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Forum Index : Electronics : Nano Power Inverter - Roll Your Own Style

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wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 510
Posted: 08:22am 31 May 2020
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  Warpspeed said  One thing to consider when connecting L1, L2, and L3 in parallel is that all of the combined return current then flows back through the same common neutral.

You have three twenty amp phases, plus a twenty amp rated neutral.
So the total power must be limited to twenty amps total, or you could potentially burn up the neutral.

The neutral has no fuse or circuit breaker over current protection, so its a potential hazard to be aware of.


You are quite correct Tony, when I had the extra 3 Phase outlet fitted I was thinking unidirectional (feed  only) and 10+KW for bench testing stuff seemed more than adequate.

But my thoughts began to wander "what if the power goes out tonight, how could I easily utilise the inverter power for the house" ? - I know, I'll use my new 3 phase connection along with gee I wish I had put in 32+A cable  .

I'm contemplating installing a contactor in the main switchboard to accomplish an automatic changeover.  I can use the nano phase compare to keep in step with the mains so it minimises any upset when this occurs.  Maybe I could just run a suitable rated single phase cable back to the switchboard if the inverter stays in my workshop and common up the phases at the contactor.

The last detail to be worked out is how to ensure the 3PH solar inverter never tries to feed my inverter and always has the mains supply (if its available) to dump power to.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 510
Posted: 07:21am 01 Jun 2020
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  noneyabussiness said  fuse holder

Proper dc rated fuse holder..

fuses

Fuses...


  renewableMark said  
Re the start up procedure, it's no big deal having to pre charge. I have the same setup on my house and van  units. The house one obviously just runs 24/7 and never gets turned off.
The van one I just leave going on stand by. All it's doing is keeping the caps charged, which is bugger all energy requirement. When the unit is required, just a quick press of the momentary button starts up the control board and it's going in a couple of seconds.
That saves mucking around with the pre charge.

Re the phases, would it be possible to wire all the house requirements onto one phase? and then have an Auto changeover switch between the grid power and your inverter.


Noneya, thanks for the fuse & fuse-holder info. Are the fuses rated for DC - they looked to have a ~ next to their current.  Not being picky but I have seen first hand the results of a >50V DC ARC and it was scary, they appear to be ceramic which would be a plus.

Mark, yes I agree that once powered up the pre-charge is not an issue but in this testing phase where it is on and off multiple times, you need to keep well focused on what sequence you need to meet.  Re-Wiring the house would work but I want to try to avoid that and work with what is - a contactor that links all phases after disconnection from mains should work ok.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
noneyabussiness
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Joined: 31/07/2017
Location: Australia
Posts: 279
Posted: 11:37am 01 Jun 2020
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Unsure of where the ~ is, however i have been assured by a reputable friend these are more than needed. And have worked twice now with accidental shorts with no bang / flash personally.
I think it works !!
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 510
Posted: 12:29pm 01 Jun 2020
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The ~ is the little mark next to the 500V ~ & 600V ~ with their associated fault current interruption ratings (120kA & 50kA ?) .  The Main current rating ie 150A does not appear to indicate AC or DC.  I do accept that they have worked ok with DC without disaster.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
wiseguy

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Location: Australia
Posts: 510
Posted: 04:54pm 24 Aug 2020
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Time for another update - this inverter build is taking a very long elapsed time....

I bought the kilovac solenoid rated at 900V 500A a few weeks ago. I intended to use a simple toggle switch to power up the inverter including an automatic enable of the high current path after the pre-charge is finished. The solenoid has now been sitting on my shelf patiently staring at me for about 3 weeks now, time for some fun.

The first obstacle to overcome was that I ordered a 24V coil solenoid as they were ~$100+ cheaper than the 48V or 12V units - why I have no idea - maybe the 24V units have high sales volumes. I always intended to find a simple drive mechanism to operate the 24V unit from 48V.  The next feature I liked is that the hold in current is much lower so my circuit had to hit the unit with 24V and then transfer to hold at ~ 8V.

I developed a circuit that can produce two separate PWM periods the first has a duty cycle of ~ 50% the second has a duty cycle of ~ 17% the frequency is ~ 2kHz.

The operation is, when enabled, first apply the 50% duty cycle, the solenoid pulls in with ~ 22.5V on a 45V supply, after a ~0.5 second delay the PWM lowers to 17% the coil voltage is ~ 8V, a FET buffers the pwm to drive the solenoid which has a catch diode across it which acts as a flywheel diode to keep the current flowing during the off time. I used a whole 2 schmitt trigger inverters and a FET to do all of this.

The supply current (from 45V) is ~ 220mA during the 22.5V phase this then drops to ~ 30mA whilst maintaining the holding 8V.

My start up & stop sequence will be:
1) Turn small toggle switch on - this pre-charges the caps via a 100 Ohm resistor
2) A comparator waits until the Vcaps is ~95% charged then enables the solenoid high
    current path.
3) Nano now begins to soft start Inverter to supply backup mains power.
4) Use mains power for stuff
5) Turn toggle switch off, signals low voltage to low batt detector circuit
6) Nano is commanded to stop - and enters soft stop period & off timer started
7) After selectable 2,4,8 second timer delay (for soft stop to finish) solenoid is
    commanded off, goodbye world.
8) Lets do it all again......

Circuit of solenoid drive scheme if interested:
solenoid drive.pdf

D1 stops oscillator & holds Fet off initially when its anode is high.
When D1 Anode is set low oscillator starts to pwm FET & solenoid for 24V.
For a delay set by [R1,C1 & U1B], D3 shunts second feedback path to ground.
After the delay, U1B goes high, reverse biases D3 & second timing path via D2 & R3 is enabled to reduce pwm high period & sets solenoid to 8V.
It works a treat.
The Nand latch is to set the solenoid on or set it off with a low trigger to either the set or reset inputs. When triggered to run it stays running even if trigger input is gone, until triggered to stop which is a whoa camel stop - power is removed so needs a restart.
Edited 2020-08-25 03:07 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 679
Posted: 03:56am 25 Aug 2020
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One of these will do the same as your circuit DRV103

I use them quite often to lower the power to relay coils, especially when confined in small cases's to prevent over heating.

