How to fix power related issues with your concrete floor grinders
Do you have the issue of your grinding just stopping? Does your concrete floor grinder trip out? Is your concrete floor grinding machines being starved of power onsite? It’s time to consider your power supply options to your concrete floor prep, grinding and polishing machines.
ALL PREPARATION EQUIPMENT – POWER GUIDE
It is always wise to be pre-emptive rather than reactive when it comes to power related issues. Repeated power issues will quickly damage the capacitors in a start/run capacitor motor such as Schwamborn DSM 250mm, 400mm, 450mm, 530mm, 650mm, 800mm Concrete Floor Grinders as well as other brands such as the Cub 250, Sharks, Meteor 250 Grinder or Satellite 480, 650 and 760 Grinder, Husqvarna 280, 530, 680mm and 800mm, HTC 280, 420, 530, 650 Concrete Floor Grinders and others. This will result in immediate repairs being required and failure during critical tasks such as jobs with time limits.
Don’t wait until you see a power related symptom before you take action.
Read our guide, be aware, and ensure you aren’t stuck on a job without working tools. This power guide has been designed to help you rectify power related interruptions to your equipment, protect and reduce damage to your equipment, and to help you use your equipment more efficiently and effectively.
It’s worth reading the whole thing, even though it may seem obvious, as we use the basic concepts at the beginning of the guide to explain more complex concepts later in the guide. Don’t worry, it’s not too intense – we’ve kept it basic and simple for everyone to read. We guarantee you’ll get a real benefit from this guide and that if you’re using electric grinders or floor lifters you’ll have more productive times on your jobs after you read it. So what are you waiting for? Dive right in!
1. WHAT IS POWER (ELECTRICITY)?
A. THE SIMPLE EXPLANATION:
Electrons travel through conductors (wire). A force is applied to the wire known as Voltage which causes the electrons to move in a specific direction. The orderly movement of the electrons is called Current.
- The product of Current and Voltage is known as Power.
B. THE DETAILED EXPLANATION:
- What’s a conductor made of?
Consider a basic conductor of electricity – say, a common piece of wire comprised of lots of tiny copper ATOMS which are themselves comprised of smaller parts – Protons, Neutrons, and Electrons. These are arranged like in the picture – the Protons & Neutrons are basically stuck together and the electrons orbit around just like our planet orbits the sun.
- What’s so important about the electrons?
The thing about electrons is that because they aren’t stuck to the Protons and Neutrons, they can move from atom to atom.
As long as each atom retains the correct amount of electrons, it can exchange them to and fro. The orderly process of this movement of electrons is what we call Current – or what we all know as the phenomenon of electricity. The diagram beside illustrates electrons moving through a piece of copper (CU Atoms).
- So what makes all the electrons move in the same direction?
Well, a thing called Voltage does. Voltage, which is also known as Potential Difference, is the force that draws electrons through a conductor. It works in the same way as magnetism – like a magnet sticking to a fridge, or gravity – like how we are stuck to the ground.
If we consider two plates, one with a positive charge and one with a negative charge spaced an arbitrary distance from each other, then there is a force which is trying to draw all the negatively charged electrons towards the positive plate to make them equal in charge and this force is referred to as Voltage.
When we have Voltage present, and there is a conductor between the two differences allowing the flow of the electrons, we get current. The speed or amount of that current is referred to as Power. It is directly related to the strength of the force pulling the electrons through the wire (Voltage). That is, the more voltage present, the more current will flow and therefore the more Power is created.
The standard equation for power is:
P (power in Watts) = I (current in Amps) x V (voltage in Volts)
- P = I x V
Let’s try this equation. Example: The power used to run an item at maximum current (10Amps) on a standard 10A domestic residential circuit on mains power in Australia (230V) would be P = 10 x 230 = 2300W
So the maximum power draw on a 10A 230V supply is 2300W. Just to prove it to yourself, go have a look at any of your domestic electric devices. You’ll notice none of your single phase 10A machines have a power rating of more than 2300W.
Later, in this guide, we will use the formula P = I x V in a different way. We will transpose the equation so that we can calculate the Current Draw (Amps) by dividing both sides by V: P/V = I x V/V which gives us a new equation:
- I = P/V
NOTE 1a: When electrons move and/or atoms vibrate they generate HEAT. That means the MORE CURRENT we use, the MORE HEAT is created in the CONDUCTOR (copper wire).
