Using battery charger as a power supply

[Oily Rag]

There is no power supply transformer fitted, but there is a socket and a breaker supplying shore power to some 13 amp sockets and the immersion heater. When in a marina (rarely), I run the fridge and the lights off the battery and keep a small 5 amp battery charger connected just using crocodile clips as I would do if charging the battery on a bench at home. It seems to do the trick. The battery is kept topped up, the charger doesn't get too warm and the fridge does its job. Any thoughts on what to look out for if anything?

 

[Kelpie]

What voltage is the system sitting at? My main concern would be that a charger would have quite a high working voltage, which some devices might not like.

 

[Refueler]

Its fine ... and all you are doing is similar to when engine is running and alternator is keeping battery charged ... while powering items.

If the charger is playing happily - then all is fine. A charger will usually default OFF if asked to exceed its specs ... and yours appears to sit happily ..

FYI - my boat sits on pontoon at home with charger providing to a splitter ...... its always on ... and I use my gear on board without any concern ... hasn't been any problem since 2007 when boat came over to here ...

 

[Refueler]

What voltage is the system sitting at? My main concern would be that a charger would have quite a high working voltage, which some devices might not like.

Charger will be supplying similar to what engine alternator would .... so whats problem ??

 

[andsarkit]

Agree with Kelpie. Get a voltmeter/multimeter and keep a check on the battery voltage.
Car alternators run at 14.4V for extentended periods but this is too high for continuous charging.
Normal float voltage is 13.8V. If you can look up the battery manufacturers specification they might give a recommended float voltage.

 

[Bouba]

Many battery chargers have a setting ‘supply’ for powering stuff directly

 

[Boater Sam]

Not a problem but you need a proper charger that does bulk, float and maintain charging rates automatically to give the battery a decent life.

 

[Refueler]

Why ??

Standard chargers reduce amps as batterys charge up .... till basically they are barely charging at all ... yes the charger usually sits as Constant Voltage when battery near full .. but at such low rate - its not a problem.
The problem comes with some chargers that allow users to ramp up the amps and over-ride the reduction of amps.

Here the OP is actually drawing power from his battery bank and backing up by using the charger ... it does not need to be one that has float modes etc. The charger will provide at a rate dictated by the state of charge of the batterys / power draw of the items.

The only reason some chargers have switch to turn into a Power Supply - is that chargers don't like being used as such - and without such switch - way to do it - is to connect charger to a battery ... which then powers items. That way charger can act normally.

As I said before - its literally no different to running the engine and alternator doing the job ... only difference here - is that due to the power draw of OP's fridge ... the alternator will be doing a little more work than usual.

 

[geem]

Why ??

Standard chargers reduce amps as batterys charge up .... till basically they are barely charging at all ... yes the charger usually sits as Constant Voltage when battery near full .. but at such low rate - its not a problem.
The problem comes with some chargers that allow users to ramp up the amps and over-ride the reduction of amps.

Here the OP is actually drawing power from his battery bank and backing up by using the charger ... it does not need to be one that has float modes etc. The charger will provide at a rate dictated by the state of charge of the batterys / power draw of the items.

The only reason some chargers have switch to turn into a Power Supply - is that chargers don't like being used as such - and without such switch - way to do it - is to connect charger to a battery ... which then powers items. That way charger can act normally.

As I said before - its literally no different to running the engine and alternator doing the job ... only difference here - is that due to the power draw of OP's fridge ... the alternator will be doing a little more work than usual.

This only works if the voltage set point of the charger is low enough. A charger that provides a constant 14.8v would over charge the battery if left at that voltage

 

[Alex_Blackwood]

This only works if the voltage set point of the charger is low enough. A charger that provides a constant 14.8v would over charge the battery if left at that voltage

Yup, He needs to ascertain the voltage at the battery terminals to ensure there is not overcharging, Most small basic chargers won't actually give more than 12 volts anyway, but check. Also if there is a heavy current draw, such as engine start, on the battery this will also draw from the charger and can destroy it, Yes it can. I know! That is unlikely in OP's case so apart from charge voltage he should be OK.

