'Best' way to run a 24v fridge

[Waynerrr]

I am a new narrowboat owner and have been staying on board for the last week. The last few days I have been moored up and running the engine whilst stationary to recharge the batteries. I am experimenting on how long is required based on what I use throughout the day. However, having ran the engine for 2-3 hours before 8pm, I find in the morning there isn't enough charge for the heating system to pump the hot water around. The only system using power overnight is the fridge... This is a 24v fridge that also has a Waeco 'box' behind it that can convert 240v to 24v. So, my question is, is it better to run the fridge straight off the 12v, or, plug it in to the inverter and have it run on 240v?

 

Perhaps I'm simply not putting enough juice back in the battery bank, but more than 3 hours seems excessive for the usage I am putting on them.

[Strads]

HI, its hard to comment, but it will helps those that are technically knowledgeable if you can tell us more about yr boats batterys / electrics

 

How many baterys do you have, what size are they, how old are they?

 

And how do you know they were fully charged before you set off?.

bit in general terms you loose some power when you convert it to another format

eg the inveror will probably use @ 10% of the power needed for teh fridge in converting it to 230v.

 

Sounds like you dont have enough battery oomhhf, but let us know the above and any other electrics you have, with what they consue power wise!

[ditchcrawler]

I am a new narrowboat owner and have been staying on board for the last week. The last few days I have been moored up and running the engine whilst stationary to recharge the batteries. I am experimenting on how long is required based on what I use throughout the day. However, having ran the engine for 2-3 hours before 8pm, I find in the morning there isn't enough charge for the heating system to pump the hot water around. The only system using power overnight is the fridge... This is a 24v fridge that also has a Waeco 'box' behind it that can convert 240v to 24v. So, my question is, is it better to run the fridge straight off the 12v, or, plug it in to the inverter and have it run on 240v?

 

Perhaps I'm simply not putting enough juice back in the battery bank, but more than 3 hours seems excessive for the usage I am putting on them.

Is your inverter switched on, if so that is using power all night as well. best run it on 24 volts

[Chalky]

Are your electrics 12 or 24V?

We turn our fridge (mains inverter 240V fridge) off at night and back on in the morning. It's A+ rated and the insulation keeps it cold enough.

[nb Innisfree]

I am a new narrowboat owner and have been staying on board for the last week. The last few days I have been moored up and running the engine whilst stationary to recharge the batteries. I am experimenting on how long is required based on what I use throughout the day. However, having ran the engine for 2-3 hours before 8pm, I find in the morning there isn't enough charge for the heating system to pump the hot water around. The only system using power overnight is the fridge... This is a 24v fridge that also has a Waeco 'box' behind it that can convert 240v to 24v. So, my question is, is it better to run the fridge straight off the 12v, or, plug it in to the inverter and have it run on 240v?

 

Perhaps I'm simply not putting enough juice back in the battery bank, but more than 3 hours seems excessive for the usage I am putting on them.

 

Unless the fridge is a 12v/24v model then a 24v fridge needs 24v, not 12v. Fridge is better straight from battery.

 

Sounds like you are undercharging, to fully recharge takes several hours, as a compromise we run engine for 2 hours daily with a long 8 hours+ charge once a week to keep up.

[Dovetail]

Providing you don’t need any freezer box if your fridge has one that is I suggest you turn the fridge off you can cope without one plenty of cold spots to keep things cold at this time of year.

Best to save on diesel and your batteries

[bottle]

Are your electrics 12 or 24V?

We turn our fridge (mains inverter 240V fridge) off at night and back on in the morning. It's A+ rated and the insulation keeps it cold enough.

 

SNAP!!!!!! + the inverter, also the full size freezer, charge on average 3Hrs per day via 50a @ 24v charger, Battery bank (when new) 339 amp,hrs @ 24v.

[frangar]

If its a Waeco fridge with a Danfoss BD35 compressor then its 12v/24v.....The Waeco 'box' turns 240v AC into 24v DC...this has losses in itself so you are better of running directly from the batteries unless on a 240v hookup.

 

HTH

 

Gareth

[Keeping Up]

Ditto the Shoreline fridge with the same compressor.

[Waynerrr]

Great, some good stuff to go with there, thanks.

 

I have 3 leisure batteries, 2 are 95amps and the other one is 90amps. I don't know how old they are unfortunately.

I'm 80% sure the fridge is 24v...

I don't have the inverter on overnight as there is nothing that requires it.

 

I'm not sure how I can the fridge off. It doesn't have an obvious "Power" button on the front. I'll double-check later that the 'low power light' isn't also a button.

 

Would it help to run the engine at 1100rpm as opposed to the 900rpm at tick-over? Obviously that will use more diesel over a shorter period of time so might be less economical.

[Robin2]

Great, some good stuff to go with there, thanks.

 

I have 3 leisure batteries, 2 are 95amps and the other one is 90amps. I don't know how old they are unfortunately.

I'm 80% sure the fridge is 24v...

I don't have the inverter on overnight as there is nothing that requires it.