Those Kilovac relays normally have a pwm driver associated either internally or externally, not sure how they will work being also driven by a PWM source.

Mike
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 510
Posted: 08:24am 25 Aug 2020
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  Solar Mike said  One of these will do the same as your circuit DRV103

I use them quite often to lower the power to relay coils, especially when confined in small cases's to prevent over heating.

Those Kilovac relays normally have a pwm driver associated either internally or externally, not sure how they will work being also driven by a PWM source.

Mike


Thanks for the information about the DRV103 series, it is almost OK but unfortunately the absolute max operating voltage is only 32V, I need about 55V.  The other difference is that it applies the full applied voltage to the relay - in my case up to 55V to a 24V solenoid during the pull in period. The max voltage for the 24V solenoid is 30VDC so not a good plan.

My circuit PWMs the 48 to 24 for the initial solenoid pull in and then PWMs to 8V to hold it in. Maybe there is another version of the DRV103 around but it cant do the same job as my circuit.

The kilovacs that I could find, 41 to be precise there were only 8 versions which have electronic pwm circuits so < 20% is not quite "normally" and of those only 2 were suitable for 48V use but then the other issue, they were $230 & $246 $AUD. Mine with a standard coil was $111.40.  A FET still had to be used to switch the relay so why not modulate it with ~$2.00 worth of bits. A failure of their pwm circuitry may render the expensive device as junk.

Do you really think I would try to drive a PWM circuit with a PWM circuit - come on....
Edited 2020-08-25 18:55 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 679
Posted: 12:05pm 25 Aug 2020
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  wiseguy said  
The kilovacs that I could find, 41 to be precise there were only 8 versions which have electronic pwm circuits so < 20% is not quite "normally" and of those only 2 were suitable for 48V use but then the other issue, they were $230 & $246 $AUD. Mine with a standard coil was $111.40.  A FET still had to be used to switch the relay so why not modulate it with ~$2.00 worth of bits. A failure of their pwm circuitry may render the expensive device as junk.


OK my normal is not the same as yours, all 12 of the various ones I have here have the factory PWM economizer fitted, either internally or externally. And yes two have stopped working, the economizer's have failed; and I cannot locate a circuit anywhere for them. ;
your circuit is pretty good, at least its repairable.
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 510
Posted: 06:41am 13 Sep 2020
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Recently I redesigned my earlier isolated DC/DC circuit for lower cost and simpler design. I decided to post this if it may be of use to anyone else who wants a simple isolated supply/supplies. Dont be put off my use of a pcb winding - I am basically lazy and find it tedious, boring and a time waster to wind these little transformers by hand.

By using 2 PCbs we have a primary drive winding & 3 isolated secondaries, 1 for the 2 x common low side legs and 1 each for the LHS high and RHS high legs.  By adding another winding pcb we can have another 2 isolated 12V supplies if needed (5 x isolated supplies in total).

The purpose of this circuit is to supply adequate isolated DC gate drive bias for the opto-coupler and FET buffer/drive circuitry in mosfet H bridge power stages, and should be quite adequate for 20kHz switching with 4-8 Fets per leg.

A few pages back I designed an RM6 PCB winding to simplify construction. It did not provide a lot of isolation and had to run at >300KHz due to the 7 turn primary winding.  The UCC3808 was also a bit expensive, harder to obtain and probably overkill for what was needed.

The new version has a 4 layer board for the windings with more creepage/clearance and a 12 or 13 turn primary (jumper selectable). By placing a 1nF cap in parallel with the (12T) primary it resonates at ~ 160kHz and removes switching glitches and noise when tuned properly (adjusting R1).

The parts list is a Cmos 555 ie TLC555 a couple of resistors caps and and a C6003 60V 3A mosfet in a TO251 through hole version (~12c ea from LCSC).

The circuit is about as simple as it gets with just enough to make it all work. The gate drive resistor is 100R which slows down the fast switching edges eliminating noise glitches and ringing almost entirely. The circuit uses ~ 8mA from 12V unloaded, and when delivering ~1W runs at ~ 80% efficiency.

It is not a flyback converter, essentially a forward converter, so the input to output voltage is directly related to primary and secondary turns. With 12.1V & 12Turns for the primary supply and 13Turn secondaries with schottky rectifiers, output voltage is ~ 11.9V @ 30mA. When lightly loaded (~0.5mA) output voltage only rises ~ 0.5V (to ~ 12.5V). Note only one of 3 output winding/rectifier/filter Caps is shown for simplicity. Apologies for crappy image but print to pdf is playing up.



Yellow trace is Q1 drain
Light Blue is Q1 gate drive

Tuned for best performance


Osc Freq too low


Osc Freq too high


Now its documented I can clean this phase off my bench for some more space I have about 5 concurrent things I'm working on.....
Edited 2020-09-13 20:19 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
poida

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Joined: 02/02/2017
Location: Australia
Posts: 815
Posted: 09:57am 13 Sep 2020
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this 12V isolated supply of yours is looking good.

I like the use of the 555, you could even get some form of closed loop
control with it, maybe a cheap opto and a TL431.
But that would be too much for something that just needs to
make a few mA at 12V sort-of-ish

The lazy bastard in me thinks "just use a RB1212S or RE1212S"
and forget about it. But this project is future-proof.
wronger than a phone book full of wrong phone numbers
 
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