Garden supply chainsaw not working

Knowsome · Dec 11, 2014

Hi
I have a garage supply unit supplied by a radial 2.5 cable from a fused MCB in the house. My new Black and Decker chainsaw 2kw won't run for long before tripping the garage supply unit in my shed. Since the chainsaw will run off by a cable reel from the house it would seem to be working OK. If the saw is drawing more power than 2kw on start up I understand that I could replace the 16A Type B MCB with a Type C. Is that correct?

unphased · Dec 11, 2014

2kW is 8.7A. If the chainsaw is pulling out the mcb on start-up then yes you could try a type C breaker. However, if it is tripping it after running for several minutes then it could be something else causing the mcb to pull out. I hope you have RCD protection on that circuit!

Jitender · Dec 11, 2014

Had this problem, we had a attic radial circuit on a 16A type B breaker, during the roof work this supply was used to power an 91/2" angle grinder, at start up it would trip the breaker.

Deleted member 33931 · Dec 11, 2014

Something amiss here. He says it's tripped after a few minute's use, not start-up.

Even if the chain is so worn he's really straining it, I'd be worried if the current draw doubled. Tho' it could...

Knowsome, does this happen at obvious times such as when the saw is under a full load?

And it's def an MCB and not an RCD wot trips?

stateit · Dec 11, 2014

Volt drop -> more current drawn.

How far away is the shed from the house?

Deleted member 33931 · Dec 11, 2014

Ooooooohhhh! Volt drop due to increased resistance (long cable) = less current drawn...

unphased · Dec 11, 2014

Longer cable=increased impedance and drop in voltage therefore reduced current. Tut tut stateit! Well spotted DA.

Mr. Handyandy · Dec 11, 2014

Dodgy supply trip(MCB) in the garage/shed(tripping at 10A).

Mr. HandyAndy - Really

Deleted member 33931 · Dec 11, 2014

unphased said: ↑

Longer cable=increased impedance and drop in voltage therefore reduced current. Tut tut stateit! Well spotted DA.
Click to expand...

I neffer said nuffink about 'impedance'. Anyways, what does a floppy willy have to do with anything?

Knowsome · Dec 12, 2014

unphased said: ↑

2kW is 8.7A. If the chainsaw is pulling out the mcb on start-up then yes you could try a type C breaker. However, if it is tripping it after running for several minutes then it could be something else causing the mcb to pull out. I hope you have RCD protection on that circuit!
Click to expand...

Thanks unphased. The chainsaw is pulling out the MCB on startup and only on startup. The saw works perfectly off a cable reel plugged into the house ring. The supply to the shed garage CU two way 6amp and 16amp MCBs Clipsal box bought from Screwfix some time ago.

The radial to the shed is just over 20m from the house. Voltage is 239v at the shed and 237v in the house!

Knowsome · Dec 12, 2014

Jitender Gangar said: ↑

Had this problem, we had a attic radial circuit on a 16A type B breaker, during the roof work this supply was used to power an 91/2" angle grinder, at start up it would trip the breaker.
Click to expand...

I also had the same problem with a 9 1/2" angle grinder which I tried to run off my daughter's garage supply same Clipsal garage CU box

seneca · Dec 12, 2014

Knowsome said: ↑

Thanks unphased. The chainsaw is pulling out the MCB on startup and only on startup. The saw works perfectly off a cable reel plugged into the house ring. The supply to the shed garage CU two way 6amp and 16amp MCBs Clipsal box bought from Screwfix some time ago.

The radial to the shed is just over 20m from the house. Voltage is 239v at the shed and 237v in the house!
Click to expand...

Voltage is 239v at the shed and 237v in the house! Other way around i'd reckon!

Jitender · Dec 12, 2014

Some of these large angle grinders don't have a soft start feature, so I think it is due to the initial start up, again it all worked when plugged into the house socket ring main.

unphased · Dec 12, 2014

Knowsome said: ↑

Thanks unphased. The chainsaw is pulling out the MCB on startup and only on startup. The saw works perfectly off a cable reel plugged into the house ring. The supply to the shed garage CU two way 6amp and 16amp MCBs Clipsal box bought from Screwfix some time ago.

The radial to the shed is just over 20m from the house. Voltage is 239v at the shed and 237v in the house!
Click to expand...

In that case try a type C. You could go for a 20A instead of 16A which may also help. Regards

Knowsome · Dec 12, 2014

Devil's Advocate said: ↑

Something amiss here. He says it's tripped after a few minute's use, not start-up.

