Question about battery charging

[Irish Rover]

My boat has 4 x 90ah + 2 x 74ah house batteries and 2 x 74ah starter batteries. All the batteries were fitted new in July. It has 2 solar panels and, given my location in Turkey, they get plenty of sunshine almost all the time and even in winter I use the boat on average 4 times per week. I only took possession of the boat in April so I'm still feeling my way a bit. Up to now I've almost never used shore power and the solar and regular running of the engines have kept the batteries fully charged. Last weekend the forecast was for 4/5 days of cloudy weather and rain and, as I was going away for a few days, I decided to connect the shore power just in case. The fridge was left on at a low setting and apart from 2 bilge pumps on standby everything else was switched off. I'm wondering if the solar panels become redundant when the 220V battery charger is operational, if it's OK to have the 2 systems running together and if there's any way to arrange for the shore powered battery charger to operate only if the solar is not producing enough power to do the job.

 

[RichardS]

It should be fine to have both shorepower and solar connected at the same time, assuming that both systems are installed in the normal way.

I've never heard of an off-the-shelf system which detects a low battery voltage on solar alone and then turns on the shorecharger as required but it would be possible to build a bespoke circuit although it might be easier to just fit more panels if required.

Richard

 

[macd]

I've never heard of an off-the-shelf system which detects a low battery voltage on solar alone and then turns on the shorecharger as required but it would be possible to build a bespoke circuit although it might be easier to just fit more panels if required.

Richard: the charger won't, of course, 'know' the solar system is present. But surely it will respond to any drop in battery voltage and shove more in? Precisely how the panels contribute in this partnership will, I suppose, depend on the characteristics and settings of the solar regulator (and charger regime).

From observation, that's what seems to happen. We used to spend winters with the solar connected and the charger just chiming in when it felt the need: reduced the leccy bills. How many people isolate their panels when the shore power charger is connected?

But I may be wrong

 

[lw395]

My boat has 4 x 90ah + 2 x 74ah house batteries and 2 x 74ah starter batteries. All the batteries were fitted new in July. It has 2 solar panels and, given my location in Turkey, they get plenty of sunshine almost all the time and even in winter I use the boat on average 4 times per week. I only took possession of the boat in April so I'm still feeling my way a bit. Up to now I've almost never used shore power and the solar and regular running of the engines have kept the batteries fully charged. Last weekend the forecast was for 4/5 days of cloudy weather and rain and, as I was going away for a few days, I decided to connect the shore power just in case. The fridge was left on at a low setting and apart from 2 bilge pumps on standby everything else was switched off. I'm wondering if the solar panels become redundant when the 220V battery charger is operational, if it's OK to have the 2 systems running together and if there's any way to arrange for the shore powered battery charger to operate only if the solar is not producing enough power to do the job.

Depending on the solar controllers and shore power chargers you have, there may be a possibility of overcharging when you are not using the boat. Not likely to be a real issue if you are checking the boat regularly. What batteries do you have? If they were wet cell, I'd be checking the levels now and then.

 

[RichardS]

Richard: the charger won't, of course, 'know' the solar system is present. But surely it will respond to any drop in battery voltage and shove more in? Precisely how the panels contribute in this partnership will, I suppose, depend on the characteristics and settings of the solar regulator (and charger regime).

From observation, that's what seems to happen. We used to spend winters with the solar connected and the charger just chiming in when it felt the need: reduced the leccy bills. How many people isolate their panels when the shore power charger is connected?

But I may be wrong

Indeed so. As I said, leaving the shorepower charger permanently on, as the OP is doing at the moment, will not cause a problem.

However, I'm assuming that the OP is wondering about a system where the shorepower charger is disconnected from the mains supply unless it is required, which would need a relay circuit which determines the battery voltage and switches on the charger only when necessary, presumably to provide improved protection against fire risk and save on leccy costs.

Richard

 

[LadyInBed]

As I see it, charger will see solar voltage, so if solar voltage is up and batteries are down charger will not supply high current as it thinks batteries are up.
Chargers work best with solar over night when solar voltage is down.

 

[lw395]

...
However, I'm assuming that the OP is wondering about a system where the shorepower charger is disconnected from the mains supply unless it is required, which would need a relay circuit which determines the battery voltage and switches on the charger only when necessary, presumably to provide improved protection against fire risk and save on leccy costs.

Richard

Wouldn't that just be much the same as a shore power charger which stayed in float mode until it sensed the batteries were dragged down by a load (the fridge)?
The shorepower charger will probably do this, particularly if its float voltage is a bit lower than that of the solar.

 

[RichardS]

Wouldn't that just be much the same as a shore power charger which stayed in float mode until it sensed the batteries were dragged down by a load (the fridge)?
The shorepower charger will probably do this, particularly if its float voltage is a bit lower than that of the solar.

I guess that it depends upon one's definition of "same".

I would view a charger which is isolated from the mains supply unless and until it is actually required to supplement the solar panels as significantly different to a charger which is permanently live. I can see the safety/potential cost-saving benefits of such an approach although before making an informed comparison I would need to understand how much is being spent on electricity and how much the switching circuit would cost to build and how intrinsically safe that circuit is.

Richard

 

[PaulRainbow]

I have A Victron MPPT controller and a Sterling 30a mains charger. If the mains charger is left on there is almost no output from the solar panels. The solar controller shuts down when it senses the mains charger output, but even if it didn't, i still wouldn't get much from the panels as the batteries would be fully charged anyway, as the charger was on all night.

During the Summer, i leave the mains charger off and the solar panels keep up with demand. During Spring and Autumn they keep up some of the time, i also have a Victron battery monitor that features a small internal relay that can be configured to open/close under certain conditions, such as SoC or low voltage. I have this relay connected to a 12v/240v relay that is normally open and switches the mains charger on in the event of a low battery voltage. In the Winter i find the mains charger would need to come on more often, meaning more cycling of the batteries, so i leave the mains charger on during Winter months.

It would also be possible to switch the mains charger on automatically by sensing the panel voltage. The logical way to go this route would be to use the streetlight function of the controller to operate the 12v/240v relay. This would turn the mains charger on all night, which would mean the batteries would be charged by morning, only leaving the solar panels to maintain the batteries and hopefully keep up with daytime loads.

I suppose i could fit an On-Off-On switch to the 12v relay coil, marked Spring-Summer-Winter. Spring would use the battery monitor to occasionally switch the mains charger on, as and when low battery voltage dictates, Summer turns the relay off and we rely on the solar panels, with a low voltage alarm from the battery monitor, just in case. Winter uses the streetlight function of the controller to ensure the batteries get fully charged overnight, then use the solar controller to supply as much of the daytime load as possible, safe in the knowledge that the battery bank can cope with any shortfall in solar yield and the mains charger will fully charge the batteries over night.

As always, this arrangement might not suit everyone, it obviously relies on the availability of shore power, for one thing.

 

[Graham376]

Every winter we haul into a yard for 4 - 6 weeks. Solar left connected (Victron SmartSolar regulator) and I run the battery charger as well, no problems with overcharging.