Overheating battery charger

[budm]

Re: Overheating battery charger

What is the batteries Voltage rating?
Changing the charging method to constant current charging is not going to solve the problem due to bad batteries.
Batteries look good does not mean it is good electrical.
So again, what are the batteries spec?

[madan1]

Re: Overheating battery charger

OK, just got more readings.
It turns out the charger does not want to start charging even at room temperature - 22-25*C. I had to leave it outside ( ~-10*C ) for some time to get it working.
Once working steadily I measured 2.5A @10.7-11V.
I also disassembled the battery and found a temperature fuse in it, but again absolutely no controller.
I do not know if the battery is bad... but I got the drill on Thursday, back then I partially charged the battery twice ( 20 minutes - test the drill till there is no power - 10 minutes charging ) and left it in the case. Today the drill worked fine for another 10 minutes before the battery died again. Basically what I'm saying is that it looks like the battery holds charge. Visually all battery elements are fine.
On Tuesday I am getting the new electronic components ( diodes, transistors, caps and resistors ) and will see what happens.

By the way, that lm317 sounds great! I will dig into it and see if the charger can be modified. By the way I'm already thinking about substituting the graetz with a single-element solution like KBP206G

[budm]

Re: Overheating battery charger

Shorted cells in the batteries.
What DCV do you have on your batteries with load connected? Battery spec? NiCad?
So the Transistor is dissipating about 3W of power.
Check the Vdrops on that large white 390 Ohms bias resistor.
BTW, that power transistor is still tested good?

[petehall347]

Re: Overheating battery charger

its probably got an internal problem like the internal resistance because of old age .
i was thinking you could add a 1 amp regulator chip but not too sure what then happens to the other 2 amps . i guess it would still cause an overload . i have never tried it so if anyone else knows better please advise ..
i was looking at something like an lm317 .

[madan1]

Re: Overheating battery charger

but why?

[petehall347]

Re: Overheating battery charger

means the battery is pulling too much current .

[madan1]

Re: Overheating battery charger

I just measured the current - ~3A. The output specs say 15V 1A... what does that mean?

[madan1]

Re: Overheating battery charger

So we have a verdict
I will replace the diodes and the caps. Most likely I will also replace and the A1757. Should I go all the way and replace the transistors?


edit:

I would check the charging current to the batteries, as you can see that pass power Transisor provides the charging current to the batteries, more current more heat, when over temp is detected, the bias Base drive circuit for the transistor should turn off the power transistor, or when the batteries is fully charged.
What did you use for the scope ground?

I connected the oscilloscope to the battery terminals ( red and black wires )
I do not think the charging is interrupted due to high current. When the charger is cold it works for like 20 minutes, but after that it almost immediately goes to "green LED" mode when the battery is connected... so I guess it is related to the temperature.

by the way what determines/controls the output current?
ps. ok, got it - that transistor just switches on and off the current to the battery. I thought the circuit was smarter and constantly controlls ( increases/decreases ) the current according to the battery state, temp., etc.

[budm]

Re: Overheating battery charger

I would check the charging current to the batteries, as you can see that pass power Transisor provides the charging current to the batteries, more current more heat, when over temp is detected, the bias Base drive circuit for the transistor should turn off the power transistor, or when the batteries is fully charged.
What did you use for the scope ground?
The scope does show 100Hz.
https://www.badcaps.net/forum/attach...7&d=1484274177

[stj]

Re: Overheating battery charger

rectified mains would be 100Hz
*but* it should look like a series of humps without spaces between them.
which is why it may have 1 or 2 open-circuit diodes.
i would desolder & meter them all.
then do a recap - all 2 of them!

[madan1]

Re: Overheating battery charger

Do not believe what this shows as freq. value. I'm not sure this cheap DIY oscilloscope calculates it properly. With different timeframe the frequency was ~50hz so I guess it lacks cpu power.
Anyway, the freq is N-times-power_network_freq ( 50hz ) and about 1V peak-to-peak. Is this something I should take care of or is normal for this kind of hardware?
Now when I'm reviewing the pcb, there only 10 elements on the power side ( the rest are for the thermal/control circuit I guess ) - 5 diodes, 2 transistors, 1 cap, 2 resistors .. so I just might replace them all .

