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Trying to repair a shaver charger

Tha fios agaibh

Aug 11, 2014
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Looks good to me.
Yes, the neutral (N) should go to the wider blade on a polarized plug. If the plug can be oriented either way (non-polarized) don't worry about it because there should not be anything grounded.
I would not use it in countries that use 240v like AU and UK. (could exceed rating) Also know the charge rate will vary a bit because they run 50hz instead of 60hz.
PLEASE BE CAREFUL while experimenting with this or any live circuit. Be sure to use a durable insulation such as shrink tube to cover exposed conductors. I would not trust electrical tape because heat can cause it to unravel or slide off.
Thanks ChrisBlueNZ for comming up with this circuit.
 

PeterC

Jan 28, 2015
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I soldered the diodes together and then onto the red wire but I'm not getting any current through them. I didn't think to test for current across each diode before doing the soldering. Given that the heat shrink tubing (Harbor Freight) is only a few inches long, I knew it wouldn't cover the whole job unless I cut off some of each end of the diode wires. I've never used heat shrink or done much soldering before but I watched dozens of youtube videos yesterday. Given that I'm not attaching these to a circuit board, I thought it would be ok to remove the excess length on each end.

Could the heat from the soldering iron have been too close to the diodes and destroyed them? I didn't touch either diode directly with the iron but did notice the tubing shrink down (even though it was on the other side of the diode, away from the soldering iron) before I even used the heat gun. I only held the iron on the diode wire for a couple of seconds.

In the photos (I carefully cut off the heat shrink), the silver band on each diode is to the right, towards the red wire. The black probe is plugged into COM. I get the same OL reading on the multimeter even if I switch the position of the red and black probes. Could everything be ok and I just not testing them the correct way? I do get a reading when I touch the probes next to each other on the straight wire but not when a diode is in-between the probes.

If I damaged the diodes, I'll order about ten more given that I'm new to this and might make more mistakes before I get it all together. Maybe you're not supposed to shorten the diode wires in order to keep heat away from the diodes while soldering?

Thanks for your helpful advice and sorry I don't have more experience but I'm learning.

DSCN5628_zpsyjmrz3zt.jpg


DSCN5630_zpskczzh8ei.jpg
 
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ModemHead

Dec 2, 2010
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Your Sperry DSA-500 only reads up to 4000 ohms. Due to the low testing current of a digital ohm-meter and the V-I characteristics of a diode, the "forward" resistance of a diode can read much higher than 4K. You need a DMM with a proper diode test function, or perhaps use an older analog VOM.
 

Tha fios agaibh

Aug 11, 2014
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I agree, not the best meter for testing diodes.
Most Diodes are pretty hardy and can withstand quite a bit of heat. So, I'd be surprised if you blew them both up.
Since you don't have access to a DVM with a diode function, you could use a continuity tester, or just use components of a flashlight to test it them.
Hook a battery + terminal to the anode side of the diode, then the battery - terminal to a flashlight bulb, then the other side of the flashlight bulb to the cathode (side with stripe). The Diode should now light your flashlight bulb, but should not give continuity if you swap the Diode leads.
 

PeterC

Jan 28, 2015
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I was able to get everything hooked up successfully and it works! Thanks for the comments about the testers and using them on diodes. I did find another tester I had that has a diode function and got a reading using that one.

After hooking it all up, I charged the shaver for about twelve hours and its working fine. I don't really mind how long it will take to charge but if it is an issue, I have those other components I could try but I think I'll be fine. It's really nice fixing things instead of just throwing them away and buying new.

Thank you everyone for helping out with his. Thank you Kris for designing the circuit for me and picking out the components and thanks to you Fios agaibh for your assistance along the way.

I can see why people get hooked on electronics projects. I have a few other broken gadgets laying around too that I'm going to start tinkering with and I just bought "How to Diagnose and Fix Everything Electronic" by Geier.

-Peter
 
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PeterC

Jan 28, 2015
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I'm about to do a first charge after putting the new power supply module into its charging base. That first charge I did (before putting it all together) lasted 6 months! Yesterday, I put the power supply module and all into the charger base.

Before charging the shaver, I thought I'd do a quick check on the voltage. It's reading 3.7 to 3.9v. Is that correct? Based on the circuit that Kris designed (see the Jan. 29, 2015 entry previously), shouldn't it be putting out 1.2v? I hope I didn't hurt any of the diodes or resistor when pushing it all into the charger base. Before I put the shaver into the charger base, please let me know if this sounds correct?

