15.9v - Err, whassup?

[Tintin]

New alternator (Bosch 70a replacement for the old Valeo).

During an extended bit of motoring the other day I noticed the voltage was up to 15.9v (charge current approx 6 amp) - I popped the fridge on sharpish to get some load on and it dropped down to 14.3v.

The next day all was fine (after a night on the hook with lights on etc..) but after another hour or so motoring when the batteries were charged it went back up again.

Revs were 1700.

Dropping back to 1200 dropped the volts down to 14.3v

The battery bank is 660aH (huge I know, but I have kids with lots of leccy toys).

Should I be concerned ? (am thinking I should be)

I have an Adverc to fit and will do the regulator mod - will that keep it down?

 

[No Regrets]

Try a voltmeter just to be sure...

15.9 sounds a bit high tbh. Might just be an optimistic gauge?

 

[Tintin]

Try a voltmeter just to be sure...

15.9 sounds a bit high tbh. Might just be an optimistic gauge?

It wqas showing the same on my Victron Battery Monitor and on my Chartplotter, so am fairly certain it is correct.

 

[VicS]

I have an Adverc to fit and will do the regulator mod - will that keep it down?

It may not if the Adverc operates in tandem with the existing regulator like the Sterling regulators do.

Check the specs, installation and operating instructions for the Adverc carefully.

I think you will have to sort out what ever is causing the problem first. I may be a dodgy regulator, or a bad sensing connection if its battery sensed

 

[cinnabar]

Hi Red,

I am not sure if this will help but we had a similar sudden overcharging event some years ago when we were offshore and needed to use the engine.

Our system of an Adverc running in parallel with a traditional external regulator has worked very well for more than ten years. The event occurred when a problem developed in the back-up regulator causing both it and the Adverc to shut down. We cured the problem by disconnecting the regulator and allowing the Adverc to run solo: We later replaced the regulator and returned to the old system.

 

[JumbleDuck]

I have an Adverc to fit and will do the regulator mod - will that keep it down?

No. An Adverc can only ever increase the alternator output above what the internal regulator is trying to do; it will not and can not reduce it. sounds to me as if your new alternator may have a stuffed regulator. An auto electrician should be able to test it.

 

[Tintin]

Jumble & Cinnabar - thanks for confirming my understanding of how the adverc works - Grrr, "will someone rid me of these meddlesome charging problems", to *******ise an old saying.

 

[Tintin]

Latest update, before taking the alternator off the boat I gave the suppliers a call (Electro-Diesel, who have several branches in Cornwall and are Bosch "specialists").

The expert said that 15.9v is OK if the charge current is low.

he suggested bringing it into them to bench test, but I pointed out the problem only occurs after several hours running with full batteries - his response was to bring it in but if they can't see the problem there is not a lot they can do.

Is 15.9v OK ? My understanding is that it causes battery problems and problems with the stuff plugged in.

 

[Plevier]

15.9V is definitely not OK for the battery if sustained, or for some older electronics which might self destruct much quicker than the battery.
The alternator's regulator is probably set at 14.2V or possibly 14.4V, certainly not more, you should never see 15.9V!

 

[charles_reed]

It may not if the Adverc operates in tandem with the existing regulator like the Sterling regulators do.

Check the specs, installation and operating instructions for the Adverc carefully.

I think you will have to sort out what ever is causing the problem first. I may be a dodgy regulator, or a bad sensing connection if its battery sensed

From bitter experience with the Adverc - it's most probably a faulty cell in one battery (probably the sensor battery, usually #1). The Adverc bypasses the on-board controller.
Left too long it will, literally, melt the alternator.

 

[charles_reed]

15.9V is definitely not OK for the battery if sustained, or for some older electronics which might self destruct much quicker than the battery.
The alternator's regulator is probably set at 14.2V or possibly 14.4V, certainly not more, you should never see 15.9V!

He is, apparently using an external controller, which is sensing one battery not accepting a charge. Feeding into fit batteries the Adverc will start at about 15.1 and soon go down to 14.4 14.5.

 

[charles_reed]

Latest update, before taking the alternator off the boat I gave the suppliers a call (Electro-Diesel, who have several branches in Cornwall and are Bosch "specialists").

