Tuesday, February 6, 2024

New Inverter System

In this earlier article I talked about my less than satisfactory experience with Outback's newer VFXR inverters.  That cliff-hanger left the obvious question of what replaced the Outbacks.  Well, here you go....

I considered a couple of alternatives, but wanted something with proven power boost capability since that's the key feature that I need, and that kept pointing back to Victron.  They were certainly the popular choice, and I had good access to several example systems working exactly as I wanted.  So that became the default answer.

Limited space for new inverters

 
Limited space in breaker panel

One constraint I now had vs a new build was the available space, existing wiring, existing breaker configurations, available space in breaker panels, etc.  In my experience, a retrofit is driven at least as much by the as-built configuration of a boat, as it is driven by what you ideally would want.  Compromises are almost always required.  Also, Victron's product line is not exactly consistent.  They have the Multi inverters, and also the Quattro inverters.  The big difference with the Quattros is that they have two AC inputs, and the inverter will do a priority selection of which it draws power from.  This is handy is you have one shore power connection and one generator because the Quattro becomes your transfer switch and automatically switches between the two.  But I have two shore power connections and two generators, so need separate power switching regardless.  That means a Multi would be just fine, but it's not that simple.  The transfer switch in the Multi is rated for 50A, where it's 100A in the Quattro.  One of my generators is 100A, so the higher rated switch is important.  Also, the Quattros are available in higher power ratings, at least in 24V models.  All this meant that Quattros fit the bill better than Multis.

But wait, there's more.  At the time (this was all 18 months ago), Victron was rolling out the Multi II model line, with some capacity & voltage versions available, but not all.  And there were hints of a Quattro II line as well.  But the product line was not fleshed out, and some of the II models could not be paralleled where the older versions could.  Their form factor is also quite different, and they simply wouldn't fit without major reconfiguration of the laz.  Now you can see why trying to figure this out initially started to make my head explode and drove me to Outback.

Then there are all the different control buses that Victron has, and trying to figure out what uses what, how they are different, how they connect, and to what benefit.  It was another brain scrambler.  There is VE.bus, VE.CAN, VE.Direct, VE.net, VE.Smart, USB, Ethernet, NMEA 2000, each with different topology rules, different cable length limits, and different devices to interconnect them with different capabilities.  And then there are all the configuration software programs. VEBus, VEConfigure, VictronConnect, VRM, and the GX devices.  Each works with different devices, to manage different things, requiring different physical connections, and running on different platforms/devices.  Compared to other product lines where there is one communications system that connects everything, and one set of tools to configure it all, this was frustratingly complicated.

Anyway, the final decision was to use dual 8kva Quattro inverters, linked to my existing OctoGX that already tied my solar charge controllers together.  The Octo is an odd-ball device that has never had any documentation, and is no longer shown as an available product.  But it has 4 VE.Direct ports which I needed for my solar charge controllers, a VE.Bus port needed for the Quattros, a VE.Can port to connect to my Skylla chargers and my MG BMSes, a second CANbus to connect to N2K for monitoring, and an ethernet port to display and control the device itself.  Most of the Victron GX family of devices include their own display, but the Octo has none.  However you can access it via a web browser over ethernet and you get the same user interface as the built-in displays.  I planned to do the majority of my monitoring over N2K, so this all worked out fine for me.

When you go to install a Victron product, you quickly realize that it's not designed for the North American market.  4/0 DC cables are common for high current devices, and big inverters are exactly such a device.  But 4/0 cables and lugs won't fit in a Victron inverter.  Below you see two 4/0 cable lugs on the power post in a Quattro, and can see that there isn't enough space for them to lie next to each other.  The only way to get them to fit is to cut them down.

 

Not enough space for side by side 4/0 lugs


Lugs must be cut down to fit
 

Also, 4/0 cables won't fit through the opening in the chassis if there is any heat shrink on them, which of course there should be to seal the cable lugs.

4/0 cable doesn't fit through chassis opening

From this I learned that the trick is to use 3/0 cable, not 4/0.  You lose a bit of cross sectional area in the cable, but the lugs and cables fit as intended.

Victron's inverters pose another challenge when you want to build a high capacity inverter system, which is that they are 230V single phase only, and do not have support for North American split phase 120/240V power.  So you somehow need to convert the single phase inverter output into split phase.  You can do that with a full-on isolating transformer where the input side is 230V from the inverter, and the output is a 120/240V split phase.  This is how shore power is handled with an isolation transformer, and it works very well.  However 100% of the power has to run through the transformer, so it needs to be rated accordingly which makes it big, heavy, expensive, and always wasting power.

