Help with DC/DC converter to boost voltage

Thread Starter

NickB

Joined Feb 1, 2016
88
Hi guys

I’d like to use a DC/DC converter in a simple circuit I’m prototyping but am struggling to get it to work and wondered if someone could help. I’ll provide as much detail as I can but I’m a beginner so bear with me.

The project I’m building uses an EM coil to move objects with hidden magnets in them. The coil is 375 winds of 26SWG. The circuit will be operated via remote control so the coil will only be on for a fraction of a second. Ideally I want to power the project using 4 x AAAs and am using the DC/DC converter below to get 72v into the coil.

https://power.murata.com/en/nmt0572sc.html

I’ve tried it once but think I fried the converter by hooking it up incorrectly as it just got very hot and now it’s unresponsive. I’m also concerned the flyback from the coil will damage the converter although I understand the internals are isolated. I’ve attached a diagram of what I’m thinking – can anyone give me any pointers as to where I may be going wrong?

I don’t want to trash another converter as it’s expensive at £10 a pop! Any help greatly appreciated.

Cheers!Converter circuit.jpg
 

LesJones

Joined Jan 8, 2017
2,641
What is the resistance of the coil ? Unless it is a very large diameter I think the resistane will be too low. The converter you linked to ia rated at 3 watts output. As you have the 72 volt version that meant it's maximum output current will be 41.6 mA. So for it to be working withinn it's ratings the coil resistance must be at least 1728 ohms. You term fraction of a second in not very meaningful. It could mean anything from less than a picosecond up to 0.99 of a second. What is the actual time you require ? What will be the time betwen pulses ? It might just be possible to achieve by storing energy in a capacitor and discharging it into the coil.

Les.
 

Thread Starter

NickB

Joined Feb 1, 2016
88
What is the resistance of the coil ? Unless it is a very large diameter I think the resistane will be too low. The converter you linked to ia rated at 3 watts output. As you have the 72 volt version that meant it's maximum output current will be 41.6 mA. So for it to be working withinn it's ratings the coil resistance must be at least 1728 ohms. You term fraction of a second in not very meaningful. It could mean anything from less than a picosecond up to 0.99 of a second. What is the actual time you require ? What will be the time betwen pulses ? It might just be possible to achieve by storing energy in a capacitor and discharging it into the coil.

Les.
Hi Les, many thanks for the reply. The coil is flat and wide (5mm thick x 50mm wide). Tried to get the resistance using the lowest setting on the meter and it says 04.2 - not sure if that's any use? When I mention fraction of a second the circuit is activated by a single press of a button on a keyfob remote for the receiver to activate the FET. The receiver is the momentary type so it's on for as long as you press the transmitter button. I only require a single 'jolt' from the coil. Hope this provides a bit more context.

Since I posted the diagram I noticed the switch is in the wrong place as the converter needs to power up first. First mistake I guess. I suspect more volts doesn't necessarily mean more current through the coil hence the capacitor. Based on my limited knowledge I guess it will need to be capable of fast discharge - any thoughts on how I should add it to the circuit?

Many thanks
 
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