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Forum Index : Electronics : Warpspeed’s MOSFET mounting method

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Warpspeed
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Posted: 03:51pm 07 Mar 2019
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  kanchana said   I have 48v leaf module setup (aiming to operate between 57.5 to 55 volts )
what kink of circuitry should involve the battery charger in Tony's configuration

Sorry for the delay Kanchana, only just now found your post.

The battery charger is a buck regulator set up to provide a constant charging current. In my case 10.0 amps (to charge a 50Ah battery).

It runs flat out at the full ten amps, but above a certain battery voltage, the current tapers down to zero as the battery reaches its full rated charging voltage. The cell voltages will not all be exactly the same at that point, but it is just one of several layered safety features that can prevent overcharging.

What actually shuts off the charger is the battery monitoring system that terminates charging when any one cell reaches the maximum. That always happens before the average cell voltage reaches the same maximum. This shutdown is done by opening a relay to interrupt dc power to the charger. I did it that way in case the mosfet in my buck regulator ever fails shorted, as that would surely cook the battery.

There is a third quite independent layer of protection provided by the main battery digital voltmeter which has undervoltage and overvoltage alarms which can trip the battery isolation circuit breaker.

So I have three completely independent ways of preventing battery overcharging, and the video display of all the cell voltages shows me which of the three systems terminated charging. Its pretty easy to see if the highest voltage cell failed to halt the charging when it reached the maximum voltage line on the video display.
Cheers,  Tony.
 
kanchana
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Posted: 05:32pm 08 Mar 2019
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Thanks tony. My knowledge on buck converters is not much , I am going through the MPPT charge controller design threat to gain some incite. I could try to use the existing charge controller to charge the batteries , although not sure connecting the charge controller and the inverter to same solar array ,80V would work as intended .
battery monitoring system- does it use some kind of micro controller base control logic
what is the battery digital voltmeter you used ?
Regards kanchana
 
Warpspeed
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Posted: 11:06pm 08 Mar 2019
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Kenchana,
A lot depends on the size and type of battery how best to control the charging.

An existing commercial (Chinese ?) charge controller might be best if you can find one to suit your battery. I am using a non standard battery voltage, so really had no choice but to build my own from scratch.

Connecting both the inverter and battery charger to the solar array together presents no particular problems, that is how I am doing it.

My own charger uses a buck regulator and a switch mode control chip, plus a couple of op amps. Its all analog, no microcontroller.

My battery monitoring system measures the voltage of each individual cell, and does use a microcontroller, but it only switches the battery charger on and off, it does not control the charging current. It starts charging in the morning, then switches off and stays switched off once any cell reaches the maximum voltage. I am told that is the best method with lithium cells.
If you have a lead acid battery, you can float charge it once it has finished bulk charging.

This is what I am using for a main battery voltmeter.
https://www.lightobject.com/Programmable-4-Digit-Red-LED-ACDC-Volt-Meter-with-Dual-Control-Good-for-HHO-System-P408.aspx
Its quite a nice unit, and it has undervoltage and overvoltage alarm relays that I use to fire off a 100v dc shunt trip coil on my battery isolation circuit breaker.
Cheers,  Tony.
 
kanchana
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Posted: 03:58pm 09 Mar 2019
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I am eager to built this. Since inverter has 2:1 control ,what if I build the inverter for 100v , then I will connect the 100v(max 120V) panels and run directly from solar with the support of capacitors and at night change over to battery (55- 58 V). Will it work ?
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Warpspeed
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Posted: 11:58pm 09 Mar 2019
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Going from 55v minimum battery, up to 120v peak solar is stretching the 2:1 voltage range a bit too far.

You either need a higher battery voltage, or reconfigure your solar panels to have a lower maximum voltage.
Cheers,  Tony.
 
kanchana
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Posted: 01:30am 10 Mar 2019
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Ok, So I have to wind the transformers to the minimum voltage it will ever see and lover the solar voltage, say to 100v max , What will happen if the voltage go out of the range ? output voltage of the inverter will be start to drop or rise depending on the lower or upper limit discrepancy?

How many KW of solar do you use for a day time running
I have 150w panels at the moment open voltage is around 20v , s o if i use 5 panels it is only 750W , I wounder it will be enough to cover the modest use during the daytime

Regards Kanchana
Regards kanchana
 
Warpspeed
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Posted: 01:56am 10 Mar 2019
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The control board regulates over a 2:1 input voltage range.
Any 2:1 voltage range you like, its just a resistor change in a voltage divider to move it.

Below minimum input voltage the output drops out of regulation, and the inverter output falls as the dc input voltage continues to fall.

Above maximum rated input voltage, it also stops regulating, and inverter output rises as input voltage rises further.

You wind all of your transformers to suit the lowest voltage the inverter will ever see.

