Hi there.
Here's the situation. I have a 36Vdc golf cart and I want to run gadgets on 12Vdc. Pretty basic situation. Of course, I can take 2 of the 6Vdc batteries and make a 12Vdc out of them, which is how I'm setup right now. I could say the reason I want to have a converter is to keep the load on the battery balanced, but with my lamps running rarely, it's not really an issue.

No, the reason I want to make one is that... I want to make one for the fun of making one.

Now, on the LM338 spec sheet, there's a lot of examples and they all works. My problem is that, at "low" the batteries gives bout 28V and when charging, they're being pumped at 45Vdc by the charger.
Now, I would like to keep my output at 12V. How to do that?

There was a schematic using a LM318, but I fried it when I cranked my variable power supply over 35V.

Any idea of how to make a DC-DC converter, at 15Amp min, that would give a steady 12 (or 13.8Vdc) output with the input varying from 30 to 45Vdc??

There's always the solution to "unhook" the converter when recharging, but I would like to go witout it.

Regards,
Pierre.

 

Have a look on DC/DC buck converters.

 

You are thinking of a linear regulator.
36V - 12V= 24V.
24V x 15A= a whopping 360W of heat.
Most of the power from the battery is being wasted by making heat which is very inefficient.

Instead make a SMPS which switches the output on and off at a high frequency. It wastes only about 18W making heat.

 

Go to www.national.com, they have many SMPS chips.

 

Digikey and other sell these

The datasheet is linked above. They "ready to go" converters, assembled, tested, in case, etc. The output is isolated to avoid grounding issues as well.

How much current did you need at 12V?

 

Haven't you heard a golf-cart that has a 12V 500W car sound system?
It also has a 12V refrigerator to cool the beer.

 

Haven't you heard a golf-cart that has a 12V 500W car sound system?
It also has a 12V refrigerator to cool the beer.

yes, They even make air conditionning for golf carts...

 

Digikey and other sell these

The datasheet is linked above. They "ready to go" converters, assembled, tested, in case, etc. The output is isolated to avoid grounding issues as well.

How much current did you need at 12V?

Thanks. I looked at those, but all their 12v output is only 5amps.

I would like at leaste 15amps. Just the headlamps at 25W each, draws 4 amps total, and I want to add gadgets.

And like I sait, I would like to "build" one. I can have 15 amps dc-dc for golf catts on Ebay for about $60

 

You are thinking of a linear regulator.
36V - 12V= 24V.
24V x 15A= a whopping 360W of heat.
Most of the power from the battery is being wasted by making heat which is very inefficient.

Instead make a SMPS which switches the output on and off at a high frequency. It wastes only about 18W making heat.

Never heard of that method. Will have to look at it.

 

Do golf carts have headlights because silly people play golf in the dark?
Like blind people?

 

Thanks. I looked at those, but all their 12v output is only 5amps.

I would like at leaste 15amps. Just the headlamps at 25W each, draws 4 amps total, and I want to add gadgets.

And like I sait, I would like to "build" one. I can have 15 amps dc-dc for golf catts on Ebay for about $60

If you can find one for 60$ then buy it. It is at a reasonable price.

 

or use a couple of these on a heat sink

I have plenty to go around

I can send u two if u like for whatever u like plus shipping. kekeke

 

Also have a look at Amtex and Powerbox DC-DC converters. Maybe a little expensive but very reliable and and easy to hook up.

 

Do golf carts have headlights because silly people play golf in the dark?
Like blind people?

Friend of mine has his golf cart pimped out for Recreational use, hauls it along with his RV to drive around campgrounds/run to town/etc.

Sweet paintjob with flames, new rims/tires/suspension/motor/seats, I guess it's not really a golf cart anymore, but it started out as one. Now it's more of a "road rated 4 wheeler" with a bench seat.

 

Don't really know how handy you are building circuits, but I was looking at the LM3150 by National (Simple Switcher Controller, 42V Synchronous Step-Down) IC.

It can take inpur voltages from 6V - 42V and produce output currents as high as 12A. Not sure if it can do 12A at 12V.