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Changing shunt for battery charge monitor

I would like to ask a few questions about the June 2008 battery charge monitor. Can the shunt be mounted remotely from the unit, say 2m away using shielded cable? Can a higher value current be measured using a 150A shunt (>.0334Ω)? We have a 110A alternator with an intelligent regulator that allows the full 110A to be delivered to our 1000Ah battery bank. (R. F., via email).

• The shunt can be located away from the charge monitor. The leads back to the charge monitor should be shielded by using heavy-duty microphone cable. The shunt can be changed to a lower resistance to suit the higher current, as you suggest.

Speed control is not progressive

I recently purchased a Full Wave Mains Motor Controller (SILICON CHIP, May 2009) from our local Jaycar Electronics store. After assembly and testing of the kit, a problem became apparent. When adjusting the speed control using speed potentiometer VR1, the actual speed of the attached jigsaw varied from zero to about 10% in a smooth progression and then jumped to full speed for the rest of the adjustment range.

I have made several adjustments to trimpot VR2 without any effect on the speed control operation. Could you please advise me on how I can rectify this problem? (A. B., via email).

• It seems likely that trimpot VR2
has an open-circuit wiper. Check that you can vary its resistance down close to zero ohms.

Note that power must be switched off and the mains plug unplugged from the mains outlet before removing the lid and doing this check.

Flat battery should not cause data loss

I have the 3-Channel Rolling Code UHF Remote Control (SILICON CHIP, August & September 2009). It has been in use for around two years, very successfully. Recently, two of the remotes have stopped working due to flat batteries. I replaced the batteries but they still would not work. The third remote is still working, although the battery is low.

On this transmitter, I connected a 9V battery with small crocodile clips to the battery terminals to retain power, swapped the 12V battery and removed the “jumper” battery. This third Tx still works OK with the new 12V battery. I’m assuming this means that every time the battery goes flat in one of the transmitters you either have to provide a “jumper” battery BEFORE the internal battery goes flat or re-assign the transmitter to the receiver after every battery change. This is a pain as the receiver is not easily accessible. Any suggestions? (P. C., via email).

• Removal of the battery should not affect the transmitter, as all necessary data for rolling code transmission is stored in EEPROM and so is not lost with loss of power. The microcontroller does not rely on the volatile RAM to store the rolling code data on each switch press.

It’s possible that the battery was so flat that a switch press caused the rolling code to change but there was insufficient power to allow the EEPROM to be written to correctly.

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