# help about battery charger

#### the kid

Joined Jan 4, 2015
81
Hello every body
I m searching a three stage battery charger with triac and have a sesult as picture below

but i dont know how this schematic operate. can every one help me

#### Dodgydave

Joined Jun 22, 2012
10,964
What you have there is a dimmer circuit, with the transformer as the load, and will give a variable output voltage on the secondary side, it maybe a bit rugged and not a pure sinewave.

#### Alec_t

Joined Sep 17, 2013
13,793
..... and it's nothing like a three-stage battery charger.

#### the kid

Joined Jan 4, 2015
81
Thank you for attenion
I need building a three stage charger based this schematic and mcu. But i dont know to measure charging current for driving the dimmer. How to measure a non-constant current by mcu.
Other problem, i dont understand about role of diacdiac D1 in schematic, please help me

#### Alec_t

Joined Sep 17, 2013
13,793
How to measure a non-constant current by mcu.
You pass the current through a low-value 'sense resistor' and use the mcu to measure the voltage developed across the resistor.
The diac allows charge to build up on C2 until the diac breaks over, dumping the charge into the triac gate to turn the triac on.

#### the kid

Joined Jan 4, 2015
81
You pass the current through a low-value 'sense resistor' and use the mcu to measure the voltage developed across the resistor.
The diac allows charge to build up on C2 until the diac breaks over, dumping the charge into the triac gate to turn the triac on.
thank you, but i think that charging current be vary to instant voltage at brigde diodes, so I think it is very difficult to measure

#### Alec_t

Joined Sep 17, 2013
13,793
I think it is very difficult to measure
Not really. Use a zero-crossing detector to tell the mcu when the bridge output is zero volts. That gives you a reference point so the mcu can then measure current at a predetermined time relative to the reference.
But by using your posted circuit you are making life difficult for yourself. Most battery chargers do the control on the DC side of the bridge, not on the transformer input.

#### hp1729

Joined Nov 23, 2015
2,304
Hello every body
I m searching a three stage battery charger with triac and have a sesult as picture below

but i dont know how this schematic operate. can every one help me
Wow! A PolyPak part number. I haven't seen that in a long time.
3-stage? Well, variable charger.

#### the kid

Joined Jan 4, 2015
81
Wow! A PolyPak part number. I haven't seen that in a long time.
3-stage? Well, variable charger.
It is three stages charger. I m sure that. Do you know that

#### tcmtech

Joined Nov 4, 2013
2,867
I'm guessing you put almost no effort into searching for and studying anything about the what and how that goes into a multistage battery charger system being what you have shown there is not anywhere close to being the correct let alone a reliable workable circuit for a three stage battery charger system.

It would be way easier and far more reliable to do the voltage and current control by phase angle firing one the secondary side with two SCR's in place of either the top two or bottom two of the bridge rectifiers not the primary side with a triac.

By putting everything on the secondary side you don't have with trying to accurately and evenly control the phase angle firing points for each half of the sine wave in order to keep the transformer from going into partial DC saturation and burning up plus all the voltage and current sensing is being done on the lower voltage side so no isolation circuitry is needed either.

To give you an idea of how difficult and complicated it is to do voltage and current regulation of the secondary side by phase angle manipulation of the primary side power feed take a look at how it's done on a basic Constant Voltage mini MIG welder unit and imagine trying to graft a three-stage battery charging control into that.

Lincoln SP-100, page 60.

http://www.manualslib.com/manual/95205/Lincoln-Electric-Sp-100.html?page=60#manual

Do you rally think you could build that and have it work?

Also you have not said one thing about what kind of battery (LIPO, Lead acid, NiCad, NiMH, other?) or what voltage (1 cell or 20+ cells?) how small or big it is (.1 Ah or 1000+ Ah?) either which is also very critical information as to what type and size of circuits and control systems you will need to make it work correctly.

An actual three stage charger circuit for lead acid type batteries. It took me about 1 minute of Google searching for 'Three-stage battery charger circuits" to find.

https://pure.ltu.se/portal/files/39903961/iasj.pdf

18 pages of info schematics on how it's done at the simplest level.

Last edited:

#### the kid

Joined Jan 4, 2015
81
I'm guessing you put almost no effort into searching for and studying anything about the what and how that goes into a multistage battery charger system being what you have shown there is not anywhere close to being the correct let alone a reliable workable circuit for a three stage battery charger system.

It would be way easier and far more reliable to do the voltage and current control by phase angle firing one the secondary side with two SCR's in place of either the top two or bottom two of the bridge rectifiers not the primary side with a triac.

By putting everything on the secondary side you don't have with trying to accurately and evenly control the phase angle firing points for each half of the sine wave in order to keep the transformer from going into partial DC saturation and burning up plus all the voltage and current sensing is being done on the lower voltage side so no isolation circuitry is needed either.

To give you an idea of how difficult and complicated it is to do voltage and current regulation of the secondary side by phase angle manipulation of the primary side power feed take a look at how it's done on a basic Constant Voltage mini MIG welder unit and imagine trying to graft a three-stage battery charging control into that.

Lincoln SP-100, page 60.

http://www.manualslib.com/manual/95205/Lincoln-Electric-Sp-100.html?page=60#manual

Do you rally think you could build that and have it work?

Also you have not said one thing about what kind of battery (LIPO, Lead acid, NiCad, NiMH, other?) or what voltage (1 cell or 20+ cells?) how small or big it is (.1 Ah or 1000+ Ah?) either which is also very critical information as to what type and size of circuits and control systems you will need to make it work correctly.

An actual three stage charger circuit for lead acid type batteries. It took me about 1 minute of Google searching for 'Three-stage battery charger circuits" to find.

https://pure.ltu.se/portal/files/39903961/iasj.pdf

18 pages of info schematics on how it's done at the simplest level.
Thank you very much. Can you help me about painting voltage wave at output of diode bigde?. Can you measure charging current. Hepl me please. Sory for my english

#### MrAl

Joined Jun 17, 2014
10,608
Hi,

Yeah the original diagram is a three stage charger:
1. Connect.
2. Turn on.
3. Blow up battery.

That's three stages right? <Chuckle>

Ok seriously, that's definitely not a three stage charger. It's basically just a run of the mill charger that happens to try to use a triac to lower the output to a more acceptable level for charging a battery. It's also not a good idea to do it that way for a number of reasons.

In the original diagram they are trying to regulate the primary, which is not really needed in a modern design. It is easier to regulate the secondary due to the much lower voltage level and the availabiliity of cheaper MOSFET transistors that can handle the current. This results in a much quieter design both electrically and audibly, and a bit safer too.

If you want to really do a there stage charger then you might be better off with a three stage controller chip which you should be able to find on the web. If you want to do it ad hoc then you'll have to study the theory on how and why it is done that way, then implement in software in some microcontroller.

#### tcmtech

Joined Nov 4, 2013
2,867
Thank you very much. Can you help me about painting voltage wave at output of diode bigde?. Can you measure charging current. Hepl me please. Sory for my english

Sorry but no. The most important and hardest part to learning things yourself is the having to take the time to do the actual searching reading and then getting familiar with how it works to the point of actually understanding what it is you read in order to design what you want.

If you want to build a real working three stage battery charger there are literally hundreds of schematics and 'how to' write up's on the internet to follow that explain everything you need to know in detail and if they don't explain something than more than likely you are asking a question that is not relevant or applicable to the design or function of the system which means that now you have to go and do some more reading and learning about what it is you asked and why it doesn't apply as you think it would.