Should battery charger be run continuously?

[srah1953]

Hi all
Batteries have a limited number of charging cycles, so, ignoring any electrolysis issues deriving from being plugged in, for those on a marina berth with access to shorepower, is it better to have the battery charger constantly working or only to switch it on occasionally?
Thanks

 

[MoodySabre]

I've just had a couple of days away and no shore power so the fridge and lights have been used on the domestic batteries. I've left them on charge with a charger that goes into float mode once the full charge is restored. I've done this for a few years now with no ill effects. A cheapo charger with no float mode is best not left on.

 

[Richard10002]

Given that battery life is shortened each time they are cycled, i.e. discharged a bit, then charged, and the greater each discharge, the shorter the life....... keeping the charger on, and keeping them permanently full for as long as possible, ought to be good for them.... or least bad??

 

[srah1953]

Given that battery life is shortened each time they are cycled, i.e. discharged a bit, then charged, and the greater each discharge, the shorter the life....... keeping the charger on, and keeping them permanently full for as long as possible, ought to be good for them.... or least bad??

That was essentially my question, as the batteries are being used most days, lights, instruments, therefore even with a battery charger they are being cycled continuously, so is it better to have a smaller number of deeper cycles than continuous short cycles?

 

[noelex]

With a good battery charger that goes into float mode it is better for the batteries if they are left permantly connected.
Make sure the float voltage is appropriate for your batteries. If there is little load on the batteries slightly lowering the float voltage is beneficial.

Most marine battery chargers are sized so that will completely keep up with house loads. If this is the case it is probably helpful for most batteries to periodically, say once a month, to do a slight discharge and recharge cycle. This tends to stir up the electrolyte. Switch the battery charger off and allow the batteries to drop down to a SOC around 85%. Restart the battery charger and it should go into bulk mode before dropping down to float. Some battery manufacturers also recommend equalisation when used in this manner.

Check the start battery is getting some charge and not not slowly running down from self discharge.

Don't ignore the issue of galvanic corrosion when permantly connected to shore power and don't do the above if the voltage is not appropriate. Be particularly careful if you are using a car battery charger, these often have just a single charge voltage which is too high for perminant connection.

 

[cliffdale]

Here are 2 reasons why I dont leave the batteries on charge when I am not on board.

Batteries do go wrong and I switch off the electrics to reduce fire risk!

Secondly, I completely disconnect the mains from the boat to reduce wear on the anodes. My boat seems to suffer badly when connnected to mains.

Cliff

 

[pteron]

so is it better to have a smaller number of deeper cycles than continuous short cycles?

Noelex has pretty much covered the rest, but in answer to your question, for lead acid and similar responding batteries (Li Ion for instance) it is far better to have many small discharges and recharges than fewer deep discharges. This is because the damage or wear done by discharging is non-linear, i.e. the wear done by discharging to 50% is more than twice that of discharging to 75%.

 

[Plevier]

Noelex has pretty much covered the rest, but in answer to your question, for lead acid and similar responding batteries (Li Ion for instance) it is far better to have many small discharges and recharges than fewer deep discharges. This is because the damage or wear done by discharging is non-linear, i.e. the wear done by discharging to 50% is more than twice that of discharging to 75%.

Agreed (for lead acid).
A major cause of damage in cycling of lead acid batteries is caused by the expansion and contraction of the active paste during the discharge/recharge cycle. The shallower the cycle the less the damage.
I don't know about Li Ion etc.

 

[halcyon]

Hi all
Batteries have a limited number of charging cycles, so, ignoring any electrolysis issues deriving from being plugged in, for those on a marina berth with access to shorepower, is it better to have the battery charger constantly working or only to switch it on occasionally?
Thanks

Short answer, no, just run periodically.


Longer answer.

Float charge has nothing to do with maintaining lead acid batteries, it relates to when the telephones were powered by large battery banks at the exchange. These were kept on charge at float voltage from the mains, so should you have a power cut, there was no lose of phones. But periodically ( 2/3 months ? ) they had a high voltage charge to maintain battery life.


I introduced a dual voltage charger for Sealine in 1984, it charged to bulk voltage 14.2 volt ( there are reasons why we did not go to 14.4 / 14.6 ) and droped to 13.6V power supply mode. This is were the float voltage came from. When you left the boat you turned the mains and batteries off.

We did a lot of testing in the early 1980's, and running at 13.6 volt for extended periods reduced battery life.

The ideal is the last system we bought out in 1998 ( gave up with re-badged imports from China ) this monitored uasage and shut down when not wanted, and entered a maintainance mode, this also did de-sulphation.


Brian

 

[srah1953]

Excellent. Thank you one and all.

 

[little_roundtop]

Some interesting and very informative replies to this post, and it's something I've been wondering about too. We're full-time liveaboards and in the winter the batteries are on float all the time (the 4-phase mains charger is on all the time).

This last winter I've taken to turning the charger off during the day because our solar panels can carry the load, except on really cloudy or rainy days. In the early evening I switch the mains charger back on overnight.

Is that sensible or dumb do you think?

 

[david_bagshaw]

(the 4-phase mains charger is on all the time).
?

I take it this is a charger that runs on either 3 phase or single phase supply?

 

[noelex]

Some interesting and very informative replies to this post, and it's something I've been wondering about too. We're full-time liveaboards and in the winter the batteries are on float all the time (the 4-phase mains charger is on all the time).

This last winter I've taken to turning the charger off during the day because our solar panels can carry the load, except on really cloudy or rainy days. In the early evening I switch the mains charger back on overnight.