2. WHAT IS AC AND DC?
DC is short for Direct Current. Direct Current is another way of saying Current Going In One Direction. If we look at the picture of the two plates again, you’ll notice all the electrons going in one direction to try to equalize the charge of the plates. DC is commonly found in batteries. The picture of the two plates represents a cell in a battery.
AC is short for Alternating Current. Alternating Current is another way of saying Current That Alternates (Changes) Direction.
AC current swings back and forth, one way then the other. Basically, the plates in the picture alternate from being positive to negative.
This is a simple explanation only, in reality the current doesn’t just instantly change direction, the plates reduce in their positive and negative charge until they become the same, then the increase in the opposite direction – thereby changing the current direction.
In Australia, our AC Mains power switches current direction 50 times per second (50 Hertz).
3. DIFFERENT TYPES OF MOTORS – AC MOTORS AND DC MOTORS
There are two types of motors, AC & DC. Each motor is designed differently but both essentially use electricity to create an electro-magnetic field (EMF) to influence magnets (or electromagnets) to turn a shaft.
Because AC current alternates in direction, it’s far more complex to create a motor that continually spins in one direction.
Why is this important? If we used AC current on a DC motor it would basically spin back and forth rather than turning in one direction constantly. This difference in design makes them behave differently when the supply changes outside the voltage they are designed to operate within.
I. DC MOTORS
DC motors use Direct Current (as found in the batteries used in your car). There are some different designs including brush and brushless designs.
- 1. When VOLTAGE REDUCES, the motor basically draws proportionately less current and produces less power. Essentially it runs slower. This is the basis of speed control in a DC motor.
- a. P = I x V. A 5A motor at 12V would be P=I x V = 5A x 12V = 60W
- 2. When LOAD INCREASES, the motor draws more current up until it’s STALL CURRENT. NO MORE CURRENT IS DRAWN TO OVERCOME THE LOAD from this point on.
- 3. If the LOAD COMPLETELY STOPS THE MOTOR, that is, If the force required to spin the motor is greater than the motor is producing at the STALL CURRENT then the motor simply stays stalled and keeps drawing the stall current.
- 4. Given that the current is the same (or less in practice) there are no heat related problems created in a DC motor by simply reducing the voltage without respect to the load. (See NOTE 1a in section 1.)
II. AC MOTORS
AC motors use Alternating Current (as found in mains power such as domestic supply). These motors are manufactured to support Single Phase and Three Phase in many different designs.
- 1. IMPORTANT! Firstly, remember this: An AC Motor is always designed with a CURRENT OVERLOAD protection circuit. This will cut power (known as TRIPPING) to the motor if it tries to draw an unsafe high current for too long. This usually has a manual reset switch to reset the overload protection circuit so that you can restart the motor. The problem is that if you’re tripping this protection, you have a problem that needs to be rectified or you will likely damage your machine. Continually resetting the overload switch without rectifying the cause is likely to quickly lead to complete failure of the machine.
- 2. When VOLTAGE DECREASES, (Assuming there is no load) the motor draws more current to try to keep it at the same power level. CURRENT INCREASES. Using P = IV, at a regular nameplate voltage of 230V, a 3HP (2200W) Meteor motor draws 2200W (P) = I x 230V (V). Using transposition we get I = 2200W (P) / 230V (V) = 9.56Amps. Now, if the voltage drops 10% to 207V we end up with I = P/V = 2200W / 207V = 10.62A. Here is a graph of how a Meteor or Satellite motor behaves when voltage drops:
- 3. When LOAD INCREASES, the motor draws more current to keep the motor running at the same speed. CURRENT INCREASES. When combined with VOLTAGE DECREASE this can produce huge current demand (well over 10A!) and will almost always trip the overload protection circuit.
- 4. When LOAD COMPLETELY STOPS THE MOTOR, that is, if the force required to spin the motor is greater than all the power that the motor can practically consume (given the circuit restrictions of the circuit it is being used on) then it stops rotating. At this point it becomes a SHORT and draws maximum current available – which is very similar to the element in a heater and the WHLOE MOTOR BECOMES A HEATER ELEMENT. It gets VERY HOT VERY QUICKLY.
