Battery voltage not the same “downstream”

[Boatname]

I recently noticed that when my fridge came on the led display fluctuated massively.

Subsequent checks showed that all the downstream readings were less than readings taken directly from the battery with the fridge on.

When the fridge is not running they all agree.

I have an engine start battery which works in isolation to the two service batteries.

These are controlled by a selector 1,2,all, off switch.

I have wired the fridge compressor DIRECTLY to battery 2. (Battery 1 was through the normal circuit, under light load, everything normal). I had a wire running across the saloon floor from battery 2. Everything ran perfectly and after 48 hours the battery resting voltage was 12.3, running 12.0 which the boat has always been happy with. (I then change to the other battery giving me 4 days on battery power.)

I have changed the master switch but as the figures were the same I changed back to the original one.

I have taken the master switch out of the circuit and ran the switch panel positive directly down to a battery.

When under 240v charge there is no problem.

All 3 batteries charge to 12.8v and stay there resting for an expected amount of time.

I am at a loss as the batteries are good (48 hours under load)

The master switch is good (taken out of the circuit two different ways ... cable across the floor,  switch panel wired direct to battery and then changed)

All the connections look/feel good but here are the observations:

Fridge off, all read the same.

Fridge on (sample numbers depending on state of battery when reading taken)

Battery 12.5
LED 11.7,12.1,12.7,12.5,11 whatever,12 whatever. Sometimes settles to following readings:
Bus bar (?).  Positive stud, negative strip 11.6
Power socket 11.6
Instrument panel 11.6, BUT wind, gps, speed, depth, pilot all run fine. They have actually been on when I opened up the instrument panel and took the readings.

I’m totally lost.

The volt meter could be suspect but it ALWAYS gives the same readings wherever I test i.e. battery  says 12.3, bus say 11.6 ... consistently.

The good news is that everything works.

The fridge runs 10 mins on, 20 mins off (on average), the instruments, water pump, lights all work.

If it hadn’t been for the led giving such crazy figures I would never have known there was a problem.

My wife is leaving me as all I do now is jump up every time the fridge starts, throw everything off the seat to test the battery, check the led, mutter, sweep everything off the chart table to get to the bus bars, plug the gps into the socket and dash into the cockpit to take readings.

And mutter.

Actually sometimes I don’t domall that, everything is clear but then half the boat is inaccessible.

Sorry for the length of this post but 7 pages of readings on, off, different start voltages, scribbles, not sure what I wrote has taken its toll 

[Symphony]

First thing is to replace the 1,2 both switch with a VSR so that charging is automatically dealt with - charging the engine battery first then the service bank. You can keep the original isolator switch for when you leave the boat, but better to wire the two banks to their own individual isolators. You can achieve all this by using a switch cluster such as the one made by BEP Marine. This is how I wired my old 37 - same age as your boat. The old isolator becomes redundant and I left mine in place in the on position so it is just a terminal connecting the negative.

Not sure why you wired your fridge to just one battery. Your service bank is effectively one battery even if it is made up of two. The fridge should draw from the 12v distribution panel through a fused switch. This will mean that the fridge draws from both batteries in the bank equally rather than running down just one and creating an imbalance between the two batteries in the bank. You can also have a battery monitor for the service bank (or even one that also monitors the engine battery) and this will give you a reading for all your service circuit draw.

[Boatname]

Um, can’t see why I need to change what has worked perfectly for 18 years.

The current set up has worked up until recently.

I know it was a long post but the reason that I ran a cable from battery 2 across the floor to the compressor was to ISOLATE it from any other boat related systems. It was what I would call a pure test. Did the compressor work directly from just one battery? Yes it did. It was a matter of removing possible problem areas and seeing what worked.

This is why I then took the master switch out of the circuit

That is why I tried a new one.

Whatever I did to remove possible areas of conflict didn’t change anything.

What if the fridge switch on the panel was causing problems?

I took it out of the circuit.

What if the master switch was happy at rest but didn’t like the fridge draw?