The alternative is an autotransformer which does not provide isolation, but can be used to derive a neutral for a split phase system.  And in this application, the autotransformer only needs to be sized for the imbalance between the two 120V halves of the split phase system.  So where a 100A isolating transformer would be needed on my boat, I can instead use a 25A autotransformer.   It's smaller, lighter, cheaper, and wastes less power.  The catch, which we will have to save for another day, is that autotransformer selection, grounding, and neutral to ground bonding on the boat can be very tricky, and leave you with surprising circulating current in the system when there are no loads, or a neutral for the inverter loads that is elevated several volts relative to ground.  Both of these things are cause for alarm for anyone inspecting or operating an electric system, so can create quite a problem, even if not particularly dangerous.

I decided on the autotransformer route and selected one from - wait for it - Outback Power.  They have had this product, unchanged for decades, and I have used it before successfully.  The power rating was what I wanted, and it's a nice package with a cooling fan, etc., at a reasonable price.

Outback autotransformer


Then there is another challenging issue with an autotransformer used this way.  An inverter installation will have over current protection on the inverter output sized for it's max current.  In my case that's 100A.  But my autotransformer has a max current rating of 25A, so I need a breaker for it that is 25A.  The challenge is that if the autotransformer breaker trips, the loads lose their neutral, but they still have 240V across L1 and L2 from the inverter.  With an open neutral, the line to neutral voltages will depend on the various 120V loads, and could be anything between 0V and 240V.  120V appliances do not react well to 240V, and damage is almost certain.  Worse yet, starting a fire is a distinct possibility.  So you can't, under any circumstances, allow an open neutral while still applying 240V across L1 and L2.  This means you need some sort of interlocked breaker system such that if the 25A autotransformer breaker trips, it also trips the 100A inverter output breaker.  I accomplished this using an auxiliary contact on the 25A breaker, and a shut trip on the inverter output breaker.  These are snap-on "side-car" devices for ABB breakers, designed for just this sort of thing.  Power from the Inverter output runs through the aux contacts, and to the shut trip device.  Anytime the 25A breaker is opened, it sends any 240V power that is present to the shunt and opens the inverter breakers.  So it's impossible to have the autotransormer breaker open witout the inverter breakers also opening, and you have to close the 25A breaker first, followed by the 100A breaker.  It seems complicated at first, but once you sort it out it's actually a really simple and dependable setup.

Autotransformer breaker with auxiliary contact

 

 

Inverter output breakers, each with a shut trip "side car"

It was quite the wrestling match to get the old equipment out, cables re-routed, breakers moved around, new cable access holes cut, and the new equipment mounted in place.  All I can say is that getting old sucks.  Stuff that I would just push through in my 20s and 30s, even my 40s and 50s, is noticeably more difficult in my 60s.  I'm forever thankful for a young, capable, and enthusiastic son-in-law who lives nearby.

It's good to have youthful help

 
Major components installed

Initial power-on and configuration went well.  After you get your head around all the different tools, and what to use when, it does all work.  But when I switched over to shore power, the inverters didn't start charging as expected.  Further investigation revealed that Victron inverters behave differently from all the others that I have encountered.  In particular, when AC power appears, they do not automatically start a full charge cycle.  Instead they check to see if the battery voltage is a fixed amount below the Absorb voltage, and only start charging if it's below that value.  In most charger parlance, this is called a "rebulk" setting, i.e. the voltage level where the charger will return to bulk charging.  In other products this only applies when AC power remains attached, like when connected to shore power.  If for any reason the batteries get low enough, bulk charging will resume in place a float charging.  But when AC power is gone and then reappears, bulk charging starts right away.

On a boat, this is really important when you are at anchor.  If you start the generator to make water or cook a meal, you typically want to opportunistically charge the batteries while the generator is running.  But Victron inverters won't do that unless the batteries are pretty low, and it's not an adjustable parameter.  Digging through the Victron maze of info I discovered a firmware update that reduced the voltage drop trigger point for LFP batteries, which helps, so I did the update.  But it still wasn't want I wanted.

Up until this point, I had not used so-called DVCC which stands for Distributed Voltage and Current Control.  It's used to allow the battery BMS to direct charging, rather than programming each individual charger to operate on its own.  I decided to give it a try since a friend had been using is successfully on a nearly identical power system.  With one clock of a button in the GX device, everything worked.  The batteries charged right up to full, then settled down to a lower float voltage to maintain 100% with no ongoing charge current into the batteries.  Exactly right, and I have left it on ever since.

Although the power system does what I need it to do, the Victron products are not without warts.  Here are the key things I have run into.

