Need Help w/ Generator Electronics

[opus1]

I have an issue that I need to get resolved with a DC/AC generator and am willing to pay for some help. I had a previous post but it was removed. I apologize if it was not to spec. I am a real person looking for a real solution and I know this is where the brain trust is on these issues. My buddy that is smarter than I (but not as smart as you guys) sent me here. For details or the best way to proceed, please reach out to me.

[wpowokal]

a) whats the problem?
b) this post would be better in Newbies section, will someone please wake a moderator
c) where are you? I don't seem to be able to reach you.
d) this site offers free advice, payments can be made to board owners as donation see donate button above

Allan

[TomW]

a) whats the problem?
b) this post would be better in Newbies section, will someone please wake a moderator
c) where are you? I don't seem to be able to reach you.
d) this site offers free advice, payments can be made to board owners as donation see donate button above

Allan

Allan;

He cross posted this all over the board same text and no actual information Seems he wants to hire someone so I put this one in Classifieds. I wish folks would put some effort into posting clear questions and at least basic information on their questions.

The folks here are exceptionally savvy but I dare say not one of us is even remotely  telepathic.

Anyway I have been explaining myself too much today.

Off to some turbine work.

Tom

[wpowokal]

Well at least his post is now classified!

[opus1]

I appreciate everyone's help. here is my dilemma:

This concerns a DC/AC generator. The AC side is fine and we need not do anything there.

On the DC side, we have a constant current scenario (complete wiring diagram attached) at around 120 amps.

The generator puts out between 25 and 56 volts. When the engine is running the volts at the 56V end and as a load is applied the volts go down to around 25V under full load.  So, to make sure I am clear (as best I can be as I have not the vocabulary to discuss this properly with you guys)...  The DC side of the GEN puts out 120A at 25.2V with total Watts available at around 3000W.

What we need however, is constant (or close to) voltage at between 24 and 28 volts to run some various aviation equipment. We still need around 80A total, but the volts not go over 28V as it will fry some equipment )or at least blow fuses).

Is there a way we can we rework the existing control box (wiring diagram attached), or put something between the generator and the power bus of equipment, to achieve this (besides a battery bank)?

[ghurd]

We still don't know what it is.

I do not see where there is any AC, but the pdf is kind of fuzzy.

Almost looks like a old gasoline powered DC welder.

[opus1]

Yes, it is a generator welder. 1200w AC and 3200w DC. The AC is powered by the top stator in the diagram. The DC from the bottom one going to 7 diodes. The top diode is the main one (I guess) and the others tie together through a switch knob - adding together from 40A to 60 then 80 and so on. We will just set it to the maximum or use a block and take switch out - or whatever you think is best.

[ghurd]

The top stator in the diagram looks like it is rectified to DC.

Do you have something against batteries?

Are you trying to stick an antiquated welder in an airplane to power the electronics?

[bob g]

are you ever wanting to use it as a welder again?

if not it might be possible to rework the unit to do only battery charging, but
you will need to get control of the field/rotor and use some form of regulator
which in strangely missing in the schematic.

not sure it would be worth the effort because gas welders are about the most inefficient generators
ever conceived in my opinion, they are built to be rugged brutes made to put out current to weld with
reliably while putting up with dead shorts and all sort of other stuff that would kill a regular generator.

the tradeoff for being so tough it giving up efficiency.

for bulk charging it might be ok as is, but you will need some form of sophisticated field control to manage the
charge rate when the battery gets to about 80% state of charge or you will likely be making a lot of heat and boiling
the crap out of the batteries

this is for a flooded cell?

if you are thinking of using it for gel or some other finicky battery, forget it.

my opinion only, ymmv

bob g

[opus1]

Will not need/use as welder again.

Yes, on ground will be using to power some electronics on an airplane.

Battery charging would be secondary.

We can do whatever we think best to get this to do what we want.

[ghurd]

We still do not know what you want.

You want to power avionics, in a plane, on the ground?

Why, Exactly?

What, Exactly, electronics?

What do you have against batteries?

You don't have long to come up with some real, solid, specific, HONEST, information.

