parky58 Posted August 9, 2010 Share Posted August 9, 2010 Yesterday I did a PA hire job at a local show ground which was situated in a large marquee. I used a 6KW PA and took along 4 X NJD Spectres to add some light to the stage. The power supply was from a 100KVA generator from which the site electrician supplied me with 2 32 A feeds (one for PA and one for lights). The generator was from a plant hire firm and the output was 3 phase, neutral and earth. The PA worked fine, however when I plugged in the lights they flickered on and off uncontrollably with or without DMX control cables connected. Changing the address made no difference, nor did swopping them to the other supply. I asked the electrician to earth the generator which he did and this made no difference either. I abandoned the lights and luckily it was a bright day so they were not essential. I did wonder since whether the neutral was not bonded to the chassis and whether this may have been the problem. Has anyone had the same problem given the same scenario? Steve Link to comment Share on other sites More sharing options...
Ben Posted August 9, 2010 Share Posted August 9, 2010 This could have been to do with a neutral fault on the supply which is a common cause of problems in situations such as this however the problem could also have been cables or a faulty unit that was transmitting odd data. Without being able to test certain things with it all still in place its really all guessing. Check the units and data cables are all good when connected together and if they are all ok then the chances are this was a fault in the supply. Link to comment Share on other sites More sharing options...
parky58 Posted August 9, 2010 Author Share Posted August 9, 2010 The lights still flickered (all 4 of them) with no DMX cables attached and even a terminator on the outputs. Link to comment Share on other sites More sharing options...
Ben Posted August 9, 2010 Share Posted August 9, 2010 The lights still flickered (all 4 of them) with no DMX cables attached and even a terminator on the outputs. Are you now back at your unit with a stable mains supply? Link to comment Share on other sites More sharing options...
parky58 Posted August 9, 2010 Author Share Posted August 9, 2010 The generator voltage appeared stable and frequency between 49.8 and 50.1 according to the genny meters. It wasn't hunting and we considered effects of under load, checked fuel filters etc but supply seemed stable. My lights normally remain in one state when plugged in to a supply without DMX cable(i.e. off or on but remain stable). I'm just going to connect them up in my workshop to confirm there are no problems. Link to comment Share on other sites More sharing options...
Ben Posted August 9, 2010 Share Posted August 9, 2010 This is almost certainly an issue with a doddgy neutral in the gen but you will know more when back at your unit with a clean supply to test them on. Link to comment Share on other sites More sharing options...
parky58 Posted August 9, 2010 Author Share Posted August 9, 2010 Hi Ben, Have now checked them over with same cables and controller and all working OK. I've just notice an analogue input on the units with its own supply so I will make up a couple of link plugs in case it happens again. This may enable me to force the lights to on in an emergency. That is assuming the analogue input is not simply creating a DMX value, in which case it may still flunge. Steve Link to comment Share on other sites More sharing options...
KevinE Posted August 9, 2010 Share Posted August 9, 2010 I suppose there could have been harmonics on the generator output, the spectres use triacs and mains bulbs and harmonics might upset the firing to give random effects (or even the spectres generating their own) ; I'd have thought that any neutral fault would cause obvious problems elsewhere; so long as the spectres have 240 across L & N I dont think they'd care where the neutral was wrt earth. Link to comment Share on other sites More sharing options...
swampman Posted August 10, 2010 Share Posted August 10, 2010 Did you ballast the generator: give it some resisitive load? You probably had enough load on the other phases but the lights one most likely started fluttering about and the electronics could not synchronise. Advice: take some common halogen floods (150-500w) and plug one into each phase: if one blows you are warned, if one goes dim: you are warned and you can always make a bit of toast or heat a burger! Helps for the get out too! Link to comment Share on other sites More sharing options...
paulears Posted August 10, 2010 Share Posted August 10, 2010 If the power was bad enough to cause issues with lighting, I'm surprised the sound system didn't object - they are usually much more intolerant of dodgy power? Link to comment Share on other sites More sharing options...
Brian Posted August 10, 2010 Share Posted August 10, 2010 ...harmonics on the generator output, the spectres use triacs and mains bulbs and harmonics might upset the firing ... I don't think they'd care where the neutral was wrt earth. Agreed. Possibly noisy mains around the zero-crossing point upsetting the timing. PS, am I the only one worried by... ... 100KVA generator ... 3 phase, neutral and earth ... I asked the electrician to earth the generator ... So it wasn't earthed to start with? Link to comment Share on other sites More sharing options...
ramdram Posted August 10, 2010 Share Posted August 10, 2010 Parky 58, would it be out of the question to check out your kit on another jenny identical (sans any fault of course, ** laughs out loud **) to the original you hired? If the lights behaved as expected, then the original jenny may have been faulty in some way (neutral fault?) so perhaps you might be able to get a discount on your next hire. Especially in this economic climate you should not have to accept duff rental kit; the event could have been in the evening, and blaming the jenny for your lights not working as desired by your client might be seen as you blaming somebody else's equipment, ie. the PA worked OK so to the layman how could the jenny be at fault? It must have been your lights... And of course bad press ALWAYS travels fastest. Link to comment Share on other sites More sharing options...
Brian Posted August 10, 2010 Share Posted August 10, 2010 ...(neutral fault?)...'Neutral Fault' has been mentioned by a few people but I'm intrigued as to what they mean by it? Link to comment Share on other sites More sharing options...
ramdram Posted August 10, 2010 Share Posted August 10, 2010 Me too. Back to you Ben. Link to comment Share on other sites More sharing options...
parky58 Posted August 10, 2010 Author Share Posted August 10, 2010 Thanks for all your input chaps. It would appear that this is not a common problem and I have used the same lights on various generators with no problems. On the day I assumed it to be a dirty supply ( harmonics, parasitics or similar), or dodgy neutral to chassis connection. Although it is not a requirement to earth a standalone generator to the general mass of earth (BS 7909 2008: sec 7.4.2.3) It is always possible that airborne interference could be induced on the cable screen and get into the equipment, corrupting data (the show was about 5 miles away from several low frequency transmitters). Earthing the generator to the general mass of earth should arrest any RF component from entering the equipment. As Swampman pointed out, it is good practice to ballast the generator. I will take 3 halogens with me to similar events and ask for a 3 phase supply which I will split myself. As it isn't possible to repeat the setup with the same genny, I will have to put this one down to the gremlins. Any other theories, however unlikley will be entered into the database for future reference. Thanks again. Steve Link to comment Share on other sites More sharing options...
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