Here are a couple of photos I just took showing the voltage reading.

Thanks very much

DSCN6978_zpsqnqrklup.jpg

DSCN6981_zpseycme2dx.jpg

.
 

dorke

Jun 20, 2015
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This module is a universal AC input,should work fine anywhere on earth.

Diodes point o.k cathodes(line mark) away from +Vo.

The resistor has no direction,
but it does not look like a 2Watts part,
more like1/2W: that is not good!

N,L :Does your charger have an AC cable?
If it does , How many prongs on the plug ?Is it "polarized"?
In general the L(live) should be connected to the "Hot"-right side of the plug.
 

PeterC

Jan 28, 2015
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The neutral on the power supply module is going to the wider blade of the AC plug (there are two prongs on the plug). This worked fine at charging the shaver 6 months ago when I had it all sitting on my workbench. Maybe it was registering the same 3.7v back then but I don't know as I didn't think to test the output voltage. Now that I have all the parts stuck into the charger base, this 3.7v (or 3.9v) is what I'm getting. I'm sure the diodes and resistor are correct as I used the ones Kris suggested and, as I said, the circuit worked fine at charging the shaver the first time.

Maybe everything is fine and I just don't understand correctly but Kris said the voltage should drop down to 1.2v based on the battery in this shaver. Am I using the voltmeter correctly?
 

dorke

Jun 20, 2015
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The voltage is too high.
Can you test the voltage on the +Vo and -Vo of the module itself?

Btw,how accurate is your DMM?
Try testing a new AA or AAA battery with it.
 

Tha fios agaibh

Aug 11, 2014
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:(Perhaps when you stuffed it in the base the diodes got shorted, giving you the full output of the module?
The 3.7-9 is a little higher than anticipated, so you may need to add a 3rd diode. Which should put the output about 1.3v.
I'm sad Kris is no longer here to finish his post.
 

ModemHead

Dec 2, 2010
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You're depending on diodes and a resistor to drop the voltage. The high input impedance of the DMM draws a negligible amount of current, hence no appreciable voltage drop on those components. So you're essentially measuring the open-circuit voltage from the output of the module.

Achieving a certain voltage is not the goal here, after all that will be determined by the battery being charged. The goal is to limit the *current* to a safe level for charging the battery. Measure the voltage drop across the 3.3 ohm resistor immediately after connecting a discharged battery. (As the battery charges, it's terminal voltage will rise, and the current will decrease.) Divide the voltage reading by 3.3 to obtain the current. The label on your battery indicates that 500 mA is an acceptable rate.
 

PeterC

Jan 28, 2015
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Thanks very much for the suggestions. It isn't easy to measure the voltage across the resistor as I have everything wrapped up with shrink tubing and I'm afraid to pull it all out of the charger base. I had to cram it all in there and do a lot of bending to get it all to fit so I'm afraid pulling it out will break a wire.

I tried another digital multimeter and got a very different reading --- about "065" which I don't understand. So, I decided just to try charging the shaver----I left it in the base for ten hours and kept a close eye on it. It seems fully charged now as it did 6 months ago when I did the first charge. It never felt hot in the base during those ten hours.

Your posting ModemHead was very interesting---I didn't fully understand all of it due to my electronics inexperience. It sounds like you're saying that the 3.7v I was registering on the multimeter may not have been representative of the 1.2v that Kris designed the circuit output for.

Anyway, I guess its working fine. I only need to charge this shaver once every several months so I'll keep an eye on it. I just wish I understood all this better than I do.

Thanks for your help.
 
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ModemHead

Dec 2, 2010
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It sounds like you're saying that the 3.7v I was registering on the multimeter may not have been representative of the 1.2v that Kris designed the circuit output for.

That's correct. The circuit will work as intended only when the battery is connected and the charging current is present. A discharged but otherwise healthy NiCd cell, while charging, will start out at 1.2V and rise to somewhere around 1.6V at the end of the charge. Assuming the converter module output (under load) is 3.3V, and a diode forward voltage drop of 0.8V, I calculate the starting charge current will be 152mA decreasing to 30mA at the end of charge. That's probably less than was intended, but very safe for a 24-hour trickle charge.
 
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