Hello everybody!

My name is Oleg, I’m from Russia, Saint-Petersburg, so first of all I please you to excuse my English and also I’m new to electronics, and my question can be to lame, but I need answer anyway…I've already asked this question at DIYAUDIO, but i haven't received any answer.

Few months ago I bought used Philips Fidelio p9 – portable bluetooth speaker. A bit later it broken and local service told me that they couldn’t repair it, so I decided to build same thing by myself.

So. I’m going to build a Bluetooth speaker which will use SLA 12V 7Ah battery. And the main question is under voltage and overcharge protection. I want it to be pretty simple as it is in Philips – you plug the supply jack and charging started, if battery is charged – charging process doesn't start.

Question 1:
Block diagram:

This is my diagram of battery protection and charging: «power supply - power supply jack - Automatic Battery Charger – battery - Undervoltage-lockout – amplifier». So the first question: is it logical diagram? Is it right? Will it work? How will it work if my speakers are turned on, will the battery being charged, and will it take longer to charge?

If this block diagram is correct, than I can move further. And here’s the next question:

Question 2
Battery charger and overcharging protection. As a charger, I want to use this scheme using L200C:

Resistor R2- R6 depends of the battery capacity (0.1C, so i chosen R4 - 0,75A). I want to add a relay, which is driven by transistor (I found this scheme in internet. Here it is: http://www.homemade-circuits.com/2011/12/simplest-smf-automotive-battery-charger.html ). This addition must to turn off the further charging process if the battery is fully charged. So, please , look at this scheme, is it correct, will it work?

As a undervoltage protection i'm going to use this scheme. It has adjustable cut off voltage and adjustable hysteres and . It is sold in Russia.

Question 3
Also, I presume, hysteresis is needed here for this situation: let’s imagine, that we connected the power source (I mean 220V socket and power supply) to the system, the charging started, meanwhile the speakers were working. When battery became fully charged (It’s important to say that we use cycle regime, so it’s around 14.5V), the system locked off the charger, but when the voltage became not 14,5 but 14, 4999 the charging process started again. Overcharge protection would turn off and on the charger many times - jittering would happen. That's why the system must turn on charger only at level of 13,5V (as example). This is hysteresis. So the question is HOW TO ADD HYSTERESIS IN OVERCHARGE PROTECTION SCHEME?

Question 4
I also made some findings, please read and agree/disagree with me:
1) Battery work in cycle regime. Not in storage regime.
2) The cycle regime charging voltage - 14.5V
3) As soon as battery charged it must be locked off the load!
4) As a result of item 3, we need hysteresis

I’m sorry for such a huge text, I was trying to write it shorter, but…) I also read a lot of information but i still need to get information. I can’t use some turnkey solutions because of the cost. I hope answers would help other boombox makers)))

 

Welcome to AAC!
SLA batteries need a controlled charging profile. Have you checked the Battery University site?
There are ICs dedicted to charge control. Have you considered those?

 

Alec_t, thank you for your link!

Yes, i've already read this article and i tried to understand it as i could understand technical terms. The thing is that the charger that i showed here (charger that uses L200c) works accordingly to the graph of proper charging (which is seen on the page ), from high current to low current.

But! there are two types of battery regimes: cycle (this one, i presume, is used in portable lights) and another one is storage which is used in UPS systems. So the first one must be turned off of the charger as the battery is fully charged and another one can be charged from time to time with small current without need to be turned off of the charger. The cycle regime needs a higher charging voltage - 14.5 volts. The storage regime needs 13.5 - 13.8 volts and can stand long time under this voltage (but with small current of course).

That's why i found additional scheme of relay - it is for cycle regime.

So please, check my findings from my first post. You can see, i read a lot about charging and maybe i need to read more, because i have some mess in my head)))

 

Question 4
I also made some findings, please read and agree/disagree with me:
1) Battery work in cycle regime. Not in storage regime.
2) The cycle regime charging voltage - 14.5V
3) As soon as battery charged it must be locked off the load!
4) As a result of item 3, we need hysteresis

Isn't it right?)

P.s: i want to use l200c scheme because it's very cheep and easy...

 

you're better off using an op amp comparator, using an Lm358, and set your hysteresis levels with resistors,and that can switch your relay on/off as needed.

 

Dodgydave, thank you very much for your reply! I will learn about op amp comparator, using LM 358, surely)

So if you can, please tell me if my first scheme from question #1 - BLOCK SCHEME is right or not? Now it's a very important question for my moving further...

 

looks ok, i would use the relay to disconnect the load from the battery, and use the charger voltage to power the relay, so it doesn't drain the battery, use higher value resistors for the comparator circuit so it draws less current from the battery.

 

Ok! thank you very much ! I'll think about it more deeply)