# Diy multi bank battery charger

#### Ryanc5413

Jun 30, 2017
10
Hey guys, newbie here. New to the forum not electronics. I am more into DC electronics so I have a few questions about a diy multi bank battery charger I am thinking of building.

So I am going to use a 120vac to 15vac transformer to a 4 amp bridge rectifier. My question is can I power(for lack of a better word) multiple bridge rectifiers from a single transformer. That would allow multiple outputs to battery's. They would be connected in parallel from the transformer output.

Question 2: 15 volts is going into my bridge rectifier and the one I plan to use has a . 6 volt drop. Brings my dc output to 14.4. I need to bring it down .6 volts more. What should I use to do this? A zener diode? Or something else? Can someone recommend a part number. Also would I be better off dropping voltage while in ac or after the bridge rectifier in DC voltage.

3: could someone recommend a simple regulating circuit and how to tie it into my current circuit.

4: is there a way to control the amperage? If I wanted to charge at 1amp 2 amp or 4 amp? Or is this getting too complex for a novice like myself?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,730
can I power(for lack of a better word) multiple bridge rectifiers from a single transformer.
Yes you can. But it is not necessary. You can use a single rectifier and filter capacitor and power your charging circuit from this. This will save you space and money.

15 volts is going into my bridge rectifier and the one I plan to use has a . 6 volt drop. Brings my dc output to 14.4.
15 V iusually would be the RMS rating. This means peak voltage is 15 V *sqrt(2) = 21 V! This is what the filter capacitor (or smoothing capacitor) will store as peak voltage.
To bring this down to 6 V at reasonable Amperes will require a switch mode regulator (e.g. this one or use your favorite search engine). Any other means of reducing the voltage will dissipate lots of energy as heat. The advantage of a switch mode regulator is that you can draw more amps from the output than are available at the input:
power out = Iout*Vout = 0.8*power in = 0.8*Iin*Vin
-> Iout = 0.8*Iin*Vin/Vout

could someone recommend a simple regulating circuit
See above.

is there a way to control the amperage?
Control in which way? For charging you'll need a current source. Or a dedicated charging circuit, dependig on the type of battery to protectthe battery from overcharging. This is just one example of a kit suitable for NiMh batteries.

#### Audioguru

Sep 24, 2016
3,650

A full wave bridge rectifier has two silicon diodes in series for both phases. A silicon diode has a voltage drop of about 0.7V at low current and about 1V at the high peak current in this circuit. Therefore the peak voltage is reduced by 2V.

You do not have a charger circuit that regulates the voltage and the current.

#### Ryanc5413

Jun 30, 2017
10
I am charging led acid car batteries. I need a . 6 volt drop not a 6 volt drop. Thanks for the ideas so far.

#### Ryanc5413

Jun 30, 2017
10

A full wave bridge rectifier has two silicon diodes in series for both phases. A silicon diode has a voltage drop of about 0.7V at low current and about 1V at the high peak current in this circuit. Therefore the peak voltage is reduced by 2V.

You do not have a charger circuit that regulates the voltage and the current.
Can you tell me a simple circuit to build to take care of that?

#### Audioguru

Sep 24, 2016
3,650
You need a battery charger circuit that is designed to charge old lead-acid batteries. I have never used a lead-acid battery except the one in my car.

#### Ryanc5413

Jun 30, 2017
10
You need a battery charger circuit that is designed to charge old lead-acid batteries. I have never used a lead-acid battery except the one in my car.
Correct. I have been playing with bringing them back from the dead with great success

#### kellys_eye

Jun 25, 2010
5,111
Simple charge/discharge cycling can restore 'some' lead-acid batteries but unless you have a means of testing the capacity of the battery (its ampere-hour value) you can't determine if what you're doing is actually worthwhile.

Such capacity testers aren't expensive nowadays but you can achieve a basic test result by connecting a fixed load (say a 12V 12 watt lamp - which makes a 1A drain load) and measuring the battery volt drop over time.

Many lead-acid batteries can be made more usable by 'pulse-charging' methods - these are implemented to de-sulphate that plates and restore amperage capacity. There are many circuits on line to achieve this result.

#### Ryanc5413

Jun 30, 2017
10
Simple charge/discharge cycling can restore 'some' lead-acid batteries but unless you have a means of testing the capacity of the battery (its ampere-hour value) you can't determine if what you're doing is actually worthwhile.

Such capacity testers aren't expensive nowadays but you can achieve a basic test result by connecting a fixed load (say a 12V 12 watt lamp - which makes a 1A drain load) and measuring the battery volt drop over time.

Many lead-acid batteries can be made more usable by 'pulse-charging' methods - these are implemented to de-sulphate that plates and restore amperage capacity. There are many circuits on line to achieve this result.
I have a 2300 dollar battery/charging system analyzer. I own a garage so I do have a way to test the batteries. Different subject than what I was asking for. I understand how to test and how to repair battery's. I have 5 outside that are 15 years old that have more cranking amps than they were rated at new. Just wanting a charger that I can do multiple battery's from. I am getting sick of drop cords and splitters. And building one will give me something to work on nights and rainy days.

