Unsteady Voltage Regulator

[Barns]

I run a small ecolodge in rural Laos and have a floating restaurant down on the river with several fridges. Being where we are, the electricity supply is patchy at best. It works nearly all of the time but the voltage rises and falls constantly.

As a result, I invested in a small 3000 VA voltage regulator for the floating restaurant which has two tall upright fridges (bottom part fridge, top part freezer), one ice cream freezer and a small regular fridge plus basics such as lights, a TV, DVD player, amp and toaster. I mainly bought the voltage regulator since the brand new beer fridge I bought wouldn't get cold. The fan and light worked but the compressor wouldn't fire up and I was told that this was because the incoming power to that fridge with everything plugged in hovered between 200 and 210 V which wasn't enough for such a tall fridge and it needed to be a constant 220V.

I wired the voltage regulator in correctly (although I'm certainly not a qualified electrician it was just simple connections) but it will run perfectly for about ten minutes at 220 V and about 2 amps or even less but will then suddenly drop down to about 110-140 V while the amps will shoot up to about 20 amps (Which should trip the 15A breaker on the unit, no?). The lights dim, the fan slows, the fridge compressors stop etc and it will stay like that for a few minutes before you can hear the voltage regulator kick in again and everything will be back to normal. However, this cycle continues constantly.

The incoming power to the voltage regulator hovers around 220 V according to my multimeter and the rest of the resort, which is all powered from the same breaker box, doesn't have the same problem

The wire from the main breaker box down to the restaurant is VAF 2 x 2.5 sq. mm 300V. Is that maybe too small? Another thought I had was that the small section of wire from the voltage regulator to the restaurant breakers is a bit smaller than the main cable I mentioned before. Could that be a bottleneck? Would something like that cause the situation I mentioned?

Any assistance gladly welcome. There are no reliable electricians around here in rural Laos unless you just want a light bulb fitted so I have to do it myself.

Thanks.

 

[Pete999]

Difficult one mate, being so far away, my immediate thoughts 3000va is a bit small for all that gear, only a thought though.

 

[Barns]

If the 3000VA was too little for the fridges etc would that cause the regulator to cycle like that? I can probably go and pay an extra £40 and change it for a 5000VA and I'm happy to do so if I know that too low a wattage would cause the unit to do this. However, I don't really want to go and spend the money if too low a wattage wouldn't cause this problem.

While I'm here, can I just clarify that when UPS' and voltage regulators etc have a VA rating that is exactly the same thing as wattage since volts x amps = watts. Or am I completely wrong?

How many watts/VA would one standard fridge usually require? And why would three of them work and not the fourth?

 

[Pete999]

va in an AC environment represents "apparent power" as opposed to the "true power" as a rule of thumb, and this is just that, you can multiply the va figure by 0.6 , so 60% of power being delivered. So in answer to your question "yes you are wrong" there are too many other thing to take into consideration when purchasing UPs or Voltage regulators, one example is the reactance of the circuits involved. It would be wrong of me to say "yes just bung in a larger VR, can you not get someone locally to size up the installation for you? sorry can't be of any more help

 

[Badged01]

While I'm here, can I just clarify that when UPS' and voltage regulators etc have a VA rating that is exactly the same thing as wattage since volts x amps = watts. Or am I completely wrong?

As above - VA is the "apparent" power supplied to the equipment and Watts represents the "true" power being used by the equipment. In laymans terms, your equipment only needs the true power (resistive) to work. But because of reactance (inductance/capacitance) in the equipment fighting against the current being drawn, you end up needing more current to get the true power. So you pay for apparent power but only actually use true power! -- apparent power being greater than true power. The difference between the two being the power factor --- the rule of thumb 60% mentioned above

How many watts/VA would one standard fridge usually require?

They all vary but an around 800W wont be far off the mark!

And why would three of them work and not the fourth?

Cant help you there without actually seeing things in action so to speak!

 

[Barns]

Yes, sorry, I do realise it's difficult to diagnose a problem when you can't see it hands (eyes?) on but there are only two Western electricians in Vientiane, Laos' capital, that I know of and, as a result, they are constantly busy and to get one of them to travel 20 miles out of town is hard so I just have to work it all out myself. That's why I've come to Internet forums!

What I now need to know is whether having too low a VA rating on the voltage regulator could cause it to fluctuate like it does? If this is possible then I'll try to swap it for a bigger one next time I'm in town.

I can see that 800W x 4 far exceeds 60% of 3KW so it does seem likely. I wondered why an 800 VA UPS was unable to keep my PC going in the office when it only has a 650W power supply. Thanks for clarifying!

However, 60% of 5KW is 3KW so even that may not be enough for 4 fridges plus the other general electrics. When you say about 800W for a fridge/freezer, are you talking about the big tall ones, standard little ones or a chest freezer? Or is that just an average and the bigger ones would need a lot more than 800W?

I presume they usually have a plate on them somewhere saying what wattage they are? I'll have a look tomorrow!

Thanks ever so much for trying to help.

 

[Pete999]

how long does the UPs last at 650 watts loading?

 

[shanky887614]

that pc will not be pulling 650watts.

for example ive got a 750watt psu in mine but realistically it cant draw more than 450watts at the moment. thats with core i5 and 7970 gpu and other stuff

that spec is way over office spec machines unless it is a workstation spec machine

 

[Pete999]

I'll rephrase the question then, how long does the UPs last when the power fails?

