Reducing voltage

[Petemate]

Hi Everyone.
A customer of mine has a house sewerage system which includes an aeration pump. It is only low wattage - maybe 50 watts and rated at 220 to 240 volts.
However it keeps cutting out after about 20 minutes due to an internal thermal switch. The unit is brand new.
When I measured the supply voltage, it is 257 volts. The local authority in Cyprus won't reduce the voltage unless it is above 260 volts.
What is the cheapest way to reduce the voltage to the pump. I was thinking about a dimmer switch, but does this reduce the voltage or just clip the waveform. Suggestions please.

 

[radiohead]

Google Voltage optimiser

 

[Pete999]

Hi Everyone.
A customer of mine has a house sewerage system which includes an aeration pump. It is only low wattage - maybe 50 watts and rated at 220 to 240 volts.
However it keeps cutting out after about 20 minutes due to an internal thermal switch. The unit is brand new.
When I measured the supply voltage, it is 257 volts. The local authority in Cyprus won't reduce the voltage unless it is above 260 volts.
What is the cheapest way to reduce the voltage to the pump. I was thinking about a dimmer switch, but does this reduce the voltage or just clip the waveform. Suggestions please.

Voltage opimiser to limit voltage output to equipment and keep it constant at required limit. Plenty of suppliers I used them to with sucsess. Just tell them the parameter you require, job done.

 

[freddo]

Voltage optimiser is rather expensive, the cheapest option for such a small load would be a small 'buck' transformer. (search online)

 

[Pete999]

Voltage optimiser is rather expensive, the cheapest option for such a small load would be a small 'buck' transformer. (search online)

Depends on the equipment and what you require at the end terminals?

 

[freddo]

I assumed it was to be permanently connected and only supplying the aeration pump.

 

[Pete999]

I assumed it was to be permanently connected and only supplying the aeration pump.

Agree, but you need something that is reactive to voltage fluctuation, not having used Buck TXes are they reactive can they be left to their own devices?

 

[freddo]

A buck transformer will drop the supply voltage by the winding voltage, there is no automatic control. As the pump is ok at 220-240V I wouldn't worry if the supply dropped a bit. a 24V transformer would drop the current voltage to 233V well within the pumps rating.

 

[Pete999]

A buck transformer will drop the supply voltage by the winding voltage, there is no automatic control. As the pump is ok at 220-240V I wouldn't worry if the supply dropped a bit. a 24V transformer would drop the current voltage to 233V well within the pumps rating.

Like I said depends on the vagaries of the needs of the load really, but it is another option to be considered. At least with the VO it cn be left to optimise the output with regard to the fluctuating inpu, and the firm I used provided excellent Customer care, and after sales, sorry been a while and I can't recall the Firms name.

 

[pc1966]

It appears that CEF sell one for £361 (inc VAT, part MCG63ES2) but I doubt you would see that in electricity savings. However, if your high supply voltage is causing problems then you might see some benefit in reliability, etc., in the property as a whole to justify the cost.

 

[David Prosser]

Is it an air lift pump or is it providing aeration to reduce septicity ? Just wondering as it may be cheaper to provide a more robust/electrically forgiving unit rather than trying to rectify the voltage issue.

 

[marconi]

https://cpc.farnell.com/ducati/4-16-10-08-14/capacitor-5uf-450vac-lead/dp/CA05803

Put a 5uF 450V ac motor run capacitor in series with the motor.

Required voltage across motor is 240V. Power is 50W. Ignore efficiency and PF.

Effective resistance of motor is 240 x 240/50 = 1150 Ohms = R

Current through motor is 240/1150 = 0.2A so when R and reactance X are in series across 260V supply required impedance Z is to be 260/0.2 = 1300 Ohms.

Zsqd = Rsqd + X sqd ==> 1300 x 1300 = (1150 x 1150) + X sqd.

Thus X = 600 Ohms = 1/(2pi f C) ===> C = 5uF for 50Hz 260V supply to drop 240V across motor .

 

[Paul L]

Impressive applied knowledge there from Marconi, always good to look for lateral solutions

 

[Megawatt]

Hi Everyone.
A customer of mine has a house sewerage system which includes an aeration pump. It is only low wattage - maybe 50 watts and rated at 220 to 240 volts.
However it keeps cutting out after about 20 minutes due to an internal thermal switch. The unit is brand new.
When I measured the supply voltage, it is 257 volts. The local authority in Cyprus won't reduce the voltage unless it is above 260 volts.
What is the cheapest way to reduce the voltage to the pump. I was thinking about a dimmer switch, but does this reduce the voltage or just clip the waveform. Suggestions please.

Petemate the internal thermal can be made closed. A lot of people don’t even use P1 and P2 they just tie them together and it won’t trip the motor. You already have short circuit and overload protection on the motor. Yes the do serve several applications like a way for programmers to use as inputs but they can be a nuisance, you have to add in the ambient temperature which could make the motor run hotter than usual. If it was me I would Tie them together

 

[EricMark]

I would use a transformer with tapping as an auto transformer.

 

[Pete999]

I would use a transformer with tapping as an auto transformer.

So how would you utilise the Auto TX for a client / customer that required a constant voltage \ frequency from a that a supply provision could not guarantee regular Vs and Hzs?
Surely you would need some equipment that was alert and responsive to irregular supply parameters, wouldn't you?

 

[EricMark]

I was thinking of simply dropping the voltage not stabilising it, I was assuming always on the high side?

It is unusually for a motor to over heat with such a small over voltage, I know many places used 220 volt, but before we dropped voltage in UK I used many Dutch items without a problem.

I would be looking at frequency, I have found 240 volt USA stuff which is 60 Hz not 50 Hz and have found it over heats, same with 110 volt stuff, one would think dropping 120 volt to 110 volt even if designed for 60 Hz on 50 Hz would not be a problem, but in the past I have found dropping frequency does cause over heating.

The voltage optimiser is a auto transformer which is switched in and out of circuit, but I have found when trying to buy an auto transformer they are often specials so rather expensive, so feeding a transformer with tapping at highest voltage and then connecting motor to lowest voltage does same as auto transformer, but often at fraction of the price.

 

[Mike Johnson]

Now that's interesting, I have a VFD on my pool pump, but had never considered, or measured the operating temperature difference when slowing the pump down, must have a look this summer, I run it generally at 35Hzs but for longer, just to cut the noise down and the saving in the electricity bill, it runs all summer so the saving is significant.

 

[marconi]

Petemate: It has just dawned on me that in my #12 I assumed a pump drawing 50W; if the pump draws a different power please use that figure and follow my working to arrive at the correct value of series run capacitor.

 

[Lucien Nunes]

A unit rated 220-240V is unlikely to overheat so much that it trips its cutout at 257V. It might be faulty despite being new, or designed for 60Hz. Well worth checking; perhaps check its load current.

Some air pumps of this size do not use a conventional motor, but a vibratory armature operated by an iron-cored coil. This makes frequency doubly important, and might impact on the effectiveness of Marconi's capacitive series dropper if it is significantly resonant.

As a quick fix I would probably go for the autotransformer or buck transformer and knock 20V or so off, unless the supply is also known to go badly low too.

I cannot agree with the suggestion in post #14 to bypass the thermal cutout, that assumes there is overload protection elsewhere. On a 50W pump that I suspect is simply a stand-alone device plugged into a 230V outlet, bypassing the protection (if even possible) is likely to leave it unprotected and hence a fire risk.