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| 5 V gauge upgrade puts out 7V https://slantsix.org/forum/viewtopic.php?t=56744 |
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| Author: | drtwgn [ Thu Dec 18, 2014 3:23 pm ] |
| Post subject: | 5 V gauge upgrade puts out 7V |
Greetings. I built the transistor/capacitor/heatsink 5V output for my gauges. I hooked the assy. across a 12 V battery to test the output, and it was 7.0 V. I double-checked the transistor number, and it is correct (not to say the transistor is truly correct). I know the transistor got hot while soldering, but I'm pretty good at soldering, and it did not get hot too long. Questions: Could the heat of soldering increased the V output 2.0 degrees? Kinda doubt it. If I test the assy. by putting full car battery 12V through it briefly, would that destroy the components? A 7.0 V reading suggests the transistor is not destroyed by such a test. I've built another assy, using the same transistor part no. 7805. I think the cap is only 10 uf. What would be a better way to check the assy's. output? Could I run the gauges on 7V, or would they read falsley hi or low? Super close to getting this 8 year project back on the road, so please help if you can. Thanks!!!!!!!!!!!!!!! |
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| Author: | nm9stheham [ Fri Dec 19, 2014 4:17 pm ] |
| Post subject: | |
No, the heat should not increase the output by 2v. Melting the silicon or the internal bonding wires would pretty much be guranteed to have a much more damaging effect. Double check your connections to the 7805 to make sure you don't have 2 of the leads reversed; I suspect that is the case. Do you have a diagram depicting the pins out of the 7805 package? And, are you measuring the output voltage from ground to output? You could get 7 volts if you had your voltmeter connected between input and output..... I am not sure what you mean by 'putting 12 volts through it'. The 12v goes from IN to Ground (pins 1 and 2) and the output is from OUT (pin 3) and is referenced to Ground (pin 2). By the way, this is not just a transistor, it is a single packaged integrated circuit. This ought to produce a very stable 5V even down to no load current. |
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| Author: | drtwgn [ Sun Dec 21, 2014 5:16 pm ] |
| Post subject: | |
You were right on, nm9stheham. I was measuring between the input and output pins. Made sense to me to measure between those, but I'm ignorant of what's inside that black little box. Measuring between pin 3 and ground gave a nice, 5.00V. "Putting 12 V through it" should have said, "Applying 12 V to it." A little more excitement to motivate me towards the goal line. THanks for taking the time to help!!!! |
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| Author: | nm9stheham [ Mon Dec 22, 2014 8:09 am ] |
| Post subject: | |
Cool ! It's always good to find the 'problem' AND the reason! |
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