# Need 7 Volts of Instant Power Using AA Batteries Only!

Discussion in 'The Projects Forum' started by dc original, Sep 25, 2009.

1. ### dc original Thread Starter New Member

Sep 25, 2009
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Hi Everyone -

My name is Jason. I found your Forum browsing the net and hope you can make things a little more clear than other information I've found. Here we go...

I need to fire a solenoid (tubular, push-type) with 5 pounds of force using only batteries (anything you could find at Walgreens, whether it's AA's, a 9-volt, D's or whatever else). According to the solenoid specs I'll need around 7 volts instantly to produce the 5 pounds of force. I don't have the solenoid in hand yet to experiment but I'm told batteries alone will not give the instant voltage I need. So I'm researching capacitors and how they could help in this system (I was told to do some research on how a camera flash works). As far as recharging I'd need a new full charge within 30 seconds to a minute.

I'm a mechanical engineer working on a home mechanical project and am pretty much a layman when it comes to the above scenario. Any help would be appreciated.

Jason

2. ### blueroomelectronics AAC Fanatic!

Jul 22, 2007
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How far does that 5lbs of force have to move? What's the solenoids part number?

Apr 5, 2008
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Hello,

Each AA battery (Alkaline) is 1.5 Volts, so when you take 5 pieces it will make 7.5 Volts.
The voltage will drop over time (as the energy of the battery gets less).

http://www.educypedia.be/electronics/componentbattery.htm

Greetings,
Bertus

4. ### Wendy Moderator

Mar 24, 2008
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Use large capacitors to store that energy and for quick release. The batteries themselves can't do it, but they can charge capacitors, which can.

5. ### bountyhunter Well-Known Member

Sep 7, 2009
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NiCad batteries can deliver very high peak currents. You could use sixe cells in series. Alkaline or carbon zinc can not because their internal impedance is too high.

Sep 25, 2009
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7. ### dc original Thread Starter New Member

Sep 25, 2009
7
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Bertus - I was told just using (5) 1.5 volt AA's will not work due to the fact the power release will be too slow. I'll do some testing with this method on Monday when I recieve the solenoids but expect not to reach the 5 pounds of force I need.

Bill Marsden - I was thinking I may be able to use a relatively small capacitor (something just larger than the voltage I need) but am unsure how I would set-up the circuit. I'll be using a push button to activate the solenoid and an on/off toggle to active/kill the system.

Bounty Hunter - I'll be using NiCad's for my testing on Monday.

Thanks everyone for the quick replys. I think for my initial testing I'm now looking for some direction (circuit schematic) on how to route the batteries with the capacitor and solenoid. I read something briefly this morning that suggested I might also need a resistor to quickly recharge the capacitor after dumping it. Thoughts?

8. ### blueroomelectronics AAC Fanatic!

Jul 22, 2007
1,758
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Don't use ancient NiCad batteries, use modern NiMH batteries and 6xAA can deliver quite alot of current rather quickly.

9. ### dc original Thread Starter New Member

Sep 25, 2009
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For sure, picked up the NiMH today. Thanks.

10. ### dc original Thread Starter New Member

Sep 25, 2009
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What about using a single 9V battery?

11. ### Bernard AAC Fanatic!

Aug 7, 2008
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A " 9V " NiMH battery [8.4V ] is rated at 150mAH, GP 15F8H. @ a discharge rate of 10 C or 1.5A I believe, will fall short of your need of 5A, with out additional circuits. Photo flash unit should?? work @ about a US buck.Battery required??? Always more questions: How long does solenoid need to be on? What is maximum size of unit?

12. ### SgtWookie Expert

Jul 17, 2007
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From the page you linked to; which solenoid did you order?
The top one at 1/10 duty cycle with 7.1v has a coil resistance of 0.6 Ohms.

Have a look at the attached schematic and simulation. Click on the thumbnail below; you may have to click on the image again once it pops up in a new screen to see it full size.

V1 through V6 are six "AA" batteries connected in series.
S1 is a single-pole single-throw toggle switch; your power on/off switch.
The "A" in the yellow circle corresponds to the yellow trace below, showing about 9v when power is turned on at 0 seconds.

R1, D1, D2, Q1, and R2 make up a (more or less) constant current circuit. Maximum current output from the batteries is limited to about 30mA to extend their life, while keeping capacitor charge time reasonable; about 3 seconds to 95% charged

C1 is shown as a single large 10,000uF capacitor. It should be a minimum of 16v rating. It would be best to use multiple low-ESR type capacitors, but you could probably get away with 5 caps of around 2,200uF rating.

When S2 (a normally open pushbutton switch) is depressed, about 4.5A of current will get dumped through the solenoid's coil for a very brief amount of time; a few milliseconds.

D3 is necessary to take care of any reverse EMF that may occur due to "switch bounce" and the effect it has on starting/stopping current through a coil. Without D3, the solenoid coils' field collapse could generate very high peak voltages.

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13. ### bountyhunter Well-Known Member

Sep 7, 2009
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They still make NI-Cads. They have as low of lower internal impedance as NiMH, they just don't have as much A-hr rating which doesn't matter in this case. Ni-Cads are more tolerant of fast charging than NI-MH (and cost a lot less). NI-MH will work, just be careful about charging them.

14. ### Bernard AAC Fanatic!

Aug 7, 2008
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A 10k cap [ 10V @ 10k- 40mmX22mm ] charging thru 180 ohm from 9V alk. takes 10 measured seconds for 98% charge. Should work with either 22 or 23 AWG winding.

15. ### dc original Thread Starter New Member

Sep 25, 2009
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The solenoid only needs to be on for milliseconds. Maximum physical size should only be around an 1" in diameter.

16. ### dc original Thread Starter New Member

Sep 25, 2009
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Yes you were correct in picking the top solenoid 0.6 ohms of resistance. Thanks for the effort put forth in the schematic. A few milliseconds of current dump is all that's needed and capacitor recharge time could even be longer if it simplified anything. Forgive my simple questions but what does "Q" stand for in your schematic?

17. ### Bernard AAC Fanatic!

Aug 7, 2008
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For your impulse requirement, one of the cap. discharge ckts. should do fine, depending on which winding you selected.

18. ### Bernard AAC Fanatic!

Aug 7, 2008
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Q1 in Sgt's schem. is a PNP transister.