Power supply

[RorieT]

Hi folks,

My AX10 came with a 16amp plug. The reviews stated that with a plug converter, everything would be fine....

When i press the 'on' button, sometimes it doesnt start and i need to hold the button on until the motor gets up to speed, then all is fine. The duration of time i need to hold the button on varies.

I may be 'inventing' this situation, but it appears that it starts fine when cold, but as i use it (even just a couple cuts) i need to hold the button on for longer and longer until it will stay running.

I called axminster and they told me that the reason this is happening is because i am running it off a 13amp socket and not a 16amp. Would this be right? In my simple mind, if the 13 amp fuse is not blowing, then it cant be demanding 16 amps..... I do wonder if (and may be totally wrong here) the reason it doesnt start after a few uses is because the cables are warming up and not able to deliver?

Thoughts appreciated.

 

[hagdahuk]

You're right. If you run it off a 13 amp socket that mean that it does not draw 16 amp. Or that the fuse is not working...
But this hardly can explain why it doesn't start fine. Even cables heating can't explain that: the resistance of a cable is very little affected by the temperature. This risk is more that if it get too hot the insulation will melt...

This said, I've no explanation to propose :-(
One generic explanation I can propose -but doesn't really explain why it is different when hot- would be that the transformer in the line, not being powerful enough, drop the tension and thus the delivered power (a motor draw more power when starting).

 

[John15]

I have one of these saws and have it on a 16amp socket. I believe it's because of the extra load when starting up.

John

 

[finish_that]

I would be checking to see if when "hot" there is more resistance when manually turning the blade than when "cold"- basically if there is something getting warm/hot and tighter if it is a new machine this is very possible.
Obviously when disconnected from power and wearing gloves to avoid anything sharp.

 

[Monkey Mark]

I'm not familiar with the AX10, but as suggested above it could be to do with the start up current but I would then be expecting it to still blow the fuse/trip the RCD.

Does it have a NVR switch? It could be related to that. It's also worth checking the connections within the plug (if not a molded one) as a poor connection would increase resistance which could account for things varying with the heat.

I couldn't find which item it was on the axminster site. If you post details of the motor specs, we can work out what the inrush current would likely be to see if that can be ruled out.

 

[HOJ]

Be careful here, all may not be as it seems, your circuit conductors may not be rated for the current being drawn on start up, or continuous loading.

Which may also lead to high volt drops, resistance in cables does increase with temperature, which is why a cables current capacity is calculated at certain values of temperature.

A fuse's rated current is the current it can pass indefinitely, the current at which it blows can be significantly higher, which is why your not blowing out the 13 amp.

Get a Sparky in!

 

[Claud1]

I also have the same problem with a three phase radial arm saw most of the time it is ok but sometimes I have to keep the button pressed for several seconds for it to keep running and it can happen at anytime hot or cold. Before I got a 3 phase supply I ran it off a converter so I thought that was the problem, The saw is a Graulle ( maybe spelt wrong) I spoke with the supplier and they couldn't give me a reason has to why it should happen.

 

[griggs]

Could be the capacitor possibly?

 

[RorieT]

Thanks for all the replies folks.

The saw is this one: http://www.axminster.co.uk/axminster-tr ... ench-25363

It has a NVR switch

I called a sparky today and he didn't think there would be a problem running off a 13amp as if the CB is not blowing, what would be causing the issue. He's going to come over and have a look. But i think i will call Axminster tomorrow to get more details as the guy seemed convinced this was the problem.

I'll let you guys know what i find out, but would appreciate any other help from you guys!

 

[Eric The Viking]

I think I know what's going on.

Lets look at some fundamentals:

A "13A socket" can usually deliver a lot more than that. Fuses are supposed to blow at twice the nominal current (in this case, 26A). If your socket is part of a ring main, that will normally be fused at 30A (or have a breaker nowadays).

Fuses, incidentally are intended to protect wiring downstream - they blow to prevent wiring fires happening, mainly.

Your motor probably draws in excess of 13A on startup. That's not a problem for a 13A plug, probably - it depends on how much more than 13A, and long it does it for.

So in theory, the 13A plug is probably fine, although the fuse might blow from time to time (they get 'tired'). If that happens it's a nuisance, but not necessarily a fault. If one fuse blows immediately after another, then there _is_ probably a fault. Once a week or so is probably just an indication it would be happier on a 16A plug/socket (if worried, call a sparks in!).
. . .

There is another issue: the resistance of the circuit. By that I mean the wiring of the house/workshop. If there is appreciable resistance, the voltage at the machine will drop significantly when you try to start the motor. It's similar to putting a dead short across the mains (well not quite!).

