4mA current flowing back from the battery to the controller. Is that normal?
Have you ever published an MPPT
solar charger that would suit a 32V
200Ah battery being charged from
three standard 20V solar panels? (R.
W., Loxton, SA)
• The amount of current drawn by a
charger from the battery depends upon
the circuit design. It is normal for there
to be some current drawn by the controller (whether it is an MPPT charger
or not). After all, the charge controller
circuit needs power to operate, and
that can only come from the battery
when there is no solar power available.
The 4mA drain is not huge compared to the overall battery capacity
– it would take nearly 290 days to fully discharge your battery at that rate.
However, the less the charger draws
from the battery, the better.
Unfortunately, we have not published an MPPT solar charger to suit a
32V lead-acid battery. That is a somewhat unusual voltage; 12V, 24V, 36V
and 48V are more common. It’s close
enough to 36V that a charger designed
for a 36V lead-acid battery might work;
as long as it’s adjusted.
Modifying the 40A DC
Motor Speed Controller
I have a customer who is using a
number of your March-April 2008
40A DC Motor Speed Controllers
(siliconchip.com.au/Series/48) to
vary the speed of trolling motors on
their boat.
They want to speed up the soft-start
ramp or remove it. Currently, the soft
start runs for about 10 seconds, but
they need it to be under three seconds.
I’ve had a brief look at the assembly code for it, but my knowledge of
assembly is so rusty it would take
months to dissect it.
I did have a go at assembling the
source code which is available for
download from your website, but I got
several errors regarding missing functions named float_ascii2 and float_ascii4. They don’t appear to be part of
the standard library.
I also found that I had to add these
two lines at the top of the main .asm
file, which got rid of several other errors:
#define P16_MAP1 0
#define P16_MAP2 1
I know that you have since released
a more modern speed controller which
has the soft-start control they’re after,
but they’ve already built these kits and
have been using them for a little while.
We didn’t make a kit of the updated
one so it would still be a fair amount
of running around for them to switch.
(Tom Skevington, Kits Manager, Altronic Distributors)
• The float_ascii2 and float_ascii4
functions were in another file which
was not included in the ZIP download
for that project. That has now been
corrected. Thanks for the tip about the
two added defines which are needed.
The software has two variables in
which values are stored to increase or
decrease the PWM duty cycle, named
pdeltah and pdeltal. These are loaded
with +1 on lines 819-821 of the main
ASM file to decrease the speed, or -1
on lines 824-827 to increase the speed.
Since this gives a soft start time of
around 10 seconds, changing the increments to +4 and -4 should give a
ramp time of around 2.5 seconds. To
achieve this, change line 819 to:
movlw
0x04
movlw
0xFC
and change line 824 to:
This will also make the motor speed
ramp more quickly in response to the
rotation of the speed control pot, or
changes in load (ie, feedback).
SC
Advertising Index
Altronics...............................81-84
Ampec Technologies............. OBC
Dave Thompson...................... 111
Digi-Key Electronics.................... 3
Emona Instruments................. IBC
Jaycar............................ IFC,53-60
Keith Rippon Kit Assembly...... 111
LD Electronics......................... 111
LEDsales................................. 111
Microchip Technology.................. 5
Ocean Controls......................... 11
Premier Batteries........................ 8
RayMing PCB & Assembly........ 10
Rohde & Schwarz........................ 7
SC Vintage Radio DVD.............. 34
Silicon Chip Christmas Kits...... 52
Silicon Chip Online Shop....98-99
Silicon Chip PDFs on USB....... 25
Silicon Chip Subscriptions....... 35
The Loudspeaker Kit.com........... 9
Tronixlabs................................ 111
Vintage Radio Repairs............ 111
Wagner Electronics................... 63
Notes & Errata
Digital Lighting Controller pt2, November 2020: on p101, the parts list correctly includes a 27W 1W resistor for the Micromite
master unit but incorrectly lists it as 25W 1W for the CP2102 Adaptor module (it should also be 27W 1W).
Tiny LED Christmas Ornaments, November 2020: the parts list incorrectly lists the Bauble PCB dimensions as 91 x 98mm
when they should instead be 52.5 x 45.5mm. Also, the Cane PCB is incorrectly listed as 84 x 44mm when it should be 84 x 60mm.
Two new 7-band Audio Equalisers, April 2020: in the first batch of stereo equaliser PCBs sold (code 01104202), the connection
between the 220pF capacitor and 51kW resistor in the lower right-hand corner of the board went to the top of the resistor instead
of the bottom (which was floating). This can be fixed by cutting the track between the two components and running a short wire
from the bottom of the resistor to the nearest pad of the capacitor. PCBs sold from November onwards do not have this problem.
The January 2021 issue is due on sale in newsagents by Thursday, December 31st. Expect postal delivery of
subscription copies in Australia between December 27th and January 15th.
112
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
