Inverter installation

[Elena2]

Dear all,

I have motor cruiser with an Onan generator. On board I have a 240 volt only fridge. Is it possible for me to fit an inverter to power the fridge from the engines 24 volt system whilst cruising?

If so, what capacity inverter should I buy?
Should I consider a larger capacity inverter to power 240 volt appliances?
How would I connect to the 24 volt system?

Thank you in anticipation of any advice.

 

[jfm]

Dear all,

I have motor cruiser with an Onan generator. On board I have a 240 volt only fridge. Is it possible for me to fit an inverter to power the fridge from the engines 24 volt system whilst cruising?

If so, what capacity inverter should I buy?
Should I consider a larger capacity inverter to power 240 volt appliances?
How would I connect to the 24 volt system?



OK,

1. you need to decide whether to get big inverter for lots of appliances, or a small one just for fridge. Forum cant decide that for you

2. If fridge only, a small one will do, and doesn't need to be pure sine wave. Just read the wattage of the fridge and match the inverter to that. If you want to power say a ring main used for electronics you need more power and pure sine wave

3. BTW, you could get a 24v/240v fridge instead

4. You need heavy copper cables twixt inverter and batteries. Ther negative will just go to the negative busbar. The positive should ideally go thru a remote control circuit breaker solenoid - your boat might have a spare one (Fairlines often do, for example) or you can fit one. Or if there is headroom in current capacity and you're content to piggy back the switching function (ie on/off at same time, not independant) you could use a solenoid that supplies your winches, bowthruster, etc. Do not bodge the 24v wiring. It is heavy current stuff and can get hot, so fire risk, it MUST be done right

5. Take the 240v output from inverter and run it to fridge via an automatic relay so that the inverter supply is automatically not used when you have shore power or genset 240v avaialble. Eg a mastervolt masterswitch, or any relay with a 240v coil (and enough current capacity on the switched circuit) will do

6. It's handy to be able to turn inverter off when not used. The remote solenoid in 4. above will allow this, or get an inverter with a remote control panel like Mastervolt. Or fit it where you can reach it, if that works for you

7. There is big price/quality range. Proper pukka gear will be £1500 for this lot, just parts not labour. Cheap and cheerful inverter just for the fridge is perhaps £150

8 . I can't stress enough that the 24v wiring must be pukka, because the heavy current on the 24v side means there is fire risk

 

[Gumpy]

2. If fridge only, a small one will do, and doesn't need to be pure sine wave. Just read the wattage of the fridge and match the inverter to that. If you want to power say a ring main used for electronics you need more power and pure sine wave

One point to mention
If you get an inverter the same wattage as the fridge it may shut down and not be able to start the fridge.
A compressor on a fridge can draw up to 15 times the rated power on start up. Some small inverters will cope with this many wont. You may find that you need an inverter of 750-1000w to reliably start the fridge.

Personally I would go for a decent 1500w inverter/charger mounted as close as possible to the batteries so that when you are running the genset the batteries get charged and all the change over between genset and inverter is taken care of automatically by the inverter charger.

 

[BartW]

mastervolt and Victron have combined
charger / invertor units
so when there is 230V available, the unit switches over automatically from invertor to battery charger.


Victron has got a new unit called "quatro"
that allows to connect 2 x mains 230V sources,
both the gen and the shore power
it will switch over automatically to one of the 230v supplies when they are available.
everything is handled in one box, and eventually controlled from a small remote panel
http://www.victronenergy.com/inverters-chargers/quattro/

 

[pheran]

mastervolt and Victron have combined
charger / invertor units
so when there is 230V available, the unit switches over automatically from invertor to battery charger........

.....everything is handled in one box, and eventually controlled from a small remote panel

As do Vetus. We have a 2000W combined unit fitted. Another post above makes a fair point about the extra power required on start-up although I would have thought 15X was something of an over-estimate. We've measured the start-up surge at 2x the stated rating.

 

[sailorman]

Dear all,

I have motor cruiser with an Onan generator. On board I have a 240 volt only fridge. Is it possible for me to fit an inverter to power the fridge from the engines 24 volt system whilst cruising?

If so, what capacity inverter should I buy?
Should I consider a larger capacity inverter to power 240 volt appliances?
How would I connect to the 24 volt system?

Thank you in anticipation of any advice.

what Amps does the fridge draw

 

[Gumpy]

As do Vetus. We have a 2000W combined unit fitted. Another post above makes a fair point about the extra power required on start-up although I would have thought 15X was something of an over-estimate. We've measured the start-up surge at 2x the stated rating.

