JCB Grinder NB

[paulrossall]

Was using my 15 month old JCB 240 volt 2000 watt grinder on my trailer and after a few minutes smoke started coming out of the angle grinder. Rested it a minute because I could not believe what I had seen but on running again smoke came out. It was only the third time I had used it, bought from Argos and just out of its 12 month waranty.
Next I used my 500 watt Black & Decker drill to put 13mm hole through angle iron at front of trailer to secure replacement tow hitch. Starting the second hole and drill slowed down and ... yes guessed right, smoke started coming from the drill. Thought maybee I had strained it but bit was newish, blacksmith quality, and was oiling the hole and drill was only slowing slightly until the smoke occured.
I then realised I was using an extension lead that said "not to be used for more than 1000 watt" because SWMBO had borrowed my industrial quality lead to watch television in the bedroom.
Do you think I buggered the grinder by having a big voltage drop and thus using more amps, and then buggered the drill for a similar reason?
I presume the drill is a write off (2 years old + well used) but what should I do about the grinder?
All advice welcome. Paul

<hr width=100% size=1>" there is nothing-absolutely nothing-half so much worth doing as simply messing about in boats".

 

[chriscallender]

I'd be very surprised if the underrated extension had caused the problem - of course the extension itself could get hot and start smoking, but the tools would just run slower if there was insufficient voltage and not be very usable.... they wouldn't be damaged.



My guess is that its just coincidence... the angle grinder blew up cos its faulty and has been since new - the drill at 500w was probably overloaded and not really up to the job. Especially when drilling metal at low speed they can get hot because they usually have a cooling fan that is driven directly off the motor so low RPM = more heat, especially if you are putting quite a bit of pressure on it and loading the motor, and you're using a big 13mm bit.

As for what to do, if the motor windings are knackered on either tool, they are probably not economically repairable. Unless someone knows different.

Chris

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[anchorhandler]

Its unlikely that the problems you encountered with both your drill and angle grinder were caused by the extention cable you were using.
The extention cable is rated as 1000 watts purely because that is the safe current carrying capacity it can handle before it overheats. By drawing a higher load than 4.5 amps (equivalent to 1000 watts at 240volts) the only thing you are accomplishing is to heat up the copper conductors in the cable. The drill/grinder would still have 'seen' 240volts and continued to draw appropriate current.
If the tools were smoking then there was obviously too much heat being generated this is normally caused buy operating on the wrong voltages or frequency or by pure overloading.
This sounds like a possible frequency problem than anyhting else, were you using a portable generator or was it mains power?, Its inportant to check what frequency the grinder/drill are rated for (most are 50/60 hz compatible) this is especially true if using a portable generator on the wrong frequency to power the tools.
Has anyone tampered with or re-wired the connections on the extention cable?

Simon


<hr width=100% size=1>I'v got 2 ears.2 eyes and 1 mouth....if only i could use them in that proportion!

 

[john_morris_uk]

I disagree. An extension cable supplying too low a voltage can cause tools to draw too much current and burn out. In haste - no time for lengthy explanations now.

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[paulrossall]

Was off mains and I have just checked voltage, reading 230 volts and plugged tester into the extension and it is correctly wired. However just noticed extension is plugged into a 2-way adapter. Once the grinder at 2000 watts starts up isn't it possible that the voltage would drop (understands it drops if wires are not big enough, or connections are not that good). Once the voltage drops doesn't that mean grinder will try to draw more amps so the volts X amps gives 2000 watts or doesn't electricity work like that?
Just posted this and seen John Morris's posting which seems to agree with what I thought.

<hr width=100% size=1>" there is nothing-absolutely nothing-half so much worth doing as simply messing about in boats".<P ID="edit"><FONT SIZE=-1>Edited by paulrossall on 15/03/2004 21:39 (server time).</FONT></P>

 

[No1_Moose]

Yes, you will get a voltage drop which will cause the motor to draw a higher amperage and therefore heat up.
I did a very similar thing to you at school this week!

