Any know wher I can get a 12volt to 6 volt transformer......
 

For an 50yr old car that i'm thinking of rebuilding, it's currently 6v, but I would like to rewire it to 12volt, but some of the equipment cannot be replaced due to being too rare, so therefore i'd need to run a dual voltage system...... could be a tad complicated, but it must be do-able, manily the charging, starting, lighting and convenince things that need to be 12volt......

Ron.

2 x 6v batteries ( YUASA/motorbike derived ) wired thusly :


http://www.maj.clara.net/crapdrawing.jpg

http://bbs.scoobynet.co.uk/images/icons/icon14.gif

Could do that, didn't really want to though, not too much space to play with........

you could do it with a big fcuk resistor. What bits are 6v?

forgot to say.... 2 x 6v batteries should sit in the space you have and if you size them correctly should give you enough cranking amps. I saw a guy the other day with a 2.0L turbo westfield - the battery ( 12V ) was tiny in comparison to the normal ones.

There's the problem, the original 6v battery is quite big, the engine is an old 3.6 ltr flathead V8! the original wiring is falling apart, and there's not a single fuse in the car!! there are lote of bi-metalic strips though! wipers, heater blower, and ignition may not be able to be changed to 12volt!

The way you have that wired currently it would blow up! :eek:

any big meaty loads will mean you have to have a dobber of a power supply/ trannie = bulky/ expensive. 2 x 6v batteries will give you 2 big dobbing power supplies, for the 12v circuit you are just using them both at once.

I cant say I know much about auto electrics, I had a quick look at RS, there doesent seem to be anything to suit.
what voltage is the alternator?

Try this:

http://img2.uploadimages.net/936481crapdrawing2.jpg

?


naaahh.

yuuuhuh! ;)

ajm`s diagram makes better sense to me.

apologies, I am choking on humble pie here ( yer bastad ;) ) - you are quite right, I nearley killed RON with some *stella* fuelled internet bad advice :(



one battery link too many :D

RON - ignore anything I post about batteries from now on :D

There is no alternator, it has a dynamo!! i would change that to 12 volt aswell........ it's a massive job though, the car has more switches and things than a supercar of today......... gulp!

LOL :D

ajm's diagram is correct, that'll do the job.

The scary thing is, when i first looked at the original picture i couldn't see anything wrong with it.

BTW, i'm an electronics engineer. :eek: :freak3:

Time for some sleep i think. :)

http://bbs.scoobynet.co.uk/images/icons/icon14.gif- ta :)

Nor could I, good job I didn't have two batteries to hand......

What needs to be 6V? Do you have any idea how much power is required?

I think you'd be better off with a conventional 12V battery and a DC/DC converter to power your 6V accessories. You could even run a separate 6V battery and charge it from the mains in between journeys - presumably the car isn't going to get all that much use.

ps. the first diagram does indeed show about the best way to destroy a pair of lead-acid batteries in a cloud of acid vapour and steam. Not a good idea :)

Thanks all, I think I need a specialist auto electrician.... one that specialises in classics......

:eek:

I hereby promise never to offer electrical *advice* after booze again. :o

shocking :)

Laying off the African Mumbo weed at the moment then? ;)

sort of - "her indoors" has confiscated it :mad:



though I have a secret stash in the cellar :norty:

There's a place called CPC Batteries in Twickenham (google says phone 020 8898 6972) which I used when I had the dutton. It had a tiny battery compartment, and kept killing the new batteries I kept putting in. When I went there I said I need a battery that starts a Ford Kent engine and fits these dimensions. Turns out a Kent needs a lot of cranking power and the Mini batteries I was buying off the shelf just couldn't handle it!!

Chap looked up the requirements on a chart, found an appropriate battery and sold it to me at a respectable price. I never needed another one.

They've always stuck in my mind as a useful place to know, after that :)

wouldnt it be less hassle to lob a 12 volt battery in and take a feed to all the circuits requiring 12 v then take another feed to a 6v or variable voltage transformer (clairtronic sell these)to power the 6v circuits. on your diagram there you have a wire connected straight from live to neutral still.

I was hoping to do it with just the one 12volt battery, and then use a single feed for the 6 volt.... still thinking.....

You can't transform dc, you need a switched mode PSU or dc/dc converter to produce a steady 6V from a 12V supply. You also need to know how much power will be required from the 6V supply before you can choose an appropriate converter.

Dam, you beat me to it ;)

It should be perfectly possibly with current DC-DC converters but they are usually made to power computers & electronics rather than motors etc. so tend to give 3.3 or 5v DC outputs.

You may be able to use a much simpler solution if the current requirement is less than 5A. A 7805 Voltage regulator, with a couple of diodes will give you a 6v output at 1-2A depending on the model and a suitable heatsink. This little baby http://www.farnell.com/datasheets/55775.pdf can handle larger currents up to 5A and they cost 78p each.:D If you need more than 5A in total you can always have several of these, one for each 6V circuit.

If you need a hand understanding it all, just give us a shout.

What type of car is it? Is it negative earth already?

ok smarty pants i fooooked up a dcdc converter then that will give ya a regulated 6v from a 12v supply im off for a beer my brain hurts:)

I knew that, that's why I suggested 2 batteries. :p