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Old 17-04-2009, 04:25   #1
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Buss Bar Question

Let's assume you have a main buss Bar for your biggest circuits. One from your generator, one to your batteries for charging and in this case one to each of 2 electric motors. Since the generator is running and your feed is to the buss bar from it, wouldn't the power tend to flow to the engines when running since that was the path of least resistance if the batteries were fully charged or not?
Thanks,
Steve
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Old 17-04-2009, 10:59   #2
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Alternator/generator

If I understand your question correctly you describe an alternator (hardly see old dc generators any more) output connected to a positive bus from which other loads and sources connect. Because alternators have a set of diodes that rectify multi-phase ac into dc no current can flow from the buss back through the alternator whether the engine/generator is running or not.
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Old 17-04-2009, 11:07   #3
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Hi Rick,
The Generator is outputting DC.
The Motors are both DC.
The Batteries are DC.

Hope that makes more sense.

Steve
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Old 17-04-2009, 11:16   #4
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Should be no problem. Even 200A alternators leak less than 25mA @13V. Good PV panels have negligible dark current and do not need external diode protection (fuses, yes). You should be able to connect many loads and sources to a buss without a problem. A dc clamp-on ammeter can verify that the wires to each load/source from the bus carries no significant leakage current.
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Old 17-04-2009, 11:25   #5
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Rick I was wondering if the voltage could jump from the Genset to the motors. In other words if I'm running the generator could the power be pulled from it to the motors rather than the batteries. Case in point if the generator outputs 80a and the motors needed 100a and the batteries are rated at 144a. If the all three are on the same buss could the power be pulled directly from the generator instead of the batteries since their connected at the same buss bar. My generator will kick out if I exceed the 80a load but the motors will continue to run since the batteries are there.
I'm just wondering if it made sense to move the generator breaker off the buss and if so where?

Thanks for the help,
Steve
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Old 17-04-2009, 13:01   #6
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voltage doesn't jump

Of course the "generator" (what exactly is this "generator"?) will provide power to the buss from which the motors can extract their power. You are correct in that if the batteries provide current sufficient so that the generator is not overloaded then everything is fine. Tell me about this "generator".
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Old 19-04-2009, 20:23   #7
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Hyprdrv - I think there may be some confusoin around parralel DC circuits.

Generator - The generator (if it really is a generator) is regulated by sensing the bus voltage. If the bus voltage drops for whatever reason the regulator demands more output.

Batteries - Are like a big reservoir or lake of power. The "pipe" from the batteries is almost limitless, to the capacity of the system wiring, and it and the batteries ability to handle the heat that comes from drawing large current flows. A shorted battery basically melts down from the heat. The pipe from the generator OTOH is like a rain gutter.

The point is though that they are both in the same plumbing system.

When you activate low load items like radios and such the power is generally being supplied by the generator and the batteries remained topped up.

When you activate a high load item like a starter that needs 100 amps, the bus voltage drops, the generator ramps up but the reality is that the power is almost all coming from the batteries. The batteries deplete somewhat, and the generator remains ramped up until the sense votage senses the batteries are topped up.

The DC system is almost always a parrallel bus system - I am not sure how relocating the generator breaker will help anything as you will be required to wire it in the system somewhere.

I am assuming that you are talking about a portable genset and not the engine alternator. If you had concerns you could isolate the generator when starting the engines butI don't think this is necessary.
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Old 19-04-2009, 22:14   #8
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As Ex- Calif stated there is some confusion. First of all the generator has a maximun output capability. I don't know about the fact that the generator will shut down if the draw exceeds 80A, that is not common. If this is indeed the case then you have a problem. Don't you have a regulating speed control circuit between the battery and the DC drives or is it full on or off? If you run your DC drives to full load current requirments of 100A, that has to come from somewhere. The generator will ramp up to max to try and maintain the battery voltage, failing to do that the batteries will deplete and your motors will slow down until the output matchs the input, whatever your generators are able to put out. The batteries are just temporary power storage devices. If your generator does not have current limiting protection it will trip. You can get a circuit that will do this.
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Old 20-04-2009, 01:15   #9
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I just installed a Northern Lights genset and the manual explicitly states that it should not be connected to the engines starter battery. When I queried this I was told it is because the generators tiny dc alternator is just a dynamo type charger and the sudden draw from an engine starting would cause the dc charging circuit to be overloaded and blow. So I hooked it to the house bank and left the main engine on the starter battery

What I was told and what I did anyway if that helps anyone.

Cheers

Mark
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Old 28-04-2009, 07:35   #10
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I'm sorry I haven't gotten back quicker guys but I've realized how little I know about the electrical system on board this new to me boat. I've tried to gather some more info and knowledge but it seems the more I read the more confused I get so please bare with me on this. I'll try and get as much info on this so I can as the right questions. My original question was what I thought would be a simple yes or no answer so let's start with an equipment list then see if I can fill in any other questions.
I have 12 AGM batteries for a total of 144v and 3 house batteries.
I have an HFL 15kw dc generator model #E v1505-EU1
The Generator output at 157v and 15kw is 95a and at 172v, 87a. The output is controlled by a rheostat at the control panel and normally set to 164v. The generator has to be manually started to charge the batteries and the rheostat set to 164v per previous owner and the book.

