12V from a 24V system

Scary Des · 15 October 2003, 07:47

I suspect this has been discussed before and I am probably being stupid but what I can not understand is why, with a 24V setup, you can not get 12V by taking a feed in parallel from each battery. In other words + to + - to - for 12V. + to - for 24V. In the past I know there has been talk of 24V to 12V converters but these are expensive and another thing to go wrong. Can anyone help?

Richard B · 15 October 2003, 08:55

Your split 12/24 circuit is OK as long as your 12volt devices take zero power. If (when!) they take any power, they will produce a voltage drop on the 24v circuit.

Pete7 · 15 October 2003, 10:25

Des, I did try a converter recently but the interference on the VHF and echo sounder was awful. In addition the GPS was not happy. So for the moment they run off one battery and the 24v engine runs off the two. Have been advised that this will eventually wreck the battery with the 12v supply, however I can buy lots of batteries for the priceof some of the converters and its another thing to go wrong. How far are you navigating without GPS/Echo sounder/compass lights ? hmm.

Pete

Garygee · 15 October 2003, 10:25

DONT DO THAT !!!!

you get 24V from two batteries by connecting the -ve of one battery to the +ve of the other then take the 24V from the +ve of one battery and the -ve of the other.

-ve feed----veXXXXX+ve---------veXXXXX+ve---+ve feed

Now if you take the +ve of both cell and the -ve of both cells and connect then together you end up shorting out both cells

If you boat suvives the fire from burning wire you will end up with flat batteries

If you want 12V either use a 24 to 12V converter or power the item from the battery which is connectrd to the boat -ve and supply the item from that battery +ve only.

ake sure you connect the item -ve to the battery -ve which is connected to the boat -ve. If you get the wrong battery you will end up with the item -ve at +12v in respect to the boat which can cause lots of problems.

Regards Gary

Scary Des · 15 October 2003, 11:47

Thank Gary, I knew there must be some reason. As luck would have it I have connected to the -ve boat, the gods were smiling on me with that one. However I do find that this does draw down the single battery. I've got GPS, VHS and Fish on 12V so the drain is not great, but it did flatten the battery the other day which is the reason for my question. These are difficult boat to jump start and bump starting is almost imposable!!

Pete, as a fellow Pac22 owner you might be able to help, on the right side of the consul beside the charging plug is a two pin plug that my volt meter tells is 12V is this the same on yours or is my volt meter lying (wont be the first time)

Des

J C Hughes · 15 October 2003, 14:01

Why do you have dual voltage in the boat is it because your engine has a 24v system and your auxiliaries all run off 12volts, if so is it not better to change your alternator and starter motor two 12v type, just a thought!!

Pete7 · 16 October 2003, 09:17

Des, think thats the special ops plug that is used for aux power supply. I don't have one anymore as I changed the console to side by side.

JC, thats big bills, and the stern drive trim motor, fuel gauge, and instruments would also need changing. Since the block is a ford truck engine the cost of 24v spares shouldn't be expensive, hopefully, fingers crossed.

Pete