View Full Version : Whilst JB is apprently shite, I bet....

23rd Nov 2013, 11:50
... someone will know how much power a central heating pump (say 650W) draws as it kicks in. I am led to believe it can be a lot more than that at startup?

I'm subject to power cuts where I live (semi rural) whenever the weather is windy. I have a really cheapo (gift) 2 stroke, 1kW genny which I hoped would run heating (so heat and water), lights and Sky.

It shows power to the combi boiler, but the boiler,a worcester, cuts out under demand.

I wondered if the pump cutting in was overloading the genny and the boiler sensed this and cut out.

Any ideas based upon sketchy details? I have considered hiring a 2kW job for a test...



23rd Nov 2013, 11:57
That's one hell of a pump!

Most in my experience are rated at around 150w max, maybe draw twice that on startup.

23rd Nov 2013, 12:31
Yes, two to three times the running current depending on age, wear, furring-up etc.

23rd Nov 2013, 13:51
Point taken. Any ideas why it won't run on generator produced leccy then?


23rd Nov 2013, 14:14
As others have said - expect 2 - 3 x load on start up. If your genny supplies its power out through an RCD (Earth Leakage Circuit Breaker in old money) it may be that this is what is tripping the genny off line.

Big start up load lots of juice going down the live wire bugger all coming back up the neutral - RCD spots the difference and will trip out - thats what they are supposed to do - to help save your life when you are attached to the live wire. Similarly if protected by a B type MCB then they might be sensitive enough to trip out with a start up load.

A decent electric motor will often trip things on start up - a chunky Hoover or garden shredder or an electric 9" angle grinder will often trip B type MCB's. If the Zs value of the wiring is low enough then you can swop the B type MCB for a C type - less sensitive but still does what it should do.

Similarly you can swop B type RCBO's for C type RCBO's - again if the Zs value is low enough.

Modern boilers have plenty of computing power inside and can sense many things. It may be that the very temporary reduction in voltage as the pump kicks in is enough for the boiler to think its had a power cut. Worcester Bosch are pretty good for customer service on faults etc - try their telephone help line - you stand a good chance of getting a sensible answer as its not in the Punjab! A WB engineer would call for a suitable fee and would probably plug in his lappy and give you the answer.

23rd Nov 2013, 15:16
A 2 kw genny should hack it, if there's nothing else plugged in. Over here where gennies are a common backup, it's recommended that you chose a genny with double the capacity of what you intend to run continuously to allow for random start-up loads and occasional use items.
A 20(ish) energy meter may be able to measure the higher current on startup via it's maximum power function, if the time/sampling period is set small enough. I would imagine a good electrician would have a suitable meter. I borrowed one to check the running/startup loads on all the appliances that I put on my boat, as I had a similar problem of power limits. It enabled me to work out what needed to be switched off to run something else. Can't remember the brand name I'm afraid.

Loose rivets
23rd Nov 2013, 15:56
If it was capable of really supplying 1,000 watts - say, 4.5 amps at 230 volts, then there should be no problem at all. So, what's wrong?

Cheap genny. Dirty output? The boiler's electronics wouldn't like a spiky mess arriving at its input. A clean, reasonably sinusoidal wave is probably required.

RCD / GFI ? Doubt that. How would the genny detect that without being earthed / grounded? Theoretically, you could cop hold of one side of the output and not feel a thing. No, I've never had the [email protected] to try it. But detecting earth leakage from an isolated source is very problematical. Anyway, I very much hope if it tripped, it would stay tripped and you'd know.

Could be a drop in voltage due to a poor quality cable run. It's amazing just how much a cheap accessories cord will drop voltage. Keep that short and at least 14 gauge. 12 if possible. Costly, that.

Voltage dip on pump start sound the most likely. A workaround might be to not have the pump cycling - if you can get it going once. Take the rad stat out of the equation (turn it way up ) and run the system on the water temp control during the power cut. I did that for the summer (in freezing UK) having had a faulty Seimans radio-remote fail.* Just set the water temp to 48 - 52 and leave it on.

You need a good old moving coil meter to look at the voltage arriving at the boiler. You can see the dips more easily than with DVMs.

Hiring a 2kw unit would prove the point.

*such a well-known name, but hundreds of them failing due to a duff relay. Folk on forums saying they had to give them a clout to get them going. Seimans told me their stockists are responsible for returns - and you can imagine just how they reacted to that extra work. Nice display, and no wiring, but just unreliable. Stockists say they just throw them in a box as they're returned. 90 quid down the drain.

23rd Nov 2013, 16:42
Is the pump motor an induction type with capacitor start? (many are) If so there is a good chance the lousy power factor of >> 0.8 during start might be your problem. There will not only be a high inrush current but it will be leading the voltage by a horrid amount and that could really upset the generator voltage control and cause it to collapse, especially if the generator is only lightly loaded.

