Battery discharger - need some help.

[PeAK]

You can look at this schematic: http://kaspars.id.lv/projects/electronicload/load.pdf
from here:http://www.geocities.com/hagtronics/load.html

It is 100% working, i have built one, some info at my homepage under "other projects"

Thanks, I had a look at the circuit and it is essentially the same circuit with some nice "bells" thrown in. You can seen the ground connection (circled in orange doted line ) in the schematic that Steve Hagerman's circuit has included and which is related to the discussion at hand:

Care to chime in Steve ?

Mr Happy has forced my hand on my background and I'll just say that I'm a senior analog designer of IC circuits recently facinated with mobile power circuits and chargers. I enjoy his posts but I think this circuit is just slightly beyond his level of understanding. I'll leave it at that and will let this thread rest.

 

[Andrea87]

Steve's circuit is good, but I wanted something simpler. I've rebuilt it using the OPA177 from BB, powered by two 4xAA packs. It works well, I'm dicharging a 18650 trustfire lithium cell at 2A without any problem. Power consumption is about 0.65-1mA per rail. it should work off for some long time off two cheap AA packs. I'm going to build steve's version too, but before that I'll stick a bit with this simpler design

 

[PeAK]

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I've rebuilt it using the OPA177 from BB, powered by two 4xAA packs. It works well, I'm dicharging a 18650 trustfire lithium cell at 2A without any problem.
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Good to see you sort things out with the OPA177 op-amp change, especially as, I never did comment back on with regard to compatability.

The PDF file says that the op-amp works best when both the inputs and output are about a volt higher than ground and requires more margin at low temperatures. This can be accomplished (for a 2 amp) charge rate making two changes to your circuit:

1. Setting the voltage Vref on the non-inverting mode to 1.0V (vs 0.1)
2. Replacing the external 0.1 ohm resistor Rset with a 0.5 ohm unit.

The result will be that both the inputs and output will be DC biased at 1 volt and comply with the application notes for the OPA177.

The output current source is set by the ratio of the voltage Vref and Rset. (i.e. Iout = Vref/Rset)

Last, what the heck do you use these things for ?

PeAK

 

[Andrea87]

I am using this circuit as a battery discharger, or as a high current regulator for leds or laser diodes .

The 18650 comes from my ultrafire WF-502B cree flashlight, I'm just curious to see how near they are to the rated capacity

 

[PeAK]

I've rebuilt a new circuit using the OP177 precision opamp, a 0.5ohm sense resistor, IT WORKS WELL! I'll post some pics soon

Andrea,
Missed this small post of you before I suggested the 0.5 ohm circuit mod for using the OP177. No wonder it worked right out of the gate.

I'm looking to due some small PCBs and noted that you mentioned the toner transfer paper method. Can you provide some links and comment on your personal experiences and tricks to make it a no-brainer process ?

PeAK

 

[Andrea87]

For some odd reason it worked well, I was in the need of some really low dropout drivers, so I've gone straight with the 0.1 ohm resistor block.

As for toner transfer method, by now I'm using the finest paper I have around, I'm waiting to pick up some gloss paper. I just print the pcb with my laser printer on a thin paper or gloss, cut it to the shape of the wanted pcb, place everything on some cloth to avoid burning what's under, add a layer of toiled paper (allows ironing without risking to move the paper and blend the tracks) and then iron on at the maximum heat to melt the toner. I've even made double sided boards with this method. the pcb must be perfectly clean, and maybe oxids scraped off with a green kitchen scrubby, or some thin sanding paper. After having ironed down the toner, I drop the board in some hot water, adding cold water to cool everything off. I then start to peel off the paper with my thumbs, being careful to avoid to rip off any trace. If there's some interrupted traces, I'm using a liquid ink permanent marker to repair the uncovered traces. If the circuit is ironed well, and the right kind of paper is used, only a little amount of marker work is required. The circuit is then dropped in the etching solution, ferric chloride or H2O2 + HCl. If using the first, I prefer to leave the board to float on the surface of the liquid. After having it etched, toner is a little hard to get off. Alcohol wont rip it, acetone may but not that easily. I'm using some acrylic tanner to rip it off, works pretty well. Some dremel work then to add holes or cut off some unwanted copper remains, and the circuit is ready for solder. All the circuit you have seen in my posts are made by this method, and pretty on the cheap too

this tutorial is pretty good: http://myweb.cableone.net/wheedal/pcb.htm

 

[TheSpeakerGuy]

So, sorry to revive a long dead thread (not really). But a long story.... I am the author of the app note in question, and yes indeed correct and much used. Do not make the red line connection, it is not needed for sure.

The name of this circuit is Larry Load.

It has been over 10 years since I used this circuit, and wanted to recreate it. But the original Electronic Design article no longer has the schematic!

I just did a new layout at OshPark, search for Larry Load. I will add full schematic someday, but the information there should get most anyone on their way.

The new design is tiny, 0.6" x 0.6", all SMT, and operates off 2 AAA batteries. There is also a momentary battery check function. The switch can be left on for days, but should be shutoff when not in use. use the battery check function to verify batteries are still good, then keep on testing.

Also, although I wrote the article, the circuit was designed by Larry Carr, a former colleague. The article i wrote was supposed to be amended to a Vintage Design Idea feature ED ran for a short time, but cancelled. So they ran it as an original design. The most brilliant thing of Larry's design was the way he achieved multiple ranges without having to use high power switches.

john