P38A What can kill a battery?

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Grrrrrr said:
13.8V is the old alternator set point. Not enough for a calcium battery. You can replace the alternator regulator to give 14.3 or even 14.5V but it will only have the same power so takes longer to charge a big 1k CCA battery. Replacing the regulator is about £20 and will need to be done anyway. After that you're looking at parasitic drain or RF interference.
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Sorry that is just not true, the higher voltage will increase the current flow into the battery and so charge it more quickly. The charge current will never be at the alternator output current maximum for long or with 150 amps available, it would overheat and potentially explode.
The Mobiltron regulator will allow up to 15 volts in some circumstances, normally 14.8 just after starting gradually dropping as the battery charges to 13.8 or even lower on a long run.
 
Datatek said:
Sorry that is just not true, the higher voltage will increase the current flow into the battery and so charge it more quickly. The charge current will never be at the alternator output current maximum for long or with 150 amps available, it would overheat and potentially explode.
The Mobiltron regulator will allow up to 15 volts in some circumstances, normally 14.8 just after starting gradually dropping as the battery charges to 13.8 or even lower on a long run.
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The max power is set by the number of turns on the coils. Only rewinding the alternator will change that. Volts go up, amps go down.
 
Grrrrrr said:
The max power is set by the number of turns on the coils. Only rewinding the alternator will change that. Volts go up, amps go down.
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It's got nothing to do with the turns on the coils, the higher the voltage across the battery, the greater the charge current which rarely reaches the alternator maximum output. V over R = I The P38 diesel alternator is a 150 amp unit I think, more than enough to cook a battery.
 
Datatek said:
It's got nothing to do with the turns on the coils, the higher the voltage across the battery, the greater the charge current which rarely reaches the alternator maximum output. V over R = I The P38 diesel alternator is a 150 amp unit I think, more than enough to cook a battery.
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The power cones from the number of coils - that's roughly what is causing R[esistance] in your formula, albeit with a bit of feedback so it varies on demand. Volts times amps is watts (power). If one goes up the other goes down but the power remains the same. The only way to change the power is to change the number of coils unless the thing isn't at its limit in which case that changes. The early ones, especially the models with lots of toys, clearly were near their limits because they put the bigger 150 amp alternators on later models. Short journeys probably caused some issues until they put bigger alternators on them.
 
Each phase in an alternator produces up to ~100v at however many amps the alternator is rated for.
Whether it's stepped down to 14.7 or 13.6v, surely the current output remains the same?
 
Grrrrrr said:
The power cones from the number of coils - that's roughly what is causing R[esistance] in your formula, albeit with a bit of feedback so it varies on demand. Volts times amps is watts (power). If one goes up the other goes down but the power remains the same. The only way to change the power is to change the number of coils unless the thing isn't at its limit in which case that changes. The early ones, especially the models with lots of toys, clearly were near their limits because they put the bigger 150 amp alternators on later models. Short journeys probably caused some issues until they put bigger alternators on them.
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You forgot the internal resistance of the battery which is where V over R comes in and also the PD between the alternator output and the battery voltage. the number of windings on the field oils and the gauge of the wire determines the maximum out put of the alternator but in practice has bugger all to do with the charging current going into the battery.
 
Datatek said:
You forgot the internal resistance of the battery which is where V over R comes in and also the PD between the alternator output and the battery voltage. the number of windings on the field oils and the gauge of the wire determines the maximum out put of the alternator but in practice has bugger all to do with the charging current going into the battery.
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No, I didn't. That's just another part of the overall system but it cannot affect the max output from the alternator. It will of course affect how much is drawn down from that max. What you're suggesting is that if you put a bigger load on an alternator it will always mysteriously come up with more power to service that load. It cannot adjust the load past its max output, hence why they realised they needed a bigger alternator and put it on later cars. Below that max output the alternator will adjust to the load put on it, one of the reasons they are preferred over a dynamo.
 
Grrrrrr said:
No, I didn't. That's just another part of the overall system but it cannot affect the max output from the alternator. It will of course affect how much is drawn down from that max. What you're suggesting is that if you put a bigger load on an alternator it will always mysteriously come up with more power to service that load. It cannot adjust the load past its max output, hence why they realised they needed a bigger alternator and put it on later cars. Below that max output the alternator will adjust to the load put on it, one of the reasons they are preferred over a dynamo.
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No I am not suggesting that the alternator will mysteriously come up with more power for a bigger load and that has nothing to do with the conversation about batteries. The regulator maintains the output voltage as the load increases by increasing the current in the armature coils and will continue to do so until the maximum output of the alternator is reached at which point the output voltage will start to drop. Where batteries are concerned, max alternator output is not really relevant as the current drawn will drop rapidly after starting. Dynamos are less efficient than an alternator but the output can be regulated.
 
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