Team Associated Reedy 1216-C2 battery charger really stinks

[QuantumLogic]

Ahh, the smell of burning electronics.  It's a great thing when you are purposely applying 120V to something that is supposed to run on 5V, but not when you just bought a brand new charger and are evaluating its performance and trying to decide if it is defective or not!

Here's the story:
I bought a brand new Team Associated / Reedy 1216-C2 battery charger this week.  Link to manufacturer's website: https://www.teamassociated.com/parts/details/27200-ASC27200-reedy_1216-c2_dual_ac_dc_competition_balance_charger/
This charger is supposedly very highly regarded and considered to be a quality charger.

After verifying that the voltage switch was correctly set to 115V (the charger is selectable between 115V and 240V), I plugged it into AC power (US 120V 60Hz) and it booted up just fine.  Nice backlit LCD display with a blue background.
I connected a 7.2V 1800mAh NiCd battery pack to the left output.   I did not plug anything into the right output.
I went through the left-input NiCd charge parameters and set the proper values, such as 3A charge rate, 4mV peak detection, etc.
I pressed the Start button to begin charging and the charger got to work as it should.  It ramped up current slowly at first, getting to 3.0 Amps.  Once in a while it would reset to 0.0 A and then ramp back up.  I suspect this is an "evaluation phase" that the charging program uses to help determine battery health, charge progress, etc, however there is no mention of this in the manual.  There isn't much detail in the manual regarding how the charging circuitry or programming works.  Not that I would ever expect it anyway since the RC industry likes to keep secrets like battery charging algorithms from their competitors.

After a couple of minutes of charging, I begin to smell a slight "burning electronics" smell.  It was not very strong, so I chalked it up to "it's new and needs to burn off the manufacturing leftovers/coatings/flux/whatever", but after a few minutes of smelling it I decided to open the charger up and have a look inside just in case there was something really wrong with it.  If something looked charred, I'd know for sure that I had a defective unit.
After opening the charger up, plugging it into AC power and starting to charge the same battery pack again, I used my Flir E4+ to take a picture of the circuit board to show what component(s) were getting hot.  The attached pictures show what I saw.
Apparently, the smell turned out to be a power resistor that, in my opinion, is getting WAY too hot for my liking.  Like 220 - 250 C hot!  It is the one just under the large transformer.  From what I can tell, it has not changed color.  If the resistor was truly being abused, I would expect that it would turn brown and start smoking.  It has not done that.
Now, I know power resistors are designed to get hot.  I know some power resistors are designed to get really hot, even up to 300 C.  But I find it slightly disturbing that a battery charger would be designed to use power resistors that reach 220+ C.  I do not know what the resistor is being used for in this circuit.

I did send an email to the manufacturer a couple of days ago explaining the above but have not yet received a reply.  I think a reply will never come because the circuit was likely designed and manufactured overseas and the US branch of Team Associated won't bother to even forward my email to the people that would know the answer to my question.

After not receiving a reply to my email for the second day, last night I charged two battery packs at once, both NiCd 7.2V and 3.0A charge rate.  I figured that I might as well kill the charger dead if it is in fact defective so I can get a new one before the 90 day warranty runs out. The smell was still there, but did not get worse as I expected.  Once the charger reached 50 C on its internal temperature sensors (it has two of them), the cooling fans turned on and cooled it back down to 30 C and then the fans turned off.
It could be my imagination, but the smell seemed to be less strong after this charge cycle. It could have been that I had been smelling it for so long that I got used to it.

So, my question to you fine folks is:  Is 220+ C too hot for this style of power resistor?

[SeanB]

Fine for the resistor, but not good at all for anything near it, or the board itself. That resistor is the snubber resistor for the PSU primary, there to clamp and absorb the voltage spike when the SMPS power switch turns off each cycle. That amount of heat will repidly degrade the small electolytic capacitor near it, and will make the charger stop working shortly after around a year of operation. As it is both at line voltage and is running very hot it really should have been mounted higher off the board, not with one end direct on the board, which will guarantee a dry joint ( and a detonated power supply) in short order, and it really should have been a higher power part, thus with a larger surface area and a cooler operating temperature, and should have been mounted off the board on some ceramic beads to keep it stable and allow air flow around it to cool it. I would replace it with a 5W version and mount it at least it's diameter off the board on some ceramic spacer beads to ensure long life and reliability, along with changing that little electrolytic capacitor to the left of it as well with a better quality one.

[QuantumLogic]

Thanks SeanB, your comments confirm my initial thoughts as well.  I think I will look up the resistor value and replace it with a 5W with more spacing as you said.  Where can I get ceramic beads?  Digikey?  I'll probably be getting the resistors from there.  I will replace the other resistor that you can see to the right of the transformer as well.  It doesn't get quite as hot, but I don't like how close to the board it is either.

