# Operate a 12v/6Amps air pump, with DIY battery pack?

Hello guys...

I have an electric air pump and i want to operate it with a battery pack (for camping purposes, away from any kind of electricity source).
Its a 12V/72W pump (works with car lighter connector) so by my poor calculations, i need something that can give me 6Amps for at least 5-10 minutes.

I have a lot of 18650 batteries in my disposal, so i thought that i maybe can put together a portable battery pack, so when i go camping for example i can carry it with me.

My circuits design skills are... nonexistent...
My DIY skills are reasonable... so my questions are:
1) Is it possible to create something that can provide at least 5-10 minutes operation, once per every charge?
2) If yes... can you please tell me or point me at the right direction so i can accurately calculate the amount of batteries that i need and the proper way to connect them?
3) or... any other easier "portable" solution? for example something lighter and cheaper than a motorcycle battery...?

Thank you for your time! :)

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1 year ago

So each 18650 battery is a 3.7 volt 3 Ah = 3000 mah

http://www.amazon.com/EBL-18650-Performance-Rechar...

Each string is 14.8v at full charge capable of 3 amps for an hour.

Combining the strings in parallel gives 6 amps for an hour.

Do NOT solder to the batteries... Use two plastic quad battery holders.

Be sure to click the pic, to see the whole image...

the_phantom_boy (author)  iceng1 year ago

So... if my batteries are 3.7V/3000mAH:
1) i need 2 of these (or 3 if my batteries are 3.7V/2000mAH):
http://ecx.images-amazon.com/images/I/61xIO6D3IWL....
2) strip and connect red wire with red and black with black.
3) connect this to the red+red/black+black wires:
http://ecx.images-amazon.com/images/I/31MYPhGaKTL....
...and i will have a 14.8v/6000mAH battery pack ready to go. Correct so far?

And an other thing...
My batteries will be extracted from old laptop batteries, so there is a good case that the voltage, or the amperage will not meet those standards of 3.7/2000mAH!
Lets say that i can attach one more 4*18650 case (or a smaller one), in order to reach higher voltage/amperage.
Is there a circuit that i can attach to that battery pack, that can ensure that my voltage/amperage will not exceed the device limitations?

1 year ago

1) You don't want a higher voltage.

2) But put as many strings in parallel as you want. The pump will only use as much current as in needs.

the_phantom_boy (author)  iceng1 year ago

Last one...
Do i need to worry about those really thin cables?
http://ecx.images-amazon.com/images/I/51xI0sxGyUL....

1 year ago

Fair question each of those wires should handle 3A but triple the gauge to your receptacle ( every 3 gauges wire dia doubles )..

If the vinyl melts 105'C its too hot (you and I can hold 50'C metal).. If it gets warm to the touch you may be loosing voltage and need to add more wire.

BTW those battery holders, like to (or were designed) to split plastic at the top and bot due to spring pressure. Banding helps to prevent that.

the_phantom_boy (author)  iceng1 year ago

So... here we are...
I put everything together (except the switch | i don't believe that is necessary after all).

But i measure an output of 16v, because of the "flexibility" in some of those batteries.
Some can hold up to 4.10v, when some are around 4.01v.

I assume that i measure 16v because there is no load on that thing and when I do plug that pump, it will fall a bit lower than 14v maybe...

Am i correct? Or i will have a problem with that 12v pump?

1 year ago

Any machine made for 12VDC has to be able to work on a car that battery that can see 14.5 Volts when the engine is charging or more when using some power AC to DC battery chargers...

If your seriously worried about your pump you can always put one or two 1N400x diodes in series with the pump ( each diode drops 0.7v ).

I would have the volt meter on the battery and just try it for a minute to see if the voltage drops to the calculated level and the pump starts to fill your mattress..

the_phantom_boy (author)  iceng1 year ago

Once again, you cover every aspect with your answer!
Thank you so much!

the_phantom_boy (author)  iceng1 year ago

I order 4 battery cases, a small on/off switch, and a female car socket...
In 20 days (give or take a few) we will know! :P

(i will update with the results)

1 year ago

No lung power

the_phantom_boy (author)  iceng1 year ago

Meaning?

1 year ago

Humor, as to the annoying job of inflating camping gear in the old way by mouth :-)

the_phantom_boy (author)  iceng1 year ago

haha... sorry... english is not my native language so... i m a bit slow! :P

and.. you can NOT inflate that beast with your mouth!
my lungs will be like... "oooooh no! i'm outta here"!!!

and i will be standing like a fool in the sand... watching my lungs rolling away...!

the_phantom_boy (author)  iceng1 year ago

Thank you for your time and answers...!
I really appreciate it!

1. use standart battery from UPS backup system

3.5-40A

2. lipo battery + dc-dc stepper

3. car battery

1 year ago

Thank you for your suggestions...
1) I am trying to be as light as possible... so car/motorbike battery is out of the picture.
2) I choose 18650 batteries because i have a lot of "bad" laptop batteries
in my disposal... so there is no extra cost for lipo battery.
3) UPS battery is a choice, considering the low cost... but after all its a small DIY project! Thats the interesting part! :)

iceng1 year ago

Yes, Correct..

Remember each string should be charged separately.

rickharris1 year ago

Radio control battery packs are both energy dense and come in a variety of voltages.

http://www.hobbyking.com/hobbyking/store/__86__85_...

You will also need a charger.

the_phantom_boy (author)  rickharris1 year ago

I choose 18650 batteries because i have a lot of "bad" laptop batteries in my disposal... so there is no extra cost for batteries.

Downunder35m1 year ago

What's the point of being able to run it for just a few minutes until you need recharging?
Simple multiply the amps required for the pump by the hours it needs to be able to run - that's the AH required for your battery.
Keep in mind that you should ue a deep cycle battery rated for the max amp your pump needs.

the_phantom_boy (author)  Downunder35m1 year ago

The point is that i will only need that thing once per trip, to fill the mattress with air!
Something that can be done in 2-3 minutes.

After that i will recharge the battery pack and keep it ready for the next time!
That is the only use that i want it for, but i also want it to be as light as possible and that is why i am going for a DIY project and not a car battery...

If i read correctly on "google_blabla_random_website", i need to know the C rating of the batteries that i am using.
I have for example an "SE US18650GR" battery but i can not find anything about C rating.
Thats why i can not calculate the exact amount of batteries that i need to provide 6A!
Lack of knowledge! Thats my main issue here...

Lets say that the one 18650 battery is 3.7V/2000mAH, and I need 12v/6Amps.

If i connect 4*18650 in series, i will have 14,8V and if i connect 3 sets of 4*18650 in parallel, i will have 18.5V at 6Amps...
Is that correct so far?