#### Ryanc5413

Jun 30, 2017
10
Does anyone have a useful multi bank charging circuit with charging control built in. Something that will lower the amperage as the battery nears 12 + volts.

#### kellys_eye

Jun 25, 2010
5,111
OK - the 'direct approach' - I like your style!

Another suggestion would be to visit the semiconductor manufacturers websites for application notes on the process - there are linear and SMPS solutions to this kind of thing amongst them (from memory) but it may involve more 'design' than you're willing to spend time on???

Typical (if perhaps OTT) example....

Depends on how much time/effort you're prepared to put into it. I may be able to find some simple solutions in the form of 'projects' that appeared in back issues of various electronics magazines (I have 100's Gb of such stuff). Gimmee a few hours to trawl through and I'll post up a couple of potential examples....

#### Ryanc5413

Jun 30, 2017
10
OK - the 'direct approach' - I like your style!

Another suggestion would be to visit the semiconductor manufacturers websites for application notes on the process - there are linear and SMPS solutions to this kind of thing amongst them (from memory) but it may involve more 'design' than you're willing to spend time on???

Typical (if perhaps OTT) example....

Depends on how much time/effort you're prepared to put into it. I may be able to find some simple solutions in the form of 'projects' that appeared in back issues of various electronics magazines (I have 100's Gb of such stuff). Gimmee a few hours to trawl through and I'll post up a couple of potential examples....
Awsome! Thank you!! I am not trying to build a high tech charger that will also fix eggs and bacon as well as wash my truck. Just looking for something simple. So far I know I can use a transformer to a bridge rectifier but I need some sort of charge regulator. Could that be done with a voltage regulator? I need something that will put full amps from anything below 11 volts, then start backing down the amperage as it gets closer to 13 then once it reaches 13+/- volts the amperage should drop to a 1/4 of a amp or 1/8 of amp. I wouldn't mind having a switch that would bypass the regulator and let me take the battery to ask high of voltage as I want(transformer willing) sometime 15-16 volts is needed to knock the Sulfur off the plates. I would like to have a charge amp guage(led or lcd) as well as a volt guage(led or led also)

#### Ryanc5413

Jun 30, 2017
10

Is this charger regulated? If so this would be perfect if you can help me figure out how to do this multi bank, move the transformer inside the charger, add a amp and volt guage.

OK - the 'direct approach' - I like your style!

Another suggestion would be to visit the semiconductor manufacturers websites for application notes on the process - there are linear and SMPS solutions to this kind of thing amongst them (from memory) but it may involve more 'design' than you're willing to spend time on???

Typical (if perhaps OTT) example....

Depends on how much time/effort you're prepared to put into it. I may be able to find some simple solutions in the form of 'projects' that appeared in back issues of various electronics magazines (I have 100's Gb of such stuff). Gimmee a few hours to trawl through and I'll post up a couple of potential examples....

#### kellys_eye

Jun 25, 2010
5,111

As it stands it is limited to a 2A maximum charge current but if you look at the L200 datasheet (there's a link in that article to one - see page 8/12 fig 24) where it shows how to use bypass transistors to increase this to whatever you require.

As wired the circuit gives a constant voltage (set by the ratio of R1/R2) at a limited current set by R3.

To make a multi-charger you simply connect the output of a suitable power supply (rated at a minimum of 18V DC and capable of delivering 'x' amps times the number of charging modules you use) to the paralleled input of all L200 modules.

You can monitor current at each output with separate meters or use a multi-pole switch to read each output via a single meter - your choice.

Check out the datasheet - it's full of examples on how to use the device.

#### Ryanc5413

Jun 30, 2017
10
Ok 4 amps max would be great. Could you draw me a diagram on how to build it. And how to incorporate a multi pole switch and amp/volt meter as well as adding the multi bank. If you could take the time to draw it I can build it and I'd owe you a huge favor. I would even be willing to share my secert on how to make your lead acid battery's last forever. There is a special treatment that cost hardly anything. And best of all is safe

As it stands it is limited to a 2A maximum charge current but if you look at the L200 datasheet (there's a link in that article to one - see page 8/12 fig 24) where it shows how to use bypass transistors to increase this to whatever you require.

As wired the circuit gives a constant voltage (set by the ratio of R1/R2) at a limited current set by R3.

To make a multi-charger you simply connect the output of a suitable power supply (rated at a minimum of 18V DC and capable of delivering 'x' amps times the number of charging modules you use) to the paralleled input of all L200 modules.

You can monitor current at each output with separate meters or use a multi-pole switch to read each output via a single meter - your choice.

Check out the datasheet - it's full of examples on how to use the device.

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