low voltage cut out

[Rogue_monkey]

does anyone know where to get a lot voltage cut out or how to make one. I have 12v led lights in my house and I want to protect the battery from being drained to low. Just looking for the easiest way to do this.

 

[James Jackson]

It's great to hear of someone else doing this.

I have installed a set of 12 Volt LED MR-16 bulbs in my living room, too! What I have done is to place a small solar panel outside, and charge a 12 volt battery in the day time. At night, I use the battery to power the LEDs.

It works great! - but like you, I wanted to disconnect the load (LEDs), when the battery got low. I couldn't find a LVD (low voltage disconnect) circuit, so I designed one, and had PC Boards made.

I use 10.80 volts as the point where the battery is dead, and I drop out the load. I do not reconnect the load until the battery gets up above 12.30 volts.

I have not had any issues with this - so far - and I have not discharged the battery lower than 12.10 or so.

If you're interested, let me know.

Regards,

James

 

[Rogue_monkey]

I finnally found what I was looking for in the clearance bin at my local hardware store. It was designed for cd players and other 12v portable devices. It states it will shut off the power to the load when the voltage drops below 11.2v and will turn back on when the power is charged back up above that range. the only part i don't like about it is that there is a led that lets you know if it is good or has cut the power. I'm sure it doesn't draw that many amps but it will still draw some power when the system is not being chagered. hopefully this will work and do what i want. the best part was it was cheaper then the clearence price so nothing really lost if it doesn't work out.

 

[James Jackson]

...It states it will shut off the power to the load when the voltage drops below 11.2v and will turn back on when the power is charged back up above that range. the only part i don't like about it is that there is a led that lets you know if it is good or has cut the power. I'm sure it doesn't draw that many amps ...

11.2 volts is probably a good place to drop out the battery, too. I think that's about 10% above 'dead'.

As for the LED - I too light up an LED to indicate that the battery has fallen to the 'drop out' level. I flash the LED. It only consumes about 6 mA - not Amps.

Yours probably only uses about 6 - 15mA - not something to get overly concerned about, IF you're using a large SLA - like I am (17Ah). If you're using something small, then it might be a concern.

Regards,

James Jackson
Oztronics

 

[hank]

I've seen these sold for auto batteries, and in general solar power supplier equipment lists. Don't have a link at the moment but I'll hunt around.

I'd also like to see a circuit diagram if anyone has one.

I've never bought one because they always seemed a bit pricey.

As I grow older and more forgetful, I increasingly favor this belt-and-suspenders approach.

I also want to flag the risk of overcharging a small sealed lead-acid battery even with a fairly small solar cell.

I have the kind of cheap solar panel sold as a trickle charger for car batteries, and last week hooked it directly to a small SLA battery while camping, to power a LED light for the tent.

After a few hours, I got worried, picked the battery up and put it to my ear. Snap-crackle-pop-bubbling noise. I'd overcharged it and it was venting some gas. I seem to have caught it in time.

The solar panel "should have been safe" -- according to its rated maximum output it should have been putting out no more than 14-something volts at 1.25A, lower than the rated charging allowed for the little battery.

But --- my bad -- I didn't actually meter the panel before directly connecting the battery.

The smallest "charge controller" I've found --- they're necessary for any of the larger solar panels to protect even a big auto battery --- is about $35 or so, and a good investment.

But I think I need both the low-voltage cutout _and_ a charge controller for each of my smaller setups too.

 

[James Jackson]

The smallest "charge controller" I've found --- they're necessary for any of the larger solar panels to protect even a big auto battery --- is about $35 or so, and a good investment.

But I think I need both the low-voltage cutout _and_ a charge controller for each of my smaller setups too.

Yes. A good idea to use a charge controller to limit the voltage to the battery.

I use a Morningstar SunGuard SG-4 controller. Not cheap, but it uses a PWM signal to charge the battery. In the long run, the $30 - $40 spent on the charge controller will be worth it - if it saves the battery.

The LVD circuit - I engineered it, and am not willing to share that, but I am thinking of sharing the P.C. boards - as bareboards, or boards & parts, or assembled & tested - for a price.

Like I have said - it's been working like a champ for over 4 months now, and no issues.

I also have an LED voltmeter attached to the battery, to monitor its' voltage. That helps a lot, too.

Regards,

James Jackson

 

[hank]

Here's a warning for low-voltage (but you still have to be there ...)

http://www.solorb.com/elect/solarcirc/lvbeep/index.html

Lots more stuff too

 

[James Jackson]

Hank,

That's an interesting circuit. It's a bit dated (using the CA3140 opamp), and he doesn't disconnect the load.

What I did with my circuit is not only drop out the load at 10.80v, but not allow it to reconnect until the battery is charged back up to 12.30v.

