Battery drain: 500mA current draw from AM1 fuse (3 Viewers)

[David60series]

Hi,

Hoping someone can point me in the right direction.

I have an HDJ80R 1992 cruiser (Australian delivery) with manual 1HD-T. 12 volt.

For over a year now, I have had a current draw when the key is in off position and all accessories are turned off.

This problem seems to come and go drawing varied current from 150mA upwards. Right now, it is back and drawing between 450 and 500mA through the AM1 50A fuse. No other fused circuits are drawing any current.


Any guesses on where to start looking? Could it be a relay or solenoid held shut somewhere? Glow relay?

Very frustrating to say the least.

I hope someone can help!

Dave

 

[george_tlc]

Get the wiring diagram for your vehicle (most of us on this forum have petrol 80's) and follow things that lead from the AM1 fuse and check each for current draw. AM1 has various loads (at least on the petrol version) and not all ignition switched (e.g. dome lights) - pull their associated fuses to see if the parasitic draw goes away.

If you have a current clamp (compact one with DC capability) you can clamp it over various parts of the AM1 feeds to narrow down the offending circuit.

You're going to have to do detective work to narrow it down. Wiring diagram will be essential.

cheers,
george.

 

[David60series]

Thanks George,

I will try and track down a diagram. I have a full chassis and body FSM, but this does not appear to have a full wiring diagram.

I have pulled all factory fuses with no change in current.

Cheers for reply
Dave

 

[Tapage]

I assume you already check any aftermarket circuit you have in your 80 ..

 

[george_tlc]

^2 verify that there isn't some after market handiwork that's causing you issues assuming you're not the original owner. Check for previous owner hacks. Got an alarm system in there?

Pretty well anything that is actually toyota OEM in the 80 should be on the other side of a fuse (except starter motor, alternator output and headlights etc).

Is the head unit stock? Could be drawing parasitic current when 'off/asleep'.

Good luck on tracking it down.

cheers,
george.

 

[David60series]

Thanks again,

No alarm. Not original owner, but have had six years. Have added many accessories, but these are are either through the factory power outlet box, or from the aux battery which us isolated.

I have pulled headlight relay and dome also with no change.

I'm thinking of looking at the starter and glow relays next.

What do you mean in terms of alternator output? Just the charge wire that comes onto battery +ve via FL?

Cheers and thanks
Dave

 

[David60series]

UPDATE:

Current draw is stopped when alternator is disconnected at regulator harness.

The alt is brand new, and problem was occurring with previous alternator.

No change when starter relay is disconnected.

Have not tried glow relay yet.

 

[george_tlc]

If disconnecting the alternator output resolves the issue, then likely one or more of the diodes is kaput. Brand new OEM alternator or brand new Supercheap unit??

cheers,
george.

 

[David60series]

Thanks.

I don't use anything cheap on the 80.

I just had this alternator sent from the USA. It is a 270A Smart Battery Charger.

The previous alt was an OEX which is the only thing locally available.

I have the OEM but it has 300k on it and a worn housing. Still operating ok when removed.

It has run for about 10 minutes in order to test it and get motor to running temp after installation.

The only mods on this charge circuit are 2AWG wire from B+ Stud to battery, and same wire gauge from alternator house to engine block for negative return.


As advised, the previous alt has been doing this for 12 months, whilst still operating ok.

Are there any other diodes in the factory loom such as dash warning light?

 

[David60series]

Rectifier consists of 12 40 amp sanken press fit diodes.

 

[David60series]

Pulling charge and ignition fuses does not stop current flow.

 

[george_tlc]

There is no fuse between the alternator output and the battery (other than the fusible link).

IF disconnecting the Alternator output lead (the thick/heavy one that runs to the battery) stops the parasitic current then it is HIGHLY likely there's a faulty diode in the alternator. Test each of the diodes - on both your new and old alternator. You can have a faulty diode and still get 'ok' charging to the battery (since the alternator is typically a 3 phase unit), but a faulty diode will create a discharge path that through its associated winding that shows up as parasitic drain.

cheers,
george.

 

[David60series]

George,

You've been very helpful.

Unfortunately, when I disconnect the charge lead the drain drops back to 10mA.

I'm not sure how to check the diodes; I imagine the regulator is internal?

Not good news.

Not sure where to next.

 

[David60series]

I have checked the 3 pin harness into alternator, and there is power at the largest black wire.

The yellow wire and thin (blue?) wire have no power.

I know one is L which goes to charge circuit and one is to the ignition both via 7.5A fuses, but the large black wire is neither, as it has power when these fuses are pulled.

Is this my problem? What is this wire?

Regards
Dave

 

[Pin_Head]

Check the resistance across the diode bridge in both directions. Disconnect the large wire at the B+ lug first. A draw of 0.5 amp would be consistent with about a 25 ohm resistance in the reverse direction. The resistance in the forward direction should be close to 0 and thousands of ohms in the reverse direction.

 

[David60series]

Hi pin head, can I do this with out disassembly?

I have an OEM ALT sitting next to me at computer if you can describe where the diode bridge is.

I am assuming the think black wire to Alt reg is 'S' voltage sensor and has power at all times as is not switched?

If the alt is faulty, it would be extremely disappointing to say the very least.

 

[Pin_Head]

Disassembly not required. You measure between the big threaded lug on the alternator and the case. Reverse the leads black/red to measure in the opposite direction. Post the results.

 

[David60series]

Results:

Alternator on vehicle with battery disconnected and charge lead removed:

Black probe on B+ stud/red on alt case = 125 000ohms (125@200k)
Forward = no value on reading

Connect battery, connect 3 pin plug (no charge lead) =
4.39(20k)
09.9 (200k)
0.063(2m)

OEM alt off car
Black probe on B+/red on case = 93 000 (93@200k)
Forward - no value on reading.

Sorry for the confusing figures, but I'm confused myself as to what is going on with the alt on the car on the forward readings

 

[george_tlc]

You can't measure resistance with a meter when there is power applied to the circuit (e.g. once you've hooked the battery up).

I'd suggest you take the alternator to an auto electrician and get them to test it for you. Explain the problem that you're having and they should be able to figure out if there's a problem with the alternator. I presume from your initial post you're in oz? If so should be easy to find a small shop that knows what they're doing.

The real simple test:

Engine off, disconnect the B+ on the back of the alternator. Set meter for amps and put +ve of meter to the cable (that went to B+) and put the -ve of the meter to the B+ on the alternator. If you see more than 1mA then a diode has failed in the alternator.

Here's some more info for you: assets.fluke.com/appnotes/automotive/beatbook.pdf

cheers,
george.

 

[CJF]

Engine off, disconnect the B+ on the back of the alternator. Set meter for amps and put +ve of meter to the cable (that went to B+) and put the -ve of the meter to the B+ on the alternator. If you see more than 1mA then a diode has failed in the alternator.

Yup; simple as that.

Used that method to diagnose a bad alternator that was draining the battery in my Cressida.