Un-usual 3 phase problem

[needasparks]

Hi guys, I have an un-usual problem that i can't seem to economically solve for a client so i need some input for ideas if you can.

Situation is i need to be able to coin operate a three phase supply which controls heaters.

This has upto now been done with a single phase credit meter on one of the load phases controlling a contactor which in turn operates a three phase DB with all single phase heaters on, this was fine as meter was turned up to take into account of other phase loadings, simples.

Now the situation is clever buggers have worked out if they turn off the heaters on the controlling phase the others are free thankyou very much :lol:
Am after a cheap solution but they don't make a 3 phase coin meter so looks to be down the electronic route any ideas.

 

[johnboy6083]

could you not ensure that each switch for the heaters is 3 pole, and that you can only turn on a set of heaters at a time, rather than individualy.

 

[Knobhead]

Nice idea, but each heater needs a local point of isolation.

Got admire them, an ingenious money saving scam.

 

[Deleted member 26818]

The only options I can think of, is either a 3 phase coin meter, or 3 single phase coin meters.

 

[needasparks]

could you not ensure that each switch for the heaters is 3 pole, and that you can only turn on a set of heaters at a time, rather than individualy.

Still thinking on that one JB, but if the load on that phase goes it will still happen. There are 8 heaters run in pairs North/south/east/west so difficult as at least 2 would still be on a phase etc. I can see where your going though, many thanks.

 

[needasparks]

Nice idea, but each heater needs a local point of isolation.

Got admire them, an ingenious money saving scam.

Yes that is the problem, each can be switched, never thought of it until i was asked why the meter always had credit on it. yes clever.

The only options I can think of, is either a 3 phase coin meter, or 3 single phase coin meters.

Thats the problem, no-one makes a 3 phase coin or credit meter. Possibly three separate meters may be only solution but will make it complicated for them.

 

[Silly Sausage]

Interesting problem!

After banging my head against the wall for a while, how about this, put the meter on the neutral associated with these 3 phases only??? Probably needs more thought.

edit

probably a very dangerous way of doing it!
The heaters would still be live when the meter disconnects the neutral.

 

[needasparks]

Interesting problem!

After banging my head against the wall for a while, how about this, put the meter on the neutral associated with these 3 phases only??? Probably needs more thought.

Lol. yes it seemed an easy problem to fix until i gave it myself more thought.

Mmmm not sure about reversing the polarity on the meter though as neutral is linked and only switches live output.

 

[Knobhead]

There is a way around it but you may not like it. It needs a 2[SUP]nd[/SUP] contactor and a current sensor.

View attachment 8176

 

[Darkwood]

not ever heard of 3ph coin meter but you can get prepaid polyphase card meters but as goes the best prepaid card system you may have to ask around, and if i recall your not allow to make a profit from it if its domestic so be careful when setting the tarriffs.

 

[Darkwood]

There is a way around it but you may not like it. It needs a 2[SUP]nd[/SUP] contactor and a current sensor.

View attachment 8176

Although it will work they only need to have a 1 heater on monitored phase and leave off the majority and landlord out of pocket again. There is no way of monitoring the total usage and can be easily abused and if you set current monitor to only come on with all heater loads on then what happens if heater goes faulty or they dont want them all on then it wont pull contactor in, he would find himself in a awkward position if the heating refused to work in the middle of winter just because the tenant wanted to save money and only put a few on.

 

[Knobhead]

Just read Archy's thread, it's given me an idea but I need to know the total loading and the switch rating of the meter.

 

[Darkwood]

Il stick with my previous post a simple meter change to a prepaid card polyphase meter and as i said before only bit of homework to do is which card payment system is the best but i assume you can get the ones that can be topped up at the post office etc.

 

[needasparks]

There is a way around it but you may not like it. It needs a 2[SUP]nd[/SUP] contactor and a current sensor.

View attachment 8176

Thanks Tony, I was on my 3rd sheet of paper.
I see the current drops the contactor but the coin meter still won't be monitoring total load.
The problem is the heaters are sometimes required in different areas at different times so this would lead to certain ones always being used to get others to work. Been looking at smart metering but not much info on web so may ring RDL on monday see what they can come up with.

 

[Darkwood]

Interesting problem!

After banging my head against the wall for a while, how about this, put the meter on the neutral associated with these 3 phases only??? Probably needs more thought.

edit

probably a very dangerous way of doing it!
The heaters would still be live when the meter disconnects the neutral.

EEEK!... you would create a star point on the neutral bar and send 415v through all the system.

 

[needasparks]

Just read Archy's thread, it's given me an idea but I need to know the total loading and the switch rating of the meter.

I'm all ears.

total of eight heaters 3kw a pop spread across the phases (slightly out) with one phase on standard 100amp coin meter. operating a 100amp 240v 3 pole contactor cutting feed side to ryb to DB.

