Maxi Mouse lectrosonic charging problems

[pontiacpete]

I'm wonder if someone can help me out here.
This amp isn't doing the charging properly. It doesn't have the original charging transformer,
instead the customer gave me an 18vac /1A charger.
He tells me that batteries are not being charged. I had repaired the output previously(it had a shorted output transistor) and perhaps something happened. At one point in that repair I popped the 2 fusible wires. Anyway the amp sounds good now.
So when plugging in the charger the LED flashes on then off. I see 20vac coming into the bridge rectifier and 20Vdc coming out of it. I believe when the charger is plugged in that light should be on until charging is complete. With 20vdc out of the rectifier there is 20v on the LED anode which isn't lit.
Could someone clarify what is going on here? Shouldn't there be less voltage on the LED, like 9V?
Is the bridge rectifier bad?
Or..... are the batteries shot.?

[52 Bill]

So when plugging in the charger the LED flashes on then off. I see 20vac coming into the bridge rectifier and 20Vdc coming out of it. I believe when the charger is plugged in that light should be on until charging is complete. With 20vdc out of the rectifier there is 20v on the LED anode which isn't lit.
Could someone clarify what is going on here? Shouldn't there be less voltage on the LED, like 9V?
Is the bridge rectifier bad?
Or..... are the batteries shot.?

You are correct, the led lights up while the batteries are charging and turns off when the batteries are charged. The LED monitors the voltage drop across the 4R7 resistor which changes as the batteries draw more or less current. Having 20 volts on one side of the LED only matters when you compare it to the voltage on the other end of the LED. If there is 20 volts on both sides it will not light up.

How old are the batteries? How long have you tried charging them? Lectrosonics suggests that you leave the unit plugged in for extended time periods to force the batteries to take a charge. They also suggest that the batteries not be left uncharged for any length of time.

[g1]

Here's a link to the user manual: http://www.lectrosonics.com/US/categ...l?download=192
Page 3 of the pdf discusses charging. It says the charge light will go out when the batteries are charged. It also says poor batteries may take up to 10 days to reboot, during which time the light may not come on.
I would think the batteries may be in poor condition or completely shot. Very poor batteries can come up to voltage very quick but have no current capacity. In such cases, the "full charge" indicators will sometimes show full charge.

[pontiacpete]

I'm getting 20vdc to gnd on both sides of the LED. Maybe it's shorted? Or in backwards?

I was thinking that the batteries had discharged too much.
When I sort out the LED issue I'm going to plug it in for a long time

[52 Bill]

I'm getting 20vdc to gnd on both sides of the LED. Maybe it's shorted? Or in backwards?

I was thinking that the batteries had discharged too much.
When I sort out the LED issue I'm going to plug it in for a long time

No, if it flashes it is working. I don't think that there is an issue with the LED. If there is 20 volts on both ends of the LED, that means that there is zero voltage across the terminals, which means it will not light up. There will normally be about 2-3 volts across a typical LED when it is lit up.

What voltage do you get at the output of the regulator circuit, or across the two batteries?

[pontiacpete]

The LED is now in the correct way and just flashes quickly on/off when plugging in the charger. I reversed it by mistake
Across the 2 batteries it is reading 12vdc, so they aren't shorted?
I should plug it in now for an extended time and see if the LED comes on.

BTW, when the leads of an LED are cut equally how do I determine which is the anode and which is the cathode?
I see that putting the DMM in diode mode, touching the LED one way turns it on, I suppose I should pull this one again and find out for myself.

[52 Bill]

BTW, when the leads of an LED are cut equally how do I determine which is the anode and which is the cathode?
I see that putting the DMM in diode mode, touching the LED one way turns it on, I suppose I should pull this one again and find out for myself.

An LED will test just like any other diode. The voltage reading will be higher than a typical silicon diode, but it will conduct in one direction and not in the other.

Even though the batteries show a 12 volt reading they may still be suspect. What voltage reading do you get at the output of the regulator? For charging purposes this reading is more important than the voltage on the batteries.

And yes, try charging the batteries for an extended period to see if they are still usable.

[g1]

There is often a "flatted" side of the plastic part of the led that denotes the cathode. Looking down at the top, rather than a perfect circle it will be a bit of a D shape.
It's possible a cap with a series resistor in place of the batteries would show if the Led and charging circuit are working right.

[pontiacpete]

There's a -6.3v on pin 3 of the regulator, where the .15uf, .1uf and 2.2r meet.

I tried subbing in a .1uf and a 10k resistor in series for the two batteries and the LED flashes the same
as with the batteries.

[g1]

I was thinking more of a big filter cap, like 4700uF or something.
I would guess you should have neg.6 or 7V at pin 1 of regulator, pos. 6 or 7V at pin 3.

[pontiacpete]

Here are the voltages on the regulator. I messed up on the readings.
Pin 1 neg 8vdc
Pin 2 26vdc
Pin 3 -3vdc
Pin 4 -3vdc

Is this regulator not working? Or the bridge?

Tried the 4700uf and 10K resistor in place of the batteries and the LED lights a little and stays lite.
what does this mean?

[52 Bill]

Here are the voltages on the regulator. I messed up on the readings.
Pin 1 neg 8vdc
Pin 2 26vdc
Pin 3 -3vdc
Pin 4 -3vdc

Is this regulator not working? Or the bridge?

The bridge is putting out 26 volts dc, so it is working. The output of the regulator is sitting at -3 volts. Either the regulator is bad or something in the feedback circuit is giving you that reading.

Did you mess with the trimpot?

Tried the 4700uf and 10K resistor in place of the batteries and the LED lights a little and stays lite.
what does this mean?

It means that the led circuit is probably okay and working.

Do you understand the basic principles of lead acid battery charging? It's just like the battery in your car, except the light goes on while it is charging and not while it is discharging.

The voltage coming out of the regulator must apply a voltage greater than 12 volts (nominal) across the two series connected 6 volt gel cels in order for the batteries to charge up.

Unplug the amp and read the voltage across the two batteries. Now turn on the amp and read the voltage across the two batteries. Now plug in the charger into the amp, what voltage reading do you get across the two batteries?

[pontiacpete]

"Did you mess with the trimpot? "

No, not yet.

Do I understand lead acid battery charging? I think so. But I really appreciate anything you have to say about this subject.

with amp unplugged for the charge there's 12.9vdc
with amp on no charger 12.7vdc
with the charged plugged in there's 12.9vdc

[52 Bill]

With those voltages, it looks like the batteries are charged. Is the amp working?

[pontiacpete]

Yes the amp is working. It was brought back to me(after I repaired the output) he said the batteries didn't last very long and the LED didn't come on when charging and he didn't think the batteries were charging.
Perhaps I'll try leaving it on for a couple of hours then try charging.