GHA
Well-known member
Sounds like voltage drop in the wiring, you could try a temporary piece of cable direct from the batteries to the fridge, see if that makes a difference.
Are my batteries knackered?
- Thread starter Ammonite
- Start date
Ammonite
Well-known member
I'm going to try this but if it were the wiring why would the voltage at the fridge start off at 12.8 v under load and then drop to the cut off voltage of 10.7v after several minutes. Wouldn't it drop as soon as the compressor kicked in if it were the wiring?
GHA
Well-known member
It does sound odd indeed! But if the voltage at you up batteries is staying at 12.6v then that suggests the problem lies further down the line..
Good luck
prof pat pending
Well-known member
Take the batteries to your local auto retailer and ask them to do a dump test.
They will be able to tell you instantly if you have a duff battery and most will do this free
They will be able to tell you instantly if you have a duff battery and most will do this free
Ammonite
Well-known member
The story so far....
Have taken all the advice on board (well most of it) and tried running the fridge from each domestic battery in turn with new cabling direct from the battery to the fridge. The end result was exactly the same. Nasa was reading 12.7v in both cases and when I switched the fridge on the voltage fell away to the fridge cut-out voltage in circa 30 secs. What I didn't do was to measure the voltage at the battery end during the test (not enough meters or hands). I've no idea what reading the Nasa was giving during the test but as soon as the fridge cut out it was back to 12.7v (I can't monitor the fridge voltage and watch the Nasa at the same time!)
My conclusion thus far is that either the batteries are knackered or the Nasa isn't reading correctly, although it reads exactly 13.8v when the 240v charger is running (which is set to deliver 13.8v via the dip switches) and exactly 14.4v when being charger by the alternator, so this seems unlikely. I did put my multimeter across the battery terminals when the fridge wasn't running and this gave 12.4v rather than the 12.7v on the Nasa but I put this down to using a cheapo meter??
The boat is on a swinging mooring so lugging 50kg of batteries into the dinghy isn't something I relish the prospect of so have decided to invest in a decent battery tester.
Any further suggestions if you disagree with my conclusion gratefully received!
Have taken all the advice on board (well most of it) and tried running the fridge from each domestic battery in turn with new cabling direct from the battery to the fridge. The end result was exactly the same. Nasa was reading 12.7v in both cases and when I switched the fridge on the voltage fell away to the fridge cut-out voltage in circa 30 secs. What I didn't do was to measure the voltage at the battery end during the test (not enough meters or hands). I've no idea what reading the Nasa was giving during the test but as soon as the fridge cut out it was back to 12.7v (I can't monitor the fridge voltage and watch the Nasa at the same time!)
My conclusion thus far is that either the batteries are knackered or the Nasa isn't reading correctly, although it reads exactly 13.8v when the 240v charger is running (which is set to deliver 13.8v via the dip switches) and exactly 14.4v when being charger by the alternator, so this seems unlikely. I did put my multimeter across the battery terminals when the fridge wasn't running and this gave 12.4v rather than the 12.7v on the Nasa but I put this down to using a cheapo meter??
The boat is on a swinging mooring so lugging 50kg of batteries into the dinghy isn't something I relish the prospect of so have decided to invest in a decent battery tester.
Any further suggestions if you disagree with my conclusion gratefully received!
yachtorion
New member
My original comments were based around an (unstated) assumption that the Nasa was reading incorrectly, otherwise the things you are seeing don't make much sense. But there are other possibilities.
CTek do a battery analyser, I wonder if that would be worth a go?
CTek do a battery analyser, I wonder if that would be worth a go?
sailinglegend420
Member
Did you only run new positive cabling, or both Pos and Neg. Have you done the tests as suggested in #19?
GHA
Well-known member
Another fairly easy test might be to put a car headlamp bulb or something drawing a few amps straight onto a battery for a while and watch what happens to the voltage.
