Battery question

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bopbargains, Jun 18, 6:57am
I need a 12v, high amp power supply and I thought a car battery would do the job. Is the any way of reducing the voltage down to a consent 12 volts.

tmenz, Jun 18, 7:07am
Yes - but to do this reliably and consistently you will need to use a DC-DC regulated converter to convert the battery's nominal 10~14 volts (flat ~ fully charged) to a constant 12 volts.
Can you clarify just what you want to do!
Do you need a completely portable solution - hence the battery - or do you have mains available!
What current/power capacity do you need! Are you needing 10s of amps, 100s of amps or what!
If you have mains available, a regulated power supply would be the best option.

bopbargains, Jun 18, 7:16am
Hi. Thanks for the answer. Yes, I do have a transformer (25 amp constant-35 peak) at the moment, but I need more amps. Somewhere around the 40amp would be great. To buy a new 40 amp transformer is about $450, so a car battery would (should) work out a lot cheaper. It's for a slot car set.

tmenz, Jun 18, 7:18am
Wow, how many slot cars are you running!
Way back when I played with slot cars we had 6 tracks and they drew about an amp each!

bopbargains, Jun 18, 7:28am
Just a 3 lane track. Under load our normal motors (58,000 rpm)draw about 5-7 amps, so it is just coping, but the open class will draw a lot more (they sound like a high pitch dentist drill).

tmenz, Jun 18, 7:31am
Drawing 40 amps from a car batterywill soon flatten it, so it will need a 40 amp charger across it to make up the power draw. (A truck size battery would be better).
Assuming that the battery/charger combination will 'float' at about 14 volts and you want a constant 12 volts for the track, then it is feasible to put in a linear regulator to do this.
BUT, the combined cost of the battery, a 40 amp charger and a 40 amp custom linear regulator is likely to be more than a straight 40 amp power supply!
12v 40A regulated supplies are a bit hard to find and are Expensive.
It's possible to use lesser supplies, say 2 x 20A in parallel but they're still going to be Expensive.
Have a look at this site:

bopbargains, Jun 18, 7:38am
Hmmm. Thanks for your answers. Looks like I better start saving then. Or would this work. If I get another 25 amp transformer (about $250) and joined them in series (they have a adjustable voltage), would that give me 12 volts @ 50 amps (6 volts/25 amp x 2)

m16d, Jun 18, 7:42am
Crikey,if the cars are sucking that many amps maybe you should re engine them and up the voltage to 240v.

bopbargains, Jun 18, 7:53am
Cheap. That's me. How would I go about doing that!.

tmenz, Jun 18, 7:54am
Ah, no!
Putting them in series like that gives 12 volts @ 25 amps so you haven't gained anything.
What you need to do is put them in parallel - 2 x 12 volts @ 25 amp in parallel gives 12 volt @ 50 amps.
BUT! In order to successfully parallel 2 power supplies requires that the supplies are essentially identical in output parameters and regulation characteristics, otherwise they will not share the load equally and the more heavily loaded one will fail, followed closely by the other!
Usually, to be successful in this requires 2 identical supplies designed for parallel operation, set accurately to the required voltage and isolated from each other by diodes.

twaymouth, Jun 18, 7:56am
Also check this out: not sure of the price but it may not be to bad. This page: describes how to use a pc power supply. It may be best to get an old one and have a go at converting it before buying a new one.

tmenz, Jun 18, 8:01am
Have a look at these!z=p&p=PSUANT0650&name=Antec-EA-650-Power-Supply-80-PLUS-certified--120mm

I'm not sure if you can successfully parallel the 3 x 12 volt outputs to get what you want!
I also suspect that you can't draw the maximum from all 3 x 12 volt rails at the same time - I think there's a total power limit.
On the other hand, they're cheap!

bopbargains, Jun 18, 8:03am
C00L It gives me something to think about. Thanks for all your help.

tmenz, Jun 18, 8:09am
I'd be interested in knowing what this supply is priced at.
I've had to deal with similar Astec parallel supply 'bricks' in the past and I know they cost around $2500 each!

tmenz, Jun 18, 8:17am
Or this one:!z=p&p=PSUCLM1650&name=COOLER-MASTER-GX-650W-PSU--Single-+12V-rail-for-up

You'll be able to turn off the lights and race the cars by the light of the glowing tracks!

As a matter of interest, where do you have your racetrack - when I raced slot cars many many moons ago it was on a track in rooms above a dairy in Otumoetai.

taipan4, Jun 18, 8:20am
get hold of an old arc welder and throw some heavy diodes on the low volt outputwith perhaps a bit of cap for some smoothingI would probably go for a lincoln or similar as I have one and they are totally maINS ISOLATED MINE IS ESSENTIALLY 2 separate coils on a common laminated steel core & current
is varied by moving one coil in relation to the other you couild throw a variac onto the mains input to vary voltage output, do not use the variac by itself as these are essentially an auto tranny & not totally isolated from mains

skin1235, Jun 18, 8:26am
aren't they 24 or more V, some even pump 48V

audi_s_ate, Jun 18, 8:26am
Computer powersupply is the go here. My one I have here runs 35a x 2 rails and is 12.02v very consistently. It will be a fraction of the cost of a dedicated 12v supply.
I have built one to power a lipo rc car charger and it took a resistor and half an hour max. Heaps of guides online.

taipan4, Jun 18, 8:28am
read my post vary voltage with a variac heaps of amps available

electro2000, Jun 18, 9:06am
Christ it's not that hard12 volts how many amps do you want , Werun 3000 watt 13.8 voltrack mount psu'sAnd that's a small supply in the telco game!page=shop.product_details&flypage=flypage.tpl&product_id=93&category_id=4&option=com_virtuemart&Itemid=2
These are $380 . There switch mode so no horribleheavy linear stuff .We get a lot of psu's from these guys spend a heap every year .

ralphdog1, Jun 18, 9:13am
How about running a seperate supply for each track, then you are only looking for around 15A per supply

bopbargains, Jun 18, 8:09pm
You might know some of the older guys then. have a look at this link as it has a bit of history of racing in TGA. Youmight even find yourself in thephoto. I haven't done much to my web site as I'm been busy build the new track, but here is the link to the main one as well

tmenz, Jun 18, 9:13pm
Hell, yeah!
I was a founder member of the Brookfield club. I still have the BOP Photo News with those photos in it. I'm not in those photos but I was in another that was published.
I was one of the ones who travelled to Whakatane and Matamata for the interclub events.
Ah - the good old days!

74nova, Jun 18, 10:57pm
Why don't you just hook up a deep cycle 12V car battery on a smart charger to keep it topped up. Why is the constant 12V so important! 13-14V wont damage anything just make things alittle faster!

bopbargains, Jun 19, 10:03pm
tmenz .with this power supply is it a simple job to wire up.!z=p&p=PSUCLM1650&name=COOLER-MASTER-GX-650W-PSU--Single-+12V-rail-for-up
when they say 400W is that make it 12v @ 400amps
would I be better getting 3 smaller ones and having 1 for each lane.
thanks for your help. Trevor.