S60 Electrics: Testing for current draw

[dubstar116]

Thanks, thats a great help. If it is the bridge rectifier that is causing the problem, is it just a case of replacing the bridge rectifier?? Also any ideas of what the replacement part may cost??

[Bernard333]

Most car alternators are three phase and have either a diode pack or three packs of three , its likely only one gets an internal short at a time but you still have to replace the pack , some use single button type diodes . My interest in this is I have an RAC booster battery charger fitted with 50amp button diodes same as fitted to car alternators , I tracked them down to Okay Motors in China but they have an moq of 1000 for which they want about £200 plus shipping costs so thats me out . For my battery charger I found a better alternative , using stud mounting 85amp IR diodes which I got for £2.46 each and are much better than button diodes as you can make a good solid connection to them and not much need for a heat sink but they are too big to fit inside a car alternator , I am still mad at Argoss and RAC for selling the battery charger with these button diodes fitted because they are crap and not fit for the job (the OKAY Motors made ones may be OK ! and I am not referring to this company ) , they went up in smoke first time I used it on a Volvo . I searched around for a supplier of button diodes in the UK but could not find one , RS , Farnell , Maplin etc , does anyone knows a supplier or importer who will supply this type of component in small quantities at a reasonable price , a few years ago there were loads of little shops selling this stuff but now when I look around they have all dissapeared .

[rippedoffagain]

If you're not bothered about original bits, and are prepared to do a bit of DIY botchwork, Maplin should sell all the diodes and bridge rectifiers you need for a reasonable price. You just need to make sure that whatever you put on can cope with the maximum expected current draw, and heat sinks (or if you want to be really hi-tec, a peltier heat pump) may be necessary.

If my maths is any good, the max empected current draw from the alternator works out like this:

I = (P/V)*1.41

Where I = current in amps, P is power output, V is voltage, and we multiply by 1.41 to get from RMS to peak power out because its AC.

So for, say a 70W alternator giving us 13.8 volts we get:

I = (70/13.8)*1.41 = 7.15A

So that means theoretically on a 70W alternator, each diode must be able to cope with at least 7.15 amps. In practice though I'd be looking for ones a bit more beefy just to be on the safe side.

So that's the theory, all that remains to be done now is to put it into practice. Good luck with that

Oh, but first, before wasting any time and money, you need to make sure that the fault is a failed diode/bridge rectifier. If your battery is recharging normally while the engine is running, then I doubt that's it. If it is going flat all the time and taking ages to recharge on a run out, then you've got a likely candidate.

[Bernard333]

I tried Maplin , most of their diodes are for mains power supplies so current rating too low they dont do much above 10 amps in single units , they dont sell button diodes and for an alternator you should use 25 or 50 amp diodes to allow for heating and overloading is there something in their catalogue that I have missed ? Farnell are the best I could find but they are expensive . The button diodes in my battery charger are rated at 50 amps which is a joke , I would be surprised if they can safely handle that for more than half a second even with a properly designed heatsink which it dosnt have and these are the same diodes used in some car alternators .

[rippedoffagain]

Try RS Electronics:
http://uk.rs-online.com/web/search/s...50A#breadCrumb

I haven't been into electronics for years, but when I was, RS was the other big name after Maplin. In fact RS were better for specialist bits, whereas Maplin were better for generic bits.

[BobS]

Hi,

I haven’t looked at the alternator used but check that the 'diode pack' does not contain the regulator. Some modern alternators have the diodes and voltage regulator in a sealed epoxy/metal pack. Also I thought the V70/S60 alternators were able to supply more than 100 amps (140)?

Each diode will drop around 0.7 of a volt. Even at 50amps that is 35 watts of heat for each diode! So a good thermal connection to a heat sink is essential.

I would strongly recommend getting the proper ‘diode pack’. If you can get one it’s probably not much more expensive. Try companies that recondition alternators or alternatively try a secondhand one?

RS and Farnell will do them but at a price. Look for ‘Bridge Rectifiers’.

Bob

[rippedoffagain]

I'd have though the voltage regulator would always be a separate unit to the bridge rectifier? The reason I say that is that to get from AC from the alternator to smooth DC in the final output, you need a bridge rectifier, a good sized capacitor, and then a regulator. Of course it would be possible and sensible to put the bridge rectifier and the regulator in the same unit, as long as there are terminals off that unit for the capacitor to go to. Maybe there are? My knowledge in this area is largely generic and not based on experience of how cars are set up.

[BobS]

Hi,

It's all down to cost. The 'capacitor' is the car battery and it's cheaper to make the electronics (diode and controller) in a single unit.

Bob

[agallo]

Folks,

You have helped confirm the issue - and in turn have potentially saved me a lot of money. My hat goes off to you and this forum - and the tremendous value you and it provides.

Thank you so very much for your guidance and help.

Kind regards,
Angelo

[agallo]

Follow-up....

Hi folks,

Well, the saga continues....

The issue doesn't seem to be related to the alternator. The alternator is changing the battery - 14.4 volts.

I've brought the car to a mechanic. He has gone through further testing and believes the issue could be:
1. The ECU. The module that manages all the devices in the car.
2. The ETM. When he plugged the reader it came back with a ton of errors - including the ETM. Mind you - the mechanic believes it could be more related to the ECU.

Other than the battery drain - the car's running beautifully. No other issues.

Any other idea's folks?

Kind regards,
Angelo