Voltage sensing electronics.

[Allan]

During our recent long trip the Sterling battery charger failed and we had some battery problems. I'm sure I'll be asking advice about rectifying these problems in the future. In the meantime I have a more general question.
The Sterling charger and the Victron both sense the battery voltage but they must be confused by each other? The same thing must apply to the voltage when the engine is running. Is there anything I can do to stop this happening?
Allan

 

[William_H]

You don't say what the "Victron" is. Possibly a solar panel controller or engine alternator charge controller.
With all of these devices the charger and the controller are there to cut back charge when the voltage rises. This to avert overcharging the battery. So the alternator regulator will cut back field current to the alternator to reduce power out of the alternator. Like wise a battery charger or solar controller will limit power when voltage rises enough.
Note here I use the word power. In fact voltage is reduced so reducing current quite dramatically so reducing overcharge.
Now the voltage of the battery is the aspect that is sensed to determine if and when the battery has had enough charge.
If you then have 2 charging sources both sensing the same voltage. (battery terminals) then they will both cut back charge depending on the actual chosen charge (cut back) voltage point. In practice one will be set at a lower voltage than the other so will cut back sooner. Now all this is confused by the fact that with smart charging regime the chargers will be looking to charge at a high voltage at first to get bulk charge in followed when voltage rises enough to a lower maintenance or float charge rate/voltage.
The outcome is OK the battery does not get overcharged but is charged to good voltage as quickly as possible and while one charge source might cut back earlier than another it does not matter. good luck olewill

 

[PaulRainbow]

During our recent long trip the Sterling battery charger failed and we had some battery problems. I'm sure I'll be asking advice about rectifying these problems in the future. In the meantime I have a more general question.
The Sterling charger and the Victron both sense the battery voltage but they must be confused by each other? The same thing must apply to the voltage when the engine is running. Is there anything I can do to stop this happening?
Allan

Need a bit more info on exactly what hardware you have fitted and how you are using it please.

 

[Allan]

The solar regulator is a Victron 75/15, the alternator is the standard Volvo unit that puts out 13.8ish volts and the battery charger, which has failed, is a sterling unit which has a bulk and absorption cycle like the Victron. My question was a more general one. With all theses units that both sense the voltage at the battery and produce charging voltages are they not confusing each other? For instance, the Victron can produce quite high voltage but may not be charging more than a few watts. If the sterling charger reads the high voltage it stops charging, as it thinks the battery is charged. We have also had times when the Victron display is showing high voltage which is obviously just surface voltage.
Allan

 

[GHA]

For instance, the Victron can produce quite high voltage but may not be charging more than a few watts.

That's not really to do with the solar but down to the battery, if it's up above about 80% state of charge and the charge source has a limit on how high the voltage can go then doesn't really matter if it's a solar panel or power station connected - the battery will just take what it wants. So can't see that it will make much difference what's connected, the battery will take what it wants.

If the sterling charger reads the high voltage it stops charging, as it thinks the battery is charged.

That's cos if the voltage is up 14. something and there's next to no amps going in the batteries are charged


Also, 13.8v is low if you want to get the batteries anywhere close to fully charged from the alternator - will take forever. Smart reg might well help a lot if you want to get more from the alternator.

 

[PaulRainbow]

The solar regulator is a Victron 75/15, the alternator is the standard Volvo unit that puts out 13.8ish volts and the battery charger, which has failed, is a sterling unit which has a bulk and absorption cycle like the Victron. My question was a more general one. With all theses units that both sense the voltage at the battery and produce charging voltages are they not confusing each other? For instance, the Victron can produce quite high voltage but may not be charging more than a few watts. If the sterling charger reads the high voltage it stops charging, as it thinks the battery is charged. We have also had times when the Victron display is showing high voltage which is obviously just surface voltage.
Allan

I have a similar setup, Victron 75/15 and Sterling ProCharge Ultra and alternator(obviously). Alternator is connected to the engine battery, solar to the domestic bank and the Sterling to both, also have a Victron dual sensing VSR. I have USB interfaces from the Victron controller and a Victron battery monitor, connected to a laptop.

I have done no monitoring of alternator charging to see how it interacts with the solar controller. I don't think it really matters because the power from the alternator and the solar panels are both free, will both be charging whatever and no matter what they won't overcharge the batteries.

