Advice on solenoid activation circuit

Thread Starter


Joined Apr 8, 2020
Hello all,

I've been having this little project on the shelf that seems to linger around without getting finished. So I thought I'd come here to ask some advice and help.

In short: I programmed and made a PCB for a 'remote activated random timer solenoid activation'. What the hell is that you say? Well, in short: I press a button on a cheap RF transmitter, a random timer (between 4 and 6 seconds) is started and once that timer finishes, it activates a solenoid magnet to drop a startgate (for sports).

However, I purchased some 12V solenoids and use a 4S Lipo battery to activate the circuit and solenoid. Plenty of power I thought. Well, the solenoid activation is so weak, that if I put a little bit of force on it, it won't retract/extract. First I used a 9V battery, but it was too weak. Allthough switching to the 4S Lipo changed nothing...

My guess is that there is not a big enough 'rise' in amps going through. Normally the traces on the PCB should be large enough to allow for the necessary amps to go through, however it might be that it rises to slow over the darlington NPN. What are your thoughts?


Kind regards,


Joined Aug 12, 2014
Does the solenoid operate fine across the battery supply?
I think this is the key question, worth reiterating. Before second guessing the rest of the circuit, I'd advise testing the "strength" of the solenoid connected directly to the battery.

My guess is one of two things:

1) the solenoid isn't as powerful as desired for the given situation, and no battery or circuit will change that, so a different solenoid is needed

2) the battery simply can't deliver enough current, and a larger battery (not higher voltage, just larger capacity and available discharge rate) would solve it.

It's also possible that there's something to change in the circuit, but the first step should definitely be proving whether or not the solenoid and battery are up to the task at all. Only after those work perfectly on their own should we reconnect the circuit and test its effect on performance.


Joined Jul 18, 2013
Although it generally requires much less current to keep retained once pulled in.
It used to be customary on very large DC brakes for lower the current, once activated to reduce power/heating etc.

Thread Starter


Joined Apr 8, 2020
Hey guys,

Thanks for the feedback. It's very constructive.

The battery isn't the issue. It's a 4S 10C Lipo battery. Capable of 100A.

When I connected the solenoids tot the battery directly, they were quite strong. However, you are a right. During the stroke they seemed quite as weak as on the circuit. And the circuit only provides a second of power. So the lightest touch can inhibit them from activating, allthough once actived you need more force to overcome that force. I should have taken that into account.

Do you guys have any suggestions for something else that can trigger a mechanically heavy object with the current circuit? I was thinking of an electromagnet.

Kind regards,