[kurt]

basically he wants to make 24v dc airplane maintenance generator out of that welder don't ask me why as you can buy used ones that are designed for that purpose military surplus relatively cheap people used to buy them to try to make 24v gas battery chargers out of them all the time.
 

http://cgi.ebay.com/ebaymotors/Prestolite-Generator-28v-180A-11640180-Leese-Neville-_W0QQcmdZViewItemQQhashZitem1c14ddfbf8QQitemZ120609176568QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

there is a listing with 5 of them available all you gotta do is add an engine and away you go.   

[opus1]

I am sorry - it seems as though I have somehow offended people here. Do not ask how as I do not know. I am simply looking for answers and have provided everything asked of me. Now I am being called dishonest. I thought I would come here for help from those smarter in this area than we are. If I need to be doing something different here please advise.

[opus1]

I appreciate the advise on the maint gen. This will be great next time how er we already have a significant amount invested in this one. Specific cage, etc. I really just need to get this one up to speed I we can.

[ghurd]

You keep asking the same questions over and over, but you provide no useful information.


How about answering some straight forward simple direct questions.
You have been asked these questions before, but refuse to answer them.

What do you have against batteries?

Can batteries be in the system, or why not?

What is the specific brand and model of this welder thing?

What are the electronics?  Specifically.

What are you trying to do.  Specifically and Exactly.

[wpowokal]

I say it is quite old, lets look at the AC side the 3 phase is rectified then regulated by electronics I assume because there is no voltage regulation of main winding and or if AC was used at the same time as DC then AC voltage would swing wildly.

Secondly your proposal is to use the DC side at 74% duty where most welders have at best a 50% duty rating therefore make sure of this point or you will overheat the windings.

I would use a DC to DC switch-mode power supply, it is the only way I can see of obtaining a stable voltage, it has already been explained that welders are made crude and tough so that DC is probably a little rough, ie lots of ripple on the output although with so many windings they may cancel each other a bit.

The only way with that unit to regulate the DC voltage is by varying the motor speed at a given load, there is no fine adjustment for the welding output so presumably the operator is expected to vary motor speed for that.

Allan

[rossw]

The folks here are exceptionally savvy but I dare say not one of us is even remotely  telepathic.

I *KNEW* you were going to say that.   <grin>

[dnix71]

56v with no load and 24v at full load is EXACTLY what a welder is supposed to do. You need the higher voltage to strike the arc and a stable lower voltage when welding.

So we know that the welder is doing what it was originally made to do. I doubt there is any simple safe way to regulate the dc side voltage. It was designed to be regulated by dissipating energy in heating metal. If you only needed an amp or two a zener would suffice.

http://www.trcelectronics.com/Meanwell/drt-960-24.shtml   two of these connected to the ac side of your generator would give you 80 amps total nice clean adjustable pf corrected power for sensitive aircraft electronics. The total price would be about $650 plus shipping. Much cheaper than repairing the damage to aircraft electronics. The device above is stackable for current sharing and more or less indifferent to the voltage and phase of your ac supply.

[wpowokal]

The AC side is only 1200 watts

[dnix71]

The AC side is only 1200 watts

Yeah, unfortunately the dc side is also really only 1500 watts unless you want to fry the windings on the generator. 50% duty cycle on a good welder.

He doesn't have the needed power on either side. This one takes 60vdc or less and makes 24v regulated dc out. Up to 500 watts.

Two of those of the dc side, plus one of the http://www.trcelectronics.com/Meanwell/drt-960-24.shtml on the ac side gives you 80 amps total at 24vdc.

Personally I think there has to be a better way to do it.

one of these on the ac side gives 40 amps and two of those on the dc side give 40 amps more and distributes the load so that it stays within design specs.

[kurt]

ya there is an easier way already showed him one of those military surplus generators off eBay it will give a regulated voltage of  28v and handle 80 amps easy all it needs is an appropriate engine.  his application is what they were designed for for the military.

[joestue]

The cheapest solution is to get a used 5k generator off craigslist for a few hundred dollars and buy an 1800 watt 28 volt supply.
That is if you can find one. Ebay is full of 5 volt 300 amp units just asking for a transformer rewind.
Another option is to get someone on the diyaudio forum to build you one. someone over there just built a 4Kw +/-40volt unit, it wouldn't be but another 20$ worth of diodes to make it a 4Kw 28 volt unit.