I've spent quite a bit of time monitoring the batteries, the solar controller, mains charge and onboard equipment, i wanted to understand exactly what was doing what and what my equipment was using. By default the mains charger is off because my solar panels produce enough for my needs. I upgraded the solar panels in Feb and increased battery capacity from 220ah to 390ah recently, so i have some data from before i was able to use solar only. I do know that if the mains charger is turned on during the day that the solar controller will "see" the charger output and shut down. I could look at the controller output and watch the controller actually turn off if i put the mains charger on. A short time after turning the mains charger off again the controller restarted. What i did was to leave the mains charger off all day to get as much from the solar panels as possible, in the late evening i'd check the battery voltages and decide if they would discharge too much during the night, if i thought they would i'd put the mains charger on for a while. I generally avoided putting it on all night, as that would mean the batteries would be fully charged in the morning and there would be little for the solar controller to do, but every few nights i would leave it on to make sure the batteries got a full charge.

Now, the solar panels charge more than i use, in the past 30 days (history from the controller) they batteries have only fallen below 12.6v once (12/59v). I have not put the mains charger on since Feb, apart from a couple of days when i had to change my domestic batteries, so the mains charger stays off. The Victron battery monitor has a built in relay, this can be configured to open and close at user defined SOC or voltages. I have fitted a 240v relay with a 12v coil in my consumer unit that the battery monitor triggers and turns the mains charger on if the battery SOC gets low.

 

[BabaYaga]

The solar regulator is a Victron 75/15, the alternator is the standard Volvo unit that puts out 13.8ish volts and the battery charger, which has failed, is a sterling unit which has a bulk and absorption cycle like the Victron. My question was a more general one. With all theses units that both sense the voltage at the battery and produce charging voltages are they not confusing each other? For instance, the Victron can produce quite high voltage but may not be charging more than a few watts. If the sterling charger reads the high voltage it stops charging, as it thinks the battery is charged. We have also had times when the Victron display is showing high voltage which is obviously just surface voltage.
Allan

I think it is a misconception that a solar charge controller can "produce" a certain charging voltage. The charging voltage should rather be seen, in my view, as a result of pushing current into a load, the battery. Because the resistance of the battery gradually increases as the charging progresses, the voltage also gradually increases.
So if you read a set point voltage, say 14,4V, but only a few watts going into the batteries, it means they are nearly fully charged and will accept no current increase, whether from the solar panels or from other sources. (With similar solar conditions, but with batteries well discharged, you would have read a lower voltage and a higher power flow).
So in my view there is no "confusion". You are right however that an additional charging source that is just being switched on will not "know" the state of charge of the batteries when it reads 14,4V. It might be that the set point was reached a minute ago – or charging could have been going on at 14,4 for hours.

 

[Allan]

Many thanks for all the information. I've been giving it more thought. Often, just after charging, we see high voltage, so called "surface voltage". I believe this could be causing the Victron to turn off.
Allan

 

[PaulRainbow]

Many thanks for all the information. I've been giving it more thought. Often, just after charging, we see high voltage, so called "surface voltage". I believe this could be causing the Victron to turn off.
Allan

I never see high voltages, how high are we talking ? "Just after charging", by what means ?

More generally, what's your split charging and isolating switch arrangement Allan ?

 

[Allan]

We have 3 domestic batteries and one start. The split charging is done via a large diode for the alternator, the failed Sterling unit has two outputs and the Victron goes straight to the domestic bank. I use the Victron display for the voltages and have seen 14 volts.
Allan

 

[PaulRainbow]

We have 3 domestic batteries and one start. The split charging is done via a large diode for the alternator, the failed Sterling unit has two outputs and the Victron goes straight to the domestic bank. I use the Victron display for the voltages and have seen 14 volts.
Allan

Same battery arrangement as me.

So you have a Victron cable or bluetooth dongle ? I have cables from the controller and Victron battery monitor, very useful to see exactly what's going on. 14v is not high, as such, the controller and the Sterling will both charge at 14.4/14.6v before going to float and your alternator could well be doing the same. The Victron shuts down if it sees the Sterling, so it may well do the same if it sees the alternator, i'll watch for that next time i use the engine.

Question is though, does it matter is the controller goes off when the engine is running ? It clearly does matter if it shuts down when the mains charger is used, as you don't want to waste the free solar power. IMO, provided the alternator can at least match the solar yield and the controller restarts when the engine is stopped, it does not matter. It's worth considering a dual sensing VSR instead of the diode, that way both banks get charged by the alternator or solar and you don't get the voltage drop from the diode.