240V Fridge

[Paringa]

This is an annoying trait my fridge has...

 

When i run it a Zanussi ZRX-407W domestic compact fridge through my 1800W Powermaster inverter it will on occasion make the inverter beep a warning that it has reached the limits of the inverters capacity. This becomes more likely if i am running any additional appliances.

 

From what i understand compressers require a large boost at start, maybe 8 to 10 times what they use while running and that this is the problem, trick is how to stop it. Any ideas? These are my thoughts:

 

1: Turn off the beeping alarm - Simple but does not solve the problem!

 

2: Buy another fridge - Pricey and may give exactly the same problem.

 

3: Buy a bigger inverter - Pricier still!!

 

4: Try a soft-start or hard-start device like this: http://www.ebay.co.uk/itm/Compressor-Saver-CSR-U1-2-3-Hard-Start-5-2-1-QTY-1-5-/220818594378?_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D5%26po%3DLVI%26ps%3D63%26clkid%3D2471596900754460900

 

The last option is the one i want to explore as these devices supposedly reduce that initial spike on starting. They seem to be for air-con units but i thought the principle would be the same.

 

Anyone come across them? Any other ideas as to how i might improve this situation?

 

The details again:

 

1800W Inverter from 24V battery bank.

 

240V Zanussi ZRX-407W domestic fridge. Not sure what it draws...

 

Thanks in advance.

Edited September 1, 2011 by Paringa

[steelaway]

This is an annoying trait my fridge has...

 

When i run it a Zanussi ZRX-407W domestic compact fridge through my 1800W Powermaster inverter it will on occasion make the inverter beep a warning that it has reached the limits of the inverters capacity. This becomes more likely if i am running any additional appliances. So it seems to me like the load on start-up is the problem and near the limit of my inverters capacity and when other loads are on that "headroom" is even less and the spike as the fridge starts sets off the alarm.

 

From what i understand compressers require a large boost at start, maybe 8 to 10 times what they use while running and that this is the problem, trick is how to stop it. Any ideas? These are my thoughts:

 

1: Turn off the beeping alarm - Simple but does not solve the problem!

 

2: Buy another fridge - Pricey and may give exactly the same problem.

 

3: Buy a bigger inverter - Pricier still!!

 

4: Try a soft-start or hard-start device like this: http://www.ebay.co.u...596900754460900

 

The last option is the one i want to explore as these devices supposedly reduce that initial spike on starting. They seem to be for air-con units but i thought the principle would be the same.

 

Anyone come across them? Any other ideas as to how i might improve this situation?

 

The details again:

 

1800W Inverter from 24V battery bank.

 

240V Zanussi ZRX-407W domestic fridge. Not sure what it draws...

 

Thanks in advance.

 

 

 

 

My only does that when the battery's are almost flat - lack of voltage/amps at the fridge start up.

Not an overload of the inverter.

 

Alex

[Paringa]

My only does that when the battery's are almost flat - lack of voltage/amps at the fridge start up.

Not an overload of the inverter.

 

Alex

 

Batteries and voltages all ok...

 

But yes it is lack of amps at that start-up phase...

[WotEver]

I'd be very surprised if your fridge motor doesn't already contain a start-up capacitor, so I can't see that Yankee device doing anything for you.

 

As I see it, a change of fridge or inverter are the options open to you. Or maybe earplugs

 

Tony

 

Besides, the 5-2-1 device doesn't claim to reduce the start-up current, only the time that it's drawn. So even if it did work, the inverter would still squeal.

 

Tony

[Gibbo]

I've just read the description on that site. I want to know how they can get a compressor to start up faster (this is what it says) without drawing even more current.

 

I think yor battery cables to the inverter are insufficiently sized or you have a slightly dodgy connection on them. Or perhaps a dodgy battery isolator switch.

 

I don't think it's overloading the inverter. I think it's the low battery voltage.

[WotEver]

I think it's the low battery voltage.

That's logical.

 

Tony

 

I've just read the description on that site. I want to know how they can get a compressor to start up faster (this is what it says) without drawing even more current.

I don't think they claim that, do they? I've just re-read a fair bit of their site and the only start-up claim I can see is 'faster'. They do then make some vague claim about not losing 10% efficiency because the run capacitor will be saved from premature death, which left me befuddled.

 

Tony

[Gibbo]

I don't think they claim that, do they? I've just re-read a fair bit of their site and the only start-up claim I can see is 'faster'.

 

Precisely. It takes a certain amount of energy to accelerate the compressor from stationary to spinning at full speed. If you do that faster, it still requires the same amount of energy but in less time. Therefore the power drawn during the start up will be higher. Therefore the current drawn will be higher.

 

I smell reptile lubricant.

[Guest Quo Vadis]

I'd be very surprised if your fridge motor doesn't already contain a start-up capacitor, so I can't see that Yankee device doing anything for you.

