Maximising battery life overnight.

[Pete-T]

Following a full days cruising (approx. 6hrs) and despite minimal use of lights and other electrical equipment (no tele.) during the evening, my domestic batteries are very low the next morning to the extent that my fridge warning light is on and the Eberspacher will not start due to low voltage. I've checked the batteries with a multi meter and they are registering 12.5 volts. Are there any other power saving measures anyone can suggest (turning off the inverter for example?) to make the batteries last long enough for the Eberspacher to come on?

[sigsegv]

We've recently discovered that turning the oven off at the (240V) socket saves us about 20W via the inverter (a surprising amount), but if your batts are measuring 12.5V and dropping to below the eberspacher's cutoff for low-voltage (iirc its 11V?) when being loaded, it sounds like your batteries might be on the way out.

[Alan de Enfield]

32 minutes ago, Pete-T said:

Following a full days cruising (approx. 6hrs) and despite minimal use of lights and other electrical equipment (no tele.) during the evening, my domestic batteries are very low the next morning to the extent that my fridge warning light is on and the Eberspacher will not start due to low voltage. I've checked the batteries with a multi meter and they are registering 12.5 volts. Are there any other power saving measures anyone can suggest (turning off the inverter for example?) to make the batteries last long enough for the Eberspacher to come on?

 

 

There are two factors that define a battery - voltage and capacity.

 

You can have a 12v battery the size of a finger nail and you can have a 12v battery the size of a car, the difference is 'capacity'.

 

Typical boating batteries are 100-110 amphour, but that is when new, as they are used and not 100% recharged immediately they start to lose their capacity, the next time you discharge them and again do not recharge them to 100% they lose a little more capacity, in a matter of weeks the batteries become useless as the capacity become less that you are trying to take out.

 

Ane eberspacher draws a lot of current on start up which drags the voltage right down and below the cut-out voltage that the eber will start at.

 

The voltage can still be 12 volts, but the battery capacity could be as low as 10Ah.

 

Question : So, How do you charge your batteries, how do you know when to stop charging your batteries and have you ever done a capacity test on them ?

 

It sounds as if you have killed your batteries and need to replace them, but, unless you know how you killed them the next set will go the same way.

Tell us how you monitor and control your batteries  and we can make suggestions.

Edited March 7, 2023 by Alan de Enfield

[Pete-T]

The batteries are connected to a marina shore line when the boat is moored for any length of time. They charge off the engine as normal when the boat is travelling. They are monitored via a  voltage indicator on our Whispergen system. The Whispergen however is defective and does not charge the system as it should, its only the voltage indicator whic works.

[Alan de Enfield]

13 minutes ago, Pete-T said:

The batteries are connected to a marina shore line when the boat is moored for any length of time. They charge off the engine as normal when the boat is travelling. They are monitored via a  voltage indicator on our Whispergen system. The Whispergen however is defective and does not charge the system as it should, its only the voltage indicator whic works.

 

When cruising, do you travel every day, or moor up for a day or two ?

How many hours per day do you have the engine running ?

Have you undertaken an electrical audit to identify what your daily usage is ?

Do you know how to do a battery capacity check ?

 

It is no use if your daily usage is 150Ah and you only put back (say) 120Ah whilst running the engine (lets say you have 40Amp alternator which on average will give you possibly about 20Ah, so if your engine runs for 6 hours you will only be putting in 120Ah)

 

What engine do you have and what size is the alternator ?

[dmr]

I assume the batteries have little capacity left, this might be ageing or sulphation, but either way the batteries can give correct voltages, its like they are a good battery but with a much lower capacity than when new.

Best power saving at this time of the year is to turn the fridge off overnight, as long as you don't open the door it should stay reasonably cold.

[Pete-T]

32 minutes ago, Alan de Enfield said:

 

When cruising, do you travel every day, or moor up for a day or two ?

How many hours per day do you have the engine running ?

Have you undertaken an electrical audit to identify what your daily usage is ?

Do you know how to do a battery capacity check ?

 

It is no use if your daily usage is 150Ah and you only put back (say) 120Ah whilst running the engine (lets say you have 40Amp alternator which on average will give you possibly about 20Ah, so if your engine runs for 6 hours you will only be putting in 120Ah)

 

What engine do you have and what size is the alternator ?

Alan

Thanks for your help with this, I fear as a relatively new boater that I can't answer all of these questions fully. However.

1. when cruising we move every day and the engine runs for about 6 hrs.

2. How do I do an electrical audit and capacity test?

3. our engine is a Beta 43 but I don't know the alternator size.

[MtB]

2 hours ago, Pete-T said:

I've checked the batteries with a multi meter and they are registering 12.5 volts.

 

But when though?

 

After your day's cruising? Or in the morning while the fridge is blinking at you?

