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pemaldini

Hi

I am currently out in Africa experiencing horrendous power outages. I therefore have the need to hook up my DEFY combi fridge/freezer (model DEFY DAC512) to a small standalone backup generator from time to time. It is important to have the backup power option as the fridge houses livestock vaccines and needs to maintain the contents at a temperature range of +2C to +8C.

The manufacturer's website only lists the following tech specs on this model:

  • Energy consumption (kwh/24h / kwh/yr)1.01 / 372

Is this sufficient information for one of you learned chaps to advise on a minimum sized single phase petrol generator I should look for? Folks here talk of genset output ratings in kVA.

If one needs more information, what specifically should I try to find out further?

Many thanks
Paolo

 
Hi permaldini and welcome to the forum, I have approved access to the main forum so you can get faster responses, when Admin' is next on line this thread may be relocated to the DIY section and and your status updated ... cheers.
 
Unfotunately that is the average power consumption over time and not the actual motor load when it is running. The running load is probably in the 100-200W range, and even allowing for the power factor any generator of 500VA or more should be happy with it, but what is most important for an ordinary compressor refrigeration unit such as this is the starting load. This could be more like 2-3kVA and generators will differ in their ability to support that load for the half-second or so it takes the fridge compressor to start. Most domestic freezers will be similar in this regard, so a generator that will start one freezer will probably start most others. There may be a certain amount of experiment required, as generator makers are often rather optimistic in their ratings.
 
I had to advise my brother-in-law who has a chain of mobile catering vans using an upright fridge -freezer, an upright fridge and a flourescent light, to be powered for 12 hours every day.

The power of a fridge freezer is of the the order 300 to 400 Watts. The kVA will be slightly higher so 0.5 kVA. Starting kVA is of the order 6-8 times running kVA so 6-8 x 0.5kVA = 3-4 kVA.

We looked at the the makers of petrol generators and settled for a HONDA GX160. They also do a Liquified Petroleum Gas(LPG) version) which my bother-in-law uses. The GX 160 has an output of 2.7kVA. My brother-in-law has ten catering vans and has had no problems starting the F-F and F.

I also have one at home to supply my home in the remote event of a long power cut to run my wife's medical fridges and equipment.

I looked at the specification for your fridge but like you could find no power figure. I compared the size of your F-F to the ones my B-I-L uses and my wife's LIEBHERR fridge and found yours is similar. Ours use 300 watts.

Hope this helps.
 
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If you can give the make and model number from the compressor I'll look up the start and run current for you.

I also GUESS you'll need a 2KVA generator if it's a good brand name like a Honda. If it's a cheaper lesser known brand you might need a 3KVA.
 
Dear Marvo, My response and recommendation was not a GUESS. It is based on a good understanding of electrical engineering concerning ac motors and generators coupled with some REAL experience of a problem which I solved satisfactorily for my BIL. Again, I confirmed the similarity of the OP's F_F with my wife's medial fridge and my BIL's. For example in 24 hours the OP's consumes 1.01 kWh. My wife's LIEBHERR see MKv 3913 uses 1.315kWh and draws when running 1.5 Amps at 230 volts equals 345VA.

I challenge you to justify your figure of 2kVA. (But above all let us not fall out which would mortify me.)

:)

http://electrical-engineering-portal.com/basics-of-3-phase-induction-motor-1 to justify my starting to running ratio. Ok I said 6-8 - this says 6-7.
 
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I can't speak for Marvo but when I say 'guess' I usually mean 'make a numerical Fermi estimate based on sketchy data I that haven't got time to refine or justify' and in this case the data are a bit fuzzy.

Your reference is for 3-phase motors under typical load duties which this is not. The compressor's starting characteristics are governed by a greater number of factors including the typical head pressure and behaviour of the PTC, plus the rather refrigeration-specific problem that if it gets short-cycled and tries to start against excessive head pressure it is designed to stall, trip the Klixon (usually after a few seconds of locked-rotor current), and retry starting a few minutes later. We have not yet considered the type of generator and its tolerance of poor pf and overload. A self-regulating brushless unit, one with an AVR and an asynchronous inverter type will all behave differently and have different real power (engine output) headroom.