 

I'm not sure how I can the fridge off. It doesn't have an obvious "Power" button on the front. I'll double-check later that the 'low power light' isn't also a button.

 

Would it help to run the engine at 1100rpm as opposed to the 900rpm at tick-over? Obviously that will use more diesel over a shorter period of time so might be less economical.

 

I'm not sure that your additional information throws light on the subject...

 

How can a 240v - 24v box work if your inverter is off? Or is the box converting 12v to 24v?

 

With about 270Ah of battery capacity you should have plenty of overnight capacity unless (i) the batteries are worn out or (ii) something else is using electricity such as a TV or PC, or cabin lights between 8pm and bedtime?

 

Have you the option of disconnecting the batteries completely for 3 or 4 hours (the longer the better) when you think they are fully charged and then measuring their voltage and / or the specific gravity of the acid? That would give you some indication of whether they are properly charged, but may not be conclusive if the batteries are worn out.

 

It would be useful if you had an amp-hour counter and possibly a Smartgauge but they are not cheap.

[Keeping Up]

Note that if you are running the fridge from 12 or 24 v, or even if you are running it from a 240v inverter that is to remain switched on overnight, then switching the fridge off overnight will gain you absolutely nothing unless you delay switching it back on until you are running the engine (indeed to be pedantic it will gain you nothing at all unless you wait until the batteries have finished the bulk charging phase). This is because you use all the energy that you thought you had saved, in cooling the fridge back down again after it has spent all night warming up.

 

You may say "My fridge is so efficient that it doesn't warm up overnight when I switch it off" If that is true, then the thermostat will not have switched on the motor overnight anyway.

[Justme]

You are fairly obviously under charging or the bats are not holding that charge. my money is on under charging.

 

If you go to running the fridge directly of the dc make sure you up the wire sizes to cope.

 

(in your first post you say its running of the 240 yet in the later one you say that its not using the inverter, which is it?)

[blodger]

Great, some good stuff to go with there, thanks.

 

I have 3 leisure batteries, 2 are 95amps and the other one is 90amps. I don't know how old they are unfortunately.

I'm 80% sure the fridge is 24v...

I don't have the inverter on overnight as there is nothing that requires it.

 

I'm not sure how I can the fridge off. It doesn't have an obvious "Power" button on the front. I'll double-check later that the 'low power light' isn't also a button.

 

Would it help to run the engine at 1100rpm as opposed to the 900rpm at tick-over? Obviously that will use more diesel over a shorter period of time so might be less economical.

 

Since the wiring to the fridge needs to be heavier there is often a straight run to the batteries/isolator with a heavyish switch somewhere; On my nb it is on the engine room bulkhead.

 

At idle rpms many engine/alternator combinations deliver very little electrical power. If you do not have an ammeter somewhere it would be worthwhile investing in a clamp on ammeter so that you can ascertain the charging rate(s).

 

Queries are what engine and what alternator and its capacity?

 

In my view, even if your three batts are good you could do with more (say 4x110ah)provided your engine/alternator can charge them, etc. I suspect your batts are knackered

 

Your fridge is probably burning in the order 50ah/day, could be more. If the batts still have 70% capacity at 100% SOC your bank is 192ah and the fridge 50ah itself bring SOC down to about 70%. Your other uses, pumps lights radio/tv, probably bring you down to 50% SOC with 100ah plus ineficiencies to put back into batts in your two/three hours daily charge. I somehow doubt you are getting an average of 30+ amps charging, etc.

 

Hope it helps your understanding

Edited January 25, 2011 by blodger

[Waynerrr]

Justme: It's a 24v fridge but can run off the 12v batteries or the 240v inverter (I assume for when you're on shoreline).

 

Given that I'll be living aboard I may invest in a bigger battery bank.

 

I have a multimeter. It that enough to test the power in the batteries once they're fully charged? What volt(?) reading should I be getting?

[bottle]

I do not remember if you have been given these links before but they will answer your questions on how to check batteries SOC (State Of Charge)

 

http://www.batteryfaq.org/

 

http://www.smartgaug...technical1.html

 

or as advised many times on this forum fit a Smartgauge

Edited January 26, 2011 by bottle

[blodger]

Justme: It's a 24v fridge but can run off the 12v batteries or the 240v inverter (I assume for when you're on shoreline).

 

Given that I'll be living aboard I may invest in a bigger battery bank.

I have a multimeter. It that enough to test the power in the batteries once they're fully charged? What volt(?) reading should I be getting?

 

Would that it were that simple.

 

There are a few things you could measure but they will allbe affected by the fact that you have just been charging or are discharging.

 

It would be of interest what the voltage is before you charge during charging at various points and sometime after charging.

 

To keep it simple 12.2 volts is 50% State of Charge, SOC, and above 12.7 fully charged but as pointed out earlier 100% SOC does not necessarily mean you have 275ah stored.

 

More batts will not help if you cannot keep them charged up.

 

There are lots of 'power' threads on here which will lead you to web sites with useful info for you

[Speedwheel]

What brand/make is the fridge?

