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Old 23 April 2013, 10:30   #1
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Battery or Regulator?

When at fairly high revs my Navman warns of 'over voltage'. We are running a 2 stroke Yamaha 85hp with a Bosch S3 maintenance free battery rated at 53Ah. I have read that the battery may be the problem rather than the regulator rectifier. Any ideas?
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Old 23 April 2013, 13:11   #2
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Unlikely. More likely it's the battery switch or regulator.

I've got exactly the same motor and I had the same prob, turned out it was a dud battery switch.
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Old 23 April 2013, 14:16   #3
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Everywhere I look it says not to use maintenance free batteries. I assume by the battery switch you mean a cut off switch?
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Old 23 April 2013, 16:25   #4
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Everywhere I look it says not to use maintenance free batteries. I assume by the battery switch you mean a cut off switch?
Yes.

If it has a poor connection your voltage across your electronics will jump up and down.


If your battery is FUBAR then you'll get a low voltage or problems starting. They won't give more than about 13.2v even when fully charged,
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Old 24 April 2013, 12:04   #5
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If your battery is FUBAR then you'll get a low voltage or problems starting. They won't give more than about 13.2v even when fully charged,
While running? My F115, at higher revs shows 14.2 to 14.4 across the battery.

Since the battery switch is only dealing with the +12V, I don't see how this could affect the supply voltage to the GPS in a way that would increase it.

The output from the motor at speed and with no load (which is not a good thing to do, by the way) is likely to be in the 16 to 18V range or higher (talking potential here, as running with no load may damage things.) With a battery as a load, that usually smooths things out to anywhere from 13.5 to 14.6 or so volts. That range should not cause an overvoltage condition on your GPS.

Two things you should do: Put a voltmeter on the alternator output at the motor and see what that reads, and compare it to the voltage across the battery at a similar rpm, which will give you your cabling loss (which I would expect to be not more than a couple/few tenths of a volt, up to maybe a volt or so.) Do the same with the GPS power input. Any large discrepancy means your cabling is dropping voltage somewhere. Might want to check teh grounds by putting one lead of the voltmeter on the neg at the engine and measuring voltage at the battery (-) and the GPS (-) to see if a ground connection is resistive.

If all the (+) voltages are roughly similar (first step above), then you've got a component causing the problem, and need to start isolating that. Swapping in a different battery temporarily is probably a good place to start.


Luck;

jky
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Old 24 April 2013, 13:33   #6
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While running? My F115, at higher revs shows 14.2 to 14.4 across the battery.

Since the battery switch is only dealing with the +12V, I don't see how this could affect the supply voltage to the GPS in a way that would increase it.



jky
If the switch is intermittent, you'll get voltage spikes as the battery connection drops in/out.
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Old 24 April 2013, 13:36   #7
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While running? My F115, at higher revs shows 14.2 to 14.4 across the battery.

Since the battery switch is only dealing with the +12V, I don't see how this could affect the supply voltage to the GPS in a way that would increase it.

The output from the motor at speed and with no load (which is not a good thing to do, by the way) is likely to be in the 16 to 18V range or higher
turning the battery switch off or a dodgy switch may have the same effect?
if the battery switch had a resistance then there will be a higher voltage across all the circuits than the battery terminals.
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Old 24 April 2013, 18:34   #8
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The Yamaha manual states battery should be 70-100ah and 252-360kc.
Ours is 41ah and 360cca. What difference does that make?
(Kc and cca are not typos!)
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Old 24 April 2013, 18:43   #9
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The Yamaha manual states battery should be 70-100ah and 252-360kc.
Ours is 41ah and 360cca. What difference does that make?
(Kc and cca are not typos!)
What is a "Kc"? Never heard that term before.

Alot of manufactures spec some pretty big batteries. 100Ah would be larger than the battery in my 381hp pickup truck. My attitude is as long as you have enough cranking power to turn over and reliably start in cold weather any extra is just wasted weight, unless you need it for a bilge pump while not running etc.
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Old 24 April 2013, 19:18   #10
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What is a "Kc"? Never heard that term before.
Thats because he missed the f out in the middle
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