# Voltage and Battery

#### biferi

Joined Apr 14, 2017
389
I am Looking at this 9. Volt Battery Cass.
It takes Four 9. Volt Batteries.

I Need 12 Volts and Yes I know I will just use a Resistor to get my 12 Volts from it.

And then I found a Cass that takes just Two 9. Volt Batteries.
And I know I would use a Resistor to get my 12 Volts from it as well.

But if I use the Cass that takes Four 9. Volt Battereis and use a Resistor to get my 12 Volts I need will it last Longer because I have more Voltage?

Or what am I not understanding?

#### MrChips

Joined Oct 2, 2009
30,442
Excuse my ignorance. What is a Cass?

#### Jim@HiTek

Joined Jul 30, 2017
59
Cassette? Like those plastic multi-battery holders?

What biferi could do is get two of the 2X 9V cassettes and wire them in parallel. Then use a dropping resistor. He'd get twice the life out of them. Putting them in series would be wasting a lot of energy as it would be dissipated as heat from the dropping resistor. Check that 4X 9V battery cassette...it might already be wired to put 4 batts in parallel for 9 V out at higher current (amps), or 2 in parallel for 18 V out at higher amps. It could also be set up to output 36 volts, at the standard 9 volt batt current. So you gain voltage by stacking them, but loose max current, but in parallel you have lower voltages, but higher current & longer life at lower currents.

#### Tonyr1084

Joined Sep 24, 2015
7,757
Using a resistor to drop your voltage is not a good approach. For starters, you'd need two resistors to act as a voltage divider. however, the problem with that is that its design is intended for a voltage reference. You CAN use it as a voltage divider to get the 12 volts you want but as soon as you attach a load to it the whole thing will change its values and the voltage you're looking for will not be there. Second, the voltage divider will constantly waste power until the batteries are dead unless you intend to only use it momentarily. Even then it's a huge waste of power.

Instead of planning on a failed project from the get-go tell us what it is you want to accomplish. What you're trying to power, what voltage it needs (you did say 12 volts) and how many amps it takes when operating normally. If it's a motor then the amperage will be higher when the motor starts. And if the motor should encounter a larger than anticipated load then the amperage will remain higher. So if you want/need help - tell us what you're trying to do.

I see someone else has posted while I was typing.

#### biferi

Joined Apr 14, 2017
389
I am sorry this is the Item

As you can See it takes Four 9. Volt Batteries.
So it will give me 36 Volts and I just need 12 Volts.

So I know how to use a Resistor to get my 12 Volts.

But then I found a Battery Cass that will Hold Two 9. Volt Batteries.
So this will give me 18 Volts and I know I still will have to use a Resistor to get my 12 Volts.

I just want to know if I go with the Cass that Holds Four 9. Volt Batteries and use a Resistor to get my 12 Volts will it Last Longer?

#### MrChips

Joined Oct 2, 2009
30,442
No. That is a battery charger, not a battery holder.
Tell us what device you want to power and then we can advise.

#### DickCappels

Joined Aug 21, 2008
10,120
The word is "case".

Joined Feb 20, 2016
4,426

You will be better off to forget the 9V battery idea and go with 8 x AA cells.

#### biferi

Joined Apr 14, 2017
389
I have a 8. Inch LED Light Strip that takes 12 Volts.

I am making a Decoration and I have a Battery Holder that will Hold Four Dabble "A" Batteries.

But this Battery Holder will only give me 6. Volts and I will not be able to Power the 12 Volt LED Light Strip.

So this is why I thought I can use a 9. Volt Battery Holder.
I think I shouldd be Calling it a Battery Power Supply?

#### BobTPH

Joined Jun 5, 2013
8,654
I have never seen a battery holder for multiple 9V batteries, though that does not mean it does not exist.

Either find a holder for 8AA cells, or use two that hold 4 in series. Or, better yet, get an 11.1 V lithium ion battery or 12V lead acid battery, which are rechargeable.

Bob

#### ElectricSpidey

Joined Dec 2, 2017
2,756
What the hell is this internet obsession with voltage dividers?

Why would you need 2 resistors to create a voltage divider when a simple series circuit with a single resistor and a load already create a divider?

/end rant

#### MrChips

Joined Oct 2, 2009
30,442
Tell us what device you need to power then we can go from there.

#### Audioguru again

Joined Oct 21, 2019
6,604
Why would anybody buy no-name-brand (Chinese?) batteries and charger from Amazon? Maybe many were returned then Amazon does not sell them anymore.
Google does not know about the "LP" Battery Company.
The Cass is not a battery holder, instead it is a charger for four 8.4V batteries.