I have a BRUSA Model #NLG5-11 charger. for the 144vdc batteries.

I have a DC-DC converter(144v to 12v) CENTAUR by Victron Energy to the house batteries then on to the house panel.

I have a 6kw Inverter from 144vdc to 120vac to the house ac panel.
All of this goes through a main Distribution Box including the 2-ST 74 Solomons electric motors.

At the helm I have a xentrex Link-10 and 2 amp meters, 1 for each engine and used some what like rpm gages to insure equal load. On Thursday I went down th the boat to do a few things and the reading at the nav station gauge for the battery charge was 148v which should have been at 164v. I checked the battery indicator at the Brusa and the batteries were not charging. Turns out the shore power plug (new one at the box) wasn't fully seated and it worked it's way loose so I wasn't charging with the frig and freezer on. I also see that the links-10 indicator is showing low battery as well as 2 of the 4 selection readings is also flashing, the V and Ah then the A and T. The batteries are fully charged now but the Links-10 is still showing only 1 indicator on the state of charge. Any help on this would be greatly appreciated since it's the main gauge I'm looking at to insure I start the generator to recharge.

I'm trying to get a grip on the system so I can get a better understanding of how to approach the redesign of the control systems. I want as much automation and warnings to insure I don't damage any expensive equipment I have. From what I've been told a lot of the parts are very good ones, they just need better controls. I'm also dealing with an owner who made several changes but hasn't fully disclosed them. A designer/inventor who no longer works for the company that is selling his design, a company who seems to not want to deal with an older design that was built by a D/I who doesn't work for them any more.

This coming weekend there is a Lagoon meet in Annapolis and I'm sailing up on Thursday. I'm hoping to meet with a rep from Lagoon as well as another owner of a 44E boat that I can suck up some info from as well as see what changes are being made to the newer boats. By the way last weekend My lovely wife and I had a great day of sailing on Saturday and didn't start the generator other than to exersize it before leaving out of Solomons, MD. Life is good. It's just these little things...

Again thanks for your help guys,

Steve
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Old 28-04-2009, 09:01   #11
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for someone who is admittedly short on electrical knowledge you sure bit off a big chunk...I'm a EE and I'd hate to have to deal with your boat's electrical systems! I hope you're a fast leaner. Purchase a good VOM and learn to use it. Keep all the wire to terminal connections in good order. I highly recommend that all connections be crimped, soldered and coated in liquid tape. They are going to be your biggest issue in years to come. Also learn to apply ohms law. VOLTAGE = CURRENT x RESISTANCE

best of luck to you
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Old 28-04-2009, 09:56   #12
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Randy,
My background is Mechanical/Plumbing design so I have enough knowledge to be dangerous when it comes to Electrics. This is more of a once I understand how it's suppose to work I'll be ok. It's the little things like on the control side that I need to delve into the wiring to figure out how I can make it better or easier I'm interested in. It didn't scare me, but I have a lot of respect. So why not ask the guys who are smarter or already walked this path.

Thanks,
Steve
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Old 28-04-2009, 10:38   #13
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It would seem the info. is a little inadequit. The batteries are a big capacitor, will draw depending on state of charge and Amp hr rating, plate size. The motors are inductors and will draw depending on the windings and state of flux, start up or running. As long as the gen. has a capacity to satisfy both there should be a problem. If it doesn't it will trip a breaker or dope the voltage. Probably wouldn't hurt the batteries but might well smoke the motors or gen.
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Old 28-04-2009, 11:00   #14
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First off to understand your system you need to do some reading on electrical systems for boats.
Here's a link US Navy Basic Electricity Course or New Boatbuilders Home Page - Basic Electricity DC Page 1

Recommended reading.
Boatowner's Mechanical and Electrical Manual: by Nigel Calder.
Powerboater's Guide to Electrical Systems, Second Edition
Ed Sherman, Published 2000, by Boating Magazine (See ad to the left)
Boatowner's Illustrated Handbook of Wiring:
Charlie Wing, Published 1993 by McGraw Hill
Your Boat's Electrical System: Manual of Electrical and Electronic Projects Conrad Miller, Elbert S. Maloney, Published 1988 by Hearst Marine Books.
Sailboat Electrics Simplified, Don Casey, 1999 International Marine.

Then we need to understand how it is all put together. To do that we need a wiring diagram. Something simple that shows what's hooked up to what. Then we cn start to diagnose if there may be any problem with this set up.

By the way: DC generators are rare these days. Usually it's an Alternator putting out AC, which is rectified to DC. So the measured output may be DC but the device making it is AC. But these are alll generically referred to as "generators".
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Old 28-04-2009, 11:06   #15
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