Heavy duty AC to DC converter required

[mche1997]

HI All
I'm looking to see if anyone can supply me or make me an AC to DC converter ?
I had basically searched through the internet and electronics and electrical suppliers looking for a minimum of 16 amp converter from 240vac to 300 or over vdc. It is for running a DC hydrogen generator.

Thanks everyone

[dmills]

35A 600V Bridge rectifier on a heatsink plus a handful of 400V Electrolytics?

Non isolated and crude as fuck but it will give you a NON ISOLATED 300V or so at plenty of current.

300V strikes me as a really weird voltage for electrolytic H2 production, usually a couple of volts at large currents is more like it, after all \$H2^+ + e^-\$ is all about charge not voltage, and the bond strength in H2O is not THAT strong.

Regards, Dan.

[mche1997]

Hi
Thanks for your reply, sorry I didn't mention adding a voltage regular. I tried the bridge rectifier but by adding a regulator as I needed to adjust the voltage for variable gas output, it trips the breaker. A normal angled regulator is not compatible with a bridge rectifier. I don't have really good knowledge on electrical or electronics. The simple solution I found and been told was using an AC to DC converter but a heavy duty one I can find was only available in the US. When the hydrogen generator was hooked up to the bridge rectifier, running at 6 amps, it was showing 260 to 270 vdc from mains. Thats why I needed a converter capable of handling at least 300vdc.

[Ice-Tea]

You haven't mentioned the most important thing yet: budget. But I wouldn't bother cooking up one yourself unless you consider it a learning experience.

Get one of these and call it a day:

http://be.farnell.com/ea-elektro-automatik/ea-ps-8360-10r/power-supply-1ch-360v-15a-adjustable/dp/1607347

[Circlotron]

I tried the bridge rectifier but by adding a regulator as I needed to adjust the voltage for variable gas output, it trips the breaker. A normal angled regulator is not compatible with a bridge rectifier.

When you say an "angled regulator" do you mean a triac phase controller like a light dimmer? Better of using a variac ahead of your bridge rectifier, preferably with an isolation transformer too. Even with the isolation transformer it is still very dangerous. 

[IanMacdonald]

If you use that high a voltage you will get arcing instead of electrolysis. The main product will be steam.

[mche1997]

Thanks for the link, sorry yeh not mentioning the price, very expensive.

[oldway]

How much current your circuit breaker is calibrated for ?

Lets think about the problem: you ask for a dc power of, at least 16A 300V, that means 4.8KW...If your power supply has an eficiency of 100% (what's impossible) and a pure sine current in phase with the mains, the current from the 240Vac mains will be 20A.

To have a perfectly sine current with cos phi =1, you need a Power Factor Correction.
You can't achieve a so low rms current with a simple bridge rectier because the load is not linear.

So, there is no easy solution if your circuit breaker is calibrated for 25A.
With a 40A circuit breaker, the simple solution of a bridge rectifier is possible.

[oldway]

If you use that high a voltage you will get arcing instead of electrolysis. The main product will be steam.

An elementary cell with 25% KOH electrolyte has working voltage between 18V and 2.4V.
Current density is choosen between 0.2 and 0.4 A/cm²
Efficiency vary between 52 and 70%.
Some manufacturers claim their industrial alcaline electrolyser has an efficiency up to 90%

As T.S. says that working voltage of his electrolyser is 240V, it is probably an electrolyser of about 100 cells in serie.

Is that a comercial or a DIY electrolyser ?

Does it produce H2 or Brown's gas? (mixt of H2 + 0.5 O2)

If possible, it would be better for safety to reduce the number of cells in serie and choose a lower voltage not higher than 50V, with several electrolysers in parallel.

Whe don't know if the output voltage of the converter must be isolated or not....for safety, better an isolated output.

[mche1997]

It's a 32a MCB breaker, I tried a 40a bridge rectifier and all works fine but if I add a linear voltage regulator rated at 16a as I would like to adjust the voltage, it just constantly trips the breaker. I was recommended using a variac transformer but its too heavy and bulky to fit into the enclosure.

[mche1997]

Yes, I tried adding a voltage regulator to lower it but it just trips the breaker straight away.
Hard wiring from bridge rectifier to generator works fine, had it running for 40 min several times and its quite cool max at 50 oC, no steam just hydrogen and it even set my carbon monoxide sensor upstairs off.