Charger output will likely fall short of specifications.  I haven't been able to figure out why, but with these larger Quattros it's common for people to see closer to 170A of charge current vs the specified 200A.  And that's at 25C ambient or lower where it's supposed to deliver full output.  And to add to the mystery, mine actually does come pretty close to specs, but I don't know why mine and not someone else's.  In contrast, the Skylla chargers put out 100A, as specified, all day every day.

Inverter output is not what you might expect.  An 8kva inverter is 8kva only under a very special load condition, and is really 6.5kva by all other measures.  And that's at 25C ambient.  At 40C it drops further to 5.5kva.  The result is transient overload warnings for loads that you wouldn't expect to cause a problem.

Idle power consumption can be significantly higher than the specs claim.  I haven't measured it specifically on the boat's 8kva 24V Quattros, but I have measured it on a pair of 48V 8kva Quattros and it's DOUBLE what the specs say.  The two inverters, doing nothing, consume a constant 200W.  That makes them the largest power consumer on the boat.  More than refrigeration (all fridges and freezers combined), more than Starlink, just more.  It's rather obscene.  I asked a senior Victron employee about this at METS this fall and he told me that I was measuring it wrong, and that the sampling interval of my current clamp was inadequate.  For that to be the case, the sampling from the clamp meter must be exactly in sync with the AC component of the battery current, and in phase such that every sample is picking up a peak of the AC component.  What are the chances of that?  And it means that everybody else's clamp on meter who has measured this is similarly in perfect sync and phase with the inverter.  There's NFW.  And this includes Victron's own ammeter inside the Quattro.  Man, it's lottery day if that's the case.  So I asked if I put a scope on the cable, would it show the correct current, and he said yes, it would match the spec.  OK, I'm going to do it when I'm back on the boat and we will see what we get... but I call BS on this one.

DC Ripple voltage can be an issue with Victron inverters, even though no other inverter manufacturers seem to have an issue with it.  This goes hand in hand with the current issue above.  An inverter is an electronic switch that turns on and off rapidly to create the output waveform and drive loads.  That switching results in pulse loading on the batteries at the switching frequency.  There is also lower frequency pulse loading at the AC output frequency of 50 or 60hz.  So if you look at the DC voltage at the inverter with a scope, you see a slightly wiggly line rather than a perfectly straight line.  The wiggliness (a technical term) is the "DC ripple".  Too much of it can stress capacitors and shorten their life.  For some reason, Victron monitors this, and generates warnings and alarms, and will even shut down if it's excessive.  Nobody else cares about this, so does it mean that Victron is doing us some special favor that nobody else is?  If they were, then I'd expect to see lots of failures in other inverters, but that's not the case.  Alternately, it could mean that Vicron has a vulnerability that others don't, and they are protecting themselves.  This seems much more likely to me, but we will never know.  Regardless, if your DC cables aren't fat enough, or are too long, you can end up with ripple warnings under higher loads.  And there is no sure way to know how fat or how short those cables need to be.  You can just do your best and cross your fingers.  I got lucky on this, and seem to be free of ripple warnings, but others have not been so lucky.

All this has been in operation for over a year now, and meets the major requirements, despite the little annoyances.  The one thing that really does piss me off is the idle power draw.  Twice the spec?  Are you kidding me?  If I thought there were a better alternative, I would honestly be going the Outback route and making Victron take the equipment back and refund my money.  But they seem to be the lessor of evils.  It's sad that that's considered a success.

4 comments:

  1. What about skipping the split phase altogether? By that I mean take the 230V output from the Quattro pair and feed your 240V panel. One output from the 240V panel goes to a transformer that outputs 120V single phase, which then feeds your 120V panel.

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    Replies
    1. You could do that, but there are issues. One is that all the 120V load has to run through the transformer, so it needs to be sized for the max possible 120V loads. With the autotransformer approach it only needs to be sized for the max imbalance between the two 120V legs, which is typically much smaller. The second issue is that the 240V service needs to be grounded, one way or another. With split phase, that's done with the neutral. With European power that's done with one of the two lines that make up the 240V. If you did that with what is ostensibly and North American power system, it would really confuse anyone working on the boat in the future since it's such an oddball arrangement. There also are some 240V appliances that actually have some 120V internals and use/rely on the split phase neutral. My feeling is that if you are going to have split phase, then have split phase. Otherwise stick to all 120V.

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  2. My older Magnum Inverter / Charger has the same “Rebulk only when AC power reestablished behavior”. It will only bulk charge if the house batteries are below a set value at the time AC power is applied. It used to drive me nuts as in a low SOC the solar panels could create a higher house battery value & trigger a float charge only from the charger.

    Switching to CC/CV mode eliminated that problem.

    Newer Magnum controllers allow for an override of this rebulk limitation but you have to buy a whole new remote. No firmware updates allowed.

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  3. love the detail and analysis. keep on moving on

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