52 Installation and trouble shooting low voltage d.c. lighting

52 Installation and trouble shooting low voltage d.c. lighting

DC lighting installation guide for Thin-Lite, Light It Technologies and

Iota Engineering products.

This page is designed to help you in your low voltage d.c. lighting

installation or retro-fit as well as helping in troubleshooting your

existing system.

Before you start your installation project, lay it out on paper. From

past experience this will help insure that it is done right the first time.

A very important thing to keep in mind is: low voltage (lower than

the rated voltage) will reduce the life span of a low voltage

d.c. fluorescent light fixture. The electronics in a dc fluorescent

light is actually an inverter/ballast. It takes low voltage d.c., inverts it

into alternating current - then steps it up to a high voltage/high

frequency to fire and run the fluorescent tube. From this point on we

will refer to the inverter/ballast as simply a ballast.

Let's do some math. For example, a 12 volt d.c. ballast driving a 12 watt

fluorescent tube will consume a little over one amp. Volts times Amps

equals watts. Volts are the pressure, amps are the the quantity and a

watt is the power of the work being done. If the incoming voltage is too

low, the ballast will make it up in amperage. Amperage also equates

to heat in the electronics. This reduces the operating life of the ballast.

Please note, a ballast can draw from 100 percent to over 200 percent of

the rated amperage on start up. The factors that can affect this are:

low supply voltage, a cold fluorescent tube or an old fluorescent tube.

Here are a couple examples of what can go wrong with poor planning

of a system:

First Example:

In December of 2008 we received a call from a customer in New York.

They need some 24 volt / 32 watt ballasts shipped next day air. The

customer did not say what they needed them for, just that they needed

them. Well, they got them as planned

About a week later I received a call from the customer saying that all

of the ballasts had self-destructed. Here is the picture after I grilled

them. Each 32 watt ballast was connected to a 36 watt fluorescent

tube - it will work but the tube would not be driven to full brightness.

Next, each ballast had its own 10 ga wire going to the same switch.

The 10 ga. wire is okay but having eight of these ballasts connected

to the same switch is a recipe for failure. Please note that these lights

were in an outbuilding near a runway and in the snow. It gets better,

the batteries supplying the ballasts were in another building over

fifty feet away. The wire run, using 8 ga. wire, would have been a

minimum of seventy feet. When the switch was turned on, all of the

lights tried to fire at the same time, the voltage dropped dramatically

which caused the ballast to over-amp and smoke.

Second Example:

Last year (2009) we received a phone call from a repair shop in the

San Francisco Bay area. They had a mobile disaster command post,

a full size bus, in for repair. The vehicle had twenty-four 12 volt / 30

watt fluorescent light fixtures. The command post conversion was about

six months old and all but a few of the light fixtures had failed. Each

light had its own switch but the people using the vehicle left all of the

switches on for convenience. There was a master switch inside the

doorway and on entering or leaving the vehicle they would flip the

switch. All of the non-essential gear such as lights and radios drew

power through this switch. There was one circuit for all of the lights.

Let's see, twenty-four 30 watt fluorescent lights (not counting the

other 12 volt loads) coming on at the same time - that sounds like

a minimum of 60 amps on startup. It is surprising that the lights acutally

came on in the first place. This was another installation that was

doomed to failure because of poor planning.

Third Example:

Last year we received a call from the owner of a forty-foot house boat.

The batteries were on one end and there was a single 12 ga. lighting

circuit supplying power for several 1056 tail light bulb fixtures. He

wanted to replace these lights with fluorescents for more light and

efficiency. The electrical system was 12 volts and there was no way

to replace the existing wire with a larger size. The bottom line was

that this installation could not be retro-fitted with fluorescent lights. It

could have been upgraded with LED lighting but the cost would have

been prohibitive due to the amount of area to illuminate.

Fourth Example:

Several years ago one of our customers who lives off-grid with a 12

volt photovoltaic system wanted to replace their incandescent lights

with 12 volt compact fluorescent lights. With very little sunlight during

the winters in Michigan, they were often running low on battery power

and had to use propane wall lighting. He replaced the incandescent

lights and everything was fine until the following winter. They had one

lighting ciurcuit which supplied three bedrooms in a line. In the

farthest bedroom the compact fluorescent lights started failing, then

the ones in the middle room. The bedroom closest to the battery bank

had no problems. Because of the difficulty in rewiring a circuit for

each room, they went back to low voltage incandescent lights for the

end bedroom. They also used 12 volt LED lights in all of their reading

lamps which worked out fine.

