Power supply recommendation

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Re: Power supply recommendation

Postby dnmun » Tue Dec 11, 2012 2:08 pm

that little cermet in the corner has 102 printed on it. that means 10 X 10^2 ohms or 1,000 ohms. the other resistors and the blue cap all in a row along the side (R37-R40) are part of the feedback from the output voltage back to that 14 pin IC at the other end, which runs the oscillator that drives the current through the transformer to the output terminals.

we wanna know which of those resistors is on the high side and which on the low side of the feedback terminal on the TL494.

but first, power up the power supply and put your meter on the output terminals and measure the voltage, using the 20V DC range on your meter.

then use a small phillips screwdriver and adjust that cermet with 102 on it.

you will see the output voltage change up and down as you dial it back and forth. see how high it will go in voltage with just that adjustment first.

then you will have to take the power supply apart some more. but do that first.
Last edited by dnmun on Tue Dec 11, 2012 2:09 pm, edited 1 time in total. View post history.
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Re: Power supply recommendation

Postby Denisesewa » Tue Dec 11, 2012 2:24 pm

14.10 is Max with the 102 turned all the way up
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Re: Power supply recommendation

Postby SamTexas » Tue Dec 11, 2012 2:39 pm

This looks interesting. I'm learning too.

This charger is 12V, 9A (according to the OP), so 108 watt capable. And the voltage can be increased to 14.1V (via the cermet potentiometer). Does that mean the charger output is also increased to 127 watt (14.1*9) or does it remain at 108 (14.1*7.7)?

Edit to add: Does anyone know? If it were me, I'd definitely like to have an idea of what the outcome would be before I make any modification.
Last edited by SamTexas on Tue Dec 11, 2012 2:56 pm, edited 2 times in total. View post history.
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Re: Power supply recommendation

Postby dnmun » Tue Dec 11, 2012 2:41 pm

record the minimum too. then look for the screws that hold the pcb in place.

there are several screws on the outside that clamp the npn transistors on the end and the schottky diode to the side which have to be removed along with all the screws that hold the pcb down on the bottom of the case.

you need to take it apart to get the pcb free and then turn it over and take pictures of the traces that go past those resistors R37-R40 and where they go back to the TL494.

they will return to either pin #2 or #3, can't remember, but it will be obvious.

make sure all the screws are loose first then the pcb will come out easily, you can pull the schottky and the npn's over a little if they hang on the sides but don't damage them.

worry about the power later. maybe you can try the balancing charger at 14V from the power supply to see if it will run with the 14V.
Attachments
tl494.pdf
pdf for TL494
(595.73 KiB) Downloaded 33 times
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Re: Power supply recommendation

Postby Denisesewa » Tue Dec 11, 2012 3:11 pm

dnmun wrote:record the minimum too. then look for the screws that hold the pcb in place.

there are several screws on the outside that clamp the npn transistors on the end and the schottky diode to the side which have to be removed along with all the screws that hold the pcb down on the bottom of the case.

you need to take it apart to get the pcb free and then turn it over and take pictures of the traces that go past those resistors R37-R40 and where they go back to the TL494.

they will return to either pin #2 or #3, can't remember, but it will be obvious.

make sure all the screws are loose first then the pcb will come out easily, you can pull the schottky and the npn's over a little if they hang on the sides but don't damage them.

worry about the power later. maybe you can try the balancing charger at 14V from the power supply to see if it will run with the 14V.



Minimum volts is 10.05 I dont see anything with TL494 on it

Image

Image

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Me thinks i'm in deep water here, interesting though
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Re: Power supply recommendation

Postby dnmun » Tue Dec 11, 2012 4:21 pm

if you look at the traces, you can see the charger plus wrapping around the end, with two of the pins of the cermet soldered into the trace. the other leg of the cermet does a dogleg around the led and the led resistor R40. that dogleg is attached to the second resistor R39 if i am correct.

the other end of R39 is connected to a trace that goes back to the 14 pin IC which is the TL494. that resistor R39 is 1600 ohms as i recall. your cermet trimpot when adjusted to the max got to 14V. so total of 1600 + 2,000 is 3600. but when it was 1,600 only (when you adjusted it down to 10V) so 4V out of 2k ohms. you wanna get to 24V right? or 22V? or 20?

if you have some small resistors around 4-5k ohms, you can try sticking that in the place of R39. maybe here is a good time to determine your soldering skill too.

if you have little jumper wires with tiny alligator clips on the end, you can unsolder one end of that 1600 ohm resistor brown green red R39 as i recall.

then solder the 4k ohm (or close 4k-5k ohm) resistor leg in the hole you pulled the old leg from so you have the two resistors standing up. then connect the jumper from the up leg of the 4k to the leg that goes into the trace on the 1600. plug it in and test the output voltage, if not close, then we can select another resistor for the replacement. and you can jumper across the top from one to the other to put them in series and test. or if you have a 6k ohm resistor you can try that size to start, somewhere in that range since we have the trimpot.

when you are working with the resistor sticking up like that, it cannot touch other stuff either, but you can test the voltage without reassembling the entire charger. just put it on a surface that is insulated, the transistors and the diode don't need to be heatsinked since they don't supply much current when you are just testing the voltage. make sense?
Last edited by dnmun on Tue Dec 11, 2012 4:25 pm, edited 1 time in total. View post history.
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Re: Power supply recommendation

Postby Denisesewa » Tue Dec 11, 2012 4:43 pm

Well, I really dont have access to resistors nor do I have a small enough soldering iron so I'll try it with the 102 turned all the way up but I think its just too far off.
For all the time you just spent trying to educate me I should put you on my X-mass shopping list, Thank you very much !!
My current projects
viewtopic.php?f=28&t=46891 ( GNG mods thread )
viewtopic.php?f=28&t=45919 ( 1st trials build )
viewtopic.php?f=28&t=46658 ( 2nd trials build )

http://www.austinev.org/evalbum/1363
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Re: Power supply recommendation

Postby dnmun » Tue Dec 11, 2012 4:48 pm

ask around of your friends who can solder. resistors are everywhere too. i had it backwards initially thinking i was working on the low side of the feedback. but i think something in that range of 4k-6k would work and get you up to 22-24V. pretty easy from where you are now since you have it open and apart.
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Re: Power supply recommendation

Postby RayGo » Tue Dec 11, 2012 7:43 pm

I have a suggestion you might be interested in.

Check out this website: https://sites.google.com/site/tjinguyte ... ects/HP47A

You can buy 2 HP power supplies on ebay for about $30 or less including shipping. You follow the instructions specified in this blog and put the 2 PS in series per his other blog. You get 1150 watts at 24 volts on the cheap. You now have both a 12v and 24v PS. The modifications connecting the 3 wires specified took me about 1 hour for both PS. Then you need to run your connector wires. I just use alligator clips for now.
Last edited by RayGo on Tue Dec 11, 2012 8:13 pm, edited 1 time in total. View post history.
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