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INVERTERS - Your opinion on best, and worst


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50 minutes ago, MrFish said:

Have you tried fitting a hard start capacitor to the fridge? 

 

No, I haven't tried anything at all to diagnose or fix it yet. 

 

What's a "hard start capacitor", exactly? Anything like an ordinary start or run capacitor? My level of understanding is low. I've yet to understand the difference between a start cap and a run cap. Now we have a hard start capacitor too! 

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A hard start capacitor is often fitted as standard in newer fridge freezers as well as aircon units. It is a unit that has two main elements, a capacitor and a relay. The relay is required to isolate bthe capacitor after a second or so. It will reduce the start up current spike and reduce the stress on the compressor. You can pick them up for about £20.

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12 minutes ago, MrFish said:

A hard start capacitor is often fitted as standard in newer fridge freezers as well as aircon units. It is a unit that has two main elements, a capacitor and a relay. The relay is required to isolate bthe capacitor after a second or so. It will reduce the start up current spike and reduce the stress on the compressor. You can pick them up for about £20.

Don't see how that would work -- the high startup current for compressors is because the motor takes a lot more current (for multiple cycles of the mains) until it gets up to speed, not a short spike. A capacitor won't fix this...

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1 hour ago, IanD said:

 

That's because fridge power ratings (e.g. 50W) are usually average power over a day according to testing (50W would be 1.2kWh/day or 438kWh/year, which seems rather high).

 

If this is the case and the compressor is only on for (say) 3h a day then the power while it's running would then be 400W. Typical startup current is often taken to be 3x-4x running current, which would then be up to 2kW for a fraction of a second. If the 50W is power while running then the peak power would be much lower than this, but then that wouldn't trip the inverter...

 

I don't know what the measurement interval on your Cerbo is (1 second?) but if the duration of the startup current is less than this (very likely) it could well be under-reading the actual peak value, which is what would trip an inverter.

 

P.S. Inverter overload data for Victron attached, this gives 6x nominal current at startup for single-phase motors like a fridge compressor.

 

 

Utter BS.

 

The fridge motor is about 50W according to both the datasheet and verified by the current output of the Multiplus. When it starts, occasionally if the Cerbo happens to log at exactly the right point it sees 900W, but often it does not register because it misses it. The start up current is thus 18 times the rated motor capacity. Perhaps all the workings of the Multiplus and the measurements are not accurate during this transient and it is recording high, but I posted it in response to MtB's and Tracy's observations that the recommended 10x factor was perhaps a little low and something more conservative would be better.

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A hard start capacitor effectively parallels the start capacitor in an AC motor increasing the phase shift angle thereby increasing the starting torque slightly. It does not give a boost charge from the capacitor. 

Use on a DC motor is different but bear in mind that the popular Danfoss compressor motor has an electronics box which sequentially switches the start and run windings simulating an AC voltage so I don't see how it would work. It is not a 12v DC brush motor at all.

Edited by Tracy D'arth
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37 minutes ago, Tracy D'arth said:

A hard start capacitor effectively parallels the start capacitor in an AC motor increasing the phase shift angle thereby increasing the starting torque slightly. It does not give a boost charge from the capacitor. 

Use on a DC motor is different but bear in mind that the popular Danfoss compressor motor has an electronics box which sequentially switches the start and run windings simulating an AC voltage so I don't see how it would work. It is not a 12v DC brush motor at all.

This set me Googling and I pulled up two items, The first I don't have a clue how it works but it seems to limit the current inrush on starting, https://www.envirogadget.com/energy-saving/savaplug-energy-saving-device-for-fridges-and-freezers/

 

The second seems much more plausible for overall power saving by reducing cycling but not start current https://www.mdggroup.co.uk/energy/fridge-unit-energy-savers/

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47 minutes ago, PeterF said:

 

Utter BS.

 

The fridge motor is about 50W according to both the datasheet and verified by the current output of the Multiplus. When it starts, occasionally if the Cerbo happens to log at exactly the right point it sees 900W, but often it does not register because it misses it. The start up current is thus 18 times the rated motor capacity. Perhaps all the workings of the Multiplus and the measurements are not accurate during this transient and it is recording high, but I posted it in response to MtB's and Tracy's observations that the recommended 10x factor was perhaps a little low and something more conservative would be better.

Not utter BS -- I said *if* the fridge power was rated that way, which many are as part of the energy rating scheme. If it's a running power figure (which I also said was possible) then as you say the startup will be 50W multiplied by a large factor, which can still be enough to trip an inverter. Different manufacturers use different ways of specifying power consumption -- ideally they'd give all three figures (peak startup, running, 24h average) but most don't.

 

Whether it trips or not is 100% dependent on the fridge *and* the inverter -- a given fridge may trip one inverter and not another, a given inverter may be tripped by one fridge and not another. The only way to be sure is to suck it and see.

Edited by IanD
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Inverters also differ in their abilities to supply short term power over their headline rating. For example, many Victron inverters can supply double their official capacity for a short time. The definition of short time varies too, but the second or so of a fridge starting up is pretty short. Something else to look for on the inverter specs.

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16 minutes ago, Jen-in-Wellies said:

Inverters also differ in their abilities to supply short term power over their headline rating. For example, many Victron inverters can supply double their official capacity for a short time. The definition of short time varies too, but the second or so of a fridge starting up is pretty short. Something else to look for on the inverter specs.

I posted the overload times for Victron inverters earlier -- the 2x rating is valid for 0.5s, which is probably longer than the motor startup time of a fridge compressor.

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I'm not saying people are wrong but 50w seems like a very small motor ?

I looked to see what a typical fridge power rating is but all the specs quote annual KWh 

 

50w seems unfeasibly small to run a compressor in a fridge are they really that small ? 