As another aside to this charger PCB, the soldering quality is terrible in my opinion.  Check out this picture.  There are power transistors and/or diodes on the bottom side of the board and they are heatsinked by the case using thermal grease, but I would still expect to see solder through the hole, not just on one side of the PCB, even if the pad on the top side here isn't connected to anything.   There are other solder joints that are similar looking to this one for the though-hole components.  The surface mounted stuff seems OK.

[QuantumLogic]

I removed the resistor that was below the transformer in the above pictures.  It measured 29.24K Ohms.  The color bands looked like orange-black-brown-gold to me, but apparently it's orange-black-orange-gold and the orange color has changed due to heating.
Finding a 5W replacement appears to lead me to resistors that look exactly like what I already have.  So perhaps I need to be looking at 10W instead.  But on Digikey, these are hard to find in-stock.

The only ones I could find in-stock were these:  http://www.digikey.com/product-detail/en/ohmite/20J30K/20J30K-ND/2019976
Ceramic spacers: http://www.digikey.com/product-detail/en/essentra-components/CER-1/RPC1082-ND/3811718

Would these work?

[mariush]

You could just put two resistors in series there, for example 2 x 14.5-15k 5w-7w which will get you 29-30k which is close enough to 29.4k ... and individually each resistor would heat less, so even 5w may be enough.

At 15k you even have nice (but expensive) to-220 resistors rated for 20-25w (if heatsinked) so you could put two on each side of a to-220 heatsink and solder two leads together to have one big 30k resistor.

[SeanB]

Use the 2 series 5W resistors, and remember that the leads will be at around 1kV from the flyback pulses from the transformer, so make sure they are spaced far apart from the top of the case, and keep the body of the resistor from touching anything, as the case is regarded as conductive when it gets hot. The spacers will work, and use on the other resistor as well, and simply reflow the semiconductors on the bottom of the board, so you fill the through hole, which will reduce the chance of having a dry joint later on.

[QuantumLogic]

Series resistors: Good idea.

In that case, I'm thinking to buy the following:
Resistors (quantity 10): http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=211679930&uq=636146231815780590
Reasons:  Cheapest option (I think paying over $2 per resistor is silly here), I do not think the 300ppm/C makes any difference in this application since the purpose is to absorb excess power/spikes from SMPS operation, rated for up to 250 C, can install in series to get approx. 30KOhms.

Ceramic Spacers (quantity 10): http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=211679913&uq=636146231815780590
Reason: Appears to be the only thing close to the right material (ceramic) and size (length, inner/outer diameter) that is in stock at Digikey at the moment where you can buy 10 for cheap.

Final thoughts before I order?

[QuantumLogic]

Quick followup:
I ordered the resistors Monday and received them today.  Installation went fine.  The series 15K resistors are reaching around 125 C with the case open.  I predict they will reach 150 C with the case closed and no fans running, which is more than 75 C cooler than the original resistor.  The new resistors have an operational max temperature of 250 C so they are operating well within spec.  I am pleased with the result and the charger is working perfectly.  Best of all, there is no smell any more.

Thank you SeanB and mariush for the help.

[SeanB]

Still worried about those small electrolytic capacitors there near the resistor. I predict that they will fail next, with a symptom being it will not power on.

[QuantumLogic]

SeanB, are you suggesting replacing the small cap under the transformer with a 105 C because you believe the current one is sub-par?

[mariush]

I think he suggests replacing it because the current capacitor was kept hot from heat radiating from that resistor directly through air but also partially through the printed circuit board, through the capacitor leads.
Capacitors have a certain lifetime, for example 1000h @ 105c and it's generally agreed that for electrolytic capacitors, their lifetime doubles for every 10c decrease in temperature.. if you want a more advanced formula see picture below or the calculator here : http://www.illinoiscapacitor.com/tech-center/life-calculators.aspx



So the existing capacitor may already be a bit degraded but still within its specs ... it would still be used at somewhat high ambient temperature so it will gradually weaken further. It's a cheap solution to just prevent future failure by replacing existing capacitor now with one that's better, with higher lifetime rating, while you still know why you're doing it. For example, Panasonic FM or FR series capacitors  have up to 10k hours @ 105c rating.

[QuantumLogic]

Given the number of flaws in the design of this charger I'd end up spending half the purchase price to replace the sub-par components with higher quality versions, yet still not have a permanent solution because ultimately the component spacing and cooling design is terrible.  There are many 5W resistors that get to 70 C in many places all over the board and many of those are right next to one or more electrolytic capacitors.
I'm not going to replace any more components now.  The charger has 10 hours of use on it at this point.  I think the junky caps have some life left in them still.