MARKET CENTRE
Cash in your surplus gear. Advertise it here in SILICON CHIP
FOR SALE
WANTED
KEITH RIPPON KIT ASSEMBLY &
REPAIR:
* Australia & New Zealand;
* Small production runs.
Phone Keith: 0409 662 794
keith.rippon<at>gmail.com
tronixlabs.com.au – Australia’s best
value for supported hobbyist electron
ics from Adafruit, SparkFun, Arduino,
Freetronics, Raspberry Pi – along with
kits, components and much more – with
same-day shipping.
Speaker enthusiast needs a copy of a
book once sold by Jaycar entitled “High
Power Loud Speaker Enclosure Design
& construction”. It had a catalogue num
ber BC1166.
DAVE THOMPSON (the Serviceman
from SILICON CHIP) is available to help
you with kit assembly, project trou
bleshooting, general electronics and
custom design work. No job too small.
Based in Christchurch, NZ but service
available Australia/NZ wide.
Email dave<at>davethompson.co.nz
LEDs, BRAND NAME and generic
LEDs. Heatsinks, fans, LED drivers,
power supplies, LED ribbon, kits, com
ponents, hardware, EL wire.
www.ledsales.com.au
PCB PRODUCTION
MISCELLANEOUS
VINTAGE RADIO REPAIRS: electri
cal mechanical fitter with 36 years ex
perience and extensive knowledge of
valve and transistor radios. Profession
al and reliable repairs. All workmanship
guaranteed.
$17 inspection fee plus charges for parts
and labour as required. Labour fees $38
p/h. Pensioner discounts available on
application.
Contact Alan, VK2FALW on 0425 122
415 or email bigalradioshack<at>gmail.
com
PCB MANUFACTURE: single to multi
layer. Bare board tested. One-offs to
any quantity. 48 hour service. Artwork
design. Excellent prices. Check out our
specials: www.ldelectronics.com.au
ASSORTED BOOKS FOR $5 EACH
Selling assorted books on electronics
and other related subjects like audio,
video, programming etc. The books are
relatively old in most cases and vary in
condition.
You'll need to come in person to see
what books we have and what we're
willing to sell:
Silicon Chip
1/234 Harbord Road (up the ramp)
Brookvale NSW 2100
(02) 9939 3295
KIT ASSEMBLY & REPAIR
NEED A NEW PCB DESIGNED?
Or need to update an old board? We
do PCB layouts from circuits, drawings,
photocopies or sample boards. Contact
Steve at sgobrien8<at>gmail.com or
phone 0401 157 285. Get a new PCB
and keep production going!
Will pay $50 (including postage) to the
first person who has a pristine copy, i.e.,
little use but slight dog ears ok.
Contact Melanie (on behalf of inquirer
on 02 8832 3100)
ADVERTISING IN MARKET CENTRE
Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in
Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST.
Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, ad
dress & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293.
hotter than the Mosfets. Why is that?
I will be using the circuit to power
two type 895 24V motors (360W each)
on my bicycle, so I need to make sure
I keep these components cooled appropriately.
I am planning to use three or four
Mosfets. The multimeter testing I did
on the Mosfet/diode cases suggest
the Mosfets and diode D2 can’t be installed on the same heatsink, so how
can I best keep the circuit cool? (C. V.,
Ballarat, Vic)
• The speed pot varies the control
siliconchip.com.au
voltage from 0 to 5V, but this voltage is
also affected by the feedback resistors
from the motor negative (M-) terminal.
This feedback is what is causing the
motor to run faster at the lowest speed
setting. You can alter the feedback resistor to reduce the effect.
The 18kW resistor is located near
REG1 on the PCB and can be increased
in value. We suggest you try 47kW. Alternatively, if you don’t need the feedback, omit this resistor entirely.
You are right that it’s probably just
the Mosfets which have been damaged.
Australia’s electronics magazine
Check that the PCB tracks connecting
to them are intact and not fused. Diode D2 can run hot; it depends on the
motor speed setting as to whether the
diode conducts significant freewheeling current.
Changing D2 to a schottky diode
with a sufficiently high voltage and
current rating should significantly reduce its dissipation, to less than half
that of a standard high-current diode.
You can attach both diode and Mosfet
to the same heatsink as long as you use
insulating washers and bushes.
SC
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