alternator charging voltage drop when hot 1.6 petrol

[saskak]

Hi all,

I have a neighbour with an M59 (2007) 1.6 petrol (TU5JP4 engine). He has a dashcam and the plug has one of those voltage LCDs and he said it was ~11.8-11.6 and dropping while driving and he checked with multimeter on the battery and that was correct. He replaced the alternator as he thought that it was not charging correctly. The new (remanufactured) alternator is a Bosch 14V 120A alternator. The original was mitsubishi with the same specs/plugs.

Right, so when the car is cold the charging at the alternator and the battery is ~14.2V at idle. Once the engine warms, the voltage gradually drops to ~13.6-13.8V or so and stays there. With all loads on in the car there is a bit of a drop of ~0.3V to ~13.5. With an increase in rpm it does not change.

He asked me how it is on my 1.6HDi, but my M59 holds it extremely steady at 14.3V regardless of if the engine is hot or not. Also with all my loads I get a drop of course of ~0.3-0.4V to ~14V.

I do not think his is a smart alternator as it has one bit + cable and a plug and no sensor on the battery to measure actual V/amps. I do not think mine is a smart alternator either. Maybe I am wrong on that, but both cars are 2007, so probably not smart ones.

Do you think that is kind of normal or not for the 1.6 petrol. Seems a bit weird that the voltage drops with the warm up of the engine. Seems like there is some sort of resistance somewhere and with the temperature of the engine increasing there is further drop as of course the resistance will increase. My 1.6HDi does not do that, but of course ECU/BSI and alternators are different.

Any help is more than appreciated. Checked some of visible earth connections and they look alright. Cabling seems ok, no melting nothing. No whine from the alternator or other stuff.

Many thanks for any input.

[jemselectrical]

Hi all,

I have a neighbour with an M59 (2007) 1.6 petrol (TU5JP4 engine). He has a dashcam and the plug has one of those voltage LCDs and he said it was ~11.8-11.6 and dropping while driving and he checked with multimeter on the battery and that was correct. He replaced the alternator as he thought that it was not charging correctly. The new (remanufactured) alternator is a Bosch 14V 120A alternator. The original was mitsubishi with the same specs/plugs.

Right, so when the car is cold the charging at the alternator and the battery is ~14.2V at idle. Once the engine warms, the voltage gradually drops to ~13.6-13.8V or so and stays there. With all loads on in the car there is a bit of a drop of ~0.3V to ~13.5. With an increase in rpm it does not change.

He asked me how it is on my 1.6HDi, but my M59 holds it extremely steady at 14.3V regardless of if the engine is hot or not. Also with all my loads I get a drop of course of ~0.3-0.4V to ~14V.

I do not think his is a smart alternator as it has one bit + cable and a plug and no sensor on the battery to measure actual V/amps. I do not think mine is a smart alternator either. Maybe I am wrong on that, but both cars are 2007, so probably not smart ones.

Do you think that is kind of normal or not for the 1.6 petrol. Seems a bit weird that the voltage drops with the warm up of the engine. Seems like there is some sort of resistance somewhere and with the temperature of the engine increasing there is further drop as of course the resistance will increase. My 1.6HDi does not do that, but of course ECU/BSI and alternators are different.

Any help is more than appreciated. Checked some of visible earth connections and they look alright. Cabling seems ok, no melting nothing. No whine from the alternator or other stuff.

Many thanks for any input.

Logically, the engine when cold would idle at a slightly higher rpm initially before warmed up enough for the ECU to drop the idle speed. given that the voltage output from the alternator appears to plateau to a stable consistent voltage irrespective of engine revs, maybe the ECU regulates the output? One would have thought that diesel variants would require a higher output due to the higher initial demand, much like the battery is larger to account for that?

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[geoff]

My experience with auto electrics is biased to much older vehicles using compensated voltage control so I'm not likely to be of much help to you but based on what I know I'd be looking at the battery first.
Not saying to get a new one rather can he borrow one to run and test his vehicle with ?
It might just help ?
Quick and easy.

[saskak]

Many thanks both for the input, appreciate it!

I also thought the battery might be a suspect, but checked with my battery tester and seems alright. It has been replaced in the last 3 years, exide premium 610A, but might have gone anyway. I went to his M59 over the previous day and over night it has not dropped voltage, ~12.7V. I might try to fit mine in there, although it will not probably fit. The 1.6HDi battery is a bit larger.

I also though that the ECU is probably regulating the voltage, but I doubt 2007 is that smart to measure the voltage/amps going in the battery and adjusting accordingly.

I plugged in my diagbox and there are no errors, so probably alright.

[Sol]

Ok @saskak, here is something to try. If it is a LIN network connected alternator, and Citroen have had these for a while, try with the engine running, pull the plug on the alternator (it's a single wire plug yeah? Green probably) and make sure to be measuring the battery voltage before and during this.

Let's say you get 12.3v at the battery and then when you pull the plug from the alternator, the battery shoots up to 14.3v then it is likely the alternator is (or should be) the LIN controlled model. The voltage is communicated to the ECU using the LIN network connection, on which the ECU is master and the alternator a slave.

See what happens. If zero change, then it's likely a conventional alternator where the field exciter is the purpose of the plug and it should then have 12v in that wire when the ignition on. When the field supply is removed on a conventional alternator, the charge light will come on at the dash but the voltage won't change while running, as the field is already being held up by the charge voltage.

LIN alternators will not show a charge light when unplugged. If it's a smart alternator and the LIN module inside is faulty, the voltage will jump to full output and no light will be seen.

[saskak]

Ok @saskak, here is something to try. If it is a LIN network connected alternator, and Citroen have had these for a while, try with the engine running, pull the plug on the alternator (it's a single wire plug yeah? Green probably) and make sure to be measuring the battery voltage before and during this.