Even if the chain is so worn he's really straining it, I'd be worried if the current draw doubled. Tho' it could...

Knowsome, does this happen at obvious times such as when the saw is under a full load?

And it's def an MCB and not an RCD wot trips?
Click to expand...

Thanks Devil's Advocate

It the MCB that trips, went out to check as I had been using it today connected to the house circuit with no problems. I then went out to plug into the shed and it tripped the MCB I then tried again and the saw wouldn't trip the MCB! So I am non the wiser. I also tried plugging my cable reel into the shed socket and the saw worked fine. The chainsaw is actually 1900w not 2000w and is almost new but bought over a year ago. It is still sharp. The voltage at the cable reel fully unwound (50m) was 238v.

Knowsome · Dec 12, 2014

unphased said: ↑

In that case try a type C. You could go for a 20A instead of 16A which may also help. Regards
Click to expand...

Thanks unphased will try that.

stateit · Dec 15, 2014

Devil's Advocate said: ↑

Ooooooohhhh! Volt drop due to increased resistance (long cable) = less current drawn...
Click to expand...

Not with a motor. With a fixed load (ie heating element), then yes.

With a motor under load lower voltage than design voltage= higher current drawn.

Also if the chainsaw is under a heavy load (log too thick, forcing the saw through the log, blunt blade) the motor will slow down and draw more current to compensate.

Deleted member 33931 · Dec 15, 2014

Ball locks.

So, according to your calculations, if you were to run this chain saw under a heavy load and fed via a 2-mile cable, it'll draw more amps...?

That's ok - apology accepted

stateit · Dec 15, 2014

This is one of many articles you could look at. It explains overvoltage problems as well as undervoltage problems: (Click to expand)

The Highs and Lows of Motor Voltage
May 1, 2000 12:00 PM, By Ed Cowern, P.E.

Operating a motor at the "outer limits" of its voltage requirements reduces its efficiency and causes premature failure.

The economic loss from premature motor failure is devastating. In most cases, the price of the motor itself is trivial compared to the cost of unscheduled shutdowns of processes. Both high and low voltages can cause premature motor failure, as will voltage imbalance. Here, we'll look at the effects of low and high voltage on motors and the related performance changes you can expect when you use voltages other than those noted on the nameplate.

Effects of low voltage. When you subject a motor to voltages below the nameplate rating, some of the motor's characteristics will change slightly and others will change dramatically. To drive a fixed mechanical load connected to the shaft, a motor must draw a fixed amount of power from the line. The amount of power the motor draws has a rough correlation to the voltage 2current (amps). Thus, when voltage gets low, the current must increase to provide the same amount of power. An increase in current is a danger to the motor only if that current exceeds the motor's nameplate current rating. When amps go above the nameplate rating, heat begins to build up in the motor. Without a timely correction, this heat will damage the motor. The more heat and the longer the exposure to it, the more damage to the motor.

Sidebar: Rules of Thumb for High and Low Voltage

• Small motors tend to be more sensitive to overvoltage and saturation than do large motors.

• Single-phase motors tend to be more sensitive to overvoltage than do 3-phase motors.

• U-frame motors are less sensitive to overvoltage than are T-frames.

• Premium efficiency Super-E motors are less sensitive to overvoltage than are standard efficiency motors.

• Two- and 4-pole motors tend to be less sensitive to high voltage than are 6- and 8-pole designs.

• Overvoltage can drive up amperage and temperature even on lightly loaded motors. Thus, high voltage can shorten motor life even on lightly loaded motors.

• Efficiency drops with either high or low voltage.

• Power factor improves with lower voltage and drops sharply with higher voltage.

• Inrush current goes up with higher voltage.

The existing load is a major factor in determining how much of a decrease in supply voltage a motor can handle (see sidebar, below). For example, let's look at a motor that carries a light load. If the voltage decreases, the current will increase in roughly the same proportion that the voltage decreases. For example, a 10% voltage decrease would cause a 10% amperage increase. This would not damage the motor, if the current stays below the nameplate value.

Now, what if that motor has a heavy load? In this case, you already have a high current draw, so voltage is already lower than it would be without the load. You may even be close to the nameplate's lower limit for voltage. When you have a voltage reduction, the current would rise to a new value, which may exceed the full-load rated amps.

