# How to charge a battery while supplying power to my device

#### Tonyr1084

Joined Sep 24, 2015
6,611
No matter WHAT you're powering, it comes down to usage and availability. How much power is the amp drawing (using) (whatever kind it may be), and how much power does your battery charger supply. Know those factors and apply my drawing and you're good. If your numbers don't work out then rethink your design.

This is your project, you have enough information to complete it. If no matter what anyone says you're still afraid to move forward with it then why are you asking in the first place?!

If not - then get a bigger supply. It's all in the numbers. And no, I don't care to engineer your project. Not unless you're willing to send me a check for my time and knowledge. Even with the very limited state of my knowledge, this project is one WELL WITHIN my ability. I'm resisting GIVING you the details. I HAVE given you the knowledge - that's what this website is for - learning something. By now you should have learned how to tackle this project on your own with hardly any further input from any of us.

#### ronv

Joined Nov 12, 2008
3,770
It's not a car stereo. It's a Bluetooth boom box using one of these. No fuse
https://www.amazon.com/gp/aw/d/B01B..._11?colid=1J3XNSPY5JP8L&coliid=I2GSZQN1KDRELB
Let's use a lead acid battery because they are easier to charge. And like the original poster stated it is a small 5 AH battery.
Now lets say the battery is dead. The charger should limit the current to .5 amps and not go over 14.6 volts.(Google how to charge a lead acid battery)
So now you turn on the amp. Lets say it draws .2 amps - that's about .6 watts which is actually pretty loud.
All is well. the voltage will be over 11.5 volts (dead battery) volts and the battery will be charging at .3 amps average. it will be full in about 17 hours and you can listen to your music forever. With no charger you can listen for about 20 hours or so. If you turn the volume up higher it will take longer to charge. If you play it real loud and your charger doesn't have current limit it could smoke.

#### Spencer Hutton

Joined Sep 1, 2016
17
Let's use a lead acid battery because they are easier to charge. And like the original poster stated it is a small 5 AH battery.
Now lets say the battery is dead. The charger should limit the current to .5 amps and not go over 14.6 volts.(Google how to charge a lead acid battery)
So now you turn on the amp. Lets say it draws .2 amps - that's about .6 watts which is actually pretty loud.
All is well. the voltage will be over 11.5 volts (dead battery) volts and the battery will be charging at .3 amps average. it will be full in about 17 hours and you can listen to your music forever. With no charger you can listen for about 20 hours or so. If you turn the volume up higher it will take longer to charge. If you play it real loud and your charger doesn't have current limit it could smoke.
Thanks @ronv.
I am struggling to find the current draw for this little amp, but cannot imagine it is too much current after research beyond my original post last week when i thought it was 5 amps. I guess i can wire it up to a ac adapter (no battery) and measure it.

I was looking at a charger that does not exceed the initial current of the battery. So a 1 - 1.5 amp charger seems like it would do the job. I won't be using a pair of 50 W speakers and will set the resistance to 8 ohms so I will not be at capacity of the amp.

I do these kinds of projects because I want to learn, not because I already have the knowledge. Your replies to my posts have been insightful.

#### ronv

Joined Nov 12, 2008
3,770
Thanks @ronv.
I am struggling to find the current draw for this little amp, but cannot imagine it is too much current after research beyond my original post last week when i thought it was 5 amps. I guess i can wire it up to a ac adapter (no battery) and measure it.

I was looking at a charger that does not exceed the initial current of the battery. So a 1 - 1.5 amp charger seems like it would do the job. I won't be using a pair of 50 W speakers and will set the resistance to 8 ohms so I will not be at capacity of the amp.

I do these kinds of projects because I want to learn, not because I already have the knowledge. Your replies to my posts have been insightful.
I wouldn't worry to much about the current draw. It's not so much the speakers but rather with the volume control and the music.
I based the numbers on this little IC that I have used before. It is low power but if you are close to the speakers (same room) it is loud enough.
So you can see from the center graph .8 watts is about all it can do.

#### Tonyr1084

Joined Sep 24, 2015
6,611
Your logic is flawed. If you are drawing 2 amps and your charger can only supply 1 amp then the other amp will come from the battery, thus draining it. Over a longer period of time the battery will eventually go dead if you don't stop drawing 2 amps.

#### ronv

Joined Nov 12, 2008
3,770
Is it true that if the amp and any other components require more than 1 amp and the charger is only 1 amp that the additional current would be supplied by the battery? Assuming it is not drained. My logic thinks "no".
It is important that the power supply is a battery charger. Then it will have circuits to limit the current that the charger can supply. Then the first statement is true. Once the current is higher than the charger can supply the rest will come from the battery.

Joined May 30, 2017
1
I am beginning a very similar project, and have read that the charger sends a "ripple" charge that would be amplified by the amp and heard through the speakers. Any idea if I use a 12v 6A power supply (made for an LED strip) to charge battery and power the amp with 74W max output?
Also should/could I use a charger controller to prevent over charging of the battery and still power the unit?

#### Tonyr1084

Joined Sep 24, 2015
6,611
Just recently I built my car radio power source. It started with a 12 volt supply from an old satellite system. The supply was designed to put out 12.2 volts (no load). With help from others here on this website I modified the supply so that I could adjust it up to what a car battery should be set at. I upped the output to 13.6 volts and connected it to a fully charged car battery, an old battery I had laying around. Working well. However, the battery charge never got over 13.54 volts. So I later upped the unloaded voltage to 13.66 and now the battery sees a constant 13.6 volts.

