question Portable 4 stroke mains generator query - are they all like this?

[Chris Warne]

For 2011. when we setup our AAF display, I want to have some background music, and for the evening when we're camping, some lights would be good I thought, so I went a bought a SIP 'Medusa' T1000 'suitcase' generator. I researched this model and it got good reviews in alot of mags/websites, and at a shade under £100 for 'as new' I am happy.

It arrived this week and we fired it up yesterday to test all is ok with it - starts first time, seen little if any use, but then we came across a 'problem' - or is it??

To test AC mains output, we plugged a 300w Black & Decker power file into the socket. This has a normal mains plug on it, but the Earth pin is unused. It did nothing - not even an attempt to work. It worked on the mains socket, so the powerfile was fine.

We then tried a halogen spotlight (500w) and this has a metal earth pin on its plug, earthed I guess to the metal lamp unit - this lit up fine and generator adjusted for the load on it. We tried other devices and anything that didn't have/require an 'active' earth pin would not work. We tried using a 4 way extension and same happened - earthed devices worked, no earth devices would not work.

So the generator works fine (starts and makes 240v AC), but I don't understand why it appears every device must have an 'active' earth on the 3 pin plug? I mean, if you wanted to run an old fashioned lightbulb, you would only have 2 wires, so does this mean you could never use the generator to power lights? Likewise for portable music systems - most are solid state and have no earth, so unless there's something wrong with my generator, I guess you can;t use it for such devices? I had thought the 3 pin socket on the genny should behave exactly the same as a household socket, but it doesn;t on this one?

Anyone know why the above happens, any work-arounds or tips to get these non-earth items working?

 

Thanks in advance,

 

Chris

[commander]

We had this problem also on a genny and the solution was to plug a lamp into one of the extension outlets

turn it on then plug what ever into the other outlet and hey presto it worked don't know why but it does on ours

C

[Chris Warne]

cheers, I'll give it a try.

[Chris Warne]

well, I plugged a 4 gang into the AC outlet, connected a 500w halogen lamp to it (this lamp has an earth 'circuit') and the light lit up as expected. I then plugged a no-earth (solid state) portable 'boom box' into one of the other sockets and it also turned on.

I then unplugged the halogen lamp and within 1 second the boombox went off aswell. Seems I need to have at least 1 'earthed' device connected to the genny if I want any solid state items running off it.

 

It does limit what you can run off one of these things. :-(

does anyone knw of a 'dummy' device that can be plugged in to simulate an active earthed device, so I can plug in and use only what I actually want to use.

[Tony B]

Have you tried a portable RCD on an extension?

[Chris Warne]

Good idea Tony - that was on my list to try.

 

SIP tech support gave me a clear explanation for this when I called them. Cheaper gennys are not voltage regulated, so the voltage supplied can go up/down with fluctuations in load/engine speed. Without a voltage regulator, the generator cannot determine the current/power required by a solid state device (non active earth connection) and therefore doesn't supply anything. By plugging the halogen lamp in, this draws enough current for the generator to determine the requirement and so electricity 'flows'. When I plugged the boombox in afterwards, all I was doing was 'stealing' some of the power the genny was providing for the halogen lamp.

SIP tech support were very helpful, and said they don't know of any plug in voltage regulators out there. They suggested I should aim to use at least one appliance that has an earth circuit wired up to 'turn on' the electric, and then use the 4 gang to power anything else I want to use - earthed or solid state. One point they did make is to use a spike/surge protected power strip if using any stereo/sensitive devices as these could be damaged.

 

They added that you usually only get regulated supply on the moore expensive generators - such as the Hondas etc...

 

If I find an easy, safe, way to 'fix' this requirement, I'll let you know. Thanks for the help on this topic.

[steveo578]

I heard this before specifically with regard to 'Medusa' generators. I sure the instruction leaflet for this type specifies an earth rod (950s certainly have a earthing stud on the chassis) making the system a TT system but that in theory could cause problems if any livestock came into contact and of course you cant bang a rod into concrete or tarmac.

 

An alternative is to make the unit TN.C by connecting the earth and neutral on the input side of a line with an RCD supplying the load- your tools- microwave lights whatever - really you souldn't run multiple equipment from a small generator - but obviously a powertool and spot lamp often are essential. If you do add a link across the input side of a RCD make sure it is 1). only used with the generator and 2). a clear indelable label is attached stating that a combined earth and neurtal system TNC is in use.

 

Electricals are very complex and of course dangerous so as I can't see the problem I am giving you this advise with the standard disclaimer -I'm not responsible if you fiddle with something you don't understand -you are probably not a competant person as defined in law- no insult intended - might be an idea to speak to some-one locally who is an approved electrician esp. some-one who for instance does caravan sites and caravans.

