Open Wallet Surgery

[MauriceMynah]

I think I have a problem!

The first part of my problem is that I don't know what my problem is.It could be one of 3 or four things that I have noticed the symptoms of, or it could be something totally different1

The Symptoms. The fridge has gone very quiet, yet is still cold. My battery charger is telling me that my batteries are fully charged, and has been telling me that for about 18 hours now.

The History.  I plugged into shore power on Wednesday morning for the first time. I connected up my battery charger to keep the batteries tickety boo. Yesterday (Friday at about 14:00) the charger display changed from "Charging" to "Battery fully charged". I disconnected the charger from the mains, but not from the batteries. It still displayed "Fully charged" It has remained in that state, as I said, for about 18 hours. (while typing this the fridge has cut in and I can hear it, but it does seem quieter!).

I am aware that alternaters do not fully charge batteriesso this is the first time that the fridge haws hat this full voltage. Coult that be a reason it's both quieter and I suspect colder ?

So! this has me thinking. Is the fridge on it's last legs? Are the batteries on their last legs? (Age unknown) Is the alternater on it's last legs? Or is my battery charger telling me porkies?

A quick note about the charger. Whenconnected to the batteries but not the mains, it usually displays "Charging" even though it cannot be. It is not in any way a smart charger, being only marginally smarter than it's owner.

The reason I am suspicious of the batteries/alternater is that even after some extensive engine running, the batteries only seem to last for about 3 days before the fridge fails, the TV shortly after that. 

The domestic batteries are 3 x 110 amp-hour jobbies made by Stirling.

The only thing I am quite sure of, is that the solution will involve open wallet surgery!  

[Regulo]

23 minutes ago, MauriceMynah said:

Is the fridge on it's last legs? Are the batteries on their last legs? (Age unknown) Is the alternater on it's last legs?

Perhaps it's the owner on his last legs?

Seriously, something doesn't sound right. How can a battery charger be "charging" if it's not connected to the mains? What does the charger operating manual say? Three days with the fridge, TV (and heating?) is pushing it for battery life, I would think. Does your fridge have a low level input cut-off? Some can be set to cut off at a lower battery level. What rating is your alternator, and do you have a smart regulator? That will recharge the batteries much quicker than the standard internal regulator. Sounds like you're right - this may be expensive!

[Smoggy]

My fridge has an added smart controller that makes it run harder when on charging voltage and much lower lever when the volts drop making it quieter, as Regulo says 3 days is pushing it at the best of times on batteries without any extra top up.

If I am plugged in with battery charger going  my solar controller display indicates charging in the dead of night as it's going by the voltage at the battery side rather than what the panel is producing so it may well say charging if the engine is running without the charger plugged in.

What type of fridge and what age? If it gets cold it's probably fine.

[Meantime]

My first thoughts are I'm not sure you actually do have a problem. If your batteries are lasting three days between charges with the fridge on, occasional TV and other things like pumps and lights then I think they are doing ok.

You should only really 50% discharge your batteries so your 3 x 110Ah gives you a reasonable 165Ah usable. Which three days or 72hrs is approx a couple of amps per hour you have to run everything. The fridge alone depending on make could easily consume that.

You have told us a lot about your possible problem, yet left out quite a bit of pertinent information. Some fridges will detect when you are on charge and run the fridge harder in effect taking advantage of the external charging source rather than deplete the batteries. Some fridges even have an absorption unit which in effect charges up and stores the cold, letting it back into the fridge later when you are just running on battery power. The make and model of the fridge would go a long way towards determining the type of compressor and average current drain etc. Most compressors will sound noisier if struggling to run on a lower voltage, so your fridge going quieter is probably nothing to worry about.

Again the make and model of charger would be useful to work out how good it is, and whether it is good for conditioning the batteries or whether prolonged usage is likely to be more damaging to the life of your batteries.

One other thing of note on your batteries, you say they are Stirling, or are they Sterling as in the people who make battery chargers. I believe Sterling only sell the very expensive Lithium batteries which are excellent, but very expensive at around £600 per 100Ah battery. They also need specialist chargers and some form of current limiting charger between the alternator and the battery otherwise you will very quickly kill your alternator.

Confirmation on the make of batteries and make and model of fridge and charger would be useful, but at first glance I don't think you really have a problem, well with the boat anyway. 

