auto-switch off a device when full charge circuit

[Metzen]

hello, I post this question again, I still need help with such circuit and the other thread has been closed due to my explanations about the project I needed it for. So please let's not talk about my project here and focus on the circuit.

Basically I need a circuit that switches off a device when a 12v 45Ah Sealed Lead Acid battery reaches 13v and starts it over below 12v. The device is a normal DC 12 1.8Amps motor, but the current could be more due to some load. It should have an apropiate fuse or two against shortcurrents in order to keep the battery and the motor safe.

alec_t posted this circuit but I don't have a clue on how to build it, any help will be appreciated.

Thanks.

 

[georgetwo]

hello, I post this question again, I still need help with such circuit and the other thread has been closed due to my explanations about the project I needed it for. So please let's not talk about my project here and focus on the circuit.

Basically I need a circuit that switches off a device when a 12v 45Ah Sealed Lead Acid battery reaches 13v and starts it over below 12v. The device is a normal DC 12 1.8Amps motor, but the current could be more due to some load. It should have an apropiate fuse or two against shortcurrents in order to keep the battery and the motor safe.

alec_t posted this circuit but I don't have a clue on how to build it, any help will be appreciated.

Thanks.

Hi,
You have to do more research, that circuit may not be ideal for your design. Your charger power should be about 15 - 16v with about 3 to4 amps. Your control circuit should be a differential amplifier that will measure the current consumed by your battery, stop charging when little current is flowing from the charger to Battery. So google something about current to voltage converter and differential amplifier which will drive the fet that will control charging.

 

[MikeMl]

A 12V sealed lead acid battery under charge is nowhere near being charged when its terminal voltage reaches 13.0V.

 

[Dr_Doggy]

HI, I learned alot about "efficiency" from projects similar to yours, as someone who shares a common interest in this regard i will tell you same as them: save your money.

If you would like to learn about the whys, then its best to read up on things like efficiency(energy in vs energy out), power output, power over time, resistance, work, force, and power losses. even if you have 100% efficient device you will still loose all power when you add a load(ie spin tires on road or add a lightbulb to electrical), similar to a dynamo

if you want to turbo your car use nitrous , if you are saving money get a smaller cylinder engine.

if you really want to test this get a solar cell and some LED's, hook it up in a pitch black room(ie.. no additional input power from lights), bring a flashlight so you can kick start it , but results are always same. also adding a battery(or capacitor) is just a buffer and only delays the inevitable failure.

or if you want to test your motor/gen config, don't bother with inefficient circuits and junk, such as 12v batteries, if your device is even 99% efficient and low resistance in mechanisms the motor/gen will continue to spin several cycles while slowly slowing to a stop.

another test you can do is hook the motor to battery , and measure the Volts AND current used to power it(under load),, at the same time measure the volts AND current at the output of alternator:
Pout < Pin always
Power=Volts * Current
Pin - Pout = how fast it will slow down

Again, If you are truly interested in learning some of these things im sure we can help, but i think moderators ban overunity conversations due to the fact that most people that do this are just trying to save/make a buck and in the end are not interested in learning why it is not feasible or anything else, which in turn is a waste of our time trying to explain. since there is so much to know.

you will notice that you find alot of these people on youtube, but for some reason no one has marketable products. (I wish i could blame the govt for that, but alas,)

OVERALL, your switch is not needed , cos it will never be used, cos it will never turn off, cos a battery running a alternator to charge itself will never get anywhere without external energy being added(ie the flashlight),,, ie your design is literally wasting energy trying to save energy.

hopes helps!

 

[Metzen]

A 12V sealed lead acid battery under charge is nowhere near being charged when its terminal voltage reaches 13.0V.

The circuit posted is meant to stop at 13.5v, which is more like it, but as we get hot summers here maybe it should be less, even though inside the house the T is lower.

Hi,
You have to do more research, that circuit may not be ideal for your design.

I agree I have to do more research, but I lack the basics for understanding, that's why I'm looking for someone to help me with that. Why do you think that circuit wouldn't be good? Appart from me not understanding the calculations that there's behind it, looks like it may work.

Your charger power should be about 15 - 16v with about 3 to4 amps

I'm afraid I can't set that, the charger is a 12v 200watt or more generator, would you attach it a 12 to 24v step-up regulator? so the current gets below 10A? I've seen the maximum charging amps this kind of baterry stands is something like 13A, even thought the battery wouldn't last as much.

Your control circuit should be a differential amplifier that will measure the current consumed by your battery, stop charging when little current is flowing from the charger to Battery.

I think the LM339 is meant to do so. This circuit is a given formula, but it's what I'm looking for cause I should take a course for me to be able to figure it out, and it's not the moment.
Unfortunately I'm not able to contact alec_t so I need help on how to connect the circuit.

I'm starting to get fussy with this, oh Lord! give me patience! but NOW! haha

 

[Metzen]

OVERALL, your switch is not needed , cos it will never be used, cos it will never turn off, cos a battery running a alternator to charge itself will never get anywhere without external energy being added(ie the flashlight),,, ie your design is literally wasting energy trying to save energy.

Sadly you might just be right.

 

[alec_t]

I'm not able to contact alec_t

As I said on the other forum, it's pointless using the circuit I posted for your project (Dr_Doggy agrees). For that reason, and also because you clearly need to start at a basic level to understand circuits, I don't think you'd gain much from my explaining that circuit.

 

[Tony Stewart]

hello, I post this question again, I still need help with such circuit and the other thread has been closed due to my explanations about the project I needed it for. So please let's not talk about my project here and focus on the circuit.

Basically I need a circuit that switches off a device when a 12v 45Ah Sealed Lead Acid battery reaches 13v and starts it over below 12v. The device is a normal DC 12 1.8Amps motor, but the current could be more due to some load. It should have an apropiate fuse or two against shortcurrents in order to keep the battery and the motor safe.

alec_t posted this circuit but I don't have a clue on how to build it, any help will be appreciated.

Thanks.

Your requirements do not specify load, surge voltage, battery age, model and are inconsisent with a good design. The design previously given can meet your requirements with some filter delay to prevent false triggering or constant cycling with a badly sulphated cell (high ESR)

You require a reference voltage of 12.5V and 8% positive feedback for hysteresis of +\-0.5 V and any MOSFET power switched either low or high side with RdsOn much lower or <2% than load resistance for cool switching.

Note graph difference between charge and float is 0.9V for 12V SLA using Ah/5 rating. This will vary if your rate is different.