S60 Electrics: Testing for current draw

[BobS]

Hi,

Even with a faulty diode the alternator can still charge the battery.

The only way to check is to disconnect the +ive lead from the alternator and recheck the current.

Bob

[Bernard333]

The ECU ( ECM ) dosnt control everything just the engine , there are over 20 similar modules in your car and some of them have a shut down procedure where they continue to run even with the ignition off . There could be a component such as a capacitor in any of these which is leaking current to earth but you would expect this to cause the module not to function correctly . You have an automatic so you also have a TCM module sitting next to the ECM . I have a 2.4T V70 which I bought for spares and have tried disconnecting modules and sensors and then runnning the car and found that so far none of them have failed to boot up again when reconnected although for example you are not supposed to disconnect the CEM as stored information can be lost and then need reprogramming so if you use this approach you may be taking a risk with your cars electronics , on mine it dosnt matter as I only paid £500 for the car so I havnt got much to lose . Disconnecting the TCM from the auto transmission , running the car and then plugging it back in got the car moving forward again and changing gears normally which was the reason the previous owner sold it because it would only go in reverse , today everything works on this car despite me messing around with the electronics quite extensively . Anyway the point of all this is that if one of your control modules is the cause of the current drain you could try disconnecting them one by one to see if the drain stops . On a different V70 disconnecting the MAF , running the car and plugging it back in seemed to solve a long standing problem . My problem with this method is I still dont know if I could completely wreck one of the modules , I wouldnt be confident enough to do this with the modules on my D5 which I rely on every day although I have done it with most of the sensors and they have come to no harm .

[Georgey dee]

Mine was charging the battery (14v) and was running fine too. Doesn't mean it's not the alternator.

[agallo]

Hi there,

I should elaborate on the testing I've conducted to date. As perhaps my assumptions to what I was verifying were inaccurate. Here goes:

A prelude:
The issue I've been having has been somewhat intermittent initially. There were times I would leave the car parked in the garage for two weeks - get in - and it would start. Other times, I would use the car for the day - park it - and in the morning the battery would be drained.

This issue seems to be getting worse. In other words, it seems to me that the battery now would be draining consistently. Instead of the occasional bleed. But that was clarified by the mechanic who stated that the car as one point was draining - then started to drain. I tell ya - these modern cars are perhaps the first generations of AI!

Now for the specifics:
I have been measuring the current drain from the main bolt/screw adjacent to the fuse box inside the engine compartment. The screw/bolt has two leads attached to it. One is a straight lead and the second is a bent lead that leads into the firewall of the engine compartment. My assumption was that the straight lead comes from the alternator. The bent lead comes directly from the battery.

I placed a multimeter in series - one lead touching the screw/bolt and the second touching the bent lead. When I do this, I have a 3.8-9 amp drain - always. When I connect the leads of the multimeter between the screw/bolt and the straight lead - I don't have a drain.

I do measure a voltage of 12.4 volts from screw/bolt to bent lead, bent lead to the car chassis, and bent lead to the straight lead. I don't measure a voltage from the straight lead to the screw/bolt.
Note: the two leads (the bent and straight leads) both secure to the screw/bolt adjacent to the fuse box inside of the engine compartment.
I have left the multimeter measuring the 3.8-9 amps across the screw/bolt and the bent lead and have tried to remove the fuses in the fuse box in the engine compartment (1 by 1). But here perhaps has been my error? Perhaps I'm measuring the wrong points?

Note, while I have been measuring the drop across the screw/bolt and the bent lead - I have opened my driver's side door - and have seen the current drain go up to 5-6 amps.

I've dropped off the car again this morning - and the mechanic will continue the search for the drain. He's going to look at the control modules. I can only hope.

Thanks for your comments - I'm sharing them with the mechanic. I've also told him about this site (he's not a stealer) - and that it's members are some of the most knowledgeable folks out there when it comes to VOLVO's. Too bad there aren't more folks in this site from Calgary Alberta.

Cheers!
Angelo

[Bernard333]

I agree with Georgy Dee and Bob S you still cant discount the alternator being faulty and the current you are measuring 4 amps is way higher than any of the modules would draw . Also dont forget about all the other fuses not just in the engine compartment , you also have those with the CEM in the passenger area and with the REM in the rear . The output from the alternator ( voltage measurement ) is done by the CEM and not the ECM , and I think there is a capacitor mounted on the alternator connected across the output to earth , this could be leaking , will check this on mine tommorow to see if there is a capacitor .

