electrical dectives required!

duncan

duncan

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facts
battery gives 12.57v after standing for a week
with engine running on tickover 14.3v
battery under load (fridge from scratch), no alternator, goes down to 12.3v - no lower
sometimes the engine will start - sometimes no current. this includes times when buzzer will work but engine wont start and times there isn't even a buzzer.

I am of the view that either I have a faulty (intermittent) battery isolation switch or I have a connection problem in the main battery cables (earth or power)...............

any other thoughts?
starting engine causes electronics to switch off
use of drive trim causes electronics to swicth off
windlass worked, stopped and then later worked ok

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif
 
take your battery to a garage and get them to test it under load - it is possible that you have a plate that is going.

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Hi Duncan,

I suspect you're right about the bad connection. The scenario you describe certainly leads me that way, though as I assume you've removed, cleaned and re-made all the obvious ones, that doesn't seem likely.

Your battery readings appear quite normal, so unless you have a faulty battery cell that 'dies' under load, there must be another problem.The battery voltage drop under modest (fridge) load you note is also normal, and I expect you will have noticed the voltage returns to near normal after a while with no load.

Have you checked that your starter motor connecting bolts are tight (to provide a good negative return) unless like me you have a separate neg. back to the battery? The other possibility is that the positive connections (main and solenoid)to the starter motor are not clean and tight, or that there is a fracture/bad connection between the terminals and wires.

My best guess, especially considering the point you make about the electronics and windlass dying, is that the battery has a defective cell, allowing the appearance of normal voltage but that is unable to sustain this under the very heavy loads imposed by a starter motor or windlass.

Try using jump leads (or fitting another battery temporarily) and see if the problem is resolved.

Hope you manage to sort it out easily and cheaply!

Good sailing!

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Loath to look just at the engine side at there are other problems, the 2 common items being the battery and the battery switch. As he mentions no buzzer that is the low current side of the engine electrics -as is the solenoid activation for the starter motor.

I would vote for the isolation switch. Resistance Ok for the low consumers but shoots up under large draw and shuts them down, if the battery was faulty I would expect to see a much bigger drop with the fridge start up.
If its one of those black rotating "make before break" type pop the (red?) cap in the centre and tighten the screw underneath - if it is loose you will get the symptoms described... and/or just unscrew it from the bulkhead and have a look
for crud on the contacts

Otherwise as mentioned jump leads to isolate various parts of the circuit.

Happy hunting...


<hr width=100% size=1>Paul
<A target="_blank" HREF=http://www.polarity2.com>http://www.polarity2.com</A>
OSTAR 2005
 
Does the starter motor click sometimes and fails to turn?

I am no expert, but when I had a dodgy battery (read fine on voltmeter but crapped out under load) the starter would sometimes make a half hearted effort to turn, or the solenoid would click.

The lack of clicking would make me think faulty switches or a broken connection rather than tired battery.

Getting the batteries load tested will help you decide what avenue is best to explore.

Good luck

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Re: electrical detectives required!

You've probably an ineffective contact in circuit.

First: remove, clean thoroughly and replace with a light smearing of petroleum jelly both battery terminals.
Then check all the circuit and connections for loose nuts/bolts.
Then try again.

If this doesn't cure it you may have a faulty cell in the battery - have it out and drop-tested (that means you fast-discharge it using a special tool, not throw it on the ground). Any decent battery supplier should do that for you fir free.

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Hi Duncan,

Did you get a hydrometer, in the end? If so, what did it show?

The voltage readings all seem fine, and I would expect the electronics to go awol during cranking, as that can drop the voltage down to 10V or so.

It reads like sometimes everything (i.e. windlass, starter, buzzer etc) goes out from time to time. When this happens, does anything at all work? Nav lights? VHF?

I would start with a hydrometer to check for a dead cell (all cells should read in the green, and should be with 25mmHg of each other), and then try bridging the terminals on the battery isolator switch with one lead from a set of jump leads, to see what happens...

<hr width=100% size=1><A target="_blank" HREF=http://homepage.ntlworld.com/graham.wignall/boats/eulimene600x800.jpg>The old and the new</A>
 
Hydrometer.....25mmHg???......what ever do you mean?

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>
 
Yes, good point. Should have said 25mg/ml... Anyway, a good cell should read around 1300 mg/ml at 18 degC or so, and all the cells should be very close to one another.

<hr width=100% size=1><A target="_blank" HREF=http://homepage.ntlworld.com/graham.wignall/boats/eulimene600x800.jpg>The old and the new</A>
 
My money is on the isolater. If it is the red removable key type (rather than the "all/1/2/off" type)
They are always prone to breaking down.

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/colspics> Cols Picture Album</A>
 
thanks to everyone for their comments - I will post when the problem is isolated but it won't be untill a week Saturday when I am next down.

I can however cover a few points off
-Yes they are the red key types
-I did get as far as cleaning the battery terminals and adding vaseline etc because I was going to change the battery. I didn't change it when I had 12.57v across it but nothing to start the engine (or buzzer)
-I checked the terminal connecting to the back of the isolators but no others (as yet)
-I used to be able to start the engine without it kicking the chart plotter out
-I did get the hydrometer but forget to take it down to the boat last weekend; it will be used next time.

My check list runs in this order -
1. connect to one terminal on earth isolator, then live - bypassing each isolatoer in turn. Try starting with electronics on..............if either enables this function without cutting electronics then replace isolator (probably both with better quality units actually) - job done.
2. if that fails go hunting further up the wiring but still at 'big wire level!'.
3. if nothing there then use the direct radio power feed for the plotter and repeat - if engine starter turns but plotter kicks out then haul out battery and drop..............

here's hoping it's the isolator.../forums/images/icons/smile.gif

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif
 
Re: and the top detectives were....

those suggesting the battery isolator might be on it's way out.

the boat has both +ve and -ve isolators and the positive one proved shot. It seemed to be permitting some volts but not a lot of amps to pass through it.

when I returned to the boat I tried things as I had left them and got a nice beep from teh audible warning when I put on the ignition. However I got little else on turning the key and that was that. Battery tested out at 12.48v with 1250 (bang in teh middle) on the hydrometer thingy. Bypassing the +ve isolator got everything beeping, turning and fireing as it should and aftr changing both isolators a long day on the alternator seems to have the battery happy holding 12.8v off load after being allowed to stand a few hours ie seems ok.

thanks to mailspeed marine who delivered to the schedule they promised; although the little not inside the pack explained that I had further items to be sent later - the new super dooper isolator of course. Have had to stick a couple of cheap red key jobs back in temporarily...........is it just me or is mail order more of a liability than a convenience?

Anyhow - thanks to all for their contribution.

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif
 
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