[bob g]

i told myself i wouldn't get involved further in this discussion, however
i just can't seem to help myself.

that welding generator will make for a nasty 28volt source in my opinion, the rectifiers are likely so
damn noisy (read that spikey) that it would likely damage any electronics that would be connected to it.

a welder is a crude/rude/brute power source meant to do one thing and one thing only very well, and that
is put up with supplying power into what is effectively a dead short.

this is not to say that there are not some very good welder/generator units that can produce some nice clean power
but generally not out of the DC welder section in my opinion.

there is just so many better ways of getting the job done, that would likely not damage anything.

in my opinion connecting a dc/dc converter to get a stable 28vdc output is probably putting good money after bad.

bob g

[opus1]

Would this work?

http://zahninc.com/sd15.html

4th one down:

CH63125F-S w/2-LC225s filters (parallel)

[dnix71]

That's over $2000. But no it won't work because you don't have enough continuous power rating on the dc side to output 80 amps at 24v without burning out the dc generator windings. See my post above and this one
Posted by: wpowokal
I say it is quite old, lets look at the AC side the 3 phase is rectified then regulated by electronics I assume because there is no voltage regulation of main winding and or if AC was used at the same time as DC then AC voltage would swing wildly.

Secondly your proposal is to use the DC side at 74% duty where most welders have at best a 50% duty rating therefore make sure of this point or you will overheat the windings.

I would use a DC to DC switch-mode power supply, it is the only way I can see of obtaining a stable voltage, it has already been explained that welders are made crude and tough so that DC is probably a little rough, ie lots of ripple on the output although with so many windings they may cancel each other a bit.

The only way with that unit to regulate the DC voltage is by varying the motor speed at a given load, there is no fine adjustment for the welding output so presumably the operator is expected to vary motor speed for that.

Allan

[opus1]

Under full load the GEN puts out 120A at 25.2V CC and can surge to 135A (peak). 80-100A is all we require.

Motor speed is already governed, controlled and regulated and will keep at the sweet spot no matter what.

The AC side is a separate issue altogether as it has its own system - again, this is a dual stator/rotor design (one for AC and one for DC).

Aside from the cost, will the proposed solution work for my requirement?

[opus1]

I meant to write:

On the DC side and under full load the GEN puts out 120A at 25.2V CC and can surge to 135A (peak). 80-100A DC is all we require.

[bob g]

opus:

everyone here is trying to give you the best advice they can give you
it is very difficult to help one who is set on not helping himself however.

the welder is constant current, but the voltage will swing significantly depending on load
and you have no way of stabilizing the voltage that i can see.

then there is the issue of voltage spikes when the load varies, new alternators that provide power
to sensitive electronics/computers use avalanche diodes to clamp these damaging spikes.

the welder does not use avalanche diodes.

not having any means of clamping these spikes means that under the right circumstances you can have
a spike of many times the design voltage of 28volts, perhaps upwards of 100 or maybe even twice that
on a short term basis.

batteries can clamp a certain amount of these spikes but nowhere near all of them, and especially those that
are likely to be generated by the welder/generator you reference

it also appears from the pdf schematic that while the welder has dual stator windings, the recepticals are provided
with DC power at something like 120volts, and not AC,, this is very typical of a small portable welder/generator
where brush type drills and grinders are generally used and don't care whether the power supplied is AC or DC.

also it is very typical for the duty cycle to be well under 50% at near full output on many welder/generators of such small
size, although there are examples of others such as ones made by miller that are capable of 100% duty cycle at full range output.

it is not my belief that this welder is a miller or one that likely has much more than perhaps 30% duty cycle at 100amps.

you have to remember a welder generally is not a 100% duty cycle proposition, one usually has a lot of down time, setting up, chipping
slag, grinding, and just changing rods.

you have been asked what you plan to power with this setup, but so far i haven't heard what that might be, so
i for one would never counsel you to use such a setup under any circumstance, especially when the word aviation is mentioned.

its one thing to burn up a set of cheap golf cart batteries for a small power shed, as something to dabble in, but
quite another if you plan on using this setup on anything that might get airborne with folks aboard.

i want no part of getting someone hurt or killed either from falling out of the sky, or being hurt or killed by something falling out of the sky
which can be traced back to some crazy idea of using a welder/generator to power up anything related to it.

in short and not so sweet terms

don't do it!  its crazy, its nuts!  and you will likely either damage a bunch of equipment or get someone hurt!! or worse!!!

