Parasitic draw with new Tundra alternator

[EricG]

Final word on this (I hope). After I got it out, I checked the resistance between the B post and the alternator shell on the old and new units. The "new" one (from a yard) showed infinite resistance. The old/bad one showed a measurable resistance - don't recall the number. So that may be another check if somebody comes across this problem again.

 

[86tuning]

Now you can sell your old one as a core! Sucks to do the r&re but glad you've got it fixed.

 

[EricG]

Ok, apparently I'm not done with this yet

Truck has been back in service for about a month now. Earlier this week I thought the starter was a little slow. Then yesterday, after sitting 5 or 6 days, the battery was dead again! Not sure if I mentioned it, but when when I was working this issue before, I took the main battery down to sears - it tested bad and they replaced it under warranty. So it's a brand new battery.

Charged it up over night then went out today to take a look. Listening closely, I again hear that faint hum coming from area of the alternator that I had described before.

I loosened the nuts on the big fuse between the alternator and the + post on the battery so I can break that connection. When the connection is broken - no hum. Put a multimeter across the gap, and again - 1/3 amp draw, just like the old one!!

WTF??

Before I installed this alternator I took it to Advance Auto and had them put it on their machine - tested out fine. And see my note above about the difference in resistance between the B post and the alternator shell on the old unit and this one.

So I'm convinced this one was good when I put it on. What is killing alternators on this truck?? Any ideas?

 

[EricG]

Other notes - the alternator appears to be charging properly - 14.1V at idle. And I did a 6 hour road trip 2 weeks ago with no problem.

Could a bad voltage regulator cause this problem?

Here's something interesting...

A bad connection or open circuit between the alternator output terminal and the positive battery terminal will force the charging current to follow a parallel route through the diode trio and out of the alternator. This heavier than normal current flow through the diodes will cause them to overheat and fail. Consequently, if you have replaced an alternator before because of bad diodes, and the replacement fails for the same reason, there is likely a bad connection or open circuit between the alternator BAT (B+) terminal and the positive side of the battery circuit. Do a voltage drop test to check the entire circuit.

from here: http://www.riboparts.com/changeBlog...utomotive Charging System&changeName=&id=2215

Seems pretty unlikely - it's only about 2' of 4 gauge cable and a big fuse between the B post and the battery terminal. I'll give it a try though.

 

[EricG]

More data - voltage drop test:

From Alternator B post to battery + post: 0.14V
From Alternator shell to battery - post: 0.24V

Should be < 0.2 V according to that article, so the - test may be a little high.

But...
I put the multimeter across the battery +- posts with the engine running just to make sure I had it set up right - and measured 15.7V The earlier 14.1V measurement I gave came from the battery charger, which is complete crap - just tried the charger again and it read 13.9 while the MM touching the charger clips shows 15.6.

Running the RPM up to 2K and the voltage goes to 16.

So that seems much to high, which would indicate the voltage regulator, right? Can anybody tell me where it lives?

 

[86tuning]

Reg is in the back of the alternator. Usually where the multi terminal plug goes.

Did you check to make sure your alternator plug is correctly wired? If the draw and hum goes away when you disconnect the multi wire plug you may have a wiring issue. ie improperly connected or crossed wires.

 

[86tuning]

Did you have to change the plug on the alternator harness to install the tundra alternator?

 

[Pin_Head]

Here's something interesting...

A bad connection or open circuit between the alternator output terminal and the positive battery terminal will force the charging current to follow a parallel route through the diode trio and out of the alternator. This heavier than normal current flow through the diodes will cause them to overheat and fail.

Unfortunately, it is not true. There is no current flow in an open circuit and a bad connection will act like a resistor, limiting current flow. You could have a higher than normal voltage on an open circuit though.

 

[EricG]

Did you have to change the plug on the alternator harness to install the tundra alternator?

Yea, you have to change the plug. It must be something to do with that ... I'll be digging into it tomorrow.