[stj]

Re: Overheating battery charger

that waveform, and frequency makes me think the output from the transformer is not being smoothed after the diodes.
and not all the diodes may be good either.

[madan1]

Re: Overheating battery charger

Just tested the charger with the battery on.
I'm not familiar with this kind of equipment so I do not know if this ripple is within the normal operational limits.
Also I noticed that it is not the transformer which is getting hot, but the A1757. After several minutes the transformer did not even get warm, while the radiator of the A1757 was very hot.

[budm]

Re: Overheating battery charger

well it seems like the thermal protection is working as intended . just a matter of finding why its getting hot .. i suspect the battery at fault .. only a new battery will confirm this quickly . or it means putting an ammeter in series with the battery when on charge .
possibly a diode is flaky passing ac so look at that too .

Yep, check the charging current.

[madan1]

Re: Overheating battery charger

15 minutes on the mains without battery - no heat generated at all.
I will have test it with the battery on.

Hmm you said bad diode and AC.. will I be able to see this on an oscilloscope without the battery or the battery has to be hooked up?

[petehall347]

Re: Overheating battery charger

well it seems like the thermal protection is working as intended . just a matter of finding why its getting hot .. i suspect the battery at fault .. only a new battery will confirm this quickly . or it means putting an ammeter in series with the battery when on charge .
possibly a diode is flaky passing ac so look at that too .

[madan1]

Re: Overheating battery charger

Does the battery actually takes any charge? what is the voltage of the transformer while charging?

Yes, the battery charges.
I will measure the voltages while charging and report.

does it go into thermal shutdown ? if not thermal sensor circuit has a fault .
you might want to monitor current draw of the battery when charging unless transformer gets hot when not charging .if it does transformer might be bad .to check that disconnect secondary of transformer and test again to see if it heats up .

Yes, exactly - it gets too hot and stops charging ( green LED lights up ) due to excess heat measured on the thermal sensor. It "thinks" that the battery is too hot, while the heat is being generated by the PSU itself. If I'm not able to find a faulty component on the PCB, I will disconnect the transformer and will measure it.

Same with my drill charger and brand new batteries Bosch Pr something I think tranny gets burning hot. Doubt its anything to worry about.

Usually I do not worry about hot transformers ( they have thermal fuses and so on ), but this time the heat causes the charging to stop, which makes the usage of the drill kind of inconvenient .

how hot does it get if there is no battery?

Good question. I will test it and report.

if it got way too hot it should burn out an internal fuse in the transformer .that is if of course it has one fitted . most have one .
i find these things do run hot .they are crammed into a small box without much thought of design .
the battery might be taking too much charge because of internal resistance . it may well perform ok when just charged . but likely wont hold a charge as long as it should do .. does the battery get very warm /hot when charging ?

I'm not sure if the battery gets "too" warm. By the time the charger turns off, the battery is still not that hot as the charger itself. Most likely this is just heat transfer from the charger, because only the closest to the charger part gets warm. By the way, there is no charging control circuit in the battery.
Most likely the transformer fuse does not burn, because the thermal sensor switches it off.

[petehall347]

Re: Overheating battery charger

if it got way too hot it should burn out an internal fuse in the transformer .that is if of course it has one fitted . most have one .
i find these things do run hot .they are crammed into a small box without much thought of design .
the battery might be taking too much charge because of internal resistance . it may well perform ok when just charged . but likely wont hold a charge as long as it should do .. does the battery get very warm /hot when charging ?

[stj]

Re: Overheating battery charger

how hot does it get if there is no battery?

[ReeceyBurger123]

Re: Overheating battery charger

Same with my drill charger and brand new batteries Bosch Pr something I think tranny gets burning hot. Doubt its anything to worry about.