Great information. I have an unusual application to bounce off you. I put a Honda 300hp K24 (w/K20 harness and Hondata K-Pro ECU) in my Lotus. After learning the Honda alt/charging system was dual-mode, I began to wonder if my alternator is in low or high mode? Would I just put my DMM from chassis ground to positive batt terminal to get an accurate charge voltage? What's the best way to determine what mode the alt is in?

As it's a Lotus, there is no ELD, so I'm not sure what the ECU is telling the alternator to put out? As I understand it, the ECU outputs +5vdc to the ELD which operates as a sort of varistor. As you indicate, the higher the ELD load sensed, the increased voltage drop (resistance). Once the ECU see's around 2vdc, it commands the alt to go into high charge mode.

The question I'm asking myself is "Since I don't have an ELD ground wire, and you make a point of stressing not chassis ground, where should I get my reference ground, somewhere off the ECU itself?" Thoughts?

My toy...

 

are u trying to do what we are doing to the honda accord and installing a resistor?

 

Yes... But according to the original poster, he seemed pretty sure the black ELD wire is an ECU reference ground. I want to try the resistor if in fact my alt is running in energy savings mode. I'll need to check that first, so I want to verify a proper method to test. I'm concerned my alt never goes to the proper charge mode?

Without an ELD, I need to consider chassis ground as an option. After studying the schematics, I'm not yet convinced that the black ELD ground wire is an ECU reference ground (for precise analog sensing). I think it may be just a chassis ground. The number associated with the ground wire on schematics is just a way of identifying the many ground locations on the car. If it were an ECU reference ground, why wouldn't it come back to the ECU like other sensors? Just my thoughts. I was curious if the original poster had additional information on the ground? Or knew for sure?

Thanks,

Ken

 

according to your statement above, your running hondata kpro. why would u hardwire a resistor?

 

The reason I started researching the Honda alternator was because my very small race battery slowly dies near the end of a track day. In the garage, it's always on a battery maintainer, and the battery is new. The alternator is new too. So I was baffled as to why the battery goes dead after a few hours. I did fix an issue with the power up/power down procedure that may have been throwing the ECU in a tizzy (dash mounted battery disconnects).

All that aside, I was doing some research last night and noticed the K-Pro has the ability to enable/disable the ELD sensor circuit. Since my tuner programmed the K-Pro, maybe he missed this setting? Usually he tunes Honda cars, not swapped Lotus cars. I'll check it out as this may be part of my problem. I'm just exploring every possibility.

 

yes thats why i was asking you this. hondata has the built in feature. there is no need to do a physical mod for this. i use hondata and its a basic feature. as to why urs is draining might be something else.
this doesnt sound normal. even with the eld switched, it shouldnt be enough for your drain.
what you need is a volt gauge in the car to see whats going on.
i sometimes have my laptop hooked to my s300 and can see everything even voltage. so thats another way. i dont think this way is convenient but if your lazy it can work.

 

awesome car!

a voltmeter will tell you if the alternator is charging - by indicating greater than 13.8VDC while the engine is running.

if the ECU does have alternator field control then i agree you want to get it to keep the alternator field current on - unless you want some extra power. ideally, you'd have a switch that would allow you to override this control. running the alt will rob the engine of some power. and actually, having the alt come on while braking but off while accelerating would give you the best of both worlds. that would be easy to do with a few relays and direct control over the field current.

 

Thanks! I was curious if the leads are left on the battery when measuring cable voltages? I'm assuming they are, but just a question I considered. I'd prefer my alternator to operate in high-charge mode all the time. At 300+hp / 1700 lbs, a little alternator resistance is probably negligible. ;-)

 

The Mitsubishi alternator used in most Hondas that turn counter clock wise (alternator on the driver’s side) are not very good, they can only handle 175 amps at best. As I understand it the “race” computers don’t really care what alternator you use, assuming you switch off the LED. Depending on your power requirements you are probably better off with a Delco or Denso alternator. For full race or street / strip, setups we run external regulators with adjustable voltage. If you run at 15 to 16 volts you will need slightly more HP to run it but you supply the ECU and fuel pump with more voltage dropping the amp load requirements, so it is a trade of or a net positive. If you would like some more info or help with alternator selection for your specific set up I am happy to help, PM send me an email Darren@rushps.com

 

Thanks Darren. I measured the voltage across the battery terminals with the engine running. 14.40 vdc. Looks to be charging well, and since the car has very little in the vein of power-hungry electronics, I should be good.

I think the issue I had at the track recently was an 'improper power-down' procedure. I have both an ignition switch and battery disconnect switch on the dash. While running, I hit the battery disconnect first to shut things down. I've since learned that can cause some weird issues with the ECU (affecting tach output). No damage done, but that might explain why the alt stopped charging that day. Now I hit the ignition switch first, then the disconnect. This only happened once (August), but if haven't driven the car since then, so the issue might be okay now.