I took it out of the circuit.

It was all a test.

[Boatname]

Just checked and I might already have a “vsr”

Shorepower 702

Sure Power Battery Isolators Eliminate Multi-Battery Drain When 2 Or More Battery Banks Are In A Charging System ; Allows Each Battery To Charge According To Its Own Needs ; Prevents Auxiliary Power From Draining The Starter Battery ; Battery Isolators Make Sure You Are Never Stranded With A Dead Starter Battery ; Sure Power Model #702 ; Fully Solid State ; 70 Amps ; 3 Studs, 6Mm ; Mounting Holes: 4 Holes At.210 Inch.

This as it says allows each battery to charge to its own needs which would cover your first sentence, if the starter needs it, it gets it.

Also your statement about the fridge drawing from both batteries at once seems flawed as I can chose battery 1, 2 OR BOTH.

What am I missing from what you wrote?

[Symphony]

You do not need a 1,2 both switch if you have a VSR. The purpose of those out of date switches was to allow you to choose which battery to charge and which to use. It was the first "solution" (about 50 years ago) to deal with the issue of when boats first started to have serious on board electrics which needed additional battery capacity. Now a VSR and separate isolated banks does all this for you and makes that switch redundant. The only thing you lose by ditching it is the ability to use the service bank to start the engine, but if you fit the switch cluster I suggested you will have a parallel switch to achieve this. Or you could just stick with the VSR and separate isolators for each bank and fit a separate switch to combine the two banks if necessary. Your system is overly complicated and what I suggested is the way the current boats (and many, many others) are wired.

I don't understand why you would want to choose to draw your fridge power (or any other service load) from your engine start battery (battery 1?). service loads should draw from the service bank (battery 2?) (one battery bank even if it is made up of 2 batteries) and only engine start from the engine battery.

If you want to see what the fridge is drawing, simply switch off all other services and turn the fridge on. Even if the draw without the fridge is not zero, the additional draw from the fridge will be the difference between with and without. I did this last weekend and the fridge on changed the draw on the BM1 monitor by just under 4 amps when the compressor was running.

[Boatname]

Thanks for trying so hard Symphony and sorry to be so trying 

I think that I get the vsr but Imam still confusing you.

I have a start battery that is stand alone.

It starts the engine. That’s it.

I have 2 other service batteries... 1&2 and can chose either to run the house/services whatever you want to call them.

So I didn’t use the engine battery to draw fridge power!

I used house 2 first of all when I connected the wire across to see how the fridge in a stand alone condition affected the battery. It was normal.

I used house 1 to bypass the master switch, therefore the led, bus bar, fridge switch were all involved.

Seems really logical to me to remove potential problems and the obvious ones in my order were the:

Compressor

Master switch

Bus bar

LED

Fridge switch.

At some point they have been bypassed but I am still left with my original problem:

When the fridge is running the led, bus bar, socket on the panel and voltage at the helm are all around 0.9 of a volt less than the actual battery, and why the led leaps around randomly.

Depressed

[Lyra]

What you describe seems to be a problem with corroded wires between the panel and the fridge - you mentioned 18 years, and Bavaria boat of these years (like mine) have non tinned wires, which get corroded over the years.
The corrosion increases the resistance of the wires.
When the fridge is not working, no current flows in the wires, so the reading on the panel (battery) and the fridge match.
Once the fridge is on, current flows, there is a voltage drop on the wires, the fridge gets low voltage.
This is why when you ran a new temporary cable directly everything worked OK
So, the solution is to replace the permanent wires

Test - you can confirm my assumption by using a multi meter (resistance mode) - touch one probe to the wire end at the panel and the other probe at the wire end at the fridge and you will probably see a resistance which is much higher than the temporary wire that you used

[Boatname]

Thanks. I’ll try that.

[Lyra]

One note - test both the positive and the negative wires as only one of them may be corroded

[tiger79]

I have a start battery that is stand alone.

It starts the engine. That’s it.

