Hi ,
My ha ha was my enjoyment of your comment of not having read all the thread-I have done the same in the past.
I realise could be read negatively so just to be clear not a dig at you in the slightest.
Best wishes
Jack
Technical Alternator only starts generating after revving
- Thread starter nigelvan
- Start date
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Technical Alternator only starts generating after revving
Hi ,
My ha ha was my enjoyment of your comment of not having read all the thread-I have done the same in the past.
I realise could be read negatively so just to be clear not a dig at you in the slightest.
Best wishes
Jack
Thanks for that link. Exactly what I'm looking for.
Brilliant idea about how to break the hold of the wheel to hub problem. I'd never have thought to try that. I once had that happen for real with my very first car, an 850 mini. Long before I knew much about cars it had been in the garage for a service but they hadn't fully tightened the nuts. They'd obviously put them on finger tight after doing the brakes but then failed to tighten them. luckily I wasn't far away so just popped back in and they tightened them up - some very red faces were to be seen! So I know that sound only too well, once heard never forgotten!
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D'you know, I was just reflecting on this interesting thread and thinking about my approach/experience to/with this sort of thing. Over the years I've attempted repairs on many alternators (and, along time ago, dynamos). Regulator packs being most common but also bearings and brushes/slip rings. Often the repair was satisfactory only for something else to fail soon after. So, for instance, maybe put a regulator pack into it only to have a front bearing fail a couple of months later and have the agro (and on some this can be a lot of agro where air con pumps are fitted) of removing it from the vehicle and stripping it down again. My approach now is to say to myself, How old is this unit and, if it's on a newish vehicle, what's the mileage trip reading and what sort of general condition is it in? If it's old/high mileage/in poor visible condition I wouldn't usually bother trying to repair it (Classic vehicles etc excepted of course). Of course with this approach you need to be quite certain it's definitely the unit itself which has failed before laying out the cash for a new one, which is getting more difficult to diagnose these days with "smart" alternators becoming the norm.
Edit. I have much the same approach to exhaust systems. Patching up an old rusty system is "for the birds" You'll find you're embarking on an endless pursuit of patching one hole only to have another appear within a short time. and then another, and then another!
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No, I've only tested it with an oscilloscope to measure the 3 different phase, I get a nice sine wave out of all of them when spinning the rotor by hand. I measured the rotor resistance (2.5 ohm which should be within general spec) and stator coil resistance. Replaced the voltage regulator as we all thought this was the culprit.
I did load test it at idle after 'starting' it with 12V. See above, put on all electricals including high beams and fog light, cabin blower and radio. Lowest it got was 13.8V at idle rpm (about 700 I think) with everything on.
So as far as I can see, it doesn't start with the 10V from the BCM but it will start if you feed 12V to the D+ briefly. I still have to measure how much current it draws (the fuses in my DMM were blown so no current measurements last time) when I put 12V on D+. But since the wire from the BCM all the way to connector D004 is very thin I think it is supposed to take very little power. Tomorrow I'll be at the van again and I'm going to run an extra wire from the BCM pin to D+ because I still think a wiring fault is more likely.
I thought about a fix if the BCM is faulty:
I might use a MOSFET to get 12V to the D+ until it starts. Without compromising the feedback signal to the BCM
The BCM gives about 10V now that I can put on the Gate of a MOSFET, I'll connect the Drain to battery 12V and SOURCE to D+. If I put a diode in between I avoid half-wave rectified voltage from D+ flowing back through the mosfet to the battery. With another diode blocking the BCM signal to D+ I make sure Gate voltage is high enough, and the BCM will still get a 14V signal back from D+ through that diode to signal the alternator is working. What do you guys think?
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Sorry, not while I cranked. D+ voltage while ignition on but engine off and when engine started but alternator not generating was 0.7V on the old regulator, 1.5V on the new one (which is weird...). I'll check tomorrow if the voltage changes while cranking. Sorry I overlooked this.
I'm finding all this very interesting and almost understand what you're doing, thank you. However I find myself just a little surprised that 10 volts isn't enough to energize the field sufficiently to get the thing started. Does the 10 volts coming from the Body module get fed directly into the field or is it going somewhere else in the alternator first? If going direct then are you measuring it connected or open circuit - ie. is the wire feeding current to the field when you are taking the measurement or are you checking the end of the wire itself ie. not connected to the unit.
Just wondering if it's maintaining sufficient supply when carrying load or does the voltage drop away?
As I've said already, I'm a bit of a "bull in a china shop" when it comes to electronics but I've push started older vehicles with flat batteries - so likely less than 9 battery volts on open circuit and found the alternator delivering charge. Of course I'm talking old type "dumb" alternators here. However I was wondering if the applied voltage is dropping off when under load on yours? I'm guessing it maintains charging once "kicked" with the 12 volts as the alternator output will maintain this higher figure once it starts charging.
Hope my "primitive" observations are of interest. Good luck with it, I'm enjoying the thread.
The 10V are open circuit, so alternator disconnected. Connected (in circuit) I measured 0,7V before and 1,5V with the new regulator. I think the results should be the same that's why I'm looking at the wiring.
But probably there are diodes in the path as well which explain the voltage. Also, I read that the field current is regulated by an IC in the regulator which puts out a PWM signal, so could be we are just seeing an average DC voltage of a pulse width signal.
According to someone in the beginning of this thread, 10V open circuit is normal.
