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redpoint5 · 10-18-2014, 04:15 PM

I don't know how I missed the important info in California98Civic's threads, (here and here) and steffen707 (here), but most of the info I needed to begin testing and constructing my alternator kill switch is discussed there.

I learned today that my alt kill may be a little easier than what is described in the threads linked above. With an ammeter connected to the alternator output and voltmeter connected to the battery, I started the TSX and took measurements.

With the battery and alternator connected normally, I immediately saw an output current of 30 amps and just above 14v at the battery. While the car was still running, I disconnected the 4-pin connector at the alternator and observed the amps drop to 0, and the voltage drop to ~12v. This shows that I can switch off some wire (or wires) on the alternator while it is running and disable it. It will not maintain the field coil voltage without being plugged in.

Next, with the 4-pin alternator plug disconnected, I revved the engine to 4,000 RPM to see if it would self excite and resume charging. I observed that the voltage did not rise, and there was no output from the alternator.

Fantastic! All I have to do is rig a DPST switch to 1 or 2 wires from the alternator to kill it. Regardless of engine RPM, or if the alternator was previously operating, I can disable the alternator and re-enable it with a simple switch.

I would assume all late model Honda's (perhaps 2004 and later) behave the same way, although you will need to test for yourself.

My extra 4-pin connector has arrived, so all I have to do is purchase some small spade connectors and wire in the switch when it arrives.

With the success I've had, I'm beginning to think bigger. My dream setup would involve a microcontroller that monitors battery voltage and enables the alternator automatically if it drops below a certain threshold. Even more, it would monitor for DFCO and enable the alternator to charge when the energy from deceleration is free. I would somehow have to monitor engine RPM and throttle position and make an If Then statement that says something like;

If RPM > 1500 AND throttle position < 1% ENABLE relay to switch on alternator.

ELSE DISABLE switch on alternator

I'm just not sure how the protocol on OBD2 systems work, or what voltage they run for signaling. The Microcontroller I have uses 5v as high and 0v as low, with the threshold somewhere around 2.5v.

If I need an additional IC to communicate with the car, it should be cheap since an ELM237 can be had for $5 including shipping. Thoughts?

10-18-2014, 04:15 PM	#17 (permalink)
redpoint5 Human Environmentalist Join Date: Aug 2010 Location: Oregon Posts: 12,822 Acura TSX - '06 Acura TSX 90 day: 24.19 mpg (US) Lafawnda - CBR600 - '01 Honda CBR600 F4i 90 day: 47.32 mpg (US) Big Yeller - Dodge/Cummins - '98 Dodge Ram 2500 base 90 day: 21.82 mpg (US) Chevy ZR-2 - '03 Chevrolet S10 ZR2 90 day: 17.14 mpg (US) Model Y - '24 Tesla Y LR AWD Pacifica Hybrid - '21 Chrysler Pacifica Hybrid 90 day: 43.3 mpg (US) Thanks: 4,327 Thanked 4,481 Times in 3,446 Posts	I don't know how I missed the important info in California98Civic's threads, (here and here) and steffen707 (here), but most of the info I needed to begin testing and constructing my alternator kill switch is discussed there. I learned today that my alt kill may be a little easier than what is described in the threads linked above. With an ammeter connected to the alternator output and voltmeter connected to the battery, I started the TSX and took measurements. With the battery and alternator connected normally, I immediately saw an output current of 30 amps and just above 14v at the battery. While the car was still running, I disconnected the 4-pin connector at the alternator and observed the amps drop to 0, and the voltage drop to ~12v. This shows that I can switch off some wire (or wires) on the alternator while it is running and disable it. It will not maintain the field coil voltage without being plugged in. Next, with the 4-pin alternator plug disconnected, I revved the engine to 4,000 RPM to see if it would self excite and resume charging. I observed that the voltage did not rise, and there was no output from the alternator. Fantastic! All I have to do is rig a DPST switch to 1 or 2 wires from the alternator to kill it. Regardless of engine RPM, or if the alternator was previously operating, I can disable the alternator and re-enable it with a simple switch. I would assume all late model Honda's (perhaps 2004 and later) behave the same way, although you will need to test for yourself. My extra 4-pin connector has arrived, so all I have to do is purchase some small spade connectors and wire in the switch when it arrives. With the success I've had, I'm beginning to think bigger. My dream setup would involve a microcontroller that monitors battery voltage and enables the alternator automatically if it drops below a certain threshold. Even more, it would monitor for DFCO and enable the alternator to charge when the energy from deceleration is free. I would somehow have to monitor engine RPM and throttle position and make an If Then statement that says something like; If RPM > 1500 AND throttle position < 1% ENABLE relay to switch on alternator. ELSE DISABLE switch on alternator I'm just not sure how the protocol on OBD2 systems work, or what voltage they run for signaling. The Microcontroller I have uses 5v as high and 0v as low, with the threshold somewhere around 2.5v. If I need an additional IC to communicate with the car, it should be cheap since an ELM237 can be had for $5 including shipping. Thoughts? __________________ Gas and Electric Vehicle Cost of Ownership Calculator Give me absolute safety, or give me death! Last edited by redpoint5; 10-18-2014 at 04:35 PM..