[mche1997]

Hi

Its a DIY 110 cell plates in series, each plate slightly over 2 volts, produces browns gas. If I reduce the plates, it'll heat up really bad. At the moment its all set-up correctly, running at 6 amps, does not go over 60oC but I need a converter as using a bridge rectifier, adding a voltage regulator would constantly trip the breaker and was told the easiest and cheapest solution is an AC to DC converter.

[oldway]

Ok, it is far more clear now.

Of course, it is a lot of power and you can't solve your problem very cheap.

It is necessary to choose an isolated output....Even so, 300V is a dangerous voltage, I hope you know what you are doing and that you are aware of the dangers of electricity.

First, look for an used isolation transformer 240/240 V of 3 or 4 KVA's....As you use it only 40 minutes, it's enough as power ratings.

Look also for an used transformer 240/48V 800VA.

Connect the secondaries of the two transformers in serie so you add the voltages , and a 40A bridge rectifier.

No need of condensators.

The primary of the 240/240V transformer is directly cnnected to the main's voltage (240V)

The primary of the 240/48V transformer should be controlled by a variac 1KVA 0-240V.
Don't forget to protect the primaries of the transformers by fuses.

Do not use a not isolated power supply, it is far too dangerous.....

NB: if current is not enough, you could add another transformer 240/48V 800VA in serie, with primary directly connected to the mains.
NB2: if you use forced cooling of the transormers (not true for the variac), you can use tranformers of lower power ratings down to max 1/2 the specified power ratings.
NB3: all this at your own risks.....

[oldway]

Industrial applications of Brown's gas :

A lot of informations here:
http://www.spirig.com/index.php?id=53?&L=0

[mche1997]

Hi oldway
How about you making them and i'll buy them off you ?
I'll be needing them in quantities but not huge and regular as I'm not that clued up, just know some basics.
Thanks for your much help.

[james_s]

What kind of voltage regulator are you trying to use on 300V? That's a very high power application, it's not trivial to regulate it.

[oldway]

Hi oldway
How about you making them and i'll buy them off you ?
I'll be needing them in quantities but not huge and regular as I'm not that clued up, just know some basics.
Thanks for your much help.

I am retired and I only repair vintage amplifiers and receivers now....
My workshop is in my little appartement, I already have no more place to live.... 

Look on EBAY or other auction sites.....

[oldway]

What kind of voltage regulator are you trying to use on 300V? That's a very high power application, it's not trivial to regulate it.

No voltage regulation, only a 1KVA variac to adjust the current.

[james_s]

I meant the OP, he said there wasn't room for a variac and that he tried some kind of voltage regulator.

[oldway]

About heating of the electrolyser: the simple ac to dc converter with transformer and bridge rectifier has a high current ripple, that means also that current is DC + AC currents.
Only DC current really produce Brown's gas....AC current increases the heating of the electrolyser....

So, it is possible that it became too hot and that electrolyte begins to boil....

Pure DC will improve the situation but probably not solve it.
You will probably have to cool the electrolyte with a heat exchanger.

[mche1997]

Yes, I will be using a thermal pelter

[oldway]

I meant the OP, he said there wasn't room for a variac and that he tried some kind of voltage regulator.

He was thinking using a variac of 5KVA's controlling all the power....I proposed to use only a 1 KVA variac, controlling only one fift of the power.

[mche1997]

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

[oldway]

Yes, I will be using a thermal pelter

You means a Peltier element? This is only for low power, you will have to dissipate a power not far from 1 KW....You don't do this with Peltier elements....

[mche1997]

Thank you oldway, I'll try and figure it out, appreciate for your help and all others but anyone knows how to make them, I'll buy it

[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

[dmills]

Were I making browns gas for some reason I would be looking to build say 6 * 50V stacks rather then a single 300V one, then use telecom rectifiers as the power supplies.

Compact, efficient, isolated and (on the surplus market) all kinds of cheap. The Eltek Twinpacks seem to be widely available and relatively well documented (2,500W each).

Regards, Dan.

