# 1.5V simple step up

Discussion in 'The Projects Forum' started by graeth, Feb 20, 2013.

1. ### graeth Thread Starter New Member

Feb 18, 2013
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First off, I apologize if this is the wrong forum. Given that this is a personal project of mine I decided here would be appropriate. Second, I'm a mechanical engineer so these will probably be simplistic questions for you experts (my school wouldn't let me take electronic classes).

I have a basic design in my head for circuit that uses a battery source to power a solenoid valve and is activated/closed by a reed switch. Its a 12v solenoid, but I would like to avoid the added weight of 8 AA batteries. I was hoping to use 1 or 2 batteries at most to charge a 12V capacitor(s) that would dump into the solenoid when a reed switch is tripped.

I'm pretty sure that I can't just connect them together because in my mind the battery wouldn't be able to get the capacitor to, let alone above, 1.4/1.5V. So I'm looking for a way to step up the voltage with minimal complexity/space/weight--no ICs, microprocessors and stuff along those lines.

2. ### wayneh Expert

Sep 9, 2010
12,379
3,232
Just use a small 12v battery, or 2 x 6V batteries, or even 2 9V.

3. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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There are few problems.

1. First how much current does the 12V solenoid needs to effectively pull the core.

2. Charging a cap to 12V tht is enuf to activate a solenoid might not be feasible unless ur cap is of very high capacitance. So to charge tht cap will take a quite long.

3. U need a boost converter to boost a low voltage to 12V. This will complicate the situation where u well need to figure out the current input the battery can supply.

Solution is to use a Li-on or a Li-po to supply the boost converter.
Simple and effective.

Check ebay for boost converters. There are cheap, small yet effective circuits that can use a 3.7V li-on boost converter. The output is variable, so U can use to almost any circuit. And the current output is quite high too

4. ### graeth Thread Starter New Member

Feb 18, 2013
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Was trying to keep it simple, trying to stay away from specialty batteries and prefabbed circuits. Someone made a joule thief that bumped to 12v, guess I could look into that again.

The numbers I'm seeing are between 300 and 500 mah for varying solenoids in my range.

My understanding is that with the higher voltage comes the slower amperage from such a small source. Since I was looking at possibly charging a whole bank of capacitors to activate the solenoid, my target charging time was around a minute or under. (I was basing my estimate off what little I know about camera flashes with their smaller mF ratings).

5. ### takao21203 Distinguished Member

Apr 28, 2012
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There is one application note where a linear voltage regulator is used as a voltage booster with external PNP.

No IC.

Built is as buck from 60v to 5v, using a coil from an old CFL.

It makes a whining noise, old circuit from the 1970s.

LM317.

I use a small LM317M with tab.

6. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
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This is the cheapest way to do it assuming the current is enough for your app. It could be run on anything from about 1.5V (standard alkaline battery) up to about 4.2V (Li battery).

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7. ### graeth Thread Starter New Member

Feb 18, 2013
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Are those 555 timer chips stand alone units? I thought they had to be hooked up to a controller.If thats the case I guess I can just build small units and that wouldn't be that much of an impact.

8. ### StayatHomeElectronics Well-Known Member

Sep 25, 2008
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The 555 timer is definitely a stand alone unit. It does not require any type of controller to operate.

9. ### graeth Thread Starter New Member

Feb 18, 2013
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Well thanks for that; all of you.

I guess if thats the cheapest, gotta weigh if I want ot got easy and just buy a prefabbed one.

10. ### takao21203 Distinguished Member

Apr 28, 2012
3,578
463
Really nearly impossible to answer without to know the rating of the solenoid.

Having a capacitor bank for such a purpose is unusual + might be more expensive than a booster chip.

All depends how much current you need for how long.

A jouletheif can not really produce 100s of mA, sure they can be patched, but then they are not a classic jouletheif anymore.

I use a small PCB sometimes to drive 12V relays at 5V, but these are small relays, not large power relays.

11. ### graeth Thread Starter New Member

Feb 18, 2013
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Yeah, I read that the supply was lower under a joule thief, that was what led me to want to use the system to charge some capacitors.

But if its really this much hassle, might as well just buy a prefabbed one from ebay?

12. ### bountyhunter Well-Known Member

Sep 7, 2009
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stand alone unit. The circuit shown is complete.