The last one of these went for £310. This mill seems to be one favoured
for CNC conversion - how does this guy survive shedding these so cheap?
Typically he kicks them off at £1 no reserve.
No connection - just seems a risky way of selling kit.
Steve
Actually the X2 isn't the best mill to convert.
It has rack and pinion feed to the Z and a weird spring loaded lever
system to support the head.
The motor board on this one can be suspect if you live in an area
where the voltage can rise to 250 or close as it's rated at 220 v
Since the introduction of the longer table and screw on the X1 that
machine actually has larger travels than the X2.
About the only thing going for the X2 is the fact it has a larger
motor than the X1 but as the electronics are flawed it's a moot point.
--
Regards,
John Stevenson
Nottingham, England.
Visit the new Model Engineering adverts page at:-
That's the cheapest for a while - they usually go for a little more, perhaps
£350 - he sells one every week - and they aren't such a great bargain, even
at the cheaper price.
Add £60 for delivery, and the price is now £370 to £410 delivered.
Chester will sell you one for £450 delivered, and while their after-sales
service isn't all that hot it is getting better. AET will sell you one for
£490 delivered, but that's "prepared" and comes with some accessories which
is worth a bob or two on the price. Warco charge $455 delivered, machinemart
don't seem to sell them any more.
Known problems include the FET's exploding when the voltage is too high - I
think AET replace them; - Chester replace the whole circuit board on the
C3/Conquest lathe (which has many interchangeable parts with the X2/Conquest
mill), and perhaps Chester do something similar on the X2. Dunno about
Warco.
The FET's are about £3.50 each BTW (not £35 as I was recently quoted!)
The Z axis on the X2 sucks too, I haven't seen one with less than a mm of
play.
However, that's getting off the point - you have some kind of after-sales
service, guarantee and backup with the big boys, and for the sake of £50 or
so, is it worth it? - perhaps, but it isn't the great bargain it might seem.
sipped
snipped
Snipped
Known problems include the FET's exploding when the voltage is too high
- I
think AET replace them; - Chester replace the whole circuit board on
the
C3/Conquest lathe (which has many interchangeable parts with the
X2/Conquest
mill), and perhaps Chester do something similar on the X2. Dunno about
Warco.
The FET's are about =A33.50 each BTW (not =A335 as I was recently
quoted!) --
Peter Fairbrother
My X2 (Chester Conquest) has just expired, so what are the FET's ?
where
can you buy for =A33.50 each and are they a easy fit. I think that all
for now.
Mike Cole
The FETS (field effect transistors) are black rectangular transistors about
12 x 9 x 3 mm with three legs which will be mounted on an aluminium
heatsink.
The AC mains input is converted to DC by the rectifier(s), and the FETs then
control how much DC goes to the motor. The FETs are the main output
switches/controllers, and they are specced for 220V ac input, not 250V, so
can blow.
Actually that's just an assumption - and it may well not be true. The US
110V boards also have FET problems, so it may not be solely a voltage issue.
Maybe it's bad FET's? Snubber or reverse diode problem? But if you stick in
a FET with more magic smoke afaict in practice it seems to work okay
thenceforward, so that's what I'd do.
I don't have an X2 so I can't say for sure whether it's an easy fit or not,
plus the boards vary slightly between different X2's and C3's. I do have a
Chester C3/Conquest lathe and I just looked at that - it has the replacement
circuit board I mentioned, and it doesn't use FET's at all, it uses SCR's
instead, so that's not much help as a guide.
Which leaves a question - does the Conquest mill have the improved circuit
board, like the Conquest lathe? I will assume not, but I may be wrong and/or
they may have changed it over time.
The FETs would be fairly easy to exchange if you have any electronics
experience, but you will have to do some desoldering and soldering and you
might have to mess around with heat-transfer compound (used to improve the
transfer of heat between the FET and the heatsink) and/or uprated components
which are of slightly different size.
Some other issues - first I'd make absolutely sure that the problem is the
FET's - likely but by no means certain, for example the brushes in the motor
can go, the wiring can go, the switch, as well as several other things -
even the potentiometer which controls the speed can go wrong. Checked the
fuse?
Of course the FETs may have small blackened holes in them where the magic
smoke escaped, look carefully, in which case ..
Second, when the FETs blow it is quite possible that other components are
damaged by the transients. I'd check the circuit generally before just
replacing the fets and plugging in - although others might not, and
apparently people don't usually bother.