 

[BrundallNavy]

John, I thought your boat started its engine every morning at 06-00 to get hot water for a shower.  They seem to do this with no intervention from the owner. 

[annv]

Hi Suggest you get a volt meter, as meantime said three days on three battery's is not bad, noisy or quirt fridges can be down to how they are installed if it is getting cold (a fridge temp gauge will be a better guide) wait until it stops working. John

[Vaughan]

4 hours ago, annv said:

Hi Suggest you get a volt meter,

That was my first thought when I read this!

[Vaughan]

My second thought is that the only problem (if there is one?) is the battery charger being too small for what you are asking from it.

As I understand it, you have sat on a mooring since Wednesday on shore power but without running the engine.

Your fridge is still running.

Good.

Have a nice day!

Edited to add :

I wish I were moored alongside you - we would have an even better day!

 

 

Edited September 4, 2021 by Vaughan
encouragement!

[rightsaidfred]

5 hours ago, annv said:

Hi Suggest you get a volt meter, as meantime said three days on three battery's is not bad, noisy or quirt fridges can be down to how they are installed if it is getting cold (a fridge temp gauge will be a better guide) wait until it stops working. John

I have no technical knowledge but would have thought 3 days is about max for batteries, while volt meters are ok if you understand them I was always given to  believe that a drop test was needed to define the condition of batteries.

Fred

[annv]

Hi Fred a drop test is for starter battery's if used on leisure can be detrimental, a hydrometer is used for leisure battery's or a volt meter. John

[Cheesey69]

Funny. My charger displays absolutely nothing when disconnected from the mains. And I hope it didn’t because that would mean it’s consuming power. 
I monitor the batteries by a separate NASA battery gauge. 
Is it meant to display anything when it’s off?
Worth remembering that your fridge is working less now it’s cooler. 

[Meantime]

5 hours ago, rightsaidfred said:

I have no technical knowledge but would have thought 3 days is about max for batteries, while volt meters are ok if you understand them I was always given to  believe that a drop test was needed to define the condition of batteries.

Fred

A drop test is used to test starter or cranking batteries and is no good indicator for leisure or dual purpose batteries and is very likely to shorten the life of non starter batteries.

There are three main measurements for batteries aside from measuring the battery voltage. The CCA or cold cranking current which is the maximum power the battery can provide for a very short period as in when starting an engine. Typically this is in the range of 800+ amps, which plainly means a 110 amp hour battery will not last for very long, but it has the grunt to power your starter motor for the few seconds it hopefully takes to start the engine. You will all know how quickly that battery will go flat if the engine proves to be troublesome to start. The higher the CCA the better it is at starting engines.

The other two measurements are the C5 and C20 rates. These are the maximum amount of amps a battery can provide for 5 or 20 hours and it is not a linear equation, so remember this when trying to compare batteries. A C20 110 amp hour battery should provide 5.5 amps per hour for 20 hours. The same battery will more than likely provide 90 amps at its C5 rating or 18 amps per hour for 5 hours or a total of 90 amp hours. Less often quoted is the C10 rate. So always compare like for like. Generally speaking the less current you draw per hour the longer it will last and the same battery will give you more capacity. This is because all batteries have the ability to recover a certain amount of charge when left to rest. The slower the rate of discharge the greater the ultimate capacity. Having said all that about the "C" rates, remember that you should never discharge a battery more than 50% or you will shorten its life. The more often you do the quicker you kill the battery. If you do discharge a battery below 50% the longer you leave it discharged the more damage you do. So in reality you need to half the manufacturers quoted C5 or C20 rates to avoid killing the battery.  

One last thing about batteries, if you need to fast charge either with an intelligent charger, or an advanced alternator regulator you are going to boil the batteries at some point. You'll get a greater depth of charge but it comes at the cost of boiling off some acid. Open lead acid batteries can be topped up and are best suited to fast charging. Sealed, maintenance free or AGM batteries basically mean they can not be topped up, or more importantly fast charged. They have vents to avoid them exploding and you will still boil the acid off them, but will not be able to top them up. Most advanced alternator regulators will provide a higher voltage than the standard output from the alternator, this comes at the price of shortening the life of your batteries unless you can keep topping them up.

