Overheating battery charger

[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?

[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

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

BTW, that power transistor is still tested good?

how? where to hook the Vmeter? ( sorry for the stupid question )

What is the batteries Voltage rating?

12V 10cells without anything written on them. Visually similar to these https://www.alibaba.com/product-deta...964662007.html

[budm]

Re: Overheating battery charger

And the Voltage reading with load is? So it is NiCad more likely and they do shorted out when they go bad.
Look up NiCad failure mode.

[madan1]

Re: Overheating battery charger

And the Voltage reading with load is? So it is NiCad more likely and they do shorted out when they go bad.
Look up NiCad failure mode.

starting voltage - 7.5V
free run at max speed - 7V
loaded (trying to stop the drill with hand) - 3V
When I got the drill the battery was totally flat, and basically I have never fully charged it.

[petehall347]

Re: Overheating battery charger

i am placing a bet on the battery pack ... until you have another pack with same ratings all bets should be called off ..
i do however find it most strange that it wont power up unless at a cold temp .
a schematic should help in sorting that part out .

[madan1]

Re: Overheating battery charger

I bet that the problem originated from the charging circuit and had already damaged the battery.
I just found out that the battery also gets very hot when being charged ( now when the unit is dissembled I was able to check the temperature on each individual component - transformer, pcb and battery without heat transfer from one component to other ).

[petehall347]

Re: Overheating battery charger

get me a bottle of leffe blond and call it quits

[cpt.charlie]

Re: Overheating battery charger

Try to charge the battery, once disconnected, measure the voltage of each cell (should be about 1.2V per cell) and while charging check if any cell gets significally hotter than the rest.

[budm]

Re: Overheating battery charger

starting voltage - 7.5V
free run at max speed - 7V
loaded (trying to stop the drill with hand) - 3V
When I got the drill the battery was totally flat, and basically I have never fully charged it.

So you think the battery is good with the reading like that?
If you keep on trying to charge that battery you will end up damaging the charger too, it is already damaged trying charge shorted cells..

[madan1]

Re: Overheating battery charger

So you think the battery is good with the reading like that?
If you keep on trying to charge that battery you will end up damaging the charger too.

Well, the battery was flat when I got the unit. I never managed to fully recharge it due to the heating issue. Except for the voltage readings, the battery does not show any signs of issues ( at least from the user point of view ) - it keeps charge and gives enough juice to power the drill.
As I said - I have not had any experience with such kind of equipment and power banks .. some user experience like drilling and sawing with power tools does not count I guess .

Right now I really do not care about damaging the charger - I already have decided to replace the components from the power side of the board. Probably my biggest worries are not to blow the battery pack ... and Indeed I still hope that I will be able to use that battery. After all, the battery is the second most expensive thing in this unit after the gearbox.


By the way, next week my IR thermometer should arrive, and I will finally be able to measure properly the T of the components



p.s. I was able to charge the battery to 10V
So now the stanby is 10V
the max speed run is 9.5V
and when I tried to stop it ( indeed I was not able to stop it because it almost tore my hand ) I got 6V

[budm]

Re: Overheating battery charger

All you have to do is to to check the voltage of each cell to tell you which cell is bad.

[madan1]

Re: Overheating battery charger

I know.. I'll probably get there. Unfortunately I do no have the equipment ( spot welder ) to get the battery back together. I'm still thinking on what will be the best way to dismantle it so that later can be reassembled without welding.

[budm]

Re: Overheating battery charger

You can measure each cell Voltage without removing any links, the batteries are connected in series, simple.

[madan1]

Re: Overheating battery charger

Damn!
Well... so my brain is just refusing to think outside its usual way
Recently I've been dealing only with single batteries or in parallel, so I've just forgotten that batteries in series exist (facepalm).
Thanks for re-opening my eyes !

[madan1]

Re: Overheating battery charger

i am placing a bet on the battery pack ... until you have another pack with same ratings all bets should be called off ..
i do however find it most strange that it wont power up unless at a cold temp .
a schematic should help in sorting that part out .

Aaand I think we have a winner ... at least partial .

So I changed all 10 battery elements ( 2x price I paid for the drill and the shipping ) and now the charging current is 1-1.1A.
I also changed the 4 diodes and the two caps ( I could not find a transistor ).
Now the charger starts charging as soon as the battery is plugged in ( so I guess getting it cool was fooling something on the protection circuit? ).
After 15-20 minutes I get 34*C on the traf, 36*C on the transistor and 60*+ on the diodes ( finally got my IR thermometer ).
I couldn't get rid of the ripple though ( see the attached image ). It is still around 1.5V. I hooked the biggest capacitor I have ( 10 000uF / 50V ) and the ripple was still there ( ~1V ) but with a smoothed profile.
Should I focus on removing that ripple or it is fine for such electronics? Could it kill the new batteries?

[budm]

Re: Overheating battery charger

Float the scope so you can look at the Base drive signal of that power transistor, more likely it will be pulsing too, I believe it is doing semi-pulse charging.
How big is the ripple between the two legs of that 100uF filter cap?
The scope signal is from between the Batteries terminals, right?

[petehall347]

Re: Overheating battery charger

looks like it pulsing in a positive direction ..this might be normal to keep things cool ..i have never studied charging these batteries .

[madan1]

Re: Overheating battery charger

Float the scope so you can look at the Base drive signal of that power transistor, more likely it will be pulsing too, I believe it is doing semi-pulse charging.
How big is the ripple between the two legs of that 100uF filter cap?
The scope signal is from between the Batteries terminals, right?

You are right. Here is a scope from the base of the powerTR.
I cannot safely hook the scope to the capacitor ( the croc connectors are too bulgy ), but should there be difference? The first scope image was from the battery terminals.