[mche1997]

Hi Dan, thanks for the advise, sorry again it's far too big and heavy, ok for static but its to go inside an enclosure the size of a 2 drawer filing cabinet and always gets transported around.
6  smaller stacks might work with lower voltage but not sure if it can produce the same amount of gas and temperature wise when running for over 1/2 hour.

[TopLoser]

Tell us how much equivalent commercially available systems sell for?

[mche1997]

From £1500 up to £8000

[dmills]

There will be a reason for that cost...

As to the size of the telecoms rectifiers, I have several 2kW units (Eltek Flatpack 2HE) that are about 1.7 inches high, 4 inches wide and maybe 12 inches long, three of those would get you ~6kW (120A @ 54V) which should get it done, I seem to recall paying £25 each for them.

My use is radio shenanigans, not inefficient gas generation, but whatever.

I take it you have considered the effect of hot H2 on most steels? Hydrogen Embrittlement is a thing you know. 

Regards, Dan.

[mche1997]

Hi Dan, holy !, I must have looked at the different ones on the internet, they're big stacks like the size of a shoe box. Thanks for the extra info, I'll have another look tomorrow.
If I can't find the appropriate ones like you mentioned, can you sell me some ?

Thanks

[tron9000]

...but its to go inside an enclosure the size of a 2 drawer filing cabinet and always gets transported around...

So something like this:


this is a 19" rack mounted case, 19" rack mounted stuff is pretty standard, save you from having to design your own enclosures: http://sierracases.com/19-inch-rack-mount-transit-cases

[oldway]

Choosing a voltage lower than 300V is a much safer solution ....
 
The switching power supplies for telecommunication have a nominal voltage of 56V, it's a great choice.

This is another approach to the problem that you had imposed in your first post.

First buy the used AC / DC converter (s) then do the electrolyser project according to what you have found...

The only limitation is the availability of such converters at a cheap price, especially if you want to make multiple copies.

[BravoV]

Hi Dan, holy !, I must have looked at the different ones on the internet, they're big stacks like the size of a shoe box. Thanks for the extra info, I'll have another look tomorrow.
If I can't find the appropriate ones like you mentioned, can you sell me some ?

Thanks

Hint where to look for, try find cellular base stations installers/contractors, do few social engineering communication either thru email or phone calls, with the main purpose of getting informations on who/where/how cellular operators disposed/dismantled their outdated towers.

Not sure in UK, but there must be someones that do these cleaning and installing job as cellular towers get refreshed quite often.

This is how I got my quality industrial PSUs, some are even bigger wattage or higher voltage, even used, they're still very usable.

Most important thing is they're dirt cheap.

Example my hoards last year, got few of these for <$30/pcs.

Most of these quality PSUs are "designed" capable of running in series, parallel, master & slave & etc.

Just google the below PSU for it's new price.   



Wish you good luck on your hunt.

[dmills]

There are some 4kW Eltek SMPSU 4000 on ebay at the moment, not the smallest things I have ever seen and very slightly off the pace for efficiency, but very solid kit, and good for 85A @ 48V each!

IIRC somewhere in the region of £125 quid each, and brand new, you couldn't build it for twice that!

Alternatively there are Eltek flatpack HEs, but they want a little too much money, they are however compact.

I would second talking to telecoms service types, cell base stations are mad for every point on the power efficiency they can win, you not so much, and the telcomms gear tends to be REALLY nice stuff.

Regards, Dan.

[oldway]

Choosing a max voltage of 56V, your new electrolyser must have 20 cells and need a current of 66A to produce the same amount of Brown's gas as your actual 300V / 12A electrolyser.

Try to stay with a low density current of 0.2A / cm² (electrodes of 330 cm² - 27.5 x 12 cm²)

[mche1997]

Great, lots of ideas now and I will start hunting, thank you all guys.

[schmitt trigger]

The only advise that I would give you with respect to used cell tower PSUs, is to open them up and thoroughly clean them inside.
And I mean thoroughly.
You will not only find dust and dirt, but the occasional life form which was attracted by the warmth and decided to crawl inside, only to be duly shocked.

I know. I used to work at a place where we built and refurbished Telecom supplies. I wish I still had the picture of a power rack, which had been installed somewhere in India, which had a thick snake, almost 5 feet long, completely fried.
Small rodents are quite common.

[mche1997]

Oh, that is scary, thanks pal