travel-wall-rapid-charger-station-hub/PLID71034418?gclid=CjwKCAjwkLCkBhA9EiwAka9QRtL2wnylPiDBGd5lxsdSS6row2Oxwxxqhf2iqpWO2v8jbFvjcZgIYBoCoW4QAvD_BwE&gclsrc=aw.ds

and this

https://www.glolighting.co.za/eurolux-ep29k-plug-top-16a-dedicated-red-solid-pin.html?gclid=CjwKCAjwkLCkBhA9EiwAka9QRiuTn4yBk4-v8uQURJHy0RJ2hzrGK6QOBEU8kJzuYPYc3TawTxugOxoCaBcQAvD_BwE

 

Edited June 16, 20233 yr by GreenFields

Another option can be an active current monitoring device where you can set the exact amps you don't want exceeded.

It automatically reconnects the load after some seconds that one can program as well

These are able to monitor current and voltage. I use them to monitor the Eskom line voltage

In your case setting it to 3A would do the trick and it would reset itself without you having to manually do anything.

I have a feeling your inverter might be modified sine and not pure sine wave so I don't know how these would perform in that case

 

4 minutes ago, MiG said:

It automatically reconnects the load after some seconds that one can program as well

Can you configure it to NOT automatically attempt reconnect after overload, ie. forcing you to manually reset? 

23 hours ago, iiznh said:

A breaker is a electro-mechanical device, meaning a high current needs to flow (for a certain amount of time) first before it can action a mechanical movement that will disconnect the contact point. Current is instant whereas the breaker will have several (hundreds) of milliseconds before the current is interrupted. So it is impossible for the breaker to trip before the load reaches the inverter. 

Correct, but actually much worse.  CBs have B- C- D- curve ratings.  As far as I know domestic CBs in SA are all C-curve (correct me if I am wrong).  A C-curve rated CB will only trip at 5 to 10 times the rated current.  See here: https://www.se.com/au/en/faqs/FA290880/

Here is what you do - an expanded idea based on @Scorp007 fuse idea.

You provide TWO standard outlets EACH being fitted with a 2A fuse.  You tell your visitors NOT to plug in anything more than 300W.  Obviously many will not listen and blow one fuse.  They then have a second plug that still works.  If they still don't get the message and blow the 2nd fuse, then they deserve to sit in the dark.  This way you don't need to come out to your BB every time it trips as there is a backup.  Once your visitors have left, you just check if both fuses are still OK.

50 minutes ago, Modina said:

Correct, but actually much worse.  CBs have B- C- D- curve ratings.  As far as I know domestic CBs in SA are all C-curve (correct me if I am wrong).  A C-curve rated CB will only trip at 5 to 10 times the rated current.  See here: https://www.se.com/au/en/faqs/FA290880/

Here is what you do - an expanded idea based on @Scorp007 fuse idea.

You provide TWO standard outlets EACH being fitted with a 2A fuse.  You tell your visitors NOT to plug in anything more than 300W.  Obviously many will not listen and blow one fuse.  They then have a second plug that still works.  If they still don't get the message and blow the 2nd fuse, then they deserve to sit in the dark.  This way you don't need to come out to your BB every time it trips as there is a backup.  Once your visitors have left, you just check if both fuses are still OK.

There was a time that I did use the curves to select MCBs. All I can say the 5 to 10 times current before they (AC) would trip is totally out of line. You have to introduce time in the tripping time. If not then it is because the old MCBs I have tested just had far superior curves than modern units. 

Edited June 17, 20233 yr by Scorp007

1 hour ago, BritishRacingGreen said:

Can you configure it to NOT automatically attempt reconnect after overload, ie. forcing you to manually reset? 

Hmm I doubt it and the instructions don't show this either

24 minutes ago, Modina said:

Correct, but actually much worse.  CBs have B- C- D- curve ratings.  As far as I know domestic CBs in SA are all C-curve (correct me if I am wrong).  A C-curve rated CB will only trip at 5 to 10 times the rated current.  See here: https://www.se.com/au/en/faqs/FA290880/

Here is what you do - an expanded idea based on @Scorp007 fuse idea.

You provide TWO standard outlets EACH being fitted with a 2A fuse.  You tell your visitors NOT to plug in anything more than 300W.  Obviously many will not listen and blow one fuse.  They then have a second plug that still works.  If they still don't get the message and blow the 2nd fuse, then they deserve to sit in the dark.  This way you don't need to come out to your BB every time it trips as there is a backup.  Once your visitors have left, you just check if both fuses are still OK.

