Battery consumption of a fridge?

[burgundyben]

A 12 volt fridge spec sheet says it draws 40 watts. Running from a 110amp/hr battery.

40w/12v=3.3 Amps

110a/hr battery / 3.3 amps = 33.3 hours run time before battery dead.

At 25 deg C ambient the fridge runs at 25% of the time.

33.3 hours/ 25% = 133 hours = 5.5 days

Is that right?

Fridge cuts off when batter gets down to 10.7 volts, that must have a bearing on it.

 

[jfm]

A 12 volt fridge spec sheet says it draws 40 watts. Running from a 110amp/hr battery.

40w/12v=3.3 Amps

110a/hr battery / 3.3 amps = 33.3 hours run time before battery dead.

At 25 deg C ambient the fridge runs at 25% of the time.

33.3 hours/ 25% = 133 hours = 5.5 days

Is that right?

Fridge cuts off when batter gets down to 10.7 volts, that must have a bearing on it.

Maths is right but you will get something like half the "theoretical/nominal" energy out of the battery before it is effectively flat, so 2.75 days

 

[vas]

BB, I fear you're quite optimistic!

I'd not expect drawing more than 70% (if so) of the 110a/h in a cycle unless you want to knacker the batteries quickly...

type of fridge, installation, ventilation to the evaporation matrix, ambient temp all play a significant role.

For example during the summer with only one (crappy) bank of batteries (2X180Ah, system is 24V), one reasonably efficient/modern weaco could last up to 6h.
ambient was close to 45C in there though and contents would struggle to get down to 10C!
Oct. onwards, it could do more than 24h (ambient down to 25C and less than 20C at night)
Fwiw, contents of this 80lt fridge were a couple of fruits, two 1.5lt bottles of water and a few cans of coke.

To answer your Q, I doubt you'd get more than 3days unless ambient is 20C - which probably defies the point of having a fridge in the first place

cheers

V.

ah, JFM beat me to it...

 

[annageek]

Assuming you're talking about a 110Ah lead-acid battery, then you wouldn't want to be running it less that about 80% depth of discharge at the absolute maximum, or it'll build up impedance and need replacing rather quickly. Personally, I'd rather play safe and size for 60% DOD, knowing you have a bit to play with... but ultimately, this means an equivalent of 66Ah.

If you are getting the battery down to 10.7V at such a low rate of discharge (for a big battery) then I'd say the battery is getting really over discharged, and will quickly begin to sulphate and 'seemingly' reduce in its ability to recharge fully. Over discharge is a real killer of lead acid batteries!

If it were me, I'd get a low voltage disconnect of some type set to about 11.6 to 11.8V (depending on the battery) and this should allow for a generally healthy battery setup and hundreds of charge/discharge cycles. Ultimately, this setup will give you something like 80 hours use (3ish days)

Anna

ah, JFM beat me to it...

ah, JFM and vas beat me to it... one of these days I'll be the first responder to a technical question that I actually know enough about to answer!!!!

 

[Bandit]

I assume you are talking about stand alone domestic batteries and not ones that also service to start engines.

If batteries serve both engine start and domestic then cold beer is not much use if you cant start the engines.

Bear in mind assuming you are living on the boat at the time, you will be running electric lights, water pump, anchor windlass etc etc as well.

 

[Momac]

From experience over several years , a stop over of 24 hours per 110Ah battery for one fridge is a good guide.
I have stopped 36 hours but I fear it does the battery no good.
This is with batteries in new condition and reasonably frugal use of lights. Hot weather can of course have an impact.

I think it helps to have the fridge full and well chilled while the engine is running. Then turn the fridge down a bit when you stop.


.

 

[burgundyben]

#3 looks like a Lakesailor to me.

Interesting, also, a 60w 12v solar panel could really extend it too.

Thanks all.

 

[jfm]

one of these days I'll be the first responder to a technical question that I actually know enough about to answer!!!!

