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Author Topic: [Solved] Solenoid Questions - Correct Transistor  (Read 1491 times)
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Radelaide!
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Hello forum,

I'm about to start a new project using an old solenoid I have - but I can't find a datasheet for it anywhere (and it looks like the manufacturer has been sold on as well). All I know is that it's rated for 9VDC and is a pushing solenoid.

With that knowledge I'm wanting to trigger it using my Arduino, but I need to figure out what transistor to get. I did try getting a resistance reading from it, but it only gave me about 2 ohms. Would I be correct in thinking I need one that can handle over 4.5A on the collector?

Also on a side note - I'm having trouble getting it to fire off a 9V battery, but I can get it to trigger with 4 AAs (6V pack). I know the battery is OK, and it does give a reading around 8.5V.

Thanks for the help
« Last Edit: February 23, 2012, 04:55:22 pm by SilkyPantsDan » Logged

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If indeed the coil resistance is 2 ohms then that is one powerful solenoid. You will find it impossible to supply 4.5 amps from a 9 volt battery, as they have too much internal resistance to allow that much current to flow. A logic level MOSFET power transistor would be a good candidate to control the solenoid, along with a 9vdc power source capable of supplying 5 amps or better. However unless you absolutely require that large a solenoid, it's a pretty power hungry device, I would look for a more conventionally size solenoid. What are you trying to activate with the solenoid?


http://www.sparkfun.com/products/10213


Lefty
« Last Edit: February 09, 2012, 06:58:39 pm by retrolefty » Logged

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Well a PP3 sized 9V battery is designed for 100mA or less, no way will be give you the current that solenoid needs - its a powerful one.

C or D cells are more like what it needs for battery power, or possibly if being pulsed only a large electrolytic capacitor (33,000uF or more) might be useful to carry the transient high currents.

For that sort of current a logic level MOSFET would be a good choice, easy to drive directly and no problem with the load - just choose one with 0.03 ohm Rds(on) (or lower) at Vgs=4.5V...  Just a 220ohm resistor from gate to Arduino pin and a 10k resistor from gate to source to turn it off by default.  Don't forget a diode backwards across the winding to prevent high voltage transients (basically look at any of the relay or solenoid driving circuits on the forum)
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Radelaide!
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Thanks for the quick reply guys.

The solenoid is from my paintball marker - and for fun I'm writing my own board, so anything larger than a 9V battery is no good. I know the solenoid can be driven from a 9V battery as the stock board can do it fine (although I'm guessing it could be stepping up the current or something along the way).

Specifically the solenoid will only be triggered for a fraction of a second (somewhere in the ballpark of 3-5 milliseconds) to push the sear pin.

I'll have a look a bit closer at the board tonight and attach a picture of the solenoid itself too

EDIT: Just to clarify in case I did it wrong - the resistance reading was simply what my multimeter told me across the pins, not taking into account anything else

EDIT #2: The part number for the solenoid is Emessem 9954/0312 9VDC-PD if that helps anyone
« Last Edit: February 09, 2012, 07:54:46 pm by SilkyPantsDan » Logged

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You can "ping" a solenoid once from a lower current by charging a capacitor, and then turning it on with a pulse. Then you have to re-charge the capacitor again to do it all over.
Does your 9V-battery-based board have one or more large capacitors on it?
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Radelaide!
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It sure does, looks to be about 2200uF (had to go by internet images).

I don't have the board on me atm, but was going to check the traces and see if I can get a reading off it running at the time later

EDIT: Further research indicates it might be a 2200uF 16V Electo type.
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Radelaide!
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OK - just ran some tests, but I think my multimeter might not be the best tool for the job as it only updates the screen every second.

Driving the solenoid from my 6v battery pack seems to hold around 2.5A, so I think the 4.5A estimate may be about right.

I haven't been able to get much of a reading from the original board as the longest time I can hold it open is 4ms, and trying to get a voltage reading gave me a max of .3V which I don't think is right.

Looking at the board itself (there are two solenoids that drive separately, and I have the datasheet for the other (6VDC @ 0.5W = ~84mA)) there are two transistor looking parts for each solenoid connector with TPS021L then under that looks like I@R440 (the @ is some symbol thats hard to make out). Looking on Element14 I can find 3 Mosfets rated around 100A

Also in regards to the capacitor - the rating on it reads 2200uF 10V, but as for the connection it's hard to make out on the board, but the -ve pin is connected to what I assume is the ground copper fill.

I do have some photos, but they aren't the best. Will try get some better ones, as well as trying to find some better measurement tools to borrow.

EDIT:
Forgot to mention, both connectors also have diodes next to them as well, and seem to trace to a SMT resistor with rating 104 (100k?)
« Last Edit: February 10, 2012, 08:25:24 pm by SilkyPantsDan » Logged

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See attached. The mosfet can be any TO220 N-channel logic level mosfet with Rds(on) @ 4.5v or 5v no more than about 0.2 ohms. Diode can be 1N4001 assuming you're going to fully discharge the capacitor each time, or if you're not sure, go for a 5A rectifier diode instead.


