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Forum Index : Electronics : Inverter building using Wiseguys Power board and the Nano drive board
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KeepIS Guru  Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
I wanted to clarify something concerning the over-voltage DC input setting, and the AC OC (over current) setting. The AC OC is the hardware OC detection and locking Reset button with OC LED employed in the Controller. Once tripped, this requires the OC Reset button to be pressed, or the DC input to be removed in order to restart the Inverter. Both of these settings require a Kilovac or similar gas filled hermetically sealed high voltage high current (> 500A) DC relay to really be effective. The Kilovac is required for the Auto start wiring model, and this is the only startup method that I would ever employ in a big Inverter, and/or high power battery and high power solar charger array. A Kilovac with economizer draws around 30mA @ 48v when energized. Once you see the absolute carnage that a high power battery bank can cause just in the inverter itself, even when correctly fused, is why I could/would never leave an Inverter unattended without this extra safety feature. It's mandatory IMHO. Do you need it every time a FET or fault happens - maybe not - so roll the dice. In the event of any fault condition, allowing the Controller to instantly remove all DC input to the Inverter is a must have - but this might be just me! But in the end, it's your decision, your home, shed and equipment. EDIT: The 50 ohm Pre-Charge resistor has been mentioned before, this is still in line if the Kilovac has tripped off and the inverter on/off switch is still in the ON position, as happens after a fault condition and your not there to turn it off. If the inverter is shorted then a 20 watt resistor will burn out, which is why you make sure it's mounted correctly. From the standpoint of an over voltage trip, any current above 500ma will drop the input voltage by 25v or more as the current increases. The FETs will be protected as the Inverter SPWM is off, and even if the voltage is still over voltage, only a small amount of current is enough to pull the voltage down to zero through the Pre-charge resistor. However with no current and no voltage drop, your problem becomes the Cap bank voltage rating and the rating of the 75v to 12v regulator. The following will take care of that, and an inverter OV event is nothing compared to a Battery over volt condition and destruction. This is why we need another means to protect it, and in turn, also protect the inverter long term. I intend to fit another Kilovac in line between the Charge controllers and the 4 Battery bank BMS devices I have. I've mentioned before why you can't rely 100% on the BMS designs. So this is a last line of defense if a BMS shorts and the current is not enough to take out circuit breakers or Fuses - or the BMS do switch off but the non running inverter is still over voltage via the pre-charge resistor. A small, independently latched solar charger over-voltage sense circuit, powered from a 30v to 200vac plug pack, or similar DC to DC supply rated at around 4A (kilovac pull in current) to match the kilovac operating voltage - only 1.5 watts of holding power required. So the Inverter protects itself from the batteries (high current or fault), and both batteries and inverter are protected from a solar charger over voltage event via a last line defense of another Kilovac. . . Edited 2024-05-05 14:40 by KeepIS It's all too hard. Mike. |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Mike, I've been trawling through your posts to see if you posted a link for the Kilovac contactors (with enconomiser) you are writing about - can't find it  Looking at the net, their price varies from well over $AU200 to <$50 from aliexpress. Where did you get yours from? I never had a MPPT problem causing over charging, so no auto over charging voltage shut down here. Sounds like a good idea to have one if its affordable. MPPT input is around 80VDC, 2 panel strings. I'm thinking of using a voltage sensing relay to control the Kilovac, messing about with a Nano is too hard for me  . |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
Hi Klaus, No I would not use a Nano for something as simple as an over voltage circuit. Just a few components and the Kilovac, could be powered directly from the batteries for 48V-72v units, or DC-DC supply for spare 24v unit I have. Tey were available from an AU supplier a few months back, prices seems to go up and and down from stupid to reasonable, I looked the other day and found them up around $75. They come in 12v-24v or 48v-72v coil, some with economizer, beware of those without. My panels are also 2 series strings, output varies from 80v to 96v VOC, I guess I'm also a bit over cautious considering the brute current and power available from a very large Lifepo4 bank - seriously scary. The possibility has always been in the back of my mind, granted an unlikely event, but for something so simple and relatively low cost, I feel I should include it, even if it's just for my peace of mind when I'm away. Just had a quick look up, the units I got were a few months back at bargain prices are not there, they come and go from places in AU, but a few more I quickly found. A lot of them are 24-48v but the ones below are 48-72v with ecom. Relay Link Ebay link . It's all too hard. Mike. |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Thanks Mike, I ordered the one from aliexpress, being a cheapskate .The ebay ones did not say if they had the economizer, cost more too. I'm going on a long caravan trip in July/August so the extra peace of mind is appreciated. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
 I'm also trying to get away in a month or two for a long - long overdue break from the madness of everything.  It's all too hard. Mike. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
Hi Mike, I looked at the Kilovac link, they seem to be just a very high current relay. So how do you set the kilovac up to detect over voltage to protect your system? I know I have come in late on this but have been busy updating my system with my new inverter, more panels and setting it up to charge our EV. It sounds like another layer of protection could be good thanks Pete |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
Hi Pete, considering the over voltage were looking at is pretty obvious, making it easy to detect with only a few components, something as simple as a comparater with FET switching or even simpler like a Zener and transistor based switch. It needs to lock in the off state once tripped, until reset. The thing about the Kilovac or equivalent is that it's designed for very high DC current and voltage switching in electric vehicles and such, and with inbuilt economizer, draws less then 2 watts when energized. I'm sure someone will post a suitable circuit before I get around to it, I just have so many things going on at the moment, I'm sure a google search will also reveal plenty of basic circuits, they've been around forever. But I will get back to it in a few weeks once I have the spare inverter finished and the main inverter converted to the Nano controller. It's all too hard. Mike. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