 

[needasparks]

EEEK!... you would create a star point on the neutral bar and send 415v through all the system.

No because it controls a contactor not the load.

 

[needasparks]

Interesting problem!

After banging my head against the wall for a while, how about this, put the meter on the neutral associated with these 3 phases only??? Probably needs more thought.

edit

probably a very dangerous way of doing it!
The heaters would still be live when the meter disconnects the neutral.

The neutral would be phase shifted on the load anyway

 

[Knobhead]

I drew it out and then chucked it in a computerised waste bin.

I’ve got to admit it’s one of the more interesting problems.

Now if we had a budget of £*** then it could be fun.

 

[needasparks]

I drew it out and then chucked it in a computerised waste bin.

I’ve got to admit it’s one of the more interesting problems.

Now if we had a budget of £*** then it could be fun.

PMSL, i got to agree. Have i found an un-answerable question. Gonna sleep on it and check back later.

 

[Nolnoc]

Was the coin meter ever actually ever monitoring all three phases.From what I can make of it it wasn't.Maybe I've lost the plot.Please keep us informed,interested in this one.

 

[needasparks]

Was the coin meter ever actually ever monitoring all three phases.From what I can make of it it wasn't.Maybe I've lost the plot.Please keep us informed,interested in this one.

No was only ever on one phase, been in service for about 30 years. was always assumed all heaters would be used so tarrif on coin meter was turned up taking into account other phases so money put in covered the cost used, all was happy all this time then people using the heaters started turning off some of the heaters and come across the fact their money did not run out when certain ones were turned off. What i should have explained and i missed in my first post was that this is a hall used by the public for hire, hence it being a coin meter as no other form of payment would be any good. Different people use the hall for different things so now not all heaters in all locations are used. its only recently the penny dropped so to speak on the problem that the electricity used over the last 12 months was totally different from the takings of the meter. It was so obvious but no-one picked up on it well apart from some regular userswho i guess have been keeping quiet on finding it out.

 

[Darkwood]

There is a way but its not cheap and you will have to build it all from scratch and programme it, you need a multi-function energy meter, plc, coin slot with reconition system. Your energy over three phase is monitored and run through a plc which you write the software to convert the coins input into killowatts allowed which then will countdown but first because this is just a idea i would talk to technical of the link supplied and see if the meter can give said info to plc http://docs-europe.electrocomponents.com/webdocs/0e36/0900766b80e364a3.pdf

I use plc's in machine control so cant see why this cant be done it all depends on the meter giving a readable output for energy used to plc.
The link shows a monitoring system that can control outputs such as contactor looks like you get software with it but as i said a chat with technical will be needed first explain what you need etc and let them do the thinking.

 

[Silly Sausage]

EEEK!... you would create a star point on the neutral bar and send 415v through all the system.

Haha...hence my comment of more thought required!

 

[ipf]

Was the coin meter ever actually ever monitoring all three phases.From what I can make of it it wasn't.Maybe I've lost the plot.Please keep us informed,interested in this one.

Started reading not long ago and I was thinking along the same lines. Head scratching. Fair assumption that all the heaters would be used all the time. Depending on for how long, how much more has been paid than should have been, prior to someone having an economical brainwave?

 

[Knobhead]

This is something you should read http://www.ofgem.gov.uk/Consumers/Pages/Resaleofgasandelectricity.aspx

 

[darcy]

Pondering this one...

 

[Darkwood]

Well its time to pop to the beerhole and im going in the mind that ive given a solution albiet expensive, i can now have a drink and peace of mind that i havent been beaten by what seemed a simple question to start with
arty:

 

[needasparks]

That was the only option Darkwood i thought would be open to me, other than using 3 separate meters. There is always the option of multiple coin timers on contactors but then you run the risk of overpaying. However the heaters can be split into 4 areas so limits turning off locally. Time could then be calculated by the KW per coin.

IPF, it has only ever been measuring 6kw (2 x heaters) so cant over charge. only ever under charged when any are turned off.

Biggest job i have is trying to explain the options available to the client, if we are struggling to get our heads round it this then they need to sit down for a while.

 

[ipf]

Fair enough. But something is wrong. Maybe it was the easiest way out without causing problems? For a while at least!

 

[ipf]

That was the only option Darkwood i thought would be open to me, other than using 3 separate meters. There is always the option of multiple coin timers on contactors but then you run the risk of overpaying. However the heaters can be split into 4 areas so limits turning off locally. Time could then be calculated by the KW per coin.

IPF, it has only ever been measuring 6kw (2 x heaters) so cant over charge. only ever under charged when any are turned off.

Biggest job i have is trying to explain the options available to the client, if we are struggling to get our heads round it this then they need to sit down for a while.

Sorry if I misunderstood NEEDA, I thought you meant the tarrif had been adjusted. Not my area really. Too much thought maybe.