 

The Waeco Fridges have 12/24v compressors. Most (I think possibly all) Shoreline and Inlander ones do too. They can be run from either 12 volt or 24 volt with no changes necessary.

 

The ‘Waeco box’ (if you have the one I am thinking of) has a 12/24 volt inlet, a 220-240 volt inlet and a 12 or 24volt outlet and will autoswitch between the two power sources. If there is main power available it will automatically switch to run from this, reducing it down to 24volt. If there is no mains power available it will switch to run on the 12/24volt power supply. If you have an inverter on it will sense the 240volt presence and use this power source rather than the 12/24 volt .

 

There is also another Waeco box that just converts 240 to 24volt. If this is the one you have then if you are only using it from 240 volts produced by an inverter then there is no point as you have the losses from 2 change of voltage, best to just wire it straight in to your low voltage system– if you have a landline for the majority of the time then this is not an issue, you can just use the box to turn 240v to 24v and bypass the batteries/low voltage side. If you then go cruising you can either plug the fridge into the low voltage system or accept the power losses running it from your inverter.

Edited January 26, 2011 by Speedwheel

[sueb]

Oh the joys of electric fridges. Glad I have gas.

Sue

[Speedwheel]

Oh the joys of electric fridges. Glad I have gas.

Sue

 

Agreed

[WJM]

I am not sure how effective this really is but - I keep my fridge (and the ice box) filled with lots of those picnic cool packs. When the engine is running during the day I turn the fridge to its lowest temperature. Then when I stop the engine I switch the fridge back to a higher temperature. My theory is that the fridge will stay cooler for longer, drawing less power from the batteries. I think my theory is right though I am ready to be disproved.

 

And I totally agree with 'Keeping Up'. Turning it off at night simply stores up the cooling process for the morning.

Edited January 26, 2011 by WJM

[bargemast]

Running the engine at 900n isn't going to pump a lot of Amps in, unless there's a special pully arangment that makes the alternator rev fast enough anyway.

 

Peter.

[Gibbo]

Note that if you are running the fridge from 12 or 24 v, or even if you are running it from a 240v inverter that is to remain switched on overnight, then switching the fridge off overnight will gain you absolutely nothing unless you delay switching it back on until you are running the engine (indeed to be pedantic it will gain you nothing at all unless you wait until the batteries have finished the bulk charging phase). This is because you use all the energy that you thought you had saved, in cooling the fridge back down again after it has spent all night warming up.

 

You may say "My fridge is so efficient that it doesn't warm up overnight when I switch it off" If that is true, then the thermostat will not have switched on the motor overnight anyway.

 

I'm glad someone else said this. It's been stated on here upteen times but still people choose to disbelieve it. Every time I see that "But I turn the fridge off at night" I burst out laughing. I've given up on that one.

 

However there is a way to achieve a power saving and that is, as Allan says, to only switch the firdge back on once you've got spare alternator capacity with the engine running. Anything else and you're either just fooling yourself or putting up with warm food in which case why not just turn the thermostat to a higher temperature?

 

I am not sure how effective this really is but - I keep my fridge (and the ice box) filled with lots of those picnic cool packs. When the engine is running during the day I turn the fridge to its lowest temperature. Then when I stop the engine I switch the fridge back to a higher temperature. My theory is that the fridge will stay cooler for longer, drawing less power from the batteries. I think my theory is right though I am ready to be disproved.

 

You're absolutely right. I do the same thing and it does work.

[Pretty Funked Up]

I am not sure how effective this really is but - I keep my fridge (and the ice box) filled with lots of those picnic cool packs. When the engine is running during the day I turn the fridge to its lowest temperature. Then when I stop the engine I switch the fridge back to a higher temperature. My theory is that the fridge will stay cooler for longer, drawing less power from the batteries. I think my theory is right though I am ready to be disproved.

 

And I totally agree with 'Keeping Up'. Turning it off at night simply stores up the cooling process for the morning.

 

gospel words

[Alan Saunders]

. . . Would it help to run the engine at 1100rpm as opposed to the 900rpm at tick-over? Obviously that will use more diesel over a shorter period of time so might be less economical.

You can use your multimeter to optimise the engine rpm for charging. Connect the meter to read volts and start the engine. increase RPM until there is no increase in voltage then reduce RPM to the minimum that maintains this voltage. If you have a tachometer note the reading - this RPM will give the optimium charge rate.

 

There will be avery small increase in fuel consumption but a much larger increase in charging rate. An increase from 12.9V to to 13.3V represents possibly a 40% increase in charge current.

 

My 'modern' engine (tick-over 850rpm, max 3000rpm) charges best at 1500rpm and cruises at 1600rpm; my Gardner 3LW (tickover 380rpm, max 1200rpm) charges best at 500rpm and cruises at 750rpm. I often cruise at the lower, best charging rate speed.

 

You can also use your voltmeter to measure voltage drop across each cable, terminal and relay or diode between the alternator amd the battery post.

 

Alan