I have been thinking about building a 12v lead acid battery charger and found this schematic floating around and figured I would see what you guys think ???

 

I think that would take quite a while to analyze.
At least the IC isn't obsolete.
One always worries, if you have to ask, can you actually assemble this?

 

I think that would take quite a while to analyze.
At least the IC isn't obsolete.
One always worries, if you have to ask, can you actually assemble this?

My problem is that I love electronics and are able to repair many electronics with out any issues but understanding how the circuit works or what does what I have no clue..I have been building a lab a little bit at a time and have alot of stuff but have no idea how to build a simply circuit...


My equipment
Bkprecision scope 20mhz analog ( I bought really cheap but had to repair it and now it works great but getting a little back feed but will fix later )
Fluke 77 series II
Mastek 30v power supply
Alot of parts

 

That circuit looks like it's about 100X as complicated as it needs to be to charge a lead acid battery. FYI, the IC's that have the "BQ" prefix were from a company called Benchmarq. I remember them from the 90's when they first came out claiming they had discovered some way to recharge any battery in five minutes by "sensing" something in the battery to prevent overcharge. It was bogus, they were pretty much discredited. They seem to have made an industry niche creating expensive, complicated IC's for battery charging. Unitrode bought them back in 1998.

 

That circuit looks like it's about 100X as complicated as it needs to be to charge a lead acid battery. FYI, the IC's that have the "BQ" prefix were from a company called Benchmarq. I remember them from the 90's when they first came out claiming they had discovered some way to recharge any battery in five minutes by "sensing" something in the battery to prevent overcharge. It was bogus, they were pretty much discredited. They seem to have made an industry niche creating expensive, complicated IC's for battery charging. Unitrode bought them back in 1998.

Well I was trying to build a smart charger that does everything and desulfating and not kill very expensive batteries for cars ..

 

Well I was trying to build a smart charger that does everything and desulfating and not kill very expensive batteries for cars ..

I am yet to be convinced desulphating does anything good, at least not the typical chargers sold on the net. Not sure what 'smarts" a lead-acid charger needs. The one I designed has worked really well. I typically get about 6 - 7 years out of my motorcycle batteries.

 

For as complex as that circuit is (I use a simple LM317 circuit), I don't see any allowance for temperature compensation. Next to voltage, temperature is probably the second most parameter, since it affects target voltage.

 

I am trying to build a multi step battery charger that will charge lead acid as well with any other battery these use in cars ..Also I have been doing some research and found out that most charger use transformers instead of switch mode power supply ????

I am yet to be convinced desulphating does anything good, at least not the typical chargers sold on the net. Not sure what 'smarts" a lead-acid charger needs. The one I designed has worked really well. I typically get about 6 - 7 years out of my motorcycle batteries.

I full agree with Desulphating process...

For as complex as that circuit is (I use a simple LM317 circuit), I don't see any allowance for temperature compensation. Next to voltage, temperature is probably the second most parameter, since it affects target voltage.

How would you go about that??

 

Temp compensated charger:

 

3A temp compensated charger with current readouts:

 

I found this charger and I would like to change features of the item
http://www.apogeekits.com/PDF_Files/Battery_Charger_Manual_K8012.pdf


The plans upgrade but not sure if it's going to work and would like some help or input
1-Use a power brick instead of a transformer
2-Increase charging amp from 1 amp to 3 to 5 amp
3-Add a voltage and amp display with a 9v battery supplying to it
4 Use Soft latch configuration instead of toggle switches


So what do you guys think

Temp compensated charger:

3A temp compensated charger with current readouts:

Cool I will have to check them out later when more time and thanks for the schematics....

 

2-Increase charging amp from 1 amp to 3 to 5 amp

T7 and D8 probably need to be respecified, since these two components are in the power path. So are the shunt resistors R29-31, so you'll need to calculate the new values (ohms and power rating) there as well. Since the shunt will be always "on", choose a power rating at least twice the expected maximum continuous power dissipation. It will last longer.

Likewise consider the heat dissipation across T7 and be sure the heat sink and transistor package can handle it. You might end up choosing to use 2 transistors in parallel, although at 5A I think you'll be OK with just 1.

Unless I missed it, that design still has no temperature compensation. It seems awfully complex to omit that important feature.

 

Well today I picked up a schumacher xc6 charger for less than 10 bucks and now it's time to take apart and see how it works and draw up a schematic with intentions to mod the circuit for better...