Attached Fritzing diagram. Not quite sure whether this is feasible. I will be intermittently switching on and off two solenoid valves (one for water, the other for gas) using a relay module while the nema motor will only be running when I'm injecting water.
Any insight or feedback would be greatly appreciated! Are there any safety concerns with this setup?
Forgot to mention that the motor shown in the diagram is a stepper motor for a syringe pump. Two arduinos will be used in this project, one to control the syringe pump and the other for the relay module/solenoid valves.
As drawn you have no control of the stepper motors. The stepper motor has two coils. Each coil has two wires. The motor is "stepped" by switching the coils on / off / reverse polarity in different combinations.
If you google stepper motor drive arduino you find a lot of information.
The solenoids look fine.
Not sure on the battery, it depends on your dutycycle. BTW the battery is a 7 Amp hour battery rated for 20 hours. So the "rated" current is 7 / 20 = amps. Still you might get away with this battery if your dutycycle is low.
Its an SLA it will output lots of amps without any difficulty (it is not rated for 20 hours - that's just the
reference time for capacity measurements).
Best to use a fuse with high current batteries like SLA and LiPo, then you can't accidently start a wiring fire.
The solenoid valves won't be a problem.
The stepper motor though is definitely not a 12V thing. Stepper motors are not voltage driven,
but current driven. Its a 1.3A NEMA17 sized stepper, so its winding resistance will be a few ohms at
most. Connect that across 12V lead acid battery and you will burnt it out rapidly.
You need to add a DRV8825 stepper driver module to your list of parts. Yes, that can happily be powered from
12V.
Key issue with lead acid (and all rechargable batteries come to that) - you need to prevent over-discharge
of the battery, ie have a way to shutdown when the battery voltage drops (for 12V lead acid 11V or 10.5V
is a possible threshold voltage). If you over-discharge such a battery you will wreck it. They must be
charged regularly in storage to 100% - every month or two - for the same reason.
The 7Ah capacity figure is for a new battery, fully charged, in optimal conditions. Expect a real-world
capacity of more like half of that in service (capacity falls with use and with age)
I have attached an updated diagram. Mark, you recommended a DRV8825 stepper driver module but I have a Big Easy Driver handy (Big Easy Driver - ROB-12859 - SparkFun Electronics). I just wanted to make sure that my battery would be able to power everything. I'm a novice at electronics so I'm at a lost as to what sort of calculations I should be doing.
If you look at the datasheet for the battery: https://drive.google.com/uc?export=download&id=0Bx8P1kzah0m8a08xTmhqeFhjSnc
You'll see that the capacity drops to about 4Ah at the 1 hour rate (ie 4A discharge), so its going
to struggle a little at that sort of current output, but the discharge curves show it will handle
a 3C discharge rate (21A) with just over a volt drop - I'd say don't pull more than 10A from this
particular battery.
So do these solenoid valve take many amps? If not you've got no problems at all.
