MARQUARDT 2711 DC lithium ion power drill trigger switch - Page 1
Forum section: electronics / beginners

author: shockpoint
author_rank: Contributor
timestamp: March 03, 2024, 12:56:43 am
content: Hi team!(yes tried the search)New here, and beginner to electronics.I have come into possession of an old C18 PD (power drill) from Milwaukee. It is an 18V lithium ion battery drill.The symptoms of it not working are:- battery connected, trigger pressed, the LED torch comes on but there is no rotationI have taken it apart and have inspected everything; I have noticed something odd.The trigger switch is of a Marquardt make, code 2711.9202, which is now out of production but the catalogue shows something similar, 2711.9305.Here is some information about the 2711 series switches. They are mini potentiometers using mosfets for graded speed PWM control and then at full press, it shorts the motor to battery positive.Datenblatt_DC_Schalter_2711_EN.pdfHere is a picture of the switch and its markings:https://i.ebayimg.com/images/g/5NwAAOSwalpiaL0L/s-l1200.jpgWhile this switch is connected, here are my findings with a multimeter (Dave's famous blue multimeter BM 235)Battery disconnectedResistance mode- while the trigger is not pressed, the leads B- and SB+ (across the diode) are shorted. This short is also present on the leads to the motor, marked M1 and M2, which connect to carbon brushes oriented orthogonally. (reading 0.000-0.001 ohms, bidirectionally across the diode)- when the trigger is partially depressed, the above is also true.- when the trigger is fully depressed, the short switches to B- and B+ (which I feel is normal behaviour), and the short disappears from the leads M1 and M2Diode mode- when the trigger is not pressed, the leads B- and SB+ (across the diode), read 0.000-0.001V, both in forward and reverse across the anode and cathode- when the trigger is partially depressed, the above is also true- when the trigger is fully depressed, the diode, forward bias measurement, reads 0.456V. The reverse direction reads 2.57VBattery connected- same as above, but with a voltage measurement across the leads coming from the battery the voltage potential is 0.001V (battery charged to 18.30V)- on full depression of the switch the difference is 18V across teh brushes and it does jolt the rotor a bit.I want to say that there is a short, most likely from the diode but possibly inside the trigger switch too (haven't opened it up yet) but I haven't worked with trigger switches before. So I was wondering if anyone could shed light on this as to whether this is normal behaviour. I cannot see how the drill can spin if even at partial switch press there is no voltage potential between the carbon brushes oriented 90degrees to each other.I can't get my head around the diode behaviour.Any ideas?

author: m k
author_rank: Super Contributor
timestamp: March 09, 2024, 01:59:34 pm
content: Have you tried connecting the input voltage directly to the motor?Some movements indicate that the rotation controller is not working.

author: tunk
author_rank: Super Contributor
timestamp: March 09, 2024, 05:56:08 pm
content: It could possibly be a dying battery, either unbalanced cells or high internal resistance.Does the motor rotate freely by hand?

author: shockpoint
author_rank: Contributor
timestamp: May 14, 2024, 11:27:37 pm
content: Quote from: tunk on March 09, 2024, 05:56:08 pmYes, the motor rotates freely by hand. I believe that the issue lies with the trigger switch and I have been looking for any shorts on the MOSFETS that are connected to the switch just to rule that out. I will also unplug the flyback diode and check, because it seems to have voltage bidirectionally!Quote from: m k on March 09, 2024, 01:59:34 pmHello, sorry for the late reply. I have been putting the project on teh back burner.Yes I have connected it directly and it did rotate the motor.