Electrical esoterica

[Kitten Sniffer]

Hullo all, please play nice as I have often struggled to negotiate the bible-sized, yet unwritten rule book on web fora. I'm in the mid to late late stages of a fit-out and am currently 100% solar powered. We have 1Kw and are generally as low drain as possible. Unfortunately, we love some of the modern toys and are proud owners of mains voltage fridge freezer and washing machine, bought with the belligerent intent to power somehow...

We are, of course, fully off-grid. 8 months of the year we are fine, we turn on 2.5k inverter in the morn and off at night. But, as they say- Winters coming... Last year, off went the fridge and we scraped by- please no suggestions about engines or generators, I'm looking at some very interesting alternative renewables but want to cut down the load through the day.

 

Crux point- Am going to buy a 300w sine-wave inverter to dedicate to the fridge and fit an appropriately sized timer switch so the batteries get more uninterrupted charging time and all stays cool. Am I correct in thinking, given a nominal efficiency of 95% that under the same load the small inverter will draw less power than the big?

 

Thoughts, suggestions and electronic insights please.

[by'eck]

Not much room for leeway given your regime. A smaller inverter may have lesser standby current draw but will likely not have a power saving facilty (were it essentially shuts down until needed) so could actually draw more from your batteries overall. Also beware of the relatively large startup current requirements for the fridges compressor when downsizing inverter that powers it.

 

I suspect if you experienced insufficient power last winter, even streamlining your system won't give enough improvement this winter. A better solution would be a DC powered fridge and more solar pv panels. As for washing machine???

[GUMPY]

A 300w inverter will not run a fridge.

You will find that you will need about 1kw to cope with the fridge start up current.

Fridge start currents are of the magnitude of 10x running current.

Edited October 7, 2015 by Loddon

[Paul C]

Solar is great - when its sunny. That means, on certain winter days its basically useless. Everyone else (not on shoreline) seems to cope by running their engine or a generator, obviously it only needs running occasionally compared to a boat with no solar.

[matty40s]

I came home today to 69% so, yesterday I came home to 79%.

I didn't bother running the engine as tommorows forecast (and tonight's sky) says I will be back to 100% when I come home tommorow.

However, it is getting nearer to the time of year when my 540w needs occasional supplementing by engine.

Last time engine ran this year just for power was Feb 18th.☺

Edited October 7, 2015 by matty40s

[peterboat]

how much ah in batteries do you have i have 1 kw of solar plus 1500ah of full traction batteries i have a washing machine and dishwasher i use these on sunny days. i have a wispergen it runs for 3 months of the year for 3.5 hours a day. i think you will have to bite the bullet and use the engine or whatever maybe a wind generator will work where you are sorry

 

peter

[PaulG]

Am I correct in thinking, given a nominal efficiency of 95% that under the same load the small inverter will draw less power than the big?

 

Thoughts, suggestions and electronic insights please.

I think that, under the same load and 95% efficiency, a small inverter will draw a similar current to a large one.

 

There will possibly be a difference under "no load" conditions, the "standby" current, or whatever you want to call it.

 

But since most of the power will be used when your fridge is running, I think the overall difference will be small.

[Kitten Sniffer]

Thank you guys, thoughts for further investigation- Haven't been using the power save function on inverter as it can scare the fridge, I shall try further investigations. Time to poke the manufacturer for peak start up current to ensure compliance if dedicated inverter route is engaged. Current fridge may be 240v but is A+++ and uses only 160w, DC fridges are ugly, inefficient and extremely expensive- if anyone can prove me wrong, please do.

I'm under no illusions that a wee power trim will solve the problems, I'm in the process of installing a supplementary, winter specific alternative energy DC charging option to augment the solar (we have 1kw and can't fit more until they make PV that is more efficient per Sq M) anything to avoid the drone and cost of a generator and my tractive engine should be reserved for that reason, my question is more to find the technical faults in my plans- I'm not an electrical engineer and an admission of ignorance can often bear the fruits of knowledge.

[Kitten Sniffer]

Paul G- you must've posted as I did. You perspicaciously and succinctly get my thinking. The fridge spends a lot of time not actively doing too much, it is this no-load load of a large inverter I'm trying to subtract from the total daily energy requirement. Hopefully new winter renewables will make the point irrelevant...

Edited October 8, 2015 by Kitten Sniffer

[Tom and Bex]

I'm interested in what you're planning to top up the solar during the winter.

 

Have you though about using a separate thermostat mounted in the fridge (with the existing set to max cold) to switch the inverter on and off directly? This would mean the inverter was only on when the fridge was running so eliminating the inverter standby current.

 

Tom

[Murflynn]

I feel a Bizzard moment coming on................

You haven't said that your fridge is a fridge/freezer combi. Assuming that it is not, if you relocate the fridge to an outside location you may not need any/much power at all for many months of the winter period, just make sure that it's sheltered from solar gain. Having said that, you could insulate it with solar panels, thus increasing your supply on those warm sunny days when your fridge needs to be switched on.

[bottle]

 

if you relocate the fridge to an outside location

 

That assumes that the fridge is designed to work in a lower ambient temperature.

 

Unless you are just using it as an insulated cupboard.

[Murflynn]

 

That assumes that the fridge is designed to work in a lower ambient temperature.

