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I have these 12 V solenoids from China.

enter image description here

I am using 6 in parallel and since each requires 300 mA, their effective resistance is about 6.67 Ω. This means the current required is around 1.8 A and should not exceed 2 A.

This is the puzzling part: When I tried powering the solenoids using a single 12 V / 5 Ah battery, the solenoids did not power properly and I needed to actually use two of these batteries to power them.

battery used

What is the problem? Am I missing something, perhaps due to the inductance of the coils or something? Another thing to note is that when I actuate the solenoids repetitively, they get hot and the solenoids somehow get weaker in their actuation also.

UPDATE I tested a single solenoid with a bench power supply. It seems that with a supply of 6V DC, the solenoid is unable to actuate. It only actuates at 12V. However the resistance measured across the solenoid is 12ohms, which is oddly weird as the rated current is 300mA. It seems like the data sheets are all off(?). Then again, I am working on a school project and I do not think my budget is enough to buy legitimate solenoids.

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    \$\begingroup\$ Your battery is 5Ah and will supply way in excess of 5A. Your clipleads don’t look like they’re rated for much over 1A. Measure the voltage drop across them. You might want to consider using a fuse in series with the battery since those clipleads will probably smoke and start a fire if you happen to cause a short circuit. \$\endgroup\$
    – Kartman
    Jan 16, 2022 at 13:17
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    \$\begingroup\$ @Iberico Don't go "I put X in parallel and then it didn't work properly so I added more batteries". Measure. Take one solenoid, one battery, measure what current it draws. Perhaps do that for all solenoids, maybe one is faulty. Then, match those numbers to the information you have, and draw your conclusions from there. Also, find and link a datasheet for all your components. \$\endgroup\$
    – marcelm
    Jan 16, 2022 at 13:26
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    \$\begingroup\$ electronics.stackexchange.com/questions/310363/… \$\endgroup\$
    – Antonio51
    Jan 16, 2022 at 13:27
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    \$\begingroup\$ This is one of the reasons why pros don't buy stuff that doesn't have a decent data sheet with links to a manufacturer who has a recognized quality system.... because it just wastes time trying to save a few pennies on what might seem attractive but is, in fact, likely to be problematic. How much do you value your time? \$\endgroup\$
    – Andy aka
    Jan 16, 2022 at 13:59
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    \$\begingroup\$ "the resistance measured across the solenoid is 12ohms, which is oddly weird as the rated current is 300mA." - Ambiguous spec. 300mA may be the maximum current for continuous operation, which does not mean it will draw this at 12V. The answer is in Antonio51's link. BTW don't trust clip leads to pass several amps without significant voltage drop! \$\endgroup\$ Jan 19, 2022 at 9:22

2 Answers 2

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To drive the solenoid, one can use this theoretical schematic ...

It "doubles" the supply voltage for a little time to drive the solenoid with a "higher" current. Just choose the necessary capacitor.

NB: schematic with 2 "switches". They can be replaced by ad-hoc transistors simultaneously driven. There is a pre-charge time, then "fire" the solenoid.

enter image description here

Or this one ...

enter image description here

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  • \$\begingroup\$ what does the 3m, 100m, 1m represent? And how is Vk connected to the circuit? \$\endgroup\$
    – Iberico
    Jan 20, 2022 at 2:47
  • \$\begingroup\$ Also, is the diagram used also usable in a microcontroller context? in the case where i would like to use a driver and microcontroller to control the solenoids \$\endgroup\$
    – Iberico
    Jan 20, 2022 at 3:02
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When I tried powering the solenoids using a single 12 V / 5 Ah battery, the solenoids did not power properly and I needed to actually use two of these batteries to power them.

Start with simple things first.

  1. Put the battery on a charger and wait until it's charged.

  2. Connect a voltmeter directly across battery terminals to monitor the battery voltage.

  3. Power just one solenoid from the battery, using the alligator leads you show.

  4. Add more solenoids - each with its own alligator lead going to the battery.

I bet you it'll work as long as the voltmeter shows good battery voltage - say 10V or higher.

The symptoms you describe may be from one of the two batteries being faulty or just not fully charged. Batteries do not need to come fully charged when you buy them. If you're charging the battery yourself, read up on how to do it. Namely - the charging voltage is quite a bit higher than 12V!

The alligator leads you have are quite thin, so I'd use a dedicated pair of leads for each solenoid, just to exclude the leads as a problem. In the name of "savings", sometimes those leads have extremely thin wires inside of them - like AWG #22 or even #24, just in a deceptively thick insulation. Not the best for pushing several Amps all at once. But one wire pair from solenoid directly to battery will be OK.

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