Hi,
On my boat I have a 24v to 12v converter and from the 12v out it goes into this circuit, left connector, and the from the right connector i used to get 12v (but an 10 ohm resistance has be burnt and some thing else, that something I don’t know what is)

I possible I need help with two things,

1: why is this circuit needed
2: anyone that can help me identify the burned components

Thanks in advance.

Dennis

 

Welcome to AAC!

2: anyone that can help me identify the burned components

A diode and the other looks like a resistor.

It would be helpful if you marked the components in question so we can be more certain about what you're referring to.

 

You may want to check the two power devices BD249 NPN power transistors.
Max.

 

Welcome to AAC!

A diode and the other looks like a resistor.

It would be helpful if you marked the components in question so we can be more certain about what you're referring to.

I think you got it, the two components that have visible burnt black surface around them

 

You may want to check the two power devices BD249 NPN power transistors.
Max.

Got it,
Will do.
Any pointers why this circuit is needed ?

 

Looks like a power supply or power converter, but like Max mentioned, lookup the transistors and you might find out.

Got it,
Will do.
Any pointers why this circuit is needed ?

 

The burned part near the big transistor was almost certainly the same as the one that isn't burned on the other transistor - a 10 ±5% ohm power resistor that looks very like a Philips PR02 2 watt metal film.

The one near the small transistor looks like it was a diode. My guess is it was an ordinary silicon diode rated at 2 to 3 amperes, but there is some chance it was a zener-type transient suppressor or an ordinary zener dode. You might be able to read at least part of the part number if you remove it from the board.

I would check all of the transistors, looking for short circuiting.

Note the small resistor (red red something gold) below the transistor below the fried diode has been overtoasted. It may be OK

The circuit is probably just a fairly ordinary linear voltage regulator.

 

It could be a good exercise for you to trace the circuit out.
This should not be too hard to do as it is all visible, and it will help you understand the circuit function.

 

The burned part near the big transistor was almost certainly the same as the one that isn't burned on the other transistor - a 10 ±5% ohm power resistor that looks very like a Philips PR02 2 watt metal film.

The one near the small transistor looks like it was a diode. My guess is it was an ordinary silicon diode rated at 2 to 3 amperes, but there is some chance it was a zener-type transient suppressor or an ordinary zener dode. You might be able to read at least part of the part number if you remove it from the board.

I would check all of the transistors, looking for short circuiting.

Note the small resistor (red red something gold) below the transistor below the fried diode has been overtoasted. It may be OK

The circuit is probably just a fairly ordinary linear voltage regulator.

Thanks

Any idea why this is added just after the 24v to 12v converter ?
I have instruments (all 12v) being powered from the converter directly and others from the output from this circuit.
What I cannot understand is why is this needed, why not just power all instruments directly from the converter.

I understand that looking up BD249a will give me some clue of why, but the totally newbee that I am,
Reading the data sheet didn’t help me

And btw. if I can get this identified, maybe a newer (simpler) model can replace the complete circuit. ( I understand that identifieng this fist is key )

 

I think it will be a good idea to replace this with a switch mode regulator as this one will be very lossy.
One of the burnt resistors, on the base of the BD249, will be the same as the other base resistor.
As for the burnt collector resistor on the smaller transistor that is mounter up side down, it too could be about 100R.
What does this drive? Is there maybe a 9V or 6V supply needed?

 

I think it will be a good idea to replace this with a switch mode regulator as this one will be very lossy.
One of the burnt resistors, on the base of the BD249, will be the same as the other base resistor.
As for the burnt collector resistor on the smaller transistor that is mounter up side down, it too could be about 100R.
What does this drive? Is there maybe a 9V or 6V supply needed?

It drives 12v instruments on my boat. While this circuit has been burnt I have bybassed it with only only instrument directly to the 24v to 12v converter. And That works perfectly.

This is why I am really puzzled.

 

Are you sure this is fed from the 12V and not the 24V?

 

Hi,
On my boat I have a 24v to 12v converter and from the 12v out it goes into this circuit, left connector, and the from the right connector i used to get 12v (but an 10 ohm resistance has be burnt and some thing else, that something I don’t know what is)

I possible I need help with two things,

1: why is this circuit needed
2: anyone that can help me identify the burned components

Thanks in advance.

Dennis

This is a simple voltage regulator, with current limit, here is what i think the circuit is , the resistors have burned out and will have taken the transistor also. If you can look at the two transistors faced down and the value of the preset to get a full idea of the circuit.

Personally i would remove it and replace it with a better Buck regulator like LM2596 series

 

View attachment 156266

This is a simple voltage regulator, with current limit, here is what i think the circuit is , the resistors have burned out and will have taken the transistor also. If you can look at the two transistors faced down and the value of the preset to get a full idea of the circuit.

Personally i would remove it and replace it with a better Buck regulator like LM2596 series .View attachment 156265

WOW - really really nice information and thanks for the diagram, do you have any idea why this is added after the 24v to 12v converter?

 

Only for a lower voltage than 12V, with current limit.

 

Hi everybody, and thank you so much for this support

@dendad you were right from the beginning. My newbee eyes didn’t follow the correct power source, so yes infact it was/is 24v to 12v apparently I have two step down converters both of them using bd249a types

@Dodgydave thank you so much for the diagram it helped me to understand that I most certainly have made some assumptions that wasn’t correct
Your recommendation to change to a buck converter is this still true if we have autopilot circuit nearby. I have read something about noise emiting from buck converters.

Everyone else thanks, I already love this forum, the level of support is fantastic

 

I would be very cautious with low-cost switchmode convertrs around radio or other sensitive equipment. Most of those I've seen have nothing for radio frequency interference suppression. Something from a reputable name-brand manufacturer would likely be OK, but I'd stay well away from ebay sources.

 

I would be very cautious with low-cost switchmode convertrs around radio or other sensitive equipment. Most of those I've seen have nothing for radio frequency interference suppression. Something from a reputable name-brand manufacturer would likely be OK, but I'd stay well away from ebay sources.

Understood any suggestions, I need 24v to 12v ?

 

What is the current rating u need?

 

What is the current rating u need?

@R!f@@ I need it to support my 12v instruments from my 24v powersource - and I need enough amps available to change different devices at the same time - if this means I need more than one then buck converter then OK - i have the space for it

by charging i mean, able to change different mobile and tablets from an normal car socket to usb plug.. makes sense?