Alternator Drain Problem

[bcrain]

My 1988 Caterham came to me with a Toyota style one terminal alternator (Denso or equivalent 12180-SECN). This means that the two large brown wires from the battery were tied together and thence to the single terminal. The brown-black (from the battery, is this the exciter?) was taped off and the brown-yellow wire (to the instrument panel charge light) was also taped off. Everything has worked fine for the year of my ownership (except the charge light) except, I just discovered that the alternator is draining 3 milliamperes with everything off. My estimate is that if I don't drive the car for 6 months or so, it won't start. I only discovered it just as I was about to hook up my new glass mat battery in a more accessible location (old battery is fine).

THE QUESTIONS: 1- Is 0.003 amps typical for these kinds of systems and is this even a problem? 2- Does anyone have experience with this to share? 3- is there any way to make the charge indicator light work again?

I was never a charging system expert, though I am a EE so be as technical as you want. All my previous experience is with cars with separate regulators.

[Jonathan Kay]

That describes it as self-exciting, that is it doesn't need another wire to do that.

3- is there any way to make the charge indicator light work again?

Probably. Do the terminals on yours match the description above? I or IG is the ignition connection, B+ the battery positive, and L the lamp.

1- Is 0.003 amps typical for these kinds of systems and is this even a problem?

Now, I wonder who might know the answer to that...   :-)

Jonathan

[bcrain]

3- That picture is the alternator installed, but I can't find any markings on it for the IG or L. I'll try again with pictures. In my searches last night, I could find how to buy one, but not an installation drawing.

1- In the mean time, I'm hooking it back up one wire only just as it was. After all, I've been living with 3ma for a year already, just did not know it.

By the way, what are the low flying library and the external search links. The internal search is certainly very limited.

[revilla]

On a 3-wire alternator the voltage regulator circuit is switched off when you turn the key off. Significant leakage would suggest a bad diode. On a 1-wire alternator the regulator is permanently powered up (as everything runs off the one common wire which is connected permanently to the battery) and will draw a small current, typically 2mA. I don't think a 3mA drain sounds unreasonable for this type of system. Yes, if you leave the car for many months this will slowly drain the battery. But compared to later cars with engine management, fuel injection and immobilisers a 3mA drain is very small. My K Series car draws about 14mA, a lot which is leakage through the injector and coil drivers in the ECU as mine wasn't wired with a master relay to isolate these with the engine off. If you're planning to leave the car for long periods, I'd invest in a small intelligent battery conditioner, something like a CTEK. That should keep the battery topped up and healthy without overcharging and electrolysing off all the water (still check the fluid level occasionally though, mine does go down after a winter on the conditioner). I really don't think you have a problem to worry about :)

[Jonathan Kay]

That picture is the alternator installed, but I can't find any markings on it for the IG or L. I'll try again with pictures.

Even if you can't find any markings if you can photograph or sketch the layout of the terminals on the alternator it will probably be possible to work out what they are from the common patterns:

http://www.brise.co.uk/images/D/image-04.jpg

Jonathan

[Jonathan Kay]

By the way, what are the low flying library and the external search links.

• Low Flying is the Club magazine. After some excellent work back copies are now available online and searchable. This is a fantastic resource.
• I choose to use external search with site restriction. I recommend testing both the internal search and that approach and seeing which works better for you.

... and if you click on either link in my signature it should fire it up for you to play with. :-)

Jonathan

[bcrain]

Thanks for all the comments. I'm taking it as no problem full speed ahead.

I already had pictures of the alternator so it is a type 1. One more question. If I hook up ignition switched 12V to the IG terminal, what does that do? Just trying to get educated.

[Jonathan Kay]

One more question. If I hook up ignition switched 12V to the IG terminal, what does that do? Just trying to get educated.

I don't know what you are supposed to with the IG terminal on a self-exciting alternator.

Or whether the L terminal will work with a warning lamp without IG being connected.

Jonathan

[Jonathan Kay]

Would you like the warning lamp to function? It might be possible...

Jonathan