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From: N_Cook on 6 Oct 2009 03:40
50 amp not 500


From: Wild_Bill on 6 Oct 2009 06:42
I don't know about the semiconductors, but the loop of wire may be a braking
"resistor".
Battery powered power tools with permanent magnet fields sometimes have a
loop of wire to dump the spinning motor current into, when the trigger is
released. This causes the cutting blade, in a saw for example, to stop
sooner than just letting the armature to coast to a stop.

You may know a procedure for testing the LRA locked rotor amperage of the
motor, which may be a useful indicator for selecting the semiconductors.

Metal current feedback circuit "resistors" that I've seen in DC motor drives
and treadmill drive circuits sometimes look like strips of bare sheetmetal,
or just a half-circle of very heavy gage copper wire.
I guess the type of material used will depend upon the circuit designer's
background and material/part cost.

--
Cheers,
WB
..............


"N_Cook" <diverse(a)tcp.co.uk> wrote in message
news:haes5q$lhe$1(a)news.eternal-september.org...
> The 2 paralelled output TO220 thyristors had their identities ground off
> before insertion. 200W, 12V motor so 17 amp so would they be say 30V 8amp,
> 10amp or 15 amp rating each? No fuse in the control anywhere but there is
> a
> main relay and more electronics than just for controlling speed so could
> there be an overload sensing cct that drops out the relay ? While at it
> there is an off board loop of copper coloured wire, perhaps microbore
> copper
> tube could that be a 20 or 500 amp fuse or just a dropper element for
> overload sensing ?
>
>

From: N_Cook on 6 Oct 2009 07:03
Wild_Bill <wb_wildbill(a)XSPAMyahoo.com> wrote in message
news:UaFym.21360$UY2.13211(a)en-nntp-04.dc1.easynews.com...
> I don't know about the semiconductors, but the loop of wire may be a
braking
> "resistor".
> Battery powered power tools with permanent magnet fields sometimes have a
> loop of wire to dump the spinning motor current into, when the trigger is
> released. This causes the cutting blade, in a saw for example, to stop
> sooner than just letting the armature to coast to a stop.
>
> You may know a procedure for testing the LRA locked rotor amperage of the
> motor, which may be a useful indicator for selecting the semiconductors.
>
> Metal current feedback circuit "resistors" that I've seen in DC motor
drives
> and treadmill drive circuits sometimes look like strips of bare
sheetmetal,
> or just a half-circle of very heavy gage copper wire.
> I guess the type of material used will depend upon the circuit designer's
> background and material/part cost.
>
> --
> Cheers,
> WB
> .............
>
>
> "N_Cook" <diverse(a)tcp.co.uk> wrote in message
> news:haes5q$lhe$1(a)news.eternal-september.org...
> > The 2 paralelled output TO220 thyristors had their identities ground off
> > before insertion. 200W, 12V motor so 17 amp so would they be say 30V
8amp,
> > 10amp or 15 amp rating each? No fuse in the control anywhere but there
is
> > a
> > main relay and more electronics than just for controlling speed so could
> > there be an overload sensing cct that drops out the relay ? While at it
> > there is an off board loop of copper coloured wire, perhaps microbore
> > copper
> > tube could that be a 20 or 500 amp fuse or just a dropper element for
> > overload sensing ?
> >
> >


Taking a closer look it is probably solid 1.7mm copper wire in a loop above
the board of about 1 inch diameter. It is in the supply line to the power
devices (maybe powfets rather than thyristors) not the power to the
electronics. But operation is via rotary pot with switch so have to go throu
gh minimum revs (pulses) before switching off. So still a mystery, no way a
fuse , the cross section of the tracks, wide yes, must be less than 1.7mm
solid wire. Incidently now all in working order on the bench, not
reassembled yet onto the caddy a G Caddy TEDC 12201 that I find no www ref
to


From: N_Cook on 6 Oct 2009 07:13
Perhaps it is just a wire link, it does cross over some tracks, perhaps
someone decided 1mm was too small a section for copper wire to reliably hold
up in a vibrational environment. Still I cannot see any obvious track
knecking or other possible weak link/fuse possibility


From: Jim Yanik on 6 Oct 2009 08:37
"N_Cook" <diverse(a)tcp.co.uk> wrote in
news:haf83a$3id$1(a)news.eternal-september.org:

> Wild_Bill <wb_wildbill(a)XSPAMyahoo.com> wrote in message
> news:UaFym.21360$UY2.13211(a)en-nntp-04.dc1.easynews.com...
>> I don't know about the semiconductors, but the loop of wire may be a
> braking
>> "resistor".
>> Battery powered power tools with permanent magnet fields sometimes
>> have a loop of wire to dump the spinning motor current into, when the
>> trigger is released. This causes the cutting blade, in a saw for
>> example, to stop sooner than just letting the armature to coast to a
>> stop.
>>
>> You may know a procedure for testing the LRA locked rotor amperage of
>> the motor, which may be a useful indicator for selecting the
>> semiconductors.
>>
>> Metal current feedback circuit "resistors" that I've seen in DC motor
> drives
>> and treadmill drive circuits sometimes look like strips of bare
> sheetmetal,
>> or just a half-circle of very heavy gage copper wire.
>> I guess the type of material used will depend upon the circuit
>> designer's background and material/part cost.
>>
>> --
>> Cheers,
>> WB
>> .............
>>
>>
>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message
>> news:haes5q$lhe$1(a)news.eternal-september.org...
>> > The 2 paralelled output TO220 thyristors had their identities
>> > ground off before insertion. 200W, 12V motor so 17 amp so would
>> > they be say 30V
> 8amp,
>> > 10amp or 15 amp rating each? No fuse in the control anywhere but
>> > there
> is
>> > a
>> > main relay and more electronics than just for controlling speed so
>> > could there be an overload sensing cct that drops out the relay ?
>> > While at it there is an off board loop of copper coloured wire,
>> > perhaps microbore copper
>> > tube could that be a 20 or 500 amp fuse or just a dropper element
>> > for overload sensing ?
>> >
>> >
>
>
> Taking a closer look it is probably solid 1.7mm copper wire in a loop
> above the board of about 1 inch diameter. It is in the supply line to
> the power devices (maybe powfets rather than thyristors) not the power
> to the electronics. But operation is via rotary pot with switch so
> have to go throu gh minimum revs (pulses) before switching off. So
> still a mystery, no way a fuse , the cross section of the tracks, wide
> yes, must be less than 1.7mm solid wire. Incidently now all in working
> order on the bench, not reassembled yet onto the caddy a G Caddy TEDC
> 12201 that I find no www ref to
>
>
>

maybe it's a current probe test point?
a loop you can hook a current probe over,without breaking the circuit.

--
Jim Yanik
jyanik
at
localnet
dot com
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