Yes 9.5v open
Yes just over 1V ignition on
1.5K D+ to case
All appox
Should be around battery voltage while cranking
Which with the starter current will be around 10V
The BCM only sends current during cranking
Once the RPM is over 700 the current is cut
These are Regulated Voltage Control (RVC) alternators
The field current can be switched on and off via body computer very quickly, Fiat were one first to implement this technique (1985) whether your vehicle does or doesn't use it, I can't say elearn is very sketchy, then again the 500 does and it's not mentioned in elearn, I can't see why not the alternator runs cooler, and there's less drag from the alternator, improved MPG
Yes just over 1V ignition on
1.5K D+ to case
All appox
Should be around battery voltage while cranking
Which with the starter current will be around 10V
The BCM only sends current during cranking
Once the RPM is over 700 the current is cut
These are Regulated Voltage Control (RVC) alternators
The field current can be switched on and off via body computer very quickly, Fiat were one first to implement this technique (1985) whether your vehicle does or doesn't use it, I can't say elearn is very sketchy, then again the 500 does and it's not mentioned in elearn, I can't see why not the alternator runs cooler, and there's less drag from the alternator, improved MPG
Your little MOSFET circuit will affect any sensing by the BCM. The voltage will be dropped by one diode drop.
A filament lamp in series with the ignition switched supply really is the bet fix. Leave the BCM connected. It can still monitor the D+ voltage, which will rise close to the main 12V supply. The lamp will also prevent excess current regardless of any further fault. It will also provide an independent alternator failure warning. Aim for 100mA / 1.2W rating but it's really not critical. It's simple cheap and works. Millions of cars use it.
The 10 V you aere reading is just leakage current. Try measuing it with a 1k resistor across the DMM on volts to measure the current without blowing fuses.
Robert.
Post crossed with Koalar.
If the vehicle has a smart alternator (I don't think it has) The only difference with having the lamp fitted is the alternator will be on all the time with a small increase in fuel consumption. This is not a problem.
If the vehicle has a smart alternator (I don't think it has) The only difference with having the lamp fitted is the alternator will be on all the time with a small increase in fuel consumption. This is not a problem.
The purpose of a low watt bulb in the dark ages(Joe lucas) was to limit the current to the alternator rotor(As well as warning no charge).....I suggest you use a low watt bulb in your proposed circuit to limit the current.
Or........ just fit a lovely filliment bulb in a dedicated charge panel light fitting wired to a switched live. Switched live so it is not on when vehicle off .
@g8rpi @jackwhoo yes I agree it is a simple and reliable solution. You are right, I can leave the BCM connected. But if D+ ever gets disconnected, won't the lamp put 12V on the D+ wire to the BCM (which is a high impedance input), leaving the warning light off when it should be on? The old school warning light only works as long as the D+ sinks to GND. If the D+ wire or connection breaks (which I've seen happen here on this forum), the lamp won't tell you anything. So yeah, computers!
The diode will drop the voltage by 0.6V which might still be within the right ballpark for the BCM. I believe it only throws the warning light below 12V.
@koalar If the BCM cuts the current why does it bother raising the rpm trying to get the alternator going then? Don't get me wrong but I do read the same voltage with ignition on and while engine running with increased rpm. Anyway I'll put it to test tomorrow.
Yes, I do enjoy this indeed. Trying to get to the bottom of this and learning along the way. I have an engineering degree in electronics but I never had the chance to put it into practice, ended up going in IT. The van is a camper and we don't need it until half of June. Still plenty of time to throw an entire new alternator at it.
Thank you all for your suggestions. I'll be back with my findings. If anyone has suggestions how I can test the alternator once it is generating I'll be happy to look at that too. Unfortunately I don't see how I can spin in fast enough out of the car. Maybe with a drill but I don't think I have a socket that fits in the pulley of the alternator.
The diode will drop the voltage by 0.6V which might still be within the right ballpark for the BCM. I believe it only throws the warning light below 12V.
@koalar If the BCM cuts the current why does it bother raising the rpm trying to get the alternator going then? Don't get me wrong but I do read the same voltage with ignition on and while engine running with increased rpm. Anyway I'll put it to test tomorrow.
Yes, I do enjoy this indeed. Trying to get to the bottom of this and learning along the way. I have an engineering degree in electronics but I never had the chance to put it into practice, ended up going in IT. The van is a camper and we don't need it until half of June. Still plenty of time to throw an entire new alternator at it.
Thank you all for your suggestions. I'll be back with my findings. If anyone has suggestions how I can test the alternator once it is generating I'll be happy to look at that too. Unfortunately I don't see how I can spin in fast enough out of the car. Maybe with a drill but I don't think I have a socket that fits in the pulley of the alternator.
The old filliment light solution is fantastic in its simpleness,
ignition on look at charge light , it's on =bulb filliment intact + wire to alternator intact + carbon brush to rotor intact. Start engine , light out? Alternator working.
Ignition on....look at charge light ,No charge light .....first check filliment bulb .......then check wire to alternator (simple by disconnecting from alternator and grounding- light should come on- if no light it is supply power to bulb or wire to alternator.
If it's none of those it's the alternator.
It is the genius solution without a computer to lie to you that it is charging when it is not , leaving you stranded on a major route/ middle of no where/ dreadful weather.
ignition on look at charge light , it's on =bulb filliment intact + wire to alternator intact + carbon brush to rotor intact. Start engine , light out? Alternator working.
Ignition on....look at charge light ,No charge light .....first check filliment bulb .......then check wire to alternator (simple by disconnecting from alternator and grounding- light should come on- if no light it is supply power to bulb or wire to alternator.
If it's none of those it's the alternator.
It is the genius solution without a computer to lie to you that it is charging when it is not , leaving you stranded on a major route/ middle of no where/ dreadful weather.
I still read it as the RVC alternator is controlled by the body computer