III. WANT TO KNOW MORE ABOUT MOTORS?
This is a very simple breakdown of the important parts of the operation of electric motors in relation to power, but If you’d like to learn how AC motors work, there’s a relatively easy-to-read motor theory here: http://www.reliance.com/mtr/mtrthrmn.htm
4. WHAT TYPE OF MOTORS DO THE METEOR AND SATELLITES USE?
- a. The Meteor 250 and Satellite 480 use an AC motor. More specifically, an AC Induction Motor with Capacitor-Start and Capacitor-Run.
- b. This is a light industrial motor with high startup-torque.
- c. See section 3(ii) to learn about the behavior of these motors in respect to power.
5. SYMPTOMS OF UNDER-VOLTAGE/POWER STARVATION (SHORT TERM EFFECTS)
Some of the symptoms of under-voltage/power or current starvation include but are not limited to the following:
- a. Heat or unusually hot motors
- b. Tripping current-overload protection (overload switch)
- c. Tripping breakers on circuit
- d. Starting problems or difficulty starting
- NOTE: These symptoms can sometimes be a result of other problems as well. These symptoms do not guarantee the problem being under-voltage.
- e. To learn why these symptoms appear, see section 3(ii) to learn about the behavior of these motors in respect to power.
6. LONG-TERM EFFECTS OF UNDER-VOLTAGE/POWER STARVATION
- a. Irreversible motor damage
- b. Complete Motor failure and/or seizure.
- c. Continued difficulty starting motor even when operated at ideal power conditions
- i. Leading to catastrophic failure of start and/or run capacitors
7. WHAT CAUSES VOLTAGE DROP?
Voltage drop occurs when there is a resistance present. The larger the resistance, the larger the voltage drop.
II. THE SIMPLE EXPLANATION:
Basically resistance is an obstacle to the movement of the electrons. The voltage drops because the force of the voltage tapers off over distance.
- TIP: Another way to consider resistivity is to think about water travelling through a hose. The resistance is greater if the hose is thinner and longer (that is, it’s harder to push a certain quantity of water through a longer thinner hose than it is a shorter thicker hose). Voltage is like the pressure the water is under. As the hose gets longer, the pressure at the exit end of the hose drops.
III. THE DETAILED EXPLANATION:
Every conductor has some amount of resistance which a product of the cross sectional area of the conductor/wire used, the length of the conductor/wire, and the resistivity of the conductor.
The resistance, R, of a length of wire is described by the expression: R = ρL/A where ρ = resistivity of the material composing the wire, L = length of the wire, and A = area of the conducting cross section of the wire.
We can calculate the resistivity of copper wire here: (rho) or resistivity of a “wire” is calculated using this formule: rho = Resistance x Area / length of material the resistivity of copper is 1.7 x 10 -8 ohm/m
Given this resistivity, we can calculate voltage drop at a given amount of power. We won’t give you the whole detailed calculation here, but if you’d like to do some calculations of your own, try this handy link: http://www.electrician-electricalcontractor.com/calculatevoltagedrop.html
8. SOLUTIONS FOR POWER STARVATION (VOLTAGE DROP)
- a. Ensure the extension lead used produces the least amount of voltage drop and is capable of carrying the current required.
- i. Use the largest available lead possible, in good working condition.
- ii. Work from the following table (based on a maximum 3% voltage drop and a short term current draw of 15A)
|Run Length||Current Demand||System Voltage||Voltage Drop||Minimum Copper Core Size|
|50 m||15 A||230 V||9.2 mV/A.m||6 mm2|
|40 m||15 A||230 V||15.33 mV/A.m||4 mm2|
|30 m||15 A||230 V||15.33 mV/A.m||4 mm2|
|20 m||15 A||230 V||23.00 mV/A.m||2.5 mm2|
|10 m||15 A||230 V||46.00 mV/A.m||1 mm2|
- b. Ensure the circuit is not loaded with other items which are adding to the resistivity of the overall circuit.
- i. If at a residential location, find another power circuit and plug in there instead
- ii. Unplug other devices on the circuit that can be unplugged.
- iii. Move other devices to an alternative circuit.
- c. Create an alternative power source by using a generator
9. REDUCING EXCESSIVE CURRENT DRAW DUE TO LOAD
- a. Reduce the load on the machine
- i. For grinders, use a less aggressive wheel on the machine.
- ii. For grinders, use weight on the handle of the machine to reduce weight over the grinding wheel.
- iii. Do more frequent, faster passes over the surface.