## Search found 287 matches

Sat Dec 08, 2018 10:00 pm
Forum: Other projects
Topic: Controlling 2 AC motors with power 2kW for each
Replies: 10
Views: 2508

### Re: Controlling 2 AC motors with power 2kW for each

you probably have found out that this forum is not the best place to get advice on this type of questions, but I can respond with my thoughts.. I would use two motor drives that are powered from single phase 230V and drive standard asynchronous three phase motors. I would not use dc motors, because ...
Sat Dec 08, 2018 9:35 pm
Forum: Automation, sensing and robotics
Topic: Simple Relay Circuit
Replies: 13
Views: 8398

### Re: Simple Relay Circuit

here is how I go about figuring out component values for driving a common relay from a GPIO. I also add some common sense comments.. 1. select a suitable relay and determine how much current is required in the relay coil 2. determine how much voltage must be applied to the relay coil to make sure it...
Mon Apr 25, 2016 2:14 pm
Forum: Beginners
Replies: 13
Views: 4419

### Re: Monitor self voltage (ADC)

my guess is that it is a noise related problem. try to take ten readings and save them in an array, sort the array and throw away the two highest and the two lowest readings, then average the remaining six readings. the reason why you need to throw away the highest and the lowest readings is that th...
Tue Feb 16, 2016 4:31 am
Forum: Automation, sensing and robotics
Topic: Base resistor value
Replies: 4
Views: 1843

### Re: Base resistor value

you could use the TIP120, at 360mA load it should work fine with a base resistor of 1k to 2k when driven from 3.3V since those 2n3906s are the only onhand pnp i have, ill just redo some wiring and use a tip120, and recommend resistor value or should i just use a 10k-ish one thanks i assume a tip120 ...
Mon Feb 15, 2016 3:59 pm
Forum: Automation, sensing and robotics
Topic: Base resistor value
Replies: 4
Views: 1843

### Re: Base resistor value

the 2N3906 is too small to drive this load, it is rated at 200mA max. you could try to drive the load with the 2N2222A instead, but to avoid that the transistor heats up you have to provide at least 50mA into the base. This is a bit too much for the GPIO output, so you may need a second transistor t...
Fri Feb 12, 2016 3:33 pm
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

Using a latching relay is OK if you have some electronics to avoid that the relay has to click on and off continuously when the battery is completely full. you could turn off the relay at 14.5V and turn it back on when the battery voltage has dropped to 13.5V, and if it starts to click on and off to...
Fri Feb 12, 2016 2:13 am
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

I think that your battery needs some type of overcharge protection with a panel that is able to provide 10A current. It depends on if you have any load on the battery, how sophisticated the charge controller need to be. The one you have is quite well suited for that panel and battery. and it disconn...
Thu Feb 11, 2016 4:12 pm
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

the CMP12 controller draws about 0.020A if you believe its datasheet, that is about 6Wh a day, so I would myself just connect the small solar panel directly to the battery, perhaps with a diode in series to block reverse current. If you have only 10W panel and a big battery there is no need to contr...
Tue Feb 09, 2016 3:38 pm
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

the key word here is "simplified" 8-) a heatsink is most likely not needed if the panel is max 200W-250W Thanks for everything, especially putting me onto this. :) I dont get why I need to spend >£100 though. See the attached schematic. Surely, all I need is the IC itself, a handful of res...
Tue Feb 09, 2016 1:59 am
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

the LT8490 contains an LT8705 controller, so you could go to the Linear website and type 8705 into the search and click on Design Tools and you can download LTpowerCAD which contains an excel spreadsheet that is really useful if you want to design your own charger. And you can simulate the power sta...
Mon Feb 08, 2016 4:05 pm
Forum: Off topic discussion
Topic: Solar Shed II - new charge controller.
Replies: 18
Views: 11536

### Re: Solar Shed II - new charge controller.

If you have a large solar panel and battery and want to maximize the amount of charge power then you need something like LT8490. It is a solar powered battery charger and can also be used with a voltage source input. There is a demo board on the Linear website that is set up to charge a 12V battery ...
Sun Jan 24, 2016 4:33 pm
Forum: General discussion
Topic: Connect Relay to Raspberry Pi and Extension Cord [Australia]
Replies: 9
Views: 5003

### Re: Connect Relay to Raspberry Pi and Extension Cord [Austra

here is a sketch that shows a relay with reinforced isolation (top) and basic isolation (bottom).
the grey circles show the distance between mains voltage pins and coil pins. When circuit board traces are added the difference in isolation distance becomes even larger.
Sun Jan 24, 2016 3:51 pm
Forum: General discussion
Topic: Connect Relay to Raspberry Pi and Extension Cord [Australia]
Replies: 9
Views: 5003

### Re: Connect Relay to Raspberry Pi and Extension Cord [Austra

Yes, well I am an electrical engineer, and as I said many these relay boards marketed to hobbyists are not meeting electrical safety requirements and can be unsafe to use with mains voltage. If someone was in the business of manufacturing say a gadget that contains a microcontroller board (such as t...
Sat Jan 23, 2016 11:57 pm
Forum: General discussion
Topic: Connect Relay to Raspberry Pi and Extension Cord [Australia]
Replies: 9
Views: 5003

