We were pretty excited when we first heard about this bad boy during Bosch's Q3 announcement - if there's only two things you should consider if you're in the market for a cordless 1/2-inch impact driver, it's the low asking price of RM619 for the Bosch GDS 250-LI set - that's complete with two Bosch 18V 3.0Ah battery packs, an AL 1820 CV charger and a carrying case - all you need is the impact sockets, some safety gears and you're in business!
The second is the torque output, the GDS 250-LI, as you might have guessed, outputs 250Nm of torque in either forward or reverse. Unfortunately, apart from the robust gearbox design, this is also where the cost-savings is apparent - the GDS 250-LI also does away with any form of torque-limiting power outputs with the only exception being the Auto Bolt Release (ABR) button located at the based of the unit above the LED.
The GDS 250-LI also employs the less-efficient brushed motors in order to keep the price down. Typically, power tools with brushed motors are also some 30% less efficient versus their brushless counterparts. In some instances, brushed motors such as the one used in the GBH 180-LI rotary hammer, will bog down under heavy load when used with a lower amp-hour battery pack.
The good news is that the brushes, much like all of Bosch's brushed power tools, are replaceable. In our experience, that's going to be a really long time as impact drivers typically don't see the same type of high-speed rpm like angle grinders or drills.
Bosch apparently limited the torque output to 'only' 250Nm with the GDS 250-LI as anyone working with automotive or engines will tell you that too much torque is as bad as too little - 250Nm is powerful enough to snap most smaller bolts - Your typical car wheel lugs requires less than half that amount. Ideally, you would only use an impact driver to loosen a nut or a bolt and only use a calibrated torque wrench to tighten.
Scaffolding + Free-falling Nut = Bad.
The GDS 250-LI is also equipped with a Auto Bolt Release (ABR) function via a button at the base of the unit. When enabled, the ABR automatically stop the tool once the bolt is impacted-free and preventing the bolt (or nut) from flying out of the socket as the impact driver free-spins to its 2,400rpm max speed. While this might be a minor annoyance when you're on the ground changing out your car tyres, it can have devastating consequences when it falls off a scaffolding.
The GDS 250-LI also comes with both a through hole (for a locking pin) as well as a retaining ring on the 1/2-inch square drive and included a lanyard as standard on the GDS 250-LI.
What's the GDS 250-LI like under real-world scenarios?
Since Bosch Malaysia did caution us that the GBH 180-LI rotary hammer drill would bog down under load when used with a 1.5Ah battery pack, we thought we would tested the GDS 250-LI with a fully-charged Bosch 1.5Ah battery pack under load as well.
Paired with a 1.5Ah pack, the GDS 250-LI was used to loosen a 27mm front sprocket nut from a Kawasaki ER-6n that was torqued down to the manufacturer's specified 125Nm. Even after 25 seconds, all the GDS 250-LI did was vibrate. When we swapped out the 1.5Ah pack for a 3.0Ah unit, the GDS 250-LI managed to break the nut loose but only after almost 20 seconds of continuous impacting.
The GDS 250-LI has a claims a 3,300 beats per minute (bpm), typically, the higher the bpm, the smaller the hammer and the longer it would take to tighten or loosen a nut. A typical pneumatic impact wrench has an impact rate of around 1,200bpm. With the same token, the GDS 250-LI also feels very smooth during operation with minimal vibration.
The similarly-sized rear axle nut on the ER-6n, torqued down to 108Nm, however came off without much hesistation under 5 seconds - even with the 1.5Ah pack. We also saw similar performance with 19mm lug nuts on car wheels that were torqued down to 110Nm (tested with the kit 3.0Ah battery).
For the record, the 6-point 27mm impact socket used was slightly worn but still serviceable. Ideally, there should be minimum play between the socket and the nut. Also, most sprocket nuts would tend to naturally bind up from a number of factors acting on the threads. However, unlike a synthetic test where the impact wrench is tested against a torqued-down nut of a pre-set value, we felt a real-world test represents a more accurate test for an impact wrench.
The gear housing was however fairly warm to the touch after this short exercise and while comes with a fairly bright LED lighting, the bottom-up position of the LED does tend to cast a shadow on the work area especially if you have a large socket in place.
While we were naturally expecting a zippier performance from the Bosch GDS 250-LI when it comes to loosening stuck bolts, the fact of the matter is there's simply no comparing a pneumatic impact wrench, even of similar torque output, to a cordless impact wrench.
Even if it took a while longer versus a more powerful pneumatic impact wrench, the GDS 250-LI can easily accomplish a majority of tasks required of a 1/2-inch impact wrench (within means, that is) but probably the most appealing factor is that the GDS 250-LI is priced to fit within one's budget with a size that easily fits in your toolbox.
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