Battery charger vs. ECU

[csuengr]

Sunday, when it was 70* out, I went to test my ECU and my wiring (Ford EEC-V on a 5.0 in my 77' Cherk), which I spent 15+ hours doing. I though I would be smart and use a battery charger for power since: 1. I don't have battery cables yet. 2. The charger is limited to 15A. 3. It has these neat clippy things and an easy to use and get to power switch, should things go awry.

So I hook the positive lead to the power distribution center stolen from a GC and the negative lead to a ground stud and flip on the switch. Ammeter doesn't move, so no shorts so far. Turn the ignition on, ECU doesn't turn on the fuel pump and there is a loud buzzing from the engine. Turns out to be the IAC. Plug the scanner into the DLC and it can't talk to the ECU. My dad and I spend almost two hours chasing wires and find nothing wrong. We give up and I start searching about OBD-II DLC's.

Next day after more info, I find that pins 4 and 5 on the DLC need to be grounded and pin 16 needs constant 12V. Quick wire job later, including a temporary MIL, I try again using a real battery hooked up using 16 AWG wires, just in case. Everything works fine. IAC doesn't buzz and I can read all sensors with the scanner and the ECU drives the fuel pump like it should.

So, a battery charger won't run an ECU. Not my charger anyway. Oh, and it is now 20* outside with 8 inches of snow.

[Stuka]

Don't use a charger to actually power things. They typically output some pretty dirty power, as a battery does not care about it. Also, some of them will not regulate their voltage correctly without a load. I am betting yours was not outputting the correct voltage with such a tiny load.

[FSJ Guy]

I agree. And sometimes they will output MORE than 12V for a while. Most car electronics will tolerate 14V, but they might not like 17-20 volts.

[csuengr]

I have a feeling that this charger's output is really dirty. And it was only putting out 10.6 Volts. I have used it to power other automotive circuits, like my rear window motor, but there were no electronics involved. If I wasn't such a wire repurposer, I would make dedicated wires with a fuse and switch. Any wire is fair game for something else.

On the plus side, I have have darn good grounds.

[tgreese]

A regulated 12VDC supply is really easy to build. If you can mess with ECUs, you can build one from a 7812 chip. Or use an old computer power supply - these will produce a regulated +12V with no modification. Add a jumper to simulate the on/off switch, and walla. Look here - http://www.helpwithpcs.com/courses/powe ... inouts.htm

[csuengr]

A regulated 12VDC supply is really easy to build. If you can mess with ECUs, you can build one from a 7812 chip. Or use an old computer power supply - these will produce a regulated +12V with no modification. Add a jumper to simulate the on/off switch, and walla. Look here - http://www.helpwithpcs.com/courses/powe ... inouts.htm

I got one that will do from 1 to 15V, but it will only put out 1 amp on a good day. It was made to power electronic circuits. It won't drive a fuel pump.

[shimniok]

Not sure how much current draw your entire system requires.

A regulated 12VDC supply is really easy to build. If you can mess with ECUs, you can build one from a 7812 chip. Or use an old computer power supply - these will produce a regulated +12V with no modification. Add a jumper to simulate the on/off switch, and walla. Look here - http://www.helpwithpcs.com/courses/powe ... inouts.htm

Only problem with a 7812 is that it only puts out 1A. You might be able to find circuit diagrams that support much higher current usually by hooking in a MOSFET or BJT transistor so that it handles the load and the 7812 just fixes the voltage properly.

A PC power supply will provide more current. I forget how much, though.

Maybe best to just use a plain ol' car battery? Borrow one out of the econobox for testing? I dunno...

[tgreese]

Yes, a 7812 would have to have additional pass devices to boost the current above 1A, so not a good choice here. Lots of circuits online though - check the 7812 data sheets first, if you want to build a supply.

I always have a spare battery on a HF battery maintainer - but not everybody does.

A computer supply has something like 3 +12V circuits at 15A each (for a 400W supply - typical cheapo supply). These are switchers, and there's a lot of capacity there.

[FSJ Guy]

Michael, you SO lost me.... But that's why I was just on the sidelines at the Sparkfun AVC and you came in second!