Unsteady Voltage Regulator

[Marvo]

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 also live in a country where the supply voltage can drop as low as 200v, most refrigerators don't have a problem until around 190-195v when their compressor often fails to start.

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

When acompressor starts you get a very brief large current flowing whilst it starts running then the normal run current will be pretty stable, it will then gradually reduce over a period of several minutes as the evaporating temp comes down (head pressure reduces) and it gets colder inside.

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.

It sounds like one of the fridge compressors is stalling. When a compressor stalls it will draw a much larger current (maybe 5 x the run current) for several seconds and possibly up to half a minute until the thermal protection on the compressor disconnects the power automatically. This protector will auto reset in 3-15 minutes usually. This high current would almost certainly cause your 3000VA regulator to trip so all the other fridges would stop. The stalling could be due to several reasons but if the voltage is stable and remains above 210v up to the point of stall then there's most likely a fault on one of the fridges that's causing it.

I'd attempt to run the system with one of the fridges unplugged. If the fault persists then plug that fridge back in and try disconnecting another one. Do this until you figure out which fridge is the rogue one by deduction.

It's also worth noting that if a fridge is restarted quickly after it's been running and has stopped then it will restart or attempt to restart before the gas system has equalised. This load on the compressor, especially domestic fridge compressors will prevent it from starting and again high current draw until the thermal protection causes disconnection. This attempting to rapidly restart may be compounding your problems. It would be a wise move to add some kind of timer to your regulator so if it trips it doesn't reset and reapply power for a period of a few minutes. Similarly it would be advisable to try come up with a system that avoids having all compressors starting simultaneously when power is applied or reapplied because the combination of all the compressor start currents simultaneously would be very high and possibly cause the regulator to trip.

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?

Depends on the total current and the cable length but undersized cables are your worst enemy if you already have low voltage problems.

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?

Definitely not ideal, splash out on a cable at least the same size or larger.

Some photos of the general setup, the regulator and the fridges would be helpful if you can attach some to your next reply.

 

[Barns]

how long does the UPs last at 650 watts loading?

The PC would immediately restart every time the incoming voltage from the mains dropped suddenly (which happens a lot here...) despite the presence of the UPS. It's quite a high-powered PC and the UPS also had the monitor plugged in to it. However, that's a separate issue which I solved by buying a 1,100 VA UPS. I now understand that real wattage is 60% of the VA rating...dunno why they don't just put the wattage on the box rather than the VA value but still...

Anyway, the pressing issue at the moment is the fridges and whether it's a good bet to exchange the 3000VA voltage regulator for a 5000VA one or whether I'll just be throwing good money after bad? I think the next highest I saw in the shop was 10,000 VA which would be overkill and probably prohibitively expensive.

Thanks.

 

[Barns]

@Richard Burns & Marvo

Firstly, the regulator is rated 90V-250V and the power doesn't drop as low as 90V so I think we can rule that one out.

According to your list (using the higher values since I don't know the difference between resistive and reactive loads...) I have:

Big Fridge x 2 = 540 W
Small Fridge x 1 = 475 W
Freezer x 1 = 440 W
TV x 1 = 300 W
14W bulbs x 10 = 140 W
DVD Player x 1 = 50 W (I guessed this one as being a bit higher than a CD player since I couldn't see it on your list)
Toaster = 1,500 W (Do toasters really take this much?? I never would have guessed!)

That makes a total of 3,985 W of "true power" needed so 6,641 W of "apparent power" needed from the voltage regulator which exceeds the 5,000 VA unit I was planning on.

However, without the toaster, I only need 2,485 W true power so 4,141 W of apparent power which would fit nicely.

We use the toaster very, very rarely so do I really need to include it in the calculations? Or would the fridge compressors just switch off for the 5 minutes when it's on?

I'll take some photos later as asked and stick them up but don't laugh at our wonky SE Asian wiring!

 

[Marvo]

I would plug the toasters into the supply without the regulator, just use the regulated supply for voltage sensitive items.

 

[Barns]

There is only one wire coming down the bank to the floating restaurant and that goes directly into the regulator to provide power for everything, including the plug sockets, so I haven't got a spare socket for it unfortunately.

I'll exchange the regulator for a bigger one when I'm in town on Wednesday and try that. If it still doesn't work we can examine other possibilities.

 

[Badged01]

.....using the higher values since I don't know the difference between resistive and reactive loads...

The higher value is the "apparent power" (reactive) which is what you will be drawing -- i.e. use that for your current calcs not the lower "true power" (resistive) value. You dont need to apply any power factor correction to the higher values (reactive) .......

 

[Barns]

So reactive and resistive are just the technical terms for apparent and true power. I understand now. Thanks Badged01.

Another question before I go and buy a bigger regulator:

If I invested in much bigger wire and replaced the connection between the breaker box and the restaurant (it varies in length between about 20 metres and 50 metres depending on the height of the river) would I actually need a voltage regulator in the first place? Does a voltage regulator actually increase the wattage available? Or, if there's not enough to start with, then it won't work anyway?

Thanks in advance.

 

[Badged01]

So reactive and resistive are just the technical terms for apparent and true power.

Not quite but for what you are doing I think helps explains it in sort of laymans terms!

Does a voltage regulator actually increase the wattage available?

Nope, it does what it says on the time and regulates the voltage to supposedly give a steady voltage. It will not increase your power!

 

[Barns]

I'm confused. Why would the cable coming directly from the breaker box to the restaurant (with no regulator in between) then not provide enough power for the four fridges and other stuff when there is 220V reaching the restaurant according to my multimeter?

Would a bigger cable increase the wattage reaching the restaurant? I can buy and wire up proper big black power line cable the same as we use for the three phases and neutral lines from the main road (black plastic with big silver wires twisted together inside...the size of one we use is 35 locally if that helps although I don't know 35 of what...although looking at it the diameter of the silver wires twisted together could be 35 mm but looks more to me). Would this make any difference?