Mains power supply for 12v dc motor

[Brian Fisher 1Participant @brianfisher1]

Hello.

I have been interested in model engineering since buying my first m.e. in 1950.

I have just made a high speed drilling spindle for spot drilling holes on a pcd on my super 7 lathe. It runs in ball bearings and uses an er11 collet.

It is driven by a 12v dc motor out of my come in handy stuff and works ok on a 12v battery but I would like to make a 12v power supply to overcome the need to charge the battery.

I was going to buy one of the dc power supplies advertised on the net for powering led lighting but am advised that it would not like the inrush current.

Can anyone advise me please as to whether this is true?

If it would not be suitable I would be happy to build a suitable power supply but am a retired mechanical engineer and am not experienced in electronic design.

I would be very pleased if someone knows where I can find one

Thanks.

Brian.

PS the motor draws 10amps according to the makers plate.

[Brian Fisher 1Participant @brianfisher1]

Circuit diagram required

[Michael GilliganParticipant @michaelgilligan61133]

To be honest, Brian … I think your best bet would be a 12V sealed lead-acid battery with a trickle charger.

Other, wiser, folk will hopefully be along soon … to support or discredit my opinion.

MichaelG.

[Nick Clarke 3Participant @nickclarke3]

I use either a bench psu from as CB radio set or a transformer that originally powered a scalextric set, whichever I grab first.

I don't know if the CB or scalextric makes me older – I don't like to admit to either.

[LainchyParticipant @lainchy]

PC power supply. Cheap. Google PSU from atx power supply. It's an easy job

[EmgeeParticipant @emgee]

Posted by Lainchy on 30/08/2019 22:17:18:

PC power supply. Cheap. Google PSU from atx power supply. It's an easy job

Do they really supply 12vDC at 10amps ?

Emgee

[Frances IoMParticipant @francesiom58905]

server computer power supplies costing ?10 or so from usual sources can supply 80A at 12.2V – I have a couple that will supply 150A at 12.5V

[Frances IoMParticipant @francesiom58905]

duplicate – BT keeps dropping my connection

Edited By Frances IoM on 30/08/2019 22:35:06

[Les Jones 1Participant @lesjones1]

You will need to know how much current the motor takes so you can obtain a power supply capable of driving it.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 30/08/2019 22:36:05:

You will need to know how much current the motor takes so you can obtain a power supply capable of driving it.

Les.

.

"… 10amps according to the makers plate."

But presumably more at start-up.

MichaelG.

[EmgeeParticipant @emgee]

Posted by Frances IoM on 30/08/2019 22:33:26:
server computer power supplies costing ?10 or so from usual sources can supply 80A at 12.2V – I have a couple that will supply 150A at 12.5V

Frances, I was referring to the ATX PSU, not a server unit but please advise your usual source.

Emgee

[Frances IoMParticipant @francesiom58905]

my own supply was the local auction house – I paid ?50 for 10 HP new 85A server PSus still in packaging – last week I bought another hp type DPS 800GB A for about ?4 – all in a box 250mm x 85 x 50mm – the two small fans are noisy (but you can slow them if you only want a miserable 10-20A – the other slight problem is buying the edge connector – but you can solder directly to the edge connector – you may need to search for the connections however as these don't come with instructions.

But just search for hp switching power supply for servers

Edited By Frances IoM on 31/08/2019 00:03:23

[I.M. OUTAHEREParticipant @i-m-outahere]

+1 for the ATX – pc power supply and there are plenty of videos on youtube or infoon the internet showing how to set them up.

I used one for my dehumidifier project (photos in my library ) but found when testing this unit using 3 halogen headlight globes in parallel the unit wouldn’t fire up as it was detecting a heavy current flow so it shut down suspecting a dead short . I would use a cheap PWM controller between the power supply and motor as this will allow the power supply to fire up without any current flow and you get the added bonus of speed control on your spindle . Even the old 550w unit i used was rated at 20 A @ 12 volts and they are dirt cheap to buy new if you don’t fancy using a second hand unit which can usually be scavenged for free from an old pc .

[Geoff TheasbyParticipant @geofftheasby]

Brian, LED's draw miniscule currents, of the order of milliamps, individually, so a lighting controller would be far too weak. The idea of a 12 volt battery is a good one, as is a PWM controller. I have one costing about £10 which will handle 60 amps. **LINK**

Hang this off a suitable power supply, say 12 or 24 volts DC , like this: **LINK** and Robert's your aged relative.

[Les Jones 1Participant @lesjones1]

Hi Michael,
Thanks for pointing out the information I missed in the first post. One point about using PC power supplies is that some of them require some load to be put on the +5 volt output before the rated current can be drawn from the +12 volt output..

Les.

[SillyOldDufferModerator @sillyoldduffer]

As Brian explained he's not experienced in Electronic Design, probably best to avoid solutions like modifying a PC Power Supply. Also the 12V supply on these tends to be relatively puny compared with the 5V or 3.3V outputs, which may need to be loaded before 12V fires up. A little fussy to get working.

Brian is asking I think about the type of LED Power Supply used to run long festoons of bright LED lamps. The power supplies deliver substantial current 4A to about 60A, for example for £31 this one on Amazon outputs 40A at 12v.

Although not designed for powering motors, I've used them to drive stepper motors without problems. In theory a stepper motor drawing rapid heavy current pulses must be the worst possible load to put on a switch-mode power supply trying to maintain a steady 12V out. Worse behaviour than an ordinary 12V DC motor. So in practice there's a good chance the electronics will cope with Brian's requirement.

