TWL: Power management aboard a boat
Enough. I am sitting here looking at my 7.5kw Onan with a shorted stator.
I figure that, between the stator and the fact the engine hasn't run in four
years, I'm at least a kilobuck away from having a noisy generator making
more power than I will ever need.
Now, I am not the type that goes out and buys the latest widget unless it is
necessary and I don't mind using older technology in new ways. I also like
to homebrew as much as possible. I am thinking of getting a small diesel
auxiliary engine and running a heavy duty alternator or whatever off of a
pulley. This would feed two battery banks that would be charged
alternately, each bank capable of supplying the days needs. I found the
plans for a 2 KVA inverter that could provide the 120 vac. No, it would
not be very automated, but I would know how it works and how to fix it.
Now, this is a spur of the moment idea and I haven't had time to think it
through, but I think that having either the main engine alternator or an
auxiliary alternator on a small engine to charge battery banks and using an
efficient inverter for the 120vac would be a good option for the big old
noisy Onan.
Now, how about some comments regarding this type of arrangement...what kind
of engines, alternators, and control technology are available, what parts
can be salvaged from existing stuff, what you think of the tradeoffs, and
what could be done to minimize the costs. We are talking homebrew here for
those who don't want to go out and spend 5-6K$ for new technology.
Lets keep it public as much as possible to see how things go.
Dale Hardin
1979 Marine Trader 40 ft. Sedan "So Good"
aiti@gate.net writes:
I am thinking of getting a small diesel
auxiliary engine and running a heavy duty alternator or whatever off
of a
pulley.
Long time ago, I saw such an arrangement. It was installed close to
the main shaft and by throwing a belt on a pulley via an idler, you
could use it as a get -home engine, if your main ever failed. Little
slow, but they tested it and it worked. Good idea.
At 02:29 PM 06/18/2000 -0400, >Dale Hardin wrote:
Enough. I am sitting here looking at my 7.5kw Onan with a shorted stator.
<<snip>>
I am thinking of getting a small diesel auxiliary engine and running a
heavy duty alternator or whatever off of a
pulley. This would feed two battery banks that would be charged
alternately, each bank capable of supplying the days needs.
Arild replies:
Precisely what I was getting at. Because I do work in the industry I
can't mention names or brands but there are four manufacturers who offer
exactly that sort of setup. It works very well! no reason why you can't
build one yourself.
With respect to the dual banks being fed alternately; may I suggest
combining them.
You also mention using an inverter.
There is no advantage to splitting the bank but there are disadvantages.
Battery life is a function of depth of discharge each cycle. A battery
bank will last much longer if you do not discharge it as much.
If you combine all batteries into one large bank and draw the same amount
of power ( Amp -hours ) the combined bank will be discharged much less as
a percentage of the totla than if you took that amount of power from one
smaller bank,
The gains in life expectancy is much more than double.
If you feed a battery bank with power from an alternator while also using
power from the same bank the charging source will supply all the current
up to its limit before the battery itself will begin to drain.
Inverters can be very power hungry but only in short bursts when using
things like microwave ovens. All appliances have a starting surge. Both
generators and inverters must be capable of handling such surges in order
to get the appliance going.
A 2 Kw inverter is a lot cheaper than a 2 K-W genset. A 2 Kw inverter
can usually handle a 4 Kw surge for up to five seconds.
Not all gensets can handle such a surge without distortion or stalling.
So you end up having to get a 3 K-W genset to start the same load that
a 2 Kw inverter does.
When a genset encounters a surge load, it bogs down and frequency drops.
If the frequency drops low enough, some appliances will not work.
Induction motors have more trouble getting up to speed since they are
frequency dependent.
As the rotational speed drops, so does the output voltage. When the
supply voltage to an induction motor drops, the current increases to
compensate. This increased current places an even greater load on the
genset which in turn drags the rotational speed down. Arrgh! the
darn thing stalls!
See what I mean by not being efficient?
