Do as mentioned above for Battery condition and drain, also worth checking your alternator output voltage, when running should be arround 13.5 to 14.2, if its less than this then pull the Neg off the battery while running and measure alternator volts again. As where having hot weather now, check that the fans dont kick in and mess up the readings.
Chris.
I would never disconnect a battery with the engine running. This could land you in an awful lot more bother.
Kevin
Been doing this for years Kevin, whats the problem?
Just my views .. nowt else ..
The battery acts as a "smoothing circuit" and "shock absorber" to the alternator. If the alternator is running and you disconnect the battery, then there is nothing in the circuit to "absorb" or "smooth" voltage spikes.
The voltage regulator will react to try and control voltages, but it is always reactive, so is a fraction behind what is actualy happening.
Thus it is possible for fairly large transitional voltages to occur. Many of the circuits in ECU's are very voltage sensitive, being solid state devices, such voltage spikes can damage them readily.
Older cars, like what I started on ( morris minor sidevalve, through to ford crossflows and upwards),, had very few electric circuits, no solid state devices and often a dynamo with a carbon pile voltage regulator !! They didn't care about transient voltage spike at all.
The same can't be said for todays "sophisticated" electronics.. which are IMHO .. far too fragile at times .. given the environment in which they operate.
I would, also, never disconnect a battery with the alternator running.
Yep, nail on the head, basically. An alternator's output is regulated by altering the current in the field winding which alters the magnetic field strength in the alternator and thus the current induced in the stator windings which provide the output.
There will be a residual field with no field current which means under low load conditions the alternator output voltage is uncontrolled. In addition, a change to the field current doesn't result in an immediate change in output voltage (the field winding is inductive, so it is not possible to change the current instantaneously anyway). The magnetic field takes time to decay (actually the same mechanism by which the winding is inductive) and while it does so, the alternator is delivering more current than the electrical system is demanding, so the voltage rises.
If there is a sudden reduction in load from the alternator (e.g. cooling fan stopping) this means the voltage will spike to a high level for a few milliseconds before, hopefully, stabilising again. The voltage regulator in the alternator might even become unstable and oscillate between very high and low output voltages,
Normally the battery will damp down this tendency by absorbing the extra current and preventing a dangerous rise in voltage but without it present any devices being powered by the alternator will instead absorb the spike. This includes engine, ABS, Autobox, Air bag ecu, any In car entertainment equipment, etc.
This equipment is protected, so it may not fail the first time you do this, but each time a spike hits their electronics the protection components are stressed and may fail so the risk is there, and it can be avoided by testing the battery and alternator condition with a multimeter while they are both still connected to the vehicle.
Kevin
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Topic: Possible flat battery??? (Read 3498 times)