Beta 20 alternator charging voltage

[MattS]

I ran the engine for half hour today as the boat is sitting unused over the winter, and I noticed that my NASA battery monitor (BM-1) was reading 15V whilst it was running.

Is this a normal charging voltage for an alternator? I don’t remember it being that high before, but maybe I just haven’t noticed it?

 

[Poecheng]

No, that is high IMHO.
I have the 65A Iskra alternator and it is normally 14 point something (<14.5).15 sounds too high even if the batteries were discharged and it is too high, I expect, for your batteries.
The NASA BM1 may need calibrating on the voltage (I have never had to) and so it is worth getting a voltmeter across the batteries to see what is actually happening.

 

[MattS]

Thanks - if it sounds too high I’ll get a voltmeter on it tomorrow and see what’s going on.

 

[BabaYaga]

If your charging system has some kind of temperature compensation (external regulator perhaps), the charging voltage may well be 0.5 V higher than normal if the ambient temperature is around 0 degrees C.

 

[MattS]

It’s just a standard factory fit Beta 20 alternator as far as I’m aware, but it was reasonably cold.

 

[Alex_Blackwood]

It’s just a standard factory fit Beta 20 alternator as far as I’m aware, but it was reasonably cold.

I wouldn't worry about it. Check with a Multimeter if you want. I would just keep an eye on it over a period of time.

 

[Ammonite]

14.4v was the max I would see on my Beta 20 if charging only using the alternator and 15v is too high if the monitor is wired / working correctly, assuming #4 doesn't apply. The alternator itself can output more than this if, for example, you have a splitter and a battery sense wire to account for any loses but this is to ensure the correct voltage at the battery. Do you by any chance have a solar panel fitted because the temperature compensation in the regulator will give you a higher voltage on a cold day?

 

[TNLI]

I ran the engine for half hour today as the boat is sitting unused over the winter, and I noticed that my NASA battery monitor (BM-1) was reading 15V whilst it was running.

Is this a normal charging voltage for an alternator? I don’t remember it being that high before, but maybe I just haven’t noticed it?

Did you have any type of solar panel and regulator connected ??
Some of the cheaper regulators do hit 15 volts if the battery is fully charged when the engine is running with a 14.5v alternator. Good idea to fit an off switch to the feed wire if it is one. A solar panel on its own will produce around 20 to 25 volts according to exact type, but the wiring, swiches and connectors to the volt meter will result in a drop in voltage, so Ammonite posted 14.4 is probably the max.

It's a real good idea to fit a voltmeter where it can be seen inside the main cabin that is wired to the battery selector output, not the actual batteries.

 

[PaulRainbow]

I ran the engine for half hour today as the boat is sitting unused over the winter, and I noticed that my NASA battery monitor (BM-1) was reading 15V whilst it was running.

Is this a normal charging voltage for an alternator? I don’t remember it being that high before, but maybe I just haven’t noticed it?

As said, double check with a voltmeter. Check the output at the alternator and the battery. If it's 15v it is too high and your batteries will have a very short life.

 

[PaulRainbow]

I wouldn't worry about it. Check with a Multimeter if you want. I would just keep an eye on it over a period of time.

15v charging voltage will seriously shorten the life of a 12v battery. If it really is 15v it needs sorting, yesterday.

 

[graham]

What do you do to check? Is it as simple as putting the multimeter probes on the battery terminals while it is charging from the alternator?

 

[Poecheng]

What do you do to check? Is it as simple as putting the multimeter probes on the battery terminals while it is charging from the alternator?

Yes.
Ideally, and so as to get a better idea of what is going on
a) test at battery terminals before you start the engine and see what the resting voltage is
b) With engine started, test at the batteries as you have described - the battery terminals (nothing else)
c) If it is safe to do so, test the output voltage at the alternator: between Ground and +v terminal [likely where the larger, red lead will be coming from]. Have a look at the set up before you start the engine then you know what you are doing when it is in less safe conditions.

 

[Alex_Blackwood]

15v charging voltage will seriously shorten the life of a 12v battery. If it really is 15v it needs sorting, yesterday.

Quite agree Paul. However as I read it, and assuming he has only an alternator charging his batteries, via whatever. I think that he has noted a high reading on a cold day with low battery charge. Which is why I said monitor it for a bit. I suppose that on reflection I could have been a bit more descriptive, shouldn't use "Being in a hurry" as an excuse! I suppose that in the worst case he may have lost voltage sensing. I believe BETA set up for battery sensing from which ever battery is on engine start duty? I haven't got the drawing handy at the moment.

 

[MattS]

I ran the engine again (equally cold day within a couple of degrees) and the battery monitor didn’t show over 14.5V charging voltage. Multimeter across battery terminals confirmed 14.45V, so as of yet I haven’t been able to repeat the previous 15V reading!

No other charging source active (solar doing very little in this weather, and I would have thought the Victron MPPT charger would know not to raise the voltage up to 15V if it’s already at 14.5….).

Will keep watching to see if it happens again!

 

[MattS]

15v charging voltage will seriously shorten the life of a 12v battery. If it really is 15v it needs sorting, yesterday.

Yep - the boat came with a cheap PVM solar charger which defaulted to keeping the batteries at 15V, and it killed a 1 year old battery.

 

[Ammonite]

I ran the engine again (equally cold day within a couple of degrees) and the battery monitor didn’t show over 14.5V charging voltage. Multimeter across battery terminals confirmed 14.45V, so as of yet I haven’t been able to repeat the previous 15V reading!

No other charging source active (solar doing very little in this weather, and I would have thought the Victron MPPT charger would know not to raise the voltage up to 15V if it’s already at 14.5….).

Will keep watching to see if it happens again!

Solar works very well on cold sunny days which we had last week and there is a temperature compensation algorithm in most controllers that adds something like 0.06v per degree below 25 degrees celsius so at 5 degrees it will add 1.2v to the set voltage.

 

[PaulRainbow]

Solar works very well on cold sunny days which we had last week and there is a temperature compensation algorithm in most controllers that adds something like 0.06v per degree below 25 degrees celsius so at 5 degrees it will add 1.2v to the set voltage.

Those figures are high. Victron controllers (for example) will add 0.005VPC/°C so for a 12V battery that's 0.03V/C That's 0.6V @ 5 degrees

 

[Ammonite]

Thanks for the correction Paul, I inadvertently referenced a 24v battery, the point being that the temperature compensation can easily give you 15v and that the controllers are designed to do this unless you alter the profile.

I'm assuming that out of the box the controller is charging at 14.4v during the bulk phase

 

[MattS]

Thanks - didn’t know they added to voltage in the cold. I will check the app next time I’m on board, and see what it’s been up to.

 

[billcole]

and I would have thought the Victron MPPT charger would know not to raise the voltage up to 15V if it’s already at 14.5….).

Victron things can be quite clever, and I believe some of them do an occasional equalising charge where they do briefly charge at higher than normal voltage, I think it may be set to default at every 3 months (and that interval is changeable via their app if you can link your phone to the controller via bluetooth ).

If the controller hasn't had a chance to do the scheduled equalising charge because of lack of much solar power during winter then maybe it seized its chance when you ran the alternator ?