Tee hee. I just read your post on another thread and realise you are a proper expert in this. Welcome to these forums! If you don't mind I might put up a new battery thread in a few days to pick your brains, because I want to replace my batteries soon (not because they're dead, but because they are ordinary lead acid and I cannot get charge into them fast enough, as I'll explain ) and would like to make the right choice given the high £££ involved

But meantime can you help me with a simple question ref your 2nd para above please. Sorry BB for slight thread drift but your Q has been fully answer so it's ok I think. Anna I have a 24v bank consisting of 2x 220AH 12v batteries, sealed lead acid, sort of 50cm long jobs. These are dedicated to starting one of my engines, which are newish so start easily, hence the bank hasn't suffered any significant DOD (till now...) nor a large accumulated quantity of discharge/recharge. 18 months old.

Problem is that a few months ago one of my Mastervolt charge regulators failed. These are http://www.mastervolt.com/marine/products/alpha-pro-charge-regulators/alpha-pro-24-v/ and they senses battery voltage and send the right excitation voltage to the engine alternator. I was cruising in the boat and saw 31 volts on this bank. I unplugged the mastervolt thing, leaving the battery with no charging, and carried on cruising.

I planned to get a warranty replacement Mastervolt thing but just haven't got around to it, so batteries have had no charging for 3 months or so. Now reading 20v, and have been like that for 1 month+

Are these batteries likely to be shot, or will they be ok if I put a charger on them this weekend? I don't mind if they are a bit sulphated because they are not mission critical and are over specced if anything. Does the length of time for which I have let them sit at 20v affect the degree to which they are busted? Should I have recharged them sooner?

 

[jfm]

#3 looks like a Lakesailor to me.

Interesting, also, a 60w 12v solar panel could really extend it too.

Thanks all.

You're forgetting BB . A lakesailor is where later poster repeats what earlier poster said, and then OP thanks the later poster. The Lakesailor is defined by the thanking, not the repeating of what someone already posted. See the Liverpool anchor slipping thread today for example

60W from a solar panel would be grand in this application. You just need the sun

 

[vas]

You're forgetting BB . A lakesailor is where later poster repeats what earlier poster said, and then OP thanks the later poster. The Lakesailor is defined by the thanking, not the repeating of what someone already posted. See the Liverpool anchor slipping thread today for example

60W from a solar panel would be grand in this application. You just need the sun

Good to know that I shouldn't be offended then

someone must add the lakesailor definition to Wikipedia as I've completely missed it (not following other parts of ybw.com forums...)
further it's rather unfair as JFM just posted a single line and I wrote a full paragraph essay AND I was also following my ebay bidding for a 24HD garmin radome which I just won for the amazing sum of 211quid wonder if it works or I wasted my money...

cheers

V.

 

[burgundyben]

You're forgetting BB

Indeed, that is the case, it became very clear to me earlier this year when somebody asked me about a Huntsman 28 and what I knew of its history, in the process of telling the chap what I knew of the boat in question I realised that I had confused two different boats. Not surprising given that I have first hand knowledge of nearly half of the 80 or so built. So, I sat at my office desk early one morning to commit to paper what I could remember, some hours later and a couple of missed meetings I had finished my initial brain dump. I have been keeping it live this year.

Where's that nerd smiley?

 

[annageek]

Tee hee. I just read your post on another thread and realise you are a proper expert in this. Welcome to these forums! If you don't mind I might put up a new battery thread in a few days to pick your brains, because I want to replace my batteries soon (not because they're dead, but because they are ordinary lead acid and I cannot get charge into them fast enough, as I'll explain ) and would like to make the right choice given the high £££ involved

But meantime can you help me with a simple question ref your 2nd para above please. Sorry BB for slight thread drift but your Q has been fully answer so it's ok I think. Anna I have a 24v bank consisting of 2x 220AH 12v batteries, sealed lead acid, sort of 50cm long jobs. These are dedicated to starting one of my engines, which are newish so start easily, hence the bank hasn't suffered any significant DOD (till now...) nor a large accumulated quantity of discharge/recharge. 18 months old.

Problem is that a few months ago one of my Mastervolt charge regulators failed. These are http://www.mastervolt.com/marine/products/alpha-pro-charge-regulators/alpha-pro-24-v/ and they senses battery voltage and send the right excitation voltage to the engine alternator. I was cruising in the boat and saw 31 volts on this bank. I unplugged the mastervolt thing, leaving the battery with no charging, and carried on cruising.