That small Chinese 5 volt dc power supply works down to about 30v input, and safely up to around 400v dc input.
Cheers,  Tony.
 
kanchana
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Posted: 02:38am 10 Mar 2019
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Thanks tony
Regards kanchana
 
Warpspeed
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Posted: 03:00am 10 Mar 2019
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  kanchana said  
How many KW of solar do you use for a day time running
I have 150w panels at the moment open voltage is around 20v , s o if i use 5 panels it is only 750W , I wounder it will be enough to cover the modest use during the daytime
Regards Kanchana


There is no simple answer to all that.

I managed to halve my power consumption by monitoring every single load, finding out where the power consumption went, and deciding what could be done.
Its silly things like electric wall clocks that draw twelve watts continuously. And replacing them with battery wall clocks that will run for a year on a single AA battery. LED lighting of course, and replacing an old CRT computer monitor with LCD flat screen monitor. Replacing a 25 year old refrigerator with something more recent and a lot more energy efficient. Many other things too, but they were the biggies.

You will never know what your daily electrical consumption is, until you start doing some monitoring.

How much power you actually get from solar panels depends on climate. Things can be very different on the two opposite sides of a high mountain range for example.

Same with sizing a battery. Impossible to even make a guess without doing some data logging through at least one summer and one winter.
Cheers,  Tony.
 
kanchana
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Posted: 03:28am 10 Mar 2019
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good advice , yes better to start some how and upgrade to according to your own needs
Regards kanchana
 
kanchana
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Posted: 03:41am 10 Mar 2019
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Is this good candidate it is around 50 $
RIFA 33000uF is about 3 times that
Regards kanchana
 
kanchana
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Posted: 03:47am 10 Mar 2019
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Regards kanchana
 
Warpspeed
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Posted: 07:18am 10 Mar 2019
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Nice find Kanchana.

Tried to find data for that capacitor.
Chemi Con data is here:
http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-all-e1001s-2018.pdf

Could not find 36DY or 9625L25 part number, but closest thing that looks similar is on page 312.
33,000uF 100v "large capacitance aluminium capacitor" Ripple current rating 15 amps.

That should work. If it gets unhappy at sustained higher power, the main problem will be temperature rise in the capacitor. That takes time to build up, but otherwise its a nice big capacitor with a lot of energy storage.
Cheers,  Tony.
 
kanchana
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Posted: 10:50am 10 Mar 2019
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Thanks tony
Regards kanchana
 
kanchana
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Posted: 05:09pm 12 Mar 2019
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  Warpspeed said   Andrew, the first one of these step inverters I ever built (now almost forty years ago) used a 68H05C8 processor with 16K of internal eprom. It used three inverters giving 27 voltage steps peak to peak, with fifteen 1K lookup tables. Still have that original inverter around here somewhere.
It worked very well for what it was, only 500 watts with 10v to 15v dc input. It was just a toy really, but it certainly proved the original basic concept to be very sound.

Thirty two lookup tables is certainly very workable, and 1K lookup tables provide more than adequate 20uS time resolution for any number of inverters.
My latest effort powering my house right now uses 256 1K lookup tables which is vastly more than is really necessary. probably 64 or 128 lookup tables I suspect would not make any noticeable difference.

The transformers must be designed to provide the required voltages, and the required output voltages for each transformer will be different depending on the number of inverters you plan to eventually have.

Assuming we are designing for 235v rms final output, which is 333v peak.
If you only plan to build a single transformer very crude square wave inverter, it will obviously need to have a 333 volt rated secondary.

A two transformer inverter will need to reach the same 333v with both secondaries aiding, and have a 1:3 voltage relationship. So the big one will be roughly 250v and the small one 83v.

Three transformers also need to add together to provide 333v peak, in ratios of 1:3:9. So the big one will need to be 231v, medium transformer 77v, and the small one about 25.6v.

Four transformers, big one 225v, medium 75v, small 25v, tiny one 8.3v. That also adds up to 333v with relative secondary ratios of 1:3:9:27

So before you start winding transformers you need to pretty much decide right at the start how many inverters you plan to eventually have. Three work perfectly well for all practical purposes, but four give a much smoother final waveform. As your rom will have eight bits, and the fourth inverter is very low power anyway, might as well have it there.

I would also suggest you fit an electrostatic screen between primary and secondary to eliminate any voltage spikes on the square wave output of each transformer. I did that and all my steps were beautifully clean. I suspect I may have had some nasty switching spikes had the screens not been there, but was not game to try that.

I have now built several quite different versions of these step inverters over the years, and each one has been simpler requiring fewer parts.

The current 5Kw inverter control board uses an Intersil twelve bit dual slope A/D converter to address the high order eight bits in rom. Low order ten bits of rom are continuously clocked from a 3.2768Mhz crystal oscillator module. The A/D converter starts a conversion every 40mS and its output is latched into the rom every second cycle right at the zero crossing.
The dual slope averaging is extremely accurate and consistent, and gives very good noise immunity to inverter ripple voltage on the incoming dc bus.



