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Old 16 June 2019, 11:50   #1
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What figure to set low voltage alarm at?

Hi,
My plotter has a feature thar allows me to set a battery low voltage alarm.
This figure can be set as required.
What voltage should I set it at to ensure I can still start the engine?
Thank you.
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Old 16 June 2019, 12:10   #2
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Trouble is if you set it at the value you can start the engine at, it will then alarm when you routinely start the engine as starting will suck the power away from the plotter...


My thoughts are why would the plotter be on if the engine is not? If the engine is on, surely the ALT is charging the battery?
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Old 16 June 2019, 12:17   #3
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It’s a plotter/ fishfinder so I do leave it on.
I also leave my vhf and radio on as well when I’m fishing
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Old 16 June 2019, 12:36   #4
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Itís a plotter/ fishfinder so I do leave it on.
I also leave my vhf and radio on as well when Iím fishing
Ideally you run a house battery for all your ancillary systems and a separate start battery for the engine, set-up on a split charge system, in theory youíll never run the risk of flattening the engine battery
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Old 16 June 2019, 12:53   #5
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I had a duel cycle on my rib with out issues
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Old 16 June 2019, 14:34   #6
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Ideally you run a house battery for all your ancillary systems and a separate start battery for the engine, set-up on a split charge system, in theory youíll never run the risk of flattening the engine battery
Iím going to that over the winter when sheís back from the marina end of September.
Just looking for a figure to put into the plotter as a quick fix for this season
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Old 16 June 2019, 14:56   #7
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If you're running with one battery you'll probably have to set the low voltage alarm at 9V to stop it tripping when you crank the starter. Makes it kind of pointless.
If you set it at 13V to give you verification of your charge it'll trip off as soon as you shut the engine down. Monitoring the voltage of an "off charge" battery while you're fishing isn't a totally reliable way of guaranteeing there's enough energy stored there to start the engine (it's not a measure of latent capacity and doesn't take internal impedance into account) but if you want a number when the engine's off, I'd be looking for something between 12.1 and 12.3 volts and just live with the alarm as you start it.
I use a system where everything runs from one battery and the second "backup" is just that, with nothing connected to it. It gets "split-charged" while the engine is running and can be deployed with a switch if it's ever needed. Both batteries are monitored with analogue gauges whenever the ignition is switched on so the plotter's alarm is just set at 9V to keep it quiet.
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Old 16 June 2019, 15:18   #8
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I think mine is set at 12.3 - it can trigger during starting etc - but as soon as started automatically goes away. As Tango says itís not a guarantee you will be able to start again (I have pull start so not too worried).
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Old 16 June 2019, 15:19   #9
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My thoughts are why would the plotter be on if the engine is not? If the engine is on, surely the ALT is charging the battery?

So you never sit at anchor with the VHF on? After 15ish minutes of no position my vhf starts screaming alerts at me. Easier to leave plotter on...
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Old 17 June 2019, 04:35   #10
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Ideally you run a house battery for all your ancillary systems and a separate start battery for the engine, set-up on a split charge system, in theory you’ll never run the risk of flattening the engine battery
+1

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I had a duel cycle on my rib with out issues
Until the day you turn the start key and nothing happens...........

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So you never sit at anchor with the VHF on? After 15ish minutes of no position my vhf starts screaming alerts at me. Easier to leave plotter on...
Mine does that! 'Where's my lat and long?!' lol


Another option, take one of those new lithium starter packs out with you ( fully charged of course ), small/light enough to put in your day bag and can start a flat car - so a smallish outboard should be doable - plus you can charge you phone etc - just a thought! https://www.halfords.com/workshop-to...UaAj3cEALw_wcB
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Old 17 June 2019, 05:18   #11
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+1



Until the day you turn the start key and nothing happens...........



Mine does that! 'Where's my lat and long?!' lol


Another option, take one of those new lithium starter packs out with you ( fully charged of course ), small/light enough to put in your day bag and can start a flat car - so a smallish outboard should be doable - plus you can charge you phone etc - just a thought! https://www.halfords.com/workshop-to...UaAj3cEALw_wcB
Thanks. Iíve got one of them onboard now.
Itís a biggish outboard- 150 hp mercury 4 stroke- but it did start my old Alfa spider v6, so it should manage the 4 cyl Merc!
I was just reading the garmin manual the other night when I had nothing to do and found the section on low voltage alarms, hence the original question.
I have put a multimeter across the battery when there is no draw and engine is off and it sits at 13 volts, so I think Iíll just set alarm at 12.1 and see if it starts ok at that.
Will let everybody know the outcome!!
Thanks.
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Old 18 June 2019, 05:07   #12
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Quote:
Originally Posted by Fender View Post
+1



Until the day you turn the start key and nothing happens...........



Mine does that! 'Where's my lat and long?!' lol


Another option, take one of those new lithium starter packs out with you ( fully charged of course ), small/light enough to put in your day bag and can start a flat car - so a smallish outboard should be doable - plus you can charge you phone etc - just a thought! https://www.halfords.com/workshop-to...UaAj3cEALw_wcB
If it bothers you that the battery won't be up to it a regular check with an hydrometer will give its condition bear in mind a battery can fail totally at any time and do that said duel batteries are a must for those that feel a need for piece of mind
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