24V-12V adaptor

[phoenix]

I don't know if anyone has tried this yet, but it seems like everyone is stuck on those 24V-12V converters. I dont know how expensive or complicated they are, but I am sure that they are limited when it comes to amperage. I have a possible simple and cheap solution to everyones problems on this.

A DIODE is a device that is made to only allow current to flow in one direction. Think of it as a one way valve. The voltage moves through the diode only in one direction.

There is a line printed on the body of the device and the line is hooked up on the side closer to the device you are trying to run. Now, there is another side effect of the diode-- It will DROP .7 volts when the power goes through it. So, if I put 24V through a diode, I would end up with 23.3 volts on the other side of it. Now, if you put 17 diodes in series, and connected the 24 volts to it, you will end up with 12 volts. It may be a little off, so you may need to use a few more or less.

You could potentially run your whole truck like this, but you have to remember one thing. A diode has an amperage rating. You need a bigger diode to run something that requires more amperage. if you need 12 volts for an ignition or something, you could get away with some diodes that Radio Shack sells. Mouser catalog has a bunch of electronics components also. I have done this on some smaller projects converting 12V to 6V.

There is also a different diode called a schotkey diode that can be used as a singe diode to change a voltage. So if I used a Schotkey diode, I could use it to convert 24V to 12V with only one diode, but it will only handle a few miliamps. I have used these before to allow me to use a silver oxide battery in an old Minolta camera that needed a mercury battery that is not sold any more. The silver oxide battery is a little higher voltage, so The Schotkey diode regulates the voltage to the camera so the exposure meter reads correctly. Not exactally what we are looking for unless it could MAYBE be used for a single gauge or something. I realy don't want to build one, since I have converted to 12V already but I could help someone if they want to make one.

Since I have only used this to run a small device and not for a larger amp draw, maybe Rboltz could also chime in. I think I read somewhere he is an Electrical Engineer. I am just a lowly Electronics Engineer.

[k8icu]

Though that would work...it would be better to get a voltage regulating transistor or IC. You can get one to handle the amps you want plus it will regulate the voltage. In other words if you drop to say 23 volts for some reason the regulator will still produce 12V instead of 11. A better and IMHO Safer set up.

[randyscycle]

For about $159 there's a guy on SS that sells Voltage reducers that are capable of up to 35A.

Another issue with anything like you described is heat. And lots of it. All the voltage reducers they sell have very large heat sinks on them to disappate any excess heat under load.

In short there isn't an easy or cheap way to get 12 volts from a 24V vehicle without discharging one battery more than the other, or putting together a dangerous contraption subject to meltdown in the cab or engine compartment.

Oh, and for $30 I picked up a 24-12V 10 amp reducer to run my gauges. Wasn't even worth making it for that price.

[rboltz]

Though that would work...it would be better to get a voltage regulating transistor or IC. You can get one to handle the amps you want plus it will regulate the voltage. In other words if you drop to say 23 volts for some reason the regulator will still produce 12V instead of 11. A better and IMHO Safer set up.

You can build a 24-12 regulator with a few pass transistors and a regulator IC or zener reference, BUT, you will be limited. I built one years ago that does 15 amps with lots of heat sinking. Don't know what commercial units cost but it may be a better deal to buy one.

[gimpyrobb]

I got a buddy on SS that is selling AMERICAN made 24-12v converters rated at 30amps. I have one and it is great. It can also support keeping a battery charged. $180 or 190 was the price I got it for. Let me know if you want contact info.

[gimpyrobb]

Sorry Randy, just saw your post.

[phoenix]

Yeah, I know about the heat it generates, that is not a problem with a heat sink. I just looked up some diodes at Mouser, There are some there that cost $6.44 each if you bought 10 or more. You probably could get some surplus diodes for a lot less. you may have less than 120 dollars into it and it will reliably give you 60 amps or more depending on what diode you choose and how many you want to purchase. They have one that will handle 100 amps. Sure you could go a lot cheaper if you only wanted 35 amps, You can get those diodes at radio shack.

I have built many many power supplies before with the ICs or TO- 220 case or a TO-3 case, but it cost a fortune to make one that supplies more than 15-20 amps. In that case, its cheaper to buy it than make it.

This diode method is dirt simple to build. As far as the voltage droping to 11 volts or so, for one, the alternator controls what the voltage is when the vehicle is running. The alternator will keep the battery charged at a couple of volts above what it is rated. So the alternator is actually puting out about 26-29 volts for a 24 volt battery so if the alternator would allow the system to dip to 22 volts then your current system would have a melt down right? No not really, so if this new diode system is mearly droping the extra 12 volts, it would be exactally the same thing as a 12 volt alternator would do with a 12 volt system.

As I said before, I don't need to build one of these since I won't be needing it. I just put it out there if someone wants to make one. If someone wants help building one, let me know.

[rboltz]

I was looking for some other items and came across these on the same site. Reasonably priced 24 to 12 volt DC-DC converters. They even have isolated units.

http://www.powerstream.com/dc1.htm