 

 

[system 4-50]

I wanted to point to the pinned battery usage guide but I can't remember its name or how to find it.  Would it be useful here?

[nicknorman]

2 hours ago, Pete-T said:

Following a full days cruising (approx. 6hrs) and despite minimal use of lights and other electrical equipment (no tele.) during the evening, my domestic batteries are very low the next morning to the extent that my fridge warning light is on and the Eberspacher will not start due to low voltage. I've checked the batteries with a multi meter and they are registering 12.5 volts. Are there any other power saving measures anyone can suggest (turning off the inverter for example?) to make the batteries last long enough for the Eberspacher to come on?

Presuming you  mean the batteries are 12.5v in the morning ... and the fridge is a 12v fridge then...

You may have a problem with the installation of the wiring for the fridge. The thing with 12v wiring is that there is only 12, or 12.5 volts to start with, and so any small loss of voltage can be significant. Voltage can be lost in the resistance of the wiring according to the equation "voltage lost = current x resistance of the wires". The thing with fridges is that when the thermostat kicks in, the compressor motor starts and there is a big surge of current such that, if the wiring is inadequate, the voltage drops below the minimum. Might only be for 1/2 second but that is enough to trip the fridge low voltage warning. Fridge wiring has to be surpsingly beefy, eg 6 or even 10 mm^2 conductor cross sectional area, to ensure small enough voltage drop in the fairly long run from batteries to fridge and back.

 

So if the battery voltage really is 12.5v at the time, but the fridge is tripping on low voltage,  you are losing voltage somewhere. Most likely in the long wires but also could be a poor contact in the battery isolator switch, the fuse, the battery terminal connections etc.

For the Eber, one should remember that the glow plug takes maybe 25amps whilst the thing is firing up, and again voltage drop in inadequate wiring or a bad connection somewhere can easily drop too much voltage. Check the voltage actually at the Eber 12v input whilst the thing is firing up, compare to the battery voltage at the same time. If there is a significant difference, that is your problem.

 

Beta 43 from within the last 10 years at least, has a pretty large alternator - 175A or so. Although of course it may or may not be working properly. This is why good monitoring of the electrical system is important as electricity is invisible and the engine panel meter only shows the engine battery voltage which is completely separate. Without adequate monitoring equipment, you can have no idea what is going on!

 

Edited March 7, 2023 by nicknorman

[rusty69]

5 hours ago, system 4-50 said:

I wanted to point to the pinned battery usage guide but I can't remember its name or how to find it.  Would it be useful here?

 

[magnetman]

12.5v in the morning for lead batteries seems quite good to me. 

 

I suppose the question is if the boat is usually on shore power do you know if the fridge ever works properly when it isn't on shore power? 

 

If the installation was done while the boat was moored and plugged in then it might not have shown up as a problem before. 

If the fridge and the Neversplasher are both not working it seems as Nick suggested above to be an idea to have a look at the battery isolator switch. They can be dodgy. 

Also are you measuring the domestic batteries ? If you accidentally measured the engine start battery and got 12.5 in the morning this would not be the battery wired to the fridge. 

Edited March 8, 2023 by magnetman
Typo

[Tonka]

11 hours ago, Pete-T said:

Following a full days cruising (approx. 6hrs) and despite minimal use of lights and other electrical equipment (no tele.) during the evening, my domestic batteries are very low the next morning to the extent that my fridge warning light is on and the Eberspacher will not start due to low voltage. I've checked the batteries with a multi meter and they are registering 12.5 volts. Are there any other power saving measures anyone can suggest (turning off the inverter for example?) to make the batteries last long enough for the Eberspacher to come on?

We had an Eberspacher D5w. Never could get it to work first thing in morning. When it went kaput we replaced it with a Webasto Thermotop connected electrically to the same wire that the Eberspacher was. Webasto works in the morning aok

[magnetman]

I don't use that type of device but think it might be quite good to have a small lithium battery dedicated to the heater unit which is connected to main battery by some sort of voltage sensing relay. Keep a bit of the charge back especially for running the heater. 

 

 

Edited March 8, 2023 by magnetman

[cuthound]

12.5 volts is nearly fully charged. See the rested (no load for 1 hour) voltage State of Charge table below.

 

As both the Eberspacher and the fridge fail to start the likely cause is as @dmr says, lack of capacity.

 

I suggest the OP reads the battery primer, so that if necessary he can adjust his charging regime and then buys new batteries.

 

 

[Tony Brooks]

45 minutes ago, cuthound said:

12.5 volts is nearly fully charged. See the rested (no load for 1 hour) voltage State of Charge table below.

 

As both the Eberspacher and the fridge fail to start the likely cause is as @dmr says, lack of capacity.

 

I suggest the OP reads the battery primer, so that if necessary he can adjust his charging regime and then buys new batteries.

