Can I simplify my battery charging?

[AndrewB]

My boat batteries are charged by one of three means: 1. Engine Alternator; 2. Mains Battery Charger; 3. Solar Panels via regulator. There is no fancy charging manager, just a switch for the mains battery charger and another for the solar panels.

In theory I'm careful to let only one of these to be charging at any one time. When the engine is running, the mains battery charger and solar panels are switched off. When the engine is off, either the mains battery charger or the solar panels (but not both) are turned on. In practice though I sometimes forget to turn anything on and the batteries have been flat.

I've used these switches for fear that the power from the engine alternator might damage the mains battery charger or the solar panels regulator if directly connected. Or that the battery charger might damage the solar panels regulator. But it would simplify my charging arrangements if I could just connect the three without switches, and let whichever do the charging. Would this be OK?

 

[peteK]

I just leave the solar permantly connected to the batteries via regulator,no need to disconnect when alternator charging,dont have mains charging.Been like that for 15 years with 3 regulators.

 

[VicS]

I've used these switches for fear that the power from the engine alternator might damage the mains battery charger or the solar panels regulator if directly connected. Or that the battery charger might damage the solar panels regulator. But it would simplify my charging arrangements if I could just connect the three without switches, and let whichever do the charging. Would this be OK?

There is no need for the switches.
.

 

[MontyMariner]

As PeteK, solar reg stays connected when engine is running.

 

[William_H]

Similarly mains charge should be happy with engine charging and solar charging. Essentially all sources have a regulator (presume mains charge has also) which responds to reduce charge current as battery voltage rises. So probably one will predominate slightly depending on regulated voltage setting but not a problem. ol'will

 

[noelex]

In theory I'm careful to let only one of these to be charging at any one time. When the engine is running, the mains battery charger and solar panels are switched off. When the engine is off, either the mains battery charger or the solar panels (but not both) are turned on. In practice though I sometimes forget to turn anything on and the batteries have been flat.

There is no need for this type of restriction in charging sources. There are occasional minor conflicts between different charging sources, but the practical consequences are minor and confined to the batteries. There is no risk that shore power, solar, wind or alternator charge sources will be damaged by this conflict.

Lead acid batteries like to be charged to 100% SOC as soon and as often as possible. Reducing charging input when the batteries can accept more current is rarely a good idea.

 

[B27]

I assume the 'minor conflict' is something like:
Battery is say 60% SOC
You run the engine so the volts go to 14.3 or something. The alternator is simple, not smart.
The solar sees the battery volts, assumes it's fully charged. it goes to 'float' mode.
So it could sit there charging very slowly?
But mostly even a small load will pull the volts down and kick the solar controller into bulk charging?

 

[PaulRainbow]

I assume the 'minor conflict' is something like:
Battery is say 60% SOC
You run the engine so the volts go to 14.3 or something. The alternator is simple, not smart.
The solar sees the battery volts, assumes it's fully charged. it goes to 'float' mode.
So it could sit there charging very slowly?
But mostly even a small load will pull the volts down and kick the solar controller into bulk charging?

That's a possibility, but it doesn't matter. It's almost certain that the alternator will have a higher output than the solar panels, so it doesn't really matter if the solar panels go into float.

Another scenario is the mains charge will override the solar controller. This might be desirable if the batteries are low and you want to charge them quicker than the solar can do it, or id it's cloudy and solar output is very low. Sometimes, the Sun might be shining brightly and the solar panels could be charging sufficiently, so you'd want to turn the mains charger off.

 

[Neeves]

I can confirm we have no switches and have almost the same charging regime as yours.

We have 2 x MD2020s with standard alternators, a Victron inverter charger, a LVM wind and water generator and solar.

The only item we can switch on and off is the inverter charger - we leave it 'off' unless we want to use it - but that's because we would only use the charger in a marina and would not normally need AC at sea (unless we are making bread ). But if we are in a marina we would not normally be running the engines. If we had serviced the engines in a marina we would run the engines when the service is completed - for obvious reasons.

