[C320-list] No charging until engine is revved repeatedly

[Graeme Clark]

Third commnet by me!

Found this on the web - note the last paragraph. maybe change the charge bulb?

"In order for an alternator to produce any output its armature or rotating winding must be rotated inside a magnetic field. This magnetic field is produced by applying a voltage to the stationary or field windings causing an excitation current to flow through them. When the ignition is turned on the initial excitation current is supplied from the vehicle's battery. Once the engine is started the alternator starts to produce an an output voltage which as well as charging the battery is applied to the field windings. The alternator is now said to be self exciting and the initial excitation current can be removed. 

The initial excitation current can be supplied via a resistor, but it is more usual to supply it via a bulb. This is the charge warning lamp. 
Sometimes a bulb and resistor are used in parallel. This has the advantage that if the bulb blows the alternator will still receive initial excitation. 
The higher the wattage of the bulb the greater the initial excitation current. If the bulb wattage is too low the alternator will not generate any output, it will never self excite and even with the engine running flat out it will not charge the battery at all.  

When the ignition is turned on 12 volts is applied to one side of the bulb, the other side being earthed via the field windings. Hence the bulb lights showing no charge. Once the alternator self excites and starts charging the battery, the bulb has 12 volts on both sides. It goes out indicating that 
the battery is being charged. 

My note... Bulb filaments do age, which could raise the charging point (higher revs)... Same goes for 'HR' Tvr wiring looms !!
You could easily prove this by disconnecting the loom charge wire at the alternator, then temporarily wire in a flying lead that includes a new idiot warning light powered from a 12v supply. If that goes out at lower revs than the cars wiring & bulb, its pretty obviously where the issue lies.”



> On 2 May 2019, at 21:43, Graeme Clark <cg at skyflyer.co.uk> wrote:
> 
> Bob
> 
> Another thought - you mention a ‘voltage regulator’. these are normally integral to the alternator - do you actually mean a ‘smart charging’ unit like an Adverc or Stirling power?
> My own boat/emgine combination  does not have an alterantor  charge light as standard, but a large green one was fitted when an Adverc advanced charging regulator was fitted.
> If thats the case, standard wiring may not apply and you made need to seek advice from the maker of the advanced charging unit?
> 
> Graeme
> 
> 
>> On 2 May 2019, at 21:09, Graeme Clark <cg at skyflyer.co.uk> wrote:
>> 
>> Bob
>> 
>> I dont have the same engine but for what it’s worth, my manual says that the PINK wire in the engine pod, is the alternator field exciter.
>> It cahnges colour on it’s journey from the pod to the alternator, and i think its  pink not purple but nevertheless may be a clue?
>> Its a pretty thjick wire and in the engine instrument pod connects to the irnition switch. So when you turn the key, the poeer flows to the alternator exciter coil.
>> This might exppain why it works on the bench because the engineer will be putting correct field voltage to the correct terminal.
>> Hope this helps
>> 
>> graeme 
>> 1996, #366
>> 
>> 
>> 
>>> On 2 May 2019, at 01:44, Bob Hoyt <rehoyt at gmail.com> wrote:
>>> 
>>> I posted this problem two years ago without resolution and since then
>>> nobody seems to have the answer. I have a 1994 320 with a Perkins M30
>>> engine and Lucas Marine alternator 55 Amp.
>>> 
>>> When I start the engine there is no output from the tach or voltmeter
>>> unless I "goose" the engine up several times (after a minute or two of
>>> running) then that wakes up the alternator and it reliably puts out 14.2
>>> volts. The idling speed is 1050 rpm and the green charge light stays on
>>> until the alternator kicks in. The voltmeter usually reads 12 volts. I have
>>> four new golf batteries and they are topped off with a solar panel and MPPT
>>> controller.
>>> 
>>> This week I took the alternator off and took it to a marine alternator
>>> specialist who claimed everything tested normal on his testing workbench.
>>> He wanted me to be sure that the small brown wire that is the "exciter"
>>> registered at least 2 volts and it registered 12.9. I confirmed that this
>>> wire goes to the charge light in the engine panel and that is exactly where
>>> it is supposed to go according to the schematics. I can find no other
>>> problems and none of the marine electricians have a clue. There is a
>>> disconnected pink wire that leaves the engine panel and runs down as far as
>>> the voltage regulator of ? significance. It does appear that over time that
>>> I have to rev the engine at even higher rpms several times for the
>>> alternator to work. I would appreciate any thoughts.
>>> 
>>> Bob Hoyt
>>> Hull #58 Ikigai
>>> Pensacola, FL
>>> 
>>> -- 
>>> 
>>> *Robert (Bob) Hoyt MD FACP*
>>> 
>>> *CAPT (Ret) USN*
>>> 
>>> *Associate Clinical Professor, Department of Internal Medicine*
>>> 
>>> *Virginia Commonwealth University*
>>> 
>>> *Richmond, VA*
>>> 
>>> *---------------------------------------------------------------------------------------------*
>>> 
>>> *Adjunct Associate Professor, College of Allied Health Professions*
>>> 
>>> *University of Nebraska Medical Center*
>>> 
>>> *Omaha, NE*
>>> 
>>> *Diplomate, Clinical Informatics*
>>> 
>>> InformaticsEducation.org  <http://InformaticsEducation.org>
>>> rehoyt at gmail.com
>>> 
>>> robert.hoyt at unmc.edu <robert.hoyt at unmd.edu>
>>> 
>>> robert.hoyt at vcuhealth.org
>>> 
>>> Cell: 850-384-5235
>> 
>