Amateur Opens Charger- Fixed!

Oh Great Sphere,

I'm a total amateur, but you might get a laugh out of this. (scroll down for photos)

My 10 year old 36V charger has taken longer and longer to turn on its red power LED after flipping the power switch on. It works perfectly once it does turn on, giving the same 2.1A current it always did, but it takes ten minutes to turn on now so I've decided to open it up and attempt to fix it. It is branded "High Power" and looks just like this one on Justin's site, except mine is rated at 2A of charging current-

http://www.ebikes.ca/shop/ebike-parts/chargers/cg364lim-ez.html

I unscrewed both endcaps but the circuit board would not slide out. I tried heating the aluminum case to expand it, but no luck. Once I removed the sticker on the side (a-hah!), two screw heads appeared- after removing them the circuit board slid out easily.

I figured the problem was likely a bad capacitor, as TVs take "longer and longer" to turn on sometimes and bad caps are the problem. It also seems like a part that fails regularly and has a time constant related to it, unlike, say a resistor. So I expected to find a bulging cap inside, but to no avail! I did find a resistor that had turned the yellow "potting goop" (see photo) brown and it became suspect number one. Now you are familiar with (horrified by) the level of my analysis.

I removed the pictured resistor and tested it with my multimeter- it was 1500 ohms just like the color code "brown green red" specified. I also realized it was connected to the red and yellow/green LED indicators and was probably there to limit current to them. Since these LEDs were still working fine, it really wasn't likely to be the problem so I cleaned the holes with some braid and soldered it back in with a sigh.

I next removed the large cap next to the wire-wound inductor. It was suspect because it had a green "passed QC" sticker on it- who would put a sticker like that on a component if it weren't prone to fail??? I've heard about ESR "equivalent series resistance" testing for caps, but don't have an ESR meter so I took it off of the board and tested it as best I could with a multimeter. It was not bulging, but I've heard (read on the net) that some caps fail without bulging. Here are the tests I performed on the multimeter-

Test 1- did it have the indicated capacitance? yes it did
Test 2- when discharged, did the resistance on the meter rise from 0 to 500K ohms? yes it did
Test 3- charge it to 12 V and see if it holds it overnight, it lost about 0.5V, seems ok to me

I then thought about it, and realized that a large cap next to a wire wound inductor both located near where the DC charge current exits the charger to connect to the battery being charged was likely part of the DC-DC buck converter to smooth out the voltage on the charge line. That shouldn't make it take "longer and longer" to turn on, so I soldered it back on the board with a longer sigh.

I could have given up at this point, but I'm a member of the Sphere, and by God, I'm not done with it yet.

Now I looked over to the side of the board where power comes in from the wall. Sure enough, two large caps wired in series (upper left of board in first photo) were connected to the red wire from the wall. Now this could be the problem! They were wrapped in black heat shrink, but showed no signs of high heat exposure or bulging. I removed both of them and subjected them to the same tests 1,2 and 3 mentioned above and they performed well. I'm guessing that these caps take a lot of current so two identical caps are used in series to produce half the capacitance with more "robust" performance. I think AC current is supposed to pass right through caps, so these must be some kind of filter. I can't come up with a reason why they would cause it to take so long for the charger to turn on, but I still suspect one or both may be the problem.

So, if anyone is still reading, what are your thoughts?

A. you really should get an ESR meter because your cap tests are meanignless/somewhat meaningless/useful but not conclusive...
B. those caps aren't likely to be the problem, but ____ is probably what is wrong...
C. just buy another charger for $115 from Justin and call it a day while doubling your charge rate...
D. buy new caps at Digikey/Mouser and whack 'em in, then turn it on...
E. at your level of knowledge, I expect to hear about KFF in the next post...

All who read this post should consider themselves blessed by the mighty solar powered Norfolk pine.

I cannot help one bit but enjoyed reading the post. Good luck.

I wonder whether it has a pre-charge circuit with a leaky cap or something... I don't think the big caps are the problem.

Some power supplies are fully isolated, others have a very high ohmic resistor (mega ohms) going from the high voltage part to the low voltage
part. The way it works is that the resistor (coming from a few 100 V and going to the 5V supply) provides a very small initial voltage that powers up
the low voltage control circuitry. Once this is running it provides its own working voltage and all is well, but it sound like in your case something
is wrong with the generation of this initial voltage... If the caps in the low voltage part are leaky (everything gets forgetfull with age) the leaking
away current is so high (wrt the current supplied via the high ohmic resistor) that the initial voltage cannot be generated.

Thanks, guys.

I hope you have a summer of great riding in Wales, brumbrum.

Rebel General Lebowski, thanks for bringing your expertise to bear. This sounds very logical- I'll scan the circuit board with a bright light behind it to see if I can find a component whose connection fits your description.

I've learned one more thing by accident- I rode out to O'hare in the cold and watched a 747-8 land directly overhead at 200-300 feet. I thought the sky was being ripped in half. When I got back my charger had been out in the 40 degree air for several hours. It took a lot longer for the power light to come on. I put it in the refrigerator for two hours and then ran a power cord into the fridge and switched it on... it never powered itself up, despite waiting 2 and a half hours. I then put it in the bathroom with a space heater on high for an hour and it powered up in five minutes. So something appears to need to actually physically warm up, not just wait for charge to accumulate.

