900 W generator won't run 124 W central heating system

I bought a Kipor IG1000 generator, an inverter type with an advertised "pure sine wave" output, nominally 900 W. I got it
largely to run my gas central heating in the event of a power cut. I have an electronically controlled boiler with an internal fan , gas valve solenoids, and of course a pump. The mains is 230 V. The pump alone takes about 0.3 A, and when the rest is added the total is less than 0.7 A (rms).
Problem is, the boiler won't start up properly when supplied from the generator. It tries to light a few times, then gives up and switches itself off. In fact it behaves pretty well as if there is no gas supply, except that I can hear that the gas actually lights and burns for a few seconds before giving up.
The generator runs a power drill, that takes about 300 W, absolutely fine. A lamp connected when I'm trying to run the boiler doesn't flicker at all during the start-up sequence. The generator voltage and frequency measure almost exactly the same as the mains. I have no easy way to view the waveform.
I'm a bit desperate as I paid for a moderately expensive generator on the assumption that as the output was sine wave I could run pretty well anything from it within the rated VA. But I suspect that it is performing within spec so I can't reject it.
The generator manual has a large list of things it will run, including many different types of equipment with motors although not specifically central heating. Obviously the solenoids will be inductive but the overall PF is not too disastrous (my meter says it's about 0.8).
So what is going on? Anyone come across similar problems? Or got any ideas?
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Tony W
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Tony wrote:

Do you have a timing diagram or text description of the heating system controller? I suspect the sequence advances to the point of energizing something that briefly dips the generator output - too short to be noticed on the light bulb, but long enough to confuse the controller via its power supply. Perhaps something like a hash filter added to the control power input or a capacitor across the DC supplied to the electronics?
Try adding some sort of resistive load (a small heater would do) to the generator and then try starting the boiler. Same sort of misbehavior?
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Tony wrote:

The short answer is, of course, that it isn't giving out a pure 50Hz sinewave. It has the classic output of a small generator - the peak to peak voltage is lower than mains, but the waveform is "broadened", to give the specified rms output voltage.
Your central heating system probably has a switch-mode power supply which essentially has its operation determined by the peaks of the input. Hence, whilst mains is fine, a small genny isn't.
You can measure the peak voltage without a scope and don't actually need to view the waveform to prove that it isn't a pure 50Hz sinewave.
What to do about it? Well, you could take it back and get a 5-6kVA generator, which is much less likely to have this problem.
Alternatively:
You could look at the specification of the equipment that you are powering. With any luck, it will be rated for 240v. If so, you can take the generator output to a variac and adjust its output towards 240v rms (as measured by a true rms meter). That increase may be enough to get everything working normally.
An alternative to the variac is a 6v 6A transformer. You wire the primary across the generator output and wire the secondary in series boost with the generator output. That should increase the rms output to around 236v - still in spec if the equipment is rated for 240v input. That increase may be enough to give normal operation.
Of course all the above assumes that you are happy working with mains voltage. As you mention pf, I assume that you are. However, if you don't know how to measure the peak voltage without a scope, you possibly shouldn't be trying the transformer work-around.
-- Sue
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Palindrome wrote:

I would have thought a switch mode PSU would be OK but it is probably an old-fashioned transformer, rectify and smooth. Not sure about me measuring peak volts. The only obvious way I can think of is to rectify and smooth the output myself and measure the DC, but I don't do electronics these days and probably don't have the components in the cupboard. What I will try next is connecting a small low voltage AC power supply with a properly isolated transformer and sending the output to my PC sound card so I can see the waveform over a period, also measure harmonics. The supplier says it is true sine wave, so if it isn't they are getting the genny straight back.
Bigger genny is not a possibility. I live in an apartment in central London and it's hard enough finding somewhere to store a small one and somewhere outdoors to run it! Also quiet running is important, that's another reason why I paid extra for an inverter type.
Thanks to all who have commented already, any more suggestions welcome. I have looked again and think maybe the gas did not light even briefly, I was probably fooled by the noise of the fan starting up. So probably the solenoid is not working to open the gas valve. The boiler is a tiny balanced flue device, pretty well sealed up and it is difficult to see exactly what is going on.
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Tony W
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Tony wrote: <snip>

I doubt that you will find another that is any better..

