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Renewable Energy Questions/Discussion => Automation, Controls, Inverters, MPPT, etc => Topic started by: welshman on September 15, 2020, 06:21:32 pm

Title: Inverter Build Project.
Post by: welshman on September 15, 2020, 06:21:32 pm
As a backup inverter I plan on utilizing this casing and transformer.

I've been brainstorming lately on how to build a power board / mosfet circuit and i think i've come up with something that is new and should be interesting to see.

over the coming weeks i'll be putting this together and documenting it's build.

this is what im starting with.

Title: Re: Inverter Build Project.
Post by: Pete on September 16, 2020, 05:43:43 pm
I am interested in how much Idle current that type of transformer draws. Old welding transformers like that are pretty easy to come by these days with everyone going for inverter welders. They may work out well for inverter builds. Just wondering about the looseness of the magnetic circuit and if they have horrendous idle currents.
Good luck
Pete
Title: Re: Inverter Build Project.
Post by: ClockmanFrance on September 18, 2020, 02:24:41 pm
I have had a APC UPS 5000va, that would self start and would give about 3.7kw of 240vac from my 1100ah 48v battery bank.

The problem was that type of sheet laminate EW transformer was eating 200 watts from my precious batteries just running.

Now days i use a toroid wound core, and with suitable Ferrite Choke my new OzInverter Inverter now only uses about 30 watts, so far more efficient using a toroid core.

However, toroid cores and the Inverter power board need to soft start.
Title: Re: Inverter Build Project.
Post by: welshman on September 26, 2020, 08:03:18 am
ill let you all know what i get up to and how it performs.. i've ordered all the bits needed and drawn up the pbd in eagle and had it printed by pcbway. just waiting for everything to arrive. im going to try to take a few lessons learnt with the other inverter and put them into practice with this "backup" device.

the mosfet board design i've gone with is quite a bit different to the normal.  i've made sure that each pwm to the mosfets has exactly the same length of signal wire so the timings of the chips should be in sync a bit better.

the actually mosfet bridge will be something im sure you will like to look at, like i said its a radical design, fingers crossed that it makes sense in the end.


i've ripped up and inspected the relay on two powerjack control boards now and it looks like they are the culprit when blowing up mosfets. my figuring is, due to the dirty contacts on the relay, when the generator stops and slows down the pj is supposed to open the relay to hand the mains back to the inverter. but if the relay doesnt break fully and is noisy. the generator as it slows down is going to get its decaying sine imprinted slightly on the inverters own sine. iv'e bought a 100amp solid state relay to replace the standard one. the state of the contacts on the standard relay is bad enough to be causing a problem on its own. maybe it's why it took many years of switching on and off between inverter and charge multiple times times a day before it blew the first set of mosfets. who knows?

Title: Re: Inverter Build Project.
Post by: Pete on September 26, 2020, 06:04:56 pm
Sounds like a good plan to swap the relays with a Solid State Relay. There may be a problem with time lag in the relays too.
Just wondering if you are going to put some delay in the SSR relay switching times to match the mechanical relays or whether you think the faster switching will not upset the mosfets more.
Look forward to reading about the build
Pete
Title: Re: Inverter Build Project.
Post by: rossw on September 27, 2020, 05:03:01 am
iv'e bought a 100amp solid state relay to replace the standard one.

Just a cautionary word.
Check which type of SSR you get. Some have all sorts of electronics to stop them creating switching transients, and they may not turn off when you think they will - so do your homework on their suitability before you put them in line!
Title: Re: Inverter Build Project.
Post by: welshman on September 27, 2020, 05:38:11 am
Sounds like a good plan to swap the relays with a Solid State Relay. There may be a problem with time lag in the relays too.
Just wondering if you are going to put some delay in the SSR relay switching times to match the mechanical relays or whether you think the faster switching will not upset the mosfets more.
Look forward to reading about the build
Pete

iv'e bought a 100amp solid state relay to replace the standard one.

Just a cautionary word.
Check which type of SSR you get. Some have all sorts of electronics to stop them creating switching transients, and they may not turn off when you think they will - so do your homework on their suitability before you put them in line!

this is what im using

some of the specs

<10ms on/off time
7.5ma 12v trigger

now there is something else that's interesting about the solid state relay. it only turns on and off at the zero cross point of the sine wave, to avoid surge, rfi/efi. could this be a solution to the charging problem?

[attach=3]
Title: Re: Inverter Build Project.
Post by: rossw on September 28, 2020, 01:19:36 am
now there is something else that's interesting about the solid state relay. it only turns on and off at the zero cross point of the sine wave, to avoid surge, rfi/efi. could this be a solution to the charging problem?

It's exactly this that I'm referring to.
I've seen some of these relays refuse to turn off at all, depending on the nature of their "zero-crossing" detector.

For a giggle, lets hypothetically ask a couple of questions?
Is the zero-crossing based on volts, or current?

