Following are three emails, representing an email exchange yesterday between myself and one of the visitors to my site.
I’ve removed the writers name at their request…
—–Original Message—–
From: AJ
Sent: Tuesday, July 08, 2008 5:10 PM
To: kenw@seanet.com
Subject: 3 phase VFD and air conditioning
Ken,
I saw your comments on your website about changing to 3 phase air conditioning chillers by using a VFD.
Be sure to do some real checking into how these VFD affect your power system.
Some of them can create electrical havoc in your power generating sources or the dock power As for the Atlas system, bad news; you should be looking at something much more technically advanced like ASEA Power Systems. .
I also saw that you wanted to remove some of your inverters. What is the reason for doing that?
I realize you said you wanted to free up space but don’t you use the inverter power for quiet time or when you can’t run a genset?
best regards
AJ
Greetings AJ!
Your comment is the first I’ve had that indicated potential problems with VFDs. I’ve spoken to both Cruisair and Technicold about VFDs and both have claimed they are solid. Cruisair today said that they insist on them for all installations over 5 tons (60,000 BTUs and up).
As to Atlas: I went through six miserable months with my Atlas system. The first major problem was that I had no way to bypass it, so for six months while Atlas tried to solve the problem, I had to run the generator! Actually, what I did was to put the generator onto auto-start and it came on about 4-6 hours a day. This was in a cooler climate. If I had been somewhere that required air conditioning, I’d have had a mess. I’m still not sure what the Atlas problem was. Atlas blamed improper installation by Nordhavn, but I doubt Nordhavn would agree. The Atlas tech effectively reinstalled the Atlas, and added additional ground wires, and since that time (about six months ago) it has worked flawlessly.
As to the inverters: I currently have 14kw of inverter capacity. My vision was to run the boat 99% of the time off of the inverters, including some air conditioning. We quickly discovered that even 14kw was not enough to reliably run even a minimal amount of air conditioning, and efforts to do so would clobber the electrical system. My boat is a power hog. It really requires something close to 16kw at all times, with even limited air conditioning. Even in cooler climates, without air conditioning, the boat consumes enough electricity that it almost always makes sense to have the generator running.
The boat was designed to have two high powered (12kw total) of hydraulic alternators. However, when I’ve done comparisons of the incremental fuel burn to run the hydraulic alternators, versus running a generator, I have always been better off with running a generator. The hydraulic alternators are no longer being installed by Nordhavn. They are finicky (at least mine are), and can cause trouble (we had them overheat and pour out smoke during an Atlantic crossing).
Historically, I did not use a generator. On my Nordhavn 62, we ran it for nine years, and put only about 450 hours on the generators TOTAL, a small fraction of the engine hours. My design for this boat was to use the same mentality as I did for my Nordhavn 62. Unfortunately, I hadn’t realized how much bigger the 68 is than the 62. The 68 is in a different category! It really is an “always generator on boat”.
This said, there is a shot that I could make the boat work as it is setup — but, there are some issues that argue for simplification (and always using the generator).
My four 3.5kw inverters put out heat, and I have heat problems in the lazarette. I put too much equipment in my lazarette, and some items take up more space than they should. The Atlas is HUGE. The four inverters take up a huge amount of space. Four a/c chillers eat a bunch of space. Then there’s the diesel furnace (Kabola) and all of its plumbing (it has separate loops for space heating, water heating and hot tub heating). The passarelle stabs straight through the middle of the lazarette, and has a large hydraulic pump that takes up space. There are two large Glendinning buckets, two 80 gallon oil tanks, 24 8d batteries, steering pumps, the ram for the twin rudders, a 16kw generator, two 800GPD water makers, and more!
I have two problems in the lazarette: space and heat. I’ve added large fans, and still find I need to run a/c in the lazarette at all times in warmer climates. Even with the big fans, the lazarette is running 135 degrees! With a/c it drops to 90 degrees quickly. On the space side, I have no access to the batteries or a/c chillers. Nordhavn asked that I check all the large 24 volt cables to/from the batteries regularly, and I said “How?” and no one had an answer.
I’m thinking that by removing half the batteries, removing half the inverters, and removing half the a/c chillers, I’ll come out with a boat that requires the generator at all times– but, I’ll open up space needed to give me proper maintenance access, and reduce heat.
Does this make sense? I agree with you — I really don’t like running the generator, but now that I’ve run one essentially non-stop for months (when away from the dock), I’ve gotten used to it. The 68 is SO quiet, that you don’t hear it. The only problem (and, I’m not minimizing this problem) is the 1+ gallon per hour cost of running the generator.
Ken W
Ken Williams wrote:
> Greetings AJ!
>
> Your comment is the first I’ve had that indicated potential problems
> with VFDs. I’ve spoken to both Cruisair and Technicold about VFDs and
> both have claimed they are solid. Cruisair today said that they insist
> on them for all installations over 5 tons (60,000 BTUs and up).
>
REPLY
The VFD do not cause problems for the air conditioners. and NOT ALL
variable frequency drives are bad.
However some of them ( mostly the lower priced models ) may cause problems for small capacity power sources such as inverters and smaller size generators.
What happens is they create transient voltage distortions by momentarily overloading the power source. This in turn causes a spike in the waveform that can cause trouble for other sensitive equipment such as your computer screens entertainment centers and large screen
TV.
Eventually these transients will cause premature failure of the sensitive equipment.
Naturally no one ever associates the equipment failures with the VFD driving the air conditioners.
It takes sophisticated power line analyzers to measure and display the waveform problems.
> As to Atlas: I went through six miserable months with my Atlas system.
