9-12vdc Latching Solenoid Schematic

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
ctand
 
Posts: 16
Joined: Sun Jul 06, 2014 2:25 am

9-12vdc Latching Solenoid Schematic

Post by ctand »

I am working on a solar gardening project (that will eventually be opensourced) that uses many parts from Adafruit although this bit isn't one of them. I am just putting this out there to see if anyone has any design comments or critiques. The design is modified from a Minty Valve Controller sourced from Ray's Hobby. I wanted to simplify his design so instead of using an H-Bridge to control polarity I went with a low-voltage DPDT relay. I have also reconfigured the voltage divider from the original design so that this can be used to control 9-12vdc Hunter DC Latching Solenoids instead of the 24vdc he is using in his project. This is my first schematic ever so please be kind. I'm not an EE, just a hobbyist. I haven't put it together yet but plan to order the components tomorrow. The only design change I will probably make is to have this connected to the Li-Poly Batt the project is powered by. I can see reset issues arising from trying to use vcc.

Note that the resistors should be 1% Metal Film and C2 needs to be at least 12v tolerant. (I'm ordering a 16v Cap)

Image

User avatar
zener
 
Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: 9-12vdc Latching Solenoid Schematic

Post by zener »

Overall it looks pretty good. Here are some issues I see:

The solenoid just wants a "pulse" (power briefly) to change state. This is how it conserves battery life. Even if you don't care about battery life, if you power it constantly it will probably draw more power than you have, and it may even overheat since it is not built for continuous power. The original design had two control pins from the Arduino. When they were both low then the solenoid is off. Raising one side or the other switched it one way or the other. (Raising both at the same time would cause a short.) I recommend you put another relay stage on the 12V supply to the direction relay, to produce the pulse.

The other issue is power again. You will notice the original design is powered from a battery, where you are using the Arduino supply. I don't think the Arduino supply can handle too much current. Another issue is if the Arduino power (voltage) is disturbed in some way then your brain (Arduino) scrambles (Resets). My main concern is the capacitors in the circuit, especially the 2200 uF. When that cap is powered up (charged) it will put a big instantaneous load on your supply, dropping out the voltage and resetting the processor. There are a couple of ways to address this:

1) Use a separate supply as in the original design.
2) Reduce the capacitance.

Another approach that could possibly address both issues I brought up is to use the regulator enable pin to produce the pulse. So you would get rid of the 2200uF cap and only turn on the regulator when you want to change solenoid direction. As soon as the 12V came up the solenoid would switch then you could turn it off again. This would eliminate the need for the second relay also.

BTW, although I could find no electrical specs for that solenoid, I found some info suggesting it operates down to 6V.

User avatar
ctand
 
Posts: 16
Joined: Sun Jul 06, 2014 2:25 am

Re: 9-12vdc Latching Solenoid Schematic

Post by ctand »

Thanks so much! Yeah I even wrote in the OP that it was a mistake to have the circuit powered by VCC. I have already changed that to 3.7v from the LiPo. I wanted to just control the pulse with the SHDN pin. I planned to just keep the pin high until I needed the pulse and then just set it low and then high again for the pulse. (the spec sheet says "Pull high to shut down the device. Ground for normal operation.") I might throw another DPDT relay in though for the pulse if that isn't a good solution. I also do plan to try and lower C2 greatly. (330uF as a starting point) I'm not really sure what you mean when you say "Voltage Regulator Pin" though. The only pins I'm not using on this IC are LBI and LBO which are used as Low-Battery Comparator Input. Also, I read that these solenoids require around 1A to fire so I can't see not having a C2 in the circuit.

The latching solenoid might work as low as 6v but I'm not willing to chance it. The normal operating voltage from the manufacturer's DC controllers are 12vdc as far as I know.

Thanks again!

User avatar
zener
 
Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: 9-12vdc Latching Solenoid Schematic

Post by zener »

The voltage regulator enable pin AKA shutdown AKA SHDN

The info I saw showed the valve controllers powered by a 9v battery and they said the valves worked with any controller that runs on 6-9 v or something like that. They also said the 9v battery would last a season. So if it is drawing an amp the pulse is very short.

User avatar
ctand
 
Posts: 16
Joined: Sun Jul 06, 2014 2:25 am

Re: 9-12vdc Latching Solenoid Schematic

Post by ctand »

Zener wrote:The voltage regulator enable pin AKA shutdown AKA SHDN

The info I saw showed the valve controllers powered by a 9v battery and they said the valves worked with any controller that runs on 6-9 v or something like that. They also said the 9v battery would last a season. So if it is drawing an amp the pulse is very short.
Yeah the pulse is like 25ms or something. It just needs a fraction of a second. Also the fact that they were powered by a 9v doesn't mean there wasn't a voltage boost in the circuit. They can be triggered by a 9vdc alkaline battery for testing but under normal usage I am pretty sure they are operated around 12v.

User avatar
zener
 
Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: 9-12vdc Latching Solenoid Schematic

Post by zener »

I will respectfully disagree. A 9v battery would be challenged enough without having to supply a booster circuit.

Only other thing I will say is put fly back protection on the solenoid. Since it is changing polarity you can't just put a diode like on the relay coil. You will need to use an RC circuit or MOV. Technically you could also use back to back zeners. I would probably use an MOV.

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”