Control circuit

Draining them that low you will likely damage the batteries.

Chris

 

To see some examples of LED indicators for battery voltage, Google battery voltage indicator LEDs lead acid

I assume your "24V" battery is actually 27.6V. If it's a lead-acid chemistry, you should not allow its terminal voltage to drop below about 21V.

Batteries are also sensitive to temperature, and the undervoltage cutoff and charge target voltage should be adjusted according to temperature. Find your battery manufacturer's web site and look for application notes.

I have to ask, though... If you can charge the battery anytime, you must have mains present, so why use a battery at all?

 

I get what you're doing. My question is, why?

 

OK. Not enough information but it's a start.

If you use the method you described, you are cycling the battery. If the power fails when the battery is near its low voltage cutoff point, the charger won't be able to charge it, and either (a) the load will over-discharge the battery, or (b) you will have to disconnect the load when the low voltage cutoff voltage is reached. In either case, the load will lose power.

There is another problem with charging a battery while you're drawing current out of it. The charger has to supply both the current into the battery, AND the current you're drawing out of it. The charger can't tell how much current is going into the battery, and how much current is going into your load. So it may over-charge, or under-charge, the battery.

The way your needs are normally met is called "float charging". The battery is kept at a fixed voltage (once its initial charge has finished), and the load is powered from a separate mains-powered power supply. When the mains fails, the battery takes over, and runs until its low voltage limit is reached. At that time, you run out of power, but that method gives you the maximum backup time, rather than a random backup time that depends on the state of charge of the battery at the time that the mains fails.

Lead-acid batteries tend to last longer if they aren't being cycled continuously, as well.

Tell me more about your application. What type of batteries? In other words, what chemistry? Lead-acid or something else? What's their capacity? Do you have a data sheet for them? What are you powering? Is the load continuous or intermittent?

 

Curious; what will you be powering that requires 24VDC?

Chris

 

Maybe it's hard to say your post is too short there are no periods it's hard to read you ran five sentences into one it's messy you need to give much more information.

Edit: the post that this post was a parody of appears to have been deleted.

 

Mobile phones have their own charge control circuit that stops charging when it decides that the battery is full. A mobile phone "charger" is just a power supply that the phone can use to charge its battery if it wants to.

Or are you talking about charging a separate battery, not the mobile phone's internal battery?

Have you worked out how to generate a pulse from a USB-interfaced circuit? Do you have the USB endpoint designed and programmed?

How do you intend to control the charger? A relay in series with the mains power input to it?

What advantage is this system meant to provide, compared to connecting the phone to the charger and letting it charge up immediately?

 

What does "850 rating" mean?

Please re-read my post #8 in this thread.

There are several problems with what you want to do.
There are several questions in that post that you haven't answered.

 

Thank you for explaining that.

Turning the charger ON AND OFF is a BAD IDEA. Please read this quote carefully:

Connecting the load STRAIGHT ACROSS the battery is a BAD IDEA. Please read this quote carefully.

That is a very complicated problem. You can buy energy monitors that plug in between the mains power and the load (the charger) and can display kWh and store information from one day to the next. It is not worthwhile trying to make your own. They are complex. It is best to buy one.

 

I think turning the charger on and off is a bad idea. Perhaps someone else on the forums will design it for you.

The reason energy meters are expensive is that they are complex internally. They may be expensive, but they will still be cheaper than buying all the needed components yourself. They also have a lot of firmware, which takes a long time to develop and test. They are also accurately calibrated. There is NO WAY you can save money by making one yourself. Making something useful would cost a lot more and would require a LOT of software development and testing. It is NOT practical in any way.

 

There are some IC's out there that does exactly what you want, I am not sure if they work in the scale that you want but they take care of all the under voltage, over voltage, temperature effects on batteries, and even a coulomb counter to know exactly the % of charge your battery is at which you can then use to display.(some of their outputs are I2C)
you should check out linear IC's, if I remember correctly it shouldn't be that expensive but I may be wrong :S

However if you wish to do things on your own then you should read about DC/DC converters and their principles on how they manage outputs that will give you an idea.

Either way you have a lot of reading to do buddy =)

 

This isnt your thread

please post in the thread created the other week for your subject

https://www.electronicspoint.com/triggered-switch-t254909.html

Dave