 

 

 

I do not think that table is typical and it overstates the state of charge. 12.5 is normally held to be AROUND 50% charged, indicating it is time to recharge ASAP to optimise battery life.

 

FWIW I too suspect voltdrop somewhere in the wiring.

[magnetman]

It would be useful to know what the voltage is at the battery when the Neversplasher is attempting to start up.

[dmr]

6 minutes ago, Tony Brooks said:

 

I do not think that table is typical and it overstates the state of charge. 12.5 is normally held to be AROUND 50% charged, indicating it is time to recharge ASAP to optimise battery life.

 

FWIW I too suspect voltdrop somewhere in the wiring.

 

12.5v = 80% from the Trojan data sheet. Not sure if "cheapo" batteries are the same, but I think most batteries are similar unless they use a different acid strength for some reason.

8 minutes ago, magnetman said:

It would be useful to know what the voltage is at the battery when the Neversplasher is attempting to start up.

and the voltage at the eber and the fridge, though this might be more difficult to measure easily.

[Alan de Enfield]

12.1-12.2 = 50%

 

 

 

Edited March 8, 2023 by Alan de Enfield

[Tony Brooks]

26 minutes ago, Tony Brooks said:

 

I do not think that table is typical and it overstates the state of charge. 12.5 is normally held to be AROUND 50% charged, indicating it is time to recharge ASAP to optimise battery life.

 

FWIW I too suspect voltdrop somewhere in the wiring.

 

Sorry, another brain fart. I agree, I take 12.5 to be about 75% charged so about half sensible discharge and 12.2 to 12.3 to be a true 50% discharged so time to stop discharge and recharge.

[beerbeerbeerbeerbeer]

2 hours ago, Tony Brooks said:

 

Sorry, another brain fart. I agree, I take 12.5 to be about 75% charged so about half sensible discharge and 12.2 to 12.3 to be a true 50% discharged so time to stop discharge and recharge.

That is my cut off point too 12.2 to 12.3      at rest. 

The most common I’ve seen stated is 12.06 for 50% discharge but I feel uneasy about that figure. 
 

so here is my simpleton question, is it ok to draw a load on the batteries if it takes them below  50%, if the batteries are know to bounce back again with no load?

I imagine it’s ok for brief periods, as the starter battery works in that fashion. 

so as an example domestic batteries show 12.30v at rest and then with a heavy load drop to 12.15v, Or 12.20v dropping to 12.05v. 

 

 

 

[nicknorman]

1 minute ago, Goliath said:

That is my cut off point too 12.2 to 12.3      at rest. 

The most common I’ve seen stated is 12.06 for 50% discharge but I feel uneasy about that figure. 
 

so here is my simpleton question, is it ok to draw a load on the batteries if it takes them below  50%, if the batteries are know to bounce back again with no load?

I imagine it’s ok for brief periods, as the starter battery works in that fashion. 

so as an example domestic batteries show 12.30v at rest and then with a heavy load drop to 12.15v, Or 12.20v dropping to 12.05v. 

 

Yes. It is the rested voltage that indicates the %SoC. The fact that the voltage dips below the resting voltage corresponding to 50% under load is not relevant and does not indicate that the batteries are below 50% SoC. It is the actual SoC, not the  voltage under load, that is relevant. And in any case, 50% SoC is just a rough rule of thumb, not some precise figure below which the batteries expire!

[dmr]

Its the off load voltage that gives the state of charge, so its ok to see a lower loaded voltage as long as this "bounces back" to a good unloaded voltage, but then again its possible that the whole 50% thing is a huge myth and misunderstanding and then nothing goes wrong if you take the batteries below 50%. I think I'm in a minority with this thinking and even the batteries suppliers say 50%, but then thats in their interest.

 

If taking mine down to 40%, or even a bit less, gets me another day without running the engine then Im ok with that.

[nicknorman]

2 minutes ago, dmr said:

Its the off load voltage that gives the state of charge, so its ok to see a lower loaded voltage as long as this "bounces back" to a good unloaded voltage, but then again its possible that the whole 50% thing is a huge myth and misunderstanding and then nothing goes wrong if you take the batteries below 50%. I think I'm in a minority with this thinking and even the batteries suppliers say 50%, but then thats in their interest.

 

If taking mine down to 40%, or even a bit less, gets me another day without running the engine then Im ok with that.

According to Trojan’s data sheets, the maximum total Ah extracted over the life of a T105 is obtained when they are cycled down to 40% SoC.

[Tony Brooks]

In my view, it is not something I would do regularly, but the occasional drop to 12V rested and recharge within a couple of hours is unlikely to produce any noticeable ill effects of the batteries. It is only like minus half a cycle on battery life. As Nick says. it is all a rough rule of thumb designed to help the less aware avoid wrecking their batteries within a few weeks.