Galvanic Isolator - Homemade

[Bones]

Has anyone made a galvanic isolator? Is it frightfully difficult?!

[WotEver]

Oh, oh. Here we go...

[Bones]

well, I was hoping one might get away from the merits and unmerits and the such like.

[rjasmith]

Has anyone made a galvanic isolator? Is it frightfully difficult?!

 

Hello Bones!

 

I suspect lots of people have, even I thought of doing it once but then I was converted by the great Gibbo late of this parish to think isolation transformer.

 

The difficulty with making a GI is that you need to think very carefully about the type of diodes to use. They might have one day to withstand a very large fault current after having sat there doing nothing for years. Heat sinking and including a large correctly spec'd capacitor is another issue. Then there is the thought that the home made jobby won't have gone through the extensive testing that professional ones have to prove conclusively that they don't go bang under fault conditions.

 

There have been posts about making them on here before (some years back) but if I remember the concensus was that it might be better to just go out and buy one!

 

I went out and bought an isol trans!

 

I think Gibbos website has useful words about all this if you want to have a look.

 

Richard

 

edited to take out too many words!

Edited June 5, 2013 by rjasmith

[WotEver]

Bones, do you remember this thread?

 

The reasons why not to go the DIY route are well covered, and the arguments for are equally well covered.

 

The actual mechanics of making one are very simple, but obtaining suitable parts at non-eyewatering prices might prove difficult too.

 

Tony

[bigste]

Watch this video and decide for yourself.

http://www.youtube.com/watch?v=vGehTCw_voI

[Bones]

Bones, do you remember this thread?

 

The reasons why not to go the DIY route are well covered, and the arguments for are equally well covered.

 

The actual mechanics of making one are very simple, but obtaining suitable parts at non-eyewatering prices might prove difficult too.

 

Tony

Brilliant! Thank you. I was looking for it and couldn't find it. Now I have.

[WotEver]

Watch this video and decide for yourself.

http://www.youtube.com/watch?v=vGehTCw_voI

 

The biggest fault with that script is where the voiceover states "So here's the solution.". A far more accurate line would have been "So here's one solution, which is cheaper than an isolation transformer, but less effective in some circumstances."

[blackrose]

 

The biggest fault with that script is where the voiceover states "So here's the solution.". A far more accurate line would have been "So here's one solution, which is cheaper than an isolation transformer, but less effective in some circumstances."

 

It's also an advertisement, so he's hardly likely to say that.

[smileypete]

Has anyone made a galvanic isolator? Is it frightfully difficult?!

 

Not really frightfully difficult but I reckon the average boater would still be better off buying one from the likes of Safeshore, ideally one with a status monitor.

 

Some people are a bit 'paranoid' about the GI failing and leaving them without a functioning earth connection. To give some reassurance and peace of mind, a £5 socket tester left plugged in somewhere visible will help indicate the earth is OK.

 

A properly wired isolation transformer (IT) is ideal from an electrical point of view but there are important safety ramifications if one is installed aboard a boat, so a boat based IT is not something I'd recommend.

 

cheers, Pete.

~smpt~

Edited June 5, 2013 by smileypete

[Chalky]

As said before it's not difficult however there are a LOT of issues. Main ones relate to liability if it goes wrong and someone is killed. If you buy a commercial device then company that made it will be responsible. If you mad it then it will be you. To get round it you would have to show all of your design calculations, hazard analysis, tolerancing, test results off a big enough batch size to show the results are valid etc. Using a test house would help. By the time you've done enough to demonstrate that you've taken reasonable care it would be significantly cheaper to buy one.

[Keeping Up]

I know that I would be easily capable of making one. I know what the issues are, and I could source the components. Having looked into it, I decided it was better to buy one.

 

My only regret is that I didn't get one with an LED status monitor. Not because I'd ever look at the LEDs, but because they have a higher turn-on voltage (usually achieved by having extra diodes) which gives you greater protection against leakage currents from other people's equipment.

[jonathanA]

I know that I would be easily capable of making one. I know what the issues are, and I could source the components. Having looked into it, I decided it was better to buy one.

 

My only regret is that I didn't get one with an LED status monitor. Not because I'd ever look at the LEDs, but because they have a higher turn-on voltage (usually achieved by having extra diodes) which gives you greater protection against leakage currents from other people's equipment.

 

i did buy one with a status monitor mainly for exactly that reason which should help with the much quoted 'switch mode power supply issue'

 

I also looked at isolation transformers and decided for what I wanted and the price difference a GI would be fine. I would recommend the safeshore Gi with status montior, on the basis that safeshore are really helpful and nice to deal with and their product seemed to me, to have a similar specification to others (often more expensive).

[smileypete]

I think it's possible to make a decent fit-for-purpose GI for reasonable money, maybe that's a topic for another day.

 

However it means connecting things the right way round with high reliability solder or crimp connections, and while this is a good thing to learn, building your own GI is probably not the best place to start learning it

 

cheers, Pete.

~smpt~

[Bones]

Thanks folks. I wasn't looking for a cheaper way of doing things. In a mad five minutes I thought it would be a fun thing to learn about and do... but I will steer clear of it for now. Good point on the LED status monitor as I had been wondering how I would determine whether the 'thing' was working or not.

 

However it means connecting things the right way round with high reliability solder or crimp connections, and while this is a good thing to learn, building your own GI is probably not the best place to start learning it

 

cheers, Pete.

~smpt~

 

I aint so bad at solder or crimping but I will give it a miss!