[Vaughan]

6 hours ago, Meantime said:

A drop test is used to test starter or cranking batteries and is no good indicator for leisure or dual purpose batteries and is very likely to shorten the life of non starter batteries.

There are three main measurements for batteries aside from measuring the battery voltage. The CCA or cold cranking current which is the maximum power the battery can provide for a very short period as in when starting an engine. Typically this is in the range of 800+ amps, which plainly means a 110 amp hour battery will not last for very long, but it has the grunt to power your starter motor for the few seconds it hopefully takes to start the engine. You will all know how quickly that battery will go flat if the engine proves to be troublesome to start. The higher the CCA the better it is at starting engines.

The other two measurements are the C5 and C20 rates. These are the maximum amount of amps a battery can provide for 5 or 20 hours and it is not a linear equation, so remember this when trying to compare batteries. A C20 110 amp hour battery should provide 5.5 amps per hour for 20 hours. The same battery will more than likely provide 90 amps at its C5 rating or 18 amps per hour for 5 hours or a total of 90 amp hours. Less often quoted is the C10 rate. So always compare like for like. Generally speaking the less current you draw per hour the longer it will last and the same battery will give you more capacity. This is because all batteries have the ability to recover a certain amount of charge when left to rest. The slower the rate of discharge the greater the ultimate capacity. Having said all that about the "C" rates, remember that you should never discharge a battery more than 50% or you will shorten its life. The more often you do the quicker you kill the battery. If you do discharge a battery below 50% the longer you leave it discharged the more damage you do. So in reality you need to half the manufacturers quoted C5 or C20 rates to avoid killing the battery.  

One last thing about batteries, if you need to fast charge either with an intelligent charger, or an advanced alternator regulator you are going to boil the batteries at some point. You'll get a greater depth of charge but it comes at the cost of boiling off some acid. Open lead acid batteries can be topped up and are best suited to fast charging. Sealed, maintenance free or AGM batteries basically mean they can not be topped up, or more importantly fast charged. They have vents to avoid them exploding and you will still boil the acid off them, but will not be able to top them up. Most advanced alternator regulators will provide a higher voltage than the standard output from the alternator, this comes at the price of shortening the life of your batteries unless you can keep topping them up.

I thoroughly agree with all of that.

I might add that the normal maximum charge level for a battery is its 10 hour rate plus 70%.  So one 100 amp/hour battery can be charged at 17 amps continuous.  More than that and it will overheat and "gas off".

So if you have a 90 amp alternator you need to have the charge spread across at least 3 batteries in parallel. Most Broads cruisers these days have one starter and 3 domestic batteries.

Electrolux will tell you that one of their smaller 60 watt fridges will use 45 amp hours over 24 hours on a medium thermostat setting.  As you can't take a battery below 50% of its charge, this means you need to allow the capacity of a whole 110 AH battery, just to run the fridge.

[Meantime]

4 hours ago, Vaughan said:

I might add that the normal maximum charge level for a battery is its 10 hour rate plus 70%.  So one 100 amp/hour battery can be charged at 17 amps continuous.  More than that and it will overheat and "gas off".

So if you have a 90 amp alternator you need to have the charge spread across at least 3 batteries in parallel. Most Broads cruisers these days have one starter and 3 domestic batteries.

As Vaughan says you can gas a battery by charging with too high a charge current, but equally you can gas a battery with too high a voltage even at very low currents. Typically a battery will start to boil or gas at 14.8V, which if the battery terminal voltage has reached that point is will be taking very little current. It is however at this point desulfation of the plates will begin to take place which is beneficial to the battery in small doses, providing you have a means of replacing any water lost over time.

[annv]

Hi I might add that advanced chargers( they fool the regulator in thinking that the battery has a lower charge and charge at its maximum for a timed period)   that charge from the alternator have a temperature sencer over ride to reduce charging when temperature rises this prevents battery's gassing and needing the electrolyte level topping up, battery acid dosn't evaporate/boil only the water content evaporates hence you only need distilled water to top up, battery's only use 1300sg to initially fill not pure acid, battery chargers automatically reduce the charging rate to stop battery's overheating, BUT unless they have a maintainer circuit(not all chargers do) DO NOT leave battery charger connected for more than 24/36 hours at a time, you can get separate battery maintainers or solar panels to be able to maintain your battery over long down times ie winter lay up. John