Low voltage can lead to overheating, shortened life, reduced starting ability, and reduced pull-up and pullout torque. The starting torque, pull-up torque, and pullout torque of induction motors all change, based on the applied voltage squared. Thus, a 10% reduction from nameplate voltage (100% to 90%, 230V to 207V) would reduce the starting torque, pull-up torque, and pullout torque by a factor of .92.9. The resulting values would be 81% of the full voltage values. At 80% voltage, the result would be .82.8, or a value of 64% of the full voltage value. What does this translate to in real life? Well, you can now see why it's difficult to start "hard-to-start" loads if the voltage happens to be low. Similarly, the motor's pullout torque would be much lower than it would be under normal voltage conditions.

On lightly loaded motors with easy-to-start loads, reducing the voltage will not have any appreciable effect, except that it might help reduce the light load losses and improve the efficiency under this condition. This is the principle behind some add-on equipment whose purpose is to improve efficiency.

Effects of high voltage. An assumption people often make is that since low voltage increases the amperage draw on motors, then high voltage must reduce the amperage draw and heating of the motor. This is not the case. High voltage on a motor tends to push the magnetic portion of the motor into saturation. This causes the motor to draw excessive current in an effort to magnetize the iron beyond the point where magnetizing is practical.

Motors will tolerate a certain change in voltage above the design voltage. However, extremes above the design voltage will cause the amperage to go up with a corresponding increase in heating and a shortening of motor life.

For example, manufacturers previously rated motors at 220/440V, with a tolerance band of 510%. Thus, the voltage range they can tolerate on the high-voltage connections is 396V to 484V. Even though this is the so-called tolerance band, the best performance would occur at the rated voltage. The extreme ends (either high or low) put unnecessary stress on the motor.

Don't fall into the trap of thinking you're okay just because your supply voltage falls within these tolerance bands. The purpose of these bands is to accommodate the normal hour-to-hour swings in plant voltage. Operation on a continuous basis at either the high or low extreme will shorten the life of the motor.

Such sensitivity to voltage is not unique to motors. In fact, voltage variations affect other magnetic devices in similar ways. The solenoids and coils you find in relays and starters tolerate low voltage better than they do high voltage. This is also true of ballasts in fluorescent, mercury, and high-pressure sodium light fixtures. And it's true of transformers of all types. Incandescent lights are especially susceptible to high voltage. A 5% increase in voltage results in a 50% reduction in the life of the lamp. A 10% increase in voltage above the rating reduces incandescent lamp life by 70%.

Sidebar: Drop Versus Sag

Be precise when talking about decreases in voltage. Using the wrong terminology can confuse everyone.

Voltage drop is a static figure that is a function of wire resistance.

Voltage sag is a dynamic figure that is a function of inductance, capacitance, and other factors. When discussing voltage problems, do not interchange these terms.

A more complete discussion of these terms appeared in "Coming to Terms with Power Quality," in the February, 1999 Power Quality Supplement of EC&M Magazine.

Overall, it's definitely better for the equipment if you change the taps on incoming transformers to optimize the voltage on the plant floor to something close to the equipment ratings. In older plants, you may need to make some compromises because of the differences in the standards on old motors (220/440V) and the newer "T-frame" standards (230/460V). A voltage in the middle of these two voltages (something like 225V or 450V) will generally result in the best overall performance. High voltage will always tend to reduce power factor, thus increasing the losses in the system. This results in higher operating costs for the equipment and the system.

A standard figure (found in motor books and in the original print version of this article) illustrates the general effects of high and low voltage on the performance of "T-frame" motors. This graph is in wide use in a variety of reference materials. But, it's only representative and does not give precise information that applies to all motors. Instead, it represents only a single motor type, with much variation from one motor design to the next. For example, the lowest point on the full-load amp line does not always occur at 21/2% above rated voltage. On some motors, it might occur at a point below rated voltage. Also, the rise in full load amps at voltages above rated tends to be steeper for some motor winding designs than others. The sidebar, on page 78, offers some guidelines for determining the effects of voltage variations on individual motor designs and frames.

Don't place stress on your electric motors and other electrical equipment as a result of operating a power system at or near the ends of voltage limits. The best life and most efficient operation usually occur when you operate motors at voltages very close to the nameplate ratings. When supplying voltage to motors, stay away from the "outer limits."
Click to expand...

There are many other articles explaining this.

stateit · Dec 15, 2014

My general experience with electric chainsaws is: A 2-stroke one is better.

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