 

As I see it, a change of fridge or inverter are the options open to you. Or maybe earplugs

 

Tony

 

Besides, the 5-2-1 device doesn't claim to reduce the start-up current, only the time that it's drawn. So even if it did work, the inverter would still squeal.

 

Tony

Most domestic fridges don't use start capacitors, they have an independent, heavy, start winding in the motor that is switched in momentarily to kick start the compressor. Old fridges do the switching with a relay, modern ones use solid state PCTs. I would think the 5-2-1 is just a faster form of switching, but we a talking fractions of a second here. I'd look elswhere for the solution.

Ian

[Paringa]

Well you have saved me a few quid on some nonsense...

 

The batteries are at 97% and 25.7 Volts.

 

The cables are monsters but i will check the master switch. The annoying thing is i had a full sized under-counter fridge running fine from Zanussi but i needed to move it under the sink to fit a Washing machine - That was another nightmare i don't want to visit again - This is the last of the fall out.

[Gibbo]

The batteries are at 97% and 25.7 Volts.

 

The important thing is the voltage right at the back of the inverter at the exact moment the fridge kicks in. Nothing else matters. And your multimeter also won't be fast enough to see the huge voltage drop you get when it kicks in.

[Guest Quo Vadis]

Just another quick thought, how often does the fridge kick in? If the fridge can't get enough cold air to cool it's condenser, it may be shutting off simply because it has got too hot, then when it trys to re-start, the pressure within the system would not have equalised, and the compressor would draw an even bigger start current. The more cooling air a fridge can get, the better.

 

Ian

[Paringa]

The important thing is the voltage right at the back of the inverter at the exact moment the fridge kicks in. Nothing else matters. And your multimeter also won't be fast enough to see the huge voltage drop you get when it kicks in.

 

Ah...got you i mis-understood.

 

Just another quick thought, how often does the fridge kick in? If the fridge can't get enough cold air to cool it's condenser, it may be shutting off simply because it has got too hot, then when it trys to re-start, the pressure within the system would not have equalised, and the compressor would draw an even bigger start current. The more cooling air a fridge can get, the better.

 

Ian

 

Interesting...

 

I shall pull the fridge out tonight so it has lots of cool air around it and see what happens. Otherwise it looks like i will have to live with it.

 

Thanks for the advice as ever people.

[Chalky]

I've been playing with this one as well. I used to get similar problems - the first fix was to get an inverter that could handle the surge. If it's 1800W is that continuous or the surge rating?

The comment about airflow round the condensor is valid. Talking to colleagues of mine who specialise in this there can be very significant increases in pressure and this can put huge loads on the compressor and even stall it.

Another thought is how healthy are the batteries. I had problems with sulphated batteries that couldn't provide the surge current and caused the voltage to collapse triggering the alarm.

[Paringa]

1800W continuous i believe...

 

Batteries on here i really don't know about. Couldn't tell you specifics but they are a couple of years old now at least. They do get treated well though as i am always pottering about, or if moored on Solar or gennie and battery charger. Slightly off topic, is it possible to not "excercise" a battery bank enough? They rarely go below 70% you see.

 

Sterling 4 Stage charger.

 

Steca 2020 and 175W x 3 panels. Charger is multi-stage including a monthly anti-sulphation charge.

 

Kestrel Alternator controller.

 

6 x110Ah bank wired for 24V

Edited September 1, 2011 by Paringa

[Bob18]

A few things.

First, and by no means least, fridges (and air-con units) are notorious for their massive start up currents. You can expect to see a small compressor attempting to draw 10 to 20 times the run current. So if your fridge runs with 1A, you could be seeing a start-up current of about 20A, and 20A at 230V is 4600W "instantaneous" demand, possibly for as long as a second in the worst case. I doubt that your 1800W (continuous rating)inverter is capable of doing that without some sort of protest.

 

If the voltage at the input to the inverter is low then it will run into overload much sooner than if the voltage is at, or above, the nominal. So for you 24V system if the input voltage is below 24V then you are going to hit a limit sooner than if its above. 25.7 is a pretty good voltage, but what happens when you put a smallish load on (say the tunnel light)? If there is more than 0.1V drop you could be heading into battery problems...

 

During start the input voltage to the inverter will drop, how far depends on the battery capacity, the state of the batteries, the type of batteries, the wiring, the state of the wiring. If you have a multi-metre which has max/min capture capability it will be possible to see what the inverter input voltage is doing during that first couple of seconds of a fridge cycle, you may be in for a shock!

The situation will be worse if you have a low cost "quasi-square" (sorry, "quasi-sine"), or "modified sine" inverter. Several reasons for this, but generally they just aren't as well engineered as the more expensive "pure sine" inverters.

 

Compressors are hard to start for a number of reasons, including:

Trapped refrigerant, if the fridge is "short cycling" then the refrigerant will not have time to get back to the right place before the next start. For most domestic fridges the time between stops and starts should be a few minutes.

