Confusing Solenoid Values: Resistance Mismatch & Maximum Safe Drive Current

[ricko_uk]

Hi,
I’m using the RS Components linear solenoid, part no. 177-0114 (datasheet attached and RS product page here: https://uk.rs-online.com/web/p/linear-solenoids/1770114 ). The available documentation is sparse, and the specification table is confusing: it appears to cover multiple part numbers, but this is not stated, making it unclear which parameters apply to this specific device.

The solenoid is marked as 24 V rated (datasheet and part marking). However, measured coil resistance is 194 Ω, which does not correspond to any value in the table. The closest listed resistances are 69 Ω and 275 Ω, far outside reasonable tolerance, so it’s unclear how to interpret the electrical data or how to relate it to the force vs. current graph.

I drive the solenoid with a DRV103 peak-and-hold driver (datasheet attached). During hold, the driver operates in PWM mode at 25 kHz, 30% duty cycle, per the attached schematic. The pull (peak) duration is currently set to 100 ms.


I’d appreciate any guidance on the following:

1) Safe operating limits – How to determine safe hold current (thermal limits) given the unclear datasheet?

2) Force control – How the PWM duty cycle (i.e. average current value) should be selected to achieve a specific pull/holding force with reference to the graph?

3) Pull time - is 100ms enough?

Any practical advice on electrical/thermal characterisation methods for this solenoid would be appreciated.

Thanks.

[PCB.Wiz]

Solenoids are simple enough.
Continual use rating is just heat removal aka overheating.
Keep in mind the resistance increases as they warm up, 192 ohms indicates ~20V but it may draw the rated ~87.5mA when hot. Easy to check.

The curves at  http://robots.freehostia.com/Solenoids/SolenoidsBody.html#4
give you an idea.

Check the dimensions, the data sheet indicates 2.1W for a 16 x 19 frame 29mm long.
If you can measure force, you can also sanity check a point(s) on the continual curve.
100ms is the right ballpark, you can check with an opto interrupter

[ricko_uk]

Thank you @PCB.Wiz,

I assume the 2.1 W you mentioned is based on the 100% duty cycle shown in the datasheet. Is that how you arrived at that value?

If so, I was wondering why does the datasheet list several other resistance values that are far outside what could be explained by temperature variation? Is the table supposed to cover multiple solenoid models?

Thank you 🙂

[aeg]

Table covers 6, 12, 24 and 48V variants. The first sample of the 24V variant had a DCR of 275 ohms. Current production batch has a DCR of 194 ohms. RS are not doing IQC.