These stories are brought up to give you an idea of what kind of planning

is needed for a successful low voltage d.c. lighting system. When done

right they perform well for years.

One of our 12 volt dc. outdoor lighting systems has a Thin-Lite mod. 153

light which has always had a 40 watt tube in it as well as a McLean 30 watt

fixture. I installed these around 1985 and they work just fine today. These

are used once or twice a day, always have the proper voltage and when

a tube starts to go bad, it gets replaced.

A note on recreational vehicle lighting systems.

Many motor homes will have a single wall switch which operates

several 12 volt d.c. fluorescent lights. The wall switch is usually designed

for a.c. (alternating current) operation and will not stand up to long

term use with direct current. As the switch is used, the contacts start

to burn and crater. This increases the resistance which lowers the

voltage going to the lights. It is not unusual to get a call from a customer

with a several year old RV where a few of the ceiling lights have

failed within days of each other.

Trouble shooting you system.

When you start to have problems with your system the first thing to

do is to check the voltage at the fixture itself. Check the voltage

while all of the lights are running. If you do a voltage test with no

load on it you can get a good voltage reading - usually the

same as if you checked it at the battery.

If the battery is low, or the wiring is too light, or the switch has high

resistance in it, or the connections are not tight - it will show up under

load.

The wrong way to wire a low voltage d.c. lighting system.

low voltage d.c. lighting wiring the wrong way

The right way to wire a low voltage dc lighting system.

The following chart gives wire size recommendations

based on the amp draw on the circuit and the distances

the lights are away from the battery(s). This is for a

12 volt system.

For a 24 volt system you can use the next smaller wire

size than shown for 12 volt.

For a 48 volt system you can use two smaller wire sizes

than shown for 12 volt.

Amps	14 ga.	12 ga.	10 ga.	8 ga.	6 ga.	4 ga.	2 ga.	1/0 ga.	2/0 ga.	4/0 ga.
1	90	140	230	360	580	912	1440
2	45	70	115	180	290	456	720	1160	1440	2120
4	20	35	55	90	145	228	360	580	720	1160
6	15	24	35	60	95	150	240	386	486	760
8	11	17	30	45	71	114	180	290	360	580
10	9	14	24	36	57	91	145	230	290	460
15	6	9	14	24	38	60	96	153	192	300
20	4	7	11	18	29	45	72	115	145	232
25	3.6	5.6	9	14	23	36	58	92	116	184
30	3	4.8	7	12	19	30	48	77	97	154
40			5.6	9	14	23	36	58	72	112
50			4.6	7.2	11	18	29	46	58	92
100					5.8	9.2	14.4	23	29	46
150							9.6	15.4	19.4	30
200							7.2	11.6	14.6	22

Knowing what the amp draw for a low voltage d.c. light fixture is very important

is setting up, or trouble-shooting, a lighting system.

Basically you take the wattage of the light, divide it by the voltage and add

about twenty percent for fudge factor.

This will give you an approximate amperage draw while the light is running.

Starting up a dc fluorescent light requires a higher amp draw than when it

is running.

The starting amp draw can be 1-1/2 to 3 times the running amperage.

This is affected by the following:

Temperature of the fixture, the colder the tubes, the harder it is to fire

them.

Condition of the tubes, as the ends darken it takes more power to

ionize the gas and fire the tube.

Battery voltage, as the battery voltage drops the draws more amps

to fire the tube.

Above is an old, nasty looking Thin-Lite (REC) model OEM-153 light fixture.

I installed this back around 1985 under a covered outdoor area.

It runs off of a gel cell battery that is charged by a 70 watt solar array.

I do not know how many tubes it has had since then but the ballast is

the original one.

This light gets turned on almost every morning for one to three hours,

depending on the time of year.

It is used in the evenings a few times a week.

The battery is always kept at the highest state of charge possible, the wiring

is heavy enough for this fixture and the connections are tight.

I figure the long life of this fixture is due to the above factors along with

a limited number of on/off cycles.

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