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New Batteries or a 12V Fridge?


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So, we were out cruising this weekend and, because we have a 240V fridge, we left the inverter on all the time. Fine the first night (we were hooked up to the main in the marina before we left) but waking up after the second night we found the 12v alarm sounding and very little charge left in the batteries. So, do I need new batteries - there's four 110 Ah leisure batteries - or should we ditch the 240V fridge and go for a 12v one? (I should also mention that we have a brand new 90amp alternator and, other than LED lights and charging our phones, there are no other major power draws being used on the boat).  Any advice would be gratefully received!

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If your 4 batteries are fully charged then you could probably run for 2 days without recharging. If you have a crap inverter if could be less. If its a good one it will have a power saving mode where it will virtually shut down while the fridge isn't running.

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If a quality inverter then your batteries are probably knackered. If its some cheap junk like stirling then it could be a toss up between batteries and draw from the inverter. Mains every time for me never a 12 volt fridge anymore.

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A 12v battery will use pretty much the same amount of 'leccy' as a 230v fridge.

 

Maybe even more as 12v fridges are not built to any particular stadards whilst 230v fridges are built to European 'star' standards.

 

If you have an inefficient inverter, then the 230 fridge could be using more out of the batteries than the 12v one will be, but I wouldn't have thought there would be a huge difference either way,

If the batteries are unable to supply the demand then I'd suggest that the batteries are defunct, deceased and have thrown off their mortal coil,

 

How are you charging the batteries ? how long were you cruising for ?

What battery monitoring equipment do you have ?

Edited by Alan de Enfield
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2 minutes ago, Alan de Enfield said:

A 12v battery will use pretty much the same amount of 'leccy' as a 230v fridge.

 

Maybe even more as 12v fridges are not built to any particular stadards whilst 230v fridges are built to European 'star' standards.

 

If you have an inefficient inverter, then the 230 fridge could be using more out of the batteries than the 12v one will be, but I wouldn't have thought there would be a huge difference either way,

If the batteries are unable to supply the demand then I'd suggest that the batteries are defunct, deceased and have thrown off their mortal coil,

 

How are you charging the batteries ? how long were you cruising for ?

What battery monitoring equipment do you have ?

Yup.

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A 240V fridge + inverter is going to use about the same amount of power as a 12V fridge, all other things being equal. So if the batteries aren't up to the one they aren't up to the other.

I suggest new batteries are needed ( as long as you have the means to properly charge them during the day).

In the meantime, turn the fridge off at night to preserve what battery power you have for other things.

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Thanks for all your advice everyone. It's a Sterling inverter - 1800 W continuous, 2800 W intermittent. There's a Sterling Advanced 4 Step Alternator Regulator and a Shark Switch Mode 26A automatic battery charger.  We were cruising for about 5 hours.  All that said it seems the  consensus is I need new batteries.

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Just now, JRT said:

Thanks for all your advice everyone. It's a Sterling inverter - 1800 W continuous, 2800 W intermittent. There's a Sterling Advanced 4 Step Alternator Regulator and a Shark Switch Mode 26A automatic battery charger.  We were cruising for about 5 hours.  All that said it seems the  consensus is I need new batteries.

 

Asking again :

What battery monitoring equipment do you have ?

 

This leads onto :

How do you know when to start charging ?

How do you know when to stop charging ?

How do you know how many Ah you have used ?

How do you know what capacity you have left in the batteries ?

 

Not fully charging (to 100%) your batteries every couple of days means you start to get sulphation, each time you do this you are reducing you battery capacity - it will still be a 12v battery, but instead of 4x 110Ah batteries, they may now be 4x 30Ah batteries, that would be why they can supply your fridge for one day, but the batteries are flat by the second day.

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Had something the same on Legacy, changed the batteries (4) and found the exact problem re-occured. Turned out the batteries were not being charged efficiently.

 

Bought an alternator charge controller from Sterling and have not had a repeat event in 4 years. Bought the 100 amp unit but should have splashed out on the 150 unit so the starter alternator could have been booked up too.

