LED charging Indicator For Duratrax ICE Charger

[Tom Frank]

I just got the Duratrax ICE charger and really like it's features, but there is no visual indicator, e.g. LED that can be seen from a distance to indicate if the charger has completed it's task. Yes, I know there is 5 different tone signals that can be selected that does this, but they are all high frequency (like my Futaba TX), and I cannot hear any of them from more than about 2 ft. away.

Does anyone have access to, or knowledge of, the ICE charger internals, or suggestions how I might add either a charge cycle LED or end of cycle alarm?

I have a 3v buzzer I can hear, but not sure how that could be added. I need to tap into the circuit board, I think. Could I simply parallel across the existing beeper pins?

[Chippie]

So why not add a flashing led across the beeper...? when the beeper sounds to indicate charge complete the led flashes too.....Would that not suffice?

[Tom Frank]

So why not add a flashing led across the beeper...? when the beeper sounds to indicate charge complete the led flashes too.....Would that not suffice?
I tried this yesterday. The LED does light when the charger beeper chirps, but the beeper has a time limit, with a maximum duration of 3 minutes. So, if I happened to step away for a few minutes, I could miss the alarm. My old inexpensive charger has a red LED to indicate when it was charging, and a Green LED (as well as an analog meter that could be seen from quite a distance) to indicate when it was done... very simple and effective.

I also tried the buzzer I had, and it, too could be triggered witht he beeper signal, but there is some kind of problem with it latching on when it shouldn't be on, and off when it should be on. It was very erratic and unpredictable for some reason. Too bad... I could easily hear it from across the room.

Finally, I found the existing beeper is very simple construction... just two spring contacts inside the plastic housing and a metal disk with piezo crystal material on the center. One contact rested on the metal disk edge and the other on the piezo crystal. If I could find a replacement disk that would sound a lower frequency, I might be able to just drop it in and hear it.

I need something lower than 1k hz, preferably 500 hz or lower.

[presslab]

Hi Tom,

I think they are driving the beeper frequency directly as the charger can output different tones. So by changing the beeper the frequency will remain the same although it may be louder or softer.

Now I've been thinking about this problem and there may be a solution. What you want to do is detect when charging has completed, which would be indicated by a charging current of less than 0.1 A. This could attach externally to the charger in series with the charging leads.

I'll see if I can come up with a circuit a bit later.

Ryan

[Tom Frank]

Hi Tom,

I think they are driving the beeper frequency directly as the charger can output different tones. So by changing the beeper the frequency will remain the same although it may be louder or softer.

Now I've been thinking about this problem and there may be a solution. What you want to do is detect when charging has completed, which would be indicated by a charging current of less than 0.1 A. This could attach externally to the charger in series with the charging leads.

I'll see if I can come up with a circuit a bit later.

RyanHi Ryan,

The charger does have different tone sequences it can produce, so I think you're right about the beeper. I have a regular miniature coil/magnet speaker I could try as well to see if more volume would do the trick as well.

I had thought something on the output end could be devised, as long as it doesn't interfere with the battery detection circuitry. I wonder if a simple 12 v LED with integral resistor across the charge leads would work (on when charging... off when done)? If you have a better solution, I'm all ears.

Tom

[Warske]

I wonder if a simple 12 v LED with integral resistor across the charge leads would work (on when charging... off when done)?
I don't own this type of charger, but I would think the charge leads are attached to the battery, and the fully charged battery would keep the LED on?

Seems like a perplexing problem. A few off the wall ideas:

1) If you google: sound activated switch
you might be able to come up with something that would turn on a lamp or a loud buzzer when it detected the beep. You could put its microphone close to the charger and turn down its sensitivity so it isn't accidentally triggered.

2) There are bat detectors that work by amplifying the ultrasonic sonar tones that bats use, then they run the signal through a frequency divider so that its frequency is reduced to the range of human hearing. Perhaps something like that would work for your application if you could get it to drive a speaker at a lower frequency. Google: Bat detector

3) Instead of wiring a LED across the beeper, you might try wiring a sensitive relay. Then wire the relay contacts to turn on a loud low frequency buzzer and power it using a separate battery or a wall wart power adapter. Of course, like the LED, it won't stay on.

A reed relay such as the Radio Shack #275-232
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=275-232
might work. It turns on at 3.5 volts, and has a coil resistance of 500 ohms, which is high enough it shouldn't damage the charger circuitry. Can't tell if this relay is sensitive enough until you try it.

4) You can turn the reed relay into a latching relay so that it stays on even after the beeper stops. Then use it to turn on an LED. This comes close to what you were asking for.

To make the relay stay closed, just fix a little refrigerator magnet close to it. It needs to be far enough away so that it doesn't close the reed by itself, but close enough so that when the reed is closed by the current in the coil, it stays closed. The magnet must also be oriented so that it adds to the magnetic field from the coil, instead of opposing it. If it doesn't work facing one direction, just flip it over.

Adding the magnet makes the relay even more sensitive, so it is likely this would work.

To unlatch the relay, you can move the magnet away, or you can bring another magnet that is facing the opposite direction close to it to cancel the field from the first magnet.

Anyway, not sure any of this is practical, but you said you were looking for ideas...:)

Warske

[Tom Frank]

Warske,

Some interesting (although more detailed) ideas there. Thanks. You're right about the battery powering the LED (I was half asleep!).

For all the neat features they built into this charger, it seems they overlooked something as simple as visual charging circuit indicators (other than the LCD screen).

[jklap]

I'd say the easiest solution would simply be a flip-flop of sorts that would trigger when the buzzer first went off-- then, even after the buzzer is done the flip-flop still stays triggered and driving the LED.

Nothing here to draw with here, so I'll try to describe what I mean--- connect the buzzer postive lead to the Base of a SS GP transistor with a diode. If the buzzer voltage never goes above the diode drop you'll need to bring the voltage up first. The Emitter of the transistor should connect (ie loop-back) to the Base of the transistor (this causes the latched flip-flop as once the base gets enough voltage to turn on the current from the Collector, the Emitter voltage goes up and feeds back to the Base) between the diode and the base--- if you connect it between the buzzer and the diode your going to drive the buzzer all the time-- plus you really don't want to push any voltage up that line--- who knows what the limitations may be. Also connect the Emitter to your LED and current limiting resistor for the LED, and then to ground. The Collector of the transistor goes to your driving current-- you'll need to dig around and find something, but +5 volts should be enough-- maybe directly tap off of the incoming voltage from your input source (LEAD battery, PSU, etc)- though that's likely up around +12 volts-- just make sure your diode and transistor can deal with that voltage level.

Couple of other notes--- you can always use a Mosfet instead of a GP transistor--- this keeps your current draw from the buzzer circuit to almost nothing-- especially since you don't know what limitations there might be on that circuit. Whatever you do, be aware that putting any type of change on the buzzer circuit could (will?) have an effect of the charger itself--- whether effect is a problem or not depends on the circuit itself. Likely not, but just keep it in mind as this means driving anything directly from the buzzer circuit.

-J

[Tom Frank]

jklap,

Thanks for suggestions... I think I understand, and I have a +5v tap off my surplus PC power supply I use to power the charger.