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

[andyball]

Re: What I have ....

you said earlier you had chargers - plural? . obviously not connected to the boat - but a spare charger contains much of what you'd need to make a small power supply - wd need a largeish capacitor ( or two smaller is sometimes cheaper) across the output & careful testing of the voltage on & off load. although I suppose if you had another charger you could use that to charge the starter battery on its own.

or buy another halfords charger & devote that to the starter batt. perhaps.

I've only seen commercial versions of what you're aiming for in details of rather larger boats + small volume or one-off "cruising" vessels. But if you made it just the (non-fluorescent) lighting circuits, for example - you could use one of the cheaper domestic "transformers". If you want to be clever - a 240V relay cd change these circuits to use the power supply as soon as 230V is available. prob cheapest to use a straightforward contactor to switch 12V to a cheapy 12V changeover relay... rather than a 240V changeover relay. Or if you did go the DC supply route, have the output of this operating a 12V changeover relay for the lighting circuits.

Having said that - a decent battery ( not a halfbaked one from a scrappy) shouldn't lose that much charge over say a couple of months; so possible that yr budget approach in itself is leading to more budget gear to solve the problems it's created.

The wife says start with an empty fairy liquid bottle & see how it goes. (helpful soul)

 

[stevebirch2002]

Nigel - Bite the bullet

Your approach to budget sailing is great but PLEASE buy a decent float charger (marine) that will do all you ask without any of teh hassle. Try Sterling or Merlin etc. I know you will do it the cheapest way possible but it is not always the best. I dont class myself as a cheque book sailor but I do spend teh money when it is needed. All in my humble opinion and not meant to upset you, honest.

 

[gandy]

Do it

If you build your own, remember that smoothing with a capacitor will give DC equal to the peak voltage, maybe 15 or 16V off a nominal 12V transformer. Sorry if that's teaching you to suck eggs. If you've got bits to lash up, why not give it a try?

 

[Norman_E]

Caution. Maplin unit is unsuitable

I looked at the PDF files on the Maplin site. The instruction sheet for the 5 amp unit clearly states that the unit must not be used to charge lead acid batteries, run light bulbs, or anything containing an electric motor. Makes you wonder just what it can be used for.

 

[john_morris_uk]

Re: Do it

Actually, off load the capacitor will charge up to the root 2 times the rms rated voltage of the transformer. (Really saying the same thing twice here)

ie 1.41421356 x 12 = 16.97052 Volts

 

[William_H]

Re: Do it

If you are going to use just a power supply without batteries paralelled then you must have a regulated supply. As stated by John Morris the DC voltage from 12v AC with capacitors paralelled becomes too high. It is smooth with no AC ripple but that voltage will fall with a load ie switch on a light and it will drop. That leaves you with too high voltage with 1 light on blows bulb to too low with several on too dim)
A regulator is a transistor through which the current passes which increases or decreases resistance automatically so that the output to the load is exactly 12v or 13.75 more usually. The down side to this is that the transistor usually has to dissipate in heat as much as 20% of total power to provide regulation. Great in winter not so good in summer.

The use of a battery in paralell as a regulator is very elegant. It can provide huge amounts of power above the capacity of the transformer rectifier for short periods and soaks up the excess at times of low drain. It is not bad for batteries to be float charged. This is in fact how your car battery operates almost all the time with the alternator providing power to systems with the battery floating across it.
I don't know much about the exotic smart chargers. They appear to be able to provide large charge (at higher voltage) when it senses the battery is low (this gets it charged quickly) then maintans a trickle charge to the battery. I fear as has been suggested that a load on the battery from lights could send it into high charge mode. I may be wrong but if you do this you should monitor the voltage on your lights etc.
The best solution is again the regulated power supply (as described from Maplins or build it yourself). This is exactly the same to the battery as a standard alternator regulator set up. ie it simply presents to the batteery and load a regulated 13.75 volts. The current into the battery depends on the charge state but will be very small when battery is fully charged. Any drain on the systems ie lights turned on will slightly reduce this voltage causing current to flow from the regulated power supply. If the drain rises so that the regulated power supply can no longer provide the current to maintain the 13.75 volts the battery will start to add current until it also falls in voltage.
It is so simpe and good that there is no reason to want to isolate the batteries. The regulated power supply still dissipates heat and power but the thing is you rate the power supply to the long term average of current use. ie 120 watts of lights for 3 hours per day is 15 watts average. double this for inefficiencies and you need 30 watts or 2.5 amp regulated power supply as a charger/ supply. (for 10 amps of lights)
This obviously will not charge your batteries if they are flat very quiickly. But it will maintain the whole system and could provide 100 Amp hours of battery charge in 40 hours.
If however your battery charger is a regulated type (ie Ok to leave on permanently)then it should do the job nicely if left on the batteries costantly.
In other words do nothing just monitor current into the batteries and from the charger and system voltage. You can not do any better. You must be convinced by now. good luck olewill

 

[steverow]

Re: You have the luxury of being more often at boat ...

Nigel,

Yes, Sorry, I should have realised you were in the Baltic for months at a time.

Have you thought about a charger plugged into a timeswitch, set to come on for a few hours each week.
This should keep the batteries topped up, is uncomplicated and relatively safe.
Put some fuses into the DC output of the charger as well as the mains fuse.
For additional safety make up a lead that plugs the charger directly into the socket on the pontoon, thereby isolating the rest of the boats 240V circuit.
If you want to make it Brick external khazi safety proof, use an isolation transformer as well.

What you are describing is the worst case for batteries.
They should be kept as fully charged as possible. Allowing them to run down slowly without recharge will allow the plates to deteriorate much quicker than they otherwise would.

Will PM you tomorrow abt a plotting issue.

Cheers

Steve.

 

[Guest]

Chargers .... plural ...

I have the Halfords Auto charger as indicated with automatic float facility .... stays on boat in locker...... ready to do duty.

The other charger is non-float connect for one day job and disconnect manually. But that stays with my UK car ... just in case.

 

[Guest]

Ok .... OK ..... OK ..... You lot win !!!

I will amend my plan and probably use the timeswitch and flaot charger again ..... I did this before but wasn't too happy about leaving it connected while away. I've asked various electrical people I know and near all have said "Why not ..... its designed to do it - so plug and forget ...."

I haven't completely given up on switching the cabin-lights over though to 12v supply from mains ... but will leave most circuits to the battery system as the thread indicates ....

As to buying a marine charger .... its interesting that when I showed the spec and details of a comparison to a guy over here - he laughed and reckoned that apart from maybe a few better quality components and higher output - there isn't that much difference ........... as he said - Nigel you have enough kit as it is to do the job ....

So roll on spring - then its boating time again ....

Many thanks to all - please don't think I have ignorted ANY post - not true ... I have read them all with great interest and value all views / comments. This thread has been very good with NO snide or rude posts etc. Excellent.

 

[Guest]

I will post my final installation ...

Once I have done the installation and all is up and running - I will post a full description.

Thanks again and Happy New Year to all ....

 

[Graham_Wright]

Re: Nigel - Bite the bullet

I don't know but isn't the raw output from a switched mode charger (Stirling etc) pretty rough?

I wouldn't like to run any computer gear from that if so. With a battery across the output as well, I guess it will be much smoother.