Small ones tend not to have by-pass valves, which are opened to allow the compressor to speed up under virtually no load, then progressively close. Obvious really, if you start under no load then its easier to spin...

Then there are things like start windings, which are designed to give high torque, start capacitors, split windings (you only use "half" the motor for a few seconds)

Variable frequency drives (getting a bit fancy, you ramp up the frequency from almost DC to 50Hz, which reduces the peak current demanded (and a few more...).

Such things are rarely fitted to small domestic fridges because of COST. From what I've seen of these they tend not to have even a start winding or start capacitor , but are "full load" synchronous motors.

 

 

So, what can you do?

First, check the STATE of the batteries, not just the voltage, but their ability to deliver a decent amount of current at the terminals (borrow one of those old fashioned high current discharge tester that garages used to use).

Second, check the STATE of the inter battery wiring, 35mmsq minimum between the cells, to the isolation switch and to the distribution panel.

Third check the STATE of the battery isolation switch, fuse holder, and wiring to the inverter - which should be AT LEAST 25mmsq (If the battery is really very close close to the inverter, you may get away with 16mm sq, but only if its really close say 1m on each of the pos. and neg cables from the battery). Make sure all connections are secure, and no visible damage to visible cables.

Forth, check the STATE of the mains wiring (with it turned off and isolated....). Make sure all connections are secure, and no visible damage to visible cables.

 

Good luck, and if all else fails, ear plugs....

 

 

 

Bob

[Gibbo]

Well there's a novelty. A new member who talks sense

[Paringa]

Thanks Bob for that comprehensive explanation.

[Chalky]

Does the problem occur every time the fridge starts or just when you turn the inverter on? If it's when you turn the inverter on then it's probably the DC link capacitors charging up. The inverter switches (Mosfets or IGBTs) create huge amounts of ripple on the DC input (12/24V) to the inverter and capacitors are added to control this. When first turned on these will take huge currents and due to the internal resistance of the battery this can cause the voltage to drop causing a low voltage alarm. Higher power inverters (read 50 kW +) have a pre-charge circuit to limit this current (can be in excess of 4000A) and will take a couple of minutes after turning on before they're ready to use. They also have active and passive discharge circuits and strategies to discharge them on switch off.

[Bob18]

The way I read the original post is that its when the fridge kicks in, so I think we can rule out any inrush capacitors on the inverter whining.

 

A couple of questions - Does the same thing happen when a heavy resistive load, like a kettle get plugged in?

And, what make and model is the inverter?

[WotEver]

A couple of questions - Does the same thing happen when a heavy resistive load, like a kettle get plugged in?

From the OP:

 

This becomes more likely if i am running any additional appliances.

 

And, what make and model is the inverter?

 

From the OP:

 

When i run it a Zanussi ZRX-407W domestic compact fridge through my 1800W Powermaster inverter...

 

Tony

 

If it is the PM-1800L (for that appears to be the only current 1800W inverter that Powermaster manufacture) then it's an LF PSW with a peak power of 3600W.

 

3600W is probably insufficient for the compressor start-up, especially if (as Gibbo suspects) the voltage at the inverter input is low.

[larkshall]

Well you have saved me a few quid on some nonsense...

 

The batteries are at 97% and 25.7 Volts.

 

The cables are monsters but i will check the master switch. The annoying thing is i had a full sized under-counter fridge running fine from Zanussi but i needed to move it under the sink to fit a Washing machine - That was another nightmare i don't want to visit again - This is the last of the fall out.

 

I might have missed something here, But these problems start when you moved the fridge? Or are we talking about a different fridge?. Because if you moved the fridge further away in cabling terms from the inverter output, I'd suspect your 'mains' wiring. If talking about a different fridge, bin this response.

[Bob18]

Interesting, I looked at a couple of sites flogging these inverters, and the OEM site, and got three different overload ratings, 3600, 4500 and 5400. Being a pessimist when it comes to how people state their ratings I'd go with the lowest, and that is "marginal" for the fridge - sometime it will, sometimes it won't, but never will when you want it to be nice and peaceful.

 

If everything else is OK, then its one of the options listed in the original post - I'd start with a decent soft-start device, if it works its only a few tens of quid compared to the hundred/thousands for the others. (Ignore comments about cutting out the alarm, there may be a time when its a "real" alarm and not a transient one...)

[WotEver]

Interesting, I looked at a couple of sites flogging these inverters, and the OEM site, and got three different overload ratings, 3600, 4500 and 5400. Being a pessimist when it comes to how people state their ratings I'd go with the lowest...

The Powermaster site states 3600.

 

Tony

[smileypete]

Try connecting a 10 amp load across the DC terminals of the inverter, and measure how much the voltage drops at that point as a result, to 2 decimal places.

 

Post the difference in voltage across the inverter input terminals, with and without the 10 amp load.

 

(When the fridge kicks in the voltage drop will be 10-15x what you have measured.)

 

cheers,

Pete.

Edited September 4, 2011 by smileypete