I have a boost converter that i want to use to step up the voltage from 12v to 15v.
(https://surplustronics.co.nz/products/7589-step-up-power-module-dc-dc-boost-converter)
my power supply is 12v 12.5A, and the maximum input current is 4A. to solve this, I have a 1.5ohm resistor in parallel with the converter. (see attached diagram) when I try adjust the voltage, nothing happens, and so far i have burnt out 2 boards. can anyone tell me how to use one of these? any help would be much appreciated.
-Rob

 

Why do you have the 1.5R resistor there? It is just wasting power.
You do not need to run your 12V power supply at 12.5A, in fact, that is a bad idea. The boost converter will only draw what is needs.
Also, the boost converter you are trying to use cannot supply 5A, that is what a 3R resistor will draw on 15V.
You will need a quite bigger boost converter for your job.
If you want 5A, get one rated at 10A or more. It is never wise to run things at their max rating. Keep some headroom.

I just spotted this one on Ebay. Note> I have not used one myself so do not know how it performs.

 

Welcome to AAC!

Remove both resistors and try again.

 

Welcome to AAC!

Remove both resistors and try again.

the 3ohm resistor is the component i need to power (i just drew a resistor for simplicity) I justtried without the 1.5ohm resistor, and just burnt my third and last one

 

I said, remove both resistors and you ignored what I said.
You are attempting to supply 5A @ 15V which the converter cannot do. So it burns up!

 

I said, remove both resistors and you ignored what I said.
You are attempting to supply 5A @ 15V which the converter cannot do. So it burns up!

I can see that working. if i had removed both resistors, i would be able to get this converter working, however, I need a higher amperage than this converter can supply, or in other words, i need a higher rated converter.
so now i have a new problem: what step up converter to get.
the 3ohn resistor is actually nichrome wire. i need it to be 15V at about 6A (90 Watts) this will get the wire to ~200C.
how do I know how much current the wire will draw? wont it just draw as much as it can until the converter breaks?

 

so get a 15V 100W PSU.
Beats buying a converter

 

You may do better to run a constant current supply for the wire.
But have you had a look for a boost converter similar to the one in post #2?

 

so get a 15V 100W PSU.
Beats buying a converter

i am on a budget, and this power supply proves useful for the other components of this project like motors etc

 

You may do better to run a constant current supply for the wire.
But have you had a look for a boost converter similar to the one in post #2?

had a little look, but theyre pretty hard to get in NZ. how do I get/make a current limiter?

 

What is your application in detail? That could help to get better answers.
One power supply you may be able to press into use could be a 19V laptop power supply. They are often available for free from dead laptops. But, whatever yo find, get one that is rated a bit bigger that you need.

 

You don’t need a boost converter or even a regulated DC power supply.
Just get a 15VAC 100W transformer and a light dimmer switch.

 

whats a constant current supply??

The supplies you are using are designed to keep the output voltage at a constant value.
The other type is to keep the output current constant. That may work better for heating your wire.
It is probably something you would have to make, or at least modify to suit, so you may find it easier to just go with a constant voltage one.
EDIT: I just saw @MrChips comment above and that makes sense.

 

Oh, one common use for a constant current supply is an LED driver. LEDs are current devices, not voltage. So, for best LED life and performance, the current needs to be controlled. In a constant current supply, you can hook one suitable LED on and it will work, then also, add more LEDs in SERIES up to the max capabilities of the supply and it will still drive the same current through the LEDs. The supply alters the output voltage to keep the current at the set value.

 

What is your application in detail? That could help to get better answers.
One power supply you may be able to press into use could be a 19V laptop power supply. They are often available for free from dead laptops. But, whatever yo find, get one that is rated a bit bigger that you need.

I am makign a machine to melt PLA plastic. this means i need it to get to about 200C. I have 3 pieces of 9ohm nichrome in series, to make a resistance of 3 ohms. this need to get 15v and 6A to get to 200C. there are other 12v motors to turn things. I would like to avoid using a laptop power supply, in order to not have to take up 2 wall outlets, and I also want to control the temperature, so i need access to the circuit, and dont want to make it complicated with seperate circuits and relays etc.

i think what i need is a current limiter? a circuit that dosent allow the converter to draw more than 6A

 

What is your 12V power supply?
Is it a linear regulated one or a switch mode?
If linear and it has a mains transformer, you may be able to use the AC from it. Whatever you do, make sure to include a fuse or 2.
And, if you have 3 lengths of 9R wire, you will have them in parallel to get 3 R. If in series, the result will be 27R.
You could have had one boost converter running each wire and that would have worked. So, 3 boost converters and 3 wires. 1.6A each is well within the boost converter's range.
just the same, place a small 12V fan blowing on them.

 

Why can’t you use a thinner piece of wire?

 

What is your 12V power supply?
Is it a linear regulated one or a switch mode?
If linear and it has a mains transformer, you may be able to use the AC from it. Whatever you do, make sure to include a fuse or 2.
And, if you have 3 lengths of 9R wire, you will have them in parallel to get 3 R. If in series, the result will be 27R.
You could have had one boost converter running each wire and that would have worked. So, 3 boost converters and 3 wires. 1.6A each is well within the boost converter's range.
just the same, place a small 12V fan blowing on them.

Im not sure what you mean by regulated or switch mode.
they 3 lengths of 9R wire are in parallel not series. (i made a mistake)
if i use 3 boost converters for 3 wires, how do I know how much current they will draw? wont it just draw as much current as it can and the burn the converter?

 

Why can’t you use a thinner piece of wire?

i think that would just act as a fuse and burn up straight away

 

if i use 3 boost converters for 3 wires, how do I know how much current they will draw? wont it just draw as much current as it can and the burn the converter?

Ok. You need to learn some Ohms law.
The amount of current the wire will draw is determined by the voltage applied and the wire resistance.
So, you say each wire is 9 Ohms.
The supply voltage is 15 Volts.
Therefore, the current = 15/9 (Voltage over Current) = 1.67Amps.
It does not matter if you have 3 wired in parallel, EACH wire will draw 1.67Amps from a 15V supply.
That is why I reckon you just need to use 3 SEPARATE boost converters if you want to stay with those, one for each wire.

A common mistake we see is folk tend to think if you put a load on a 12V 100Amp power supply for instance, it will draw 100Amps.
That is not the case. If the load was, say 12 Ohms, it will only dray 1Amp on a 12V supply. But a 100Amp supply can drive 100 of these loads while a 1Amp version can only drive one.
The load will only take the current it needs, dependent on the supply voltage and the load resistance.
Just think of your car battery. It is capable of supplying a couple of hundred Amps for starting. But a 15Watt tail light only draws a bit over an amp.
As an exercise, look up Ohms law and work out what current a 15Watt 12V lamp will draw.
Electronics is really a fun thing to get into, and Ohms law is one of the main foundations. Have a look for some good tutorials and you will find it is really handy to know.
For instance...
https://www.allaboutcircuits.com/textbook/direct-current/