<hr width=100% size=1>Ross

 

[anchorhandler]

Hi Paul
Yes you are correct in that, as the voltage falls, so the current will increase. (power in watts=voltagexcurrent for a pure resitive load which although not technically true in this case is close enough for arguments sake) however my point above was that assuming the extension cable was a normal houshold one, it wouldnt have been longer than 5-10 meters or so (especially if it was rated at only 1000 watts) which in electrical terms poses only a very minimal resistance. assuming its a 2mm csa copper conductor that equates to approx 7.95milliohms for a 10 M length.
You also stated that the power drill, rated at 500watts (half of the current carrying capability of the extension cable) also started smoking. In order to for this to happen due to a voltage drop, there would have to be something very obvioiusly wrong with the cable.
The easiest way to prove this would be to try your drill again (now that its cooled down) on a different extention cable but plugged into the same outlet in the same situation. Obviously if it starts smoking again then its the drill (or something else in the system) is at fault.
Hope i havent confused things even more
Simon




<hr width=100% size=1>I'v got 2 ears.2 eyes and 1 mouth....if only i could use them in that proportion!

 

[Seafort]

I doubt that the extension cable is the problem. Most problems with extension cables result from over-heating of the cable. Made worse by leaving some coiled in the drum.

I use a 50 ft cable in the boatyard and dont have any problems (Not a domestic size though).

BTW has anyone noticed that the cheaper dehumidifiers recommend that they are not be run using an extension cable?

As an after thought.....Allways use plugs that have a post to wrap the conductor around and a "nut" to screw down on top (if possible). I have had a bad experience with a 3Kw fan heater and a "screw down and trap" plug (A room full of smoke and a melted plug).

Dave.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Seafort on 16/03/2004 00:05 (server time).</FONT></P>

 

[john_morris_uk]

Difficult to tell exactly where the voltage drop occurred. Low voltage would produce the effect as has been explained and its too much of a co-incidence I suspect for the two power tools to fail consecutively. Could be a bad conncetion anywhere. I had an extension lead that had a poor connection where the plug pin enters the socket part once, a partly burned out socket when it was opened - but nothing in the way of obvious heat and smoke was visible while it happened.

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[john_morris_uk]

Further to my previous message, I understand that the average domestic power tool is manufactured with an expected working life of only a few hours (twenty comes to mind, but I can't be sure). Thats what my brother told me when I burnt out the switch on my well know make of drill many years ago. I was drilling multiple half inch holes in brickwork, and the drill just gave up. I now only try to buy better quality ones!

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[chriscallender]

I disagree. For a pure resistive load and Ohms law you have V=IR, which can be arranged as I=V/R. So if you reduce the voltage across the resistor, the current also goes down.

Then, since Power = I V, rewriting this in terms of V gives
P=(V squared)/R. In other words, halving the voltage across a resistive load reduces the power that it is dissapating by 4 times. P is not a constant for the power tool, it is just a nominal rating that it is given when its running off 240v so P=IV does not imply that as V reduces I has to increase to compensate. If this were so then I would increase to infinity to keep the power tool running when V dropped to zero and you would have problems switching it off!!!!

What I am not sure about at all is what electronics is inside a power tool and whether its fair at all to consider it a resistive load at all. It could be that there is some fancy stuff as well as the motor, and the electronics does some kind of feedback to maintain constant speed on the motor, eg when it senses the speed is dropping it increases the drive to the motor. If there is some clever feedback like this then I could believe that low voltage would cause problems, although I still feel that this is improbable, and if true shows that the power tool is badly designed - under voltage condition is probably to be expected for a power tool that could be in use on a building site for example.

So I still think that both tools blowing up on the same day is partially coincindence (I say partially because they were both being worked hard) and nothing to do with the extension cable that is used. Now had the extension cable itself started smoking I would accpet that was due to it being underrated.

Chris

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[Jools_of_Top_Cat]

I have run a 750W drill from a 600W generator. It just ran slower but did not kill it.

Suspect overheating due to working so hard, killed many cheapo circular saws this way. Did it have a sweet smell when it was smoking.

There used to be a black and decker shop on London Road or Edge Lane in Liverpool which sold motors, bushes etc. much cheaper than buying new. I don't know if they still exist.

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>Top Cat Homepage</A>

 

[Benbow]

This is certainly my understanding of the situation. The device doesn't know that it is rated at 2KW and try to pull more current to achieve it ! If the resistance stays the same and the voltage drops then the current drops too.

