MetalBox Electrical Test Procedures
There are six main parts to a MetalBox UV Electrical System,
they are:
1) Control Components
2) Ignitor
3) Capacitors
4) Ballast
5) Lamp
6) Cooling Blower
1. Control Components
This consists of control relays, timers and contractors
which are used to power up and check the condition of the
other components in the system. For a more detailed description and troubleshooting help on each
of these components click here.
2. Ignitor
Description:
The ignitor is used to ‘spark’ the lamp by sending a very high
voltage spike, in region of 5000v. This spike will only last a second or so,
and once the lamp is lit the ignitor effectively drops out of the circuit.
(See section 5-'Lamp', to find out more about how a lamp works). Because this
voltage spike is so high, it is recommended not to have a voltmeter or other
test equipment attached to the lamp circuit when it is being ignited.
Testing:
There is no easy way to test an ignitor. If there is any doubt about the performance
of an ignitor in a circuit, the best thing to do is replace it with a new
one.
Connections:
D: Feed from Ballast.
L: Feed to Lamp. Also provides 5000v spike.
N: Neutral- connected to the opposite side of the lamp circuit than L
The correct Lamp voltage can be read at all times (even
during ignition) by connecting a voltmeter across D and N.
This bypasses the voltage spike coming from L.
3. Capacitors
Description:
Capacitors are used to ensure a smooth power flow to the lamp. A faulty capacitor
is often mistaken as a bad lamp. Some MetalBox systems use one high powered
45µf capacitor, while others use a series of 15µf capacitors.
Testing:
Disconnect all wires from the capacitor and short the two terminals with a
metal screwdriver- do not touch the metal as you are doing this and there
may be a spark! Connect the two wires of a Capacitor Testing Meter to the
terminals and test capacitance.
The reading should be no lower than 6% of the capacitors
rating, for example, a 45µf should read 40 or greater;
a 15µf should read 12 or greater. If you have a series
of capacitors, one faulty capacitor will pull all the other
capacitors down.
4. Ballast
Description:
There are two ballasts in a MetalBox system; one large and one small. Both
are used to regulate the power to the lamp. The large ballast is used while
the system is in high or low power, while the smaller ballast is only used
as a boost when the system is in high power or while the lamp is in warm
up.
Testing:
Large Ballast: The large ballast will have wires going to two terminals, one
carries the input voltage to the ballast, and the second carries the output
voltage from the ballast to the lamp (via the ignitor).
1. With the system powered off, remove the wire carrying
the output voltage. Also note
that the terminal numbers and the actual input/ output terminal
may differ from system to system, so you may need to follow
the wires to make sure you remove the correct one.
2. Using a voltmeter, connect one test cable to the terminal that you have
just removed the wire from (the output terminal), and connect the other test
cable to the other side of the lamp (not the side that the output of the ballast
was connected to). Hold down the lamp contactor and take the voltage reading-
it should be the same ( if not a little lower) than the line in voltage. If
it is far lower than the line voltage, the ballast is faulty.
3. Hold in the lamp contactor and test the voltage between here and here (this
wire can be found on the terminal strip in the MetalBox panel- you don’t
have to go near the actual lamp).
Small Ballast: The above test can also be used on the small
ballast as long as you also hold on the High Power Contactor
(C4). Also if the larger ballast checks out OK, while the
system is running in high power, switch the system to Low
power. The lamp should dim a little and the current should
drop from around 11-13 amps to around 8.
5. Lamp
Description:
An Ultra-Violet Lamp works by vaporizing mercury within a pressurized quartz
tube. In order to initialize this process, a high voltage spike is applied
to the electrodes (this is provided by the ignitor). If the voltage spike
was successful at vaporizing part of the mercury, the lamp then enters its
Warm Up stage.
Warm Up:
As the lamp warms up, more and more mercury vaporizes. This can take a couple
of minutes. During this time, the voltage of the lamp starts off very low
(around 30-40 volts), while the current that the lamp draws is high (around
20 amps). As more mercury vaporizes, the voltage slowly rises and the current
falls. Once the lamp reaches around 80-100 volts, the speed of the voltage
rise increases. As the lamp passes approx 250 volts, the lamp achieves ‘Ready’ status.
Ready: When running correctly in High Power, the lamp should
run at a voltage of 260-320 volts, at approx 11-13 amps.
This will vary slightly from lamp to lamp. In Low Power,
the current will drop to around 8 amps and the voltage may
drop to around 250 volts.
Common Lamp Problems:
Most problems accounted to the lamp aren’t usually the lamps fault. Most
of the problems happen with the lamps power circuit, such as faulty ballasts
or capacitors, or are a cause of over/ under cooling.
Cooling is very important to a lamp- insufficient cooling
and the quartz will swell and breakdown. Once the quartz
starts to swell, the lamps normal running voltage will drop
and the efficiency of the lamp will decrease. The lamp leads
may also suffer from overheating which can melt the insulation
and cause a short. If the lamp is overcooled, it may take
longer to reach its correct running voltage or may even be ‘blown
out’ by the blower. This is when the lamp is unable
to sustain an adequate voltage to remain lit. A lamp being
overcooled will run at a lower voltage and so will pull a
larger current. This larger current will put a strain on
the other components in the system.
6. Cooling Blower
The cooling blower is often overlooked in a UV System. Regular
inspection of the blower air filter and hose leading to irradiator
are essential as a good, clean airflow is critical to a lamp’s
life.
The rotational direction of the blower is also critical;
if it is spinning in the wrong direction, insufficient airflow
will result in overheating of the lamps.
On many systems the blower has a baffle to regulate airflow
to the UV lamp. When this baffle is closed too much the lamp
will tend to overheat, which is usually seen when the lamps
become distorted in shape and end fillings and wire possibly
showing signs of extreme heat. On the other hand when the
baffle is open too much the lamp may be overcooled, this
will show when the ends of the lamp turn black. Both of these
conditions are detrimental to the life of the lamp.
Adequate extraction of the hot air from within the press
is also essential. Therefore regular maintenance and checking
of the extractor blower is also important.
Essential Background Information
Lamps
The most obvious and basic rule of UV Lamp handling is to
make sure that they are clean of foreign substances when
they are installed. The easiest way to do this is to use
cotton gloves when handling the lamps, as well as cleaning
the lamp with a soft clean cloth and isopropyl (99%) alcohol.
Even something as simple as a fingerprint will drastically
degrade the function of the lamp.
When installing the lamp make sure that the connections
of the terminal strip are secure. A loose connection could
cause problems that look more complicated. Also check to
see that the lamp wires do not lie directly on the backside
of the reflector, as the wires will tend to get quite hot
and possibly create a short.
The more a UV lamp is ignited the faster it will deteriorate,
so it is best to minimize unnecessary attempts for re-starting
the UV. Due to the nature of printing it is often necessary
to start and stop the lamps many times in a day, one way
to enhance longevity of lamps is after lamp is shut off make
sure to wait long enough for it to sufficiently cool before
attempting to restart it.
Reflectors
The function of the reflector is to focus the energy of
the lamp to a focal on the product. It is very important
to install the reflectors properly since they are responsible
for about 70% of the light that is used to cure the product.
Well cared for reflectors will make lamps appear to last
much longer since the system will be much more efficient
when most of the light emitted from the lamp is being diverted
onto the product the way it was intended. When this is the
case it will seem that the lamp is not curing the product
as well as it should.
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