If you have a reactive load, current will lead or lag volts, so when volts=0, current will be non-zero.

One would assume that in order to minimise RFI/EMI, it would be switching at 0 *CURRENT*, but most of the ZCD circuits I've seen are zero *VOLTS*.
Depending on the technology in the SSR (and I've seen it happen) - with certain scenarios of load, they simply won't turn off.
Title: Re: Inverter Build Project.
Post by: Pete on September 28, 2020, 01:59:46 am
As you say Ross rarely are loads purely resistive where Volts and Current are in phase.
In an Inductive load the Current will lag the voltage.
I a Capacitive  load Current will lead the voltage.
So depending on load the SSR may turn off early or late.
That is one reason I suggested a time lag be built in.
Maybe in some situations a very fast reaction to the mains dropping of is necessary, such as in running a computer with no UPS but otherwise what is a few seconds. Smoke coming from electronics is rarely as easy to fix as the movies show, where they just hit the equipment with a fire extinguisher and it all comes on with no problems. ( learnt that from Lost in Space when I was a kid) never seen it work in real life.
Pete
Title: Re: Inverter Build Project.
Post by: rossw on September 28, 2020, 02:12:39 am
As you say Ross rarely are loads purely resistive where Volts and Current are in phase.

It gets (potentially) much worse in the situation of switching a generator, and this is one that may slip notice for some - if you have two non-phase-locked signals (such as a free-running inverter and a free-running generator), and lets say they are both "nominally" 240V (in this country that would be the norm), now you have a signal with a peak-to-peak voltage of 340V, and another peak-to-peak also of 340V, and when they're completely out of phase, your relay COULD see the full whack across its input/output. (Depends how things are connected, obviously, but in my case it does apply). You're going to want that silicon to have plenty of headroom!

Quote
That is one reason I suggested a time lag be built in.
Maybe in some situations a very fast reaction to the mains dropping of is necessary, such as in running a computer with no UPS but otherwise what is a few seconds.

Lots of electronics stuff won't like more than a few cycles of outage.
Lots of things with compressors will absolutely hate "short duration" outages - half a second, anything up to potentially a few minutes - many will try to re-start a motor with full head pressure, stall and burn out!

Quote
Smoke coming from electronics is rarely as easy to fix as the movies show, where they just hit the equipment with a fire extinguisher and it all comes on with no problems.

Ahh yes, movies are a world unto themselves. Any relation to real life is purely co-incidental :)
Title: Re: Inverter Build Project.
Post by: Pete on September 28, 2020, 09:11:32 pm
Any clues Ross on why some inverters can handle load switching easily and others not.
I remember reading that PowerJack inverters can have problems and blow mosfets when switching from stand alone to mains inputs, and that PowerStar W7s were a bit more robust and handled it well. ( I think it was Oz that said that)
I am guessing that the transformer type may have had something to do with it.
Pete
Title: Re: Inverter Build Project.
Post by: rossw on September 28, 2020, 11:18:25 pm
Any clues Ross on why some inverters can handle load switching easily and others not.
I remember reading that PowerJack inverters can have problems and blow mosfets when switching from stand alone to mains inputs, and that PowerStar W7s were a bit more robust and handled it well. ( I think it was Oz that said that)
I am guessing that the transformer type may have had something to do with it.
Pete

Not really, because I haven't delved into their bowels to find how everyone is doing it.
I have an expensive commercial unit specifically built and marketed to be "generator interactive", they go to great lengths to do the transition "gently" - when the inverter senses input on the generator input, it monitors the genset voltage and frequency and adapts its own output to match the same voltage, frequency and phase. Only then does it pull in the contactor. Once that is done, the inverter then GRADUALLY changes its output to transition the load across to the genset, and then GRADUALLY starts taking as much power as it is permitted to by the configuration (generator capacity less instantaneous load = available capacity) to charge the batteries.

It does the same thing in reverse when isolating from the generator.

I've never heard of any of this type of inverter suffering the kind of problems some have experienced with the chinese inverters, but I suspect that is largely by the design and perhaps partly by the choice of components.

As to why some inexpensive inverters survive and others don't, I could only guess (and probably be wrong!)
Title: Re: Inverter Build Project.
Post by: noneyabussiness on September 29, 2020, 11:46:36 am
Oz explained it the best somewhere here, toroidal transformers are electrically " stiff " and as ross said to switch over cleanly they need to match the phase and frequency and voltage etc. before changing over, PJ's don't as far as im aware.  There is a version that has a series resistor accross a relay setup to " soften " the change. The W7's did it ok because they used a E/I laminated core, which has enough " give " electrically that the mosfets etc. could survive the change over..

If you do a search,  OZ and Madness, by memory go into depth about it...
Title: Re: Inverter Build Project.
Post by: welshman on October 04, 2020, 10:20:48 am
This seems to be a very nice transformer..

it even has the ability to move the coils. there is a piece of aluminium, with some grub screws that is bent by the screws to fix the coils in place.

what would be the best option here? leave them as they are or move them closer?

