Generator Vs Combi Fridge/freezer

[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

 

[Darkwood]

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.

 

[Lucien Nunes]

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.

 

[marconi]

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.

 

[Marvo]

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.

 

[marconi]

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.

 

[Lucien Nunes]

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.

 

[Marvo]

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.

 

[marconi]

post deleted

 

[Marvo]

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.

 

[marconi]

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.

 

[shanky887614]

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.

 

[pemaldini]

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.



Cheers
Paolo

 

[pemaldini]

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

 

[Lucien Nunes]

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.

 

[marconi]

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.

 

[pemaldini]

The variant of EG2200X genset that I have does also support 220v

 

[marconi]

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.

 

[marconi]

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.

 

[Lucien Nunes]

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.

 

[Marvo]

The only info I have on the jaixipera compressors is a cross reference chart that shows the max start current as 10.6A (230v @ 50Hz) which is pretty close to what Defy told you so I'd probably work on an 11A maximum requirement from your generator at 240v. I think the 2.2KVA unit may be a little shy of the mark, as Lucien says it will depend very much on the electronics in the generator's AVR. If you can try before you buy then I'd start with the 2200VA or 2500VA Honda, if not and you want to guarantee it will work I'd go with a 3000VA Honda which will give you 12.5A Max, that way there's a small allowance for power factor there as well.

*Edit* I personally wouldn't recommend you run a 50Hz compressor on 60Hz, it will affect the head pressure the compressor is under, the system may also under condense especially in high ambient temperatures in Zambia and could result in refrigeration problems and maybe even premature compressor failure. Domestic refrigeration on R600 can be a bit skittish and sensitive at the best of times. I'd suggest you stick with a 230-240v 50hz genny which should be the local standard.

 

[pemaldini]

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.

Hi Marconi

I have checked on the genset in question, and I guess it is a model that was made for our part of the world, as it outputs 220V and it clearly states on the machine 50Hz.

 

[pemaldini]

I have now had the genset serviced, and connected it up to the fridge. It runs fine whilst the fridge is in "running" mode, and every 15mins or so, I guess the compressor "starts up" and you can hear the genset take some strain but seemingly manages to power on through. Not long after it settles down again as it goes back to "running" mode.......Rinse and repeat.

My temperature logger inside the fridge som far appears to show that temperatures are being maintained, although I need to run it longer to confirm this.

 

[Marvo]

I'm glad your generator is handling things. Just out of interest how often are you experiencing power outages and what duration are they?

Also have you considered rather using an absorption refrigerator which can run on LPG or even a 12v battery? They're often sold as camping fridges. You could set up a solar panel and battery charger and use LPG as a back-up power source if there's insufficient solar. I'm sure this would work out cheaper in the long run and would remove the headaches of constantly servicing and fueling the genny not to mention removing the noise pollution as well.

 

[marconi]

I have now had the genset serviced, and connected it up to the fridge. It runs fine whilst the fridge is in "running" mode, and every 15mins or so, I guess the compressor "starts up" and you can hear the genset take some strain but seemingly manages to power on through. Not long after it settles down again as it goes back to "running" mode.......Rinse and repeat.

My temperature logger inside the fridge som far appears to show that temperatures are being maintained, although I need to run it longer to confirm this.

By Marconi A satisfactory outcome. Forgive the tooing and frooing on detail but I am sure you appreciate the detail matters if one wants to avoid doing something unsafe or which might cause damage or a fire.

I (and I am sure 'we') do not recommend you power sensitive electronic or electrical equipment - such as computers and TVs - at the same time as you power the F-F . Lighting would be fine.

 

[Lucien Nunes]

Absorption fridges are really heavy loads on 12V - the mains/LPG/12V one I used to have on the boat used 9A continuously without thermostatic control and it was a tiny 2 cu.ft. They are only supposed to run on 12V when your vehicle engine is running. I replaced it with a 6 cu. ft. 12V compressor fridge and that reduced to an average 0.5-1A depending on weather. 2A while running, 25% duty cycle up to about 50% in peak summer. That is definitely practical to run on battery / solar, although if the OP needs a similar amount of freezer space the consumption mounts up.

 

[Marvo]

Yes, the R717 (ammonia) absorption systems generally need a heater of around 100-120watts. On 12 volt this would equate to 8-10Amps which isn't a great prospect on its own because it will be a considerable drain on batteries...but you can use a 12v heater so efficiency-wise there would be no conversion losses. The massive advantage is that with an absorption fridge you can use grid power when it's available with solar/battery for back-up plus it could run on one of those little baby generators they sell for emergency/camping lighting if there was a long outage. The load it presents is linear and there's no nasty start currents to worry about. I've even seen one set up to use direct sunlight with a Fresnel lens and a curved mirror. Also the absorption fridges tend to be better insulated because whilst they'll easily achieve minus 18C, they're not as powerful and fast as a recip compressor so they usually go to town on the insulation to compensate somewhat.

