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Trickle Chargers - Page 6

post #76 of 82

I'm a bit confused in terms of your math and reading about the circuit on this thread. Based on the given formula, I was under the impression that 75 ohm resistor would be fine because 1.25/75 would come out to 16mA, which would come out to around 16 hours to charge the batteries. I haven't read anywhere about being aware of a voltage drop. Just that you want to have a supply that has more voltage than the batteries in series. Maybe I'm missing something.


With regard to measuring the current, my MM doesn't read Amperage. Instead, could I use any value resistor and measure the voltage across that? I have nothing that is super low other than a 1 ohm resistor that measures 1.2 ohms. I do have a few 1k ohm resistors. Would those work better?

post #77 of 82
Sorry, should have read the thread, I didn't realise there was regulation in there.

Measure the voltage across the resistor (75R) and make sure you have 1.25V.

post #78 of 82

Nope don't have 1.25v. I ended up with what looked like 2.5mA when I did V/R. This was between + in from the wallwart and on + on the first battery terminal with the batteries disconnected and power on. Then I turned power off and got nothing. I'm assuming this circuit allows charging with the power off. I connected the batteries and did the same measurement and blew something. Can't tell what it was, but I saw and smelled magic smoke. Looking at the schematic and at the data sheet I think I might have wired up something wrong. The data sheet for this version of the LM317 says that pin 1 is Adjust. Pin 2 is Vin and Pin 3 is Vout. On Tangent's schematic Pin 2 is Vout and Pin 3 is Vin. I'm using the part in his BOM. I wired things up based on the schematic, not based on the parts pin out. Anyways, time to reorder some new parts and start from scratch.

post #79 of 82
Originally Posted by Mullet View Post

This was between + in from the wallwart and on + on the first battery terminal with the batteries disconnected and power on.


1.25V is expected between ADJ and OUT, not IN and OUT. The voltage drop between IN and OUT varies depending on the battery voltage, even if all else is fixed.


The data sheet for this version of the LM317 says that pin 1 is Adjust. Pin 2 is Vin and Pin 3 is Vout. 


I'm not aware of any standard way to number the pins on 3-pin parts. Packages with so few pins typically have their pins function-labeled, rather than numbered.


In data sheets, such parts are usually drawn as 2D parallel projections, with no standard orientation, which makes it easy to mentally flip things around so you get the pin order backwards.


This is especially easy to do when popping back and forth between data sheets for TO-220 and TO-92 versions of the LM317, since some manufacturer data sheets draw TO-92 from the bottom view. When I see that characteristic D-shaped outline, I initially see it as from the top, probably because I'm used to seeing these parts from the top side of the board. (I made that mistake yet again while composing this message, thus the edit!)


The data sheet for this version of the LM317 


What version is that? Please give manufacturer and package type, at least.


On Tangent's schematic  


Which one is that?


The only current schematic on my site that I'm aware of with an LM317 based trickle charger is the PIMETA v2 schematic, which doesn't have numbered LM317 pins.


in his BOM 


Again, which one? I have many parts lists on my site.

Edited by tangent - 4/9/14 at 4:23am
post #80 of 82



My apologies for not offering enough information with regard to schematics, etc. The schematic I was using is from the PINT amp, since I have one that I'm building (and having major DC offset issues with, but that's for another thread). Since the design has been deprecated it's no longer on Tangent's current site. You can find it using the waybackmachine. Here's a link...


I used the parts list from the PINT pages as well...


511-LM317LZ is the part I used for the LM317. The pin out is pretty easy to identify. Here is the datasheet...


Is this the correct part to use with the PINT even? I could go with something like this instead, which looks to have an easier pin out to deal with...




post #81 of 82

The LM317 symbol I used on that schematic came straight out of the gschem parts library. I have no idea why its creator numbered the pins that way. I can't fix the PINT schematic in the Wayback Machine short of asking them to remove the content, which seems like an overreach to me.


Why did you dig the PINT out of the Wayback Machine anyway? Why not build something that has a large, satisfied user base instead?

post #82 of 82

I chose to build the PINT because I had the opportunity to pick up a board on the FS forums. I scored at PPA-S as well, which is what I'm using the trickle charger for.

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