I planned to get a warranty replacement Mastervolt thing but just haven't got around to it, so batteries have had no charging for 3 months or so. Now reading 20v, and have been like that for 1 month+

Are these batteries likely to be shot, or will they be ok if I put a charger on them this weekend? I don't mind if they are a bit sulphated because they are not mission critical and are over specced if anything. Does the length of time for which I have let them sit at 20v affect the degree to which they are busted? Should I have recharged them sooner?

Well, I realise this will incriminate me as being complicit in the hijacking of a thread... but I get to show off, so that makes it OK!

It sorta depends on the battery type. In my experience, lead-calcium batteries recover better than pure-lead or ther leaden alloys. You're right though, 20V (1.66V per cell) is quite low. I'd first try just charging. You might be alright. If not, I'd say you do have a reasonable chance you'll still get some service life out of them though. With such a low voltage, not only will you get some sulphation but also probably some dendrite growth (little filaments that grow between the plates in the lead-acid cells that create a discharge circuit in the cell). The best thing to do will be to give them a good charge, and assuming the charger you'll be using has a float voltage of 13.8V or so, then leave them on float for a good few days. This'll at least get everything into balance. Then, if possible, the best thing to do would actually give the batteries a bit of a work out. Very rapid discharge will heat things up a bit in the cell which will clear some of the sulphation, and the high current will essentially fuse some of the dendrites. Some relatively extended cranking of the engine could work for this workout... assuming you don't value your engine too much... which you probably do! Although 10s bursts every minute or so should be gentle enough on your engine, but JUST about strenuous enough on the batteries, I'd imagine? Once they've been excercised (as much as you are comfortable with) without letting the rested open cell voltage get too low, then back on the charger. That's it. You can always repeat a bit if the results are less than satisfactory, but if it hasn't sorted things out after the second attempt, then you may not get anything out of them.

If the impedance of the battery is too high, then they simply won't charge. There's not a great deal you can do, although, if you are about to chuck them away, and have the means to do so, you can always try forcing current through them at really high voltage (at work, we use up to 60V on 12V blocks that just won't accept charge, just to get an amp or so to flow through them for a few hours). If you do this for long enough and stop just after the battery has gone into overcharge (you'll know as they will be red hot and stink of sulphur!), then occasionally (about 50% of the time) it will revive the battery to 80% or so. You do have to keep an eye on things though, as they will get very hot and easily can begin to melt! Not too bad for us at work when we're trying to recover batteries that are 15 to 25Ah, but it'd be rather boring waiting for a 110Ah!

In regard to whether charging sooner would have helped... I'm afraid to say, yes... the sooner the better. But on the other hand, I've seen much worse and had perfect results with just a straight forward recharge.

HTH, and I look forward to hearing about your desire for lithiums in the future!

Anna.

 

[burgundyben]

Oooh! Someone that knows about dendrites! I have a bit of experience in investigating DC power supplies in the field, tin dendrite whiskers growing, then flashing off and no trace left behind, little buggers they are.

 

[l'escargot]

Good to know that I shouldn't be offended then

someone must add the lakesailor definition to Wikipedia as I've completely missed it (not following other parts of ybw.com forums...)
further it's rather unfair as JFM just posted a single line and I wrote a full paragraph essay AND I was also following my ebay bidding for a 24HD garmin radome which I just won for the amazing sum of 211quid wonder if it works or I wasted my money...

cheers

V.

Here is the authorised definition of a "Lakesailor": http://www.lakelandimages.co.uk/lakesailor/rules/

 

[vas]

Here is the authorised definition of a "Lakesailor": http://www.lakelandimages.co.uk/lakesailor/rules/

well impressed!
thanks for helping me waste 15min reading all that

Looks like we're safe and neither myself nor Anna lakesailored JFM after all, or do I need TCM to rule that?
IMHO there should be an acceptable time gap before the two posts in order to justify lakesailoring. Nothing is mentioned in the rules, rather poor!

back to work

V.

 

[jfm]

Well, I realise this will incriminate me as being complicit in the hijacking of a thread... but I get to show off, so that makes it OK!