In fact this all goes to support the widely held theory that all electronic devices are powered by smoke. This can be seen by the fact that when the smoke leaks out they stop working! I have personally seen this phenomenon on devices ranging from autopilots to television sets.

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[anchorhandler]

Hello Chris

"If this were so then I would increase to infinity to keep the power tool running when V dropped to zero and you would have problems switching it off!!!!"

Actually,on an iduction motor, if you reduce the voltage then the current will definately increase to compensate and, as you put it, if you tried to decrease the voltage to zero (by using a reostat or similar) the current would progressively increase to compensate to the point that the fuse in the plug would blow or the breaker would trip. The motor is just a load, current is an effect of supplying that load with a voltage. To be technically correct here the drill is an induction load not a resistive load therefore to work out the true power you have to multiply the voltage by the current draw then multiply that by the power-factor as set by the power station (usually around .8).

The simplest way to proove this it to check out 'machine marts' individual motor ranges
There you will see that a 230 volt,2HP (or 1492 watts) 2 pole motor requires a starter rating of 10-16 amps
you will also see that a 110 volt,2HP (or 1492 watts) 2 pole motor requires a MINIMUM starter rating of 20 AMPS......Why when both motors are the same power?....because one is operating at a much lower voltage therby drawing more current. And that motor has been designed to run on 110volts.....now imagine running a 230volt motor off a 110 supply!!!!

At the end of the day, apart from some slight discrepancies, we are arguing the same point......that the extension cable probably isnt to blame.

its good fun arguing though!

Simon



<hr width=100% size=1>I'v got 2 ears.2 eyes and 1 mouth....if only i could use them in that proportion!

 

[rex]

I'm with Chris on this one. The 110 and 220 volt motors you quote have different resistance windings designed for a particular voltage. If you used the 110 volt motor on 220 you would get twice the power - very briefly!

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[rex]

Re: Benbow smoke

It's nice to come across someone who knows what they are talking about on this forum. I had a drill with smoke coming out of the vent holes in the body. I have blocked all those up with epoxy filler but the drill still doesn't work. I now realize all the smoke must have leaked out before I blocked the holes. Could you tell me where I can buy good quality smoke at a reasonable price and also, if I can only get 110 volt smoke, can I use this in a 240 volt drill if I use a transiformuloda.

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[William_H]

I doubt that the cord has caused your problems although strange things can happen. The common failure of power tools due to overheating is shorted turns of the coil wire on the armature ie rotating part. When you try to use it' after failure it runs slow has a strange sound about it ( the sound of arcing at the commutator and if you can see the brushes through the cooling holes you will see a huge spark display indicative of large current drain into the shorted turns. You may be able to purchase a replacement armature however it's probably throw away time. I don't find it surprising that both tools died given your weekend of heavy maintenmance on the trailer. The moral is that power tools are not made for continuous use and you must let them cool down.

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[paulrossall]

What you have described is spot on. I can see huge sparks through the bright yellow (JCB Coloured) case. However I was not putting much presure on the grinder and only used it for 3 or 4 minutes. It has only had 15 minutes use in its short life.
Now the drill could be a different case as I was drilling a 13mm hole and was pushing it until it slowed down. Going to put another post to ask about buying a drill.
Half the replies seem to support my theory that voltage supply probably went down and thus grinder drew more amps which overheated something. If I had carried on I assume the 13 amp fuse would have eventually blown. One problem is I cannot find my receipt but I have got the item listed as "Argos" on my credit card statement, even though it is 15 months ago. Think I will go and ring the customer service number on the JCB instruction book and see what they say. I will report back.

<hr width=100% size=1>" there is nothing-absolutely nothing-half so much worth doing as simply messing about in boats".

 

[pheran]

I had the symptoms you describe with my angle-grinder. Took it apart, cleaned out the brick dust and metal filings, new set of brushes and it's worked perfectly ever since. Worth a check.

<hr width=100% size=1><font color=blue>A convert to steel boats and displacement cruising - the only way to go</font color=blue>

 

[paulrossall]

I have taken out the brushes and they look fine. I have only ever used it on metal so it actually looks like new. Paul

<hr width=100% size=1>" there is nothing-absolutely nothing-half so much worth doing as simply messing about in boats".