# General Electric volts and amps

#### Nando6996

Joined Mar 9, 2019
20
I need to power three 3v 0.28amp mini fans, do I use 3v batery or a 9v batery? I dont want to fry my fans.

#### BillB3857

Joined Feb 28, 2009
2,570
I would use two dry cells in series or a 3 volt source and then connect the fans in parallel with the fans sharing the source.

#### crutschow

Joined Mar 14, 2008
33,980
By dry cells, Bill means alkaline type batteries such as AAA, AA, C, or D size.
How long do you want the fans to run on one set of batteries?
For example 2AA alkalines will run the three fans for about 2 hours.

#### Nando6996

Joined Mar 9, 2019
20
By dry cells, Bill means alkaline type batteries such as AAA, AA, C, or D size.
How long do you want the fans to run on one set of batteries?
For example 2AA alkalines will run the three fans for about 2 hours.
Thanks for your help bud, im just beginning in this field. I only need it to run for an hour for a presentation. The goal is to run it off a button cells. How can i make it last 8 hrs? maybe a joule thief and a capasitor. Or should i use a chip with rechargeable battery?

#### MrSoftware

Joined Oct 29, 2013
2,166
If you need 8 hours of run time and each fan requires 0.28A at 3V, then you will need a battery that can supply 0.84A at 3V for 8 hours. So multiply your draw (0.84A) time the amount of run time you need (8 hours) and you come up with a requirement of 6.72Ah. Realistically you will need a little more. So look for batteries that can give you a bare minimum of 6.72Ah, plus some extra. A common CR2032 button cell is a 3V battery, but has about 200mAh capacity (will vary a little by brand, etc..). So to get your 6.72Ah you would need 6.72 / 0.2 = ~34 CR2032 button cells to get your required run time, in a perfect world.

#### Nando6996

Joined Mar 9, 2019
20
If you need 8 hours of run time and each fan requires 0.28A at 3V, then you will need a battery that can supply 0.84A at 3V for 8 hours. So multiply your draw (0.84A) time the amount of run time you need (8 hours) and you come up with a requirement of 6.72Ah. Realistically you will need a little more. So look for batteries that can give you a bare minimum of 6.72Ah, plus some extra. A common CR2032 button cell is a 3V battery, but has about 200mAh capacity (will vary a little by brand, etc..). So to get your 6.72Ah you would need 6.72 / 0.2 = ~34 CR2032 button cells to get your required run time, in a perfect world.
Thank you so much for your replaying and knowledge. I have been on other forums and their replay was so discouraging and just plain wrong. Like ( can i use your coin cell to power my tractor) i know thats not possible but oh well to each their own. I know what im trying to accomplish can happen, i just need the right help. So when you said 6.72 / 0.2 = ~34 CR2032buttoncells does that mean 2 CR2032 BUTTON CELLS

#### Nando6996

Joined Mar 9, 2019
20
So can i use a 9v and not fry the fans?

#### BR-549

Joined Sep 22, 2013
4,928
Why not try a 6vdc SLA lantern type battery, and a 6vdc to 3vdc down converter?

#### djsfantasi

Joined Apr 11, 2010
9,151
Thank you so much for your replaying and knowledge. I have been on other forums and their replay was so discouraging and just plain wrong. Like ( can i use your coin cell to power my tractor) i know thats not possible but oh well to each their own. I know what im trying to accomplish can happen, i just need the right help. So when you said 6.72 / 0.2 = ~34 CR2032buttoncells does that mean 2 CR2032 BUTTON CELLS
I think he means 34 CR2032 button cells...

#### WBahn

Joined Mar 31, 2012
29,831
Thank you so much for your replaying and knowledge. I have been on other forums and their replay was so discouraging and just plain wrong. Like ( can i use your coin cell to power my tractor) i know thats not possible but oh well to each their own. I know what im trying to accomplish can happen, i just need the right help. So when you said 6.72 / 0.2 = ~34 CR2032buttoncells does that mean 2 CR2032 BUTTON CELLS
Uh, no. ~34 CR2032 button cells means approximately thirty-four CR-2032 button cells.

But that's just for ONE of your fans. Your initial post says that you have THREE of these 0.28 A, 3 V fans. So to power all three for eight hours you need about 20 A·h of capacity.

But I wouldn't go out and buy 132 coin cells. They tend to have pretty high internal resistance, though since you would need to put 60+ stacks of two in parallel, that may actually work out okay.

To put what you need in some perspective, a typical car battery has a capacity of about 40 A·h and you about 1/2 of that. So, roughly speaking, you need a battery that is about 1/2 the size of a typical car battery. For further perspective, most motorcycle batteries are in the 7 A·h to 14 A·h range, so you would probably need two of the larger motorcycle batteries to get what you want.

#### WBahn

Joined Mar 31, 2012
29,831
So can i use a 9v and not fry the fans?
Depends on the fans, but probably not. If they are rated for 3 V, applying 9 V to them will probably not do them any favors.

#### djsfantasi

Joined Apr 11, 2010
9,151
So can i use a 9v and not fry the fans?
Let’s consider that you’re thinking of wiring the fans in series. Your draw for all three would be 0.28 A and need 9V. A draw of 0.28A for 8 hours is 2.24Ah. Divide that by the capacity of a typical 9V battery (550mAh or 0.55 Ah). The result is 5 batteries in parallel.

