Welding transformer rectified to charge battery bank, will this work

[r77]

Lots of people seem to be looking for a system to charge 48 volt battery banks, and hense my query.

I have a pickhill engineering transform based welder, 400 / 240 volt 7 0r 8kw welder, there are no electronics at all involved here, I have only ever opened it up to change the cooling oil which is the reason it is now 50 years old and still in perfect working order, and on the cooling oil front, the quantity can be upped to keep the transformer even cooler if need be, passive cooling uses no extra resources either.

I can not remember what the inside of this welder even looks like as it has not been used much since the migs came to me 25 years ago, but the gist of it is, the welder can be fed either 400 volts or 240.

On the output side, there are two main options, either 50 or 80 volts.
Then there is the adjustments for welding, there are about eight of these from 30 amp to 180 amp.

Could I simply take the 80 volt welding leads, rectify this output and use that through a charge controller to charge batteries, am thinking with a bit of filtering this would work.

The part of the equasion I understand least is, what position to set the welders amp control knob, it is one of those that lifts up and rotates and is then lowered again into a notch, which is obviously a tap off the transformer.
In my way of thinking it would seem that setting the welders amp knob to the highest setting would provide 80 volts at the highest amperage.

Now as I said, I do not remember what the transformer looks like inside the box, so when I adjust the amps knob, am I adjusting on the transformers secondary, and in any event, how does inductance help or hinder my idea of taking this 80 volts at the welders rated 180 amps in order to feed an inverter or charge controler, am thinking the indcutance is what keeps the amps steady, and the voltage will take care of its self, as altering speed is the only way to alter the voltage other than the pull of the load sinking it a bit or long lines coming into play, which wont matter to the rectified input to the charge controler as it handles a voltage within a range.

I have this welder anyway, and do not see any point in it sitting there when I can re purpose it and still have if for when needed, and avoid buying a transformer if it will work out for me.

One last point, does a transformer fed from a capacitor regulated alternator smooth out the harmonics induced, or do they multiply and get worse.

Thanks to everyone in advance.

[mike90045]

Your welding transformer is great for 60Hz     Your wind turbine is going to be all sorts of different frequencies, most of which will not work with the 60Hz (or 50Hz) transformer.

Midnight Solar also has, for wind turbines, a thing called  a Clipper  it has HV electronics to limit the voltage going into the charge controller.

So what exactly are you doing ?   Do you have a wind turbine and a HV Induction motor that you  are wanting to rectify and charge batteries with ? 
or
are you using a 180A transformer to get 240vac down to 80V to feed a charge controller ?   Charge controllers start to do funny things when you drive them with a non solar source, a Big Stiff Transformer with 180A and Hover Dam behind it, would likely smoke any MPPT controller, because they use their electronics to load down the solar array.  A 180 A transformer will not load down easily

[r77]

Hi mike 90045

The wilding transformer is 50hz, and as for windmill and solar, they have not been purchased yet, and in any event will be rectified and fed to the charge controler, their output
will not have to go anywhere near the transformer, it is for charging via my generator, and yes, my idea was to rectify the transformerThis output and feed this to a charge controler, though I would classify it more as a battery charger as it will be charging batterys with a steady input from the transformer/generator, as the solar / wind end of things are to follow and will need to be fed to a charge controler, I do see there is a distinction in the two aproaches and have solved it near the bottom of my rant which explains what I am trying to do.

Thanks mike945009

What am I doing

Am re evaluating staying connected to the electricity grid.

My intention is to get a battery bank, inverter / charger
and put together a new generator to do the charging when
wind or solar are not producing enough to charge the batterys.

I am doing this in the order the components become available to me
at the right cost, leaving the expensive ones to last in order to
pick up a bargan when am educated enough to know what I actually
need and what constitutes a bargan.

I am currently awaiting quotes for a new alternator, and like all
components required reliability is of great importance and thus
my move away form electronics, the new alternator will be transformer
controled, which should make it more reliable, easy for me to test, and if need be rewound.
I can not work on or repair an AVR which means handing out large sums of money to repair or replace
one when it goes wrong, in this case the transformer costs between 1/3 and 1/2 the price of an AVR,
depending on whether its and oem and on how complex one wants to go.