What did you measure it with?
Its impossible with most meters as it is so quick and is already decreasing by the time the meter registers.
I maybe was a bit optimistic and 10x will be nearer the mark

 

[Elena2]

Hi Guys,

Thank you all very much for your valued advice, especially jfm.

My boat is in Turkey and 12/24/240v fridges are very expensive. The inverter way is the cheapest way. I just now need to choose an inverter. What choice?

Thanks again to everyone who bothered to answer.

 

[jfm]

What did you measure it with?
Its impossible with most meters as it is so quick and is already decreasing by the time the meter registers.
I maybe was a bit optimistic and 10x will be nearer the mark

Cervinia, you're absolutely right that the spike is of very short duration and most meters wont even register it well. Oscilloscope needed! But for that reason the inverter wont "register" it either, and thus won't trip out. Nor will the 24v batteries mind the spike in current drawn from them. I do agree your general comment that the inverter rating needs some headroom over and above the nominal current draw of the fridge, but 10x isn't needed, in practice 2x will be fine

 

[rickp]

FWIW, the mastervolt 1500W inverter we have runs a Zanussi domestic fridge/freezer just fine.

 

[jfm]

FWIW, the mastervolt 1500W inverter we have runs a Zanussi domestic fridge/freezer just fine.

I have the m'volt 1500w too, and it works fine. But blimey Rick, did Elling not give you fridges and freezers than run on either 230v or 24v? That's a bit naughty of them imho

 

[rickp]

I have the m'volt 1500w too, and it works fine. But blimey Rick, did Elling not give you fridges and freezers than run on either 230v or 24v? That's a bit naughty of them imho

Really? Given that the point of having the inverter, auto-transfer switch (and generator) is that we have mains all the time - why would I want a more expensive 'marine' fridge rather than a larger, standard 'white goods' version?

Other than a very slight loss in efficiency, what am I missing?

 

[Gumpy]

Cervinia, you're absolutely right that the spike is of very short duration and most meters wont even register it well. Oscilloscope needed! But for that reason the inverter wont "register" it either, and thus won't trip out. Nor will the 24v batteries mind the spike in current drawn from them. I do agree your general comment that the inverter rating needs some headroom over and above the nominal current draw of the fridge, but 10x isn't needed, in practice 2x will be fine

Agree on the meter even the true RMS peak hold ones I have here don't get close.
Not my experience of small inverters I'm afraid. Victron, Mastervolt quite likely to work other makes don't always work especially the cheap ones.
The last thing that I would want to see is an inverter installed that is not enough to power the fridge on start up. I have seen it so many times over the years that it isn't funny, user buys a 300w inverter and wonders why it wont start his fridge (100W) or if it does then it only lasts 3 months.

 

[jfm]

Really? Given that the point of having the inverter, auto-transfer switch (and generator) is that we have mains all the time - why would I want a more expensive 'marine' fridge rather than a larger, standard 'white goods' version?

Other than a very slight loss in efficiency, what am I missing?

Hmm, yep, thinking about, it you're right really. I suppose I just prefer running stuff on 24v than 230v where possible, at sea, but that's just a gut feeling and I can't give you lots of (or even one!) reasons why!

 

[rickp]

Hmm, yep, thinking about, it you're right really. I suppose I just prefer running stuff on 24v than 230v where possible, at sea, but that's just a gut feeling and I can't give you lots of (or even one!) reasons why!

I did think (after my previous reply) that a 24v fridge gives you some backup should the inverter fail, but worse case, I could revert the generator (in bursts) until I could replace the inverter.

But its a bit swings-and-roundabouts really...

I know Anton was a bit annoyed that the new Kabola boilers are 240v rather than 24v, but probably 'cos that'd mean a bigger inverter rather than any technical reason!

 

[seamaster30]

Really? Given that the point of having the inverter, auto-transfer switch (and generator) is that we have mains all the time - why would I want a more expensive 'marine' fridge rather than a larger, standard 'white goods' version?

Other than a very slight loss in efficiency, what am I missing?

This is the option I use too, the inverter draws 3.5 amps (24v) when my 'domestic' fridge is running, and because it's thermostatically controlled, is not on very much.
The fridge was just over £100, so left a big chunk of cash towards the inverter (Sterling 1200w Pure Sine Wave) that I can use for lots of other things too.

 

[pheran]

What did you measure it with?
Its impossible with most meters as it is so quick and is already decreasing by the time the meter registers.
I maybe was a bit optimistic and 10x will be nearer the mark

Sorry I can't be specific. All done by my s-i-l who is a super-techie engineering consultant to the TV industry. But certainly not a simple multi-meter which even I would be able to use. Glad to see jfm confirms the real-life 2x we have measured.