The outcome is that you don't get the current through the motor that it needs to start properly.

I'm guessing that the voltage drop is fairly dramatic, so you need to keep the NVR switch button pressed in as there isn't enough voltage available during startup to keep the NVR's relay latched. Once the motor is up to speed, the starting winding is automatically turned off, so it draws less current (this is different to the 'inrush' current surge in the first half second or so). At that point the voltage will kick back up to near normal, and your NVR relay will stay latched ("on").

Why is it worse after a bit of use? Modern motors are designed to run quite hot, mainly because they can be made that way: it saves copper and thus it's cheaper.

Hot means higher resistance, and I suspect it reduces the efficiency of the motor just enough to make the starting issue worse -- it takes longer to reach the speed at which the motor's starter coil drops out. I don't think you are imagining it.
. . .

So that's my theory. How can you test it? First of all, plug the machine in with as little unnecessary cable as possible - no extensions - and use a socket in good condition, as close to the fuse board as you can. See if it makes a difference. Check the quality of your 13A to 16A adaptor, too - it needs to be made from chunky cable, as it has to carry more than 13A for a short period while the motor starts, and that connections in both plug and socket are screwed up tight to make a really good connection.

Assuming I'm right, you really then have two choices: either use the arrangements that worked on the test, or you'll need to get a sparks in to fit a proper 16A circuit.

[edit] Get your sparks to check the voltage AT THE MACHINE whilst it's starting. If there's a significant drop, you have your answer!

 

[n0legs]

Low voltage.

 

[Myfordman]

Do your workshop lights dim when starting the machine? if so indicates an inadequate supply to the workshop either in terms of cable size or length or both.

 

[hagdahuk]

Hi again,

really the cable can't be the problem. Anyhow for your security check they have enough section (1.5sqmm as a very minimum).
And the fuse or breaker should blow if consuming more than 13A for a very short time. Give me if you want the exact reference and I'll send you the breaking curve (indicated how much more of 13A it will accept versus time).

Now, I've been having a look to the link you published and then the user manual of your table saw. There is the electric circuit. Even the capacitor can't be the problem (it can cause the motor to last long to get normal velocity or even not really start spinning, but can't make necessary to maintain the button pushed).
What I've seen is that there is a thermal protection in the motor (see contact FR in the electrical scheme page 31). So it came to my mind, and it would correspond to that it's not working when hot, that maybe the motor doesn't cool down fast enough when it just stop. So the thermal protection trigger and when you start again (pushing the button force the start), the integrated fan cool it down enough to reset the protection.

Check if the motor fan, and the motor itself, is clean enough. Ideally clean it with compressed air.

And let us now.

 

[Monkey Mark]

Depending on which model you got.
2.2kw motor. Run current 9.6 amps. Start current depends on how it is wired and whether it has a soft start function, but for induction motors of that size you are probably looking at roughly 3 times the run current, so in the region of 25-30 amps.

Or

3kw motor. Run current 13 amps, start maybe 35 - 40amp. Again, depending on how it is wired and soft start or not.

I'm afraid I would have to disagree with hagdahuk above (sorry, nothing personal) and say 2.5mm cable minimum to take the inrush current and also to reduce the voltage drop which may well be your issue. As the cable heat up through use the resistance increases causing a further volt drop which could explain why it happens more after some use.

If you are in a garage/shed etc, how far is the power having to come from your house? Again, this will affect volt drop depending on distance and cable used.

At the end of the day, it is too hard to speculate and probably foolish to do so too. As mentioned in a previous post, a good start would be to measure the voltage at the machine during start up. If it drops below 223.1v (3% volt drop is the specified limit for a ring main according to the regs), then this could well be the issue. You may need a dedicated 16amp circuit which, if you have a distribution bored in your workshop, would likely not cost much to install. The commando sockets and plugs are fairly cheap on our favorite auction site and larger gauge cable can often be had cheap if you ask in an electrical supplies shop/trade center what they have left as end of reels as they often sell it off cheap to get rid.

 

[hagdahuk]

I do agree with you Monkey Mark about the section. 1.5mm is a VERY minimum. I personally would put 2.5mm too.

Anyhow, with 1.5mm and 20m long. At 20 degree, resistance is 0.227 Ohms, and at 25 Amp, voltage drop is 5.6V (2,3%)
At 100 degree and all same, resistance is 0.316 Ohms, voltage drop is 7,9V (3,3%). And at 100 degrees the isolation melt...

That's what I meant saying I don't believe the problem is the cable size. But again, I would anyhow put 2.5mm

And same, reading the electrical circuit, all the previous does not explain why he should maintain the button pushed (it would only explain that the motor last to start)

 

[RorieT]

Thanks for all the replies!

