I’ve built the K8012 but I’m having problems during the testing phase.
In Test #1 and #2 the voltages show correctly
In Test #3 with the resistor across the output I get the required 14.7 volts, BUT in Test #4 I get only 6.78v with only the “float” LED glowing.
In Test #5 with the resistor in series with the DC ammeter I only get .15A and only the “float” LED in on.
In Test #6 I only get .16A however the correct charge LED is on.
I’ve also noticed that the power transistor never seems to get warm
I’ve carefully checked resistance values, transistor orientation, etc. Transistors were mounted high above the board, so I doubt I burned any out, but I’m wondering if it might be a diode? Initially I was using an 18vac @2.2a plug-in transformer. Later I found out it was actually putting out 22vac. I then changed to a variac to get an exact 18vac to the board but came up with the same results. Also, I put heat sink compound under the power transistor, would that affect things?
Sorry, this forum does not allow picture uploads
If you can provide LINKS (e.g. by using a free online picture base) to HI-RES and SHARP pics of your assembly (both solder- and component side)
then we can take a look and provide some feedback.
All resistor values seem to be correct.
Transistors and diodes are correctly inserted.
Unfortunately, the quality of the solder side picture does not allow us to spot a possible problem.
A better quality picture would help a lot, as we suspect a soldering problem, judging by the looks of some joints.
After two hours puzzling this out, it turns out that the test resistor shipped with the kit was 82 ohm, instead of 8.2 ohm.
I substituted a ceramic resistor from my parts box and all the tests are good. Test #6 is .24A, but I think that’s probably close enough.
Here’s two questions now that it’s running:
1.) I’m using a plug-in-the-wall adapter putting out 18vac @ 2.2a. I’m planning on charging a 6v 4.5aH SLA battery. What size fuse should I put in the 18vac line going to the unit to protect the circuit?
2.) Out in the field, when I use my 6v 4.5ah battery, what’s a good fuse to use on the battery cable to protect against short circuiting if the battery wires cross?
Happy to read you have found the problem and sorry for the inconvenience, which is most likely caused by human error.
Regarding the fuse, the max. charge current is 1A and the adaptor can deliver 2.2A, so a 1.5A slow-blow fuse could do the job.
As for the battery protection fuse, first you need to determine the max. current that the battery needs to supply. Next, I would choose a slightly higher value and a slow blow type, to handle inrush currents which might be higher than the average currents you expect.