Let's say you get 12.3v at the battery and then when you pull the plug from the alternator, the battery shoots up to 14.3v then it is likely the alternator is (or should be) the LIN controlled model. The voltage is communicated to the ECU using the LIN network connection, on which the ECU is master and the alternator a slave.

See what happens. If zero change, then it's likely a conventional alternator where the field exciter is the purpose of the plug and it should then have 12v in that wire when the ignition on. When the field supply is removed on a conventional alternator, the charge light will come on at the dash but the voltage won't change while running, as the field is already being held up by the charge voltage.

LIN alternators will not show a charge light when unplugged. If it's a smart alternator and the LIN module inside is faulty, the voltage will jump to full output and no light will be seen.

Many thanks Zion. It is 2-wire plug (both connected) and of course the big metal +. I have not tried removing the plug while the car is running, but did try with and without the plug and voltage measured on battery/alternator did not change. Is it safe to unplug the 2-wire connector while the car is running? I do not want to damage something to the old gentlemen's M59. Mine is a different matter, I would go around unplugging things without a problem. I was thinking of altogether driving without the plug and see if the voltage drop is the same.

He drives it rarely and seeing me tinkering around my 1.6HDi wanted me to have a look before going to a garage.

I did measure the voltage drop between alternator's body and battery neg and the alternator's + to bat +, but it was not at all high, 0.05 on the -/- and ~0.1 +/+ which seems normal. Resistance is almost 0 from alt's neg to bat and the positives.

[Sol]

My own experience is that the LIN version of alternator is self excited and doesn't need the little plug in to work. A standard alternator should not produce any charge if unplugged from the beginning. Unless it has a shorted diode on one side of the 3-phase rectifier and then it can self-excite from the battery main cable.

My own alternator is the LIN version and the LIN controller on board is faulty so it kills the Comms when plugged in, and the battery drops very quickly to 12.3v, so I leave mine unplugged all the time, it charges beautifully at 14.3v with no LIN connection.

With it plugged in, I get no charge.

The 2 wire version could indeed be smart having exciter and LIN connections in the older models. Mine has no battery monitor circuit so it can only communicate over the LIN bus.

One more thing - mine also reads 1v less at the OBD port than the actual battery. This could be why his Chinese plug thing shows a lower voltage. Try it plugged into yours before condemning the alternator, as 13.8 is not bad if solid, and is still there while running with all loads on.

[saskak]

My own experience is that the LIN version of alternator is self excited and doesn't need the little plug in to work. A standard alternator should not produce any charge if unplugged from the beginning. Unless it has a shorted diode on one side of the 3-phase rectifier and then it can self-excite from the battery main cable.

My own alternator is the LIN version and the LIN controller on board is faulty so it kills the Comms when plugged in, and the battery drops very quickly to 12.3v, so I leave mine unplugged all the time, it charges beautifully at 14.3v with no LIN connection.

With it plugged in, I get no charge.

The 2 wire version could indeed be smart having exciter and LIN connections in the older models. Mine has no battery monitor circuit so it can only communicate over the LIN bus.

One more thing - mine also reads 1v less at the OBD port than the actual battery. This could be why his Chinese plug thing shows a lower voltage. Try it plugged into yours before condemning the alternator, as 13.8 is not bad if solid, and is still there while running with all loads on.

Yeah, I will try to unhook the 2-wire LIN connector while the car is running after the drop to ~13.7-8 (hot engine) and see if the voltage changes. It is a brand new, well not brand new, but remanufactured Bosch alternator, so it would be a bit suspicious, although possible to be faulty.

If that does not change much, I will try to drive it with the 2-wire plug unhooked and see if the drop is there. There is still power, but not quite 14.2-4V. I just compare with my 1.6HDi where it is like clockwork on the 14.3-14.4V regardless of how warm the engine is. It is like the alternator is a bit on the smart side and when the engine is cold, kind of battery is a bit exhausted to begin with the alternator is 14.2-14.3V and then after ~20min it drops to ~13.7 or so volts. Seems like it has done the bulk charging and then drops to float to maintain the battery with minimum amperage. Similar to a solar panel charge controller. Too smart for my thinking somehow and the year of the car.

[saskak]

It is a bit weird this thing.

Drove it today just to see how it is. With a multimeter on the battery/alternator it was giving 14.2V. The engine was cold. Drove for ~40min and then it was reading ~13.82-13.9V.  During the drive (reading from cig lghter LCD), it goes down to ~13.6, but steady at 13.7-13.8V. That is accounting for the difference of 0.1V on a multimeter on battery and the LCD thingy. Occasionally dropping to 13.5-6V when braking, which is fine.

I could not get the LIN cable off when the car was running, it was way too hot for my hand to stick it around there. Switched it off and with a metal thing managed to get it off. Started the car without the connection and the voltages were exactly the same, ~13.88-13.9V.
So, probably a conventional alternator. I did try to measure the plug to + and - on the alternator and it does give ~12V +/- a few, 11.9 or thereabouts.

I managed to swap my old battery with the one in the 1.6 petrol, quite a bit fiddly, on one side, removing the air resonator. When started, still engine hot, still the same volts, ~13.9V. So, battery is OK.

Maybe that is how this thing works. Does anyone else have a 1.6 petrol that can measure the volts from the battery on a running vehicle when hot. The guy is afraid that it will leave him on the road somewhere, but when I drove it there was no drop of rpms nothing. Works as a charm. Also, when it is hot the rpms drop to normal ~850-900 or so. When it was cold ~1,000rpm. Somehow everything is OK, but the voltages drop ~0.3V when hot. Maybe he can check it with some auto electrician for amps output on the alternator.

[Sol]

It does sound like nothing is actually wrong with it.