 

[86tuning]

Three wires in the plug.

One is constant (reference 12v, usually white)

One is ignition (switched 12v)

One is sensing (to the charge lamp)

With the key on, you should see +12v to all three wires. With the key off, there should only be a single +12v on the sensing wire, which is usually white.

 

[EricG]

Three wires in the plug.

One is constant (reference 12v, usually white)

One is ignition (switched 12v)

One is sensing (to the charge lamp)

With the key on, you should see +12v to all three wires. With the key off, there should only be a single +12v on the sensing wire, which is usually white.

Thanks - any theory on how having a pair of these switched, or one (or more) not making contact could damage the alternator?

 

[86tuning]

If your sensing wire is mis connected to the alternators ignition power that would keep
The alternator active. Same as having the key on.

 

[EricG]

If your sensing wire is mis connected to the alternators ignition power that would keep
The alternator active. Same as having the key on.

Looks like this is exactly right - I had printed out this picture when I did the install:

https://forum.ih8mud.com/attachment.php?attachmentid=218330&stc=1&d=1206306996

But I think I didn't take notice that this is looking at the back of the plug rather then the front. So my wires are a mirror image of what they should be, which reverses the sensor & ignition wires.

Now if I could only figure out how to remove the wires from the plug! The old one came apart pretty easily, and it seems like I have the right tool for this one - but I'll be damned if I can get them to release

 

[EricG]

Guess I never followed up on this, but I just got a PM asking about it so I'll wrap this up in case anybody else comes across it.

The previous post is correct - when I put in the Tundra alternator, I mis-wired the new plug. The picture in Photoman's thread was from the back of the connector, but I was looking at the front so my wiring was a mirror image of what it should have been.

What this did was to keep the field coils in the alternator active even when the ignition was off, thus draining the battery slowly (and creating the faint hum I heard). Also meant that my voltage regulator wasn't working right so I think I was over voltage as well.

Fixed the plug and no problems since then.

 

[ontopofm]

I'm experencing the same drain. Did you have to remove the battery box and/or alternator to fix the plug?

 

[EricG]

I'm experencing the same drain. Did you have to remove the battery box and/or alternator to fix the plug?

No, I don't think so. It's was definitely a PITA to reach & release it, but I'm sure I managed it without removing the alt or battery.

With regard to your PM - I probably won't be home with enough daylight to take a picture until Saturday ... and I'm not sure you can get a clear picture of it. Best advice I can give is to use this picture:

https://forum.ih8mud.com/attachment.php?attachmentid=218330&stc=1&d=1206306996

And take particular notice of that second line of text "Wires push in from this side" when you assemble it.

 

[ontopofm]

Thanks. Mine is installed axactly like what Photoman instructed. My problem probably lies somewhere else. I checked the voltage on each wire. With the ignition off, solid big black wire gets 12V, 2 other wires get 0V. With ignition on, big black wire and black with blue trace get 12V, yellow with blue trace gets 5V. Still, please verify if yours looks like mine. Sent from my iPad using IH8MUD

 

[Pin_Head]

Voltage is not a reliable indicator of a drain because even an open circuit can have battery voltage with no drain. To measure current drain, you need to put an amp meter in series with the battery cable and the battery + post.

 

[ontopofm]

Just measured and it doesnt seem to draw much but battery still drained. Last night it was 12.6V, this morning is 12.0V. First pic is the alternator wire. Second is to the blue sea bus bar where all the stock wires connect to.

Sent from my iPad using IH8MUD

 

[MrMoMo]

Looks like you have 4 wires on that battery post, how come you only measured 2? Regardless, you have almost an amp (assuming scale since I can't read what your meter is set to). I would start chasing individual wires at your blue sea bus bar...

However, when you are taking these measurements... Do you have a light under your hood that is on, or any doors open on the truck with a dome light on?

12V @ 0.8 amps is pretty close to a 10W mini bulb...