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amplify DC voltage input to universal motor (24 V -> ~ 60 V)

oblivius

Apr 25, 2023
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Hi everyone, sorry for the lame question but I am actually not an expert in electronics (I am a biologist).
I have a universal motor (got it from a washer) and I would like to have a variable voltage power supply. I managed to get a 9-24 V ordinary supply (no need for very precise output). However I was hoping to get a bit higher. I think around 60 V could be actually fine.
I thought of adding a buck/boost converter to the circuit but - perhaps due to my incompetence - I was able to get only up to 30 V... which probably comes at a price (decreased intensity?) assuming I understood properly how it works.

Is there an easy way to simply amplify the output without connecting anything in parallel to the network (just in series) ?
If cheap, an existing device could actually be an easy solution, but I am not scared of building something new (if it is simple enough for me to understand).

My aim is actually to increase the torque of the motor (which should depend on current intensity not voltage, if I got it right) more than the rotation speed (which is voltage dependent) so.. would a cheap audio amplifier do the job? like this

sorry for the incompetence :S
Thank you for any advice !
 
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oblivius

Apr 25, 2023
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the universal motor works with both AC or DC, that's why is called "universal" (as far as I understand at least :)). The power supply works now from AC to DC and delivers 24 V at perhaps 2 A or something alike. I would like to increase the torque which should be regulated by the winding shield of the motor itself. The motor is a typical Washing machine motor with field and motor connected in series ( I cannot use high voltage in order to avoid some "run away overload" as I understood it could happen due to this circuit diagram. The other option (connect field and motor brushes in parallel or even on separate circuits) did not work for me (somehow I would like to keep it as it is and just boost the input)
 

oblivius

Apr 25, 2023
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Yes, that would be great! :)
however I was looking for something way cheaper than that.
 

Minder

Apr 24, 2015
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The older automotive starters were series field motors due to their very high torque at zero RPM with a high load.
If you connect in parallel, you would need DC not AC. but the field should be fed by a separate constant voltage.
The Universal (series field motor), operates in a run away condition when unloaded.
The higher the voltage, the higher the torque due to the increase in current for a given load.
 
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Bluejets

Oct 5, 2014
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I cannot use high voltage in order to avoid some "run away overload" as I understood it could happen due to this circuit diagram.
Not only with whatever circuit diagram you are referring to but, series motors on DC have that characteristeric, that is why they are either driven via some auto speed control or use compound windings.
The series motor on dc will run to destruction if not loaded down.
 

Belmarr

May 7, 2023
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I have a similar situation I am trying to figure out. I have an early 1980s Vitamix, a 1957 Kenwood chef mixer and a 1940s oscillating fan. I believe they all have universal motors. I am looking to run them directly off my RVs 24 volt dc system instead of the inverters or generator but I'm not sure if it's feasible.
 

oblivius

Apr 25, 2023
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Not only with whatever circuit diagram you are referring to but, series motors on DC have that characteristeric, that is why they are either driven via some auto speed control or use compound windings.
The series motor on dc will run to destruction if not loaded down.
you are right in theory, yet, within certain voltage limits, the friction/resistance of the mechanical parts will slow it down automatically (no runaway spinning). that is why I would keep it at 60-80 max (up to 50 I am sure it does not heat up or go mad). I was looking for a cheap power input solution...not for explanations of how a universal motor works :D which is in any case interesting, but not my main point. I do know that connecting field and brushes separately (in parallel) I will have a better control. My point is though to have a minimal circuit, usable for my purposes (a cheap grinding machine in a corner of the shop).
 

oblivius

Apr 25, 2023
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Apr 25, 2023
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I have a similar situation I am trying to figure out. I have an early 1980s Vitamix, a 1957 Kenwood chef mixer and a 1940s oscillating fan. I believe they all have universal motors. I am looking to run them directly off my RVs 24 volt dc system instead of the inverters or generator but I'm not sure if it's feasible.
I think you can give it a try and I am sure it will work. the question is: would that power (generated at 24V) be enough for you? then yes. It is all about how you wire the motor (in series vs parallel). I found several inputs/videos/threads on washing machine motors... I suspect you have similar components in yours (meaning 2 contacts for the motor brushes and 2 contacts for the field coils and maybe some other). what I did was to simply test different connections until one worked (of course having first looked some material up online). definitely with such low input you intend to test, you are not going to blast the motor :) just try!
 
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