#### MrChips

Joined Oct 2, 2009
30,442
If you need 12VDC supply to power a string of LEDs I would suggest four options:

1) Eight AA cells in a battery holder

2) 8-cell rechargeable battery pack

3) Li-ion cell and a boost converter.

4) 12V SLAB (sealed lead-acid battery).

#### Tonyr1084

Joined Sep 24, 2015
7,757
I have a 8. Inch LED Light Strip that takes 12 Volts.
First, if you can either tell us more about the LED's OR show us a picture of the LED strip. Chances are you can power it from multiple batteries. But for us to give you the right answer we have to know what we're dealing with.

Let me state an example (probably doesn't fit your purpose - but you might learn something): Take a single LED. One that is typically powered with about 15 milli amps (15mA). You can power that with just about any battery that has enough voltage. For instance, you can power it from four AA batteries (6V). Now - LED's come in different colors, and therefore they have different forward voltages (Vf). The typical white LED is somewhere around 3Vf. No - it doesn't take 3 volts to work, it takes a current. And the way you arrive at the proper resistance is to take your starting supply voltage and subtract the Vf from the battery. Then you divide that new voltage by the amount of current (amperage) you want to operate the LED at. So, using a 9V battery, you subtract the Vf (3Vf) and you get 6V. Next you divide 6 by 15mA and you get 0.4KΩ (400Ω). Using a 400 ohm resistor your LED will have a current of 15mA flowing through it. If you start with a 12 volt battery then (12 - 3)÷15mA = 0.6K (600Ω). Two 9V batteries in series (18 volts) minus 3Vf = (15V÷15mA =) 1KΩ. So as you choose a voltage supply (battery or plug in) you don't set the LED's brightness by means of a voltage, you do so by using a resistor to limit the current.

So in hind sight, we now know you're trying to power a 12 volt LED strip. But we don't know how it's constructed, whether each LED has its own resistor or if there are multiple LED's in series or in parallel OR in series parallel. That's why we need to know what we're dealing with. A picture or something that leads us to knowing what you have will help us help you.

#### Tonyr1084

Joined Sep 24, 2015
7,757
Here is a strip of white LED's. Though I don't know the Vf of the LED's I'll assume they're 3Vf. R8 is a #121 (120Ω) resistor. Under these assumptions, 12V - 9V = 3V. 3V ÷ 120Ω = 0.025 (25mA) (at full brightness).

IF I were to power this from a 24V power source (battery or power supply) I would need to add a resistor. So 24V - 9Vf = 15V. 15V ÷ 0.025A (25mA) would require a resistance of 600Ω total. Since there's already 120Ω on the strip I would need to add 480Ω. That way I would preserve the LED's ability to run at 25mA. Changing the voltage means adding resistance.

So far we've gotten off track thinking you wanted a 12 volt source using a voltage divider. That's almost always not a good choice.

You also ask if having MORE batteries would give you a longer burn time. Yes, they will. Provided you wire the batteries in parallel. Four 9V batteries will last four times longer than just one 9V battery. IF you put them in series (also doable) you would need to adjust the resistance to continue to preserve the amperage through the LED's. But not only would you need a higher resistance you would also need a higher wattage resistor. So wiring 9V batteries in series will waste more power. You won't get double or four times the life out of the batteries. It's all doable. But for us to give you the RIGHT answer we need to KNOW what we're dealing with.

We can help. Post a picture or give us a link to what you have. Those LED's above - they're powered from a 12V PS. That's why there's a 120Ω resistor in the circuit. It limits the current to 25mA.

#### biferi

Joined Apr 14, 2017
389
Let me Ask in this way?

If every Battery is Connected in Parallel every Battery will give Current but the Voltage will be the same.
I get this and how it all works.

This is how you get more Current and the Batteries will not Last as Long.

But if all the Batteries are Connected in Series the Voltage goes up but the Current will stay the same.

I do get all of this and how it works.

Now if I Buy a Battery Holder that Holds Two 9. Volt Batteries or Four 9. Volt Batteries the Voltage will keep going up because the Battery Holder Insdie will Link all the Batteries in Series am I Right?

#### Jim@HiTek

Joined Jul 30, 2017
59
Not necessarily. It depends on how the manufacturer made the battery holders. They can make them so the batteries are in series or in parallel. So you just need to read the ad copy carefully to find out which. You can't just say it's going to be one way or the other as it depends on what the manufacturer decided was the most easily sold.