It sorta depends on the battery type. In my experience, lead-calcium batteries recover better than pure-lead or ther leaden alloys. You're right though, 20V (1.66V per cell) is quite low. I'd first try just charging. You might be alright. If not, I'd say you do have a reasonable chance you'll still get some service life out of them though. With such a low voltage, not only will you get some sulphation but also probably some dendrite growth (little filaments that grow between the plates in the lead-acid cells that create a discharge circuit in the cell). The best thing to do will be to give them a good charge, and assuming the charger you'll be using has a float voltage of 13.8V or so, then leave them on float for a good few days. This'll at least get everything into balance. Then, if possible, the best thing to do would actually give the batteries a bit of a work out. Very rapid discharge will heat things up a bit in the cell which will clear some of the sulphation, and the high current will essentially fuse some of the dendrites. Some relatively extended cranking of the engine could work for this workout... assuming you don't value your engine too much... which you probably do! Although 10s bursts every minute or so should be gentle enough on your engine, but JUST about strenuous enough on the batteries, I'd imagine? Once they've been excercised (as much as you are comfortable with) without letting the rested open cell voltage get too low, then back on the charger. That's it. You can always repeat a bit if the results are less than satisfactory, but if it hasn't sorted things out after the second attempt, then you may not get anything out of them.

If the impedance of the battery is too high, then they simply won't charge. There's not a great deal you can do, although, if you are about to chuck them away, and have the means to do so, you can always try forcing current through them at really high voltage (at work, we use up to 60V on 12V blocks that just won't accept charge, just to get an amp or so to flow through them for a few hours). If you do this for long enough and stop just after the battery has gone into overcharge (you'll know as they will be red hot and stink of sulphur!), then occasionally (about 50% of the time) it will revive the battery to 80% or so. You do have to keep an eye on things though, as they will get very hot and easily can begin to melt! Not too bad for us at work when we're trying to recover batteries that are 15 to 25Ah, but it'd be rather boring waiting for a 110Ah!

In regard to whether charging sooner would have helped... I'm afraid to say, yes... the sooner the better. But on the other hand, I've seen much worse and had perfect results with just a straight forward recharge.

HTH, and I look forward to hearing about your desire for lithiums in the future!

Anna.

Many thanks indeed for all that top quality guidance. My engines are electronically controlled so start instantly, alas. Well alas in this context. I don't not value them very much (see what I did there? Double negative, when talking to a battery geek!)
Also you said 110Ah but these are a pair of 220Ah @12v, ie 220Ah @24v total
I'll give it a go, apart from the 60 volts bit and the melt down
I'll come back on battery project proper, shortly
Many many thanks!

 

[MapisM]

you can always try forcing current through them at really high voltage (at work, we use up to 60V on 12V blocks that just won't accept charge, just to get an amp or so to flow through them for a few hours). If you do this for long enough and stop just after the battery has gone into overcharge (you'll know as they will be red hot and stink of sulphur!)

Geez...
Do tell, what happens in the "other" 50% of the time, is it only the battery that doesn't survive, or also the worker dealing with the procedure?

 

[Trundlebug]

JFM you could always try fitting a Megapulse unit to desulphate your batteries.

I've fitted them to a bank of (admittedly deep cycle) batteries in a cherry picker at work and they've dramatically extended working life for over 3 years now.
They take gradual effect and are only fully effective after 6-8 weeks but they really do work on batteries that are otherwise perfectly OK just sulphated up.
http://www.megapulse.net/
Available in the UK from http://www.actmeters.co.uk/battery-testing/megapulse-battery-rejuvenator

Reads like snake oil but does work.
No connection etc just a satisfied customer.

 

[annageek]

Geez...
Do tell, what happens in the "other" 50% of the time, is it only the battery that doesn't survive, or also the worker dealing with the procedure?

It's not one of ours, but I have seen quite a few end up looking a bit like this:


Funnier still is when a customer returns one lookin like that and then tells us they've only used it once, followed all the instructions, and this happened... needless to say we tend not to uphold the warranty claim.

So far though, we've had no fires / no explosions / no people being melted alive by being rained on with acid. The only thing that is harmed is the owner's bank account. All disappointingly innocuous really.

 

[wakeup]

That is quite scary. Off to check my batteries now..