I need to convert a +18 volts coming from a laptop battery to -18 volts. Can someone please give me some ideas / direction?

 

Why not turn the battery around?

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If you want to invert the voltage of the battery, you may need a switching (inverting) regulator. The output voltage can be greater than the input voltage (absolute values).

 

LOL Russlk,

Seriously tho, that is the best solution

 

Do you want +18 to be plus and minus 18?

If you really want +18 to be -18, use the plus side of the battery as ground and the negative side as plus.. That is, flip the battery like Russlk said.

 

Most laptop batteries supply 14.8 V (or less). So a swithcing regulator seems necessary to me.
If the battery really supplies +18 V but you need both the positive and the negative voltage, a switching regulator would be necessary again.

 

A laptop battery is not just a battery. I did an autopsy on one and they have an elaborate circuit board wired or sensed in parallel and series.

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that circuitry is a battery supervisor circuit, providing some basic functions, to prevent your battery from doing a 3-mile island style meltdown

1) short circuit protection
2) prevent excessive rate of discharge
3) prevent excessive rate of charge
4) prevent over voltage charge
5) prevent deep cycle discharge
6) prevent excessive cell temperature
7) monitor and report individual cell health
8) record battery statistics, date of manuf. and unique serial number
9) provide "fuel-gauge" calculations; state of charge, discharge rate, run-time remaining at current discharge rate, charge-rate, charge-time remaining, etc.

7 to 9 are mostly features of newer "smart batteries"

 

They said they had a +18 volt battery. What part in that says there is a 14.8V regulator? They want a -18VDC power source to something I assume. Flip the positive and negative lines

I just checked my Sony laptop and it is 16.9VDC out. I guess the 14.8 volt regulator in my Sony battery is not working tonight.

creichard: Are there only two wires from this laptop battery? Is it in the laptop when you are tring to get -18V out of it? Are you tring to tap +18V from the circuit board?

 

The regulator is not inside the battery or the laptop. It is a circuit you need to setp-up or invert a voltage. That's just one possibility ( if the battery is in the laptop while trying to get -18V )

 

Lots of replies here to a badly defined problem.

The OP has not replied to any of this, so it is not clear if he has even seen any of the answers.
I think he needs to define what it is he is really trying to do before anyone can give a definitive answer to his question.

JimB

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JimB: I agree, they said coming "from" a laptop battery and 18V led me to believe 2 wires.. But you are 100% correct.