It weighs 46.5KG.
Title: Re: Inverter Build Project.
Post by: Pete on October 04, 2020, 03:49:17 pm
Most of the coupling between the coils will be via the magnetic circuit so I am not sure about whether moving the coils will make much difference.
If it were mine I would put some power onto it and measure the idle current, then move the coils and see if it makes any difference.
The main problem with that sort of transformer will be how much idle current it draws.
Pete
Title: Re: Inverter Build Project.
Post by: welshman on October 04, 2020, 05:11:03 pm
Most of the coupling between the coils will be via the magnetic circuit so I am not sure about whether moving the coils will make much difference.
If it were mine I would put some power onto it and measure the idle current, then move the coils and see if it makes any difference.
The main problem with that sort of transformer will be how much idle current it draws.
Pete

thanks for the input Pete,

As soon as i've got the mosfet bridge up an running for this, ill do exactly that and post the results. As far as i understand the distance between the coils will determine how much flux from the primary reaches the secondary coil/winding. but i guess i'll find our what the practical effects of this are. If i increase the flux, what else do i increase and possibly lose. With this being a backup im not too bothered about the losses.. but as far as im aware, they will be in the region of (only) 10% greater than a toroid.



Title: Re: Inverter Build Project.
Post by: welshman on October 13, 2020, 06:39:36 pm
more specs on the transformer.

4mm solid copper primary
2x25mm solid copper flat bar wrapped individually for secondary

240v AC In - 58v AC out

i unwound some of the secondary until i got 33v AC out with 230V AC into the primary.

dropping just over 2 volts per wind.

was left with quite a bit of copper.

here is a 48vDC / 33V AC power supply i put together using a microwave transformer keeping the primary and winding a new secondary to give 33v AC from 230 AC input from grid. has a rectifier attached.

most of the parts i need are here now.
Title: Re: Inverter Build Project.
Post by: welshman on October 14, 2020, 06:28:01 am
i added another turn to the home made power supply secondary, as it was a bit low. AC going in is 237V from the mains. bringing  the output AC volts up to 33.2 and getting 235 V AC on the output of the big transformer.

the no load draw is 80W and i moved the sandwich coils closer together on the transformer but made no difference to the idle current.

is this the idle current loss i can expect when using as an inverter?

next see if adding inductor to the AC primary wire drops the idle current.
Title: Re: Inverter Build Project.
Post by: Pete on October 14, 2020, 05:06:51 pm
That wattmeter seems to be reading something odd. 32 volts and over 8 amps does not add up to 80 watts.
I have a PowerStar W7 inverter, I added a choke in series with the transformer on it and it did drop the idle current by about half.
My 12 volt 3000 watt powerstar was drawing around 100 watts idle current when I bought it, I managed to get that down to just under 40 watts by adding the choke. As it was my primary inverter it was worth doing.
Pete
Title: Re: Inverter Build Project.
Post by: welshman on October 15, 2020, 07:25:05 am
That wattmeter seems to be reading something odd. 32 volts and over 8 amps does not add up to 80 watts.
I have a PowerStar W7 inverter, I added a choke in series with the transformer on it and it did drop the idle current by about half.
My 12 volt 3000 watt powerstar was drawing around 100 watts idle current when I bought it, I managed to get that down to just under 40 watts by adding the choke. As it was my primary inverter it was worth doing.
Pete

You are very right Pete, i hadn't noticed.. peacefair pzem016 meter must be faulty.  I'll put a good multimeter in series to see what the real value is.

interesting that your W7 was only 40 watts at idle, that's not a bad loss at all.
Title: Re: Inverter Build Project.
Post by: welshman on October 15, 2020, 08:08:33 am
I put a multimeter in series and it's showing a no load current of 9 amps. that's almost 300 watts. huge! let's see what a choke/inductor or whatever it actually is, does to the current.
Title: Re: Inverter Build Project.
Post by: Pete on October 15, 2020, 04:50:36 pm
Maybe the wattmeter was having trouble with the powerfactor. As the coils in the transformer are very highly inductive loads the current would have been lagging the voltage by a long way. So the apparent power and true power are not similar with highly inductive loads.
On our inverters what is drawn on the DC side from the battery is what matters to us, not what a wattmeter reads. Unless we are charging ourselves for the power we use.
Have fun with it
Pete
Title: Re: Inverter Build Project.
Post by: welshman on October 16, 2020, 02:52:40 pm
Maybe the wattmeter was having trouble with the powerfactor. As the coils in the transformer are very highly inductive loads the current would have been lagging the voltage by a long way. So the apparent power and true power are not similar with highly inductive loads.
On our inverters what is drawn on the DC side from the battery is what matters to us, not what a wattmeter reads. Unless we are charging ourselves for the power we use.
Have fun with it
Pete

it seems you are right Pete. i put a small 300 watt load on it and the readings summed up properly.