I just called Axminster again to understand why they think its my supply thats to fault - they said if the saw is slow, it will be the supply, but not starting is likely to be the switch thats faulty (i dont think it is!).

Regardless, i am going to install a 16 amp type 'c' breaker with a stand alone socket for the saw. Hopefully this will suffice. I will run this with 2.5mm T&E as i believe this is more than suitable for a 16 amp supply.

In answer to some of the questions, i have a direct line from my house CB to the garage CB using a chunky cable (not sure the size). The garage is only a couple meters away from the house. The distance from the garage CB to the saw is then a further 4m of cable.

For the 'low voltage' comments - i guess this will only be due to voltage drop due to high lengths of cable etc? Rather than something more serious?

HOPEFULLY this will sort the problem and i dont need to go into all the tests mentioned above. But thanks again for the support (so far!).

 

[hagdahuk]

Type C seems a good choice. Allow 3 times rated current for around 15s and 10 times for 2s.

Take chance your doing maintenance to check if the motor/fan is clean and as suggested finish_that to check also no other mechanical reason creating a break tork when hot.

 

[John15]

Rorie,

I forgot to mention that my Axi10 was fitted with a blue socket for plugging into a 16amp socket when I bought it.

John

 

[Eric The Viking]

i am going to install a 16 amp type 'c' breaker with a stand alone socket for the saw. Hopefully this will suffice. I will run this with 2.5mm T&E as i believe this is more than suitable for a 16 amp supply.

All good ideas.

In answer to some of the questions, i have a direct line from my house CB to the garage CB using a chunky cable (not sure the size). The garage is only a couple meters away from the house. The distance from the garage CB to the saw is then a further 4m of cable.

Aha!

That "further 4m of cable" -- what size is it, and at what point is the 13A socket (where it becomes the flex for the machine)?

The analysis by hagdahuk isn't wrong, but it's not the whole story, and it's misleading in several important details:

Do either your house or garage distribution boards have fusewire fuses, or are they all on miniature circuit breakers (a little switch for every circuit)?

Fuses (not miniature circuit breakers) put significant resistance into the circuit, especially if they are used close to their blowing current (i.e. over their rated current). Given the motor sizes, whichever you have you're around the sensible maximum for anything using a 13A plug, because of the plugtop fuse. It's also the case that the rectangular pins of the 13A system are not very good connectors - they too can add high resistance (16A plugs have round pins, which are much better).

Finally there is the issue of a loose terminal somewhere - in a plug, socket, or one of the distribution boards or some cable junction we don't know about. Loose connections are high resistance (and they start fires, but that's another story). It's not at all uncommon to find that in house wiring. Something works OK-ish when you plug a table lamp into it, but run a 3kW heater and the loose joint will start to heat up and go higher resistance. It's entirely possible this is what's going on, but you'll never know unless either you or your sparks works the problem systematically.

Otherwise, hope you 'got lucky' by arbitrarily doing something. That course of action can be expensive, and possibly futile. Even if you make the problem go away, you don't know if you actually found and fixed the fault.

As I said, get someone competent to measure the voltage AT THE MACHINE when you turn it on. If you get a big drop during startup, and then it kicks back up to noticeably below your not-loaded mains voltage when the machine is running, the problem is in the supply.

You need to find out (a) if that's the case, and (b) where any fault lies, before throwing money at something you're guessing about (and I am too!).

A final test is to connect the machine to a known good supply. If it starts and runs fine, you know FOR CERTAIN you have a supply problem. If it doesn't, you ONLY know there is a machine problem (you may still have supply issues at home too).

Electrics need to be dealt with methodically and NOT by making assumptions -- those get people killed.

E.

 

[RorieT]

Do either your house or garage distribution boards have fusewire fuses, or are they all on miniature circuit breakers (a little switch for every circuit)?

Fuses (not miniature circuit breakers) put significant resistance into the circuit, especially if they are used close to their blowing current (i.e. over their rated current). Given the motor sizes, whichever you have you're around the sensible maximum for anything using a 13A plug, because of the plugtop fuse. It's also the case that the rectangular pins of the 13A system are not very good connectors - they too can add high resistance (16A plugs have round pins, which are much better).
.

You could have the problem right there!!

The power in the house went into a Consumer unit for storage heating, and also a CU for the rest of the house. With the storage heating gone, that CU was used to then route electrics over to the garage where a modern CU was used to distribute the power. The old storage heating CU uses a wire fuse!

I note all your other points. I will take this one stage at a time - first being to sort the wire fuse, next the 16 amp supply, then if problems still exist, onto the fault finding.