Thats the alternator covered.

Charging the batterys, and to do this I also want to avoid using components that can fail easily
and which I also can not repair.
This was my reason for wanting to use a transformer to reduce the voltage coming from my generator,
and use simple components such as rectifiers and a few caps to create the DC.
This may work out well enough, as again I can test and repair a transromer, so If this transformer
aproach would work, I have a welding transformer that I only need to connect into, all the leads are
redily available without opening up the unit, it is also oil cooled and in great order.
I can also buy cheapish AC welders, if anything does give up on the transformer end so am not tied up.

The main issues with this aproach other than my lack of knowledge, is that I still need a charger or charge controler
to charge the batterys, and thus am in territory I do not like, reason being I can not diagnose or fix them.
But I have no choice, and during my research I have come to realize that I will have to use an inverter also, which
is more electronics that I do not understand of can fix.

Bottom line, I can see that using a transformer is a more fault tollerent and dependable way to get the voltage and current
I need, but at what cost, there is going to be losses in efficiency, and probably more so than going the more electronic
route.
This is my conondrum, go the transformer route, and buy an inverter charger that will accomodate either my generators transformed and
rectified voltage and solar or wind input, or buy an inverter charger that can take 230 volts form my alternator, and the DC from
solar or wind.

Well complicated as it may look, thanks to people on the forums, and my own research, I have been pointed to and found numerous
products that can do all I need, victron energy do a charger inverter that can take ac OR dc input, which solves all my problems,
but at a slight cost in effiency, the product is only 94-95% efficient, but am not so sure this is all that bad, because it serves two
puroses, where for example a comparatively priced outback only does the inverting at 98-99% eficiency, this product inverts, charges,
and to top it off load shares, this load sharing will eek back the quoted losses, because I can run the generator to charge and at the same time,
keep it loaded heating water or whatever else, such as washing machine duty, it will even cut the batterys in when the preset ac level from the generator
has been reached. All this functionality saves a lot of wiring and setting up a micro controler to achieve similar.
I do however intend to impliment my transformer idea and a cheaper charger as backup and would realy apreciate peoples input on whether or not
my idea with the welding transformer will work, and what issues I should watch out for, such as current rushing in or out of the transformer on startup
and shutdown and how to protect against this, for all I know a welding transformer as oposed to a standard 240-80volt transformer could be way better at controling harmonics, ironing out ripple, stabilising current or voltage, or not as the case may be, thats why I posted here, can't understand why poeple in the business can't come out and tell me, the answers are either one is better than the other, and here is why.

Thank you all for looking in and helping out.

Kind regards, john

[r77]

Sory mike90045, someone messing with your name when I was away from computer

[Thob]

Be aware, if you are not already, that welding transformers (for stick welders) are an odd beast.  They attempt to mimic a constant current on the welding side.  When no current is flowing (no arc), they tend to have a fairly high OCV - open circuit voltage - around 70-90 volts.  When welding, you can expect around 25 volts at the rated current.  And they will maintain close to that current (only a little higher) as the arc length shortens and the voltage can go all the way down to zero.  Well, I goes to zero when I weld because I stick the rod often...  These are not the characteristics of what you typically think of in a transformer, which normally tends to be (nearly) constant voltage on the output.  Last I checked, transformer welders were not all that efficient.

Some welders adjust the current with different taps, some adjust by moving the core (or part of the core) in and out of the winding.

[r77]

Hi Thob, thank you for your input, interesting to know, but I kind of thought there had to be some reason we can not simply use
any ordinary transformer for welding, am guessing sticking would be the norm if we did, and smoke would be the most likely
outcome, otherwise no one would need two such differing transformers, just wondering in the cure is in simply stripping out whatever
means of regulation they employ, as this alone could be the main difference between the transformers. Will t some tests in the future,
though for now this significent difference between an ordinary transformer and a welding one is enough to take another route.