### Re: Connect Relay to Raspberry Pi and Extension Cord [Austra

You should be aware that the relays on Sainsmart boards are not suited for connection to mains voltage. One reason is that the relay itself only has basic insulation (1500Vrms test voltage from contacts to coil). To meet electrical safety standards you would need a relay that is designed for reinfor...
Thu Jan 14, 2016 2:56 am
Topic: ULN2803 Problem: LED and Motor (series)
Replies: 13
Views: 3106

### Re: ULN2803 Problem: LED and Motor (series)

You don't want the LED in series with your motor! Actually I want. What kind of answer is that ?! What is the voltage drop of the ULN2803 and the LED? How much voltage is left for the motor? I haven't checked the ULN2803 voltage drop, but the voltage drop of the LED is not that much I checked it as...
Wed Jan 13, 2016 2:06 am
Topic: ULN2803 Problem: LED and Motor (series)
Replies: 13
Views: 3106

### Re: ULN2803 Problem: LED and Motor (series)

Hi , This is the schematic of what I have built. The +5 volt of the GPIO is connect to a motor and LED (series). The problem is that only the LED is turned on and the motor vibrates VERY slow. Hard to notice the vibration even. If the LED is bypassed, the motor works quite strong. Any Idea for this...
Thu Dec 17, 2015 2:27 am
Topic: HELP with relay and "spikes"
Replies: 15
Views: 4822

### Re: HELP with relay and "spikes"

the solution is to add a small capacitor across the relay contacts. this will redcue the electical noise and the arcing. the capacitor could be a ceramic or plastic capacitor 0.01uF to 1uF. the load current mostly goes into charging this capacitor and the arc is suppressed. the voltage spike can be...
Wed Dec 16, 2015 3:50 pm
Topic: HELP with relay and "spikes"
Replies: 15
Views: 4822

### Re: HELP with relay and "spikes"

is solid state a definitive solution? Edit to add: can the problem be sourced by the load circuit? My guess is that the problem is caused by arcing between the relay contacts that are opening. When you have an inductive load such as a solenoid and the relay contacts open, the inductive current cann...
Sun Nov 29, 2015 4:34 pm
Topic: Pi Relay and i2c question
Replies: 3
Views: 963

### Re: Pi Relay

there is practically no distance between power traces and the pins that connect to the coil which means that if you connect it to mains voltage you have a very dangerous situation. I see plenty of threads about people struggling with interfacing relays, this may help. http://www.amazon.co.uk/Raspber...
Fri May 01, 2015 4:04 am
Forum: Automation, sensing and robotics
Topic: 5V relay - Is this a safe connection?
Replies: 7
Views: 2234

### Re: 5V relay - Is this a safe connection?

rpdom wrote:I'd add a 10K resistor between the transistor base and GND to prevent it turning on if the GPIO gets set to Input (whe the Pi is first switched on, for example) and it happens to float high enough.
if the GPIO pin is floating it should not source any current, so the npn will not turn on
Thu Apr 23, 2015 2:41 pm
Forum: Beginners
Topic: Am i useing the voltmeter correctly?
Replies: 3
Views: 919

### Re: Am i useing the voltmeter correctly?

Hello is this the right way to use the voltmeter in the GPIO?

yes. be sure to set the voltmeter for DC (not AC)
Sat Mar 14, 2015 1:10 am
Forum: Automation, sensing and robotics
Topic: When you need more power - how to be safe?
Replies: 17
Views: 4381

### Re: When you need more power - how to be safe?

When using a power supply like this I buy a plastic enclosure that is big enough for the power supply, and make holes and mount a cooling fan if the power supply does not already have one. In any case, you need to add holes in the plastic box so that cooling air can move through. you cannot just put...
Thu Mar 12, 2015 1:25 am
Forum: Beginners
Topic: High Amp Motors with the Pi
Replies: 18
Views: 13446

### Re: High Amp Motors with the Pi

without knowing anything about the motors it is impossible to give a useful answer, but if you only need to run the motor in one direction you can just use a MOSFET gate driver, a suitable MOSFET and a Schottky diode that provides a path for the motor current when the MOSFET is off. you connect the ...
Wed Feb 25, 2015 3:57 pm
Forum: Automation, sensing and robotics
Topic: Current sensing
Replies: 3
Views: 8755

### Re: Current sensing

http://www.mouser.com/ProductDetail/Triad-Magnetics/CSE186L here is a cheaper current transformer rated for 10A. but you need to do some soldering as the core cannot be separated to insert the ac wire. with all current transformers it is important that the correct resistor is connected to the sense ...
Sat Feb 21, 2015 4:49 pm
Forum: Other projects
Topic: Transistor selection
Replies: 5
Views: 1655

### Re: Transistor selection

some examples of smaller size MOSFETs: Si2302CDS, Si2312CDS, PMV16UN, DMG3414U, DMN2075U there are dozens of similar parts that can be directly connected to 3.3V GPIO output pins and can drive several Amperes at relatively high switching frequency. Look for n-channel MOSFETs with Rdson specified at ...