> The first major problem was that I had no way to bypass it, so for six
> months while Atlas tried to solve the problem, I had to run the generator!
> Actually, what I did was to put the generator onto auto-start and it
> came on about 4-6 hours a day. This was in a cooler climate. If I had
> been somewhere that required air conditioning, I’d have had a mess.
> I’m still not sure what the Atlas problem was. Atlas blamed improper
> installation by Nordhavn, but I doubt Nordhavn would agree. The Atlas
> tech effectively reinstalled the Atlas, and added additional ground
> wires, and since that time (about six months ago) it has worked flawlessly.
>
> As to the inverters: I currently have 14kw of inverter capacity. My
> vision was to run the boat 99% of the time off of the inverters,
> including some air conditioning. We quickly discovered that even 14kw
> was not enough to reliably run even a minimal amount of air
> conditioning, and efforts to do so would clobber the electrical
> system. My boat is a power hog. It really requires something close to
> 16kw at all times, with even limited air conditioning. Even in cooler
> climates, without air conditioning, the boat consumes enough
> electricity that it almost always makes sense to have the generator running.
>
REPLY
While specifying equipment for a 58 foot trawler I discovered that Marine Air and Cruise Air are hard starting.
My previous experience with air conditioning was with Mermaid in Fort Meyers.
They successfully ran their air conditioners from our inverters. At the time I was working from Xantex. Now I am independent.
Admittedly your boat requires much more air conditioning in total but the start surges for the Mermaid equipment is proportionally lower
tnan the same size Marine Air compressors. Mermaid uses the low
powered Danfoss compressor motors. It will be interesting to compare
the Danfoss with the air conditioning sold by Northern Marine. I have
sent an email to Nathan asking for technical details.
> The boat was designed to have two high powered (12kw total) of hydraulic
> alternators. However, when I’ve done comparisons of the incremental fuel
> burn to run the hydraulic alternators, versus running a generator, I have
> always been better off with running a generator. The hydraulic alternators
> are no longer being installed by Nordhavn. They are finicky (at least mine
> are), and can cause trouble (we had them overheat and pour out smoke during
> an Atlantic crossing).
>
REPLY
Hydraulics is not a good idea since there is a 5% transmission loss in
even the best of hydraulic systems and they produce huge amounts of heat.
If the system had 10% loss that would be 1.2kilowatts of extra heat
produced. That is the equivalent of a baseboard heater in a house.
Do you happen to know the brand of the actual alternators. I am
wondering if a standard brand was coupled to a hydraulic motor or of the
alternators were purpose built strictly for hydraulic drive. From your
description it sounds like a case of mis-matched parts and not
getting enough rotor RPM
In order to deliver 12kW those alternators should be spinning at 5000
RPM or so. If it spins slower than that the pulley fan doesn’t pul
enough air for cooling through the alternator
.
> My four 3.5kw inverters put out heat, and I have heat problems in the
> lazarette. I put too much equipment in my lazarette, and some items take up
> more space than they should. The Atlas is HUGE. The four inverters take up a
> huge amount of space.
REPLY
Are you using the Turbo Outback inverters at this time. These should
be liquid cooled.
As for the ATLAS; al i can say is that is th ewrong product choice.
They use older technology and again its air cooled.
Have a look at the ASEA Power system products. They now have a liquid
cooled converter that is much smaller than the Atlas.
> I have two problems in the lazarette: space and heat. I’ve added large fans,
> and still find I need to run a/c in the lazarette at all times in warmer
> climates. Even with the big fans, the lazarette is running 135 degrees! With
> a/c it drops to 90 degrees quickly. On the space side, I have no access to
> the batteries or a/c chillers. Nordhavn asked that I check all the large 24
> volt cables to/from the batteries regularly, and I said “How?” and no one
> had an answer.
>
REPLY
I saw mention of 8D batteries on your system schematic posted
elsewhere on the site. Almost all designers seem to have a mind block
against using industrial strength traction batteries. The kind used
in fork lifts. These are taller and have a smaller foot print.
Because of how they are constructed each 2V block joins the next. You
end up with only two 24V cables. One positive, one negative. Nothing
to check. There is a choice of sealed or traditional wet cells. For your
application, sealed is the best bet. They are far superior to the
traditional 8D truck battery.
I’m thinking that by removing half the batteries, removing half
The inverters, and removing half the a/c chillers, I’ll come out with a
boat that requires the generator at all times– but, I’ll open up space
needed to give me proper maintenance access, and reduce heat.
Does this make sense? I agree with you — I really don’t like running
the generator, but now that I’ve run one essentially non-stop for
months (when away from the dock), I’ve gotten used to it. The 68 is SO
quiet, that you don’t hear it. The only problem (and, I’m not
minimizing this problem) is the 1+ gallon per hour cost of running the
generator.
REPLY
Reducing the heat is primary goal. Liquid cooling would help there.
Changing to a different battery type with a more usable shape would
also open up deck space.
Nobody makes liquid cooled inverters for marine use at this time. Its
still a specialized application.
While its technically feasible, it would become a custom job and void
manufacturer’s warranty.
If you could duct cooling air and exhaust air from the inverters that
would help.
Personally I prefer the Victron brand and have had good sucess with
them for about 5 years now.
At my suggestion Steve Dashew switched from Mastervolt to Victron when
he had charging issues that Mastervolt could not resolve.
I see he is now spec’ing Victron for his FPB 64 boats.
Quite apart from the cost of running a genset, look at the increased
maintenance such as oil change and filters.
Plus every gallon you use for the genset reduces your cruising range.
> Ken W
regards
AJ