* Scan 79.JPG (65.01 KB, 1653x1165 - viewed 34 times.)
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Radelaide!
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Hey guys,

First off thanks for all the help. I'm looking at getting the parts shortly and just want to clear up which MOSFET to get as I'v got two different RDS(on) values that I shouldn't exceed.

Going with what dc42 has said I'm thinking of grabbing some of these with a value of 0.2 ohms, but just reading back over the thread MarkT and retrolefty have linked to ones with even lower values (0.03 and 0.047/0.035 respectfully).

Just curious which values I shouldn't exceed, and how to determine this in the future (or what I should look for to learn more)

Thanks again

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Hey guys,

First off thanks for all the help. I'm looking at getting the parts shortly and just want to clear up which MOSFET to get as I'v got two different RDS(on) values that I shouldn't exceed.

Going with what dc42 has said I'm thinking of grabbing some of these with a value of 0.2 ohms, but just reading back over the thread MarkT and retrolefty have linked to ones with even lower values (0.03 and 0.047/0.035 respectfully).

Just curious which values I shouldn't exceed, and how to determine this in the future (or what I should look for to learn more)

Thanks again



Everything being equal the lower the Ron value the better and the less heat will be dissapated by the mosfet package for a given current flow, (I squared X Ron is the heat loss). So if price isn't a big factor and the device is rated well over the voltage and current used in your circuit (go with with at least 200% voltage and current max rating for the device or higher) then pick the one with the lower Ron value.

Lefty
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Radelaide!
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Price isn't really a factor - of the three I found around those values it's only a matter of cents.

My main problem is I don't know the max voltage and current for the solenoid, only that it runs off 9VDC. As far as my circuit goes - this would definitely be the largest thing I'm running off it at this stage (down the line I would like to add an OLED, but want to get the basics going first).

The plan is to run the solenoid directly from the battery (with the help of the capacitor to get it moving) while everything else will be running from 5V (Breadboard Arduino for the moment).

I have the basics for coding and framework in place at the moment (with LEDs in place of where the solenoids would run) and want to move to the point where I can get them firing.

If it would help I could sketch up a more complete plan, but at the moment it's really nothing more than a switch and the two leds

Attached is nothing more than dc42's drawing done in eagle - this is how I intend to hook it up as well (just want to double check I read it right). SEAR goes to an output pin and the solenoid is connected via a small connector and a very short length of wire


* SearScheme.png (5.89 KB, 403x234 - viewed 53 times.)
« Last Edit: February 13, 2012, 08:57:53 pm by SilkyPantsDan » Logged

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With that drawing, only the capacitor will be powering the solenoid. That may be sufficient. I'd look for a bigger capacitor to make sure, though :-)
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Radelaide!
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Just a quick update - and to give more info for anyone with a similar problem.

Managed to get to my local and grabbed a 2200uF 16V cap and 6A Diode (rated for 1000V it seems  smiley-eek) and hooked up a tiny circuit with a switch in place of the MOSFET (as I couldn't find a suitable one at Jaycar in my quick visit)

Everything worked great except for the recharge rate, so I removed the 220 ohm resistor to be greeted with the solenoid firing as fast as I could hit the switch \o/

Just a query - as I'm only assuming the RC equation would fit here - would I add the resistor and the solenoid resistance together for the equation? And what ill effects (if any) can I expect from removing the resistor from the circuit?

Thanks again for all the help - learning heaps in a new and exciting area smiley-grin
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Glad you got it working. What the resistor does is to limit the current flow after the solenoid has fired but before the switch is released or the mosfet turned off. It is worth keeping a resistor in the circuit to reduce the drain on the battery. The 220 ohm resistor will give you around 90% charge in 1 second. You can reduce its value to get the recharge speed you need, e.g. 47 ohms will recharge it to 90% in under a quarter of a second. Use a resistor with an adequate power rating so that it doesn't burn out if you hold the switch down, e.g. with 47 ohms the power dissipated in it would be a little under 2W if the battery is producing 9v (which it won't do for very long unless it is a lithium type).

Which RC equation are you referring to: the one for charging the capacitor through the resistor, or the one for discharging it through the solenoid? Either way, you don't need to add the solenoid resistance and the resistor value together.
« Last Edit: February 23, 2012, 07:23:14 am by dc42 » Logged

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Thanks for the quick reply dc42

The RC equation is just the standard one - T = RC. Didn't think to use it for discharging the capacitor.

As for the resistor, I might need to play around with some values to get the result I need, as it does need to recharge pretty quickly. (if there are any paintballers reading this, it's for use with an Autococker)

The firing cycle runs about 14ms currently, but is adjustable and will also be using a IR photo transistor in the future to speed it up further. If I'm calculating it right I'd still only need around 6 ohms to have the capacitor charged ready to fire again at the end of the cycle.

The flow goes something like this (I have this all running in a 0.1ms timer and looks to run fine with LEDs)

1) Trigger pulled, sear solenoid pin high
2 4ms later) sear solenoid pin low
3 2ms later) cocking solenoid pin high
4 5.5ms later) cocking solenoid pin low
5 2.4ms later) mark that we can fire again

As far as battery life goes, the stock board is pretty power hungry so its not a big deal so far, but it would be nice to be able to get a bit more out of it smiley
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