Search found 15 matches

by G8RPI
Sun Jun 12, 2016 12:50 am
Forum: Nuts & Volts Magazine Discussions
Topic: Bed wetting alarm
Replies: 0
Views: 2349

Bed wetting alarm

Hi, Nice circuit aprart from the mains power supply. A unit like this that is by design in contact with a wet person should ideally not be powered from the mains, and if it is the power supply MUST be a low leakage medical grade type. The maximum leakage current for this type of application is 300uA...
by G8RPI
Thu May 15, 2014 2:19 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Zeener Diodes in Parallel: 72 Watt Power Supply, May 2014
Replies: 2
Views: 4756

Re: Zeener Diodes in Parallel: 72 Watt Power Supply, May 201

Hi Paul, Only the designer can give you the correct answer. There is no obvious reason for this arrangement. Possible reasons are:- 1/ Increase power dissipation. As you noted this should not be an issue with the values used here. There is also the problem that the zener with the lowest voltage will...
by G8RPI
Mon Mar 24, 2014 12:27 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Hi Paul, Sorry for the slow response, I don't follow the forum every day. The loadbank is home made. It is basically an array of IRF540 MOSFETs in parallel. There are source resistors to help distribute the power dissipation. A 100 ohm resistor close to each gate to stop oscillation then tied togeth...
by G8RPI
Sat Mar 01, 2014 10:52 am
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Hi T,
I can't identify the RD-80 module you mention. From your description they will be ideal with the 40,000uF of filtering. The Ammeter shunt and connecting cable resistance will also work well.

Regards,
Robert Atkinson G8RPI.
by G8RPI
Sat Feb 15, 2014 1:44 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Your current limit circuit will destroy the error amplifier output stage by connecting it to Vraw. With no disrespect to the many degree holders, your BSEE and MSEE only indicate your education, to acheive Chartered Engineer you also have to have significant professional experience, responsibility a...
by G8RPI
Fri Feb 14, 2014 1:41 am
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

The closed loop output impedance is a good guide to the possible peak current in a short circuit case. Other values such as Rds and capacitor ESR are specified as maximum values whereas the worst case for a short is minimum value. You cannot assume that the Rds will be at its MAX limit to protect th...
by G8RPI
Wed Feb 12, 2014 11:11 am
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

OK, Had a chance tonight to make some real life measurements. Starting from cold (13.8degC) off load I got 20.619V across the filter capacitor. on full load (14A) it dropped to 16.40 with 4.3v Pk-Pk ripple. The lowest voltage in the trough was more than 14.3V. Output ripple was 11mV. This was with t...
by G8RPI
Tue Feb 11, 2014 11:42 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Dave, You obviously have no experience of BUILDING practical high current supplies. The out put impeance of my prototype MEASURED from 0.14A to 14A is 2milliohms. your simulted 100uV drop just shows the limitations of simulation. You think an IRF4905 will survive an output short to ground with a cha...
by G8RPI
Mon Feb 10, 2014 11:58 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Hi Dave, I don't want to get into a long discussion here but. 1, I disagree, look at the regulation shown during dynamic load testing. 2 Cref in in the TI datasheet applies to fig 4 which is a different configuration for less than 7V output. This has the divider on Vreference, not the sense input. m...
by G8RPI
Mon Feb 10, 2014 3:03 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Improved Efficiency 13.8V Power Supply
Replies: 17
Views: 11747

Re: Improved Efficiency 13.8V Power Supply

Hi Dave, Thanks for reading my article. As you say you have made numerous comments, I'll try to address some of them here. Firstly your minor nit about the regulator ground connection. The 723 does not sense the negative voltage from pin 4, it senses it from the bottom of the divider that is connect...
by G8RPI
Sun Jan 19, 2014 3:11 pm
Forum: Nuts & Volts Magazine Discussions
Topic: Build a PIC-Based Remote Temp Sensor
Replies: 14
Views: 34536

Re: Build a PIC-Based Remote Temp Sensor

PatrickG wrote "I was able to get the program to compile and download onto the PIC (I think), but the chip (and I tried with 2 different ones, with the same result) does not do anything." Sounds like the clock or reset options are not correctly set. Check that MPLAB is set to use the config settings...
by G8RPI
Sat Dec 14, 2013 1:53 am
Forum: Reader Projects
Topic: My Christmas Can Light Dimmer
Replies: 13
Views: 7534

Re: My Christmas Can Light Dimmer

I'd not actually looked too closely at this article as it was too "simple". A close look shows it's truly shocking (no pun intended). And there are better ways to improve lamp life. A PTC (Positive Temperature Coefficient) thermistor is an established technique. This will reduce the inrush current a...
by G8RPI
Sat Oct 19, 2013 12:36 pm
Forum: General Discussion
Topic: Sealed Lead Acid
Replies: 16
Views: 4040

Re: Sealed Lead Acid

To answer the question, no there is no way to revivie these batteries. "Gel-Cell" is a very generic term fo spill-proof batteries. There are many different types of different applications. Even the same size from the same manufacturer can be made with different chemistry. The most common application...
by G8RPI
Thu Sep 26, 2013 10:36 am
Forum: Nuts & Volts Magazine Discussions
Topic: January 2013 Gravimeter
Replies: 4
Views: 4520

Re: January 2013 Gravimeter

Hi, I would agree that the sensor in this article is pretty useless. There are lots of better ways to do this. The use of an DAC to feed an analogue data logger on a PC is a common theme with this author. He used it on a Geiger counter design. Analogue to digital to analogue to digital - why bother?...
by G8RPI
Thu May 24, 2007 4:40 am
Forum: Up For Grabs
Topic: Network Cards <<GONE>>
Replies: 7
Views: 3849

Hi, While the cards may not be of use, they do have useful parts. If they have thin ethernet (BNC socket), they will have a 2W DC-DC isolated power converter with a 9V output. Input voltage will be 5 or 12V depending on model. These are great for making negative supplies for op-amps, RS232 interface...