Battery charger advice

[Playtime]

That indicates an efficiency of well under 30 percent for that charger.

The amps drawn on power-up of the charger (for a few tens of milliseconds) will be significantly more than the steady state - hence the larger fuse suggested by the manufacturer, rather than the unit having a low efficiency.

 

[PaulRainbow]

6 amp fuse at 230v AC probably good for about 70-80 amp charger at 12v DC.

Not what Sterling say.

 

[JumbleDuck]

Evening all. I have just changed my boat and the new to me boat has no built in battery charger. I had a mobitronic type on the last boat so want to find something similiar which I can fit and forget knowing that the shore power will keep the batteries charged up for when I need them.

I have recently acquired a Mastervolt 6A charger like this

It's completely fit and forget; it charges if it has to, maintains charge after that and recycles every 28 days if it hasn't been switched off. I chose it because it was in stock at Largs Chadlers, but it's really all I need to make up for winter weekends on board - if I do run the battery down it has ages to recharge.

For the moment I have not even fitted it, just plugged it into an extension lead modified with a 16A plug at the far end. There is absolutely no need to faff around with consumer units, galvanic isolators and the like unless you are contemplating a heavy-duty permanent installation bonded to the 12V earth. If simple is fine for you and extension lead works well - you can get caravan ones with an RCD included.

 

[JumbleDuck]

That indicates an efficiency of well under 30 percent for that charger.

It probably has a switched mode power supply in it,. They draw intermittent high currents and so generally need much bigger fuses/breakers than their average current draw. For example, an average 2A (~500W) might actually be 6A for 30ms out of every second.

 

[pvb]

Wouldn't it be helpful if the OP actually said how many batteries he has to charge, or what output he wants from the charger? I don't understand how people wanting help make it so difficult to be helped.

 

[VicS]

Wouldn't it be helpful if the OP actually said how many batteries he has to charge, or what output he wants from the charger? I don't understand how people wanting help make it so difficult to be helped.

Absolutely
What did I say in my initial reply, #2

Your incoming shorepower supply should incorporate an RCD, and mcbs for each circuit in the boat.

A garage consumer unit is a convenient and inexpensive way of providing this protection to the a shorepower system. They usually incorporate a suitable RCD and a couple of mcbs, one rated at 16 amps, which can be used to supply a small number of sockets, and one at 6 amps, which can be used for supplying a battery charger.

You presumably plan to leave your boat with the shorepower connected therefore a galvanic isolator will be an essential item to fit.

Cannot advise on the choice of charger but others no doubt will although it might help if they know the sort of size ( amps output) charger you need and also how many battery banks you will need to charge simultaneously.

 

[matthewriches]

Aware of Sterling’s tech info. Both Mastervolt and Victron basic chargers are fairly good at not sucking the grid dry although Sterling do have some fairly clever tech in them.

Got a 70A mastervolt charger waiting on some new parts for a dredger and that only draws about 1.3kw at full load. That’s still under 6 amps and was removed from a B type 6A breaker.

Not what Sterling say.

 

[pvb]

Absolutely
What did I say in my initial reply, #2

I was thinking of you when I wrote it, Vic. Interesting that the OP responded to you but totally ignored your request for info.

 

[BabaYaga]

The amps drawn on power-up of the charger (for a few tens of milliseconds) will be significantly more than the steady state - hence the larger fuse suggested by the manufacturer, rather than the unit having a low efficiency.

Could be. But would such a current draw for a fraction of a second really be able to blow the fuse or trip the mcb?
I don't really think the Sterling charger referred to is that inefficient.

It will vary, depending on the charger, a 6a MCB would be ok for a small charger (up to about 10a), anything over that might be pushing it.

6 amp fuse at 230v AC probably good for about 70-80 amp charger at 12v DC.

Quite a range of estimates!
Would be interesting to hear from someone with real life experience of a 6A mcb tripping because of the charger being too powerful.

Not necessarily, that's just the fuse rating, you're assuming that the fuse is rated at the full load current, which it isn't. Full load current for the 30a Sterling charger is 2.3a, less than the 25a Ctek.

How would you then explain the fuse rating?

 

[pvb]

How would you then explain the fuse rating?

Usually, the fuse is sized to protect the wiring.

 

[matthewriches]

I can certainly say a 70 amp mastervolt sits ok on a 6A breaker. Only removed as it was Attacked by the fire extinguisher near it giving it a soaking.

