Ask the forum - 240V stepped down to 12V + existing set-ups

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So like most boats - we have 12V lights, radio, nav gear etc. With 240V couple of sockets etc.

There is battery charging by mains supply or engine.

The question is has anyone added a 240V drop down transformer to 12V to power the on-board systems via ioslation switch - so that mains shore power supplies the onboard 12V systems ..... and batts can have a rest / be charged without a load being put on as well ???

I am considering fitting > 240V -12V transformer with a change-over switch isolating the batts from the boats lights etc. It will probably mean 2 or 3 similar transformers so sectioning up the 12V boat systems accordingly.

This then leaves the batts to be charged without dragging power from them. It also means that lights / cables etc. don't have to be doubled up fitting mains stuff ....

OK - over to the "experts" as to why more boats don't have this ... why I shouldn't do it ... advantages / disadvantages etc. etc.

?????????????
 
You can achieve the same effect by use of your 1-2-both-off switch if you are wired up correctly. I have a 45amp step charger wired to both battery banks, so can select which bank charges on its own, and which has some charge going to the domestic system.

My engine starter battery is a carbon fibre reinforced leisure battery that is dual purpose so can take the starting load as well as deep cycle.
 
My smart charger allows for charging the batteries and running the 12v electrics at the same time. It monitors battery voltage and once the batteries are fully charged, floats them whilst supplying enough for any lighting, pumps etc on board.

I monitor current in and out of the batterys, charger etc with several shunts wired to a battery, battery usage and charging monitoring system.
 
Same as above - my Sterling charger acts as a 12v power supply to everything and keeps the batteries float charged permanently if necessary. It also "de-sulphates" the batteries every 7 days or so, whatever that means, but I assume it's good for them.

Pops
 
1-B-2-O switch ...

I looked at using this as its already fitted. But decided against it as I like the fact that it does isolate totally the electrics when at O.

Following on from my other posts where I illustrated the maplins splitter ... I will connect up the charger via this and a timer. This will then cater for both batterys.
The system will be isolated from all else via the 1-B-2-O switch ... so that engine alternator exciter etc. are dead. This will also ensure that any 12V feed from mains is not corrupted or fed where it shouldn't be.

A small panel with switches will then connect in the 12V supplied from transformers ... which will doubly isolate the unwanted side ....

For the few pence on switches etc. - I think it worth it.

So without smart chargers / smart relays etc. .... a budget of say £40 .... why not ??
 
Don't do it!

First of all, as already pointed out, any half-decent battery charger would do exactly what you need (provided it is not grossly under-dimensioned).

But, more important, the transformer you are considering looks like a domestic-lighting appliance, whose output is 12V alternate current (AC).

This cannot be mixed with batteries' direct current (DC) and anyway could be used only to feed lights (which don't care of direct or alternate current), but almost all other 12V-DC devices would not work out of AC or might even be damaged.
 
AC or DC .....

I realise that this will be a factor to take into careful consideration ... the web-page for the transformer is not clear about AC or DC - so was not looked for ...

Of course before buying anything such as this - I would of course choose DC.

FWIW ... I built a transformer for powering stereo booster ... has core with large can condensor and zener diode ........ capable of 240 or 120 - 12v and up to 100W cont. It wasn't difficult and is v...e....r....y smooth .... Was specc'd by a radio repair guy and detailed for me to put together. So it can be done ... and of course I'm sure good old Maplins can supplyh something ...

I don't have large capacity charger - the above is less cost than such a beast etc.

Point well taken.
 
Nigel,

If you intend disconnecting the batteries then your trasnsformers will have to be full wave rectified and well smoothed.
The batteries act as a large capacitor on the system.
If you dont smooth to remove the ripple then you will have a fairly loud buzz on radios etc. I'm sure you have heard it before.
So the secret is to have a simple PSU with a 15A bridge rectifier, and say 2 X 10,000 uF capoacitors at 63V working voltage.
I would then follow this with say four 2N3055 power transistors for regulation, controlled either by a TIP41A or an IC.
It is important to regulate to keep the voltage constant, as smoothing increases the voltage somewhat.
In short it is not possible to remove the batteries and keep a regulated stable supply simply with a transformer on it's own.
This has to be rectified smoothed and regulated, or else you simply risk blowing up your radios, hi fi etc.