Dale wrote:
I found the plans for a 2 KVA inverter that could provide the 120 vac.
No, it would
not be very automated, but I would know how it works and how to fix it.
Be careful! Simple inverters have been around for decades. However, many
of them have a square wave output which is not tolerated by many modern
appliances. Square wave output inverters also create a lot of electrical
noise and interference.
This will create problems in your own equipment as well as others nearby.
Sophisticated wave shaper inverters are neither cheap nor easy to build.
As for the rest of your ideas, yes they are definitely workable.
Dale said
I think that having either the main engine alternator or an
auxiliary alternator on a small engine to charge battery banks and using an
efficient inverter for the 120vac would be a good option for the big old
noisy Onan.
Definitely more efficient. Now you charge your battery bank from either
source as you travel or anchor out.
If you spend a lot of time dockside connected to AC then you won't need
a big charger to keep the battery bank up since most of the big hotel
load is coverd by shorepower while lights etc. can easily be handled by
a 20 amp charger.
I live in a motorhome which is strictly 12V DC and a twenty amp charger is
sufficient for all my needs except for the microwave.
Now, how about some comments regarding this type of arrangement...what kind
of engines, alternators, and control technology are available, what parts
can be salvaged from existing stuff, what you think of the tradeoffs, and
what could be done to minimize the costs. We are talking homebrew here for
those who don't want to go out and spend 5-6K$ for new technology.
In many cases you can replace the normal automotive regulator with a
"smart" regulator that will provide a much better charging curve for a
house bank. Running a genset to create 120 Volts AC which in turn powers
a 12V DC charger is really inefficient. You have double conversion losses
to deal with.
One thing to watch out for. Alternators do run hot and they are derated
as temperature increases.
If you take a normal engine alternator, replace the regulator with a
smart unit, and then proceed to power an inverter to drive an air
conditioner for long periods of time, the alternator will get hot. Make
sure you have a unit which is beefy enough to maintain adequate output
at the elevated operating temperatures. Look for specs at the 75 degree C
temp not the room temp rating.
And this doesn't even begin to look at other alternative sources of power.
Cheers
Arild
I found the
plans for a 2 KVA inverter that could provide the 120 vac.
I think that having either the main engine alternator or an
auxiliary alternator on a small engine to charge battery banks and using
an
efficient inverter for the 120vac would be a good option for the big old
noisy Onan.
Hi Dale
I know for a fact that you live in SW Florida! :<)
There is no way you will be able to run the A/C to cool that big ol' Sedan
with a inverter/battery setup with out towing a barge loaded with batteries.
Just to run the airconditioners on my boat you would have to have a 3500watt
inverter. And that doesn't include the startup current. Add hot water,
another 1400 watts, and you can see the size of the batteries you will
require. My calculator says 292 amp/hr for the A/C. Let's see, Charge once a
day.....Hummmm... shall we say for 2 hours?? That would be around 6,500
amps used..... So you would have to charge the 13,000 amp hour batteries at
a rate of 3,250 amps. Assuming 0% loss in charging. Oh, you want hot water
too??? I don't think that many batteries exsist. Now remember that this
would be for my boat just to run the A/C. Your boat has over twice the
interior area and would need close to twice the A/C to cool it and hence the
amp/hour capacity.
I have a 7.5Kw genset in my 35' doublecabin that will just run all the
120vac things on my little boat. 2 airconditioners, 1 hot water heater,
elec stove, TV, Toaster oven, Hair dryer, etal. Just this last week I ran
the genset and loaded it with all the goodies and had my volt meter hooked
up. With all the things running except the stove, the volts dropped from
121vac to 117vac when the last item was turned on. You also need to note
that the batteries were charged up at the time. If they weren't, that would
have been another 600 watts of load.
I know that advocating a fossil fuel solution after all the bandwidth
recently may be heresy, but for myself, and if I want my wife to join me, I
will have to have the above mentioned items. I wonder what would happen if
everyone said to the Admiral " Honey, we are going to go 'Sailbote' No
aircinditioning, hot water, etc. I know on my boat I'd be talking to myself!