Third, this is mains equipment and dangerous, are you confident you can do
it safely?
I'll look out a source for the FET's - £3.50 is the correct-ish price for a
suitable FET, rather than for any particular FET.
LMS do fets for $4.95 :
formatting link
but I
can probably choose something better for you, those are for US voltages.
It would be a help if you could tell me the numbers on the FETs so I can
choose a better specced one. Probably they are IRFP-460 / IRFP-460A, but not
definitely. There may be several black packages attached to the heatsink, it
may say FET or MOSFET on the board to identify them, or just send all the
numbers. If you are stumped send me a photo of the inside of your controller
and I'll point out the relevant bits.
BTW some boards have two fets, some only have one. Just to make life more
interesting ..
Yes, we "repair" the boards. Originally, over two years ago when we
first imported them, we cleaned, adjusted, lubrated, incorporated a
captive drawbar sytem on the X2's, and sent them out to our customers.
Out of the first 10 we sent out, about 4 boards blew within about three
to six months. I do not understand the electronics part of this, so I
will explain it simply according to what I have understood from David -
our electronics bod.
There are two MOSFETS on the board. Each one is good and "genuine", and
correctly rated at 500V. This means each one can handle upto 250V in
real terms, before it blows. In each of the four blown boards, the
first MOSFET has blown, and the second is OK. However, the second does
not kick in. Can't explain why.
In our own workshop, we have measured voltage supply above 250V.
Highest measured 263V so far !.
We repaired various boards with various MOSFETS, and we finally settled
on 1x1000V IXYS MOSFET IXTH14N100 - Farnell Part No.61602954 cost
=A316.40 per piece, when we last checked. There may be a cheaper
alternative - better or worse I cannot say, but dare we take the
risk?...NO. In the repair process, the 2x500v mosfets are removed, and
the new 1x1000v mosfet is soldered into the second slot.
Since then, all boards have been repaired before the machines which we
prepared were sent out, and everything in this repect has been fine so
far...touch wood.
I have brought this to the factories attention, given them a "free"
MOSFET, but for their own reasons, they are not prepared to supply the
X2 with the new 1x1000v MOSFET, even though we were prepared to pay the
higher cost.
We have stopped selling the X2 now - this being one of various reasons.
We are however continuing to support our existing customers who have
X2's, and we may sell "repaired" boards at around =A3125.00 inc.vat and
carriage, starting next month, along with various accessories and spare
parts, in a similar manner to LMS. (Customers who have purchased an X2
from me and who are reading this message can rest assured that they can
buy spares from me at a reduced rate - if outside warranty).
Please note, C3 is not equal to The Conquest lathe. C3 is equal to the
Super Conquest. Both C3 and Super Conquest have overload protection so
chances of MOSFETs blowing on them are far reduced. On them, the speed
limit control part of the circuit is more likely to blow (mainly from
abuse...knowingly abusing/testing the lathe as I did...can't tell you
how....or...unknowingly - fat chance) before the MOSFETs blow. The
Conquest, CL300 etc, have no overload protection, and the MOSFETs on
them are more likely to blow in similar manner to the X2 boards.
Looking at the demand, we might consider repairing these boards too!,
even though we do not sell these lathes.:)
Ketan.
Hi Ketan,
Two possibilities - one, if the fuse has blown then the failed MOSFET has
likely failed short and is shorting the other MOSFET - or two, if the fuse
is okay the failed masfet's gate has failed short, and the short is stopping
the second MOSFET's gate getting any control voltage.
In both cases simply removing the failed MOSFET should restore function. You
don't really need two MOSFETS.
Fair enough - but 1000v seems a bit of overkill to me, and 14 A seems just a
little skimpy. The original FETs are rated at 20 A each, 40 A overall.
Perhaps a pair of 900V 9.5A STW9NB90 MOSFETS at £12.50 for five from
formatting link
would suffice better?
Half the total "on" resistance so should run cooler, plenty volts, and a bit
more current - at £5 the pair ...
But I'd understand if you didn't - you have a record of success with the
more expensive MOSFET.
I have a standard Conquest, with a "US-made circuit board", which does not
use MOSFETs at all.
I can see why - but it did have a niche, so it's sad in a way.
Is there anything else available between the X1 and the X3, at around the
£500 mark?
Something with a bit more oomph! than the X1, and less money than the X3,
with a non-round column?