Rom output is latched when data is stable, and that is about it.
Each latched data bit drives an opto isolated gate driver direct through a 180 ohm resistor, and the opposite complimentary output comes straight off a 74HC04 inverter.

Four bridge inverters, sixteen opto isolator outputs from the driver board on four different plugs.



Plus five volts comes from one of those two dollar Chinese postage stamp sized switching power supplies, and minus five volts (for the A/D) from a voltage pump chip.
Battery voltage powers the board and also provides the measured input for the A/D converter. There is an absolute minimum of wiring and absolute simplicity.
There are ceramic bypass capacitors across every chip located directly under each chip, the sockets have enough height to allow that.

Its all very basic. no soft start, no over current protection, no dead time in the waveforms from the control board, no voltage feedback and no microprocessor.
And it works perfectly well direct from the solar panels without having anything in between except 36,000uF.

Voltage swings from solar are massive direct off the panels, as you might expect, but the output hardly varies at all, certainly not enough to worry about. In fact its BETTER than a PID feedback control, simply because its much faster reacting and completely stable.

Overload just trips the ac circuit breaker on the output. The whole thing has enough balls to do that very safely. I have been completely off grid now for six weeks without a single problem, and the inverter worked very first time it was powered up without a single problem.

Each inverter consists of a pair of modular half bridge driver boards. These just plug into the control board via a single twisted pair. There are eight of these small half bridge boards. These also are as basic as can be, with just a 15v isolated gate supply and an opto isolated gate driver chip (with inbuilt 11v undervoltage cutout) for each upper and lower mosfet.
A small capacitor across the inverse connected opto isolators provides dead time. 1nF about 300nS for the mosfets, and 10nF about 2.5uS for the IGBTs.
The whole inverter has eight of these small half bridge driver boards.



And that is about it. The two smaller inverters just use individual mosfets fitted to screw terminal blocks and PCB tracks reinforced with solder lugs fitted both sides. The two larger inverters use 200 amp IGBT modules that plug into the same identical half bridge driver boards.

These particular IGBT modules are rated to carry 1,000 amps of fault current for one full 10mS half mains cycle, which is much more than is required to very quickly trip a normal C curve thermal/magnetic circuit breaker. That is something mosfets just cannot do as well as an IGBT.

It would be very easy to scale this up to 10Kw or 50Kw without any of the high frequency problems the PWM guys are plagued with. And its much more simple to build and get going.

Only really two obstacles to overcome, fabricating the four transformers is a bit of a pain, but its fairly straightforward, just work.
The other is getting suitable lookup tables organized.
I just wrote a program in assembler to burn a prom directly.

That is no more difficult or complex than stuffing a working microcontroller into the inverter.
But a bare rom has the advantage of not having any timing constraints.
A bare hardware rom is simple, and a lot more robust IMHO, than running a live software program in an inverter.







If it ever does spit the dummy, everything just unplugs or readily unscrews, and I have spare boards ready to go. Accessibility is particularly good too in this version, although its physically rather large. I should be able to fix a blow up very fast without requiring mains power or a soldering iron.



Nice explanation tony ,I wonder where the those 2 resisters connected to on the power board ?




Regards kanchana
 
Warpspeed
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Posted: 05:59am 13 Mar 2019
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Kanchana,
That last hand drawn sketch is how I finally did the half bridge gate drivers, I will post the final schematic for that tomorrow.

But first here is the full wiring diagram for the entire inverter.


Cheers,  Tony.
 
kanchana
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Posted: 07:21am 13 Mar 2019
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Thanks tony . Here is what I have got for the transformers . I have 1000va transformer currently attached to PWM type inverter . other 3 transformers got from china not sure how their true ratings .

This one got form a 230 to 115 v converter claimed to be 3000W





Second one form same source claimed to be 1000w. Those wires I tried used for house hold wiring here . Any way I can use those wires for transformer winding?



3rd one 230 v to dual 12v claim to be 100w


Regards kanchana
 
mackoffgrid

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Posted: 07:46am 13 Mar 2019
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I haven't got a photo handy but my 3kW transformer is about 20kg and my 1kW transformer is about 11kg. I haven't done full on load testing yet.
 
Warpspeed
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Posted: 07:57am 13 Mar 2019
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These are my four transformers. 4.5Kva, 1.5Kva 500Va and 167Va.
All have 20 amp secondaries.
Have the weights written down here somewhere, but will need to search to find the exact piece of paper.


Cheers,  Tony.
 
kanchana
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Posted: 08:34am 13 Mar 2019
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Any easy way to check the out put of the transformers with out 50V/Variable ac supply?
Regards kanchana
 
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