I also added an IR switch - so I can turn it on and off from across the room with the TV (or stereo or DVD) remote.

I also have quick-connect .250" tabs, so you can use the readily available crimp connectors, and attach wires to the board.

Oh. There is also a 5V regulator that I bring out to the board edge - so you can power external 5-volt circuitry - if you want.


All sorts of features were added to this board - even LEDs to give visual indications of the features (fully charged, 'dead' & 'IR received').

Regards,

James Jackson

 

[hank]

Neat! Any chance you're going to supply kits made up?

Heck, could you modify _his_ kit, with some replacement parts, perhaps an addon board or something, if not create a kit from scratch? He might even work with you, I gather he's well respected in the ham radio universe; he doesn't do much with LED lights though.

I can solder, got a temp-controlled iron -- and am starting to realize I ought to have a lot more little battery-solar panel-controller gadgets sitting around soaking up all this free sunshine before the next earthquake happens.

Thinking ahead to rainy-season projects.

 

[Weylan]

James, how much is one of these that you designed?

Is the turn on voltage adjustable? Say I can set the turn on voltage to be 14.4V?

I actually have a solution use for this. A circuit like this could be used as a voltage load divider or dump. This could run a device if I have excess voltage, like an atic fan durring the day. But shuts off when the sun goes down. Then I can use the lights I want and the batter will not be dead from the fan. If I have a few cloudy days, the fan may still come on, but only to a point where I don't have to worry about the battery still. and I may still have some power to use lights.

Hank,

That's an interesting circuit. It's a bit dated (using the CA3140 opamp), and he doesn't disconnect the load.

What I did with my circuit is not only drop out the load at 10.80v, but not allow it to reconnect until the battery is charged back up to 12.30v.

I also added an IR switch - so I can turn it on and off from across the room with the TV (or stereo or DVD) remote.

I also have quick-connect .250" tabs, so you can use the readily available crimp connectors, and attach wires to the board.

Oh. There is also a 5V regulator that I bring out to the board edge - so you can power external 5-volt circuitry - if you want.


All sorts of features were added to this board - even LEDs to give visual indications of the features (fully charged, 'dead' & 'IR received').

Regards,

James Jackson

 

[James Jackson]

James, how much is one of these that you designed?

Is the turn on voltage adjustable? Say I can set the turn on voltage to be 14.4V?

I actually have a solution use for this. A circuit like this could be used as a voltage load divider or dump. This could run a device if I have excess voltage, like an atic fan durring the day. But shuts off when the sun goes down. Then I can use the lights I want and the batter will not be dead from the fan. If I have a few cloudy days, the fan may still come on, but only to a point where I don't have to worry about the battery still. and I may still have some power to use lights.

Hmmm... well, the circuit I designed is using 1% fixed resistors. I did this for precision - and repeatability.

I might be able to recalculate the resistors needed for different voltages, and get them to work with the same circuit.

What I was hoping to do - was offer this board in three versions.

1) Bare board. The end user just gets a bare PC Board (good quality double-sided FR-4 - made at a fabrication house - not my backyard), and a set of documentation (I.E. Bill of Materials, etc) so that they can order the parts, and can then solder the parts onto the board. (It's a through hole design - not SMT.)

2) Bare Board - with parts 'in a baggie'. The end user gets the bare board, and all the necessary parts to populate the board with - and instructions.

3) Populated board - tested and ready to go. Along with an instruction manual, etc. Plug-n-go

Pricing of this board...

1) $24.95
2) $49.95
3) $74.95

(I hope I don't violate any forum rules by posting this... if so, I apologize)

The original intent/purpose of this board was to be used with a PWM Battery charger feeding a battery - and this just sits between the battery and the load (in my case LEDs).

When the individual wants the load to turn on - they 'hit' it with an IR controller. The battery would then start discharging. When/if the battery got as low as 10.80 ('dead' by the battery documentation I have read), then it disconnects the load, until the battery is recharged and gets to above 12.30 volts.

Now. If you have a different 'range' of voltages that you need to address... if I understand correctly, 14.40 volts is one of them... then I might be able to calculate different values of resistors, and plug them in. They would not be adjustable, though.

I hope this helps.

Regards,

James Jackson
Oztronics

 

[Wok]

This is what I use in my truck, set drop of for 11V5.
http://secure.oatleyelectronics.com...d=270&osCsid=c8814951aa745e9525c9576282c7c896

eng hoe

 

[Torque1st]

Standard relays can be set up to drop out at a fixed voltage with simple diodes and resistors etc. All relays have a specified pickup and dropout voltage. Pick one with 2X the current carrying capacity you need and adjust the voltage to the relay coil with a pot or diodes. Very cheap and easy to do.