dc Voltage step down converters

[Henry RancourtParticipant @henryrancourt22682]

Is anyone using a step down converter like the attached type? And are they considered reliable and long lasting?

[Robert Atkinson 2Participant @robertatkinson2]

Not used one of those, I generally do my own. Difficult to comment on a no-name generic unit.

What is your application?

Robert.

[Henry RancourtParticipant @henryrancourt22682]

I have a 48V dc power supply and a 24V brushed DC motor. I’ve read that that combination can make the motor run hot and possibly lead other problems.

[Peter Cook 6Participant @petercook6]

I have a couple of low power ones. One delivers 12v  (@3A?) to power the Arduino and leadscrew motor on my Taig lathe control system. The source PSU is 48v for the BLDC motor. It has worked well for 5 or so years.

The other is an even smaller adjustable output one. I use it – driven from a USB PSU – to give 1.5 – 4.5 v for testing battery clocks

[Henry Rancourt]

On Henry Rancourt Said:

I have a 48V dc power supply and a 24V brushed DC motor. I’ve read that that combination can make the motor run hot and possibly lead other problems.

If the DC-DC converter is producing smooth 24 volts DC, then the motor will not get any hotter than it will get when working from any other smooth 24 volts DC supply.

The DC-DC converter may get rather hot. The fins on its case indicate that it probably needs air to be able to freely circulate around it.

You should consider whether the motor’s inrush current may damage the DC-DC converter.

[Henry RancourtParticipant @henryrancourt22682]

I won’t be using an Arduino. I plan to put the step down between the psu and the motor.

[John HaineParticipant @johnhaine32865]

What is the motor inrush current spec? Do you have a multimeter? Measure the motor resistance with it stationary, divide that number into 24 to get an estimate. For example if the motor measures 1 ohm the current when stationary at 24v will be 24 amps. Can easily be several times the running current especially with low mechanical load.

[Henry Rancourt]

On Henry Rancourt Said:

I have a 48V dc power supply and a 24V brushed DC motor. I’ve read that that combination can make the motor run hot and possibly lead other problems.

Connected directly it would burn out the motor.

One cure is to drop the voltage from 48V to 24V with a rheostat or hefty resistor.   Both get very hot.

• A rheostat is a wire-wound adjustable resistor, large and expensive.  Can be adjusted for best results, but, unless you have one already, don’t bother!  Old-fashioned, hard to find, and pricey,
• A fixed resistor, or resistor bank, can be substituted for a rheostat, but the size of the resistor has to be calculated as described by John, not everyone’s cup of tea!   Cost depends on the size of the motor – how many amps does it consume? Likely to be pricey, and will need a DIY box and wiring up.   Not recommended.

Much better to drop the voltage with a Buck Converter of the type asked about.   The technology is well established and efficient.  They produce much less heat.   The unit shown is an IP sealed automotive type where the box is also the heatsink.  Cheap because they are used in huge numbers in everything from tread-mills to lorries.  The unit is almost plug-and-play, just wire it in as per instructions.  Necessary to match it to the motor:  how many amps (or watts)?   Important not to plug a 10A converter into a 20A motor!   But, OK to run a 10A motor on a 20A converter, which will run cooler because it has a bigger heatsink.  Heat is the enemy of electronics.

Never had a buck converter go wrong, but I’ve not used one of the type in this question.  Impossible to say anything meaningful about reliability because it’s a generic type, and no doubt some are “too cheap”. But they get reasonable reviews and the internet isn’t full of failure reports.  Cheap enough to be considered consumable and easily replaced, so stop worrying!

May I ask a fundamental question?  Why drive a 24V motor from a 48V power supply?  It’s poor engineering, a electrical mismatch that creates an avoidable problem!   Fixing it with a buck converter adds complexity and is more to go wrong.

Why not replace the 48V PSU with an inexpensive 24V PSU?  They are in the same price range.

Dave

 

 

[Keith Rogers 2Participant @keithrogers2]

Dave. It might be a good idea to read the original post!

( I looked for a smiley but couldn’t find how to insert one.)

Regards, Keith

[Keith Rogers 2]

On Keith Rogers 2 Said:

Dave. It might be a good idea to read the original post!

( I looked for a smiley but couldn’t find how to insert one.)

Regards, Keith

For me the original post is this one #834224,   Are you seeing different?  (A forum bug causes posts to appear and disappear.)

The forum generates some emoticons from their character codes, just type colon close bracket to get a smiley.  They don’t all work,  try these:

:/  (unsure) 😮 (surprised)

Dave

 

[Robert Atkinson 2Participant @robertatkinson2]

Sorry for slow reply, day job intervened.

A brushed DC motor doess not need a teady, regulated voltage. They will even run on DC. The most efficent way to run a BDC motor off a higher voltage is to switch the supply on and off in a ratio proportional to the voltage drop required. So for a 24V motor on a 48V supply the switch (a power transistor) would be ON 50% of the time. The inductance of the motor windings averages the voltage.
This method is very efficent and also alows speed control. Ready made modules are cheap, some random examples:

http://www.amazon.co.uk/Aideepen-Controller-Adjustable-Stepless-Regulator/dp/B0D97DYCTD/ref=sr_1_5_sspa?

https://www.ebay.co.uk/itm/267141366871?

https://www.ebay.co.uk/itm/397354753388?

They can of course be pre-set for fixed speed.

Robert.

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