 

[Refueler]

This only works if the voltage set point of the charger is low enough. A charger that provides a constant 14.8v would over charge the battery if left at that voltage

So you think that the charger will keep hammering away at the battery ? You ignore the fact that the amp rate reduces significantly - such that the actual amount of energy being thrown at the batterys is minimal at or near high state of charge.

Most small basic chargers won't actually give more than 12 volts anyway,

If you try to charge with that - you'll be wasting your time .. A charger in this situation must be capable of charging at over 14V to overcome the bastterys increasing resistance to charge.

Also if there is a heavy current draw, such as engine start, on the battery this will also draw from the charger and can destroy it, Yes it can. I know!

Yes - but its rare as most chargers will failsafe off when power draw exceeds its specs. You can see this in action in fact when connecting a basic charger to a completely discharged but still circuit battery ... the charger clicks on and off as the charger tries to charge. This also happens when you hit start - the power draw causes charger to shut down ..
If your charger did 'blow' it must have been an old basic non fused PSU based or possibly faulty more modern charger,

That is unlikely in OP's case so apart from charge voltage he should be OK

Back to this misleading charge voltage comment again ...

If what OP is doing was bad or wrong ... then it will be of interest to millions of boaters around the world who like myself and many others > plug in shore powered chargers when berthed and continue to run all manner of items on board from the '12v' system.

Suggestion : Look back at OP's opening post ... he states clearly that his 5A basic charger does not get hot .. sits there quite happily maintaining his batterys while fridge etc. draws power. His batterys apparently happy to do this.

 

[noelex]

As others have pointed out, the charge profile of the battery is not likely to be ideal, but 5Ahr batteries are only around £10 so this is not critical.

Just make sure you have a fuse between the charger and the battery and also between the battery and the load.

 

[Refueler]

As others have pointed out, the charge profile of the battery is not likely to be ideal, but 5Ahr batteries are only around £10 so this is not critical.

Just make sure you have a fuse between the charger and the battery and also between the battery and the load.

Where do you get 5A/hr battery info from ??? Have I missed something ?

I see 5A charger ....

 

[noelex]

Where do you get 5A/hr battery info from ??? Have I missed something ?

I see 5A charger ....

Oops. Sorry, you are correct, I misread the post. My apologies. I should wait until I consume my first coffee before replying .

If it is a dumb charger, or even one of the cheaper smart chargers, the life of the house bank is likely to suffer. Determining the charge profile by measuring the output voltage will indicate how suitable the particular algorithm used by the charger is in practice. Often with a small capacity charger in relation to the battery bank size and the load applied, the results, while not ideal, are at least acceptable.

This shortened life may be worth accepting or it may be worth buying an expensive smart charger that can be adjusted to the appropriate values. The final option is if you are handy with electronics it is possible to adjust the output voltage of dumb chargers to a more suitable level using simple components such as diodes to drop the output voltage.

 

[geem]

So you think that the charger will keep hammering away at the battery ? You ignore the fact that the amp rate reduces significantly - such that the actual amount of energy being thrown at the batterys is minimal at or near high state of charge.

It's not the amps going into the battery that is the problem. It's holding the battery at an elevated voltage for long periods of time where the electrolyte is boiling away.

 

[KompetentKrew]

It's not the amps going into the battery that is the problem. It's holding the battery at an elevated voltage for long periods of time where the electrolyte is boiling away.

OP says they're rarely in a marina, and 5A won't keep up with the fridge, so this seems like a low risk.

However, considering the cost of boating in general, I would have thought a cheap multistage charger would be a no brainer. If OP could stretch to 10A - better 15A or 20A - then there's a chance of getting the battery fully charged on these rare overnight stops, which would be much better for its health (probably too late for the current battery though). Hardwire the new charger in properly, so starts charging as soon as the shorepower is connected and there's no chance of the crocodile clips falling off and the battery accidentally being flattened.

