SLA battery Charger

[silverchris]

I have got a bunch of SLA batterys from computer UPSs. I also have a broken circut board from one. I was wondering if I could slavage parts from it to make a charger with auto shut of?
The ICs on it are

• MM774C14 (x2)
  HEF4001BP
  HEF4066BP
  LM339N
  HEF4011BP
  SG3524bn

The transistors are

• BU71A
  IRF730
  And a couple others I can't really read

I am very bad a the design part of things but I can solder pretty well.
Thanks,
Silverchris

 

[Russlk]

Looks like it was a switcher. More than I want to tackle for free.

 

[k7elp60]

I have built a lot of SLA chargers, both automatic and manual. The easiest and most reliable is for the float or standby mode. This is to say if the charger is designed to produce 2.25 volts and 2.3 volts per cell you never have to monitor the battery, and you can leave the charger on indefinately.
For a 12 V SLA battery this relates to between 13.5 and 13.8V. For a 6v it relates to 6.75 to 6.9volts.
I think the reference in the SG3524, the LM339 and the IRF730 could be used for a charger.

 

[silverchris]

so if I was only putting in 13V continusly I wouldn't need any control of the charger at all? does it matter what current I put in to it?

 

[k7elp60]

Most manufactures recommend a maximum of 0.2C for charge current.
Where C is Ah capacity of the SLA battery.'
Remember the charge voltage is 13.5 to 13.8 volts, not just 13.

 

[silverchris]

well I have a 14V transformer from the ups also so I would need to drop that down. I am a relitive electronic design newbie so any help would be apretiated. These batterys are 2 12Ah and one 7Ah. for the 12 Ah ones I would need 2.4 Amps of current right? and for the 6Ah one I would need 1.2? right?
Thanks,
Silverchris

 

[Russlk]

You could use 1.2A for both, it would just take a little longer to charge the 12AH battery. Is your 14 v AC or DC? If it is DC, you could use it direct as long as the current is limited. I would not leave the battery on the charger permanently, but 24 hours would be OK.

 

[silverchris]

14 AC but I can put a rectifier with it for dc. How would I limit current?

 

[Russlk]

14 VAC = 19.6 volts peak, so if you use a bridge rectifier and the battery is 12 volts, the excess voltage is 6.6 volts. Put a 10 watt resistor in series of 5.6 ohms to limit the current. This will overcharge the battery if you leave it on too long. It would be better to use an LM317 trimmed to 13.8 volts, then you could leave it on the charger permanently. You don't have to filter the DC, the battery is filter enuf.

 

[silverchris]

So like this one? but with a lm317? or do you have abetter recomendation for me?
Thanks for the help so far!
Chris Schimp