I have 2 other service batteries... 1&2 and can chose either to run the house/services whatever you want to call them.

Your 2 house batteries should ideally be connected in parallel, to combine them into one larger bank.  Your batteries will last longer, compared with using them individually.  They will also recharge more efficiently.

[Boatname]

Interesting as I read that a duff battery could drag down a good battery.

Thanks for the suggestion but I like it the way I have it ... I know I that I always have a battery in reserve.

[tiger79]

Interesting as I read that a duff battery could drag down a good battery.

The chances of that happening are slim, and you'd know about it because the bank's voltage would drop. 

[Boatname]

One note - test both the positive and the negative wires as only one of them may be corroded

How would I do that?

The batteries are fine, the master switch is fine so next in line is the neg. bus bar and the pos stud but I’ve already given those readings.

To reiterate, when the battery is resting all the voltages agree.

When the compressor (that I tested using it’s OWN battery ... number 2 service) is running the figures go haywire ... bus bar, led, socket, binnacle.

If I disconnect the neg and pos from the stud/bus and take their readings all I’m measuring is the standing voltage ... which is ok.

[Yngmar]

The voltage differences are normal, you have a fundamental misunderstanding about how electricity works.

Let me try to explain without writing an essay. Every electrical conductor is imperfect (superconductor research is a field trying to rectify that, but mostly still requires conductors to be made of very fancy stuff and/or cooled near absolute zero, so not practical for your boat). Therefore every cable in existence is also resistor. The smaller the cable diameter, and the longer the cable, the more total resistance it has. Since Ohm's law says that U=R*I, the voltage drop on the cable increases with the current flowing through it. Therefore, while your fridge is off, there is little to no current flowing through said cable, therefore there the voltage drop is minimal and you measure full battery voltage everywhere. When the fridge is on, some current, perhaps about 4.5A are flowing through the cable, and since the cable has a resistance, a voltage drop occurs. Every point you measure is further down the line, therefore the cumulative voltage drop increases the further away from the batteries you get.

This is perfectly normal! If the voltage drop is too big, you either have too small cables for the length of the run and the current draw of the fridge, or you have some failing cables or joints somewhere that are slowly going high resistance, usually due to corrosion, but sometimes also due to pulling out of poor crimp fittings or chafing through somewhere. But your voltages look okay and the fridge runs fine, so it seems you're just overreacting and needlessly scaring the wife when you should instead be on Wikipedia reading https://en.wikipedia.org/wiki/Ohm%27s_law 

[Boatname]

Soooo.

Why does the led flash different numbers constantly when the fridge is on ... it used to be a fixed figure like the water tank, and how can the instruments work at the binnacle with only 11.6 volts showing?

Surely the factory/commissioning agents didn’t fit the wrong size cable.

Your first sentence is spot on 

[Salty]

When your boat was built in 2001, everything on the boat was new. There was no corrosion on the wiring, but like a number of other boat builders, Bavaria used ordinary copper wiring and everything worked as it should. Over the next eighteen years that copper will have started to corrode, particularly on boats located in a salt water environment. My boat was built in 2002 and I have noticed that cabling onboard can become corroded throughout its length despite that there are two independent plastic coatings to protect each of the copper cores. Sometimes lights will not function at all because of corrosion even though voltage can be found at the light bulb, but where the resistance due to corrosion is enough to prevent sufficient current from arriving at the bulb to the point that the bulb will not light up.
In other threads you will see that contributors frequently recommend the use of tinned copper wires where tinning prevents the copper from becoming corroded.

[Boatname]

Okey doke.

Cable checking time.

Thanks to all

[Symphony]

Interesting as I read that a duff battery could drag down a good battery.

Thanks for the suggestion but I like it the way I have it ... I know I that I always have a battery in reserve.

Sorry, but that is just not logical. The reason for having 2 batteries in the service bank is to increase capacity, not to give you a choice of using one or the other for your service needs. Think about it, if you only use one battery at a time, every time you use it you typically in a day will use half its capacity, then you will be charging the whole bank with one battery half discharged and the other fully charged. If you treat it as one bank, each individual battery will be discharged equally by only 25%. Battery life is a function of the number of cycles and the depth of discharge so discharging by 50%  rather than 25% will shorten the life of your batteries.