 

If I remember correctly the cost was about £200 but worth it. Now we find that after a full days use the ammeter is showing the charge going into the batteries down to less the 20 amps in under an hour. The Beta 43 has a  95 amps alternator @ max so at cruising revs of 1300 gives 75 amps max.

 

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As you have a shore line in the marina and a battery charger, then the batteries should be properly charged. They should be fine for a weekend away with a bit of cruising. Indeed, they should be able to keep the boat running for a couple of days with no charging. That they aren't says that they are cream crackered. Time for a new set I'm afraid. Echo what others have said on 240V vs 12V fridge. It makes little to no difference one way, or the other.

Jen

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9 hours ago, Alan de Enfield said:

 

Asking again :

What battery monitoring equipment do you have ?

 

This leads onto :

How do you know when to start charging ?

How do you know when to stop charging ?

How do you know how many Ah you have used ?

How do you know what capacity you have left in the batteries ?

 

Not fully charging (to 100%) your batteries every couple of days means you start to get sulphation, each time you do this you are reducing you battery capacity - it will still be a 12v battery, but instead of 4x 110Ah batteries, they may now be 4x 30Ah batteries, that would be why they can supply your fridge for one day, but the batteries are flat by the second day.

Isn't the Sterling Advanced 4 Step Alternator Regulator the monitoring equipment. If not, what do I need?

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7 minutes ago, JRT said:

Isn't the Sterling Advanced 4 Step Alternator Regulator the monitoring equipment. If not, what do I need?

 

Alan asked about battery MONITORING equipment, not the type of alternator control.

 

Battery monitoring involves measuring the charging current and voltage at various times during the day. Some claim to do it automatically and tell you how well charged the batteries are, but most of those lie and encourage a non-technical boater to destroy batteries. A decent ammeter  and voltmeter (preferably digital) will allow you to monitor your batteries state of charge and also when they are failing. The rested voltage at least an hour after charging stops tells you how well charged they are at that time while the charging current an 14.4V plus will tell you when they are as fully charged as they can be. But you need to know how to interpret the readings and in the summer moths the slat voltage tends to make it more difficult.

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Thanks Alan. Sorry for being such a ignoramus. I'll get my voltmeter out when I'm next on the boat and see what's what. Given that the boat sat for a year before I acquired it and the problems I've been having, it seems those advising I need new batteries are probably right.

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10 minutes ago, JRT said:

Thanks Alan. Sorry for being such a ignoramus. I'll get my voltmeter out when I'm next on the boat and see what's what. Given that the boat sat for a year before I acquired it and the problems I've been having, it seems those advising I need new batteries are probably right.

 

That is fine as far as it goes but to get an idea about how well/unwell your batteries are you need the RESTED voltage an hour or so after stopping charging and then again when you get up in the morning (but unless you do a small hours tramp solar will mess with that reading). Comparing the state of charge inferred from those readings each day gives  an idea about the actual a while seeing how they alter over the months shows when the batteries may have developed an internal short. A fixed meter you can just look at is far easier. The voltage can in no way tell you when the batteries are as fully charged as you can get them though, for that you need an ammeter.

 

Read the battery primer pinned at the start of the maintenance forum.

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40 minutes ago, JRT said:

Thanks Alan. Sorry for being such a ignoramus. I'll get my voltmeter out when I'm next on the boat and see what's what. Given that the boat sat for a year before I acquired it and the problems I've been having, it seems those advising I need new batteries are probably right.

 

As I said earlier the voltage does not tell you the capacity of your batteries.

 

You can have a 12v battery for a hearing aid that is smaller than you little finger nail, you can have a 12v battery the size of a car, both are 12v but the capacity is the difference.

 

It is the capacity (Amp hours) that you are using to power your boat, it is the AH used, the AH put back in and the AH capacity of the batteries that are your key features, and the ones you need to monitor (in conjunction with voltage).

