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Axpert 5KVA Relationship between charge parameters and Solar output


Valken

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26 minutes ago, The Terrible Triplett said:

I got a Tazz 1.3 for the wife way back then, also now at 200k +, still all original, cheaper as can be to maintain.

I actually got rid of our Tazz. I replaced the valve cover gasket at some point and noticed the cam looks a bit gummed-up. You know, like when you left the oil in the pan a bit too long on the stove. We bought it from a guy who was on the brink of bankruptcy and we had known that a service was skipped. Now those 2E engines were interference designs (timing belt breakage => potential bent valves) and they were roughly quarter-million engines (though insanely cheap to fix)... but I got a little nervous and so it was sold. Anyway... I have a 1AD-FTV Diesel now, and I'm a little nervous about this one too. A few more reports of issues here and there... also, the 1KZ had cylinder head issues. Single percentages... but still. So its not all smooth sailing, but the point is that they have an amazing track record, and I'll take this over a Tata, a Chana, and most definitely over anything German any day. The open question are the Kias and Hyundais... would we say the Axpert can be likened to an Elantra yet? Maybe... :-) Anyway... now we have properly strayed off the subject :-)

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HA HA HA. To continue. Apparently the Victron guys are Toyota guys. And then the Axpert guys are the BMW folk (hope I am not offending...). Got my first 318i at 20. Sold it on 280 000 km without a days trouble. Second 318i for 100 000 km also without issues. Then 318i auto for also 120 000 km not a days issue. Now on a 320d auto. Going on 230 000km no hick or snick! All second hand. Once bought a Peugeot brand new and almost killed myself. Was more at the dealer than with me for 18 months.

Actually made a study of each of them and maintain them myself fully....

Just goes to show.

Sent from my SM-N900 using Tapatalk

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I drive a T5. Got it brand new and is now 11 years old. Dont want anything else. I just love that car. From the day they leaked the images on the internet I fell in love with it. There is nothing that comes close to the look and the 2.5 Turbo has a real kick. Nothing comes close lol

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I drive a Ford Ranger 2.5 D with 460 000 km on the clock driven mostly over 4x4 tracks. I also tow a 2.5 ton trailer. So it comes in for a bit of abuse. Have replaced a gearbox and diff and 2 set of rear springs. A Zambian bull buyer told me to sell it before it gives me trouble. It owes me nothing. My father said in the 40 and 50's a vehicle use to last 70 000 miles. Based on that score I am on my fourth bakkie.

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1 hour ago, edmundp said:

Now on a 320d auto

I had a e46 320d. Man I was nervous about that thing. It was on its third turbo by the time I got it. I did a flapectomy (remove the swirl flaps) because those engines had a habit of ingesting them, and they do nothing in this country (no MOT or emissions control on those old things). Then one after the other the cheaper items on the "common list of problems" started happening. When the second hedgehog resistor blew... I sold it very quickly before the next thing broke... which would likely have been lower LCABs or something. 5k a pop last time I checked.

Edit: One day a mechanic is going to fix that hedgehog resistor again, and he's going to have a serious good laugh. I attached a note to it, indicating this was the last straw that made me sell it.

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I had a e46 320d. Man I was nervous about that thing. It was on its third turbo by the time I got it. I did a flapectomy (remove the swirl flaps) because those engines had a habit of ingesting them, and they do nothing in this country (no MOT or emissions control on those old things). Then one after the other the cheaper items on the "common list of problems" started happening. When the second hedgehog resistor blew... I sold it very quickly before the next thing broke... which would likely have been lower LCABs or something. 5k a pop last time I checked.

Ya. Those were notoriously bad I must admit. Always did a bit of research before I bought one. The lcab thing I never understood though. Everyone warned me on them for the 2 E46s but I never had to replace a single one.

Interesting that one can see the culture of recycling, economics and practicality shining through here. Solar and vehicles. Same trend in consumerism amongst this group of fine people....

The hedgehog resistor thing I fixed myself. Bit of manhandling and good old solder jobbie did the trick nicely! And then of course we here in Pta have Bemows. BMW parts at Golf prices!!

