Random Alternator Voltage Surging to over 16V

[jonrarit]

Ok here's the set up.

2 Year old Alternator connected through a Sterling Alternator-battery charger unit to the batteries.

9 times out of 10 fire up engine, voltage comes up to 12.9v then sixty seconds later engine revs drop as the A2B kicks in. Voltage rises to 14.4v until charged then drops to 13.9v float after 30 mins or so.

However 1 in 10 fire up engine, voltage comes up to 12.9v, A2B kicks in and after 10 mins or so the voltage starts fluctuating 14v 15V 16V ... at this point the A2B has an overvoltage alarm and disconnects the load on the alternator, voltage returns to 12.9v ....then cycle repeats continuously.

Only cure is turn off engine (which turns off the A2B too) Restart and all is fine........

The voltage sense wire (yellow) that comes out the alternator is connected to the B+ as per the Sterling instructions so as not to cause "conflicting regulation between the A2B and the alternator regulator"

As this is intermittent (only 1 in 10) and it's only started doing it this season my thoughts are with the alternator regulator but I'm open to suggestions please as over 16v in the system cannot be good

Jonathan

 

[pvb]

As this is intermittent (only 1 in 10) and it's only started doing it this season my thoughts are with the alternator regulator but I'm open to suggestions please as over 16v in the system cannot be good

Have you double-checked the connection of the alternator sense wire on B+?

 

[jonrarit]

Have you double-checked the connection of the alternator sense wire on B+?

Yup all looks good but will pull it apart and check again. I guess you are thinking of a possible bad connection to the alternator's regulator?

jonathan

 

[pvb]

Yup all looks good but will pull it apart and check again. I guess you are thinking of a possible bad connection to the alternator's regulator?

Yes, if the battery sense can't "see" the voltage, the regulator can keep increasing the voltage.

 

[dom]

Agree with pvb; another wildcard question, has the sense wire definitely been connected to the same battery as the A2B?

 

[pvb]

Agree with pvb; another wildcard question, has the sense wire definitely been connected to the same battery as the A2B?

The OP said the sense wire is connected to alternator B+.

 

[VicS]

I agree with the above suggestions to check the sense wire connection(s).

Beyond checking all other connections diagnosis will be difficult due to the intermittent fault.
Monitoring the alternator output volts might be worthwhile.

I think I would like to remove the A2B charger and restore what ever system was in place before it was fitted. ( Diode splitter and battery sensing ???) This would eliminate the A2B from the equation and if the fault persists point to an alternator regulator defect.

If OTOH the fault disappears the A2B is the likely culprit.

 

[pvb]

I think I would like to remove the A2B charger and restore what ever system was in place before it was fitted. ( Diode splitter and battery sensing ???) This would eliminate the A2B from the equation and if the fault persists point to an alternator regulator defect.

If OTOH the fault disappears the A2B is the likely culprit.

I think this could easily be achieved by simply disconnecting the negative feed to the A-to-B charger; it will then effectively function as a diode splitter (albeit without a diode in the starter battery circuit).

 

[dom]

The OP said the sense wire is connected to alternator B+.

Oops you're right, and apparently in line with Sterling's instructions! That seems truly odd to me, but I'm no expert. Typical yottie engine installations all too often seem to have 'undersized' wires departing the B+, then into the loom from whence they wend their way to a main +ve switch, and the ground via some other route to the -ve switch. By undersized I mean cables that could lead to a c.3% voltage drop, i.e. around 0.4V on a 12V system

Sensed at the B+, will the A2B not prematurely limit the voltage of a modern internally-regulated 14.5V alternator to its basic 14.5V because it is sensing the voltage before the downstream 0.4-0.5V drop occurs? And what about any voltage drop on the negative side? Much less current is going to flow at say 13.9V than at 14.5V. Then there is the problem of the A2B prematurely dropping into float mode, not that this will make much difference.

Would it not generally make more sense to just piggy back some decent cable of say 10mm^2 from the alternator's B+ and -ve (depending on unit) to the main switch(es) and just get that 14.5V to the battery?

And if going the upgraded alternator route, would it not make sense to go the whole hog and install some proper +ve and -ve sensing at the relevant battery as opposed to the alternator ...or if one has an old 14.2V alternator to just buy a new one?

Basically I don't get the point of an A2B wired like that, but apols for drift and happy to be corrected on any/all misconceptions.

 

[pvb]

Sensed at the B+, will the A2B not prematurely limit the voltage of a modern internally-regulated 14.5V alternator to its basic 14.5V because it is sensing the voltage before the downstream 0.4-0.5V drop occurs? And what about any voltage drop on the negative side? Much less current is going to flow at say 13.9V than at 14.5V. Then there is the problem of the A2B prematurely dropping into float mode, not that this will make any difference.

The A-to-B charger basically places a load on the alternator and uses voltage amplification to achieve whatever charge voltage is required (according to battery type, charge cycle, etc). It senses the voltage through the output wire, but there's provision to put a remote sense lead on to the A-to-B if it's suspected that there's a significant voltage drop in the output wire to the batteries. It's a cunning system, and there wouldn't seem to be a lot of point in fitting one and then bypassing it as you've suggested.