 

[pemaldini]

I'm glad your generator is handling things. Just out of interest how often are you experiencing power outages and what duration are they?

Since September 1st we have been given increased load shedding shedules of 9 - 10 hours daily! We have also been told expect to put up with load shedding to some degree for the next 3 years at least!

Zambia is almost 100% reliant on Hydro electric power. The impressive Kariba dam on the mighty Zambezi river producing a large percentage of the Nation's power, as well a number of various other hydro electric plants. The problem we have been facing since around March this year is blamed on numerous factors:

The powers that be largely blame the usually reliable rainfall which over the past 2 years has been very poor resulting in much lower than normal water levels in dams across the country. This is true to a degree.

What isn't acknowledged so much is the mismangement, lack of planning for the future and looking at alternative power sources other than hydro electric.

Upgraded original British pumps at Kariba funded by the Chinese now require considerable extra water throughput to generate the same amount of power as their older British counterparts.

Development in Zambia has been quite positive over the past 2 decades and consequently demand for power has increased substantially (largely from heavy industry such as our expansive mining sector and growing agricultural development). Sadly investment in electricity provision has not kept up.

Power in Zambia is cheap, very cheap and this also adds to the government electricity supplier ZESCO battling for capital to invest in new projects.

The list goes on and on, and I won't bore you all with more details, but suffice to say the outlook regarding electricity in the region is quite bleak. Not only are the outages long and frequent, but power spikes and low voltages are a constant issue.

Also have you considered rather using an absorption refrigerator which can run on LPG or even a 12v battery? They're often sold as camping fridges. You could set up a solar panel and battery charger and use LPG as a back-up power source if there's insufficient solar. I'm sure this would work out cheaper in the long run and would remove the headaches of constantly servicing and fueling the genny not to mention removing the noise pollution as well.

The genset that we have been discussing has been test run for about 1hr 30mins and appeared to handle the starting amps - one could hear it taking a bit of strain on the odd occasion. The F/F compressor starts up about once every 25mins. Running amps is quite low and the genset seems to cope with that happily. What I don't want is to be reliant for any great period of time on such a small genset, its really there as a backup to our old Lister 7.5kVa 3 phase genset, which touch wood is running said fridge and a number of other components - but she is old.

For now I'm stuck with my DEFY 230V 380ltr fridge/freezer. What I may consider doing in the not too distant future is looking to invest in some kind of invertor battery based system as a backup for the vaccine F/F for when the power is off. I may also like to compliment this with solar owing to our abundance of sunshine in this part of the world. I would also like to add in the ability to power my chicken lights and borehole pump.

 

[Marvo]

I read an engineering report on the Kariba hydro a while back and it didn't paint a pretty picture. It's interesting to hear the electrical supply woes of another country, I'm in Cape Town and SA has been suffering bouts of load shedding on a national level on and off for the last few years and they've been very regular for the last 6 or 8 months. It sounds like we're nowhere near as deep in the kak as you guys but it's a forgone conclusion it's going to get worse before it gets better. At present the evening peak is the big issue and at the worst stage we were getting load shed for 2 hours each day and 4 hours on the odd days. One of the big problems is that they're running open cycle gas turbines for prolonged periods on diesel to make up the load side deficit which is costing them billions of Rands/Dollars in fuel so there's no budget to do anything constructive to address the root problems.

Anyway, back to your fridge. The problem with using a generator to supply a fridge is that the efficiency and cost will be appalling, the generator will be running for long periods when the fridge is at its set temperature and the compressor isn't running. A grid tied inverter with deep cycle batteries would be better, it would take advantage of grid power when it's available and obviously have batteries for backup. Look at the Victron Multiplus if you have a reasonable budget, they can handle multiple inputs including wid turbine, PV panels, batteries and grid power. If it's a bit much then check out the Axpert inverters which can handle PV, batteries and grid and prioritize accordingly.

If you want to use back-up power for a borehole pump then install a ramped soft-start to flatten the inrush current. If the pump isn't compatible with a soft start I'd seriously consider replacing it with one that is otherwise the spec of the inverter will need to cover the start current which will cost a fortune compared to one that just needs to cover the running current.