What voltage level should set off a low battery alarm?

[capslock118]

I have a hummingbird 170 depth / fish finder.

It likes to warn me about low battery by sending my a constant beeping noise.

I looked through my settings and noticed that it is set to warn me about a low battery if it get's below 12v; which makes sense of why it doesn't go off when underway since at that point it is on a 14v charge from the engine.

Now I am thinking that must be too high, surely a 12v battery will drop below 12v fairly easily once the battery is being used when the engine is off; and even still for high demand applications like trim/tilt.

So right now I set it to 11v, because I think that 10v would make it difficult for the engine to start. What do you think? what should be the minimum voltage level for the alarm to go off?

 

[Woodnaut]

Re: What voltage level should set off a low battery alarm?

The default setting for the low voltage alarm on my Garmin 546s is 11.3 V

 

[JoLin]

Re: What voltage level should set off a low battery alarm?

A 12-volt wet cell battery puts out 12.6 volts when fully charged, give or take maybe .1 volt depending on temperature. That's a constant of the lead-acid reaction. 2.1 volts per cell is what it produces. You'll see a slightly higher reading on a battery that just completed recharging, but in a little while it will stabilize at 12.6 volts.

A reading of 12.0 volts represents a 'state of charge' of about 50%. 11.3 volts = about 20% (personally I'd set that alarm at 12.0).

At 11.0 volts it's essentially dead- it may have just enough juice left to trigger the alarm.

My .02

 

[JimS123]

Re: What voltage level should set off a low battery alarm?

11.6 volts won't turn over a Mercruiser I/O starter.

 

[my1stboat1]

Re: What voltage level should set off a low battery alarm?

my boats charging system only maintains the battery at 12.2 volts at idle or wot ... never goes over that.... My low volt alarm is set to 11.5 volts... Been this way for 2 years...

 

[capslock118]

Re: What voltage level should set off a low battery alarm?

well, interesting segway.

my battery is a west marine AGM. It has been under a constant trickle charge all off-season (since late october 2010).

I thought it was odd that the depth finder is telling me a low reading; last season it would set off the alarm anytime I used the trim/tilt for awhile.

Even more interesting, the year before that I had my battery at the time (same model) sitting without a trickle charge off season, and the start of next season the battery was flat out dead. West marine replaced it at no cost to me since it was under warranty - but I am very skeptical of the quality of this battery.

So, either the trickle charger (also west marine) kept the battery charged under full charge or it's just a bad model that should be avoided...OR it's just something else?

one more interesting thing is that it wasn't charging at 14v until WOT; that might be by design of the engine though...

it's a 1 year old battery...

 

[sw33ttooth]

Re: What voltage level should set off a low battery alarm?

i have 2 batterys i will start on 1 and if i go cruising hit it to both then when i beach and radio i switch back to 1. that way if number 1 battery ever fails me i got number 2. also switch them out some times start on number 2. btw battery prices are up this year i think a 550 cca[cold cranking amps] was at $91.00 not sure if there due to go down soon or not but i cant offord to replace both them suckers at that price plus mine are the 650's i think.

 

[5150abf]

Re: What voltage level should set off a low battery alarm?

You don't say what engine you have but if it is an outboard they don't get to ful output until they are almost to wide open so that is right.

They call it a 12 volt but it shoudl be at quite a bit more than that, I have an onboard charger and when I first hit the water mine is at 12.8 and drops to 12.3-4 by the end of the night and I doubt you owuld get an engine started on 11.5 that is pretty dead 10 is dead.

 

[JoLin]

Re: What voltage level should set off a low battery alarm?

my boats charging system only maintains the battery at 12.2 volts at idle or wot ... never goes over that.... My low volt alarm is set to 11.5 volts... Been this way for 2 years...

Do you get that reading with a digital voltmeter at the battery terminals, or from an analog voltmeter mounted on the dash? You have wire runs/resistance to consider, accuracy of analog vs digital gauges, temperature of the battery's electrolyte at the time you took your reading, etc., etc. It's an exact science in the lab at STP (Stoichiometric Temperature & Pressure), but real-world readings will differ due to those factors.

Last time I took a reading directly from the batteries using my Harbor Freight DVM was in April. They were charged, then sat for some hours. I think the outside temp was in the 50's but not positive. I saw 12.4+ volts from one and a few tenths lower from the other. When I'm underway, the DVM in my fishfinder reads 13.9, my analog voltmeters on the dash show about 14.2.

All those readings are 'close enough' and indicate to me that the batteries and charging system are both okay. I wouldn't obsess over a couple of tenths.

My .02

 

[Home Cookin']

Re: What voltage level should set off a low battery alarm?

my low battery alarm on my Garmin was going off too frequently while drifting with a vhf and the gps on; if I turned on the pump it would go off. But the battery cranked just fine.

sometimes it would come on when I started the motor, which makes sense.

I think they may be too sensitive, or inaccurate, to give a true read, and I found it to be unneccessarily annoying. Since I have two batteries I shut it off.