These voltage relays may be useful, come in various options and detect both under\over voltage. Link Use it to control your Kilovac. I place a Kilovac or equivalent SSR on the PV inputs to each charge controller, then if a controller shorts and leads to an uncontrolled charge\over voltage situation the PV is isolated, ergo no charge. I might remove the DIY SSR's, if lightning hits nearby they could short also. Cheers Mike |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
The relay linked above looks a bit fiddly to set, prefer those with a digital display. I'm going for this onelink Check the relay connecting suggestions to see if it does what you want. |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Try again: |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Nah, still does not let me edit my posts - sorry. Type "voltage sensing relay" in the aliexpress search box, its the A30-U1 type, choose the DC switching model. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
Thanks for the replies , I am thinking of putting a kilovac on the outputs of the regulators. I have 8 regulators in all, so putting one on each controller would cost a lot. I have circuit breakers on the inputs of the regulators and on the outputs. So can easily isolate each regulator if required. If the kilovac tripped then I can test each regulator individually to see which one has a problem. Cheers Pete |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
That link doesnt work, think this is it Here Good find, may order a couple. @Godoh, may not be the best idea to place it in the regulator output, if the relay is opened accidently or on purpose all load is suddenly removed from the output and the output voltage will suddenly rise, could blow it up ...well if it already has shorted mosfets then probably doesn't matter. Many charge controller manuals specifically say turn off the input PV before the battery side and vise versa when first connecting it up. Cheers Mike |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
Thanks for all the suggestions, I really like the A30 that Klaus suggested, thanks Mike for updating with the correct link. Why would you bother making anything at that price. However, in keeping with my brain fade moments, the JUNCTEK battery monitors have an programmable over voltage contact output for just this purpose - I have four of them, one on each battery bank. Doh!    It's all too hard. Mike. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
Thanks Mike, then I will have to look at another way of doing it. Not worth using a kilovac then. I am feeding around 75 to 90 volts into the regulators and up to 35 amps, so maybe just a voltage sensing circuit, then a automotive relay wired into the input of each regulator would do. I could wire the relays through the normally closed contacts that way the relays would only use power when there is a problem. Cheers Pete |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
You only need one Kilovac to disconnect the Solar charges from the Battery, the idea is to protect the battery and inverter, one kilovac and one $16 voltage detectors will do that. I understand the problem with some Solar regulators having a fit when the output is suddenly disconnected - I have never had that problem with mine and I would have done that countless times over the years, and still do when testing, the thing is, it should only happen with a big over voltage incident - that should NEVER happen! The voltage trip must not be set too low, some Solar regulators can over voltage a "little" if the you get a Solar array flare under certian conditions. But it can be worse, and I have seen this many times and repaired many commercial solar regulators because of this strange flare event under fast moving cloud and high load conditions, and even low flying aircraft causing a sudden shadow then full sun - I have witnessed four solar regulators all fail [blown FETS] at once from that Aircraft event. You cannot use an automotive relay, and especially not on the Solar array outputs, it will be destroyed by arching. The Kilovac is gas filled and sealed for this very reason, it can take hundreds of volts and currents in the hundreds of amperes on break. It's all too hard. Mike. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
You may require 3 or 4 contacts in series to achieve sufficient distance between the contacts when they open carrying any current, to prevent an arc from destroying them all. Try removing the wires off the controller and shorting them together than open them apart; at 90v the arc would be substantial 10mm or more. I think a single automotive relay may be risking it  |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
A capacitor can be connected across the contacts to divert the current around them while they open, preventing an arc. I had success with 100µF / 100V on a 50V battery system to isolate a 15A load. When that worked I didn't try any other values thus don't know what the optimum is so that may have been overkill. Higher voltages and currents may require higher values. Edited 2024-05-07 10:55 by phil99 Footnote added 2024-05-07 15:00 by phil99 Forgot to mention, to avoid 'splatting' the contacts when the relay closes a 2R2 is in series with the capacitor. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
I doubt that would be a problem for the Kilovac - In any case, an over voltage will be pulled down almost instantly by the batteries trying to draw massive amperes - LiFePO4 - The Kilovac should catch this on the output of the regulators, the BMS may not trip instantly as the voltage at it's terminals is clamped down so fast, even more by the close proximity to the battery terminals. Granted there are a lot of ifs happening here - I have no doubt about the Kilovac from the testing and currents I have tripped - over 600A @ 52V numerous times, and more when a reverse protection diode shorted and caused a FET to short. Yes I know the voltage might be up to 100v - with ZERO load - they are supposed be designed for this low voltage and low current. It's all too hard. Mike. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
Getting back (for a moment) to the Nano controller and Power stage designed by Wiseguy: I have confirmed that the AC voltage regulation is good. Running for the first time unprotected from the might of the LiFePO4 bank, Gulp!  This is a single test toriod with undersized primary, and the bad layout posted earlier on of the test inverter, incorrect value and unbalanced chokes and all, oh forgot, and no AC filter. Zero load output voltage = 235vac @ 73% pwm A 2.3kW resistive load dumped across the inverter = 235vac @ 79% pwm. EDIT Load: 4kW - 235vac - 84% pwm Considering the state of the test inverter and waveform ringing, the Nano ADC display of voltages, current and pwm are all rock solid. I had my AC over voltage trip when the 4kw load was unplugged - slight arc - the inverter LCD displayed why it tripped and indicated an inverter restart was needed. I had purposely set AC trip low and bypassed the ACOC delay to see how quick the nano caught a spike, and how sensitive it was. I then set it to 280vac and it was fine, put the small ACOC transient delay code back in and it was perfect at 250vac. And again, that is with no AC output filtering. . Edited 2024-05-07 14:16 by KeepIS It's all too hard. Mike. |
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