Inverter - Lidl £22.99

[LadyG]

On 2017-3-29 at 19:06, OliveOyl said:

 

Thanks both, learning new things every time I come on here. If you see me out on the cut (you'll know it's me - I have put  an L plate on each side of my boat ) give me a wave.

O.

I was thinking L on port side only.

If you dont have an invertor, how are you going to charge the phone, use the laptop etc., just asking, £22.99 seems a snip

I watch TV v little, just use laptop. but have a few DVDs which will work on my TV.

Edited June 17, 2017 by LadyG

[mango]

2 hours ago, Gordias said:

Mango and WotEver

Thanks for the info.  All this analog stuff is a bit strange for a software guy.  We don't have harmonics or values coming up too high or too low: there are no grey areas between my zeros and ones  

I read the wikipedia page on inverters, and was quite surprised to see that "modified sine wave" is so close to a square wave.  This is just a matter of perspective I suppose.  For a software guy generating the "on/off" timer sequence for PWM at a few tens of Hz would be very easy. 

OTOH all this hardware stuff is weird and scary.   I looked up "Switched-mode_power_supply" (seems these work well with square waves) but started getting a headache almost immediately

This leads to a question, but sorry in advance if it's a stupid one:  why isn't this done with a digital controller + a controllable component that turns 12V DC into a controllable range of output voltages up to 240 + a controllable component to switch +12V to - 12V?  Digital controllers not reliable?  Components expensive for consumer gear?  Something else?

A switched mode power supply is commonly used to replace an old fashioned transformer.  It's lighter, cheaper and more efficient.  Most chargers and power supplies now use SMPS.

The earliest inverters used a simple low frequency oscillator driving a conventional metal-cored transformer as a step-up transformer.  I made one over 40 years ago.  It worked but it was bulky and inefficient.  The real step forward was to use higher frequencies coupled with lighter and more efficient transformers.  I have no idea how sine wave inverters work, but they are obviously bulkier and more expensive.  Maybe someone will explain how modern commercial inverters work.

[Gordias]

An interesting discovery ...  I bought my first Arduino controller yesterday, and it turns out it has a set of pins that deliver PWM (Pulse-width Modulated) power.  This isn't comparable to even a TV of course - the card runs at 5V and AFAIK is limited to 1 or 2 amps.  It's just interesting that a cheap programmable controller can provide the necessary switching speeds.

In case anyone cares: a key difference between a Raspberry Pi and an Arduino is that the Arduino doesn't run a full operating system like the Raspberry Pi. This means the logic controlling what it's doing (e.g. converting 5V into a PWM pseudo A/C) can't be interrupted for a few milliseconds by the operating system deciding it's time to do some memory or disk cleanup.  Or by another program grabbing most of the CPU for a few tenths of a second.  I could code the logic for PWM easily in the Raspberry Pi, but it wouldn't work consistently - so it would be useless for driving any appliance that wasn't expensively protected against occasionally receiving DC instead of A/C

Edited June 19, 2017 by Gordias

[WotEver]

On 17/06/2017 at 11:15, mango said:

PWM has been used for power control for years, as an alternative to the phase control used in the likes of lamp dimmers.  I don't think we will see PWM used in cheap inverters anytime soon.

Here's a cheap and simple PSW inverter design that used PWM: http://www.instructables.com/id/Adaptable-24vDC220vAC-Pure-Sinewave-Inverter-1/

[mango]

2 hours ago, WotEver said:

Here's a cheap and simple PSW inverter design that used PWM: http://www.instructables.com/id/Adaptable-24vDC220vAC-Pure-Sinewave-Inverter-1/

Fascinating.  Thanks very much.  One of these days I might get back to making my own circuit boards, but boating and canals took over from electronics many years ago.

I must pull apart my small sine wave inverter to find out why it is bigger and heavier than a MSW inverter with a similar power output.  I presume that the transformer is more sophisticated and larger.  I'm beginning to wish that I had kept my dual-beam scope.