Hohn
Well-known member
The angle grinder thread got me thinking about one of the most startling learnings I've had about tools-- right up there with air compressors being rated by suction flow
.
Namely, what is the actual difference between an angle grinder rated 6 amps vs 9 amps vs 12amps or 15 amps? If you plug these grinders into a metered outlet and measure the current draw with no load, you'll find nothing at all like the rating amperage.
And if you dig in hard on a tool, you'll find you can pull far more current than the rating amperage. I've had a 4.5" grinder trip a 15a breaker when I was seriously abusing it with an oversized cup brush and extension cord doing cast iron cookware refinishing and it's rated nowhere near 15 amps. It was so hot it was burning my hands through leather gloves.
Conversely, you can plug in a 15a beast of a grinder and get a no load draw as low as 6amps. What gives?
The Amperage rating is a measure of MAX POWER DISSIPATION-- in other words, cooling capacity. It's the most amount of current that the tool can sustain indefinitely on some standardized test lab condition (temp, humidity, etc).
This is why we see so many angle grinders "burn up" -- they get full of particles and debris and they loose their cooling capacity. Especially in metal shops where metallic dust is attracted to motor magnets.
What the current rating CANNOT tell you is how efficient the tool is. It tells you nothing about the motor's current draw as a function of load. It only tells you how much current the thing can flow before it will start to overheat, as defined by whatever temperature threshold is the operating limit of the test protocol .
And of course, that current rating is a clean, fresh, new tool used in a spanky clean lab. What's the real current/heat capacity of that crusty old Makita caked in rusty dust? Nobody knows. But certainly less than new.
This is why when you use otherwise identical tools-- like a 4.5" angle grinder-- with vastly different current ratings, the first thing you will observe about the high amp tool is the cooling flow. The high amp tools move a LOT of air compared to their low amp counterparts. They are much louder and noisier.
The implications of this knowledge are pretty significant. For example, if you have mostly light duty work to do, a low-amp grinder might not only be cheaper, but it will almost certainly be lighter and MIGHT LAST LONGER.
Last longer? Yes. Because the rate at which dust and debris is sucked into the motor is a function of fan airflow rate, given the same amount of crud in the air. Less airflow, less debris intrusion.
If you have a high amp grinder, wrap a rag around the air inlet ports and do some light work with it. Take note of just how much crud appears on the rag-- crud that your tool would have ingested.
It turns out that corded power tool selection is like many other things in life, more is not always better.
These days, I prefer the smallest lightest 4.5" grinder I can get. I grab it first.
.Namely, what is the actual difference between an angle grinder rated 6 amps vs 9 amps vs 12amps or 15 amps? If you plug these grinders into a metered outlet and measure the current draw with no load, you'll find nothing at all like the rating amperage.
And if you dig in hard on a tool, you'll find you can pull far more current than the rating amperage. I've had a 4.5" grinder trip a 15a breaker when I was seriously abusing it with an oversized cup brush and extension cord doing cast iron cookware refinishing and it's rated nowhere near 15 amps. It was so hot it was burning my hands through leather gloves.
Conversely, you can plug in a 15a beast of a grinder and get a no load draw as low as 6amps. What gives?
The Amperage rating is a measure of MAX POWER DISSIPATION-- in other words, cooling capacity. It's the most amount of current that the tool can sustain indefinitely on some standardized test lab condition (temp, humidity, etc).
This is why we see so many angle grinders "burn up" -- they get full of particles and debris and they loose their cooling capacity. Especially in metal shops where metallic dust is attracted to motor magnets.
What the current rating CANNOT tell you is how efficient the tool is. It tells you nothing about the motor's current draw as a function of load. It only tells you how much current the thing can flow before it will start to overheat, as defined by whatever temperature threshold is the operating limit of the test protocol .
And of course, that current rating is a clean, fresh, new tool used in a spanky clean lab. What's the real current/heat capacity of that crusty old Makita caked in rusty dust? Nobody knows. But certainly less than new.
This is why when you use otherwise identical tools-- like a 4.5" angle grinder-- with vastly different current ratings, the first thing you will observe about the high amp tool is the cooling flow. The high amp tools move a LOT of air compared to their low amp counterparts. They are much louder and noisier.
The implications of this knowledge are pretty significant. For example, if you have mostly light duty work to do, a low-amp grinder might not only be cheaper, but it will almost certainly be lighter and MIGHT LAST LONGER.
Last longer? Yes. Because the rate at which dust and debris is sucked into the motor is a function of fan airflow rate, given the same amount of crud in the air. Less airflow, less debris intrusion.
If you have a high amp grinder, wrap a rag around the air inlet ports and do some light work with it. Take note of just how much crud appears on the rag-- crud that your tool would have ingested.
It turns out that corded power tool selection is like many other things in life, more is not always better.
These days, I prefer the smallest lightest 4.5" grinder I can get. I grab it first.