The fuses sound like a cost effective way to go. Plug idea is great. 

Regarding the fuse holder. Im guessing this is fitted into the live (brown) wire and the neutral (blue)? 

Another thing apparently one can use DC fuses on ac electricity. (However not ac fuses on DC). In saying that would one be OK with using 2-3amp DC fuses from the car shop? 

1 hour ago, MiG said:

Another option can be an active current monitoring device where you can set the exact amps you don't want exceeded.

It automatically reconnects the load after some seconds that one can program as well

These are able to monitor current and voltage. I use them to monitor the Eskom line voltage

In your case setting it to 3A would do the trick and it would reset itself without you having to manually do anything.

I have a feeling your inverter might be modified sine and not pure sine wave so I don't know how these would perform in that case

 

See @iiznh post further up. From my understanding breakers don't act fast enough? So loads would hit the inverter before the breaker has time to react 

The ECU(energy control unit)could have worked but the lowest you get is 5 amp you need a 4 amp for the 1000w inverter you using. I use these units if clients have underfloor heating with electric stoves + 2 geysers you often exceed 60 amps.

https://www.livecopper-cbionline.co.za/products/cbi-energy-control-unit-electronic

2 hours ago, MiG said:

Another option can be an active current monitoring device where you can set the exact amps you don't want exceeded.

It automatically reconnects the load after some seconds that one can program as well

These are able to monitor current and voltage. I use them to monitor the Eskom line voltage

In your case setting it to 3A would do the trick and it would reset itself without you having to manually do anything.

I have a feeling your inverter might be modified sine and not pure sine wave so I don't know how these would perform in that case

 

The CBI Astute Smart Controler can also be set to disconnect exceeding set loads. It alows to set a delay time form startup loads. Restart time can also be set.

Sonoff pow can also be set to switch off when exceeds set load. It does not have the time delay or restart.

1 hour ago, Chris Louw said:

The CBI Astute Smart Controler can also be set to disconnect exceeding set loads. It alows to set a delay time form startup loads. Restart time can also be set.

Sonoff pow can also be set to switch off when exceeds set load. It does not have the time delay or restart.

If fuses are not OK then this is a more expensive way to go and it adds the ability to switch on via remote. 

I have been using the OPS function present in the Sonoff Powr2. I haven't tested below 0.5A but it might work as low as 0.1A if 0.5A is accepted. 

You can also use power as the trigger point. 

@BritishRacingGreen

Edited June 17, 20233 yr by Scorp007

1 hour ago, Scorp007 said:

If fuses are not OK then this is a more expensive way to go and it adds the ability to switch on via remote. 

I have been using the OPS function present in the Sonoff Powr2. I haven't tested below 0.5A but it might work as low as 0.1A if 0.5A is accepted. 

You can also use power as the trigger point. 

I looked at the cbi the other day, looks to have great features. but maybe ill implement this later on.

with the OPS function on the Sonoff Power2 would this cut off the load before it reaches the inverter. I have home assistant so can also do this route perhaps also later on

 

53 minutes ago, sunset1 said:

I looked at the cbi the other day, looks to have great features. but maybe ill implement this later on.

with the OPS function on the Sonoff Power2 would this cut off the load before it reaches the inverter. I have home assistant so can also do this route perhaps also later on

 

The moment it measures a value higher than the set point it will switch off. This is typical about 2 seconds. Well below the time the inverter would take to trip on overload. 

4 hours ago, Scorp007 said:

There was a time that I did use the curves to select MCBs. All I can say the 5 to 10 times current before they (AC) would trip is totally out of line. You have to introduce time in the tripping time. If not then it is because the old MCBs I have tested just had far superior curves than modern units. 

MCBs have two trip mechanisms.  One magnetic and one thermal.  The magnetic one is instantaneous (well as fast as a mechanical contraption can be) and it will act on a massive over-current.

The thermal trip is intended for loads that are slightly over the rating.  This could take up to a few minutes to trip, depending on how far over the limit the current goes.  Being an electro-mechanical assembly there are tolerances and even the ambient temperature will have an bearing on how long it would take to trip thermally.

You do not want a 5A MCB to trip at 5.5A or even at 7A.  This would trigger nuisance trips due to in-rush currents.