I have never seen a boat wired like yours. My boat has 3 individual batteries in the service bank but is charged and discharged as one battery.

As I said earlier 1,2 both switches were used before split bank systems were common and are redundant once you have a proper split charge system which your boat had when it was built.

[Boatname]

I understand the maths and appreciate the input but wonder why these Chandlers are stocking so many switches if it’s such old tech 


https://www.marinesuperstore.com/search?searchtext=Battery%20switch

https://www.force4.co.uk/

https://www.tcschandlery.co.uk/search/Battery+switch?search=Battery+switch

“ then you will be charging the whole bank with one battery half discharged and the other fully charged.”. The charge only goes to the selected battery not both.

See my setup:

[tiger79]

I understand the maths and appreciate the input but wonder why these Chandlers are stocking so many switches if it’s such old tech 

Because there are a lot of unsold ones in stock, because most sensible people got rid of them long ago.

“ then you will be charging the whole bank with one battery half discharged and the other fully charged.”. The charge only goes to the selected battery not both.

It doesn't matter, the key point to understand is that you're discharging the battery more than need be, thus shortening its life.  By combining batteries into one bank, they also recharge more efficiently, as well as lasting longer.  Additionally, you need to fiddle about with the switch, whereas a modern charging arrangement is totally automatic.

[Clivert]

On our old Moody we had manual switches that had 1,2 and all.
We had two service batteries and one engine start.
1 was engine
2 service
And "all" was for charging.
Routine was simple. After starting on 1 we switched to "all " while engine running and to 2 while sailing ensuring that we had a start battery ready when needed.
Old and simple but it worked perfectly.
As they say Keep it Simple.

[tiger79]

Routine was simple. After starting on 1 we switched to "all " while engine running and to 2 while sailing ensuring that we had a start battery ready when needed.
Old and simple but it worked perfectly.
As they say Keep it Simple.

But it isn't simple!  It relies on people remembering to change the switch setting every time they want to start or stop the engine.  And it has the inherent danger that, if the switch is left in the wrong position, it's possible to flatten the start battery - the RNLI spend a lot of time towing in boats where this has happened.

With a modern system, you just arrive at the boat, switch on the electrics, use the boat, and switch it off when leaving.  Nothing else to do.  Now that is truly simple.

[Symphony]

I understand the maths and appreciate the input but wonder why these Chandlers are stocking so many switches if it’s such old tech 


https://www.marinesuperstore.com/search?searchtext=Battery%20switch

https://www.force4.co.uk/

https://www.tcschandlery.co.uk/search/Battery+switch?search=Battery+switch

“ then you will be charging the whole bank with one battery half discharged and the other fully charged.”. The charge only goes to the selected battery not both.

See my setup:

OK, but you are just over complicating things for no gain, and potentially shortening the life of your batteries as well as introducing potential failure points.

The switches you reference are mostly cheap products that have not been used on new boats for more than 20  years. There is still a market as they regularly fail and there are many thousands of old and mainly smaller boats that are still fitted with them. They have no place on modern boats, which is why Bavaria (and most other builders) do not fit them.

[dgmultimedia]

Okey doke.

Cable checking time.

Thanks to all

Interesting that you have tested EVERYTHING and its all working - but you still think the Volt Indicator panel readings are correct!!!
It might just be the LED indicator seeing voltage spikes caused by an old compressor motor - either the smoothing circuit on the LED indicator or the Noise suppression circuit of the fridge controller has a fault!!!!

DG

[Clivert]

Ref battery switches on my Moody, it comes down to discipline, and that comes down to sailing in pre marina days when the day's sailing started in the dinghy going to the mooring.
A routine should be followed every time one goes on board .
I have to say that I am amazed at how many things I see today from the " get on, start it and sail away " brigade these days.