Heavy duty AC to DC converter required

[oldway]

It was just an linear angle 16a voltage regulator bought from RS components

Not true, you wrote:

I was recommended using a variac transformer but its too heavy and bulky to fit into the enclosure.

[oldway]

....running at 6 amps, does not go over 60oC ....

When It will be running at 16A, (2.66 x 6A), the joule losses will be 7.11 greater....Be sure that your electrolyser will reach the boiling temperature of the electrolyte, even with pure dc current.

NB: that's what happen when you increase the current density....!!!!!

[mche1997]

I don't think I would ever run it to 16 amps, maybe near 13 max but most times I would like to run it between 8 to 12, thats why I wanted something to control the current.

[oldway]

With the transformer + bridge rectifier solution, if you want a 8A average current (NB: the average current is that's matters for gas production) you will measure about 10 or 11 rms current (that's what matters for joule losses and heating of electrolyte).

[mche1997]

Thank you oldways

[mche1997]

Hello Oldways
Had a look at the transformers and you stated best to use the isolated transformer, would it be the yellow bucket type ones like the ones attached here

[oldway]

About Brown's gas....

[oldway]

As it happens too often on this forum, you neglected to provide essential informations.
This has a direct impact on the answers you are given.

Initially, it appeared that the ac / dc converter was to be used for experimental purposes and at minimum cost.

Much later, you revealed to us that this is probably a commercial product that you intend to build in multiple copies ....

This totally changes the problem.

Indeed, if for experimental purposes, we can not respect the standards and regulations, this is no longer the case when it comes to a commercial product.
The DIY solution of transformers with variac does not meet European standards for power factor.

It can not be applied to a commercial product.

You will have to look for a commercial  switching power supply with  PFC adjustable from 200 to 350V 12A that will meet the standards and regulations.

[tron9000]

what was your budget again?

I just did some finger in the air pricing for just the bare simple system (transformers + rectifier, simple meter for voltage, enclosure, connectors and circuit portection) and for you to buy it off someone (qualified) you'd be looking at a couple of thousand just for the prototype you described, that includes the labour, testing and shipping....if your lucky

Those transformers (also called site transformers - cos they're used on building sites) are £240 (inc VAT) each. There's nearly 1/3 my estimate there.

I don't think I would ever run it to 16 amps, maybe near 13 max but most times I would like to run it between 8 to 12, thats why I wanted something to control the current.

Add in some sort of current control circuitry and it goes up again.

Much later, you revealed to us that this is probably a commercial product that you intend to build in multiple copies ....

This totally changes the problem.

Indeed, if for experimental purposes, we can not respect the standards and regulations, this is no longer the case when it comes to a commercial product.
The DIY solution of transformers with variac does not meet European standards for power factor.

It can not be applied to a commercial product.

Compliance testing - price goes up again...CONSIDERABLY! Test houses charge quite a bit. So more pretesting to make sure you're not going overrun your allotted time at test house, cos that'll cost more too.

we'd really need to know a budget....what can you afford?

[mche1997]

OMG ! thousands, my budget is only just up to £200. Only a converter with 240Vac in and 300vdc out.

[mche1997]

Sorry Oldway, should had explained everything clearly at first. At this point, it will be for experimental purpose as everything is put together in a mess, bit by bit, removing parts and replacing parts. It's only when I get it right and having it tested time after time, then I'll make another proper one. I want to do engine carbon cleaning later if I get this to work.
Sorry guys and excuse for the confusion.

[oldway]

With a budget of only 250€ for a 240Vac/300Vdc 12A converter, no way to buy new transformers....You will have to look in the dumpster or at used transformers...


You need: a 3KVA's 240/240V isolation transformer
a 240/48V 800VA transformer
a 1KVA variac 0-240V

For exemple, I bought a used (like new)1KVA variac for 30€
I found a 1KVA isolation transformer for nothing...(you should use 3 in paralel)
It was coming from dismounting of old medical devices.

[mche1997]

Thank you again for your information Oldway
Would I be able to use a Chassis transformer but placing it in a plastic junction box, just need everything as compact as possible as my enclosure only measures 60cm x 40cm x 40cm ?

[oldway]

As it is an experimental project, not a commercial one, enclosure is not a concern.... 

[oldway]

Let us resume your question: you have no money, you have a limited volume, no knowledge in power electronics and you need a ac/dc converter with output adjustable from 200 up to 350V 12A (4200W) with power factor and efficiency good enough to not trip your 32A circuit breaker of your 240V 1 phase mains supply.....

The answer to your question: NO SOLUTION at all, you are looking for miracles.

[tron9000]

OMG ! thousands, my budget is only just up to £200. Only a converter with 240Vac in and 300vdc out.

£200....then best bet is to learn some electronics and find a source of salvageable parts - there is a section in this forum where you can find all the information you need to learn electronics

Engineers aren't cheap...

[mche1997]

Thank you for your advice Tron9000

[oldway]

I'am afraid that learning "some electronics" will not help a lot to develop a 4.2KW switch mode converter with PFC.

[mche1997]

Yes Oldway
I just need on looking then, I'm going to try using the Metal Halide Ballast to lower the current draw from generator,maybe add a few to it connecting in series or parallel and use switches to turn on/off individually so I can increase or lower the current.

[BravoV]

what was your budget again?

This question is too late, ideally should be placed on 2nd post, I've seen alot of discussions became meaningless & fruitless just because the contributors, even experienced ones as I observed, forgot about this matter quite often.

No money, no talks.

[oldway]

Yes Oldway
I just need on looking then, I'm going to try using the Metal Halide Ballast to lower the current draw from generator,maybe add a few to it connecting in series or parallel and use switches to turn on/off individually so I can increase or lower the current.

I am sure you are working without isolation transformer using directly the rectified mains voltage....This is very dangerous, water and electricity does not combine....

You risk to kill yourself...

As a beginner, you should not make experiments with voltages higher than 50V.

Why a such huge quantity of Brown's gas ?

A DIY electrolyser hardly reach an efficiency of 50%....It is a huge loss of energy.

[mche1997]

The purpose for this size is to produce a minimum of 6 litres of gas per minute and some applications up to 10 litres per minute, this is needed to clean the internal carbon from an engine and also the voltage from each plate cannot exceed 2.5 volts or lower than 2.0 volts. Higher, it will heat up the generator within 10-15 minutes of operationand if it's lower, not enough gas production.

[oldway]

It is therefore a professional application.

Can we consider a three-phase 240 or 415V main's power supply instead of a 240V single-phase ?

In fact, the power involved is high and more compatible with a three-phase power supply than with a single-phase power supply.

The three-phase rectified voltage is almost continuous with very little ripple and no power factor problem. On the other hand, it is easier to find 3.5KVA transformers or more in three-phase than in single-phase.

Using a three-phase transformer with primary 240V delta and 415V star and secondary 240V delta, one can get 322Vdc.

Just add an adjustable chopper 15A to reduce this voltage to the desired value, without influencing the power factor.

[mche1997]

3 phase won't be much of a problem by changing a few components but finding a 3 phase outlet is a problem as mostly this will be used at domestic locations and everyone only have  single phase outlet apart from commercial properties.
Thanks for your suggestions Oldway.

[oldway]

https://www.bmisurplus.com/products/10484-sorensen-dcr-300-9b-power-supply-0-300v-0-9a