If it is a 1KW gen and assuming the pump is a more usual 50 - 150W, try loading it with a nice resistive load to about 50% - an old-fashioned 500W single bar electric fire would be ideal - and then see if the CH system runs up. Once the CH pump is running you can turn the fire off.

west lakes
23rd Nov 2013, 16:45
A normal motor will take up to 7 times full load running current on start up.
As it is going to pump straight away it may take more!

23rd Nov 2013, 17:00
Point taken. Any ideas why it won't run on generator produced leccy then?

CG, I suspect the "1Kw" genny set probably isn't giving the full rated output in any case.

If it's similar to the one I have here (bought from a certain supermarket beginning with "A", but many similar ones on the market, all sub 100 and all based on similar hardware), try plugging in a simple bedside lamp with an old fashioned incandescent bulb.

You will probably see that the output varies quite a lot, indicated by changes in the light output. I only use mine for battery charging and lighting whilst working outside.

What happened to your water mill genny; did you get that working?

23rd Nov 2013, 18:08
try plugging in a simple bedside lamp with an old fashioned incandescent bulb.

You will probably see that the output varies quite a lot

Already noted that Shy- and the genny is from said LoCo shop. No work on the hydro- keep getting dragged back to work at the mo.

Perhaps the hire option to try it out is the answer.


23rd Nov 2013, 18:37
Sh!t in, Sh!out. Basic Law.

Loose rivets
23rd Nov 2013, 20:56
Rather than load it, why not introduce a starter current so as not to frighten it with the full amount right away?

I did this with a huge Mikata sp? so as to stop circuit breakers popping.

I put a fire bar element in SERIES with the load and switched that out by bypassing it in about 3 seconds. It worked fine.

I'm not sure if that would satisfy the capacitor to the point it wouldn't add to the load while it charged. I'd certainly try that. Clearly, you'd have to resort to the always on method I described above, or leap out of your chair every time you wanted a burst of heat. It is very easy to make a timer operate a relay to do the job, but perhaps more messin' than you want to do for something that's only used occasionally.

The motors that take huge currents to get them spinning almost certainly have starter windings. These windings are mechanically switched out by centrifugal force as the motor spins up.

A motor without such a starter system will take more current because it is an inductive load that is greatest while static. At 50 cycles mains input, it relies on its rotation to effectively raise the 'AC resistance' and lower the current.

Oh, BTW, if the genny does have a residual current device on its output, it would pay you to ground it to your earth/ground system. I feel uncomfortable about putting such a supply onto something with electronics in it, without it being tied to a very specific datum.

23rd Nov 2013, 21:58
Point taken. Any ideas why it won't run on generator produced leccy then?
CG Probably an American genny only producing 115v 60Hz. UK stuff won't run on foreign leccy, even European leccy. It has been reported to the European Court of Human Rights, but don't expect any responses soon.

G&T ice n slice
23rd Nov 2013, 21:59
A friend had a place in the boonies with his own electricity generator, but the output from the generator was put into a bank of batteries, whilst actual demand was taken out of the batteries. there was a black box between the generator & the batteries and another black box between the batteries & the fuse box and what came out of the sockets was yer standard 13amp 240v AC.

Mind you I always went round makinmg sure there were appliance plugs in all the sockets, because I didn't like the idea of this electricity stuff just sloshing out all over the floor

24th Nov 2013, 00:54
Timely reminder on Gen-Sets...

Dragged my 3kW Honda out of the garage today to power up the log-splitter. Bugger of a job starting it - not used for almost a year. If you use yours infrequently too, it is best to stop them running by turning off the fuel valve (if fitted). This prevents old fuel gumming up in the carb when it stops. When starting, add some new fuel first. And bung the spark-plug in the oven on 325F for 10 mins - works wonders - and drop some fuel into the combustion chamber while the plug is out.

Running great now! ;)

Loose rivets
24th Nov 2013, 06:06
There's some stuff to put in carbs if engine to be stored. Stops the lacquer blocking the jets.

Just been told the Pulan chainsaw I'm tending to may also have crank bearing seals fail after being stored. It seems it's best to run them every month or so to get the two-stroke oil into the crevices.

Yamagata ken
24th Nov 2013, 07:04
Seconded er340790

I dragged my Honda Yukios out a couple of weeks ago. Incredibly, I hadn't drained the fuel last spring and it wouldn't start. I say incredibly, because I always drain it, but for some reason it got away from me. Carburettor came off to get at the main jet, new gasket to be cut etc. etc. Runs fine now.

If you are storing for more than a few months, its worth draining the fuel completely, as it can go off. I never (normally) keep petrol for more than a few months before cycling it through the car. Honda very conveniently provide a drain in the base of the float bowl for this purpose.

24th Nov 2013, 12:01
While you have the plug out, take that pencil from behind your ear and rub the 'lead' against both electrodes, particularly in the gap between them.

24th Nov 2013, 12:04
There may be a gap between my ears, but I don't have electrodes!

24th Nov 2013, 15:12
There may be a gap between my ears, but I don't have electrodes!

Might consider installing some. Deffo adds perk to one's early day.