If it were mine I'd cheerfully risk driving a 12Vdc 10A DC Motor with a 30A LED supply costing about £20. No guarantees but if it works far cheaper and more convenient than a battery or a proper fit for purpose supply. The reason LED supplies are so cheap is there's a mass market for them, every teenage bedroom in the world…

Dave

[I.M. OUTAHEREParticipant @i-m-outahere]

Plenty of wiring diagrams out there to fix that .

**LINK**

If you don’t want a certain voltage rail like 3.3v or 5 v or a negative rail just leave it disconnected .

When you open up a supply just identify the voltage you want by either wire colour code or looking at the board as it is sometimes written on it and unsolder the wires from the other pads then trim off the wires you won’t need from the supply rail you won’t use or as i did remove all the wires and solder on some heavy duty cable to the solder pad for the voltage i wanted to use .

Seriously these power supplies are something that many model engineers overlook because we don’t understand how they work or don’t know how to utilise their ability, you can get a 20amp , 12 volt pc power supply for under $50au here in OZ from just about any computer shop and even more power is not that much more expensive considering my local electronics shop would ask well over $100 au for something similar in their power supply units .

P.s , Dave slotted in a reply while i was typing this and as he says – the OP is not electrically minded so the power supply that Dave shows is the  simplest approach – i have never had a problem running motors off them and my cnc engraver uses the exact same type for its spindle motor but utilised the voltage control potentiometer  as an RPM control via a remote potentiometer instead of the trimpot on the circuit board .

Edited By XD 351 on 31/08/2019 10:44:37

Edited By XD 351 on 31/08/2019 10:54:39

[Howard LewisParticipant @howardlewis46836]

Why not do it the simple way?

Go to someone like Machine Mart and buy a battery charger capable of delivering 10 Amps?

A 12 V DC motor does not need a stabilised, pure DC, supply, just 12 Volts. A ripple will not upset it.

Remember the Amateur Radio maxim KISS!

Howard

[Frances IoMParticipant @francesiom58905]

a charger for a 12V lead acid battery will deliver near 14V if old fashioned type – modern chargers will sense output + current and may not like a motor connected as no voltage on initial startup looks like a shorted battery

[William ChithamParticipant @williamchitham75949]

I just ordered one of these: Link from Bangood. Hoping it will run a small circular saw with a dead rechargeable battery. Spec claims it will produce DC 10-220V, 10amps and run a 2000w motor and is small enough to fit inside the old battery box. Worth a punt at less than a tenner.

 

William.

Edited By William Chitham on 31/08/2019 14:15:00

Edited By William Chitham on 31/08/2019 14:15:39

[Les Jones 1Participant @lesjones1]

Hi William,
I don't think that is really suitable for your purpose. It will be designed to control the speed of a motor designed for around 180 to 220 volts. It will provide no isolation from the mains. It will probably use phase control so when it is set to a low speed (Low AVERAGE voltage.) the output will be short pulses of a much higher peak value than the average output voltage. I am assuming that your saw is designed for an 18 volts battery.

Les.

[Robert Atkinson 2Participant @robertatkinson2]

You don't need anything that fancy in reality. JJust a 12V transformer and a bridge rectifier will d just fine for running a motor. A 100VA 12V transformer will be big enough for intermittant use and a 150VA one for constant duty. A 25A bridge is recommened they are cheap enough.

Robert G8RPI

[Neil WyattModerator @neilwyatt]

My 3D printer uses a PC power supply with a couple of power resistors to keep it happy. One nice thing is I added a switch in the standby circuit.

For my astro I have a nominal 12V 150W psu like the one in SOD's post. I deliberately went for one greatly over-rated for my needs. I run it at a higher voltage to mimic a car battery then have two switching regulators to give me 12V and 5V for other devices.

Neil

[William ChithamParticipant @williamchitham75949]

Posted by Les Jones 1 on 31/08/2019 14:40:16:

Hi William,
I don't think that is really suitable for your purpose. It will be designed to control the speed of a motor designed for around 180 to 220 volts. It will provide no isolation from the mains. It will probably use phase control so when it is set to a low speed (Low AVERAGE voltage.) the output will be short pulses of a much higher peak value than the average output voltage. I am assuming that your saw is designed for an 18 volts battery.

Les.

Ho hum, should have asked here first, still, I think there is room for it in the "bound to come in useful eventually " box.

William.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Frances IoM on 31/08/2019 13:54:06:
a charger for a 12V lead acid battery will deliver near 14V if old fashioned type – modern chargers will sense output + current and may not like a motor connected as no voltage on initial startup looks like a shorted battery

Good point, whilst old-fashioned battery chargers are simple beasts that don't care about the load the same can't be assumed about today's magic boxes. I've not taken one apart yet, but a fast-charge unit I looked at in a shop recently was too light to contain a hefty transformer. As with wall-warts, I suspect transformers are being replaced by switch-mode power supplies, and once that's done it's trivial to specialise the electronics to do proper battery charging.

So a new battery charger could well be a close relative of a LED PSU with the added disadvantage of throwing a wobbler if the load doesn't behave like a charging battery. Although a smart charger refusing to run a motor properly because it's profiling volts and amps might be seen as a step back, at least the new one is clever enough not to damage batteries as is possible with a simple transformer/rectifier. Maybe!

Dave

[Author]

Posts