 

 

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I personally cant fault this one...20221019_193106.jpg.28c5e4b718030dc657ce1838c65324da.jpg

 

Installed 18 months ago to directly supply a Lieberhh1710  150 litre capacity fridge. Hasnt missed a beat, even in this years record temperatures, and we were within 0.1c of the national record breaking temperatures 2 days on the trot.

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1 hour ago, jonathanA said:

I'm not saying people are wrong but 50w seems like a very small motor ?

I looked to see what a typical fridge power rating is but all the specs quote annual KWh 

 

50w seems unfeasibly small to run a compressor in a fridge are they really that small ? 

 

 

My fridge draws 45w, measured.

If you think about it fridges run about 1/3 of the time so  45w x 8hrs x 365days = 131.4kWh

About the yearly consumption of a fridge.

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1 hour ago, jonathanA said:

I'm not saying people are wrong but 50w seems like a very small motor ?

I looked to see what a typical fridge power rating is but all the specs quote annual KWh 

 

50w seems unfeasibly small to run a compressor in a fridge are they really that small ? 

 

 

 

Our 12v fridge draws about 3A when the compressor is running, ie 40w or so.

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My boat came with a Sterling 1600 watt modified sine wave model, and within 6 months two laptops had bitten the dust with knackered battery systems, although they still worked if permanently plugged in. To be fair, no other electrical gadgetry seemed to be affected by the nasty cheap modified sine waves. 

That 1600 watt model also had a very noisy fan that, for reasons only known to itself, kicked into action at various random hours during the night, which was extremely sub optimal in terms of one's sleeping experience. 

After it damaged two laptops, I replaced that noisy POS with a 2000/4000 watt pure sine model that cost I think £250 from Amazon, and that one is still going ok 18 months later. 

Amazon products vary wildly in quality and I took a gamble on it because it had several thousand very good reviews, but there really is no being sure with them, so its not something I'd strongly recommend unless budget is such an important issue that a posh model is out of reach.  

The 2000 watt model seems to run a 1000 watt kettle with no problem, and I discovered by error that (for a few minutes anyway) it will even run the kettle plus the 1000 watt immersion (i.e. when I've forgotten to switch one of them off).  

 

 

Edited by Tony1
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Fridge chosen as at the time, it was the most efficient non-smart fridge on the market.

It didnt particularly like the chunky MSW of our 30 year old Heart Inverter (might just have been the LED fridge light pulsing), so we gave it it's own dedicated feed.

 

 

20221019_203527.jpg

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12 minutes ago, roland elsdon said:

? Smart fridge 

One which is digitally and computer controlled(therefore more power waste), you can use an app to both see what you have in your fridge, check shelf life of products in fridge, order via supermarket apps for redelivery etc.

Yes, these things exist!!

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46 minutes ago, Alan de Enfield said:

 

No, its actually more than 20% higher than most marine fridges.

Mine is 40w. (CR80) and has a measured <30Ah per day.

 

 

 

Yes but we were talking about mains fridges running off inverters. 

I have the CR65 and a total freeze 45 fridge/freezer and that is 45w. 

So I suppose mains fridge compressors could be the similar.  So quite surprising that fairly large inverters struggle with them...

 

 

 

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1 hour ago, jonathanA said:

Yes but we were talking about mains fridges running off inverters. 

I have the CR65 and a total freeze 45 fridge/freezer and that is 45w. 

So I suppose mains fridge compressors could be the similar.  So quite surprising that fairly large inverters struggle with them...

 

 

Here is the data label from the cheapo fridge. The fridge which makes my 2,500W PSW Sunshine Solar inverter throw a total screaming wobbly of beeps and flashing red lights when asked to start it:

 

 

image.jpeg.a9333d68e363f3880f63ef26f0cd9277.jpeg

 

 

 

 

 

 

I'm gonna try connecting it to a bigger battery next, before mucking about with adding start capacitors.

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To the OP: Have you seen this thread?

 

 

Pay attention to the earthing arrangements of the inverter. The cheap ones on Amazon and eBay tend to have a floating earth. What you really need for a boat with a mains ring, consumer unit and breakers is neutral-earth bonding otherwise your breakers won't work in the event of an earth fault. 

 

I recently sold my Sterling 1800w MSW for £50 and replaced it with a Sterling 2200 SB (R) PSW model (£500 from Cactus). Both inverters are N-E bonded. 

 

I previously bought an 2000w inverter from Renogy for £250 not realising it wasn't N-E bonded. When I asked them if the output could be bonded they told me it couldn't so I sent it back. In my opinion it's criminal that the specs on so many of those cheap inverters don't detail the earthing arrangements. It could end up killing someone. If you can't find it in the product specs assume it's floating earth.

 

From my new inverter manual.

IMG_20221017_163730.jpg

Edited by blackrose
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11 hours ago, matty40s said:

One which is digitally and computer controlled(therefore more power waste), you can use an app to both see what you have in your fridge, check shelf life of products in fridge, order via supermarket apps for redelivery etc.

Yes, these things exist!!

Ah. Part of the global reset. You have seen our boat and its high tech systems.

 

It has rolls royce electric induced lighting program. A futuristic forward motion enabling device, obviating the requirement for hay power, and best of all i now find it has smart devices.

A cooling device which on finger demand smartly and unobtrusively keeps food fresh, and a cooking unit that without complaint removes the ‘coldons’from the food previously in the fridge.

Truely we are blessed with technology.

 

Need to however to sort out the ambient temperature modifying unit.

It is smarter than me. I am its slave fetching carrying emptying and scrapping to its every whim whilst in gratitude it urinates black slime down the cabin side.

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