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I'm new here and wonder if you could help me out.

I'm trying to build a Lipo warning/cutout circuit for four lipocells.

The idea is to have a bicolor led showing green above 14V, orange between 14-13.5V, flashing red belov 13.5V and red below 12.5V also switching off the load.

I built and programmed the circuit and it works fine using no load, but with a load drawing about 5A the output from the 7805 rises to about 5.5V offsetting the programmed levels (although in the right direction) but perhaps destroying the cpu.

My question is what did I do wrong when designing this circuit? Why is the output from the 7805 changing when applying a load?

Lipocheck

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Start by measuring the voltage from GND Pin of 7805 to the battery GND. –  Myforwik Dec 15 '13 at 2:16
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2 Answers

I don't see a capacitor in the input of 7805 (IN to GND), add a capacitor in the input and see if it fixes the problem

By the way, how is the system wired? Does the mosfet has its own power line or the current it carries goes through the same power line of 7805?

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Possibly a problem wiht the physical layout. The ground path from the battery connector to Q1 should be short and be a large wire or wide PCB trace, and it should not pass by the 7805 ground pin connection. A voltage drop in the connection between battery negative and the 7805 ground will cause the 7805 output to rise.

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