12v7Ah Battery low indicator help?

[adriaand]

Hi

I want to put a battery indicator on my remote control boat.
How low should the voltage be when the led comes on?
Any schematics would help as well.

Thank you

 

[4pyros]

You need to look up the specs for your battery for the voltage. Thare are many kits out thare that monitor voltage. Andy

 

[MrAl]

Hello,

One reference i have found says 12.6v minus 0.2v for every 25 percent charge loss. Thus, this battery would be dead at 11.8v. It tends to vary a bit though from battery to battery and also over temperature.

 

[adriaand]

Like I said ists for a model boat.12v7ah sealed lead acid battery. I would like to have 2 leds,red and green. I'm scared of taking the boat out with a flat battery and then ill have to swim very far to get it. So if the red led is on I know not to take it out. There must be someone on here that has attempted or build something similar.

 

[ericgibbs]

Like I said ists for a model boat.12v7ah sealed lead acid battery. I would like to have 2 leds,red and green. I'm scared of taking the boat out with a flat battery and then ill have to swim very far to get it. So if the red led is on I know not to take it out. There must be someone on here that has attempted or build something similar.

hi,
Look at this pdf, the device is old but it works ok.

The absolute Vmin for a SLA battery should be 10.8V, but I would go for not less than 11V.

EDIT:
Look here.
https://wiki.xtronics.com/index.php/Sealed_Lead_Acid_Battery_Applications

 

[MikeMl]

Here is a thread about a simple, reliable Low Voltage monitor.

For a standard Seal Lead Acid, the never go below cutoff is 11.5V. Seems like you would like to know that you are down to the last 20% capacity. The Battery Maker's data sheet will show a set of voltage vs state of charge at different discharge currents curves. For example, **broken link removed** similar to yours.

 

[audioguru]

I fly my electric model airplanes and helicopter until the low voltage cutoff stops the main motor. They can't glide far. Then I must wade through the Canada Geese and dog poop in the park to retrieve them. The low voltage detect circuit pulses the motor before cutoff but I can't see nor hear the pulsing when they (the airplanes, not the geese) are flying far away.
My friends use a timer that is nearly useless because the duration of a battery charge depends on how hard the motor is running.

Maybe I should make a circuit that rocks the airplanes and helicopter when the motor begins to pulse?

 

[MrAl]

Hello again,

If i had to depend that much on a battery i would be sure to charge it before each time i used it (boat power or other fairly important use).

I would never depend that highly on a voltage measurement unless it read a very low voltage or a very high voltage, which would tell me either it was fully discharged or fully charged.
If you read some of the better papers on state of charge estimation you will find that it's very hard to be sure of the state of charge for a battery, even li-ion, except for fully charged or fully discharged.

 

[4pyros]

Like I said ists for a model boat.12v7ah sealed lead acid battery.

You left sealed lead acid battery off your orginal post. Volt meters are a dime a dozen. Look at the LM3914 many of the kits use this chip. Andy

 

[adriaand]

What I'm looking 4 is ... If the voltage drop to 10.4v then the red light should come on. The motor runs @ constant 3500rpm. Is a bait fishing boat. So the notor will be on or off.

 

[4pyros]

What I'm looking 4 is ... If the voltage drop to 10.4v then the red light should come on. The motor runs @ constant 3500rpm. Is a bait fishing boat. So the notor will be on or off.

Yup the LM3914 can do that. look up the data sheet. Andy

 

[MrAl]

Hello,

If it drops that low (10.4v) it's too late to do anything about it

 

[MikeMl]

Hello,

If it drops that low it's too late to do anything about it

That's why I told him to set the detector to go off when the battery reaches ~11.5V

 

[audioguru]

If it drops that low it's too late to do anything about it

Kiss the battery "goodbye" then deliver it to a battery disposal center.

I had a heart attack but they fixed it. Now I am almost like new. Not like a dead battery.

 

[Boncuk]

Hi,

how about using a small backup battery of e.g. 12V/1.2 to 2.4Ah?

The MAX8211 could be used to switch over to the backup battery and activate a flashlight from a fresh supply source instead of a depleting battery.

That way you make sure you won't need to swim to recover your boat.

To save energy and see the flashlight from any view angle you could make the flashlight consisting of four bright white or blue LEDs arranged at 90 degree angles fitted with reflectors and have only one LED illuminated at a time.

That method offers the additional advantage of running the main battery down to 10.8V before switching to backup.

My 3.5m Bismarck had such a safety feature and I never had to swim to recover it.

Your circuit could look like this.

Boncuk

 

[MrAl]

Kiss the battery "goodbye" then deliver it to a battery disposal center.

I had a heart attack but they fixed it. Now I am almost like new. Not like a dead battery.

Hi there,

Yes, i use older ones as a paper weight

Sorry to hear about the heart attack. I've been taking aspirin so hope that helps. I've read it helps post HA victims too.

 

[MrAl]

That's why I told him to set the detector to go off when the battery reaches ~11.5V

Hi Mike,

That sounds pretty good to me. I havent tested my batteries that low yet but perhaps in the future i will. I use my drill so infrequently and charge it right back up again so i never get very low on voltage, at least not yet.

 

[audioguru]

Sorry to hear about the heart attack. I've been taking aspirin so hope that helps. I've read it helps post HA victims too.

I am glad I had a heart attack at home because I was rushed to the nearby hospital very quickly for the repair of the blocked arteries that feed my heart.
If I was out walking my dog then I would be gone now. But I got fixed quickly so there was no damage.

I was on a blood thinning drug (Plavix) for 3 months so that blood clots don't form on the repairs. It caused nose bleeds and any little cut to bleed like crazy. Now I have two blood pressure reducing drugs and one slows the heart rate so that each beat is stonger, a baby asprin and a huge anti-cholestrol pill.

The hospital has a health-club for heart attack victims and it made me much stronger. I ride my bicycle and run with my dog and electric model airplanes. I am young again!

 

[MikeMl]

I am glad I had a heart attack at home because I was rushed to the nearby hospital...I am young again!

And all of that in spite of Socialized Medicine.

 

[audioguru]

And all of that in spite of Socialized Medicine.

I am a Canadian with government-paid medical care. I don't know why Americans must pay themselves or pay for insurance.
Our free (I paid for the telephone in my hospital room) medical care is excellent, the machines are state-of-the-art and I am perfectly fixed and alive to prove it. I am very happy with my free heart operation.

But I paid a couple of thousand dollars for my super-duper cataracts operations on my eyes. I had the choice of free poor quality lenses that take a long time to heal and see poorly at night or the expensive lenses that worked perfectly the next day and are fine at night that I selected. I am extremely happy with my new vision.