Thus, whilst I too have some theoretical knowledge of motors and generators, I am more inclined to rely on practical experience of various models of generators and inverters staggering (or not) under various kinds of starting load.
 
I wasn't suggesting you were guessing, I was the one who was guessing. I didn't see you post to be honest, only Lucien's and after years of practice I'm qualified to pull figures out of thin air without any evidence of their validity whatsoever :).

I'd usually work on a start/run ratio of around 10 to 1 for a domestic fridge compressor, especially on R600 although it could even be higher. I took a completely arbitrary figure of the compressor being about 1/5th HP ish and came up with an arbitary start current of around 7 or 8 ampsish. a 2KVA ish Honda seemed plausible but it might be a bit close to the mark for a cheapie generator so 3KVA ish if it's an unknown brand. I can't back any of this up it just feels about right;). If the OP comes back with a compressor make and model number I'll look up some hard figures.
 
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Yep, I didn't see your post before I made my first reply to the thread... and I'm joking about being qualified to guess due to years of practice hence the smiley.
 
I can't speak for Marvo but when I say 'guess' I usually mean 'make a numerical Fermi estimate based on sketchy data I that haven't got time to refine or justify' and in this case the data are a bit fuzzy.

Your reference is for 3-phase motors under typical load duties which this is not. The compressor's starting characteristics are governed by a greater number of factors including the typical head pressure and behaviour of the PTC, plus the rather refrigeration-specific problem that if it gets short-cycled and tries to start against excessive head pressure it is designed to stall, trip the Klixon (usually after a few seconds of locked-rotor current), and retry starting a few minutes later. We have not yet considered the type of generator and its tolerance of poor pf and overload. A self-regulating brushless unit, one with an AVR and an asynchronous inverter type will all behave differently and have different real power (engine output) headroom.

Thus, whilst I too have some theoretical knowledge of motors and generators, I am more inclined to rely on practical experience of various models of generators and inverters staggering (or not) under various kinds of starting load.

By Marconi - I was not responding to anything you wrote earlier. Indeed you did not use the word guess or imply guess in your response. There is nothing in what you wrote first I disagree with.

In my responses to posts I address them to the OP (albeit I have had a few one liners to later responders). It all becomes too confusing otherwise.

With regards your second post - yes I agree as much as I can. Compressors and the like I did in the 2nd year of my engineering degree which some time ago.

But I attempted to answer the OP's question using some knowledge of electrical engineering and experience - not the same as yours nor of others, but enough to lead me with enough confidence to make a recommendation. But I stand by my recommendation of a Honda GX160 if the F_F inquestion is similar to the ones I mentioned, and reasonably I expect they are similar. I am well aware I could be wrong but I am prepared to make a reasonable recommendation reasonably thought through and researched and backed up by some experience in solving a similar problem. Indeed, so did MARVO. You explained why you are not in a position to - fair enough.
 
By Marconi - I was not responding to anything you wrote earlier. Indeed you did not use the word guess or imply guess in your response. There is nothing in what you wrote first I disagree with.

In my responses to posts I address them to the OP (albeit I have had a few one liners to later responders). It all becomes too confusing otherwise.

With regards your second post - yes I agree as much as I can. Compressors and the like I did in the 2nd year of my engineering degree which some time ago.

But I attempted to answer the OP's question using some knowledge of electrical engineering and experience - not the same as yours nor of others, but enough to lead me with enough confidence to make a recommendation. But I stand by my recommendation of a Honda GX160 if the F_F inquestion is similar to the ones I mentioned, and reasonably I expect they are similar. I am well aware I could be wrong but I am prepared to make a reasonable recommendation reasonably thought through and researched and backed up by some experience in solving a similar problem. Indeed, so did MARVO. You explained why you are not in a position to - fair enough.
when you post it is usually taken as replying to the above post unless otherwise stated or quoted for example i quoted you post so everyone can see its aimed at you or to add to the post.
 