Someone check my calcs. I’ve already taken my sleeping pills.

#### Nando6996

Joined Mar 9, 2019
20
What about using capasitors, joule thief, risistor or just a plain chip? With our technology this can be done right?

#### crutschow

Joined Mar 14, 2008
33,980
What about using capasitors, joule thief, risistor or just a plain chip? With our technology this can be done right?
None of those.
You can't get more energy out of a battery than its rating.
If you want to power the fans for 8 hours, then you need a battery than can supply that amount of energy.
But at first you said you just need it for an hour presentation.
So which is it?

If you have time to charge batteries between presentations, you could use two NiMH AA rechargeable, which should run the fans in parallel for a little over two hours.

#### WBahn

Joined Mar 31, 2012
29,831
What about using capasitors, joule thief, risistor or just a plain chip? With our technology this can be done right?
Uh, no one has figured out a way to get more energy out of something than it has in it.

How would a resistor (I'm assuming that's what you meant) do you any good as far as increasing the energy that you have available.

And what "plain chip" are you talking about? Just a random chip?

What is "our technology" that you are referring to?

#### WBahn

Joined Mar 31, 2012
29,831
Let’s consider that you’re thinking of wiring the fans in series. Your draw for all three would be 0.28 A and need 9V. A draw of 0.28A for 8 hours is 2.24Ah. Divide that by the capacity of a typical 9V battery (550mAh or 0.55 Ah). The result is 5 batteries in parallel.

Someone check my calcs. I’ve already taken my sleeping pills.
Running them in series may not be a very good idea. That forces all of them to have the same current and depending on the exact characteristics of the fans as well as the air load seen by each of them, that may not result in proper operation.

Joined Jan 15, 2015
7,445
I need to power three 3v 0.28amp mini fans, do I use 3v batery or a 9v batery? I dont want to fry my fans.
The problems you face come down to having 3 fans with each fan being a 3 volt 0.28 amp fan. So with the 3 fans in parallel you need a source power of 3 volts at 0.84 amp. Now in the interest of allowing some overhead on a battery supply I would just consider calling it 3 volts at 1.0 amp. In theory a 3 volt 1.0 amp hour battery would run your fans for about 1 hour but the reality is that a 3 volt 1 amp hour battery is not likely to provide that max battery rating for an hour. You may, for example, get 0.250 amp for four hours but I doubt the maximum for 1 hour or 2 amps for a half hour.

As has been pointed out there is no free ride. Things like buck, boost converters do work for their intended applications but when all is said and done you can't get something for nothing. Power is power and that is as good as it gets. If I want 1 amp at 3 volts I want 3 watts of power.

While coin cells are ideal for their applications they are not high current sources. Just for example this is a data sheet for a 2032 standard coin cell battery. Typical Capacity: 235 mAh (to 2.0 volts) so I doubt you would get even an hour for a single fan. Batteries are designed with a load in mind and your load(s) exceed what these batteries are designed for. You need to select or find a battery designed around your load requirements. You al;so want a battery not only capable of the load but intended application, for example is this a one time application where following a demonstration the batteries are trashed or do you want a battery source which is rechargeable?

An hour run time is one thing and 8 hours run time is another thing all together. The longer you want the power source to last, the more the power source gets larger and the more the cost increases. You can find for example 3.7 volt LiIon batteries in the 2,000 mAh range which are rechargeable and use 4 of them in parallel which would run your fans for 8.0 hours and if there is a concern with 3.7 volts a single simple 1N4000 series diode would get you down around 3 volts. Here is an example.

Ron

#### MrSoftware

Joined Oct 29, 2013
2,166
Can you get away from button cells? For example, energizer D cell batteries hold a LOT more energy than a button cell. Here's the data sheet:

http://data.energizer.com/pdfs/e95.pdf

In particular, look at this chart:

This shows you how much capacity (mAh) you can get from each battery. The left side is the capacity in mAh, the bottom is the discharge rate, meaning how fast you're pulling the power out. Notice that the faster you pull the current, the less capacity the battery has. Remember this. Also note that they consider the batteries dead when they hit 0.8V, which is nearly 1/2 of the 1.5V of a new battery.

So your current draw with all 3 fans will be approximately 0.84A, or 840mA. The chart only goes to 500mA, so we'll take a guess that at 840mA the capacity will probably be in the ballpark of 4000mAh. So to get approximate run time, divide 4000 mAh by 840mA, and you come up with approximately 4.76 hours, at which time you will be at 1/2 the voltage of when you started.

Now to get 3V you need to put 2 D cells in series. This will double your voltage, BUT the current capacity will be the same. So for every 2 D cells you will get approximately 4.76 hours run time until the batteries hit 1/2 of their original voltage. If you need the voltage to stay higher then you will need more batteries. If you add a second pair of D cells you would double your run time. So with 4 D cells you should be somewhere in the ballpark of your desired 8 hour runtime. Pardon my most horrendous CAD drawing, but this is how you would wire them:

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#### Audioguru

Joined Dec 20, 2007
11,248
The moderator on the other website forum needed to close this same thread because this kid knows nothing about batteries.