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Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 423
Posted: 10:19pm 30 Dec 2020
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So I've purchased a full Nissan leaf battery, which is 96 cells in series for 360v nominal. It's getting delivered early in the new year. I'll mount it in a trailer with warpverter and solar panels, for a silent portable power supply, but more on that in another thread.
I'm after some thoughts on how to charge it from the grid when necessary. I don't have any strict requirements, maybe a charge rate of 2kw would be fine.
I'll be using a Wolftronix controller which works with the leaf battery BMS. The Wolftronix has a relay output to turn off charging when a preset voltage is reached on the highest cell. I'm happy with charging in constant current mode only. No need for constant voltage as I won't approach the absolute max voltage of the cells.
So I'm just after ideas for a constant current 2kw source that works from 300 to 400v DC.
Any thoughts?
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:45pm 30 Dec 2020
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One way to do it might be to feed dc from a grid powered rectifier into the solar controller along with the solar panels via some diodes.
Another way might be a constant current transformer, one that uses a shunt air gap across the core between primary and secondary. Stick arc welders, microwave oven transformers, and neon sign transformers all use this technique to deliver a fairly constant current into a highly variable load.Cheers, Tony.
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 423
Posted: 11:48pm 30 Dec 2020
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Can a grid tie solar inverter work with a mains rectified DC input instead of solar panels?
Would I need extra current limiting?
The trailer will probably already have a GTI backfeeding the warpverter to charge the batteries, so just disconnecting the solar panels and connecting rectified mains sounds too easy to be true.
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 423
Posted: 11:52pm 30 Dec 2020
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Ah sorry for the incorrect thread title. Can't change it now ...
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:34am 31 Dec 2020
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I suppose it depends if the mppt system has a built in current limit feature.
Otherwise it may keep drawing more and more current, trying to increase power.Cheers, Tony.
nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458
Posted: 07:16pm 31 Dec 2020
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That would be the most simple solution, most decent gti's have current limiting. You should do a pre charge before connecting the whole rectified AC to your gti, there are a lot of capacitors to charge in a gti.
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 423
Posted: 10:24pm 31 Dec 2020
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Worth a go then. I'll use a 1000w halogen bulb in series and see what happens.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:05pm 31 Dec 2020
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If you follow the GTI connection and startup procedure to the letter as stated in the official book of words, it should be able to take care of itself.
These days, you are likely to get an error message if it detects that all is not as it should be.Cheers, Tony.
mab1 Senior Member Joined: 10/02/2015 Location: United KingdomPosts: 209
Posted: 06:11pm 02 Jan 2021
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Only issue I've found using rectified a.c. (from my hydro-generator) into a SMA sunny boy is that the GTI doesn't really like a ground-referenced supply (I gnd referenced one side for direct powering of some devices - PV is usually floating) - so it warns of an earth-fault on the 'PV' and won't start inverting if the input voltage is above ~150vdv (although, once it's going it'll keep going even if the MPP rises above 150v.
Does not the warpinverter have the option to sync directly to an a.c. supply then? I thought it did - or maybe I'm confusing with the Oz/nano - it's a while since i read them threads TBH.
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 423
Posted: 10:10pm 02 Jan 2021
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Good point! The STM32 blue pill version of the warpverter can sync but I can't find any info on that function..... I think Poida added that code to Andrews work? Not sure.
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 08:13am 03 Jan 2021
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I just tried that and the answer to above is yes and yes.
However you need to be extra careful with those lethal Dc voltages and think twice before you switch on or it could cost you a handful of mosfets.
Here is how I found out about that : Built a mains AC to DC box, just a beefy bridge rectifier and 8x 470uF/450V caps (ex Aerosharp PCB)in parallel. To charge these slowly I fitted a 400v rated switch with N/O contacts bridged by a 470R resistor. That worked fine, it took nearly a minute to fully charge the caps.
Connected that ~320VDC to the small (2KW) solar grid tie inverter I had here and it woke up, telling me it is missing the grid connection. So I plugged the grid tie output to a GPO in my workshop. There was a loud growling noise and I switched that GPO outlet off - bad idea - a bang followed and my stand alone power inverter (which powered the GPO) died.
So, do NOT rectify a mains voltage and then try to feed back Ac to the SAME mains voltage.
I repeated that experiment by rectifying the AC output of my generator, connecting that to the grid tie solar terminals and the grid tie output to a mains GPO.
After the grid tie inverter did its wait a minute and check everything thing I could see the grid tie input current slowly increasing and hear the raising load on the generator (inverter type on eco setting). The grid tie ramped the current up to seriously load the generator and I switched the generator off at around 1.7KW load. Its rated for 1.8K continuous and I know it shuts down a little after that.
So the grid tie puts out as much current as it can suck from the DC input until it reaches its programmed limit. You need to fit some current limiting for lower currents.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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