Hi All, I have a friend that has a Tuna boat, he uses two Metal Halide lights to light up the deck. The boat has a 3 phase generator onboard. This drives a large freezer compressor and an air compressor. When one of the compressors comes on the lights go out, need to cool and the refire. The lights are single phase 240 volt units. What can be done to keep the lights working during compressor startup? Would a constant voltage transformer such as this help?
formatting link
|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50 Mike
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
I've never used one, but check to make sure that the solution is better than the problem -- my understanding is that they are for regulating old-style computer power supplies; I don't know how big they'd need to be for kW capacity lighting.
Some other suggestions:
(a) use two smaller generators, one for lights, one for compressors. (b) put a big-ass rotary induction machine (i.e. a multi-horse three-phase motor) in line with the generator, to supply power during sags. (this probably won't work, but it may be worth a try...) (c) If they don't already have them, use pressure relief valves on the compressors during startup (can this be done with a refrigerator compressor?) (d) Investigate "soft-start" circuits for the motors. I DON'T KNOW if this is done, but in theory you should be able to unload the motor, then start it up through some healthy reactance (i.e. big-ass coils) until it's up to speed, _then_ connect it to the mains, _then_ connect it to the mechanical load (by turning off that relief valve). Today you can probably do this through a VFD (and may be able to do so automagically if you get the right VFD, for that matter).
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
First cover the possibility that the present wiring is done all wrong - ie, are the lights and other single-phase loads all piled on one phase, or are single-phase loads distributed across phases sensibly? Is the generator just plain too small and needs to be upgraded? Are there capacitors on the compressor motors that might be bad, or should there be capacitors, but there are not? Certainly for the air compressor, an unloader valve would be a good thing, if there is not one on it (or it's not working right if there is) already.
If the compressor doesnt come on too often then how bout a UPS system? Might be a cheaper solution and provide enough juice to keep the lights on. The problem is that the compressor might suck the juice from the ups too but what you can do here when the compressor turns on it cuts the power to the ups for a few sceonds. The ups will supply current to the lights and then be connected back.
If metal halides can be run with DC then simply using a power supply will work. Large enough caps to keep a temporary supply. In fact what you would want is to charge the caps before the compressor came on, disconnect ac from lights and connect cap then switch back. This way the cap is only on for charging and not wasting power(Although probably not an issue) and the light's are not running off dc for too long. This might be the easiest and cheapest solution if it worked.
You can try other things too like batteries to an inverter but basically your creating a UPS system. Of course you can replace the lights or get a more powerful generator.
Good idea, but you don't try to run the compressor off the UPS. It gets wired directlyh off the generator. The UPS is just for the lights. Assuming we're talking about something like a couple of 400W metal halide lights, a 1500VA UPS should be okay. Here's one for $200:
formatting link
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
That is the problem I tried to discribe which is why you might have to temporarily disconnect it from the generator while the compressor is turning on. I suppose one would simply have to test for this or by a larger ups or get more of them.
so you probably figured that the voltage is dropping too much when the compressors kicks in and the lights can't continue through the voltage dip
1) check that the lights and comps are wired to the generator with seperate wires, you don't want them to share any long calbes that would make the voltage drop worse than it is. The generator will drop some but extra shared wiring will make it worse..
2) Some compressors can be started with an unloader, which is a valve that releases the back pressure...
3) Add a few incandescent lights to the light system so that when the MH lights need to re-strike but in the meantime you have enough light to work with...
A UPS for the MH lights is an obvious answer but if they are big lights that may be very heavy and expensive..
I would submit that a UPS that does not operate properly when the input voltage sags is not really a UPS.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Well, as you well know it could only take so much. If the compressor draws enough juice it could cause it to sag. I guess the only way would be to test it out... not a big deal and not a big deal if it does need to be temporarily disconnected.
It *is* sagging-- that's what's killing the arcs in the metal halide bulbs. And it's not good for them-- they should be allowed to cool fully before restarting.
And the whole POINT of a UPS is to maintain quality power on the output if the input drops below nominal.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Probably not. A suitably rated UPS between the lamps and the generator might help. Presumably the power only dips for a few seconds when the compressor is pulling its peak maximum starting current.
The captain did mention a UPS, he has one for his computer and wondered whether one would work on the lights. Looks like I should make sure the wiring is configured to eliminate as much voltage drop to the lights as possible. If that doesn't help then look into a UPS, different lights, or auxiliary lights during the cooling and refire time.
These lights have voltage taps on them like 208V, 220V, 230, 240V. I don't know where they are set, but is there a scenario where one tap would be prefered to help keep the lights on during the brownout? Mike
Probably not-- without compromising things during normal operating conditions.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Depends on how the ups works. If it's simply hooked up parallel to the other power source then it too can sag. All depends on the compliances. I'm no expert but I guess they just use batteries and an inverter. The batteries can only put out so much surge current(although I imagine it is pretty decent for lead acid). This still might not be enough as the compressor might "steal" it too. It's only a hypothetical and I pointed it out just in case.
The problem is simply that the voltage is drooping because of the large surge current when the compressor comes on. Similar things happen, say, when peoples AC comes on and the lights dim. You gotta regulate the voltage somehow. I'm sure there are many ways but it all depends on how much regulation you need.
Your power source, the generator, can output only so much current. The compressor is a load as it the lights. When the compressor comes on it "overloads" the generator. Basically because the compressor is "asking" for much more current than the generator can output the generator drops it's voltage to compensate(since the compressor draws less current with less voltage).
The problem here is that when the generator drops it's voltage it it no longer supplies the correct voltage to the lights which they need to run. (which is different than the compressor which is mainly current driven)
What this basically means is that your generator is not big enough. Get a bigger one or supplement it.
Usually DC motors have a start capacitor to supply that extra juice:
formatting link
And AC motors can use a similar feature but that it works in a different way(offsetting the current at startup to reduce the surge)
I had another talk with the captain, The lights are 1000w each so the UPS suggested is to small to run one light. Sometimes only one light goes out, so maybe the voltage is very close to the point where the light would stay lit during the sag. The generator is a 30KW 3 phase unit. The freezer compressor is a 7.5hp 3 phase unit. Voltage normally runs at about 219 volts. The air compressor is not a concern (only used to power main motor starter) normally off. The 3 phase circuit breaker box has a breaker that supplies 2 phase to a second circuit breaker box. The second breaker box supplies two 1000watt lights on a single 10 gauge cable. Captain said the lights have taps at 110v, 220v, 240v, and 277v. They are now using the 240 volt tap. Here is a generic schematic of a metal halide light, I found.
formatting link
I'm figuring he's running the lights at a low voltage with the 240v tap and a 219V supply. Is that correct? If so, I'm going to suggest adjusting to the 220v tap. Then try disconnecting one of the lights and running just one light on the single 10 gauge wire. Maybe the combination of the two will be enough to keep the lights lit. Mike
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.