I have circuit diagrams of suitable units which I can scan and send you if you are OK with a soldering iron and basic electronics.

Regrettably the unit you link to will not be anywhere near man enough for the job,
niether will it be smoothed and regulated. It is just an LV lamp supply.
Lights do not require the same amount of care with power supply as radios, plotters etc but even 12/24 lamps running unsmoothed will have a very significantly shorter lifespan.



Steve.
 
Nigel

anything to get you away from stable building is it?

the transformer you linked to is likely an AC output, so not suitable for your purposes.

You're considering fitting £60's worth of gear, + switches etc. so the batteries can have a rest?. Is this cuz you've started off with a cheapo battery charger that won't supply the lighting load at the same time as float the batteries?

What with these latest items + the splitter you were contemplating recently + a cheapy charger - you might have been able to start from scratch with something designed for the job & the environment.



A basic 240-12V smoothed power supply may well do what you want - but what exactly are you trying to achieve that your present system can't manage?


Many marine chargers boast "power supply" abilities. In some cases this means you can disconnect the batteries if you wanted to & the charger would happily run all the 12V systems, up to it's rated output (maybe).

Others won't do that, but just boast that when the batteries are floating - you can put all the lights on & keep charging, supposedly while holding a float voltage. I have a 50A charger/inverter from Victron - & in practice, if the load is over a certain level, it thinks the batteries need charging & increases the voltage accordingly. I suspect that many others will do exactly the same .
 
I agree with those cautions.
You could do it but you would have to wire the change over switches so that only the lights are switched over and none of the onboard electronics, and that includes low volage fluorescent lights which are DC only.

You would also have to ensure that the switches were "break before make" preferably with a centre off position to be sure that the AC was never connected to the DC system.
 
Ac is not intended at low voltage ....

It was an unintentional error to link to a transformer that may be AC.

It is intended to fit DC smoothed supply ...

Maybe the way is via a smart charger ... but I weould like to hear from others who may have already solved it via the transformer route as well ....
 
Re: Suitable is available ...

Yes - of course they're available - but what really do you want to achieve & why - that your present system can't?
 
Like many before and will be after me ....

I have built up a stock of items that get me through my sailing / pastime .... chargers, batterys, leads, mains systems etc.
Using these and my in-built attempts to save money / achieve the impossible ! I often strive to find solutions to apparent problems.

I have a smoothed power supply that was built to run stereos from a car ... I have chargers, I have mains supply to the boat.
As I see it further expenditure is lower than first appears to do this work.
The radio ..... pleasure can be mains powered anyway ... VHF can if needed run from batterys - as its on a separate fused supply anyway .... not via the 1-B-2-O switch.
In fact the real requirement is to run the lights more than anything .... SWMBO does like her lights on !! and also wandering 12V light in cockpit.

So the real power reqt's are a lot lower than first imagined ... I have 3 flourescents + 1 bulb light ... probably 3 x 20W + 1 x 10W ..... = 100W max incl. waste etc.
Rest run it direct from mains.......

I think it starts to look more practical ........ please note I do not have a new boat and its only 25ft - so a) I can run wires / all-sorts without messing about with linings / interior, b) I don't have fancy panels or fittings to worry about ...... etc.

If I had a AWB with all the nice fitted panels / linings etc. - its a totally different ball-game and I would be into "kit-solutions" such as Merlin etc.

Let's put it this way ......... many people out there probably are interested in alternative ways on smaller boats .... as well as the "out of the box" answer .....
 
Re: Suitable is available ...