If you can give the make and model number from the compressor I'll look up the start and run current for you.

I also GUESS you'll need a 2KVA generator if it's a good brand name like a Honda. If it's a cheaper lesser known brand you might need a 3KVA.

Hi Marvo

And thanks to you all for all your responses so far. I have taken a picture (below) of the sticker that I believe to be the compressor for those of you who offered to try to look up the details on it.

Generator Vs Combi Fridge/freezer Fridge_compressor - EletriciansForums.net

Cheers
Paolo
 
Hi again

I have just managed to get hold of the fridge manufacturer in South Africa (DEFY) who inform me of the following:


  • Starting current: 7.5 - 10 amps
  • Running current: 1 - 1.5amps

As it happens I have access to a HONDA EG2200X (Honda engine GX140) which has the following tech specs (online manual):


  • 120V (60Hz)
  • 16.7A
  • Rated Output: 2.0kVa (2000W)
  • Max Output: 2.2kVa (2200W)

This manual I found online only talks about 120V as used in the States. We here in Zambia like in the UK work off 220V or is it 240V. So I'm still a bit confused.

In a nutshell do you think this genset would be sufficient to run this fridge/freezer?

Thanks
Paolo
 
2000VA / 120V = 16.7A rated output. For the 240V version of the generator the current will be 2000/240=8.3A rated, 2200/240=9.2A max. It might well work, especially as I think this genny has a proper electronic voltage regulator and it is engined sufficiently for 1.0pf (wattage rating = VA rating). But the poorish power factor of induction motors can affect the voltage of small generators and reduce their useful output below quoted figures, so you would have to test it to be sure.
 
Hi again

I have just managed to get hold of the fridge manufacturer in South Africa (DEFY) who inform me of the following:


  • Starting current: 7.5 - 10 amps
  • Running current: 1 - 1.5amps

As it happens I have access to a HONDA EG2200X (Honda engine GX140) which has the following tech specs (online manual):


  • 120V (60Hz)
  • 16.7A
  • Rated Output: 2.0kVa (2000W)
  • Max Output: 2.2kVa (2200W)

This manual I found online only talks about 120V as used in the States. We here in Zambia like in the UK work off 220V or is it 240V. So I'm still a bit confused.

In a nutshell do you think this genset would be sufficient to run this fridge/freezer?

Thanks
Paolo

Dear Paolo,

http://cdn.powerequipment.honda.com/pe/pdf/manuals/31ZB0010.pdf

I have looked at the HONDA GX2200x specification and it only provides 120 Volts 60 Hz output and your fridge requires 220-240 Volts at 50Hertz (Hz). Disappointingly then it is not suitable to power your F-F. MARVO reckons(earlier post) 2kVA supplied by a HONDA or other good make would be sufficient. I think to reduce the risk, unless you can try a 2kVA set out first, you should aim to procure one of at least 2.7 kVA - I know they work.

PS: The wiring diagram for the GX2200x shows an Automatic Voltage Regulator. When you buy a set enquire what kind of voltage regulator is used as Lucien Nunes has discussed.
 
The variant of EG2200X genset that I have does also support 220v

In that case try it out.

HONDA see http://powerequipment.honda.com.au/FAQ_Generators#What_Size suggest 2.5kW minimum.

If you really want to be sure call DEFY again on the matter of 60 Hz but I suspect they might be non-committal on the use of their compressors on 60 Hz. The higher frequency actually helps matters by reducing the starting current but when running the motor will spin faster which might be troublesome.

Let us know the outcome please.
 
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I have been doing some more research on operating 50 Hz F-F on 60Hz but nothing conclusive. MARVO might have clear advice. Do call DEFY. Nothing wrong in a brief trial to see if F-F will start and run. But don't run it for longer than a minute until we know for sure no damage will be done.
 
On many small gennies you can change the frequency between 50 & 60Hz by adjusting the engine governor. If the power rating is given at 60Hz it will be reduced at 50Hz, because of the lower available engine power. The VA rating might not be so much affected as this depends only on the excitation, which on a good unit should hold up at the lower speed.
 

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