Fridge + Inverter question

[Biggles]

My boat fridge freezer is an A++ rated Libherre. About 12 season old and still cooling very well.

 

My inverter is a 12/3000/120 Victron Multiplus so plenty of capacity to drive the fridge.

 

I  noticed the inverter was buzzing / humming quite loudly when the fridge kicks in. Nothing else on the boat 240v system causes this. Initially I thought it might be the inverter  but now I'm thinking it's the fridge perhaps not behaving. 

 

I would value some knowledgeable thoughts on this issue.  

 

For example,  would a fridge motor have a capacitor start? If so could this be an issue. 

 

Kevin 

 

 

[Peanut]

Does it buzz all the time, or just when it kicks in?

[Jen-in-Wellies]

Fridges and freezer compressor motors have a high inrush current for a fraction of a second when the compressor first starts. They will typically use around 50W when running, but start up can pull up to 800 to 1000W momentarily. Hence why your inverter is having to work hard when that happens, but soon settles down.

[Biggles]

27 minutes ago, Peanut said:

Does it buzz all the time, or just when it kicks in?

All the time now. Never used to and it cycling more than I recall previously. I.e. I never noticed it before but now its very obvious

[Higgs]

33 minutes ago, Biggles said:

All the time now. Never used to and it cycling more than I recall previously. I.e. I never noticed it before but now its very obvious

 

Disconnect the fridge, for a while, and load the inverter from other sources. If it still makes a buzz, you may have reason to think it's the inverter.

 

 

[DShK]

I recently purchased the same inverter. It humms most of the time (how loud it is based on the load) and makes a ticking sound when under a low/low-medium load. I believe it's normal for the units, but I may be wrong. I believe the humm is just the transformers doing their job stepping up the voltage - and should be humming at 50hz. 

 

They can also make a lot of noise when something uses a diode to switch to half power (heat gun, for example). If you notice this, don't use that mode as it's strong vibrations causing the noise - not good for it.

Edited June 7, 2023 by DShK

[GUMPY]

2 hours ago, DShK said:

They can also make a lot of noise when something uses a diode to switch to half power (heat gun, for example). If you notice this, don't use that mode as it's strong vibrations causing the noise - not good for it.

You will destroy the inverter using this mode. The diode is  shorting the output every half cycle.

 

[blackrose]

20 minutes ago, GUMPY said:

You will destroy the inverter using this mode. The diode is  shorting the output every half cycle.

 

 

So what sort of equipment uses diodes and should be avoided?

[GUMPY]

Hairdryer for one  

C knows not to use half power.

Many other things that generate heat and have a half power setting.

[blackrose]

Ok thanks. 

[sueb]

You don't get those problems with a gas fridge!

[Bod]

8 hours ago, Biggles said:

All the time now. Never used to and it cycling more than I recall previously. I.e. I never noticed it before but now its very obvious

Have you tried De-frosting the fridge?

Too much ice build up can make the fridge run more of the time.

 

Bod.

[Biggles]

17 hours ago, Higgs said:

 

Disconnect the fridge, for a while, and load the inverter from other sources. If it still makes a buzz, you may have reason to think it's the inverter.

 

 

I did that with the 2.2kw kettle,  an 1800w Hoover and the microwave with 850w output.  None of these made the inverter humm like the fridge does.

13 hours ago, GUMPY said:

You will destroy the inverter using this mode. The diode is  shorting the output every half cycle.

 

But the same inverter and fridge for the whole 12 years life of the boat. Clearly only used in cruising season. 

9 hours ago, Bod said:

Have you tried De-frosting the fridge?

Too much ice build up can make the fridge run more of the time.

 

Bod.

No it's a frost free and doesn't have any. 

[Higgs]

25 minutes ago, Biggles said:

I did that with the 2.2kw kettle,  an 1800w Hoover and the microwave with 850w output.  None of these made the inverter humm like the fridge does.

 

Checked all the wiring to the fridge to see if everything is still sound and that the connections are in good shape?

 

 

[blackrose]

20 hours ago, GUMPY said:

Hairdryer for one  

C knows not to use half power.

Many other things that generate heat and have a half power setting.

 

What about a slow cooker (non-thermostat) with different power settings? Is that something to avoid using from the inverter? It doesn't seem to mind it.

 

[GUMPY]

3 minutes ago, blackrose said:

 

What about a slow cooker (non-thermostat) with different power settings? Is that something to avoid using from the inverter? It doesn't seem to mind it.

 

You would hear it if it was a diode.

I suspect that has a tapped winding to vary the heat.

[Tony Brooks]

On 07/06/2023 at 17:09, GUMPY said:

You will destroy the inverter using this mode. The diode is  shorting the output every half cycle.

 

 

I hesitate to question you, but are you sure this is correct. I don't see how it can short out a half phase. I think the diode, in effect, open circuits the half phase. If it shorted it, then I think the actual consumption would go up and probably blow a fuse.

 

I make no comment on its effect on an inverter though.

[GUMPY]

44 minutes ago, Tony Brooks said:

 

I hesitate to question you, but are you sure this is correct. I don't see how it can short out a half phase. I think the diode, in effect, open circuits the half phase. If it shorted it, then I think the actual consumption would go up and probably blow a fuse.

 

I make no comment on its effect on an inverter though.

You are probably correct all I know is it destroys inverters.

I would have thought being open circuit it wouldn't have affected the inverter hence I plumped for short circuit.

[Tony Brooks]

Just now, GUMPY said:

You are probably correct all I know is it destroys inverters.

I would have thought being open circuit it wouldn't have affected the inverter hence I plumped for short circuit.

 

I can't work that out either, but wonder if it produces some excessive harmonics, because it certainly makes them hum.

[GUMPY]

It's early so my brain is not at 100%😉

The diode will only let one half cycle pass through and will block the other half cycle.

Hence I referred to that as shorted.

[Higgs]

1 hour ago, GUMPY said:

It's early so my brain is not at 100%😉

The diode will only let one half cycle pass through and will block the other half cycle.

Hence I referred to that as shorted.

 

Used like that, in altering an AC current, it would produce a DC current. Pulsed at 50 cycles. Half wave rectifier. Fed through a smoothing capacitor, it would produce roughly half the original voltage. 

 

 

 

Edited June 11, 2023 by Higgs

[Tony Brooks]

1 hour ago, GUMPY said:

It's early so my brain is not at 100%😉

The diode will only let one half cycle pass through and will block the other half cycle.

Hence I referred to that as shorted.

I think we agree, if it blocks a half cycle, it has in effect open circuited the circuit during that half cycle.

[blackrose]

What about a fan with different settings, is that ok to run from my inverter?

 

 

[Tony Brooks]

I think a diode is only used on two speed items. I suspect your three speed is done by different windings or PWM speed control. I am not sure how altering the mark space ratio of the supply will affect an inverter.

[DShK]

You'll definitely hear a horrendous noise from the inverter, you'll be able to tell if it's problematic if you're near the inverter. But for what it's worth, my fan doesn't cause a problem.