But if push comes to shove we would run the charger, bake bread, have the engines running, accepting solar and wind. We actually do this when accessing an anchorage as we are not purists and motor to our chosen location and we also bake bread (and run the desal unit) knowing we will motor - so the high consumption of the bread maker (and desal) is offset by the 'high' potential output of 2 alternators.

So you can simplify your charging by simple leaving all switches to on, permanently - or removing the switches, and maybe some rewiring to neaten it all up.

Jonathan

 

[Bodach na mara]

I also have a solar panel, mains charger and alternator. No switches except the one in the mains charger. In my berth the solar panel via its regulator keeps the battery bank charged when I am not aboard except during winter when the voltage tends to fall off a bit. I usually switch on the mains charger for an hour or two when I am over to check on the boat. I rarely need to use the mains charger during the season. I never use the mains charger and alternator simultaneously as when the engine is running the shore power is usually disconnected. Unless I forget and try to leave the berth and get stopped short by the cable!

 

[noelex]

I assume the 'minor conflict' is something like:
Battery is say 60% SOC
You run the engine so the volts go to 14.3 or something. The alternator is simple, not smart.
The solar sees the battery volts, assumes it's fully charged. it goes to 'float' mode.
So it could sit there charging very slowly?
But mostly even a small load will pull the volts down and kick the solar controller into bulk charging?

Generally multiple charge sources cause few charging conflicts. In the scenario you present with a battery at 60% SOC, the battery should ideally be held at the absorption voltage (if the charge sources are capable of delivering enough current to do this). It does not matter to the battery which charge source or charge sources supply the current to achieve this voltage. The energy can come from the alternator, from the solar panels or any other charge source, or a mixture of sources. This does not create any charging conflict. The battery is held at the correct charging voltage regardless of how many charge sources are active.

Where minor charging conflicts can most commonly occur is in the absorption time. In some cases the absorption time of some of the charge sources will not countdown even if the absorption voltage has been reached. The absorption times can then be applied to the battery consecutively, which will slightly overcharge the batteries.

A simple example is a yacht sailing all day with the solar panels charging the battery. The solar charge controller (if enough solar power is available) will run through its full bulk/absorption stage holding the battery at the absorption voltage for its programmed absorption time (for example an hour) and then drop down to float when this cycle is finished. If the algorithm is correct the battery will be at 100% SOC.

Suppose at this stage we start the engine. Most alternator controllers, even "smart" models, have no knowledge of the battery SOC and therefore will run through a second bulk/absorption/float cycle on a battery that is already at 100% SOC. The alternator will also hold the battery at the the absorption voltage for its programmed absorption time (another hour).

The battery has been subject to double the required absorption time and will be ( slightly) overcharged. Fortunately, lead acid batteries cope well with slight overcharging and little damage will be done, but it is not absolutely ideal.

Note that if we turned off the solar controller just before starting the engine and run only one charge source at a time, as has been suggested, it would not make any difference. The same charging conflict would apply.

There are ways you can minimise or even eliminate these minor charging conflicts, but the improvement in battery lifespan will only be slight in most cases. Many sailors point out there are more important things to worry about.

 

[Refueler]

I have Solar via controller + engine alternator + small maintenance charger for each battery.

They all are connected and which ever one is needed by circumstance at that time takes the role of charging.

If I have mains power and engine off - of course the maintenance chargers do the job. If no mains power - and sufficient sun - the Solar does the job. If engine running - then alternator does the job.

The Solar and Maintenance chargers all have their max settings as per default and that controls whether they charge or float etc.

 

[Neeves]

The OP omits to mention but - the solar panels I see on most yachts are small and subject to shade from the rigging, mast etc and contribute an insignificant amount. The OP has a mains charger and an alternator, both significant sources of power. Like us I really don't see why he will run the engines for a prologued period of time simultaneously connected to shore power (I say this as many marinas do not meter shore power usage (its free, or paid for in the base marina charge).

The OP might have a monster solar panel, he may pay for his shore power - but .... I'm really not sure why he worries.

