Are my batteries on their way out (or Using A Hydrometer)?

[demonboy]

Morning all,

My situation is thus: I have 415aH house battery capacity and two fridges that have a cut-off facility which I believe is set to 11.5v (I can't change this). Recently my fridges refuse to run the compressor for more than 10seconds before cutting out. The TEC control panel flashes the amber light that is labelled 'external power source'. I believe this to mean that it requires an external power source to run the compressor, like the engine. When I run the engine I can get one fridge to run but not both.

My suspicion is that the batteries are on their way out. They are cheap Turkish starter batteries, three years old. However the battery monitor (Mastervolt, to accompany my smart charger) tells me the batteries are at 12.53v. A quick test with the battery monitor on each battery confirms this.

Here's the rub: when I use my hydrometer on each cell, every single one shows 'red'. I assume that I have to top up my cells with distilled water, which I do. When I check again 24 hours later, after running the engine for 3-4 hours, they still show red. What does this mean? That I have to continue topping them up? If I do this they will overflow!

Does all this mean it's time for a new battery bank?

 

[captainslarty]

Presuming your hydrometer is a red bad, green good type, then yes, replace the batteries.
There is a SLIM chance that the system isnt charging at all, but if you are replacing water they probably are, or its darn hot over their !.
Check the voltage as the fridge switches on for its 10 seconds, also, try puting all lights etc on and monitor the voltage.
If the voltage doesnt rise when charging, and, the hydrometer still reads red on all cells, then use them as a mooring.

 

[demonboy]

BTW - it IS darn hot over here! Around 40 degrees yesterday. And yes, by 'red' I do mean a red=bad, green=good hydrometer.

Do you think 3x135aH batteries would make a suitable mooring for an 18 ton boat?

 

[Salty John]

If by 'starter' batteries you mean they are not deep-cycle (traction) batteries, then you have done extremely well to have got three years out of them. You need deep cycle batteries, designed and built for multiple deep discharges, for 'house' duty.
Starter batteries provide a short burst of high output, but are not designed to be deeply discharged.

 

[demonboy]

Yes, I understand this and I always wondered why I had starter batteries, but this is what the boat-yard had recommended. I think it was a cheap, cost-effective solution, knowing that despite being starter batteries they would last a few years. I was told it's what all the gullets use here. This is ok in the short term but I need a longer term solution and am thinking gel batteries as the replacement.

 

[halcyon]

One advatage of a ammeter, if your charge rate falls after a few minutes you have not used your batteries, or have a battery problem. Having a feel for power usage, you can get a feel for what you are putting back.
It also makes me think that the bar-graph voltmeter / ammeter we started making in the late 80's, is a good way forward. You can watch all voltges and amps at the same time. So if amps go up, and volts collapse, both are in view at the same time, and a problem is visable.

Brian

 

[demonboy]

I think I've already made up my mind that it is time to replace the batteries - thanks to those who have replied already.

My partner, Queenie, has just been reading up on batteries and was interested in traction batteries, especially as Alastair Garrod recommends them as a bluewater option. Any views/experiences of these? I wonder how easy it would be to pick these up in Turkey?!

 

[captainslarty]

Hi
Personally I have had great service from Trojan T105´s, but unfortuantely I have no idea on the availability in your area. If you do pay a lot for your batteries, then also consider a suitable charging system and maintnance schedule
Good luck, and yes, 3 years from cheap starter batteries is good, depending on your needs you could even go that way again depending on the price of other systems in your area.
Joe.

 

[Guest]

I agree that starter batterys are not ideal - but 3 years IMHO is not long ..even for Starters ... my batts are far older than that and only now am I thinking about changing 1 of them ...

Best is as another keeps posting at various times ... the HD ones for trucks that have to power tail-lifts as well as start big engines etc. They get abused something rotten - but carry on ... our truck - regularly batts go flat - but we charge her up and alls well ...

 

[VicS]

[ QUOTE ]
Here's the rub: when I use my hydrometer on each cell, every single one shows 'red'. I assume that I have to top up my cells with distilled water, which I do. When I check again 24 hours later, after running the engine for 3-4 hours, they still show red. What does this mean?

[/ QUOTE ]

The bad reading on the hydrometer does not mean they need topping up with distilled water, it means they are flat and require charging. You top up with water if the acid level is low. It must always cover the tops of the plates and if there is maximum mark you should not fill above that.

When you do top the cells up the water tends to stay at the top for quite some time as it is lighter than the acid. 24 hours and 3-4 hours running is probably not long enough for it to mix properly so you will still get a "bad" reading.

Personally I prefer to check the volts with a digital meter rather than use a hydrometer. The volts must be checked after the battery has rested for 12 hours without being used or charged. 12.7 to 12.8v is fully charged 12.2 is about half charged and 11.7 is effectively flat. If a fully charged battery is just allowed to stand without use the volts will drop failry quickly at first then more slowly and if it is still good then it should still read 12.6v 3 or 4 weeks later. (you might get slightly higher readings in a hot climate though and they will naturally fall more quickly)

The hydrometer does check the cells separately though. If you get different readings on different cells it indicates that the battery is probably no longer any good. A hydrometer will read lower as the temperature increases. If the temperature is 10C higher than the temperature at for which it is calibrated then it will read approx 0.007 low.

 

[demonboy]

Thanks for that, Vic. Very useful. One thing, however: you say 'The volts must be checked after the battery has rested for 12 hours without being used or charged'. I struggle with this as a live-aboard!

