Need some troubleshooting input/suggestions on 24v-12v step down panel

[MRFD715]

I've been tasked with building a 24v-12v step down for an M35A3 our FD is building into a brush truck. I have everything put together, but when I put 24v power to the panel the converter boxes don't like it and get HOT! I've had 3 other people look at it and they're not quite sure what the deal is either. I'm thinking maybe to many Amps to the converters?

This is what I have:



The silver units along the top are the step down converters. The bar on the bottom left is a ground bar, the small busbar to the right of that is 24v power, and the fuse block next to that is where I'm running my 12v power to. The converter units came with no diagram, they are just marked on the back which wires are which. They say maximum output of 20 Amps 12V, do I need to step the input down to 20 Amps? This is the first time I've done a project like this and it's got me stumped. Thanks for any insight/suggestions you can give me!

 

[m38inmaine]

How many amps @12v do you need? would be my first question. Second, when you find that out you can purchase a single unit to step down the voltage, not sure why you combined all those units unless you got them real cheap or for free. Looks over complicated when it doesn't have to be. Another solution is to install a 12v alternator to supply the 12v load.

 

[DieselBob]

I think you might be running into a problem with all the grounds tied together. Most of the time when using converters the output needs to be isolated from the input. That would explain why your converters have two black ground wire. You need to have a separate/isolated buss for the 12V-GND that is not in anyway tied to the chassis/24V-GND. All of the 12V accessories should be connected to the 12V-POS and 12V-GND buss and not to any other GND.

 

[quickfarms]

Are you connecting the converters together of keeping them separate?

The grounds should be separate and the 12 volt circuits should not be chassis grounded

 

[MRFD715]

How many amps @12v do you need? would be my first question. Second, when you find that out you can purchase a single unit to step down the voltage, not sure why you combined all those units unless you got them real cheap or for free. Looks over complicated when it doesn't have to be. Another solution is to install a 12v alternator to supply the 12v load.

I completely agree that it is over complicated. I wanted to get a single unit, but these were cheap so the Chief bought them and told me to figure it out. Sometimes its better to spend a little more.....

 

[MRFD715]

I think you might be running into a problem with all the grounds tied together. Most of the time when using converters the output needs to be isolated from the input. That would explain why your converters have two black ground wire. You need to have a separate/isolated buss for the 12V-GND that is not in anyway tied to the chassis/24V-GND. All of the 12V accessories should be connected to the 12V-POS and 12V-GND buss and not to any other GND.

I obviously don't know as much as I thought I did, I was always taught that ground is ground, voltage didn't matter. I'm betting this is the problem if they need to be isolated. How do i isolate 12v and 24v on the same truck? Can I ground the 24v side to the chassis and the 12v side to the battery?

 

[quickfarms]

I obviously don't know as much as I thought I did, I was always taught that ground is ground, voltage didn't matter. I'm betting this is the problem if they need to be isolated. How do i isolate 12v and 24v on the same truck? Can I ground the 24v side to the chassis and the 12v side to the battery?

For the 12 volt items the hot and negative both go to the converter, do not use a chassis ground.

 

[MRFD715]

For the 12 volt items the hot and negative both go to the converter, do not use a chassis ground.

Ahhhh. That makes sense now. Thank You!

 

[papakb]

Connecting the grounds together shouldn't be a problem and allows you to use the frame as a reference for both the +12 and +24 volt equipment. It's never a good idea to use multiple regulators in a system because there can always be slight differences in their voltage outputs and this can cause serious system problems. Bite the bullet and buy one regulator that will handle all of your electrical current requirements.

A better way to do this is to use a battery equalizer like those made by Vanner. They monitor the 24 volt system and keep the batteries balanced while giving you a 12 volt source for lower voltage equipment.

Kurt
KG6KMJ