Relax

Jonathan

 

[PaulRainbow]

Generally multiple charge sources cause few charging conflicts. In the scenario you present with a battery at 60% SOC, the battery should ideally be held at the absorption voltage (if the charge sources are capable of delivering enough current to do this). It does not matter to the battery which charge source or charge sources supply the current to achieve this voltage. The energy can come from the alternator, from the solar panels or any other charge source, or a mixture of sources. This does not create any charging conflict. The battery is held at the correct charging voltage regardless of how many charge sources are active.

Where minor charging conflicts can most commonly occur is in the absorption time. In some cases the absorption time of some of the charge sources will not countdown even if the absorption voltage has been reached. The absorption times can then be applied to the battery consecutively, which will slightly overcharge the batteries.

A simple example is a yacht sailing all day with the solar panels charging the battery. The solar charge controller (if enough solar power is available) will run through its full bulk/absorption stage holding the battery at the absorption voltage for its programmed absorption time (for example an hour) and then drop down to float when this cycle is finished. If the algorithm is correct the battery will be at 100% SOC.

Suppose at this stage we start the engine. Most alternator controllers, even "smart" models, have no knowledge of the battery SOC and therefore will run through a second bulk/absorption/float cycle on a battery that is already at 100% SOC. The alternator will also hold the battery at the the absorption voltage for its programmed absorption time (another hour).

The battery has been subject to double the required absorption time and will be ( slightly) overcharged. Fortunately, lead acid batteries cope well with slight overcharging and little damage will be done, but it is not absolutely ideal.

Note that if we turned off the solar controller just before starting the engine and run only one charge source at a time, as has been suggested, it would not make any difference. The same charging conflict would apply.

There are ways you can minimise or even eliminate these minor charging conflicts, but the improvement in battery lifespan will only be slight in most cases. Many sailors point out there are more important things to worry about.

This isn't necessarily correct for those that do not live aboard at anchor, or other scenarios.

If one is in a marina for a while and connected to shore power the mains charger will charge the batteries over night, leaving nothing for the solar panels to do the next day. All the time the charger is on there will be little to no solar yield, in most cases.

 

[Refueler]

This isn't necessarily correct for those that do not live aboard at anchor, or other scenarios.

If one is in a marina for a while and connected to shore power the mains charger will charge the batteries over night, leaving nothing for the solar panels to do the next day. All the time the charger is on there will be little to no solar yield, in most cases.

Not only that - but literally no charge source brings batterys to 100% SoC ..... when we refer to Fully Charged .. we actually are talking about a charge % in the 90's ...

 

[noelex]

This isn't necessarily correct for those that do not live aboard at anchor, or other scenarios.

I cruise full time and spend all my time at anchor (the last time we tied up to a dock was 16 months ago) so I am sometimes guilty of ignoring the needs of those who spend a lot of time in marinas, but I don’t entirely agree with your points.

If one is in a marina for a while and connected to shore power the mains charger will charge the batteries over night, leaving nothing for the solar panels to do the next day. All the time the charger is on there will be little to no solar yield, in most cases.

Yes, with the combination of shore power and a decent shore charger, the batteries will tend to remain at or very close to 100% SOC. Unfortunately, all solar controllers will start a new charging algorithm each solar day. They will generally initiate a bulk/absorption/float cycle despite the batteries being 100% full. There are tricks in the algorithm in some solar controllers that reduce the absorption time.

Victron use both an adaptive absorption time (based on the voltage at wake up) and a "tail current" setting that is designed to drop the controller down to float when the output is low.

These tricks do significantly help, but there still tends to be some overcharging. The "tail current" setting also causes some general charging hiccups (when not connected to shore power) and I usually advice most users to disable this setting (If there is no communication between the battery monitor and the solar controller).

Most other brands of solar controllers have a simpler charging algorithm and will overcharge the batteries far more than the Victron units when on shore power.