I assume that you have done the sums and worked out that a genny is better for you than a couple of deep discharge batteries and an inverter. I've got both, as it happens - but then, I live in the middle of Dartmoor, not the middle of London.
-- Sue
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As per my previous post, just use the transformer without the power supply while using your PC as a scope. Moreover, with your PC, you should be able to record the waveform.
Bill
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As I was reading this response U was thinking oscilooscope. If one is available, that would be the way to go.
REMEMBER SAFETY! to look at the line waveform you do not want to use an unbalanced probe that could connect the frame of the scope to the hot conductor. Use a dual scope input in differential mode with two probes. Alternatively, use a small isolation transformer. It could be a smaller version of the transformer suggested above. With the primary connected to the source you wish to measure--your generator. The secondary can then be connected to a single probe or cable safely. The transformer should be able to support a sufficient number of harmonics so that you could examine the supposedly sine waveform when starting your heating system.
Bill
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Hi Sue,
I've been waiting for you to pop up again. Do you remember us having a discussion about our holiday in Chagford. We are down in Devon in March. Can you email me to discuss as I don't want to take the thread O/T.
Reply to is valid
Stuart
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takes
(rms).
It is not power quality problem, it is grounding problem. Flame detection system (ion type) require grounded power supply to detect flame but generator outputs are not ground referenced.
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megamusic wrote:

My first thought was flame detection as well. The burner lighting and shutting back off and retrying is the key.
If the burner ran for several seconds and things shut off just as the pump tried to start I would question the regulation of the generator. But reading the OP, I don't think it gets that far in the sequence.
I don't know what sort of flame detector the OP has, so I don't know if grounding is needed. But it is true that most small generators do not have a grounded output. So if the OP is just plugging/connecting to the generator through a portable cord, it's quite likely there is no connection between 'neutral' and ground.
daestrom
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megamusic wrote:

That's what I was thinking as well. I'd be speaking beyond my knowledge to state how your normal system is wired in the UK. But I'd venture a guess that utility power has one leg grounded, much like that in the USA. Many inverters use an H-bridge switching scheme and each leg is 1/2 the rated line voltage from ground. This might be messing up your igniter. Grounding one side of the inverter output is NOT an option.
It might be possible to install an isolating transformer (220V to 220V), keeping the input floating with the inverter output and grounding the appropriate leg of the secondary.
It might be possible to feed the igniter and associated control circuitry alone from this isolation transformer and thereby reduce its VA rating. But I couldn't guarantee anything without a careful examination of the heating system schematics. The easy solution is to get a transformer capable of running the entire heating system load.
--
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
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wrote:
| That's what I was thinking as well. I'd be speaking beyond my knowledge | to state how your normal system is wired in the UK. But I'd venture a | guess that utility power has one leg grounded, much like that in the | USA. Many inverters use an H-bridge switching scheme and each leg is 1/2 | the rated line voltage from ground. This might be messing up your | igniter. Grounding one side of the inverter output is NOT an option.
If this is the case, then the inverter is grounded ... just not as expected. The OP should see 115V or so between either power conductor and ground to confirm this.
I do find it surprising such a thing would be a consumer item in UK. I would expect to see either 230V with one conductor grounded or 110V center grounded for outdoor worksite usage.
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snipped-for-privacy@ipal.net wrote:

I hope to try later today. I would love this floating supply to be the answer. Lack of flame detect exactly fits the symptoms.
I've put a meter on the generator while it's off and there is no DC path between either line socket and ground. Does that prove anything? How can I be sure that it is safe to ground the neutral? It never occurred to me to do that in case it was 115-0-115 V. If I measure ground-neutral volts with a high impedance meter I might well read something other than zero. Maybe I'll get the analogue meter out. If it looks OK I might temporarily ground the neutral via a 1 A fuse.
I know nothing about flame detectors but I'm surprised to find anything that relies on the neutral being grounded. I assume no significant current flows otherwise it would trip RCDs.
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megamusic wrote:

YES!!! Many thanks megamusic! Also to others who said the same thing was a likely cause of the problem. I found that the leakage current between neutral and ground on the generator was about 3 mA over a wide range of resistance. So I made up a well-labelled plug with neutral and ground connected inside using 5 A fuse wire. I put this into one outlet in an adaptor and plugged the boiler into another outlet. Result - works perfectly with the boiler system taking a total of 146 VA.
I am inclined not to make the neutral-ground connection inside the plug that goes into the genny, as I think if I use it for other things outdoors it might be safer with the output floating. What do the experts think about this?
Don't worry folks I am not running the genny indoors - I can read the big warning sign on the top. Although it is probably quite a good way to go if one really wants to.
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