[Georgey dee]

Alternator!

[timh30]

I'm having issues where the battery doesn't have enough charge to start the car after about 6-7 days. I've checked the current drain by putting an ammeter in series at the earth lead, and after about 20mins, it settles down to 50mA. After standing for 3 days, the voltage across the terminals is 11.6V and even after a long drive it only raises to 12.0V. When engine is running I get 14.0V across the terminals (so assume the alternator is charging properly). I suspect in my case I have a faulty battery?

[Georgey dee]

Yep... I would say that you need a new battery.

[Bernard333]

Got the alternator cover off my D5 engine and just one screw which I am stuck on to get the voltage regulator and brush assembly off and may have to remove the intercooler pipe to get enough pressure on it to turn it . Once the end cover is off you can see how it all works , there are two separate circuits the stator supplying heavy current output and the field coil fed by the voltage regulator through slip rings to the rotor . The output coils are terminated by welding directly onto the diode leads not soldered or screws so there is no removeable diode pack and if anything is goosed in this area you need a new alternator . The stator coils give a three phase output wired in a delta to six diodes to give a rippling dc output . This area of the alternator is very heavy duty , the diodes look to me to be at least 100amp rated and could be a lot higher , a diode going internal short would see a very high current get very hot and then possibly go open circuit , this would all happen in a second or possibly less , the only thing limiting the full battery fault current would be the stator coil impedance which is quite low ( without any coil impedance or internal diode resistance the battery on a D5 could put nearly 1000 amps through it but in practice its not going to happen ) , there is no fuse protection between the battery and power diodes , I see some American cars do have a 175 amp or larger line protection fuse , this would not help the diodes but would probably protect the battery and main heavy duty cable . I suppose the design of the system is that the diodes are expected to always eventually go open circuit , does anyone know if this is the case ? If its not the case then I can see a situation where diodes fry and the high current would flatten the battery fairly quickly ? I can also see that if you lost one or more diodes going open circuit the alternator could still function but give a lower output current . The stator and rectifier can be checked for drain with the voltage regulator removed .

The field coil in the rotor is fed through a slip ring and this current is much lower than the stator and is controlled by the voltage regulator , this part is replaceable and much lower cost than a new complete alternator but I still dont understand how this could cause a 4 amp drain current especially if the charging appears normal . The circuit diagram shows a capacitor accross the alternator , I suspect this is for electrical noise suppression due to the slip rings and is built into the voltage regulator ? Suppressor capacitors are normally small and not capable of passing much current , if this component was leaking and carrying 4 amps the heat generated would destroy it quickly and you would have an open circuit , this was common in the dynamo days when faulty condensors would give you snow on your TV , I think all the cars in our street were faulty when I was younger .

When you have tested the stator circuit for drain replace the voltage regulator and if the drain returns you have then isolated the fault .

Sorry for going on for so long but I want to understand how the charging system works and the possible modes of failure , I have read the book Understanding Automotive Electronics by William B Ribbens , its a good read regarding car control systems but nothing on the charging system . l find with many of these books that they are good at explaining the theory but they dont go into what really happens when a component fails , can anyone reccommend something better ?

[agallo]

Hi again,

I received a call from the mechanic. Looks like he has confirmed the problem - and in his opinion he believes the issue to be with the alternator and a faulty diode. He also stated that VOLVO has reported that the diode issue may be a cause for current drain. This I cannot confirm - but I would be interested in understanding the frequency of this issue befalling others - and that if it may be perhaps due to a design or manufacturing defect. Then again, it's perhaps just normal usage and/or wear and tear.

The mechanic quoted me a price of just under 800$ CAN for an alternator. I was able to find an alternator for 430$ tax in - that's after I return the old one. This is the same vendor I purchased a heater blower from - it installed with no issue.

The mechanic is also only going to charge me 3.5 hours for the work - the install and the trouble shooting he performed.

All of you have certainly helped me immensely in this situation - It does make a difference when you present yourself at a mechanic with some understanding in the issue. I also wonder if: what would have happened if I hadn't mentioned the diode theory...

I should receive the alternator in a few days - and we've scheduled the install for next week Friday. I'll report back on the results.

Again, thank you for all your help!