Help me NOT burn my house down

So I have some pretty basic laptop battery questions. I'm not taking a big risk as far as damaging my laptops (unless they are in close proximity when something goes horribly wrong) because I'm not using it with a laptop.

1. Is there a way I can safely use a normal DC power source to charge a laptop battery?

2. How much of the safety circuitry on a laptop battery is built on to the PCB in the battery pack? For example, do I have to worry about current overdraw or overcharging the battery?

3. Can I use the battery to power something with a simple DC input, or does the "data" connection need to receive the correct signals?

4. Has anyone seen laptop battery chargers (the type that are independent of the laptop) for cars (12v input)?

5. I assume a battery cannot be charged and used at the same time, and laptops have a special switch that turns off the battery when plugged in?

6. I have a device that can currently charge a single 3.7v li-ion cell. I assume this is useless for charging a laptop battery, unless there is circuitry to charge the next cell after the previous is charged?

If you're wondering, I have a device that is broken and seems to get no power from its battery. I think it has space for 4 cells. It has a 12v DC input. I want to build a laptop battery into the case and power it through the DC input BUT I also want to still be able to use it while plugged in AND charging the battery at the same time.

If anyone would like to help me trace the circuitry and fix it to work as originally intended, feel free. I can upload pictures of the PCB. Its a portable speaker system with an ipod dock.

Thanks in advance.

 

Since we're talking here of Lithium Ion batteries (I'm assuming...), I would say with the questions you have to steer clear of this project.

These devices are not toys - burning your house down would be a blessing - stay safe (please!).

 

Um, I don't think so lol. I suggest you steer clear of advising me on this project if you can't answer the simple questions I have. Since you are making assumptions instead of reading my post thats just another reason. What I am trying to do is very simple. The only "dangerous" part is trying to power something normal with the laptop battery. My device consumes much less current than a laptop (1 amp max at 12v) and the laptop battery is lower voltage which is just going to undervolt the device.

If its unsafe to charge a battery improperly which it probably is, I'm going to buy an external laptop battery charger which obviously shouldn't cause any problems. If anyone wants to start arguing about how crappy non OEM stuff is, please take it elsewhere.

This looks very safe if done correctly:
http://www.billporter.info/wp-content/uploads//2010/01/LiIon_tut.pdf

 

There's nothing wrong in someone giving you some, what looks like, pretty good advice. No reason to go ape*bleep* on him. If they are simple questions, why can't you answer them yourself?

 

I'm sure it's possible. But because of the different strange things done with regulating the volt, overcharge protection, data streams (if it's even used) that kind of thing, on a lot of the batteries.. I probably would have bought an external 12v battery pack with a dc connector instead (if that works for what you wanted to do, I mean).

But then again I always had a lot of respect for the things hardware manufacturers do when it comes to subtly modifying one standard part, so it will blow up if put next to another standard part. I mean, who knows what the actual specification of a dell battery is that charges on variable current. Is it really charging that way because of a limited psu, or is there something about the heat on the battery itself..? Is it the motherboard connectors? Safety concern on the actual battery cells they bought from the back of a truck in Casablanca? Impossible to know for sure.. Because the surge-protection, and cutting the power when the charge is complete, max charge level, and so on, isn't programmed into the connector interface, it's in the circuit before the battery on the motherboard.

 

Thank you, that's exactly what I'm finding to be the case about laptop battery PCBs. And yeah, I think I'm basically going to replace the PCB and build my own battery pack with this controller board: 2 pcs TENERGY Protection Circuit Module for 11.1V Li-Ion Battery Pack | eBay
and the existing laptop cells.

 

Laptop battery charging circuits have a number of specific parts (not just resistors or caps but ICs that monitor charge flow and voltage) that are absolutely needed to safely charge a battery. You, ideally, would need to look at specification sheets for both the batteries and the charging components to make sure that everything lines up nicely. A generic board like that might work but it also might do damage in the short term or the long term.

You can't just make a PCB and claim that it is fully compatible with all 11.1V Li-ON cells either. That's baloney.

-- Source: This electrical engineer who *has* built a battery charging circuit for Lithium Ion batteries for embedded systems.

 

11.1v cells?? The cells are 3.7v, that PCB is meant for 3-6 3.7v cells.

Yes, I am now aware that li-ion charging is not simple at all and requires complex algorithms. Although, discharging it seems much simpler, so if I could charge the battery with one of these External Battery Charger For HP Pavilion DV9000 Laptop | eBay I could still use a laptop battery to power the device. According to this, laptop batteries often output voltage without any activation: How to Repair a Laptop Battery – Battery University

 

Brave man. *bows*

How does it ..work, anyway? Is the idea to set up something that will have the same effect-draw over time (so variable current).. or do you just zap the cells with variable resistance, until they draw power up to a set limit, or..?

 

If you take 3.7 volt cells and put 3 in series you get the 11.1 that Greg is talking about.

Having access to data sheets doesn't even give you the whole story. I know that certain operating parameters are not disclosed unless you sign a NDA (at least the TI parts seemed to imply this that I was looking at). I have spent a bit of time looking into the types of parts used in the battery packs. You really need to know what your doing to safely handle Li-ion. Replacing Cells is one thing, designing safety circuits is another.

 

My advice would be to use AA NiMH. The nicest one’s to use right now are the Sanyo Eneloops. They will hold the charge when not using your system for a long period of time; you can get chargers off the shelf. The big plus is they don’t have the inherent risks associated with Li-ion. You could look into some creative ways to mount them. Using 9 of them to get the voltage in range of 11.1Volts (if that is the voltage you need) is nice as you can get battery holders that fit 3 either next to each other or in line.

I would be glad to provide some assistance if you go that route.

Also I don’t have any time right now but I could respond to your numbered questions with the problems you face with each one and the reasons why it’s not so easy and cut and dry to accomplish what your trying to do with Li-Ion.