The Answer to Yesterday’s Riddle

Yesterday, I posted an electricity riddle I’ve been struggling with. Actually, I was 99% certain I knew the answer, but was being told by smart people that I was off base. Between email and postings on my site, I received over 20 responses, all but one supporting my position.

 

I did a bit more searching on Outback’s site, and found a diagram in one of their install manuals which I think puts this whole issue to rest. It uses 3kw inverters in their example, and I have 3.5kw inverters, but I think what it shows accurately depicts my system.

 

 

 

 

For those wanting to dig deeper on this topic, the manual to my inverter (I have four of the Outback VFX3524Ms) is here, and the page from my electrical diagram showing the installation is here.

 

My inverters are quite complicated, and have a panel from which I program them. Unfortunately, I only understand a fraction of how to program the inverters. Over the next couple of weeks I hope to give the manual some serious hours and figure some things out. For instance, the inverters are programmed to sleep when the power isn’t being used. Here’s what I mean: Let’s say I’m only using 5kw of my maximum 14kw output. This means that just two of the inverters (2 x 3.5kw) can output enough power to run the boat. The other two inverters can rest. I have a problem with the lights blinking while on the inverter. I phoned Outback, who said that their guess is that I am running close to the threshold where inverters decide to sleep, and that I am seeing the sleeping inverters kicking on and off. Apparently this threshold is one of many parameters I can set.

 

Another issue I have is that I can program into the inverters the maximum amount of power that can be diverted to battery charging (when shorepower or a generator is connected). I’m constantly tinkering with this setting, and haven’t found a value yet that I like. And, I have gotten myself into situations where it gets very confusing. For instance, think about this situation, which happens often on my boat: Let’s say that I am running the 16kw generator, and have allocated 3kw to battery charging (from the inverters). Thus, I have only 13kw with which to run the boat, and let’s assume for this example that I’m running with 5kw of load, so the generator is 50% loaded (3kw for battery charging, and 5kw for the boat). I have 8kw of “head room.” Now, imagine an air conditioning chiller kicking on, and suddenly demanding 75amps at 240v (18kw) in starting current. If only needs it for a second, but this is a real number. Once the chiller is running, there is ample power to keep it running, but for an instant, the power requirement is much higher than I have available. Generators are made to see these spikes. They lug for a second, and make noise, but usually handle the surges just fine. Unfortunately, my inverters don’t do as well. They see what looks to them like an anomaly in the power, and immediately start inverting. Which all is correct in theory, but seems not to work quite as well in practice. I’ve blown many fuses as this process occurs. It’s the primary reason I’m shifting to a/c chillers with “soft starts.” The power surges seem to cause my inverters to do strange things. I wish I could explain better what I mean by “strange things”, but I can’t. My recent training in electricity has better enabled me to read the electric panel, and program the inverters. I think I’ll be much smarter on all of this when I’m next on the boat.

 

And on a completely different topic…

 

Braun Jones forwarded me an email from a mutual friend which contained a comment on our upcoming trip:

 

 

“…When would you plan to make this journey? I bought the books for such a voyage from Alaska and the window is very tight, about 6 weeks. You are venturing into an area where the seas are notoriously rough. I have been to Sakhalin Island many times by the way, mostly to the capital, Yuzhno-Sakhalinsk – you can see Japan from there. Milt and I did some research of making the journey that you will do and decided not to do it. 

 

The political issue between Japan and Russia concerns the four islands to the East of the Southern tip of Sakhalin. Had those islands been Japanese the sea ringed to the North by the Kiril chain would be an international sea and not a Russian sea, a sea that contains large fish stocks and of course giant gas fields. Sakhalin is an area of active volcanoes and there have been many eruptions near to the Kiril islands that have caused tidal waves. …”

 

 

Tidal waves? Ouch.

 

The preparation for our upcoming trip has been quite a journey, with good days, and bad days. News tends to come in bursts. This email, and the news of one of our four boats dropping out, means two pieces of bad news in a row, which means we’re owed some good news. I can’t wait!

 

-Ken W

 
***UPDATE***UPDATE***UPDATE

Not everyone is convinced. I just received this email from “Mr. Jones.” I sent him the picture above. 
 

Ken,

You can call Outback.


This drawing is misleading to most people.


And this doesn’t surprise me from outback. No matter how you count the KW you still only have 7 KW per leg at 240VAC. Their drawing imply’s that you add leg 1 to leg 2 for 12 KW at 240. This is wrong.


Later

 

 

5 Responses

  1. It seems like it would be pretty obvious in practice. Just put a load greater than 7kW on the inverters and see what happens. If everything is powered, I think it’s fair to say that you have 14kW of power available from the inverters…

    Sam

  2. Ken:

    I have an Outback. My Outback manual distinguishes between “Classic Series” and “Outback Series”. The “Outback Series” uses an outside 240VAC source with 120VAC legs (generator or grid) AND the two 120VAC Outback outputs to achieve 240VAC 14kw. I read it this way: 7kw at 240VAC is supplied from the generator (or grid) and 7kw is supplied from the Outback inverter off the batteries, for a total of 14kw at 240VAC.

    This would be of use if you only had a single 7-13kw grid or generator circuit available, but you had a load of more than 7-13kw.

    So I guess I would have to sing “I sold my soul to Mr. Jones”.

    Alex Benson
    Selene 5329 Wild Blue

  3. Ken,

    I have a degree in electronics and I can tell you that the wattage capacity of any generating device has absolutely nothing to do with how they are connected (in series or in parallel). Wattage is always additive regardless of circuit configuration. Current and voltage capacities are different beasts, of course. Current is additive in parallel and voltage is additive in series. So, in my opinion, you’re correct.

  4. I am reather simple minded when it comes to electricity, but doesn’t all of this depend on how the inverters are wired to the bus(es) and what devices that require power can access at any one time? Said another way, 9 women can’t make one baby in a month.

Leave a Reply

Your email address will not be published.

Be the first to know when

the game releases!

Plus, receive special insider, behind the scenes, sneak peeks and interviews as the game is being made. Don’t worry. We will not spam you, and we will not flood your box with too many emails.
 — Ken Williams

Credits     |     Video produced by: Rock Steady Media     |     Teletype photo: Arnold Reinhold     |     PDP-11 photo: Trammell Hudson