Is that sensible or dumb do you think?

Make sure the solar regulator is set to the correct voltage. It would be worth observing the voltage behaviour of the solar regulator on your battery monitor, or just use a multimeter.
Some solar regulators automatically initiate a bulk mode every 24 hours and hold this high voltage for an hour or so. This is fine if the batteries have been discharged overnight, but not ideal if the battery is as 100% SOC because it has been on a mains charger.
The better solar regulators are completely adjustable so you can stop this kind of behaviour.
When living on the boat on the hard stand recently ( with a typical high electricity fee) I set the battery charger to float of 13.4 and the solar regulator to float of 13.6 and stopped the bulk charge. The result is the batteries stay at 100%, maintained by the battery charger overnight, as soon as the sun rose, the higher voltage on the solar regulator ensured the electricity was provided free by the solar panels.

 

[[2574]]

This last winter I've taken to turning the charger off during the day because our solar panels can carry the load, except on really cloudy or rainy days. In the early evening I switch the mains charger back on overnight.

Is that sensible or dumb do you think?

My Victron charger has been on pretty much constantly for the past five years (AGM Lifeline batteries). I don't like to switch the charger on/off frequently as this initiates a bulk/absorption/float charging cycle for no good reason. The charger floats the batteries at a constant 13.2v. No problems so far and the batteries seem to be in tip-top condition. I have a galvanic isolator fitted and don't suffer with accelerated consumption of sacrificial anodes.

The differing responses to this thread seem to show that it is a black art without a correct answer. Leaving the charger on does require a high quality sophisticated charger though; I wouldn't do it with a £30 Halfords "special"!

 

[Plevier]

Float charge has nothing to do with maintaining lead acid batteries, it relates to when the telephones were powered by large battery banks at the exchange. These were kept on charge at float voltage from the mains, so should you have a power cut, there was no lose of phones. But periodically ( 2/3 months ? ) they had a high voltage charge to maintain battery life.


I introduced a dual voltage charger for Sealine in 1984, it charged to bulk voltage 14.2 volt ( there are reasons why we did not go to 14.4 / 14.6 ) and droped to 13.6V power supply mode. This is were the float voltage came from. When you left the boat you turned the mains and batteries off.

We did a lot of testing in the early 1980's, and running at 13.6 volt for extended periods reduced battery life.

Brian

But the OP said "as the batteries are being used most days, lights, instruments, therefore even with a battery charger they are being cycled continuously." This is not a standby float situation like the telephone exchange (incidentally they were normally floated at 2.15vpc just to offset self discharge and boosted at around 2.4vpc after a discharge or typically every 3 months as you said to equalise them and get rid of any stratification in the acid, and in this country they were usually solid lead Planté type rather different from pasted plate). Under these circumstances wouldn't you agree in principle the charger would be better left on?

However it depends on the quality and regime of the charger, which we don't know.

Brian, do you know what sort of batteries you were testing in the 80s? At that time they could well have had significant antimony content in which case I agree constant 13.6V would be damaging. However if they were <1.8% antimony (normal now) or were calcium I wouldn't have expected 13.6 to shorten life, although I think it's a touch high for long term float as you did have a recharge voltage available as well. 13.6 is getting close to a combined float-recharge voltage (usually 13.8). I think we (as battery manufacturers) would have suggested about 13.2 float for those conditions.

On my boat when I've been away I try to leave the charger on for a couple of days then turn off.

 

[halcyon]

But the OP said "as the batteries are being used most days, lights, instruments, therefore even with a battery charger they are being cycled continuously."

Brian, do you know what sort of batteries you were testing in the 80s?.

In that case the charger is supplying the load, and the batteries are not being cycled, hense the reason for 13.6 float.

In 1980 they were standard marine batteries as fitted to Sealin 85 or 105 amphour. Later in the 80's we were working on the Delco Freedom batteries, interesting items, charge setting for them was 15.4 charge, 14.4 float ( approx long time ago ).

As said I think the best option is to monitor use, and use a pulsed maintainance phase ( pulse cycle based on charge level ) when not required.
Saves power, and can maintain 98% charged with very little gassing.

I think a lot of chargers to-day require a charge cycle that suits them, not a charge cycle that suits there use on a boat.

The one thing I always say, check with the battery manufacture as to what charge cycle the battery needs, then find a charger that does it.

Brian

 

[halcyon]

But the OP said "as the batteries are being used most days, lights, instruments, therefore even with a battery charger they are being cycled continuously."

Just been back to the OP, as I did not remember reading that, and was worried about short term memory lose, and it is not there, memory okay


Brian

 

[noelex]

But the OP said "as the batteries are being used most days, lights, instruments, therefore even with a battery charger they are being cycled continuously."

It is in post 4 by the OP

I am doubtful the statement is correct however. Most battery chargers would easily have enough output to drive these devices and keep the battery at the float voltage, so it will remain 100% charged.

 

[halcyon]

It is in post 4 by the OP

.

I started to reply at post 3, got pulled away on a number of jobs, and hit submit many posts later, isn't work a pain

Brian

 

[Plevier]

Later in the 80's we were working on the Delco Freedom batteries, interesting items, charge setting for them was 15.4 charge, 14.4 float ( approx long time ago ).

Were those the ones in which the grids instead of being cast were produce by putting slits in lead sheet and stretching it like Expamet mesh? Very thin plates, very high current output, not so good life. I think the sheet was pure lead and the acid sg was high hence the high voltage tolerance (for short periods!). I don't think they use that construction now not sure.