Need approach: 250mS Current dump into 4 ohm inductor

Log in or register to post comments
Go To Last Post
28 posts / 0 new
Author
Message
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
#1
Posted by stevech: Wed. Jun 4, 2014 - 02:36 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Problem (I've tried but faild so far)

Circuit to run on small batteries - small as possible.
Feed a pulse of current into a 4.5 ohm inductive load that is a solenoid of sorts - moves a cylindrical magnet one or the other way, depending on +/- current flow in coil. Moves very infrequently, e.g., + current, then 10 minutes later - current, then a day or so goes by.

I tried a step-up converter charging a 3300uF capacitor. Then an H-bridge to get the current flow. Just not enough power - don't know if it's too little current or too few watt/seconds. But solenoid doesn't mechanically move the magnet sufficiently.

For drill, I tried a wall wart transformer claiming to provide 1700mA at 12V. Not. It droops to 6V with that 4.5ohm load.

I've not tried an overkill fat 12V battery and the H-bridge as even if it worked, it would be too large.

An ideas?

Tags:

Learning and Information, General Electronics
Top
ignoramus
ignoramus's picture
Level: Raving Lunatic
Joined: Sun. Aug 4, 2002
Posts: 2124 View posts
Location: Brisbane, Australia
Posted by ignoramus: Wed. Jun 4, 2014 - 02:54 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

How much current?

Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Wed. Jun 4, 2014 - 02:58 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Watts is Watts. .25 sec into 4.5 ohms -> watts = I^2 x R 12V/4.5ohms is 2.7 amps. (Batteries need to be able to hump this out for .25 sec). This is 34 watts. A garden tractor battery might work?

Imagecraft compiler user

Top
meslomp
meslomp's picture
Level: Raving Lunatic
Joined: Wed. May 2, 2007
Posts: 6136 View posts
Location: Nieuwegein, Netherlands
Posted by meslomp: Wed. Jun 4, 2014 - 05:54 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

as bob suggested, but not said....
your 12V power supply is not big enough.
12V/4.5Ohm gives 2.7Amp. You power supply is not able to deliver that, so it will immediately drop.
Note that the initial current might be a lot higher than the 2.7Amp.
Q=CU =IT
lets say you may drop 1V in the 0.25sec time span with 5Amp.....
so C=IT/U
(0.25*5)/1 gives a cap of 1F needed, don't think you will find those in 25V version(need to be a lot higher then the working voltage specially in that range) 1F cap is a gold cap and they normally do not go above 5,5V due to mechanical/electrical/chemical restraints.

But You need to get a bigger supply to start with....

regards

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Wed. Jun 4, 2014 - 02:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Battery operation is needed. The wall wart was just an experiment. This solenoid is often used with consumer products that use AA batteries. They must use some sort of energy storage from an switched power supply to be able to dump that much power for a 1/4 or 1/3 or so second. I'll look at the sizes of super-caps like that.

Top
Chuck-Rowst
Chuck-Rowst's picture
Level: Resident
Joined: Tue. Jul 19, 2011
Posts: 708 View posts
Posted by Chuck-Rowst: Wed. Jun 4, 2014 - 02:51 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

So, why don't you get one of the consumer products its used in and reverse engineer its circuitry? If not to copy, at least to understand one way it can be done.

Top
RickB
RickB's picture
Level: Posting Freak
Joined: Sun. Jan 30, 2005
Posts: 1343 View posts
Location: Junction City, OR USA
Posted by RickB: Wed. Jun 4, 2014 - 03:52 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

A much higher voltage to overcome the lr time constant? I.e. constant current drive for a short time similar to a stepper driver.

Top
tpappano
tpappano's picture
Level: Raving Lunatic
Joined: Mon. Dec 1, 2003
Posts: 2946 View posts
Posted by tpappano: Wed. Jun 4, 2014 - 05:27 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm impressed by how much 'supercaps' have evolved, now with some having *very* low internal resistance. A guy on "the YouTube" replaced the battery in his car with six of them in series.

Tom Pappano
Tulsa, Oklahoma

Top
sbennett
sbennett's picture
Level: Posting Freak
Joined: Mon. Nov 19, 2001
Posts: 1205 View posts
Location: San Luis Obispo, California
Posted by sbennett: Wed. Jun 4, 2014 - 05:42 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Jack Ganssle on "Using a capacitor to sustain battery life"
[url]http://www.embedded.com/electronics-blogs/break-points/4430050/Using-a-c...

Top
sparrow2
sparrow2's picture
Level: Raving Lunatic
Joined: Mon. Oct 7, 2002
Posts: 6979 View posts
Location: Denmark
Posted by sparrow2: Wed. Jun 4, 2014 - 05:58 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

A small hand held vacuum cleaner often use 3 AA batt. and use about 4 Amps so perhaps that quality of batt's will work.

