Silicon Chip – July 2019

110 Silicon chip Australia’s electronics magazine siliconchip.com.au

from 5V down to 0V when an AC sig-
nal is applied to the reluctor input.
Once it’s triggering, adjust VR3 for
best results. See page 51 and 52 of the
December 2012 issue for the adjust-
ment procedure.

How to find parts at

Digi-Key and Mouser

I live in the USA and want to build
your June 2018 LC Meter (siliconchip.
com.au/Article/11099). I purchased
all available parts from your Online
Shop but I’m having trouble finding
the rest of the them at Digi-Key or
Mouser. Your parts list doesn’t give me
sufficient performance parameters to
figure out which ones to order. (B. F.,
Virginia, USA)

• It’s quite a laborious job to create a
  list of catalog codes, although it isn’t
  difficult. You just need to go to the rel-
  evant website, type in the basic part
  parameters such as “47k 1/4w 1% ax-
  ial resistor”, then sort by price. Check
  the parameters of the cheapest match
  to see if it’s suitable. If not, use the fil-
  ter options to narrow down the selec-
  tion, and repeat until you have found
  a suitable part.
  In the cases of resistors, capacitors
  and so on, once you’ve found one, it’s
  often easier to look for parts with dif-
  ferent values in the same series.
  Here is a list we’ve compiled for this
  project, not including the parts you al-
  ready purchased from us:
  
  
  • The Arduino Uno is available
  
  
  
  

from many sources

• 100μH bobbin-style inductor:
  Digi-Key 811-2030-ND
  Mouser 580-11R104C


• 5V coil DIL reed relays:
  Digi-Key HE100-ND
  Mouser 934-HE721A0500


• 2-pin female header sockets:
  Digi-Key S7035-ND
  Mouser 437-8018700210004101


• PCB-mounting right-angle
  banana sockets (black & red):
  eBay 111437231973


• 4-pin female header socket:
  Digi-Key S7037-ND
  Mouser 437-8018700410012101


• 2-pin header:
  Digi-Key S1011EC-02-ND
  Mouser 855-M20-9990246


• shorting block:
  Digi-Key S9337-ND
  Mouser 151-8010-E


• LM311 (DIP-8):
  Digi-Key 296-1389-5-ND
  Mouser 595-LM311P


• 10μF 6.3V tantalum capacitor:
  Digi-Key 478-10753-2-ND
  Mouser 581-TAP106M035HSB


• 100nF ceramic capacitor:
  Digi-Key 478-7336-2-ND
  Mouser 594-K104K15X7RF53H5


• 100kW: Digi-Key S100KCACT-ND
  Mouser 603-MFR-25FTE52-100K


• 47kW: Digi-Key S47KCACT-ND
  Mouser 603-MFR-25FTE52-47K


• 6.8kW: Digi-Key S6.8KCACT-ND
  Mouser 603-MFR-25FTE52-6K8


• 4.7kW:Digi-Key S4.7KCACT-ND
  Mouser 603-MFR-25FTE52-4K7
  
  
  • 1.3kW: Digi-Key S1.3KCACT-ND
    Mouser 603-MFR-25FTE52-1K3
  
  
  • 130 W: Digi-Key S130CACT-ND
    Mouser 603-MFR-25FTE52-130R
  
  
  
  

Motor Speed Controller

questions

I have just built your High-Current

Speed Controller for 12V/24V Motors,

as described in the June 1997 issue

(siliconchip.com.au/Article/4868),

from a Jaycar kit (Cat KC5225).

I could not control the speed of my

motor over its full range. When the

speed setting is at a minimum, the

motor is still rotating at considerable

speed. Is it possible to control a mo-

tor’s speed from 0 RPM to maximum

RPM using this circuit and if so what

modifications do I have to make?

Also, I accidentally shorted out the

motor wires, and now the circuit won’t

function at all. The transistors look fine;

however, there was a burning smell

when the wires touched, so I am guess-

ing the Mosfets need to be replaced.

Would the other components be OK?

I didn’t have a fuse on the power sup-

ply (not sure this would have helped)

so am I right in saying only the Mos-

fets would be damaged?

I am planning to use a large heat-

sink for the Mosfets but no heatsink

for diode D2. I think it would only

be switched on for a short period and

would not get hot. But when I tested

the circuit with a 775 motor under

load, I noticed that D2 was getting

My question is regarding the

MPPT Solar Charger & Lighting Con-

troller from the February and March

2016 issues (siliconchip.com.au/

Series/296). I am wondering if this

charger would be suitable to be per-

manently wired to an engine start-

ing battery. Would back-EMF spikes

from the starter cause damage to the

circuit?

I am looking after a museum dis-

play diesel engine which is only

started occasionally but the engine

has no charging capability of its own.

It is a 24V system with twin start-

ers and draws about 1100A peak at

first contact!

I imagine there would likely be

some severe spikes fed back. Since

starting takes less than three sec-

onds, there is little actual charging

required. (I. M., Scoresby, Vic)

• There could be voltage spikes
  generated by the starter motors, but
  these should be at least partially ab-
  sorbed by the battery.
  The spikes are unlikely to cause
  damage to the MPPT Charger as
  there are three 1000μF capacitors
  across the charger output, followed
  by an inductor before reaching
  switching Mosfet Q1 and diodes
  D2. These are the components
  most likely to be damaged by volt-
  age spikes.
  To make sure the charger cannot
  be damaged, we suggest that you
  add a 24V DC coil relay with 10A

Protecting MPPT Solar Charger from motor voltage spikes

contacts between the output of the

charger and the battery, via the nor-

mally closed contacts.

Connect the coil to the circuitry

that energises the starter motor, so

that the battery is disconnected from

the charger during cranking.

A further refinement would be

to power the relay coil via a series

connected diode (1N4004) and with

a 1000μF 25V electrolytic capacitor

directly across the coil (ensure the

polarity is correct).

That way the relay will switch off

a short time after cranking finishes,

allowing any voltage spikes from

the starters to die down before the

relay contacts close to reconnect the

charger to the battery.