The supply is rated to push 2.2 amps at 12 volts, so at the slightly higher voltage it should be putting out 1.97 amps. This is well enough to keep the battery charged, and I get no ripple whatsoever. Many years ago I took a car battery, car radio and a regular battery charger from an auto parts store and connected the same thing. Worked well. But being young and knowing very little about DC, especially DC Ripple I first tried it without the battery and yes, I got a TON of noise. But when I put the battery on it the ripple was completely suppressed. At least not that could be heard.

In the photo below there is an IC (U1) marked 431 G. It's a precision regulator that produces a 2.5 volt reference. The 1201 resistor and the 4701 resistor set up a voltage drop so that U1 sees 2.5 volts. If the voltage goes up higher the system regulates the voltage down. My solution was to put a fixed resistor of 1KΩ and a 10 turn 5KΩ pot (if I remember the values correctly) to get the higher voltage output. I included a switch so I could take the modifications off line and produce just 12 volts. But with the modifications I was able to achieve an adjustability from about 12.6 to 14.2 volts. One other modification was needed, the over voltage protection Zener (the WJ z) was removed from the circuit by removing the 0 resistor (jumper) from the circuit. I can always put that back in with just a jumper wire if I ever wanted to.

In short, I did what the original post wanted to do. I'm sure they completed their project as well. If I were to attempt this again with standard off the shelf parts I'd probably go with a battery charger that can push 2 amps and likely a voltage as high as 15 volts and use a buck converter to drop the voltage to 13.66 volts. Connect that to a 12 volt car battery (or other type of Lead Acid battery) and connect the radio to the battery.

One thing going on with my system is that I have the memory AND the power going to the radio. Even when the radio is off the radio is drawing a little power to keep the memory and to keep the few lights on. I may just go install a switch on the "Ignition" line so I can completely turn the radio off. But that's another project for another day. For now my system is working as desired. Battery is maintained at (nearly) 13.6 volts, which is the float voltage for a LA battery, and I get no ripple, no hum. AND having the bigger power source I get plenty of base too. Sounds MUCH better than when I was just powering the car radio from a 12 volt 2 amp supply.

#### BillO

Joined Nov 24, 2008
990
Nicely done. The only thing I would suggest is looking into increasing the voltage to 14.2V-14.4V. 13.6V is pretty good, but at that level sulphation can still occur, albeit at a slow rate. If you increase the float voltage to the 14.2V-14.4V range suphation will be virtually eliminated. Anything higher than that and you will get gassing off - which you also want to avoid.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,090
This http://www.linear.com/product/LTC4414 can be a start. Other products from LT should be able to allow you to have a dedicated charger for a particular battery type. e.g. switch from dedicated charging to supplying power if you need it.

These devices are called power path controllers.

#### Tonyr1084

Joined Sep 24, 2015
6,611
I went with 13.65 because that's the float voltage. If kept at a constant voltage sulfating should be pretty negligible. I only wish the technician at Toyota would know more about batteries. The alternator in my Venza is putting out 13.4 volts and he says that's fine. Being that he's a "CERTIFIED" technician he's supposed to know more than me. I know battery voltage should go up to 14.4 at first, to clear out sulfating then it should drop down to 13.8 (typical) and under near full load the voltage should not drop below 13.6 volts at an RPM of 1500. Though I was able to show him voltage going down to 12.4 volts he refused to say the alternator needed to be changed. So what I think I'm going to do is figure a way to hurt the alternator enough so it HAS to be replaced.

Anyway, that's off topic. I agree with the 14.4 volts. But in my statement I said that the battery was fully charged BEFORE I put my battery minder on it. It's working pretty nicely and at that - it's an already old battery. I don't expect much out of it and am getting far more than I had hoped.

 There's one more reason why I didn't up the voltage on my home brewed project: The capacitors internally are 16 volts. I don't suppose 13.6 volts is going to cause any harm, but if I were to go up to 14.4 volts I'd start being concerned for the caps. And there's not enough room inside the box to put the next size cap in there. Of course, I COULD take them out all together and let the battery be the capacitor. Maybe another day. For now no sense in fixing what works.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,090
You and @MrAl ought to get together.

The float voltage has creeped up because the battery chemistry changed and there is no real way to fix it.
Check www.batteryuniversity.com He also has issues with lots of short trips and the good ole regulator isn't battery temperature compensated.

Batteries and Toyota or Batteries and charging in general. Me: "Abused battery". Long time sitting in winter so car would not start. That in itself, can ruin a battery. So, in some January, I d a hygrometer test. I would replace the battery because of uniformity and discharge issues.

In Some May following January, I ask the Toyota dealership to check the battery. They did their electronic voodo and pronounced the battery in good health.

I make a long trip a day or so later - 40 miles one way. I stop at a destination and the care didn;t feel right. I stopped the car and tried to start it. Nope. I do my business and come out in an hour and the car started. I thought I checked the belt, but maybe I didn't do it good enough.

I go through center city traffic in a large Metropolitan city about 10 blocks to a new destination. I do the same thing. It didn;t sound quite right. I did an hour's worth of business and called the tow truck. They were able to drive the car on the truck. I coudn't really open the windows. I'm in an hourly paved lot.

The tow trick driver says he has to make a pit stop to pull a car out of hole. He did and I get dropped of at a shop of the insurance company's discretion.

The shop says I need a belt and pronouced the battery in good health, I grabbed a bite to eat at a recommended diner and head home.

A day later, I try to start the car and "nothing". So, new battery.

I find out that the Toyota dealership doesn;t own a \$5.00 specific gravity battery tester. Battery University says, you can;t trust the electronic measurements, Go figure.

I get good lifetime on Toyota batteries as long as "stupid things" don;t happen., so that's a real plus. A "stupid thing" example: Battery gets disconnected when the car gets painted and never tightened. Takes out the alternator. Or on another vehicle (A Pep Boys install). No water in one of the cells. I caught that early because I checked at my earliest convenience.