A little help with a charger

[seth1846]

I have a THUNDER 1220 charger, not long ago I was discharging with it and heard a POP! After this, the highest discharge rate I can get it to actually discharge at is .01-.02amps (!! I'm assuming a resistor might have failed since the actual rate seems stuck, all tho on the screen I can still tell it to discharge all the way up to 5amps.

I'd like to fix it if I can, but, while looking for a burnt component, I have found nothing that looks like it has failed.... Does anyone here have another angle to attack this by? A certain thing or way to check something? Lol

I have a DIY discharger for 2s-8s, 50watts, and am in the process of making a larger wattage discharger now, but really wanna fix this thing if for no other reason then just because I can! Haha

Thx for any help!
Seth

[ShaneJourdan]

Did you remove the heat sinc and take a look / test the regulators?

Does it still charge?

[seth1846]

Yea I pulled the heat sink, all of the regulators appeared to be just fine. I can't find any thing that appears burnt or bad. I have not however checked the regs under load. I wasn't sure which of them was being used to dump the heat. Thus I'm not sure which should be under which load...

There is 7 regs/power mosfets inside the charger, 6 of which are set in pairs attached to the heat sink by there base, and another abit away, attached by its three legs with the base plate standing in the air.

The odd thing is,, yea the charging seems to work just fine still! The LCD screen will at times dim big time so that I can't read it easily, but it'll go back to normal quickly.

[MichaelChad]

Sounds like a failed cap to me. They usually make a pop when they go, but sometimes they are just ballooned and have a pinhole in the top, so hard to see. It'll be right in the center of the K or X engraved on the aluminum top.



It would also explain the dimming if they are used for smoothing. Are there any radial capacitors inside?



Also some fast blow fuses used in these chargers look more like a rectifier diode, and show no visible signs of failure. Easy to spot as they don't have a silver ring on one end.


Chad

[seth1846]

Yea, there are probally atleast 15 radial caps inside. Most of them are sorta small (1/4d by 3/4"h maybe). There are also a few rather large ones too!( .6"d by 1.25"h maybe)..

I don't recall seeing any pin holes in any of them! The board does have what appears to be a regular green, 12v-30A auto fuse soldered on to it. It appears to be good and has continuity between the two legs!

[MichaelChad]

Those small caps can often fail from the wrong side (where the legs come out, or inside the wrapping). There just isn't that much on a common PCB that fails with a pop, I'm betting you'll find the culprit there. Catch is, you may have to de-solder and remove the caps to find out.

[seth1846]

I have it open now, and I may have found a pin hole in a cap, it's tiny, I MEAN TINY, but I've got to desolder it to check the cap with a meter I believe!

[seth1846]

Ok the cap I think has the pin hole is a 25v 2200uF

When I check with a meter, the best I can get is 1.77nF

These confuse me, is that good or bad?

[MichaelChad]

That is not very much capacitance! Are you sure your meter will measure up to 2200uF? Many common multimeters are only capable of measuring small ceramic disc caps in the pF-nF range.

Can you check the resistance? If it is 0 then it's definitely bad. Can you check another (good) 2200uF capacitor and verify your meter will read it?

Originally Posted by seth1846

Ok the cap I think has the pin hole is a 25v 2200uF

When I check with a meter, the best I can get is 1.77nF

These confuse me, is that good or bad?

[seth1846]

I'm going to work now, but my meter reads nF beside the reading. I'm not sure what the whole u or nF means! I know it is farrads I think but that's about all..!.? Lol I think the resistance was . 3ohms if I remember correctly.

[MichaelChad]

uF = 1 / 1,000,000 Farad
nF = 1 / 1,000,000,000 Farad
pF = 1 / 1,000,000,000,000 farad

1 Farad is really alot So 1.7 nF = 1.7 billionths of a Farad. Really small! Much less than 2200uF which would be 2200 Millionths of a Farad.

If it's 3ohms, there is a mild short, and it's definitely bad. There really shouldn't be any continuity between the leads.

[ShaneJourdan]

Great job guys as usual! Yes, I believe the pop was from a cap as well. But my other concern was why. Caps do fail for no good reason all the time. You may be good replacing just the cap.

[seth1846]

Hey, sorry to ask what might be a silly question! But atleast at the moment, I haven't been able to locate a 25v 2200uF cap locally.. But, I think I have one of 2200uF in a 35v and few in 10v form. Can I use these in this ones place?

I know it's prolly not ideal, if for no other reason than its not what the design calls for, but is there a actual problem this would cause? I guess I need to study up on caps to say the least lol, just wasn't sure if this is ok and also, can we series say 3 2200uF 10v caps, to end up with a 2200uF 30v cap? Or does it not work like that? Haha

Thx fellas!!
Have a great Thanksgiving!!!!!

Seth

[MichaelChad]

No such thing as silly questions!!! Well maybe just the ones we don't ask.



You can use any cap rated to 25v or higher, and its perfectly fine. Your 35v cap will work great if it fits, you could also use 2 1100uf caps rated for the minimum voltage.

The way a capacitor works though all caps need to be rated for the minimum of that circuit. Its kinda like throwing a ball around the infield. Each player is still throwing a 60mph ball, so they all gotta be able to catch one thrown that hard. Voltage is like how hard the electricity is being thrown (current would be the ball) and that rating on a cap is how strong the next guys hand is. Make sense?


Chad

[seth1846]

Yea very much so! Thx for that reply!

I thought it might work , atleast the 35v one. Just wasn't sure if I could apply the series power rules to splice up 3, 10v 2200uf caps to end up with 1- equal to a 30v 2200uF cap.

So it sounds like I CAN use the parallel theory to connect same voltage spec caps together to end up with a higher uF spec cap and that's fine as you stated. But, we can NOT use the series theory to create a higher voltage spec.. Thinking about it , it makes sense, voltage being the "pressure" in the system, 10 weak hoses together still can only handle whatever they can handle individually, BUT, capaciety wise, they can and will deliver more volume whatever they are carrying. Just at the lower pressure only.

Thx again Chad! You guys are great!

Seth

[seth1846]

Now, if I get this cap replaced, do you think that will allow the onboard discharger to work correctly again?

I'm pretty sure it's bad, but, not so sure how a cap can affect discharging since its done by dumping it as heat, I think atleast.. ! Haha

[seth1846]

I still can't the exact cap locally but I have found 3 35v 1000uF. Also found a 35 & 50vdc linear caps, 2200 and also 4700uf in both voltage specs.

I have spare circuit board around, if its not a problem, I think I will make a board for one or some combo of these and then wire it into the originals place on the charger board!

Does this line of thoughts seem ok fellas?

Thx again for letting me pick your brains! ,
Seth

[MichaelChad]

Yes that will be fine. I have to do the same thing when I hack a PSU to output 20v+.

Just get the capacitance values close, they are pretty forgiving when it comes to small variance. If you have a choice, better to overshoot and go big, than too small. That measurement (Farads) is much like mah in measuring lipo capacity, it just measures the volume of energy it can store.


Chad

[seth1846]

GREAT!!

I thought I was good to move forward. I'll see about doing so later this evening, if I'm lucky, maybe I'll beable to report that she has discharge capabilities once more!!!

[MichaelChad]

Crossing fingers! At least this way though, you'll know if the blown cap was the cause of the effect. It should at least point the way to the solution, or a new charger.

Originally Posted by seth1846

GREAT!!

I thought I was good to move forward. I'll see about doing so later this evening, if I'm lucky, maybe I'll beable to report that she has discharge capabilities once more!!!