 

[needasparks]

I guess your correct, 30 years ago no one dreamed any of the heaters would be turned off and assumed full load but people now want it in all the colours and all the sizes with a cherry on top.

Its rum o'clock so as said gonna sleep on it.

 

[needasparks]

I like your thinking! Something like this maybe?
View attachment 8185

I wish it was that easy, Thats the part that wont work as neutral is at unity on three phase resistive load.
Think about it, if each phase runs 100amps would you have 300 amps on the neutral. 120 deg blah, blah blah.

 

[Kamikaze]

Interesting problem!

After banging my head against the wall for a while, how about this, put the meter on the neutral associated with these 3 phases only??? Probably needs more thought.

edit

probably a very dangerous way of doing it!
The heaters would still be live when the meter disconnects the neutral.

I like your thinking! Something like this maybe?

 

[ufkir]

why not work out what you get for a £1 lets say its an hour then wire from the load side of the meter to a timer thats set to give you an hour when energised and make the timer control your contactor so that it dosnt matter which heaters they turn off they only get one hour. one prob is that if they put in £3 at once they wont get 3hours unless you can adjust the meter.

 

[Knobhead]

I like your thinking! Something like this maybe?

View attachment 8189

Sorry kid that was the idea I dumped. Look in to how vector currents in the neutral work.

In = √((L1²+ L2²+ L3²)-((L1*L2)+(L1*L3)+(L2*L3)))

 

[Kamikaze]

It’s that Kirchhoff putting a spanner in the works again….lol. More thought required on this one, but I’m determined a creative solution is better than an expensive one. Back to the drawing board!

 

[malcolmsanford]

The obvious way for me is not to try and change a system that's worked for 30 yrs but to try and stop the people switching the heaters off, how are they doing this?

If there is a simple switch FCU they are activating remove the FCU and replace with a double pole keyswitch and if needed series a fuse holder into it on a grid arrangement. Or just enclose the FCU in a lockable enclosure.

If they are switching off from the equipment then bypass the switch on the equipment and utilize as above. If certain units are not needed then again on request the owner/caretaker can isolate them.

Would this work

 

[Kamikaze]

Just a timer coin meter which switches the coil on a 3 phase contactor would be the most sensible idea.

 

[Knobhead]

Just a timer coin meter which switches the coil on a 3 phase contactor would be the most sensible idea.

But not legal see #26

 

[alli]

I'd be sneaky and put the meter on a different phase and tell everybody who'll listen that you have changed the system to stop people having free electric, even though it is a load of crock! Then when they turn off the radiators they think use the money. They still be charged. HeHe

 

[ipf]

Rotate the control phase on a regular basis? If legal (#26). Wont solve it completely but will certainly put a spanner in the mix. I think ?

 

[Knobhead]

If any alterations are made they have to comply with http://www.ofgem.gov.uk/Consumers/Pages/Resaleofgasandelectricity.aspx
I’m surprised the landlord hasn’t ended up in court all ready.

The maximum amount landlords or “resellers” are permitted to charge for gas or electricity is the amount they have paid for it, plus VAT at the appropriate rate; this is termed the Maximum Resale Price or MRP. Any standing charges can be recovered by the Landlord by dividing it on a pro-rata basis according to usage between all the tenants.

 

[ipf]

Tony, I,ve a client who is splitting an old works into a couple of ind. units with individual office units upstairs. Your info leads me to believe that each office would have to be metered individually to comply. Correct? He intends to include costs in rent which would be approx not exact.

 

[HandySparks]

The OP says that this is a hall used by the public for hire. According to the "Guidance for Resellers" document, the rules only apply when the electricity is for domestic use.

I would just fit a coin operated timer and contactor. Maybe add a notice that heat is charged on a timed basis only, irrespective of the number of heaters actually switched on.

 

[Knobhead]

Tony, I,ve a client who is splitting an old works into a couple of ind. units with individual office units upstairs. Your info leads me to believe that each office would have to be metered individually to comply. Correct? He intends to include costs in rent which would be approx not exact.

Start this as a new thread, otherwise

View attachment 8194

 

[needasparks]

Well this thread really put all to the test. The latest update is after googling my pc to death i came across this site which has given me a lifeline to recover my sanity. not the best option but not far away. 3 Phase Electric Prepayment Metering

I would like to thank all that put forward their thoughts on this one, it was appreciated, and some good points raised that i would not have thought of.

will also let you know the outcome. good or bad.

Terry

 

[Darkwood]

lol was the same site i clocked near beginning of the thread hence my post pushing you towards prepaid metering.

 

[Pat Tester]

Just seen this thread but sorted out similar problem, with light industrial unit, solution via Matrix Metering this morning.
not cheap but more simple than using 3 single phase card meters 2 415v relays and a 3 pole contactor !

 

[Knobhead]

Mafeking was relived on the 17[SUP]th[/SUP] May 1900.
You’re 111 years late!