Morley
M/V Tortuga ( CT-35, 35' Ta Chiao )
Cape Coral, Florida
Arild replied:
<Precisely what I was getting at. Because I do work in the industry I
<can't mention names or brands but there are four manufacturers who offer
<exactly that sort of setup. It works very well! no reason why you can't
<build one yourself.
Dale:::A one-banger should do for the engine. I had a Yanmar once and it
wasn't TOO loud. Obviously more cylinders would be quieter, but I don't
think we are talking about more than 1.5 to 3.5 kw. I've had 1 and
2-cylinder Volvos and they are too noisy. What about the alternator? I
looked at the Newage site, but didn't see anything that looked suitable.
Anyone know what might be suitable. (Arild has a "situation" that prevents
him from recommending brands) What might be available surplus?
<With respect to the dual banks being fed alternately; may I suggest
<combining them.
Dale:::Excellent suggestion. Simple also. I was thinking of charging one
and using the other at the same time, but no reason not to do both on the
same bank.
<If you combine all batteries into one large bank and draw the same amount
<of power ( Amp -hours ) the combined bank will be discharged much less as
<a percentage of the totla than if you took that amount of power from one
<smaller bank,
Dale:::Agreed. Longer battery life also, I presume.
<Sophisticated wave shaper inverters are neither cheap nor easy to build.
Dale:::The one I found on the internet is in a state of development, but
should eventually have a decent sine wave shaper. Take a look at
http://www.technology.niagarac.on.ca/people/mcsele/i2k.htm
<As for the rest of your ideas, yes they are definitely workable.
Thanks for the input. There was so much info, I couldn't respond to all in
one message. Anyone else have suggestions about external regulators for
charging the battery bank?
Dale
What about the alternator? I
looked at the Newage site, but didn't see anything that looked suitable.
Anyone know what might be suitable. (Arild has a "situation" that
prevents
him from recommending brands)
Try API in Florida.
Found their ad in "Boats & Harbors"
magazine where they supply the commercial
shipping and fishing fleets.
They sell Leech Neville alternators
with 160 amp output for less than $300.
Bought one and put in on an Albin running
a Trace with 6 Sam's Club golf cart batteries.
These are not the over-priced Gucci "toy" alternators
that are supplied by the recreational boating supply chains.
These are heavy duty commerical and much less money than
say a Balmar. Also one size fits all if you are creative!
No problem to connect this big guy to
a Lehman 120. Had to rattail file out the adjustable
bolt bracket and add a larger mounting bolt. Runs
OK with one belt, but you can add two belts if you like.
They also have an alternator out of Canada that is rated
over 200 Amps that they bench tested by running a 5 hp
motor continuously! This guy has the same footprint as the
160 LN and is still around $300.
Both units come with adjustable internal regulators and
can also be fitted with external smart regulators.
Brian Hall
CHB 45 "any Sea"
Old Bay Marina
Baltimore
----- Original Message -----
From: Morley and Tricia MTTortuga@iline.com
To: List ,Trawler World trawler-world-list@samurai.com
Sent: Sunday, June 18, 2000 5:49 PM
Subject: TWL: Re: Power management aboard a boat
I know that advocating a fossil fuel solution after all the bandwidth
recently may be heresy, but for myself, and if I want my wife to join me,
I
will have to have the above mentioned items. I wonder what would happen if
everyone said to the Admiral " Honey, we are going to go 'Sailbote' No
aircinditioning, hot water, etc. I know on my boat I'd be talking to
myself!
Morley
M/V Tortuga ( CT-35, 35' Ta Chiao )
Cape Coral, Florida
Hooray! Thank you Morley! I like Arild's ideas on making & using energy
more efficiently, but I'm too old to go camping.
Walt Konieczko
Annie Sez Too 34 Marine Trader
Lanoka Harbor, NJ