 

[Richard Burns]

Your voltage regulator may have a minimum voltage that it can work with and if your outside supply drops below this minimum voltage then the regulator may cut out once the supply goes up again the voltage regulator then restarts.

Similarly if your voltage regulator is overloaded (which sounds like it may be the case) then it could be overheating and a safety cut out comes in that stops the voltage regulator working, then when it has cooled down it restarts.

This is all supposition because we cannot see the item in question or measure any parameters.

The reading you have given that the voltage regulator is only delivering 2 amps when thing s are working normally does not soudn right.
Admittedly if the fridges are all cold and the compressor does not need to run then this value could be correct and it may be that when a fridge starts up this cuts out the voltage regulator.
However 20A sounds a bit high unless all the fridges started together, then again it may be that the voltage regulator starts up on a test basis that is limiting the current flow to set the correct voltage once it set itself up then it delivers a sufficient voltage to allow the fridges to start that then causes it to cut out.

Using 2.5mm² VAf cable would just about be OK for the loading you want but a larger cable size would be preferable, if noting else a small cable taking the maximum current will cause a voltage drop that will only make the situation worse.

A 15 A breaker will not trip for a long time (some hours, if at all) if it is taking 20A.

Fridges and freezers contain motors that can take a high current on starting up and will also take a higher than rated amount of power from the supply as stated above. It may be worth trying to run one or two fridges until they reach the set temperature and the compressors stop and then turn on the other two fridges, this will (at least initially) take the motors starts out of syncronisation so that they are not all starting at once.

As a reference this below is a list that I found somewhere that gives approximate values for power ratings for common appliances.
You can see from the first part of the list where the reactive power is given that items with motors in can take a lot more from the supply than the steady running rating suggests.
It may be worth calculating your total power demand from this list and this will give a you a general idea of what power voltage regulator you may require.
Again this is all very rough and ready and may well not give you the results you need. Only some one on site could give you more reliable information.
(and also some one more familiar with the power supply arrangements in Laos!)

Good luck.

Sorry the table has not formatted very clearly, hope you can make it out.
Appliances Resistive Load (Watts) Reactive Load (watts)
Blender 375 500
Clock Radio 5 ---
Coffee Maker 1,700 ---
Computer - PC 300 ---
Cuisinart 450 650
Deep Fryer 1,800 ---
Electric Blanket 400 ---
Electric Curlers 300 ---
Frying Pan 1,250 ---
Hair Dryer 1,875 ---
Iron 1,200 ---
Incandecant Light Bulbs as rating
Microwave 1,050-2,500 ---
Washing Machine 1,150 2,200
Water Heater 4,000 ---
TV - Color 300 ---
Air Compressor (1hp) 1,500 4,500
Cultivator 700 1,400
Freezer 800 2,100
Furnace Fan 875-1,200 2,200
Garage Door Opener (1/4 hp) 550 1,000
Grinder, Bench 1,400 2,450
Heater, Kerosene (90,000 BTU) 500 725
Sump Pump (1/3 hp) 800 1,250
Well Pump (1/2 hp) 150 1,950
Saw, Band 1,100 1,350
Table Saw (10 inch) 1,750 4,250
Coffee maker 800
Toaster 800-1500
Popcorn popper 250
Blender 300
Microwave 600-1500
Waffle iron 1200
Hot plate 1200
Frying pan 1200
Dishwaher 1200-1500
Gbg. disposal 450
Washing machine…
automatic 500
manual 300
Vaccuum…
upright 200-700
handheld 100
Sewing Machine 100
Iron 1000
Clothes dryer…
electric (n/a) 4000
gas heated 300-400
Heater (n/a)…
engine block 150-1000
portable 1500
waterbed 400
stock tank 100
Furnace blower 300-1000
Air Conditioner (n/a)…
room 1000
central 2000-5000
Electric mower (n/a) 1500
Ceiling fan 10-50
Table fan 10-25
Electric blanket 200
Blow dryer 1000
Shaver 15
Water Pik 100
Computer…
laptop 20-50
desktop 80-150
printer 100
Typewriter 80-200
TV (25" color) 150
TV (19" color) 70
TV (12" B&W) 20
VCR 40
CD player 35
Portable stereo 10-30
Clock radio 1
Car stereo 8
Sattelite dish 30
CB radio 5
Electric clock 3
Radio telephone…
receive 5
transmit 40-150
Lights…
100w incan. 100
25w CF 28
50w DC incan. 50
40w DC halogen 40
20w CF 22
Compact Fluorescent (CF)
vs. Incandescent Wattage*
40 watt incan. 11 watt CF
60 watt incan. 16 watt CF
75 watt incan. 20 watt CF
100 watt incan. 30 watt CF
Hedge trimmer 450
Weed eater 500
1/4" drill 250
1/2" drill 750
1" drill 1000
9" disc sander 1200
3" belt sander 1000
12" chain saw 1100
14" band saw 1100
7 1/4" circ. saw 900
8 1/4" circ. saw 1400
Refrig./Freezer Conventional
20 cubic feet 540
16 cubic feet 475
Sun Frost Refrig./Freezer (DC*)…
16 cubic feet 112
12 cubic feet 70
Vestfrost Refrig./Freezer…
10.5 cubic feet 60
Freezer Conventional
14 cubic feet FF 440
14 cubic feet 350
Sun Frost Freezer (DC)…
19 cubic feet 112
Vestfrost Freezer…
7.5 cubic feet 50