Hi Peter,
What you said for the MOSFETs makes sense. We just didn't want to take
any risks at the time, and we settled on the one which I mentioned
earlier, after testing one or two others. I cant recall if we had
tested the one you suggested. If anyone tries out the FETs which you
are suggesting, and if it all works fine, do put the post on to help
others.
For the Conquest lathe, it looks like we wont be repairing boards if
the American boards are fine. (What a shame Anthoney).
Thanks, Ketan.
Peter,
It had / has a niche. There were technical issues such as circuit
board, table size (width), limited table travel, restricted Z movement,
rack & pinion movement, some of which restricted sales. The main thing
it has going for it is the motor. Commercial reasons such as
competition was just a minor issue. If and when we come up with an
alternative to the X2, you will hear about it, but there are no plans
for us to introduce a replacement model in the near future. For the
time being, we will concentrate on working with independent companies
and persons to provide more accessories for the Super X1L - long table
version and X3.
Ketan.
I found my FET's and the only numbers on them are K790 with 2A on one
and 6k on the other.Things like the brushes and fuse are fine and a
relay and power light still work. I also remembered I have a old
control board off a another scrap conquest, I might have a go with
fitting that. As I work in Chester I could allways go to ChesterUK and
see what they say. There open day is coming up in a couple of weeks.
Mike Cole
Mike
That's a 2SK790 FET, N channel, ratings are 500V, 15A and 150W max
dissipation, Rds 0.29 Ohms. It's listed as obsolete but can be found for
anywhere between £3.00 and £16.00 in the UK. The other codes (2A and 6k are
likely to be batch or date codes).
Martin
Not entirely certain, 500V is certainly enough to cope with up to 350V RMS
supply so it's unlikely to be a supply overvoltage issue. Provided that the
device is correctly heatsinked and driven correctly, it should not fail as
often as they apparently do. I'm not familiar with the circuit, but if
there's a switch somewhere in the high voltage DC supply it may be that a
high voltage spike is generated by interrupting the current to the motor or,
possibly, due to poor contact in the motor's commutator; of course, if
there's a correctly sized suppression capacitor across the motor, this
shouldn't happen.
Martin
Yes - I was wondering about that too.
Done a bit of googling into the how and why of this, and afaict it seems the
US 110V ones tend to fail short-circuit, so either the fuse blows or the
motor goes at full speed, while the 220 V ones fail open-circuit, so the
motor doesn't turn - the latter could well be a gate insulation failure, the
gate insulation fails short and that also stops the second FET's gate
getting any control voltage so the motor stops even if one FET is still
good.
Looks like an overvoltage problem in the UK, and an overcurrent/overheating
problem in the US models. But I haven't studied the circuit either, and am
just guessing.
Mike wrote:
What Martin said.
Does sound like a FET failure.
Be a bit careful if you decide to swap the FETs - they are static sensitive
devices. In theory you should ground the equipment through a resistor, and
wear a grounding strap. You also shouldn't use a vacuum desoldering tool, as
they can generate static.
In practice however a little care is all that's necessary, I blew one about
20 years ago, when they were more sensitive than they are now, and haven't
blown one since even though I almost never use a grounding strap (only when
the equipment is worth £1,000's)
Modern power MOSFETs almost all have electrically insulated cases, so you
don't have to worry about electrical insulation between the FET and the
heatsink - but it would be a good idea to use some thermal paste between the
FET and the heatsink.
And maybe drill some cooling holes, especially if you have a 110V model.
It may well run on one FET - all you would have to do is remove the broken
FET, but it will be hard to tell which one to remove. Don't swap just one
fet though, swap a pair if you will be using two fets.
If you are stuck I can fix it for you. That way I can also look at the
circuit etc, and tell you if I guessed right about what has happened. :)
Maybe swap the fix for some scrap conquest bits, plus ?? either way?
It may well run on one FET - all you would have to do is remove the
broken
FET, but it will be hard to tell which one to remove. Don't swap just
one
fet though, swap a pair if you will be using two fets.
If you are stuck I can fix it for you. That way I can also look at the
circuit etc, and tell you if I guessed right about what has happened.
:)
Maybe swap the fix for some scrap conquest bits, plus ?? either way?
--
Peter Fairbrother
Hi again Peter
Some good news, I have swapped over the control boards and the old
one
seems to work. But not tried it under any load or lenght of time yet.
If you
would still like to have a go at the other one I sure would like to
have a spare
board just in case. The conqust bits I have are the box section column
with
its fittins, rack stay and clamp thing at the bottom.
Mike
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