Sent from my SM-N900 using Tapatalk

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9 minutes ago, edmundp said:

The hedgehog resistor thing I fixed myself.

It was a potted component. Official name "final stage blower resistor". I did consider reverse-engineering it and making something that would last, but I didn't have the equipment back then. Tell me, did you ever have to do the cable-tie fix to the window regulators? I had a window fail on me as well. I cable-tied it and it worked... poorly. I bought a second-hand regulator... and sold it with the vehicle without ever installing it. At one point, I stopped using the rear windows because 1) they could not be cable-tie fixed and 2) a new one was 4.5k ex vat.

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17 hours ago, jdp said:

Am I then correct to assume the Axpert will only send to the battery what it needs. It does not send to the bank what the loads needs?

Yes, it separates the load needs from the battery bank needs.

I'm not necessarily an expert on how these things work at the high level. But I'm pretty confident that in the case where the battery is full (so the desired battery charge current is just enough to keep the batteries at float voltage, usually quite a low current), then it will draw just enough from the solar input (assuming it has priority over AC input) to supply the loads. It can't get that right at the millisecond level, so there will be a few surges here and there as the load changes, especially at moderately large load changes like an iron switching off. If all goes well, these load changes won't trigger charge stage changes, unless of course there isn't enough solar input and the battery voltage drops below a threshold.

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16 hours ago, plonkster said:

So if I've got that right, it takes the DC, steps it up to 400VDC using some kind of inductor (we had an argument here about that, re transformerless inverters being so much "better" :-P),

Actually, "transformerless" is a meaningless "marketing" term. It lacks the heavy 50 Hz transformer that makes low frequency transformer models less attractive (man, those things are heavy to lift). But it certainly has a transformer, just that it's a high frequency one. It's less than a litre in size, and would weigh only a few kg. This is possible because it operates at a frequency about three orders of magnitude higher than 50 Hz.

Quote

 

but because that step-up is fixed ratio it bucks down again from 400VDC before it chops it up into AC?

Yes.

Quote

 

So just to check then the three conversion processes are:

1. Buck converter from solar onto 48V DC bus

2. Boost converter (isolated or not?) from 48VDC to ~ 400VDC, probably 1:8 ratio?

I believe so.
 

Quote

 

3. Adjustable Buck converter from ~400VDC (I would thing between 360 and 480) to ~325VDC

After that then will follow the "chopping stage" where 325VDC peak is turned into 230VAC RMS.

 

Yes, though I'd call the "chopping stage" a normal PWM output, using a full bridge. Active and neutral of AC out must (I haven't checked) essentially connect to the output of this full bridge, via some filtering. That's why it's essential to have the galvanic isolation of the HF transformer.

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15 hours ago, plonkster said:

I could google this (and I did in fact) but google is being clever and thinks I'm looking for Texas Instruments stuff. Can you elaborate on the "TI trick" because I am curious as heck :-)

[ I attempted to paste an image here, but it doesn't seem to have worked. It's from page 10 of the PDF linked to below. Attached now, hopefully. ]

From http://www.ti.com/lit/an/slaa602/slaa602.pdf . It's an interesting trick, and I'm not sure I 100% understand it. Oops, the upper switches that are left off, I said left on, but that would cause shoot through :wub:. This example shows a 12 V battery, but obviously it can be extended to a 340 V or so DC bus. I don't know if the implication is that you should transform the mains down (to say 20 VAC, or possibly less since it may be a boost-only configuration) when charging a low voltage battery; details are a bit sketchy.

Mains charging TI trick.jpg

Edited by Coulomb
Image paste failed; still had switching arrangement wrong
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One final word on the Axpert design. I'm at a friend's place now, and it happens that on his whiteboard is still a sketch of the design we reverse engineered from some documents plus tracing some of the PCB. It turns out that there are actually three complete full bridges, plus the buck stage. There is one full bridge on either side of the HF transformer. Only one of these is useful when inverting (power flow from battery to AC output), though both could be active when charging; the MOSFETs could be used to lower the voltage drop of the back diodes on the battery side (synchronous rectification).

That's a lot of power silicon for a competitively priced product.