Top
sbennett
sbennett's picture
Level: Posting Freak
Joined: Mon. Nov 19, 2001
Posts: 1205 View posts
Location: San Luis Obispo, California
Posted by sbennett: Wed. Jun 4, 2014 - 06:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The Hunter Industries Node irrigation controller operates off of a 9V alkaline battery for about a year. It switches a low power latching solenoid valve to control a slave irrigation solenoid valve, using the controlled water pressure to drive the slave.

[url]http://www.hunterindustries.com/irrigation-product/controllers/node[/url]

Digging further, I found a similar product with specifications for their latching solenoid valve.

Battery Powered Controllers & Valves
[url]http://www.digcorp.com/irrigation-professional/battery-powered-controlle...

R710DC Solenoid - 3 Ohms
[url]http://www.digcorp.com/professional-irrigation-products/r710dc-solenoid[...

Stan

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Wed. Jun 4, 2014 - 07:42 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

sbennett wrote:
The Hunter Industries Node irrigation controller operates off of a 9V alkaline battery for about a year. It switches a low power latching solenoid valve to control a slave irrigation solenoid valve, using the controlled water pressure to drive the slave.

http://www.hunterindustries.com/irrigation-product/controllers/node

Digging further, I found a similar product with specifications for their latching solenoid valve.

Battery Powered Controllers & Valves
http://www.digcorp.com/irrigation-professional/battery-powered-controllers-valves

R710DC Solenoid - 3 Ohms
http://www.digcorp.com/professional-irrigation-products/r710dc-solenoid

Stan

Thanks... that solenoid spec sheet says 20-100mSec which is what I had guessed having been unable to find such a spec for a different brand. I'll try an alkaline 9V - I didn't think it could deliver 1-2 Amps even pulsed due to internal resistance.
I doubt a supercap is used... to new/high tech to be in such consumer products yet.

One of two I'm fiddling with
http://www.sprinklersupplies4les...

Top
sbennett
sbennett's picture
Level: Posting Freak
Joined: Mon. Nov 19, 2001
Posts: 1205 View posts
Location: San Luis Obispo, California
Posted by sbennett: Wed. Jun 4, 2014 - 08:35 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

That sprinklersupplies4less link gives a model number of Orbit58874N. Searching for the Orbit p/n I found this discussion about an orbit valve internals.
-- Ray's Hobby Projects: How to control Orbit 62035 valve
[url]http://rayshobby.blogspot.com/2010/08/how-to-control-orbit-62035-valve.h...

A supercap might be useful if charged immediately before an actuation event, otherwise disconnected from the battery. Also consider low ESR organic polymer electrolytics as an alternate or in parallel with supercaps?
[url=http://www.digikey.com/product-search/en?pv13=65&pv13=77&FV=fff40002%2Cf... Aluminum - Polymer Capacitors[/url]

Stan

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Wed. Jun 4, 2014 - 08:53 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ah, thanks a zillion. Those guys are talking about pulsed 24VDC whereas I've been struggling with 9-12V.

The AC valves are of course usually 12V but they are not magnet-memory push/pull.

Top
ignoramus
ignoramus's picture
Level: Raving Lunatic
Joined: Sun. Aug 4, 2002
Posts: 2124 View posts
Location: Brisbane, Australia
Posted by ignoramus: Thu. Jun 5, 2014 - 12:42 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

... tried and failed...

Implies You have a sample solenoid in Your sticky mitt.

The question still stands..how much current is required to energize the solenoid?

Have You measured at what current will the coil be sufficiently excited?

Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Thu. Jun 5, 2014 - 02:08 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Just post the L and the Ohms and we can calc the time constant etc.

Imagecraft compiler user

Top
gchapman
gchapman's picture
Level: 10k+ Postman
Joined: Tue. Jan 9, 2007
Posts: 12416 View posts
Location: Clay County, Texas, u.S.A.
Posted by gchapman: Thu. Jun 5, 2014 - 06:07 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

stevech wrote:
I've not tried an overkill fat 12V battery and the H-bridge as even if it worked, it would be too large.
The following LTO cell has a 30C (39 amp) max 5 second discharge:
LTO 1865 Rechargeable Cell: 2.4V 1300 mAh, 39A rated 3.12Wh (BatterySpace)
A battery can be by soldered cells on a PCB.
There are smaller cells if that 18mm dia x 65mm cell is too large.
"Applications: Ideal for High Rate and High Cycle Life Applications"

"Dare to be naïve." - Buckminster Fuller

Top
Torby
Torby's picture
Level: 10k+ Postman
Joined: Tue. Nov 11, 2003
Posts: 10327 View posts
Location: Bartlesville Oklahoma USA
Posted by Torby: Thu. Jun 5, 2014 - 10:50 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Grab a handfull of capacitors and an adjustable power supply.

Last time I was fiddling with a solenoid, and told it took 4 amps at 18 volts to operate, but would overheat and smoke if you left the power on and so on, after playing a while, I found I could reliably trip it with a 1000uF capacitor charged to 5v. Then I build a circuit to charge the cap to 5v through a 1k resistor, and an FET to dump the cap through the coil.

