Maximum current available on Water solenoid Valve connector

If I’m understanding what you wanting to do, you’re wanting to wire your pump in series with the solenoid. If you do choose to wire them in series, you’ll see a voltage drop during the in rush period, and as a result, see a large in rush current owing to two inductive loads being in series. There’s also a chance that you burn out the motor (depends on the motor design). This is likely what you’re after with your question. If you have the option, the best answer might be wiring them in parallel and ensuring your wiring and power supply can handle the combined in rush load. That way, each device can operate unimpeded by the other.

You did not understand me correctly. I didn’t write that I want to put the solenoid and pump in series. :man_shrugging:
For sure they will go in parallel! :wink:
I just don’t want to overload the output nor the PCB which feeds the solenoid. But I can’t find any max. current ratings for it.

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Hi @masze does this page help you ?

[edit 0] Err, maybe not. You want the Farmduino v1.5 specs. for peripheral output loading ?

Not really. I know that the solenoid takes 160mA. But If I use e.g. the mentioned pump in the “Capture and use rainwater” in the mods section BUT in the 24V configuration (Seaflo SF.BP2–G.350–01 instead of SF.BP1–G.350–01.) will take 1A. But I’m not sure if I will able to source that. So If I know what the limits are I can source alternatives.

[edit] @jsimmonds Exactly! :smiley:

@masze I’ve been hunting around for Farmduino v1.5 { Specs., Schematics, . . . anything helpful } ™ . . nothing.

@roryaronson please help ! :slight_smile:

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Thanks @jebba for the schematics. Would be great if they’d be accessible directly on the farmbot website.

But my initial question about the max. amp rating is still not really answered. I just need to know how many amps I can draw without running into issues. :man_shrugging:

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@jebba thanks for all that trouble :slight_smile:

The max load current on the “current-sensing” peripheral outputs ( e.g. Water ) is still a mystery !
The datasheet for the power MOSFET says 27A at 70C Ambient . . who knows what the PCB traces, the connectors and wiring can safely deliver ?

Oh, I forgot the big one !
The official FarmBot 24V PSU ( by the specs ) delivers Output Power: 24 volt, 6.25 amp DC
total :slight_smile:

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Gotcha! Thanks for the clarification. That actually would be great info to know. If you’re going to pull that level of power (24 watts at full tilt) for extended period while driving the motors and powering an LED strip (perhaps running the pump without the rainhead attachment and using the FB as a soil etcher at night…because reasons :stuck_out_tongue: ), then a thermal management system for the PCB would also need to be thought about (as you and john point out, this would depend on the PCB design). In all seriousness, thanks for asking the question.

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@Gabriel From what I’ve seen you are the hardware guy who should be able to answer the question. :slightly_smiling_face:

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I see @jsimmonds has already provided many of the current ratings already, good investigating! In addition to the power supply (24V 6.25A) and MOSFET ratings mentioned, the Farmduino bill of materials listing has additional information about the board fuse (15A) and links to power and peripheral connector specifications (10A).

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Thanks @Gabriel for the (partial) clarification.

So let me make an example to verify if I’m right:

  • My supply has 24VDC and a 12A rating (due to solar system and DC/DC converter).
  • The board connector is the limiting factor of the outputs (10A).

If I mix that all together I could use a 24VDC pump which takes up to 5A without any issues for neither the MOSFET, connector, board or MY power supply (I let the rest take up to 7A to be on the safe side).

A short answer if I’m right or wrong would be great. :smiley:

Anyone? :thinking:

Yep, I’m an anyone :sunny:

Your EE maths checks out . . . Farmduino PCBs are hard to get at the moment, though :wink: ( if there are “audio-visual” effects around the PCB after the 5A pump runs for a little while :fire: )

That’s exactly why I’d like an answer to my calculations from the person who did the PCB layout. That person should know exactly the max. constant load possible. I expect that it is 10A as the connector but that’s not verified. :slightly_smiling_face:

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We haven’t done any testing with other power supplies that can supply more power, so anything beyond 150W total (24V at 6.25A) may have adverse effects, and I would not recommend it unless you are willing to risk your Farmduino.


Thanks @roryaronson for your answer.
Totally agree that there is some risk involved if it hasn’t been tested before. But on the other hand there is the PCB which has a trace width and thickness which will clearly tell where the maximum current is. :wink:

Just had an eye on the PCB files. From my gut feeling I’d say that 1A is absolutely fine. 2A should work also fine. Even when some additional load (e.g. LED-strip) kicks in.
I’ll limit the current for the selection of the pump to 2A (preferably 1A) and see how it goes. :slightly_smiling_face:

Will keep you updated on my findings. But that will take some time…

Thanks everyone for the feedback so far! :+1:


You know that the Farmduino v1.5 adds current sensing to the 5 peripheral outputs ?
I haven’t explored that yet, but the electronics is all there ( current-sense resistor 0.02 Ohm, op-amp scaling and fed to an on-board ADC pin . . that’s where I need to go loooking )


Totally missed that. I just focused on the trace width and not on the schematics or other parts of the PCB. Thanks for mentioning it!
@RickCarlino Is there anything implemented in the FBOS which would limit the current on the outputs?

Current sensors were added to the board to make seeding easier / more accurate (a feature that we have not added to FBOS yet due to time limitations). They were not added as a means of limiting current.

I will defer to @Gabriel for specifics on this one.