problem with regulator for automobile

Erik Friesen

I have a trip computer installed in a 05 or so gm silverado. This regulator has given up for the second time on this vehicle. For reference, I have this identical design in numerous hondas and toyotas and have had no trouble. The processer is the propeller. I have measured the ma use at 12v and it is around 125-150 ma. The regulator is 8v which feeds a 3.3 volt regulator. This design has no tvs. Any thoughts? This vehicle turns off accessories when cranking the engine.

Carl Hayes

I would first examine the integrity of the ground circuit.· Grounding in modern vehicles, with their many plastic parts, is not so simple as just finding a screw and putting a wire under its head.· You really ought to have a direct feed, with real wires, right back to the battery's negative terminal.

Next I'd look for transients on the +12 feed (really anywhere from +10 to +15 under various conditions, usually about +14 when the engine is running (a little less on warm days).· You say the vehicle disconnects power to accessories when cranking.· Is your device among those accessories?· In either case, have you scoped that +12 line for spikes?· First thing to do is feed the positive with real wires from the battery, too.· If you want it to turn on and off with the ignition, use a relay.

Now that you're putting real wire feeds from the battery, you should fuse them.· Both of them.· Fuse them as close to the battery as you physically can.· Fuse the positive at about twice the expected peak current. and fuse the negative at about twice or thrice that.· The reason for fusing the positive is obvious; the reason for fusing the negative is that, if you don't, and other grounds in the vehicle go kaflooie, the whole battery current for the entire vehicle·will be flowing through your device, often with an inductive kick behind it.· This, you may be sure, is undesirable.· The negative-lead fuse won't keep your device from being damaged, but it may keep it from catching fire, or exploding.· Car batteries store a lot of energy.


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· -- Carl, nn5i@arrl.net

Post Edited (Carl Hayes) : 12/28/2008 4:20:18 AM GMT

Erik Friesen

The vehicle is a number of states away unfortunately. I had the owner check the wire feeding the device though. I suspect transients though. The reason I posted this was to get a feel for what it takes to blow a hole in a regulator like this. The Reg has an absolute maximum of 20v input.

I need to make some sort of transient suppressor I guess.