Electronics Basics

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Many issues that people have with openinverter can be solved with basic electronics knowledge. Since many folks who convert EVs rather have a mechanical background this is often a shortcoming.

This page aims to be a quick guide on basic electronic engineering practises that let you diagnose and fix most issues.

More specialized FAQs are: Inverter FAQ and Tesla Setup FAQ

No LEDs light up on the board

All boards that you buy either in the openinverter shop or at EVBMW have at least been powered up once to program them. So unless damage was done during transit they are an unlikely culprit.

You are having a problem with the supply voltage. On most openinverter boards there are 3 voltages: 12V, 5V and 3.3V. Start at the very feed-in point of the voltage, then work your way down (TODO: add pictures here). Attach your multimeter black lead to a solid ground point (the negative supply voltage) and then work with the red lead.

Now you may find that 12V do not even arrive on the board. That is easy, check for bad solder joints, loose crimps or broken cables.

You may find that the 12V supply arrives ok but then the 5V supply is too low or 0. Since the boards have undergone testing this is likely caused by something external. The boards usually also supply external circuitry such as gate drivers, current sensors etc. with supply voltage. If one of these external circuits is broken, it can short out or overload the power rail. This results in onboard LEDs being off or dim. Note that lower voltage supplies are derived from the higher voltage ones. So if 5V is overloaded, 3.3V will also not receive (sufficient) power.

So disconnect ALL external circuitry and only supply 12V to the board. Then plug things in bit by bit to find the culprit.

I get desat or overcurrent error before the motor even moves

3-phase bridge

This can point to a broken power stage. IGBTs usually fail shorted so it is quite easy to check with one measurement if one IGBT might have failed. As you can see in the image on the right the 3-phase bridge consists of 3 pairs of IGBTs. In parallel to each IGBT you see diodes and these are going to help us.

We put a multimeter in diode mode and stick the positive lead on + and the negative lead on -. Now we should see a slowly rising voltage. That is the multimeter charging bus capacitor with its test voltage. Once we reach around 2V the multimeter maxes out. If already here we see 0V it means at least one full pair (or leg) has failed shorted. That is rare.

Ok, now we reverse the test leads. The diodes are usually Schottky types, so each drops about 0.3V. Two in series drop 0.6V. If none of the IGBTs failed shorted we first see a negative voltage because the bus cap is still charged and then it should slowly climb to said 0.6V. Or maybe 1V. If it only climbs to 0.3V we know that at least one IGBT has failed shorted, bridging its parallel diode. Watch this video for a practical demonstration: https://youtu.be/ZvlzGm709zg