Regards, john

[mike90045]

Define "Alternator".   Something like an ST-5 @ 1500 RPM or a 115A Automotive alternator @ 4000rpm ?   

The phasing and frequency band of the transformer, HAS to match the alternator output  (well, it should)

[r77]

Hi mike90045

I intend to use a standard 50Hz 230 volt alternator, it may be single or 3Ph depending
on the prices and availability of a new 10 Kva trnasformer controled unit.
A few years back single phase transformer controled units were easier to
locate around here, now it seems they are not producing them due to the
downturn globally in such sales, so I may have to go for 3Ph, am
definately avoiding an AVR controled unit for this job.

Regards, john

[BruceM]

John, I'm not sure what problems you've had with AVRs are, but they are no longer very expensive.  They are relatively simple and reliable.  If you can have a spare on hand for less then $70,  that should satisfy the need for backup.  Take a look at what Central Georgia Generator carries; Tom there is long noted for good customer support. 

For DC generation, 3 phase is much superior.  I use a single phase ST-3 for my AC and 120VDC battery bank charging, since that lets me use some AC while charging, but mostly so I can use it for my primary AC power.  I rarely charge my batteries with my generator since I'm in Arizona.

I use a big toroidal transformer linear supply with a homebuilt motorized variac for current adjustment (automated by my homebrew Picaxe based battery bank controller).  Filtering rectified AC from a single phase generator head is bulky and expensive, and requires chokes as big as the transformer. 

3 phase would be much nicer for dedicated DC generation.  Someone on this or the Lister forum is using a Midnight classic for generator charge regulation; I would check the specifications closely on those and perhaps check with the folks on some solar forums about that use.  You should be able to use the stock harmonic winding regulation with this setup, if the charge regulator can tolerate the AC voltage peaks, and doesn't have issues with generator power.

You are absolutely on the right track to fully check out all your system needs and compatibility before buying any part of it.  Unless you like fussing with electronics, you should try to stick to a proven setup with popular products.  They will be better supported over time.

[r77]

Hi BruceM

The AVR's from Mecc Alte are not cheap, one is €545.00 and the DSR version is €555.00.
I would worry about the reliability of aftermarket ones.
Personaly, I have never had an AVR problem, but at the same time would trust a transformer
more, I have one 50 years old and still working.
The transformer controled alternators are also capable of starting huge loads and their voltage
actually rises, they just seem more dependable and tolerant.

I will pursue the transformer rectified and fed to a cheapish 4 stage charger as a backup and educational exercise.
The same generator will power it as will power whatever setup I end up with, so no waste.
I too will be utilising the full output of my generator via a victron charger inverter, which has load sharing built in.
Beats me why it is so difficult to find a dc generating end at a reasonable price, I must check with my local forklift dealer
what it would cost for a replacement DC motor for an electric forklift, have a feeling it will be big bucks,  if not one of these
that runs on 48 volts may be suitable to re apropriate as a charging supply, I had one and sold it like a fool, man bought it
to use with a hydro setup to charge batterys.

Regards, john

[BruceM]

The Mecc Alte prices for AVR would send me running away, also. 

[r77]

The Mecc Alte prices for AVR would send me running away, also. 

Strange thing is, only last year I could buy 8Kw AVR controled single phase 2 pole TWIN BEARING
Mecc Alte alternators for well under the price of their cheapest AVR, and now when I go back
to price units, this is the extortionate price one guy quoted me,
ECP3-2S/4 B3/14    8kva     1050.00 + vat, and I have to collect it from the other eind of the country.
It is like everything else in Ireland, we are run but the elite and theiy control the business world, they
would rather sell you nothing than charge you a decent price, their model is charge four times the price
and shift 1/4 the amount of units, shure cuts down on expenses staff and hard work for them.
In this particular sector, Ireland is flooded with companies who produce generating units, they
neither want nor care for anyone other than the guy who comes to them to spend a ransom
on something they will be paying for for years to come, if the banks don't lift it first, where
ther cycle starts again in someone elses name.

Regards, john