pvb
Well-known member
He may not have an automatic bilge pump. Lots of people don't. And he did say that the charger was the only thing connected.
Battery shock!
- Thread starter bigwow
- Start date
He may not have an automatic bilge pump. Lots of people don't. And he did say that the charger was the only thing connected.
bigwow
Well-known member
Charger is hard wired to each engine start battery and the house bank. 12v master was switched off, bat meter has its own permanent feed and is the only feed outside the master switch240 plug was out of the socket in the cockpit. Charger is 20amp with 3 separate outputs
EuanMcKenzie
Member
That's the first place i look
I usually leave one battery dedicated to the bilge pump and the other isolated so I have something left when I return to the boat. Engine battery is separate. Agree with everyone else. put your multimeter across the terminals and measure the voltage. If you haven't got one buy one its one of the most useful things you can have on a boat
Richard10002
Well-known member
If the charger is 20A, and the batteries were close to flat, I would have thought they would draw the full 20A for quite some time, ( many hours if discharged by over 300Ah).
Unless there has been a problem with the charger at exactly the same time as the batteries have been flattened during an absence, (for the first time ever?). Not impossible, but quite a coincidence.
Richard10002
Well-known member
If the charger is 20A, and the batteries were close to flat, I would have thought they would draw the full 20A for quite some time, ( many hours if discharged by over 300Ah).
Unless there has been a problem with the charger at exactly the same time as the batteries have been flattened during an absence, (for the first time ever?). Not impossible, but quite a coincidence.
William_H
Well-known member
As said if the battery cumulative AH meter shows little left in the battery then you should confirm by checking the voltage at the battery. If that is low then yes something has drained the batteries. If however the battery voltage seems OK then battery is not so low.
The cumulative AH battery meter is an attempt by manufacturers to give you a "fuel gauge" of battery power. But this concept is fraught with problems and is not the simple fuel gauge that owners might want. Imagine you had a fuel gauge for your car which operated on the principal that you fill the tank then based on fuel taken out in driving and fuel put in at refill you have an idication of how much fuel you have. Now this system might seem reasonably accurate initially but if either input or output measuring is inaccurate or there is any evaporation then the only way to get accuracy is to regularly fill the tank to full and rset the cumulative gauge.
Now with our battery meter this works in the same way. You need to regularly reset to full when you know the batteries are charged. The problem with batteries is that the actual battery capacity may not be what is claimed by the manufacturer and then declines with age. But the meter does not know the actual capacity unless you tell it.
The whole meter is most useful for short term assessment of battery state eg after a nights discharge then a session of charge from engine you can assess if you have replaced what was used.
Voltage of the battery can be a useful additional measure of battery state. But een that is not simple.
So although this sudden low cumulative reading has come as a shock I don't think you should rush to buy a new charger or panic. You cna as said check actual discharge when everything is apparently turned off and this would be useful. Otherwise just understand that your battery meter is very fallable and keep an eye out for other electrical problem symptoms. good luck olewill
The cumulative AH battery meter is an attempt by manufacturers to give you a "fuel gauge" of battery power. But this concept is fraught with problems and is not the simple fuel gauge that owners might want. Imagine you had a fuel gauge for your car which operated on the principal that you fill the tank then based on fuel taken out in driving and fuel put in at refill you have an idication of how much fuel you have. Now this system might seem reasonably accurate initially but if either input or output measuring is inaccurate or there is any evaporation then the only way to get accuracy is to regularly fill the tank to full and rset the cumulative gauge.
Now with our battery meter this works in the same way. You need to regularly reset to full when you know the batteries are charged. The problem with batteries is that the actual battery capacity may not be what is claimed by the manufacturer and then declines with age. But the meter does not know the actual capacity unless you tell it.
The whole meter is most useful for short term assessment of battery state eg after a nights discharge then a session of charge from engine you can assess if you have replaced what was used.
Voltage of the battery can be a useful additional measure of battery state. But een that is not simple.
So although this sudden low cumulative reading has come as a shock I don't think you should rush to buy a new charger or panic. You cna as said check actual discharge when everything is apparently turned off and this would be useful. Otherwise just understand that your battery meter is very fallable and keep an eye out for other electrical problem symptoms. good luck olewill
pvb
Well-known member
A lot of people seem to have little understanding of how battery monitors work, and there are many myths circulating. Most decent battery monitors, including the OP's, reset themselves automatically when the batteries are charged.
Paddingtonbear
New member
The charger is by no means big enough for a 400 amp hour rig. Perhaps you should check out 'Gibbo's' fantastic information on the Merlyn web site. Just hope that the batteries are ok .
pvb
Well-known member
The charger will work OK, just takes a little longer. On my old boat, I had a 30A charger feeding a 660Ah domestic bank - worked fine. Anyone reading Gibbo's thoughts should bear in mind that he's trying to sell a non-shunt battery monitor, so will be naturally critical of traditional battery monitors.
Paddingtonbear
New member
Agreed but I was thinking more about the background info. re the science of it all. He certainly knows his stuff but is also a mite grumpy if you don't understand and follow his thinking 
not a user of his good and services as I don't understand any of it but very clever people of my aquaintence seem to swear by him. Contractor to MOD so he must be doing something right.
not a user of his good and services as I don't understand any of it but very clever people of my aquaintence seem to swear by him. Contractor to MOD so he must be doing something right.oldvarnish
Active member
This is a good example of trying to diagnose a fault on the basis of insufficient evidence - and ending up with a guess.
Had I been in a similar situation I would have measured the battery voltages with no load, and then with a heavy load. I would have measured the current flow from the charger, and I would have measured the current draw from the batteries with everything in the same condition as when I found the fault.
Have I missed anything?
Had I been in a similar situation I would have measured the battery voltages with no load, and then with a heavy load. I would have measured the current flow from the charger, and I would have measured the current draw from the batteries with everything in the same condition as when I found the fault.
Have I missed anything?
bigwow
Well-known member
Then you would have been in for the silent treatment from my other half, having promised her a week on the boat without leaving her sitting there while I " messed about " As the monitor has not shown any input in double figures since I got here, we are now up to 48%, I will assume the charger has had enough after 15 yrs!
oldvarnish
Active member
Ah, now I understand!
I don't know if you've heard of Ockham's Razor? http://en.wikipedia.org/wiki/Occam's_razor
In broad outline it says that simplest solutions are the ones to go for. So yes, buy another charger.
bigwow
Well-known member
Now steady on, no-one got rich by wasting money!
After a week on the boat the meter shows 100% 400 amp h. Not only have I disconnected the 240 supply I've detached the battery charger wire to the house supply.
All will become clear next week-end, I hope