Power cuts & Generators.

[Lectrician]

Just as a side remark - we install generator backup systems fairly regularly on larger commercial sites.

Automatic start and transfer switches are more complicated these days than years back.

There are usually 5 timers incorporated. When the mains fails there is an adjustable time delay before the generator is called for (to establish if the power failure is going to be a substantial one). The generator then starts and the control panel looks for a stable voltage before then operating the transfer switch. The transfer switch could be two interlocked contactors or a motorised switch. There is often a time delay between break and make, especially if it is a contactor transfer.

Once the mains returns there is then a further time delay, usually of several minutes before the transfer switch is operated. This is to ensure that the mains has returned for good. Once this delay as expired and the switch transfered back, there is a final timer which runs the generator on before stopping it.

There is also often a manual mains restoration option. Rather than the transfer switch switching from generator back to mains automatically, an alarm sounds (or similar), and someone has to manually press a switch when ready to transfer back. This is not required where UPS's are used on all critical and semi critical kit, but can be useful on many sites.

 

[ericmark]

Having spent time in Algeria and Falklands I have worked with many systems and generators from 1.5KVA to 750MW in Sizewell but this guy is really interested as far as I can see in the very small units and I think a simple plug and socket arrangement is ample. Unless one does daft tricks like a lead with two plugs already referred to as widow maker there is really no problem.

Except for the two I have tried to raise.
1) Where multi items are used then really needs an earth rod.
2) Duel voltages cause problems.

The latter is due to some manufactures Honda for example not connecting the earth to the output classified as neutral but to the centre tap of one winding when set to 110 volt (55 - 0 - 55).

This results when 230v is selected having a 0 - 50 - 190 volt supply approx and the 50 volt not the 0 volt being connected to earth.
As to getting a shock under the magic 50 volt so they can get away with it but overload wise one can draw well over the ratted capacity with a neutral earth fault without opening an over current device and either damaging generator or cable.

There is also another problem often missed is the selection of RCD with modified sine wave inverters. Type AC are not suitable. It must be type A.

I am told items like washing machines with inverter control should also be supplied with type A yet it seems most fitted are type AC. Never did try the earth loop impedance meter with the inverter. I was worried it would blow it up.

Would be interesting to compile a list of items that will work with a modified sine wave inverter. I have used without a problem. Laptop, LG Washing machine (at least as far as washing machine goes), Many battery charges for radios, drills etc. In fact never had anything fail. Although I know near every washing machine except LG say there machines will not work.

I would guess where the supply goes through a transformer the transformer will make the wave form much closer to true sine wave anyway.

I have used rotary inverters including ward-lenard and even synchronous vibrators and with the latter I did note how the transformer did seem to turn it into near sine wave. Worked the Pye radios a treat.

With every system one comes across something that does not work. The ward-lenard was messed up in the cranes due to an inverter going wrong and it caused the load to drop and hit the floor. Lucky no one under it. Unfortunately often we are unaware of EMC problems until there are too late.

However the chances of this type of problem in the home is low and really there is nothing one can do anyway. But of course one can always employ some one to do the job then if it goes wrong it does not cost you money. With Part P considerations likely that is a good idea anyway.

 

[frankc]

well thanks for all the replies. But basically its about as clear as mud to me. Its ok talking ups and op and cu if you know what the *** a op and a cu or ups is. Personally I am one for calling a vertical impacting horticultural rotovating impliment, or a VIHRI to you elecricitians, a spade.

I am sure if I wanted to run a small factory or industrial unit all this would be relivant. But all I want to know is what sort of inverter and battery I should buy and how I connect it all up.

Ah I hear you cry it depends on such and such with your boiler. But surely there is one inverter type I could buy and it would work no matter what sort of inverted sign whatevers the boiler works on? Or there is an elecrician out there that knows the Worcester Bosch Boiler Heatslave 12/14 will need to have to work off a battery?

After searching the net I have found this link to the boiler details. click here It will no doubt tell you what power it consumes etc. Does this help at all?

Still no reply from Bosch. So much for a "within 4 hours"reply. Perhaps they have worked out I am not actually going to buy anything from them and cant be bothered.

So thanks for the replies. But remember I am no professional e-lecy and dont know anything about earthing rods etc if I did I would not need your advice would I?? I may not have deep pockets, but I am willing to listen.

 

[ColJack]

not much use at all..

lets do this the easy way.. pull the fuse for the boiler ( in the plug or fused spur that feeds it ) and tell us what rating it is..
to make it even easier, if it's red it's 3A, brown it's 13A, black means you'll have to read the numbers off it..

 

[ban-all-sheds]

Blue?

White?

 

[frankc]

not much use at all..

lets do this the easy way.. pull the fuse for the boiler ( in the plug or fused spur that feeds it ) and tell us what rating it is..
to make it even easier, if it's red it's 3A, brown it's 13A, black means you'll have to read the numbers off it..

Now you are talking my language. Its a red 3A.



It that rating I guess it does not draw much power. Am I correct in assuming that if a battery is a 24 Amp Hour the battery should last 24/3 8 hours life min? Or have I oversimplified that?

 

[bernardgreen]

Yes you have over simplified.

3 amps at 230 volts is 690 watts ( W = V time I )

690 watts at 12 volts is 57.5 amps ( I = W divided by V )

So to provide 3 amps at 230 volts the invertor will need to pull 57.5 amps from the 12 volt battery. ( That assumes the invertor is 100% efficient which it will not be )

 

[holmslaw]

..

 

[bernardgreen]

Deleted got my sums wrong.

Beat me to it

If they had been right then you would have created an invertor that gave out more power than it took in.

I have been looking for that device for years and never found it

 

[holmslaw]

..

 

[Lectrician]

Doubt the central heating boiler and controls will pull 600 odd watts - The pump is the largest thing (assuming gas boiler), and will be around 30 - 100 watt depending on the size and the speed setting.

The other parts are likely to use a few watts at most.

Say 250watt to be safe.

I would look to get a UPS if it was me in your shoes - this will automatically cut in, which I know you are not fuseed about, but it will also then automatically charge back up too.

A cheap UPS is going to be cheaper than a car battery and inverter but may not have the same run time.

A 3000 watt APC UPS will last 3 - 4 hours at 200 watts. APC are not cheap, but gives you an idea.

 

[ban-all-sheds]

The pump is the largest thing (assuming gas boiler)

C'mon - keep up, keep up...

However the ideal situation would be to find someway to run a household light and the fuel oil central heating boiler.

 

[ColJack]

Blue?

White?

not officially recognised colours..
red = 3A
brown = 13A
black = non standard rating.

 

[frankc]

Doubt the central heating boiler and controls will pull 600 odd watts - The pump is the largest thing (assuming gas boiler), and will be around 30 - 100 watt depending on the size and the speed setting.

The other parts are likely to use a few watts at most.

Say 250watt to be safe.

I would look to get a UPS if it was me in your shoes - this will automatically cut in, which I know you are not fuseed about, but it will also then automatically charge back up too.

A cheap UPS is going to be cheaper than a car battery and inverter but may not have the same run time.

A 3000 watt APC UPS will last 3 - 4 hours at 200 watts. APC are not cheap, but gives you an idea.

Something like this? clicky Or is this a cheap and nasty one??

 

[frankc]

Or perhaps this? clicky Then I can charge up a couple of batterys and have two on standby? Would the oil fired boiler work on one of these?