Should I look for anything in particular? Maybe there is a loose solder joint that needs thermal expansion to make contact? I have no idea... any thoughts are welcome!

i think you should just buy a new charger. i saw no evidence of any voltage measurements or even attempts to measure and voltages inside the unit with your voltmeter so i suspect you don't have a voltmeter.

since you have now removed critical components there is no way to know if they were replaced properly so now the ability to diagnose it is eliminated even if you had a voltmeter.

the capacitors do not take 10 minutes to turn on. they are usually filled within 30 milliseconds of when the current flows into the charger.

silentflight said:

I've learned one more thing by accident- I rode out to O'hare in the cold and watched a 747-8 land directly overhead at 200-300 feet. I thought the sky was being ripped in half. When I got back my charger had been out in the 40 degree air for several hours. It took a lot longer for the power light to come on. I put it in the refrigerator for two hours and then ran a power cord into the fridge and switched it on... it never powered itself up, despite waiting 2 and a half hours. I then put it in the bathroom with a space heater on high for an hour and it powered up in five minutes. So something appears to need to actually physically warm up, not just wait for charge to accumulate.

Should I look for anything in particular? Maybe there is a loose solder joint that needs thermal expansion to make contact? I have no idea... any thoughts are welcome!

Click to expand...

The little mouse in there doesn't like the cold as he gets old. (You did say "any thoughts are welcome!" :wink: )

Sorry, I don't have a more scientific explanation, but chargers are nothing to "play" with. They -in concert with batteries- are primary constituents for most fires on the 'Sphere. unless you are very confident in it's operation and your repair, I would get a new one. At 10 years old, it's done a decent job and had a nice life.

I would agree with cal3thousand that you're probably better off with a new charger.
To dnmun's point...the thing is already 10 years performing and there could be several things failing in unison...now that you've hacked it up a bit, it's more likely to fail catastrophically.

If it was me, I'd get a new charger...but I would also probably still frock around with that old one anyway, trying to learn what was wrong with it.

I'd look for a cracked trace, broken wire, or bad solder joint on the input side.

wesnewell said:

I'd look for a cracked trace, broken wire, or bad solder joint on the input side.

Click to expand...

I would agree with the above and re-solder anything that even looks suspicious. After that buy a new one if it does not werq.

Thanks for your thoughts, guys, those of you who are cogent anyway.

I'm enjoying the hunt. Buying a new charger is coming up one way or another as I'm moving up to 48V so this might just be a paperweight soon.

Those with only a little experience in power supply design and EE in general know that a multimeter can only get you so far sometimes with all of the components soldered into circuit, as I mentioned in the first post, an ESR meter is one tool that works checking caps in circuit- I wish I had one!

Despite that handicap, using a $5.99 Harbor Freight heat gun and a $9.99 IR thermometer I had laying around I was able to pinpoint the problem! Thanks again to those who replied with their advice. Lebowski in particular- seeking out the area where the traces connected the high-power to the low-power helped narrow things down, and that was in fact where the problem was.

I went out for groceries on Saturday and the long tail came in handy- great inspiration to keep looking for the problem with my charger- trucking along like this for ten miles at a time is what it helps make possible!



Using the temperature dependance of the problem, I draped the patient in various ways before applying just enough heat from the heat gun to turn on the red power led. I then checked various temperatures on the board and components with the IR thermometer. I put black electrical tape on the heat sinks to get a better emissive signal.



I first blew hot air onto the backside of the pcb (with the solder and traces) and then the front side (with all of the components). It took 2 minutes to turn on when heating the back and 1 minute when heating the components, so I inspected the back with a magnifier for any problems and found none, leading to the working hypothesis that a component was at fault. Given that I started all of this with an assumption that a capacitor would be failing, I did some reading on the "bad caps" forum which was very interesting and helpful. They have a whole section devoted to power supplies and helpful advice on removing caps from the board, finding replacements, and other tricks of the trade.

The bad caps forum- http://www.badcaps.net/forum/

The area between the heat sink and the large yellow transformer had three tiny 1µF 50V 105 degree C caps. They were subject to all of the heat buildup and were my next suspects, especially since aiming the heat gun at the gap where they were turned on the power led the quickest. So heat killed it and it took heat to get it to work! Here is the gap where it was hiding, after I removed it.



The exact spot is shown in this close-up.



I removed the cap with a forceps surgery style, going in "fast and hot" with an 80 watt wide blade iron. I then resoldered the cap to the back of the board to confirm operation of the charger and apply heat to just the bad cap to prove it was the problem. Here it is, the soldier that fought a good fight, but lost out to the heat over the years- Note that there is no visual bulge or indication of failure.



It took some time, and no doubt other components are next in line to fail, but the education was priceless and for now a 50 cent digikey replacement cap might keep it running for a few more years. It is amazing how many expensive electronic devices are thrown away every day with faults in only a single cheap component.

Now I want my reward and bask in the light of the Great Pine


nice 8)

unlike the occasional high post count blowhard with an astronomical noise to signal ratio, the great pine never uses a keyboard to express himself...

Great to see people figure things out. Nice that it failed with heat so you had a way to look for it. Good troubleshooting you did there.

This was a fantastic read, greatly amusing with a hint of science. Thanks for ignoring the naysayers and following through to conclusion, I learnt something too

did you test the capacitor with the voltmeter to prove it was shorted?

I also enjoyed reading this because of issues charging batteries.

I learned some things that I didn't know about chargers.