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Electrical advice

shermans
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Registered: 07-09-2007

Electrical advice

I am not very good understanding current / voltage and AC / DC but have a little problem.  I have an old electrical item (nothing to do with ICT at all,  but in fact a water softener !) which is on the blink.  It is a little premature as I am due to change it in a few months for a new one, after renovations have been completed and the new one can be installed in a more convenient location.

The motor on it, which simply controls the various valves, is powered by a simple 240 volt / 12 volt 150 milli-amps transformer which has literally burnt out and broken open its own casing due to heat.  Why I do not know.  I am assuming it is just a case of old age.  The only other thought which goes through my mind is that one of the small valves became jammed and caused it to overload. But while I admit that I do not understand DC, I imagine that would be unlikely due to the low voltage / current ?Huh

I have tried another transformer very briefly but it was only 6 volt / 350 milli-amps.  It was enough for the controller's LED screen to illuminate, which suggests that the controller may still work.  I did not leave it long enough to prove anything because I was not sure whether 350 milli-amps would be too much - I am sure it would not be but discretion is the better part of valour !

Now, in my arsenal of old transformers, I have nailed it down to two, one being 12 volt / 500 milli-amps and the other 10 volts, 300 milli-amps.  Could anyone advise if in principal either of these might be suitable as a temporary measure ?  If the controller works, then I could always go and buy the correct size of 12 volts 150 milli-amps but I do not want to waste money if the controller is already broken.  All I want to do is to experiment without making matters worse !

Incidentally, the "Destructions" just specify the electric motor as "660 12 volt", in case that helps.

Any advice appreciated.

10 REPLIES
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Re: Electrical advice

Power = Volts x Amps.  Most things electronic will require broadly the specified voltage.  

 

If you use the 12V 500mA transformer it should be capable of a bit more power so might just unstick a stuck valve.  But if something has gone open-circuit (or nearly so) then it will draw more power than was intended and get even hotter than before so you might get a bang and a smell of burning.

With 10V 300mA you won't be able to supply quite as much power as your original transformer could.  I'm not sure if 10V is sufficiently far off 12V to upset any electronics. 

RobPN
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Re: Electrical advice


ReedRichards wrote:

Power = Volts x Amps.  Most things electronic will require broadly the specified voltage.  

 

If you use the 12V 500mA transformer it should be capable of a bit more power so might just unstick a stuck valve.  But if something has gone open-circuit (or nearly so) then it will draw more power than was intended and get even hotter than before so you might get a bang and a smell of burning.

 


Shouldn't that be short-circuit? Undecided

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Re: Electrical advice


shermans wrote:

 

 one being 12 volt / 500 milli-amps and the other 10 volts, 300 milli-amps.  Could anyone advise if in principal either of these might be suitable as a temporary measure ?

 


Both will probably work, the DC output of such transformers is notoriously vague, but the devices they drive are usually pretty tolerant.

I'd try the 12V/500mA one, it can't do any harm. It just means it "can" deliver 500mA if it needs to, but running at a lower power is totally fine.

And if it does work, just keep using it.

Obviously check the polarity before connecting and powering up. Wink

shermans
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Re: Electrical advice

Thanks for all the advice.  So I have now run it now for an hour with the 10 volt transformer and all is working.  Fingers crossed it keeps on so.  The motor is turning as it should and I have re-generated the water.

 

I tried the 12 volt transformer but the LEDs did not light.  There may be something wrong with the 12 volt transformer which is why I changed to the 10 volt one - it does get quite warm !

Community Veteran
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Re: Electrical advice

To qualify what @HPsauce said..

 

If you have a power supply capable of 500mw...  and your requirement is for 300 or even less,... then that will supply only the amount of power that the "requirement" needs...  i.e. "draws" from the power supply

 

Your car will give you enough power to drive at ( say ) 100 mph... but, you, (the requirement)  only need to do 70mph... ..unless you are a drug dealer being chased by the cops ! ! !.. so you only "draw" sufficient power to be able to do that...

 

 

VileReynard
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Re: Electrical advice

Your 10V transformer is rated at 300mA secondary windings - but you could be running it at up to 500mA. So it "could" be sucking a trifle extra current than it should. Hence, a little bit warm.

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Re: Electrical advice


RobPN wrote:


Shouldn't that be short-circuit? :


Yes.  silly me.

shermans
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Re: Electrical advice

I am learning a lot.  The transformer is now resting" and no current is being drawn as there is no regeneration due for a week or so.  It has also cooled right down (it did not help that SWAMBO keeps all her old plastic bags on the shelf around the transformer which were providing wonderful insulation - now removed !).

Now, to continue the electrical lesson, I have understood that volts x milli-amps = power.  But how is "Power" measured ?  Is that milli-watts ?  In other words how would you work out the amps for a 100 watt bulb ?  Would that be 240 volts / 100 watts = 2.4 amps ?

 

Also, I do not understand what the volts measure.  Is that something like water pressure in a pipe ?

Must try harder !

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Re: Electrical advice

no thats 100/240 = 0.4166 amp

 

Also some loads are active and some are passive. a pure resistance load will (in amps or watts) fall as the volts fall. but some are active such as rectifiers or i think some types of motor which will draw more amps as the volts fall to provide the same output (this generally means an active control system) Thumbs Up

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VileReynard
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Re: Electrical advice

Think in plumbing terms. Smiley

Volts = pressure

Amps = quantity of water flowing

Resistance = resistance to flow

Some formulate:- (where I = current)

V = I x R, I = V/R, R = V/I

If you have a purely resistive load then power (P)

P = V x I,   P = V^2/R

You might look up power factor in Wikipedia.

Units of power are watts, if current is measured in Amps & Voltage in Volts.