 

[capslock118]

Re: What voltage level should set off a low battery alarm?

You don't say what engine you have but if it is an outboard they don't get to ful output until they are almost to wide open so that is right.

They call it a 12 volt but it shoudl be at quite a bit more than that, I have an onboard charger and when I first hit the water mine is at 12.8 and drops to 12.3-4 by the end of the night and I doubt you owuld get an engine started on 11.5 that is pretty dead 10 is dead.

Right, and that's in my sig - it's a '91 135hp v-6 mercury outboard 2-stroke.

Well i'll consider replacing my analog dash reading with a digital. I'll bring my analog reader out next time to check with yet another device; it would be a shame to have half a battery over the course of just one year.

Maybe it needs to be charged by something more than WMs battery maintainer

 

[AndrewsArk]

Re: What voltage level should set off a low battery alarm?

My Analog gauge on the dash always reads 12v. I've never had a problem though. I kind of wondered about it though, most times charging is about 13-14v for lead acid batteries or so I thought.

 

[dingbat]

Re: What voltage level should set off a low battery alarm?

my low battery alarm on my Garmin was going off too frequently while drifting with a vhf and the gps on; if I turned on the pump it would go off. But the battery cranked just fine.

sometimes it would come on when I started the motor, which makes sense.

I think they may be too sensitive, or inaccurate, to give a true read, and I found it to be unneccessarily annoying. Since I have two batteries I shut it off.

FYI
I set my alarm at 12.0 and the alarm goes off just about every time I shut the motor off. Brand new batteries. Checked the voltage at the back of the unit. Getting 12.5 volts, unit says 11.8.

Called Garmin. They told me that they have never heard of such a thing. Voltmeter on dash shows the correct voltage. Fish finder shows the correct voltage. The next test is to make a rig to check the voltage at the back of the unit with it powered up. Can't see how I would be getting a 0.7 volt drop in a 36" lg. 14 gauge cable, OEM power cable but I need to confirm before I call Garmin again.

 

[dingbat]

Re: What voltage level should set off a low battery alarm?

one more interesting thing is that it wasn't charging at 14v until WOT; that might be by design of the engine though...

That a motor issue. I had a 175 Black Max. Only charges above 2500 RPM. Will not put out full juice until WOT as you found.

 

[capslock118]

Re: What voltage level should set off a low battery alarm?

That a motor issue. I had a 175 Black Max. Only charges above 2500 RPM. Will not put out full juice until WOT as you found.

So what issue would that be then?

I replaced the rectifier and regulator last year.

 

[dingbat]

Re: What voltage level should set off a low battery alarm?

So what issue would that be then?

I replaced the rectifier and regulator last year.

Nothing wrong or anything you can do about it. Most outboards that depend on the stator to generate power have this issue.

 

[capslock118]

Re: What voltage level should set off a low battery alarm?

oh - so it's not an issue then i.e. something that needs to be looked into and replace parts, but just the way the engines design inherently works.

well that's good news

 

[snowman48047]

Re: What voltage level should set off a low battery alarm?

I had the same problem when I installed my H'bird 787. The factory setting was 12v. The problem is they are very sensitive. What is happening is it is picking up the voltage spike from the battery when another system is turned on or off. If the voltage goes to 11.9 or 12.1 its going to signal an issue and trigger the alarm. Mine would go off using the livewell, or the bilge pump, turning on the navigation lights at night...you get the idea. If your battery is good and your chargng system is working, don't rely on a fishfinder to give you battery warnings. I turned the battery warning alarms off. I have had the livewell on and bilge run on and off all day just drifting and it was never enough to kill a good battery. BUT, I have back ups. My Starcraft has 2 batteries and my 50hp merc on the Lund can also be pull started.

 

[capslock118]

Re: What voltage level should set off a low battery alarm?

I have the west marine 2 amp portable battery maintainer.

Now I'm not sure what's going on here, but I had it set to 1amp over the winter and left it on to maintain the battery - per instructions.

My battery is weak right now though, my analog ohmmeter states 11v, the dash says about that, and my depth finder sets off the low battery alarm when i turn it on to say it's below 11.5v.

So I have three items telling me the battery is low.

The battery is a west marine 105 ah, 500 CCA, AGM deep cycle battery.

So I brought it home and i'm using the same charger but set at 2amps but the thing is saying the battery is fully charged (green light).

Is the maintainer bad? Is it not sufficient to charge the battery? (max charge on my battery states 5 amps) - should I wait this out further?

how long should it take the charge the battery (currently stating 11v)?

I am just not having good feelings with the battery, even though the engine starts with no problem (although I have noted the starter is sounding sluggish).

 

[Lakemeadan]

Re: What voltage level should set off a low battery alarm?

I bought the Sears AGM Deep Cycle marine battery over 2 years ago and it has got down to 11v a couple of times. Put ears on the boat and it cranked started me up well. I also carry a portable hand agm jump battery when I go. I set my fish finder at 11.5 and have let it go down numerous times starting it up now and then when alarm go off fishing through the night. Have never once had to use the backup.