There are a few solutions. You can install a sophisticated charging system with communication between a battery monitor and the charge sources. This can be an excellent solution, but is more complex and expensive. The alternative is to manually control or adjust the charge sources. A simple solution is to reduce the bulk/absorption voltage to the recommended float (or even better storage) settings for your batteries When on shore power for long periods. The solar controller will still initiate a bulk/absorption cycle but this will really simply be a float cycle. The final option is to turn off solar charging completely, but this causes problems if someone inadvertently disconnects your shore power cord.

All the time the charger is on there will be little to no solar yield, in most cases.

This depends on the settings on your solar and mains charger. If the voltage set points on the solar charge controller are a fraction higher than those on the mains charger the solar system will take over during the day. If the shore power is metered and significantly expensive, as it is in some parts of the world, this can be done deliberately.

This will cause the solar charge controller to always be the preferred source of power. The solar controller will deliver all the consumed power during the day (assuming it can keep up). The solar yield will still be lower because the mains charger will keep the batteries at 100% SOC during the night, but there will be significant solar output and this will reduce your shoreside electric bill. The mains charger will take over when the solar is not keeping up so if set correctly there are no extra issues for the batteries.

 

[noelex]

Not only that - but literally no charge source brings batterys to 100% SoC ..... when we refer to Fully Charged .. we actually are talking about a charge % in the 90's ...

It is not unusual for charge sources to be set up incorrectly. The default settings are usually conservative, so under, rather than over charging is more common.

But good charge sources with the correct settings should be hitting 100% SOC (when there is enough energy available) if you have lead acid batteries. Hitting 100% SOC at least occasionally is important for the lifespan of these batteries.

 

[Refueler]

It is not unusual for charge sources to be set up incorrectly. The default settings are usually conservative, so under, rather than over charging is more common.

But good charge sources with the correct settings should be hitting 100% SOC (when there is enough energy available) if you have lead acid batteries. Hitting 100% SOC at least occasionally is important for the lifespan of these batteries.

We will just have to disagree on that last statement .... to achieve true 100% is actually impossible as the charge tends to infinity in terms of time as the charge level approaches 100%.

FACT.

Second Lead Acid batterys do not like discharged state - but also do not like being pushed to their max as it encourages gassing and heating up of plates.

FACT

The use of the mid 90% bench mark is deliberate for those reasons.

Both facts as per Senior Tech who worked at Mallory ...... you know that large international battery manufacturer ......

 

[lustyd]

I think you're being pedantic. 100% SOC by any normal definition is as much charge as you can get into the battery, and that reduces over time as the battery ages. As such it's irrelevant that you're not hitting some theoretical maximum, it's full and we in the real world call that 100% SOC

 

[noelex]

We will just have to disagree on that last statement .... to achieve true 100% is actually impossible as the charge tends to infinity in terms of time as the charge level approaches 100%.

Battery manufacturers usually define 100% SOC as a particular voltage and tail current setting. If charged to this level the battery should deliver its published capacity.

Absorption voltage (for example, 14.6v ) with a tail current of 2%-0.5% is typical, but it depends on the particular type of battery. In practice, the tail current drops rapidly as the battery approaches 100% SOC so the difference between battery types is not as great as this large percentage spread would suggest.

If your battery manufacturer does not produce any guidelines, absorption voltage with a 1% tail current (4A for a 400Ahr battery) is a good starting point.

If the lead acid battery manufacturer you quote is indicating that more energy can be squeezed into the battery, but at the expense of damaging the battery, it makes no practical difference. We would want to stop charging before the damage occurs. We would also want our battery monitor to indicate 100% SOC at this point. The battery should meet its published capacity figures when the charge is terminated in accordance to the manufacturer’s guidelines (if the manufacturer is honest).

The one rule to keep in mind is that if you consistently terminate the charging too early before the recommended tail current value is reached, the lifespan of the battery will be reduced. The often conservative default settings on some charge sources will do this.

Note the above is for lead acid batteries only.

BTW the only reference I can find to Mallory batteries is as a manufacturer of small dry cell disposable batteries. Have they ever produced lead acid rechargeable batteries? If so I would be interested to see their published charging recommendations and if these differ from other manufacturers.