 

[Refueler]

OP says they're rarely in a marina, and 5A won't keep up with the fridge, so this seems like a low risk.

However, considering the cost of boating in general, I would have thought a cheap multistage charger would be a no brainer. If OP could stretch to 10A - better 15A or 20A - then there's a chance of getting the battery fully charged on these rare overnight stops, which would be much better for its health (probably too late for the current battery though). Hardwire the new charger in properly, so starts charging as soon as the shorepower is connected and there's no chance of the crocodile clips falling off and the battery accidentally being flattened.

???????

This is what OP says ....

"It seems to do the trick. The battery is kept topped up, the charger doesn't get too warm and the fridge does its job. Any thoughts on what to look out for if anything?"

Nowhere does he say the charger is not keeping up ....

And on this :

"It's not the amps going into the battery that is the problem. It's holding the battery at an elevated voltage for long periods of time where the electrolyte is boiling away."

Sorry - but only if the charger is set to have current as well ... which most chargers as I already said default down to a trickle once battery reaches near full .... voltage alone is not the cause of boiling ... its the 'watts' or in other words the old 'energy in - energy out' ... that is pumping in Watts and then it dissipating as heat.

Explain how a car or mobo can have engine purring away all day long and alternator working ... and batterys still fine ?? Because the alternator does similar ... it still has its 14+ volts ... but the amps are now so low as to be negligible.

But anyway ... all this forgets the fact that OP is drawing power from the batterys while charger is connected .... seems people are intent on ignoring that important fact ...

 

[PaulRainbow]

A proper, multistage charger, with a proper PSU mode isn't that much to buy.

Victron Energy Blue Smart IP65s Charger 12/5(1) - BPC120533024R

Or for a little more, get a 10a one.

 

[geem]

???????

This is what OP says ....

"It seems to do the trick. The battery is kept topped up, the charger doesn't get too warm and the fridge does its job. Any thoughts on what to look out for if anything?"

Nowhere does he say the charger is not keeping up ....

And on this :

"It's not the amps going into the battery that is the problem. It's holding the battery at an elevated voltage for long periods of time where the electrolyte is boiling away."

Sorry - but only if the charger is set to have current as well ... which most chargers as I already said default down to a trickle once battery reaches near full .... voltage alone is not the cause of boiling ... its the 'watts' or in other words the old 'energy in - energy out' ... that is pumping in Watts and then it dissipating as heat.

Explain how a car or mobo can have engine purring away all day long and alternator working ... and batterys still fine ?? Because the alternator does similar ... it still has its 14+ volts ... but the amps are now so low as to be negligible.

But anyway ... all this forgets the fact that OP is drawing power from the batterys while charger is connected .... seems people are intent on ignoring that important fact ...

That's nonsense

 

[noelex]

A proper, multistage charger, with a proper PSU mode isn't that much to buy.

Victron Energy Blue Smart IP65s Charger 12/5(1) - BPC120533024R

Or for a little more, get a 10a one.

I have one of these chargers (the 24v 8A version) and they are very good for not much money. Completely user adjustable so you can select the right parameters, which is especially important if you are planning to leave the boat for long periods with no load. They are reasonably waterproof, double insulated (so do not require an earth connection ), have a Bluetooth interface and will put out their full rated power continuously, unlike some other chargers.

They do have some shortcomings. They will not operate on 110v AC and cannot act as a power supply. Mastervolt and others offer similar chargers with these facilities, but the user adjustability and the interface is not as good as the Victron product.

There is no doubt that a charger like this would be kinder on the batteries than simple dumb 5A charger. However, is it worth the extra cost?

We need some more answers, such as voltages seen under use, before being able to answer that definitively, but I suspect given the limited information in the original post the extra battery life achieved would not be enormously greater.