ign Company - 51 Nassau Avenue - Brooklyn NY 11222-
USA
USA
718 599-0170 718 599 -0172
www.goddarddesign.com
LilDMXter (FD DMX-1) Power Supply FAQ V1s
How long should a battery last?
There is no exact answer to this question. If you leave your unit in deep discharge in the cold
trunk of your car in winter, you can kill a battery in three months. On the other hand we have seen
units with 4-year-old batteries that still work. We feel that when a battery is more than two years
old it definitely time to replace it. A unit in hard use may require a new battery every 12 to 18
months.
1)
We are having problems with a number of our DMXters. Even when plugged
into AC power the operation is intermittent. In particular, cable test causes the unit
to crash, often writing random characters to the display.
2) We are having problems with our LilDMXter; it works fine from the mains
supply, but isnt charging the internal battery.
The single most likely cause of a problem with your LilDMXter (FD DMX-1) is a dead or
dying battery.
It is important to realize that the LilDMXter always runs on battery. This is a floating battery
design, there are no large storage capacitors in this supply. The battery charges when AC mains
are at peak and discharges when the line is low. For a unit running on AC with a battery that is
nearly charged the net charge current to the battery is very low. When the battery is discharged,
the net charge will be high.
As batteries age they get less able to accept charge. At first they do charge but the charging
current is greatly reduced. The cell voltage will rise properly and they will drive the load but have
lower amp-hour rating.
I leave my DMXter in my road tool box in my car. It is often discharged when I go
to use it. Am I hurting the batteries?
Yes, The lead-acid gel cells we use are not harmed by shallow charges. While charging any
battery wears it out gel cells are damaged far quicker by being left in fully discharged (a.k.a. deep
discharge) for a long period of time. While I know it is a pain, get in the habit of opening the unit
after a job and switching off the battery. Or if you are feeling flush, buy a new LilDMXter2 that
has a 4-6 month battery shelf life. Page -2-
At what point does the DMXter start showing feed me messages?
A fully charged battery provides about 6.3 volts. Reasonably quickly this will drop down to 6
volts. When the battery voltage drops to 5.6 - 5.5 volts (5.56 volts nominal) the DMXter will start
sending low battery warnings. When the voltage drops to 5.28- 5.14 (5.2 volts nominal) the unit
will shut down. The battery voltage is somewhat dependant on the current drawn hence some
operation will cause low battery messages sooner. Cable test consumes the most power and will
cause low battery messages soonest.
How much voltage must a battery have for a DMXter to work correctly?
To turn on The LilDMXter must have a charge of at least 5.6 volts on its battery. Since the
battery voltage drops under load a unit with a standby voltage of 5.7 will start but will most likely
send low battery messages almost immediately. A unit that has a charge of 5 volts when in
standby and NOT plugged into AC will probably work immediately when plugged into AC power.
A unit with a charge of 4 volts will require recharging time before working.
My DMXter is discharged, I plugged it in for two hours and it still does not work. Is
there any point in letting it charge further?
Yes, a battery that has been deep discharged may take charge very slowly at first. After a period
of time the rate of charge will increase greatly and the battery will return from a near death
experience. We find that charging a unit for 24 - 48 hours may salvage a battery. A good test of
your batterys condition is how long it will run double end cable test. We have seen batteries sent
to us as dead recover to the point that they will run double ended cable test for six hours. (A new
battery will do this for seven to eight hours.
But if you have to resort to a long charge to get your unit to work you have a damaged battery
and should consider buying a backup one.
I know my DMXter has a good battery but it will only run when plugged into AC
and then it does not produce good DMX-512 out. I also notice that the display
back light flickers what is wrong?
Did you remember to turn on the internal battery switch? This is a common cockpit problem. Is
it possible that one of the push terminals used to connect the battery has come lose? You should
also check that the battery wire hasnt broken or the crimp connection to the terminals has come
loose. This is also a symptom of a dead battery, use a volt meter and check that good battery.
