ChasB
Well-Known Member
Is there a relatively quick way without going down into the depths of the boat without a hydrometer?
Quick way to test batteries?
- Thread starter ChasB
- Start date
savageseadog
Well-Known Member
Monitor the voltage while cranking the engine. You need to be connected onto the battery terminats via the other wiring. Off the top of my head anything less than 10V might indicate a poor battery but it's more a matter of comparing results
VicS
Well-Known Member
[ QUOTE ]
Monitor the voltage while cranking the engine
[/ QUOTE ] but NOT via the other wiring! Get the meter probes right on to the battery posts themselves or a poor connection beteen the clamp and the post will give you a low reading while cranking even if the battery is good.
Checking the no load volts is a useful test. Charge the battery fully and let it sit for 12 hours with no further charging or load then check the volts with a digital voltmeter. A good battery will give a reading of at least 12.7 volts. If you can monitor it for several days or even a few weeks without any charging or load you will get some idea of how well it holds its charge. It should take several weeks to drop to around 12.5, although it will fall quickly to begin with and slowly level out. This test will not tell you if it has developed a high internal resistance but the cranking test will do that.
The hydrometer is useful for spotting one (or more) cells that are below par. Once that happens the end is not far away.
Monitor the voltage while cranking the engine
[/ QUOTE ] but NOT via the other wiring! Get the meter probes right on to the battery posts themselves or a poor connection beteen the clamp and the post will give you a low reading while cranking even if the battery is good.
Checking the no load volts is a useful test. Charge the battery fully and let it sit for 12 hours with no further charging or load then check the volts with a digital voltmeter. A good battery will give a reading of at least 12.7 volts. If you can monitor it for several days or even a few weeks without any charging or load you will get some idea of how well it holds its charge. It should take several weeks to drop to around 12.5, although it will fall quickly to begin with and slowly level out. This test will not tell you if it has developed a high internal resistance but the cranking test will do that.
The hydrometer is useful for spotting one (or more) cells that are below par. Once that happens the end is not far away.
ChasB
Well-Known Member
[ QUOTE ]
Monitor the voltage while cranking the engine. [ QUOTE ]
For how long? There will be a voltage drop won't there, the rate of which will show the state of the battery?
Currently the voltage shows about 14 on the boat's meters and then drops on starting. How fast a drop is bad?
Monitor the voltage while cranking the engine. [ QUOTE ]
For how long? There will be a voltage drop won't there, the rate of which will show the state of the battery?
Currently the voltage shows about 14 on the boat's meters and then drops on starting. How fast a drop is bad?
A
Anonymous
Guest
This is a VERY FAQ and there have been some excellent recent threads here where all the issues have been covered. You could try doing a forum search.
Shame there isn't somewhere that FAQ type threads can be archived or a link put in.
Shame there isn't somewhere that FAQ type threads can be archived or a link put in.
VicS
Well-Known Member
[ QUOTE ]
Monitor the voltage while cranking the engine
[/ QUOTE ] It'll fall almost straightaway to 10v, off the top of savageseadogs head, or 9V off the top of mine. But should then stay reasonably steady for the time it takes to start the engine.
Monitor the voltage while cranking the engine
[/ QUOTE ] It'll fall almost straightaway to 10v, off the top of savageseadogs head, or 9V off the top of mine. But should then stay reasonably steady for the time it takes to start the engine.
ChasB
Well-Known Member
Thanks.
Judging from some of the answers I've got here now and in the past, there's something very wrong with my system, and I can't track down what it is. I've changed one alternator, a starter, and recently put a new battery in. Everything was working fine (if a big sluggish to get going) until yesterday when one engine failed to start. Again. And it's always been the port one.
I'm going to change the wiring, and swap out the other battery. But why do I think that won't fix?
Maybe my problem's these huge engines which take a lot of oomph to get going. Maybe when it was brand spanking new (1982) they started straight away, but now the batteries have to be at their peak, and anything short of that won't get them going.
Any ideas? /forums/images/graemlins/confused.gif
Off to marina now to run some tests before it gets too late for the neighbours.
Judging from some of the answers I've got here now and in the past, there's something very wrong with my system, and I can't track down what it is. I've changed one alternator, a starter, and recently put a new battery in. Everything was working fine (if a big sluggish to get going) until yesterday when one engine failed to start. Again. And it's always been the port one.
I'm going to change the wiring, and swap out the other battery. But why do I think that won't fix?
Maybe my problem's these huge engines which take a lot of oomph to get going. Maybe when it was brand spanking new (1982) they started straight away, but now the batteries have to be at their peak, and anything short of that won't get them going.
Any ideas? /forums/images/graemlins/confused.gif
Off to marina now to run some tests before it gets too late for the neighbours.
A
Anonymous
Guest
Checking the electrical installation is down to a meter, and just time messing about around the batteries and engine. It really isn't rocket science, just Ohms law stuff. If you want to DIY you will need some knowledge and there are plenty of books available. Anything by Nigel Calder is good, he has an excellent reputation.
ChasB
Well-Known Member
I've got the last two editions of the book, and I've worked as a theatre and then film electrician for some years, so I am familiar with electricity. But this boat is spaghetti junction! And a lot of it horribly inaccessible. I have had 'professionals' look at this and thrown their hands up in horror.
(I'll have to delete this thread if i ever want to sell this boat! /forums/images/graemlins/grin.gif)
(I'll have to delete this thread if i ever want to sell this boat! /forums/images/graemlins/grin.gif)
A
Anonymous
Guest
OK, what you might not have had is experience of very high currents at very low dc voltages, fed from a far-from-stiff supply /forums/images/graemlins/smile.gif It is problematic and you have to concentrate on ultra-low resistance connections.