Id go for the 10A version. from Maplin
That is very cheap, a lot cheaper than you could build it for with components.
If you find there's not enough current, then add another one.
You could also use it as a simple standby float charger.
Not enough voltage to fully charge the batteries but enough to get you going.

Steve
 
Re: Like many before and will be after me ....

appreciate all that - and yr boat in UK I know, cos used to have berth next door but one .

So at the moment.... you have a charger? why can't the lights be on as swmbo prefers?

Maybe I missed some earlier thread about this - & heaven knows I'm all for fiddling & saving money & doing things just because I can.... so genuinely & honestly asking for the briefest summary of what you've got fitted now to charge batts & why this needs supplementing or what benefits that wd give. Is it that the charger can't cope with charging and lighting? or a desire to isolate the batts when charging ( & why) or...?
 
Re: Like many before and will be after me ....

Nigel,

I cant quite get my head around why you want to isolate the batteries from the circuit.
The amount of drain on the batteries will be fairly negligible with a Charger on constantly, particularly if the charger voltage is set above the batteries.
Current will be drawn from the unit offering the highest voltage first.
Only when the voltages equalize will current be drawn from the batteries.
It will be quickly replaced if the charger is on constantly particularly if left on in daytime when there is little load on the system.
I dont want to get into the stuff about whether to leave batteries on charge constantly all the time or not...but suffice to say, if you have healthy batteries, then charging them for the time you are on the boat at weekends, as long as the charger has sufficient current capacity to handle battery charging plus domestic load, will be absolutely fine. This is something we have practised for four years on the boat and for twenty years before that with the caravan, and never had a problem.


Steve.
 
What I have ....

Halfords auto float charger ..... Halfords Auto Charger

2 on-board batterys .... one start at 80 A/hr, other domestic at 110+ A/hr .... both via the 1-B-2-O switch.

Charging also from standard alternator fitted to the Perkins 4-107 ... estimated 40A job.

Split diode box fitted but not connected as alternator is machine sensed and hasn't been converted yet.

Mains supply to sockets via breaker box. Not connected to any item other than the sockets ... so isolated.

Didn't know you were near me at HYCo ... knew about boat across water on other pontoon from me ...

My domestic battery is due for replacement as it must be 10 yrs or more .... start battery is ok - needs better charge regime .....

My biggrst problem is length of time boat sits idle ... have used solar trickle chargers - worked fine - but they all suffered cracked cells after time ... plus of course the starling sh...e from above doesn't help !

My aim is reduce the call on the battery systems by substituting 12v from mains supply ... and laeving the batterys to be charged via possibly the maplins splitter .... I am not really contemplating - unless all other avenues fail - buying another charger ..... Just nice to connect up alongside and enjoy power without being concerned about the batterys ...
 
You have the luxury of being more often at boat ...

My boat stands for months on end .... without use .... secure but idle.

Start batt is about 5 yrs old .... many times been left flat ... charged up again and survived.

Domestic was with the boat when I bought her 8 - 9 yr ago ... and is the last of the two that were on her .. other replaced by above start batt. This is now due to replace ....

I am not too keen on leaving boat on charge alone ... but am interested in reducing call on battery's when I am there - so that they get best charge possibility in short visits I do have .... therefore wish to have charger supplying battery's only.

I disagree partly with the power draw bit .... as .... if charger cannot supply the power required ... it will either click-out due to overload protection or batterys will make up difference. Whatever happens - charger will be called uponto divide its attention and reduced effective charging occurs. Bit like your notebook computer .... switch it off and it charges up quickly, switch it on and multiply charging time considerably.

.....
 
240V stepped down - Don\'t do it!!

Nigel,

Don't do it. Buy a marine battery charger which will achieve everything you want to achieve. There are serious technical issues with what you are proposing - others have covered many or all of those points and I don't want this message to miss getting across the point.........

DON'T DO IT.....DON'T DO IT.....DON'T DO IT....!
 
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