Article
Sep 2004
Measuring Battery Drain.
Why is it important?
OK, you’ve got a dead hearing aid and you want to
know what’s wrong. You take it to Charlie the tech who plugs it into his
drain meter and immediately says, “looks like a broken receiver wire”.
Amazing! How did he know this so quickly without even cutting the hearing
aid open? First of all, Charlie has probably been doing this awhile and
has some experience, but more importantly he knew how to interpret the
battery drain of the hearing aid.
What is Battery Drain anyway?
Battery Drain is actually a non-scary name for the amount of
electronic current being used by the hearing aid circuit. Everything
electronic uses a certain amount of electrical current, no matter if it
plugs in, or runs from a battery. We normally think of electrical current
in larger terms, such as an appliance you plug into the wall. For instance
your refrigerator probably uses 10 amperes (amps) of electricity at times,
and your clothes dryer may use 20 amps. It is no different for hearing
aids, except we are talking about maybe .5 milliamps, or .0005 amps.
How is Battery Drain measured?
Typically, to measure battery drain you need a device that can supply
power to the hearing aid, and at the same time the device needs to be able
to measure how much electronic current the hearing aid is drawing. Many
acoustic testing units are capable of measuring battery drain, and some
stand alone units such as the BDM-1 and BDM-2
Batter Drain Meters also do this.
You also need a coupling device commonly referred to as a battery pill.
The battery pill plugs into the drain
measuring unit and has a contact that will plug into the hearing aid
battery compartment, simulating a battery.
What will Battery Drain tell me?
The battery drain of the hearing aid can tell you a lot about how the
hearing aid is working. It is always a good idea to include it in your
pretest before fitting to ensure proper operation. Sometimes, a hearing
aid can acoustically test just fine, but have a circuit problem where it
is drawing excessive electronic current. Remember, battery drain
represents how much electronic current is being used from the battery. The
higher the drain, the shorter the battery life.
Drain Meters are a great time saver
Now, if you repair hearing aids and you don’t have a dedicated drain
meter for your workstation, you are really missing out. This can be a real
time saver because you can power the hearing aid and even listen to it
while measuring the drain. And some drain meters, such as
BDM-2, have a voltage probe to measure DC
voltage. This is a handy feature as you only need the positive probe. The
negative is supplied through the negative battery contact. This also holds
true for using other test equipment, such as an oscilloscope. Because the
negative contact is connected to earth ground through the electrical plug,
only the measuring probe is needed – very convenient.
How do I know if the Battery Drain is normal?
That is really going to depend on the type of circuit inside the
hearing aid. The best way to find what a normal battery drain is for any
particular circuit is to check with the hearing aid manufacturer. But, a
typical battery drain for your average circuit could be anywhere between
.3 ma to .8 ma. Push Pull and high powered circuits can be as much as 2
ma.
Don’t I have enough to do without testing battery
drain?
Probably. But if you have a dedicated Battery Drain meter, you can use
it to power the hearing aid while performing your listening test.
Multitasking saves time, and if you can catch just one problem hearing aid
before it reaches your customer you win!
About the Author
Chris Perkins is the owner of Lightning Enterprises, and facilitates
the Lightning Enterprises newsletter. He has worked in the hearing aid
industry since 1991 in hearing aid manufacturing and product development,
as well as equipment and process consulting.
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