So, with a handful of capacitors and an adjustable power supply, figure out if any of them can reliably trip your gadget.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Fri. Jun 6, 2014 - 06:31 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I have done some tests, but not enough. I think the average current (excluding the inrush) is about 200mA, and < 100mSec is needed.

The OpenSprinkler schematic shows a super-simple pulse from the MCU to a transistor driver to ring a small inductor and a diode/capacitor to store the pulsed power. It has the MCU's A/D hooked up such that perhaps the MCU pulses until the voltage reaches X. Then it toggles the dump switch to feed the capacitor's energy into the solenoid (with the desired current flow direction). This is to alter the solenoid's resting latch condition (on/off valve).

I pencil and paper looked at using the solenoid's coil as the inductor for the charge pump. Got mired in FET switches. It probably could work.

Well, I'll get time to fiddle with 18 or 24V pulses and see what happens.

Top
Torby
Torby's picture
Level: 10k+ Postman
Joined: Tue. Nov 11, 2003
Posts: 10327 View posts
Location: Bartlesville Oklahoma USA
Posted by Torby: Fri. Jun 6, 2014 - 12:50 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Cute. They're using a simple boost converter to charge up a capacitor, then dumping the cap through the solenoid. Just need a great big capacitor.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

Top
Bronze Markdavid.prentice
david.prentice's picture
Level: 10k+ Postman
Joined: Sat. Feb 12, 2005
Posts: 30063 View posts
Location: Wormshill, England
Posted by david.prentice: Fri. Jun 6, 2014 - 01:04 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Think about a camera flash or a electric stock fence.

The camera flash charges up a BFC and then discharges it through the lamp/tube. I am not sure of flash voltages, currents or energy.

Stock fencers charge a BFC and then use an inductor to create the 20kV pulse. Battery fence energisers deliver less than a Joule. Some mains energisers deliver a few Joules. There are laws that regulate how much energy you can put into the fence. i.e. you don't want to kill the cows.

Oh, a regular AA cell stores quite a few Joules.

David.

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Fri. Jun 6, 2014 - 07:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I hope to fiddle with a simple BFC design this weekend. If I can find a suitable inductor in my junk boxes.

Top
Bronze Markdavid.prentice
david.prentice's picture
Level: 10k+ Postman
Joined: Sat. Feb 12, 2005
Posts: 30063 View posts
Location: Wormshill, England
Posted by david.prentice: Fri. Jun 6, 2014 - 09:05 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The Boost will use an inductor of some sort. The faster the oscillator, the smaller the inductor.

The BFC is generally a good plastic dielectric. i.e. not electrolytic. Electrolytics do not like being discharged rapidly.

David.

Top
stevech
stevech's picture
Level: Raving Lunatic
Joined: Tue. Dec 18, 2001
Posts: 6119 View posts
Posted by stevech: Fri. Jun 6, 2014 - 10:41 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

david.prentice wrote:
The Boost will use an inductor of some sort. The faster the oscillator, the smaller the inductor.

The BFC is generally a good plastic dielectric. i.e. not electrolytic. Electrolytics do not like being discharged rapidly.

David.

Thanks for the capacitor tip.

Top
tpappano
tpappano's picture
Level: Raving Lunatic
Joined: Mon. Dec 1, 2003
Posts: 2946 View posts
Posted by tpappano: Fri. Jun 6, 2014 - 10:55 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
The BFC is generally a good plastic dielectric. i.e. not electrolytic. Electrolytics do not like being discharged rapidly.

Really?? How many millions of xenon strobe lights have been sold in the last 60 years or so? They pretty much all used electrolytics to good effect 8)

Tom Pappano
Tulsa, Oklahoma

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 24375 View posts
Location: Melbourne,Australia
Posted by Kartman: Sat. Jun 7, 2014 - 11:12 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Strobes have pretty low repetition rates, whereas if it were a CDI unit for an engine, an electro probably wouldn't last too long.

Top
tpappano
tpappano's picture
Level: Raving Lunatic
Joined: Mon. Dec 1, 2003
Posts: 2946 View posts
Posted by tpappano: Sat. Jun 7, 2014 - 03:53 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
Strobes have pretty low repetition rates, whereas if it were a CDI unit for an engine, an electro probably wouldn't last too long.

Sure, but the OP's application seems to be a sprinkler timer, a very low repetition rate situation. Anyway I just thought is was unfair to say electrolytics don't like being discharged rapidly. Electrolytics *do* like their heating from internal resistance to be kept within acceptable limits so that their design lifetime can be achieved. Rapid charging and discharging could cause excessive heating shortening a caps life, but then one could also consider a physically larger/lower esr part for that sort of application. A film cap for a CDI is a good fit because, among other things, the energy per spark is low. A film cap big enough to operate a solenoid might might take up too much room in the OP's box 8)

Tom Pappano
Tulsa, Oklahoma

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 24375 View posts
Location: Melbourne,Australia
Posted by Kartman: Sun. Jun 8, 2014 - 04:52 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yep, poor ol' electro's get the blame for a lot of things these days! Where would we be without them?

Top