 

Unless you are just using it as an insulated cupboard.

my fridge-freezer has a heater bulb (the door light, which can be set to be on permanently) located next to the thermostat, designed to kid the fridge that it needs to work when the ambient is relatively cold.

mind you, that is intended to ensure the freezer section continues to work when the fridge doesn't need to.

[bottle]

I'm impressed.

 

I only flagged it as many people do not understand that fridges and freezers are designed for different ambient temperatures.

 

Not boat related but some people have had problems putting a freezer in the garage and not checking it was suitable.

[by'eck]

I'm impressed.

 

I only flagged it as many people do not understand that fridges and freezers are designed for different ambient temperatures.

 

Not boat related but some people have had problems putting a freezer in the garage and not checking it was suitable.

 

Certainly had this issue on my boat during winter layup. As I was finding that food in the freezer compartment was defrosting during low outside temperatures, I turned up the thermostat (cooler) to compensate. This worked until I found a burst can of coke after weather had warmed up - sometimes you just can't win

[Kitten Sniffer]

So, it is a fridge and a freezer

http://www.samsung.com/uk/consumer-images/product/refrigeration/2014/RB31FERNBSS-EU/RB31FERNBSS-EU-2200755-0.jpg

 

And the image will show it's not really and outdoors sort, so ambient temp will be within household nominals.

 

Tom- I'm probably being dense but please expand on your thermostat thoughts. One of the reasons I was thinking of a small dedicated inverter for the fridge is that I can fit a 30 amp timer switch. My large inverter has a 400 amp fuse and 70mm cable- try finding a timer switch that could handle that load that isn't seriously industrial... Not a thermostat, but would allow the fridge to work hard for an hour then rest for two or three whilst the power trickles into the batteries. I'm still chasing Samsung technical to find out the start up volt/watt/ampage that might kaibosch the idea anyhoo..

 

With reference my winter alternative to power generation, I'm designing and building a thermoelectric generator system that uses burner heat and makes electricity and hot water. Remember- energy cannot be destroyed, only changed or wasted. Once perfected, I'm going to sell and install the system to those of us who want off-grid with renewables but without the generator...

[by'eck]

So, it is a fridge and a freezer

http://www.samsung.com/uk/consumer-images/product/refrigeration/2014/RB31FERNBSS-EU/RB31FERNBSS-EU-2200755-0.jpg

 

And the image will show it's not really and outdoors sort, so ambient temp will be within household nominals.

 

Tom- I'm probably being dense but please expand on your thermostat thoughts. One of the reasons I was thinking of a small dedicated inverter for the fridge is that I can fit a 30 amp timer switch. My large inverter has a 400 amp fuse and 70mm cable- try finding a timer switch that could handle that load that isn't seriously industrial... Not a thermostat, but would allow the fridge to work hard for an hour then rest for two or three whilst the power trickles into the batteries. I'm still chasing Samsung technical to find out the start up volt/watt/ampage that might kaibosch the idea anyhoo..

 

With reference my winter alternative to power generation, I'm designing and building a thermoelectric generator system that uses burner heat and makes electricity and hot water. Remember- energy cannot be destroyed, only changed or wasted. Once perfected, I'm going to sell and install the system to those of us who want off-grid with renewables but without the generator...

 

I would assume the thermostat control to inverter would be via its software controlled on/off switch with virtually no current to worry about.

[Phil Ambrose]

Hmm, 12v fridges are ugly? hey it's just a white box. 12v fridges are inefficient? never noticed, been living aboard for 15 years, on and off grid

12v fridges ate expensive, yes but in mu mind worth it

I first had 500w PV array over 12 years ago.

However I wish you well in your quest.

Phil

ETA we have a 12v freezer plus washing machine and tumble dryer which our Genny takes care of.

Edited October 12, 2015 by Phil Ambrose

[Robbo]

Hmm, 12v fridges are ugly? hey it's just a white box.

The fridge I want looks like the below (Isotherm Cruise CR200) and I can't find a 240v one that's anywhere as similar.

 

Edited October 13, 2015 by Robbo

[Phil Ambrose]

The fridge I want looks like the below (Isotherm Cruise CR200) and I can't find a 240v one that's anywhere as similar.

 

 

?

Phil

[by'eck]

The fridge I want looks like the below (Isotherm Cruise CR200) and I can't find a 240v one that's anywhere as similar.

 

 

Available with AC/DC operation or DC only but at humungous price.

 

Click for info.

[Neil Smith]

If you are in an exposed area then a large wind genny on a tall pole will put some power in your batts in the winter if its windy.

 

Neil

[by'eck]

If you are in an exposed area then a large wind genny on a tall pole will put some power in your batts in the winter if its windy.

 

Neil

 

[Robbo]

 

Available with AC/DC operation or DC only but at humungous price.

 

Click for info.

As said, can't find anything similar. All 240v fridge freezers seem to be free standing and not undercounter. And if you do find a nice looking one it will be more likely similar price. Edited October 14, 2015 by Robbo

[by'eck]

As said, can't find anything similar. All 240v fridge freezers seem to be free standing and not undercounter. And if you do find a nice looking one it will be more likely similar price.

 

Could never understand why a different shape costs more money. Same with clothes although my partner would argue the extra money is well worth it.