bob g

[joestue]

opus:
the welder is constant current, but the voltage will swing significantly depending on load
and you have no way of stabilizing the voltage that i can see.

then there is the issue of voltage spikes when the load varies, new alternators that provide power
to sensitive electronics/computers use avalanche diodes to clamp these damaging spikes.

the welder does not use avalanche diodes.

not having any means of clamping these spikes means that under the right circumstances you can have
a spike of many times the design voltage of 28volts, perhaps upwards of 100 or maybe even twice that
on a short term basis.

batteries can clamp a certain amount of these spikes but nowhere near all of them, and especially those that
are likely to be generated by the welder/generator you reference

it also appears from the pdf schematic that while the welder has dual stator windings, the recepticals are provided
with DC power at something like 120volts, and not AC,, this is very typical of a small portable welder/generator
where brush type drills and grinders are generally used and don't care whether the power supplied is AC or DC.

also it is very typical for the duty cycle to be well under 50% at near full output on many welder/generators of such small
size, although there are examples of others such as ones made by miller that are capable of 100% duty cycle at full range output.

it is not my belief that this welder is a miller or one that likely has much more than perhaps 30% duty cycle at 100amps.

you have to remember a welder generally is not a 100% duty cycle proposition, one usually has a lot of down time, setting up, chipping
slag, grinding, and just changing rods.
bob g

Most of us I think made the assumption that someone with a few kilowatts worth of aviation equipment would be slightly qualified for the job...
I'm no stranger to this field, a kilowatt of 28 volt equipment is worth at least a few kilobucks...

On that note.. what you mean by "clamping these spikes" is almost certainly what we call "overshoot" it isn't that big an issue, as long as the dc-dc converter can handle the open circuit voltage +50% there won't be enough energy to push the filter caps over 110-130% open circuit voltage.

I would never suggest using an MX80 with some filter caps and the battery charge point set to 28 volts.. although that might work.. what's the max voltage on that again?

Any mil-spec linear regulator would use a minimum 100 volt pass transistor for a 26-30 volt output, and would have enough input capacitance to absorb a 100% load step transient for a 50% efficient supply. it would also weigh a few ounces per watt, and cost a few dollars per watt.    

[wpowokal]

I vote this be closed I smell drugs

allan

[TomW]

I vote this be closed I smell drugs

allan

I Vote we back up.

He forgets about this "source" and just starts with what he is trying to do. rather than all the cryptic crap up til now.

You may have a point Allan. Something doesn't square here.

I would be very disappointed to see us unwittingly help someone remote pilot a C47 full of Semtex or some equally nasty thing.

The world is a weird place anymore.  And something ain't right here and I smelled it from the start, kids.

Besides, I thought all things aviation were pretty tightly controlled as to what can fly and what cannot fly.

So why is anyone legitimate in here seeking advice on how to do something with an aircraft?

That is my comment at 6 AM my opinion may change but this is a waste of forum resources chasing this vague need.

Tom

[Volvo farmer]

That is my comment at 6 AM my opinion may change but this is a waste of forum resources chasing this vague need.

But Tom, you fail to consider the entertainment value of this thread. 

I vote that this opus fellow makes a donation to the board, as he was originally willing to pay for advice and he is now on his third page of free advice.

[bob g]

joestue:

overshoot, will amount to a couple hundred volts when a serious load dump occurs, because there is no
electronic fast acting regulator involved to control the alternator it might remain over these limits for several
milliseconds.

all of this has been sorted out in small alternators for cars and trucks with the advent of sophisticated computer controls
and many heavy loads such as A/C, heated seats, windows and muchowatt audio systems.

you load that welder generator down to 100amps and then take 80amps load away from it and there will be a serious voltage
spike that is likely to at least wear on the electronics attached if not outright kill the stuff.

i would suggest anyone thinking of doing such a project read up on "load dump" as it pertains to automotive alternators
and how it is handled when there are computerized or other sophisticated loads attached or being powered from such charging
sources.

certainly there are a plethora of ways to alleviate these and other issues, but why?

why spend the bucks to add all manner of dc/dc converters, other stuff to control the load dump, and likely a decent regulator
when there are many far better and more efficient options available that will just work right out of the box?

of course unless one likes a rube goldburg approach to things?

and yes, i too think this topic has been posted by someone with rather strange aspirations

bob g