 

[dom]

The A-to-B charger basically places a load on the alternator and uses voltage amplification to achieve whatever charge voltage is required (according to battery type, charge cycle, etc). It senses the voltage through the output wire, but there's provision to put a remote sense lead on to the A-to-B if it's suspected that there's a significant voltage drop in the output wire to the batteries. It's a cunning system, and there wouldn't seem to be a lot of point in fitting one and then bypassing it as you've suggested.

Oh thanks, I think I've got it now. Incidentally I was more thinking of a bypass in order to get the alternator's output voltage to the batteries, as opposed to overriding an A2B.

So for a normal sla battery which requires a 14.5V boost (assuming a normal 14.5V internally regulated alternator), the A2B's main use when in battery sensed mode is to back-down to a float at some point and also to perhaps whack up the voltage to compensate for any voltage losses in wiring, diodes or whatever? Also for open lead acid and certain AGM & lead batteries, being wired in series the A2B can push-up/pull-down voltage as required, as well as backing-off an alternator if its internal temperature compensator is not that great. Fair enough, very clever. Thanks again.

 

[pvb]

Oh thanks, I think I've got it now. Incidentally I was more thinking of a bypass in order to get the alternator's output voltage to the batteries, as opposed to overriding an A2B.

So for a normal sla battery which requires a 14.5V boost (assuming a normal 14.5V internally regulated alternator), the A2B's main use when in battery sensed mode is to back-down to a float at some point and also to perhaps whack up the voltage to compensate for any voltage losses in wiring, diodes or whatever? Also for open lead acid and certain AGM & lead batteries, being wired in series the A2B can push-up/pull-down voltage as required, as well as backing-off an alternator if its internal temperature compensator is not that great. Fair enough, very clever. Thanks again.

Perhaps the 2 main advantages of the A-to-B charger are 1) that it doesn't require any mods to the alternator (which ordinary alternator boosters do) and 2) it has the ability to drop to a float voltage (which ordinary alternator boosters don't).

 

[Seamechanic]

Hi,

the measured (too high) voltage is the A2B's outputvoltage (i assume as it's OV alarm goes off). What about the voltage at alternator B+ / A2B input at that time ?
If it's high too and the yellow (sense) wire is properly connected it's probably the regulator itself. If the voltage is in range and the wiring (see above posts) is ok it's more on the Sterling's side...

Frank

PS. Wiring between alternator and A2B, plus and minus, is critical as one of the A2B benefits is it's squeezing the final drops (of power) out of the alternator ! If the A2Bs output is loaded enough (with charging batteries and running the boards systems) the alternator is running with maximum amperes at it's nominal voltage, a state it usually has not very often! The original wiring might be insufficient for that!
As the A2B doesn't "know" the maximum power of the alternator ( nor the momentary power depending on the engines rpm ) it drains the alternator always until it's voltage drops a little from it's maximum (unloaded) voltage.

 

[pvb]

the measured (too high) voltage is the A2B's outputvoltage (i assume as it's OV alarm goes off). What about the voltage at alternator B+ / A2B input at that time ?

The earlier generation A-to-B charger only has one high voltage alarm, and it indicates a too high input voltage, and disconnects the charger.

The current generation Pro Alt C has two high voltage warnings, one for the input voltage, one for the output voltage, If the OP has one of these newer units, he can presumably advise which alarm he's seen.

 

[jonrarit]

Many thanks to all that have taken the time to reply. I will of course check all connections but as the wiring was all new when the unit was installed I think it's unlikely to be the cause.

On checking the manual it states there are two "high voltage" warnings. Solid LED means high voltage into the unit from the alternator most likely alternator regulator failure or Flashing LED means high voltage out from the unit whereupon it will shut down and "not come on again until reset, ie engine switched off and on again" ....now that sounds familiar however I cannot remember if it was flashing or not.

So this weekend will be

1 - checking all the wiring,
2 - Determining if the voltage alarm was for input or output (I suspect the latter)
3 - Monitoring Alternator B+ voltage

Will report back next week

Jonathan

 

[pvb]

Many thanks to all that have taken the time to reply. I will of course check all connections but as the wiring was all new when the unit was installed I think it's unlikely to be the cause.

On checking the manual it states there are two "high voltage" warnings. Solid LED means high voltage into the unit from the alternator most likely alternator regulator failure or Flashing LED means high voltage out from the unit whereupon it will shut down and "not come on again until reset, ie engine switched off and on again" ....now that sounds familiar however I cannot remember if it was flashing or not.

So this weekend will be

1 - checking all the wiring,
2 - Determining if the voltage alarm was for input or output (I suspect the latter)
3 - Monitoring Alternator B+ voltage

Will report back next week

There are different types of flashing LED warnings, which indicate different faults, so it would be worth checking carefully.

Just a thought, do you have a solar panel connected to the batteries? In some circumstances, this could trigger a high output voltage alarm on the Sterling.

 

[jonrarit]

No solar panels or any other charging devices