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Plonkster, I have to admit I am rather impressed that the Axpert can charge batts separate from the load. That is nirvana for me!

Does Victron have anything on the same level to oversize the panels, using a small battery bank?

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7 hours ago, Coulomb said:

Actually, "transformerless" is a meaningless "marketing" term. It lacks the heavy 50 Hz transformer that makes low frequency transformer models less attractive (man, those things are heavy to lift). But it certainly has a transformer, just that it's a high frequency one. It's less than a litre in size, and would weigh only a few kg. This is possible because it operates at a frequency about three orders of magnitude higher than 50 Hz.

Yup, sort of my opinion too. I read up on these topics a while ago, so pretty much the only ways I know to step up a voltage is a charge pump (using capacitors) or some kind of inductor (which, if you think about it, are also charge pumps). So you have forward converters, flyback converters, boost converters, SEPIC/Ćuk, etc. and all of them really only chucks energy into a combination of capacitors and inductors and then releases that energy again at a higher voltage. Now the transformer that's so "old technology" does precisely the same thing really. You store some magnetic energy in there, and then you release it again using a different set of windings.

So totally agreed with this. It's meaningless marketing.

Just for interest sake, what kind of topology does the Axpert use for the boost stage? Sounds to me like it has a transformer with a full bridge driver on both ends (depending on whether it is charging or inverting)?

Edit: A nice summary of topologies: http://www.we-online.com/web/en/index.php/show/media/06_passive_components_-_custom_magnetics/pictures_and_graphics_1/midcom_blog_photos/SMPSChart.pdf

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4 hours ago, The Terrible Triplett said:

Plonkster, I have to admit I am rather impressed that the Axpert can charge batts separate from the load. That is nirvana for me!

Does Victron have anything on the same level to oversize the panels, using a small battery bank?

 

The TT is weakening at the knees next thing we'll know is he will have packed away his Morning Glory - released the Blue pixie and become a heretic and joined the happy throng  of Voltronic customers.

 

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5 hours ago, The Terrible Triplett said:

Does Victron have anything on the same level to oversize the panels, using a small battery bank?

Well yes, but 1) it is going to cost you and 2) you may need to do things a little differently.

First off, back to basics. If you have an oversized array and a small battery bank, you're likely doing this because you self-consume a lot of the energy as it comes in, you're not storing it for later use. That means you really shouldn't be bringing the solar in on the DC-bus, you should be running a GTI.

So the "correct" way would be to install a GTI. Now a Victron inverter can deal with GTIs very well, prioritising solar, charging the batteries from the AC side. The (very good!) battery management in the Multiplus/Quatro can now also do its job properly.

If however you insist on pushing the solar in on the DC bus, which is the less expensive option, you need to run hub-1. With hub-1, you can add a ve.can<->ve.bus cable (this thing is like 5k on its own) and then the Multiplus/Quatro takes over control of your MPPT and can adjust charge current according to load conditions.

So despite how "negative" that answer may sound, think for a second how the cost of a GTI compares to the cost of a charge controller. Because that is really what we're talking about :-) The 150/70 is like 12k right now, and I think an entry-level Fronius is 18k or so. So if you think about it... what you want to do is "wrong" in the Victron universe... but still possible. :-)

 

Edit: So the real "proper" use case for hub-1 is where you want to store the majority of your energy for later use (hence the solar on the DC-bus), but to feed excess back to the grid. This is for the man who is not at home during the day, but want to use the energy tonight.

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57 minutes ago, Chris Hobson said:

The TT is weakening at the knees next thing we'll know is he will have packed away his Morning Glory - released the Blue pixie and become a heretic and joined the happy throng  of Voltronic customers.

I was till you ruined the glory!!! :D:D:D

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Truth be told, I have no need today to move anything.

But, as the Voltronic devices mature more, and they have, and this forum gets really excited about a new model that has all the can be asked for (or as close to as it can be), then I may just make that call and install a system for the rest of the house.

But to get rid of the Victron inverter ... eish, not so sure about that. It is my Toyota, my Isuzu Granny Wagon ... I really do like it.

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