Would be interesting to hear from someone with real life experience of a 6A mcb tripping because of the charger being too powerful.

 

[matthewriches]

Yes. Not seen a charger without internal glass fuse to protect itself.

Found one once on a fishing boat with an Allen key cut to fit.

Usually, the fuse is sized to protect the wiring.

 

[PaulRainbow]

I don't really think the Sterling charger referred to is that inefficient.

Sterling quote 90.4% efficiency.

How would you then explain the fuse rating?

Best ask Charlie, he specified the fuse.

 

[BabaYaga]

The amps drawn on power-up of the charger (for a few tens of milliseconds) will be significantly more than the steady state - hence the larger fuse suggested by the manufacturer, rather than the unit having a low efficiency.

It probably has a switched mode power supply in it,. They draw intermittent high currents and so generally need much bigger fuses/breakers than their average current draw. For example, an average 2A (~500W) might actually be 6A for 30ms out of every second.

A bit of further googling suggests to me that the explanation for Sterlings high fuse rating probably has something to do with what is stated above.
But I also believe what is stated below to be true.

I can certainly say a 70 amp mastervolt sits ok on a 6A breaker.

 

[gordon029]

Evening all, firstly apoligies for not responding earlier but it was one of those days. Just reading through all the information in the replies and once again I have to thank everyone for taking the time to respond.
There are 2 batteries one domestic 90 amp and a 110 amp starter.I am not sure how old they are but am sure I will find out quick enough once I start using them regularly. As no one mentioned the Mobitronic so assume they are finished with this type of thing . I do like the neatness of the model pictured from the Spanish site and the fact that it is fit and forget really appeals to my reluctance of having to fiddle with it regularly.As for the breaker unit for the 220volt sockets I will go with the idea of the garage unit mentioned first and will take the advice offered so thanks all once again for all the information .

 

[LadyInBed]

Am I missing something here?
OP wants a mains charger to keep his bank topped up when the boat is left in the marina, or have I got that wrong.
If I haven't, then to my mind a cheap 3 stage charger that can output 3-5 amps will do the job perfectly well, as it is more than probable that the boat will arrive at the marina under engine with the batteries charged. There will be virtually no drain on the battery whilst the boat is unoccupied, so why is it necessary to have a massively expensive charger that can deliver 40 odd amps? Unless of course the boat is left unoccupied with all its nav kit on.

 

[PaulRainbow]

A bit of further googling suggests to me that the explanation for Sterlings high fuse rating probably has something to do with what is stated above.
But I also believe what is stated below to be true.

No reason that both can't be true, no-one suggested Matt was wrong about the Mastervolt fuse, but the Sterling charger specifies a different fuse.

Brings me back to........ "follow what the manufacturer specifies"

 

[PaulRainbow]

Am I missing something here?
OP wants a mains charger to keep his bank topped up when the boat is left in the marina, or have I got that wrong.
If I haven't, then to my mind a cheap 3 stage charger that can output 3-5 amps will do the job perfectly well, as it is more than probable that the boat will arrive at the marina under engine with the batteries charged. There will be virtually no drain on the battery whilst the boat is unoccupied, so why is it necessary to have a massively expensive charger that can deliver 40 odd amps? Unless of course the boat is left unoccupied with all its nav kit on.

Fine if he's day sailing, but if he's spending time aboard when plugged into shore power 3-5a may not be enough to keep up with demand, let alone charge the batteries at the same time. Although i'm not suggesting any particular size of charger, let alone 40a. Without knowing his pattern of usage, it's not possible to say how powerful the charger needs to be.

 

[pvb]

Fine if he's day sailing, but if he's spending time aboard when plugged into shore power 3-5a may not be enough to keep up with demand, let alone charge the batteries at the same time. Although i'm not suggesting any particular size of charger, let alone 40a. Without knowing his pattern of usage, it's not possible to say how powerful the charger needs to be.

If he only has a 90Ah domestic battery, he perhaps needs to spend some money on more capacity before worrying about the charger.

 

[Tranona]

If he only has a 90Ah domestic battery, he perhaps needs to spend some money on more capacity before worrying about the charger.

The 110Ah for a start battery seems a bit odd as well.

However without knowing his boat, engine, gear fitted and pattern of usage difficult to make any sensible suggestions.