My LilDMXter charges fine but does not hold a charge on the shelf. What is
wrong with the charger? Page -3-
Unfortunately the LilDMXter-model FD DMX-1 only has a charge shelf life of fifteen to twenty
days. If left with the battery switch on it will discharge to the point that it will not operate without
recharging. This characteristic has been greatly improved on model FD DMX-1B LilDMXter 2.
If you are getting a shorted shelf life the problem is most likely an aged battery. If you wish to
eliminate any electronic problem as the cause of a short shelf life, you can measure the standby
battery current.
With the battery switch off connect a good DC ammeter in series with the battery. Turn the
battery switch back on. To get a valid measurement you must turn the unit on and have it
running correctly. Then shut it off using the <OFF> key. Once the is sleeping message is
removed from the display the unit has entered standby. The current now showing on the meter is
the standby current. It should be 2.8 mA or less, 250µA or less for a FD DMX-1B.
On a few units produced in 1993 and 94 we have had problems with the .1µF bypass capacitors
becoming leaky with age. This causes the increased drain noted above. These units should be
returned for service.
What is the nominal power supply voltage? How much current should it be able to
supply to the LilDMXter?

Over the life of the LilDMXter 1 there were three major revisions to the power supply card. The
first version is all PCBs R2 or less. The other two versions are R3 and R4-R5-R6. All versions
can supply 5 volts +/- .1 volts at 200mA. All three versions are current limited. R2 and R3
versions will fold back to 95mA or less under a dead short. R4 boards will supply about 300mA
into a dead short and will supply considerably more in a low load for a few moments. The R4
version is thermally protected and will shut down when the device temperature requires.
I have tested the output from the charging circuit and am getting 6.9 volts dc @
47ma when the DMXter is turned off.
Into no load with the battery replaced by a 1000uf capacitor the charger should put out 6.9 volts.
This voltage is controlled by the trim pot on the board. This will be the voltage into a fully
charged battery. I consider that a battery that only accepts 30mA is fully charged. Your battery is
very nearly charged. It may also be very nearly dead.
A new battery charged to say 5.5 volts should accept an average charge current of more than 150
mA. The supply should at least supply 6.6 volts peak into a 30-ohm load.
When turned on the current drops to about 8mA.
I would suspect an old battery. The charger is a simple device consisting of the mains transformer,
a full wave bridge, and an LM317 adjustable voltage regulator set for 6.9 volts as per above. Page -4-
I have tried new batteries but this doesn't improve the situation.
If the supply is not able to supply the current required, it is possible that one of the four windings
in the transformer is open. Each primary winding has a DC resistance of approximately 330-ohms
(A total of 660-ohms wire for 240VAC and 165-ohms wired for 120VAC.)
Each secondary winding has a DC resistance of approximately 4.4- ohms. They are wired in
parallel by the PCB so you will see 2.2 on a good unit. I would not expect these values to be too
exact, just a good guide. (This problem is extremely rare.)
I use my DMXter on my test bench. It is always plugged into AC. Will this shorten
the battery life?
Yes, Leaving a unit always plugged in can shorten battery life. It is not as bad as letting it sit on
the shelf in deep discharge but it does not help maters that much. There are several things that you
can do to improve matters. The first suggestion from our V1.70 manual is something that we
recommend that owners of all units shipped before April 1997 do.
Page -5-
The second suggestion is one that will keep your LilDMXter ready to go without overcharging
the batteries. Purchase an air conditioner timer of the type that is a 24-hour clock that switches on
and off the AC power at set times. Set it to be off for 23 hours and on for one hour. Whenever
the LilDMXter is just sitting around plug it into the timer.
12.3 MODIFICATION FOR CONTINUOUS LINE OPERATION
If you plan to use the unit plugged into AC on a continuous basis, you may wish to make a simple
modification to the unit to prolong battery life. As above, remove the unit from the case. Place the unit on a
table with the Goddard Design Co. logo on the left. Approximately in the center of the open side of the end
toward you, you will see a flat cable connector. Below it, on the other side of the PC board is the shunt. Pull
this straight down, using your fingernail, to remove it. This removes the trickle charger; the unit will work
just the same without it. Do hold onto the shunt you have removed in case you use the u