 

There are a number of sites which give further advice opinion such as IET forums IEE is the BS7671 regs for electrical instalation but unless you are a grade 3 electrician (2391 or above) you might find it hard to comprehend -certainly none of the apprentices or even some of the sparkies understand it in depth.

 

Steve

Edited February 14, 2011 by steveo578
addition

[andym]

What SIP have said agrees with my thoughts that this isn't an earthing problem at all - it's all to do with current. You need to have at least one device (earthed or otherwise) connected that draws sufficient current for the generator to realise that it has a load. I suspect that if you removed the earth connection from the halogen lamp (safety considerations aside!) it would still work.

 

Andy

[Chris Warne]

Thanks for the input Andy, having looked into this some more, it seems that gennys have a floating earth, and the option to mimic 'household mains electrics' by connecting the Neutral and Earth pins (on the socket or an extension lead for example) isn;t recommedned, unless you earth the genny frame and use an RCD on the output socket.

 

I've spoken to a couple of other companies who sell the more expensive gennys and they said there shouldn't be any issue on a floating earth genny with any device type (earthed/solid state or otherwise), so I think the SIP team may have advised 'how it is' with their gennys and I'll need to run a 100w lightbulb or similar to get the juice flowing!!

 

I don't think it's going to be a problem at shows, as I'll be running a 3 component sound system (midi sized hifi if you like) aswell as a 60w light, and that lot will draw about 400w in total.

Everything else we use is powered by gas, paraffin or uranium.

[mogmaner]

You may be sufering with a load sensing problem ,this is caused by the electronics in modern speed controlers and radio gear having no resistive load witch the set is looking for ,so you might find puting a lamp as small as 25w across the output will solve your problems.this is also a problem with set fited with auto idle, we youst to fit over ride switches when they were yoused to run inverter welders as it on load to the sensing circit in the set.

[andym]

Thanks for the input Andy, having looked into this some more, it seems that gennys have a floating earth, and the option to mimic 'household mains electrics' by connecting the Neutral and Earth pins (on the socket or an extension lead for example) isn;t recommedned, unless you earth the genny frame and use an RCD on the output socket.

 

I'd strongly suggest that you earth the generator frame anyway, in fact I'm pretty sure that the SIP manual advises this. Relying on the lack of earth reference to provide any form of safety is dangerous, especially if you're feeding an electronic load with a switched-mode power supply. These often have RFI filter capacitors fitted between earth and the other lines which will provide a path for the fault current. Double insulated equipment with no earth connection is fine, but for anything else you MUST earth the generator.

 

Andy

[steveo578]

Chris Warne

Thanks for the input Andy, having looked into this some more, it seems that gennys have a floating earth, and the option to mimic 'household mains electrics' by connecting the Neutral and Earth pins (on the socket or an extension lead for example) isn;t recommedned, unless you earth the genny frame and use an RCD on the output socket.

My previous comment regarding TN-C systems has been misunderstood -I expect that the output earthing pin would already be connected to the generating set frame and any other "expossed conductive part" -ie metal work. Without an earthing rod or a low impedance connection to an earthed source the entire generating set is in effect an IT system, as I said electrical installations are more complex than most people realise- the quote

 

to mimic 'household mains electrics' by connecting the Neutral and Earth pins (on the socket or an extension lead for example)

proves my point there are 3 types of supply used in domestic installation TT, TN-S and TN-C-S only the later has a connection between neutral and earth (connecting the supplers earth steel/lead sheath to the neutral line at the point the supply enters the house), TN-S the earth is the outer steel lead sheath of the supply cable and TT is a supply which does not have any earth supplied by the electricity company -it is the consumers responsiblity to supply an adequate earthing electrode. In no case is it legal to connect the earth and neutral in a domestic installation and should that be done upstream of an RCD the system will not energise.

 

andym

I'd strongly suggest that you earth the generator frame anyway, in fact I'm pretty sure that the SIP manual advises this. Relying on the lack of earth reference to provide any form of safety is dangerous, especially if you're feeding an electronic load with a switched-mode power supply. These often have RFI filter capacitors fitted between earth and the other lines which will provide a path for the fault current. Double insulated equipment with no earth connection is fine, but for anything else you MUST earth the generator.

17th edition IEE regs BS761 551-4-4 2 requires all circuits (not just those supplied by sockets and plugs) supplied by a portable generating set to be protected by an RCD not exceeding 30mA.

 

As I've said before find a local qualified electrician for advice.

 

Steve