The expert said that 15.9v is OK if the charge current is low.

he suggested bringing it into them to bench test, but I pointed out the problem only occurs after several hours running with full batteries - his response was to bring it in but if they can't see the problem there is not a lot they can do.

Is 15.9v OK ? My understanding is that it causes battery problems and problems with the stuff plugged in.

Not a problem with your alternator - it most probably lies in your battery bank - just one duff cell!!!

 

[Tintin]

He is, apparently using an external controller, which is sensing one battery not accepting a charge. Feeding into fit batteries the Adverc will start at about 15.1 and soon go down to 14.4 14.5.

No I am not yet. The adverc is fitted / located, but nothing actually connected as I have not done the alternator mod yet (thankfully).

The voltage from the alt is fine until the batteries are close to fully charged and the charge current has dropped below (for example) 6 - 9amps - it is a large bank of 6 x 110ah.

So no battery is being sensed.

Do you still reckon it is a battery problem?

 

[halcyon]

No I am not yet. The adverc is fitted / located, but nothing actually connected as I have not done the alternator mod yet (thankfully).

The voltage from the alt is fine until the batteries are close to fully charged and the charge current has dropped below (for example) 6 - 9amps - it is a large bank of 6 x 110ah.

So no battery is being sensed.

Do you still reckon it is a battery problem?

Suspect it's the way controller regulates and battery bank size, try disconnecting 4 batteries and try charging just 2, see if that corrects the problem ?


Brian

 

[Tintin]

Suspect it's the way controller regulates and battery bank size, try disconnecting 4 batteries and try charging just 2, see if that corrects the problem ?


Brian

Thanks Brian. I can try that with 3 at a time as it is set up as 2 banks of 3 x 110ah due to battery / locker space.

 

[Plevier]

Suspect it's the way controller regulates and battery bank size, try disconnecting 4 batteries and try charging just 2, see if that corrects the problem ?


Brian

Can you explain that please Brian? I can't follow the logic. I would have thought if the alternator regulator was going to go to a rogue high voltage, it would be when current is negligible, and so less likely to happen with lots of battery capacity?

 

[halcyon]

Can you explain that please Brian? I can't follow the logic. I would have thought if the alternator regulator was going to go to a rogue high voltage, it would be when current is negligible, and so less likely to happen with lots of battery capacity?

It is possible that the regulator has slugging so it runs on for a minimum time, may be a couple of seconds to stop a high frequency noise. The battery voltage rises rapidly above 14.6 / 14.8 volt above 15.3 / 15.4 volt it is almost vertical, so for little amps going in voltage goes very high, thus with the short time on voltage grows. Adding the fridge load drops capacity / voltage and runs the system okay, i.e. 14.3 volt.

Reducing battery size may cause the regulator to get into it's operation mode.

At the moment it's a gut feeling that is hard to explain.

Brian

 

[Plevier]

Not sure about the "nearly vertical" especially with a battery that's not fully charged. Well it'll be interesting to hear the results of the experiment.

It's a 70A nominal alternator and 660Ah of battery so around 10% max current, reasonable. If the batteries are in good condition they will take that charge current for a while holding the voltage down.
OP sees the voltage rise when the battery current is around 1%. It doesn't take a huge voltage to get 1% current in batteries that are not fully charged.

My money stays on a defective or disconnected regulator (provided that the Adverc is not connected and battery sensing is not connected, i.e. the alternator is being used in bog standard form, as stated by the OP). Alternatively perhaps the diodes supplying D+ (not the main output diodes).

Just one other thought, is the pulley size right, the alternator isn't running insanely fast is it?

 

[halcyon]

OP sees the voltage rise when the battery current is around 1%. It doesn't take a huge voltage to get 1% current in batteries that are not fully charged.

Depends on battery level, but after 90% the voltage to charge the battery rises rapidly to around 16 volt, it's not a bucket that you pour amps into. The output voltage of the alternator regulating at 14.4 volt on your multimeter, on a scope has peak voltage of 16 volts or more with a fully charged battery.

Turning on the fridge drops voltage to normal, so not a lot of load sorts the problem, so first job is find the problem, in this case does the large battery bank size have a effect on output voltage, halving it, does it alter voltage?

Brian

 

[VicMallows]

This is looking more like a measurement issue to me. OP, do you have an old-fashioned analogue meter you could try? (of course a 'scope would be ideal).