 

Your new batteries have a capacity of 110Ah, but every time you discharge them and recharge them you use (lose) a bit of their life - typically your batteries will have a discharge / charge cycle life of (maybe) 300 cycles, big expensive batteries will have a higher cycle life.

 

When you discharge your batteries you change the chemical composition of the lead, to put it simply :

The plates shed lead (drops into the bottom of the battery) during discharge, and when you recharge the batteries this is converted back to lead on the battery plates.

 

If you don't FULLY recharge you leave some of this 'mud' in the bottom of the battery, this 'mud' goes hard and you cannot ever get it to go back onto the plates.

Keep doing this and the 'mud' builds up in the bottom of the battery and the battery now has a much reduced capacity.

 

This process is called sulphation.

 

The average boaters usage appeasr to be around 100AH per day, if you are getting your low voltage alarm going off on the 2nd day I'd suggest that your batteries are (probably) heavily sulphated and your capacity is below 50% (ie ~50Ah)

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I'd be inclined to check your alternator is actually charging correctly as well. 

 

My issues with power draining faster than expected when cruising turned out to be the fact it was *only* recharging in the October sun. Which was resolved by screwing in a bulb on the control panel properly!

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2 minutes ago, enigmatic said:

I'd be inclined to check your alternator is actually charging correctly as well. 

 

My issues with power draining faster than expected when cruising turned out to be the fact it was *only* recharging in the October sun. Which was resolved by screwing in a bulb on the control panel properly!

 

And that is where a fixed voltmeter and ideally an ammeter as well helps considerably. You can see what is going on once you understand the voltage characteristics of alternator output.

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Can I just check something that was said earlier - running an inverter and a 230V fridge uses about the same LX as a 12V fridge directly off the batteries? That's really interesting.

Would that be because 230V fridges are more efficient than 12V ones? I am assuming that the inverter is a reasonably efficient one.

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25 minutes ago, Rick Savery said:

Would that be because 230V fridges are more efficient than 12V ones? I am assuming that the inverter is a reasonably efficient one.

 

With that proviso - YES.

 

The inefficiencies of the 12v fridge (lack of insulation) make up for the inefficiencies of the inverter (roughly) an 85w fridge will use 85w be it from 230v or 12v.

 

An 12v 85w fridge will draw roughly 7 amps when running.

A 230v 85w fridge powered via an inverter will draw roughly 8 amps.

 

The 12v fridge will 'loose its cool' and run for longer periods than the 230v fridge, using more AH per day so (roughly) balancing out the AH used.

 

Its all very approximately, roughly, guesstimates as fridges and inverters are not all the same, but it is not unreasonable to suggest consumption will be 'around' the same.

 

Assuming you already have an inverter so don't need to buy one -  think of the money :

A 12v fridge will be £600+

A 230v fridge will be £89 (70 litre fridge from Currys)

 

Simples !

Edited by Alan de Enfield
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6 minutes ago, Alan de Enfield said:

 

With that proviso - YES.

 

The inefficiencies of the 12v fridge (lack of insulation) make up for the inefficiencies of the inverter (roughly) an 85w fridge will use 85w be it from 230v or 12v.

It's more a matter of the standby power requirements of the inverter that cause the percieved inefficienses between low voltage DC fridges and similar domestic units. An inverter typicall has a standing current of 1 amp - that's 24 Ah 'wasted' per day. Some inverters have a lower standby setting, but these aren't 'sensitive' enough to switch on an Eco mains unit. I carried out some tests a couple of years ago and my comments are based on actual experience...

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4 hours ago, Tony Brooks said:

 

  A fixed meter you can just look at is far easier. The voltage can in no way tell you when the batteries are as fully charged as you can get them though, for that you need an ammeter.

 

 

If like me when you go for a wee when its still dark

1 hour ago, OldGoat said:

 Some inverters have a lower standby setting, but these aren't 'sensitive' enough to switch on an Eco mains unit. I carried out some tests a couple of years ago and my comments are based on actual experience...

They definitely wont see a modern electronically controlled fridge, it should see the load coming on of a mechanical thermostat switching the motor on fridge. (bit garbled that)

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