All sounds a bit odd.
prof pat pending
Well-known member
The boat doesn't move then .... doesn't take long to whip a battery out and do a dump test
GHA
Well-known member
A garage Cca test might tell you something useful about a starter battery but not really much about the capacity of a domestic..The boat doesn't move then .... doesn't take long to whip a battery out and do a dump test
http://batteryuniversity.com/learn/article/how_to_measure_capacity
prof pat pending
Well-known member
And using a bulb and a volt meter tells you more???
Bilgediver
Well-known member
+1 The Fridge is experiencing an additional loss of 1 volt in the feeders according to your figures so it sees the reduced voltage at about 11.5 so seems you need to
check connections and wire. Certainly do not buy new batteries till you have reduced the losses between the battery and fridge.
GHA
Well-known member
prof pat pending
Well-known member
Twaddle
sailinglegend420
Member
.... doesn't take long to whip a battery out and do a dump test
This is very bad advice for a service battery
A drop tester is designed to test starter batteries under a high load not deep cycle service batteries under low loads. A starter battery uses about 1% of its capacity each time it is used! A service battery could use 50% each time it is used. A drop tester will tell when a battery is dead but not how much life it has left in it. A deep cycle battery may easily pass the test to deliver a high current for a short time, but if their capacity has been reduced by sufation then these testers cannot test the remaining Ah capacity so the batteries life at anchor may be very limited.
You can test a battery with a voltmeter, but you must use a small load and see how quickly the voltage falls.
Being rude doesn't do you any favours, it just shows your ignorance.
prof pat pending
Well-known member
It really depends on the type of battery. In this case, they are Lucas 110 Leisure batteries.
All of the Lucas units I have come across in this range are dual purpose. They are rated for cold cranking and are good for high load uses such as motor movers, so a high load test is suitable
All of the Lucas units I have come across in this range are dual purpose. They are rated for cold cranking and are good for high load uses such as motor movers, so a high load test is suitable
KAM
Well-known member
Sounds like mine. Sailed all the way down the coast of France with warm beer and also thought I needed new batteries. Added a second positive wire and never had a problem since.
ghostlymoron
Well-known member
I have a collection of suspect batteries kicking around and would like to test their capacities and ascertain which are useful and which can be dumped. If I do a drop test with a small lamp taking say 1amp and measure the voltage every hour, how do I interpret the results to tell me the ahr capacity. Do I need to measure the current as well? Excuse my ignorance.
Jim@sea
Well-known member
Perhaps they could be older than 4 years old, some battery dealers buy stock and it could be months before they sell the last one of a batch, in the meantime they will have been sitting on the floor uncharged for perhaps a year. Its only when they sell them that they date stamp them.
On the boat I have bought both 110ah batteries were "New" in 2011, (so the invoice from the previous owner indicates) They struggled to turn over my 2.5l Diesel engine when I had to keep bleeding it when I tried to find the fault which was present with the boat when I bought it.
Certainly for the start of the sailing season next spring I will be replacing my batteries then, and with some decent tractor batteries, these cheap £70? 110ah batteries cant be that goof for that price.
Plevier
Active member
Doing an accurate test is not easy (you need temperature control, current stabilisation etc.) but you can certainly get an idea.
Make sure the battery is soaked at 20-25 deg C and test in that sort of ambient temperature.
Aim for a load of 5% of claimed capacity (since capacities are most often on a 20hr basis.) - e.g a 60W headlamp bulb for a 12V 100Ah battery.
Take voltage and current readings from time to time, increasingly frequently as the voltage starts dropping quicker.
Terminate the test (and recharge immediately) when you are down to 10.8V (assuming a 12V battery).
Estimate your mean current from the readings and multiply by test duration.
You have a rough approximation to the capacity the battery is delivering.
In industrial applications you normally scrap if achieved capacity is below 80% of nominal - but some nasty cheapo leisure batteries probably barely achieve that when new!
I would probably scrap at 50%.