The other thing I'm unsure of is this: if I gave my batteries a good charge (100%) from shore power a week ago, never allow them to drop below 75% capacity and frequently run the engine to keep them charged at 80%, then why will they not run my fridge effectively?

 

[pyrojames]

If you have one "red" cel and all the other are white or green, then is it very likely that one cell has collasped. This is the common way for batteries to fail, so I am afraid you are probably up for a new set.

 

[orizaba]

and am thinking gel batteries as the replacement.

IMHO not a good idea for long term,they take along time to recharge, and do not like high voltages.it is said that you can discharge them deeper without affecting them true,but what you take out you have to put in .its better to have batteries you can charge faster.
i 've used standard good quality wet 100a lorry batteries for years both in my work with motorhomes and living afloat for 15 years with no problem,as mentioned a good charging system is the key ,never let your batteries go below 50%,top up with water etc and they should last for years
one thing i have found works well is that instead of running your engine once a day for say 2 hrs,run it twice a day for 1 hour,leave as long as you can between charges and the batteries will perform better.in the uk used to run for 3/4 hr at lunchtime and then at 6 after work.by doing it this way it allows the cells to soak up the power(simply speaking) batteries are like a sponge,
by the way last set of batteries lasted 6 years,this set so far 3,ooooh must go batteries need charging

 

[demonboy]

[ QUOTE ]
If you have one "red" cel and all the other are white or green, then is it very likely that one cell has collasped. This is the common way for batteries to fail, so I am afraid you are probably up for a new set.


[/ QUOTE ]

Actually, they are all red!

 

[Ruffles]

[ QUOTE ]

My suspicion is that the batteries are on their way out. They are cheap Turkish starter batteries, three years old. However the battery monitor (Mastervolt, to accompany my smart charger) tells me the batteries are at 12.53v. A quick test with the battery monitor on each battery confirms this.


[/ QUOTE ]
Surely if you have 12.53 volts at the battery and the fridge is cutting out due to under voltage then you have a loose connection in the wiring. Or am I missing something?

 

[Billjratt]

TEC controller flashes yellow when low voltage, that matches the"red" electrolite sydnrome. If you have only run the engine for 4 hours... how big is the alternator - 200amp? You have the same LED on the TEC glowing constant yellow when the voltage has risen high enough to be charging, you need to run for hours after that to fill the batteries. If you can get to shorepower for a week and have a good multi-stage charger on board, that may help. Buying new batteries will not help if you don't have a good charging regime, they'll just end up like the ones you've already got. Waeco fridges will cycle (start for a few secs, then stop for a few secs then start again) if there is a bad connection in the circuit, or low power.

 

[tobble]

Batteries may well read 12.5 V when they are on their way out, because if you've just been forcing charge into them they will still hold it for a short time. However, as soon a s you load them, the voltage drops, hence the way to see if they are any good is to put a volt meter across the terminals then load them, i.e try starting the engine or other heavy load, such as two fridges... if the voltage goes below 9.5 then the battery is pretty iffy. My car refused to start a while ago and I performed this test and got 6.2V!

The reason is that as batteries wear out they loose their ability to re-convert the energy stored chemically in an efficient manner. at best they are only about 85 - 90% anyway. so if the efficiency has gone down to, say, 30% your 100 ah bvattery is now efectively only 30 aH, so the voltage (vaguely proportional to the amount of charge in there) drops of very quickly.

the 12V bible for boats has a very good section explaining all this stuff

 

[demonboy]

[ QUOTE ]
Surely if you have 12.53 volts at the battery and the fridge is cutting out due to under voltage then you have a loose connection in the wiring.

[/ QUOTE ]

and....

[ QUOTE ]
Waeco fridges will cycle (start for a few secs, then stop for a few secs then start again) if there is a bad connection in the circuit, or low power.

[/ QUOTE ]

Possibly, but where is that loose wiring? It can't be the fridge because it's still connected, ie flashing amber. The amber light never stays lit, it just flashes.

 

[demonboy]

I guess what is confusing me is this:

The battery monitor says 12.53 (well, actually it has now fallen to 12.34v since this morning). The fridges do not run unless I run the engine to charge the batteries above 12.5v. When I turn the engine off the fridge/s continue to run for half an hour or so until the voltage drops below a certain level (not sure what).

If it is loose wiring then surely they would cause problems irrespective of whether the engine is running or not. So that just leaves low voltage in the battery. However if the fridges cut off at 11.5v then why are they cutting out if my battery monitor says 12.34 or more?

Finally, if my batteries are showing 12.34v on the monitor then why when I use the hyrometer does each cell show red?

FYI: I charge the batteries back to 100% every couple of weeks or so and they rarely go below 70% discharge. I have a rock-solid 3-step Mastervolt charging system.

Clearly I'm not understanding something very simple regarding 12v electronics here.....

 

[tobble]

apologies if my previous post was a little unclear; when a battery is duff you can still put charge into it to get it to 12.5 or more volts, but they are not actually storing much energy. therefore, it doesn't take much to suck out enough charge to make them dip below 11.5 V at which point your fridge cuts out.

To test your batteries, conect them (one at a time) to your engine- they are after all starter batteries - and measure the voltage cross the terminals, on the battery while you try to start the engine. if the voltage drops below about 9.5V while the engine is turning over, the battery is no good.

the thing about Hydrometers is that they don't tell you what sort of state the plates are in, but useful for assessing either the charge or the state of the electrolite