Two Generators

[BandB]

Why? What?

Wifey B: Not what? Why? Why the "Why? What?"? Who?

 

[psneeld]

Sorry, read it backwards that they should run all the time.


They certainly can be wired either way still...but I like the pump shutting down when the AC stops for the night when the evening temps have dropped enough.


The fan keeps going circulating the air which keeps things comfy...but many hours of the pump not pumping is all that time is good on many levels.


The AC system I just tore out had the pump wired totally separate...didn't like it rigged that way but it does have a few advantages for troubleshooting and rigging the pump for other emergencies.

 

[SCOTTEDAVIS]

For priming purposes I cut the pump wires and added a male and female plug in line so when I need the pump to run for service I just unplug the connection and plug into the outlet in the AC room. Easy and simple.

 

[Larry M]

... With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position...

That's how we installed ours. We have 2-16K BTU Dometic Turbo units running from one pump with no switch box or relays. The pumps gets turned on when one or both systems go on for either heat or cooling. Simple is good.

 

[N4712]

Our pump comes on when any of the 5 AC's come on. That's powered up, with the flan just blowing too.

 

[ksanders]

There is also another thing to consider...

If you have say 1500 watts of Air Conditioning that runs at for discussion sake a 33% duty cycle on a typical evening you might be actually better off running that on an inverter.

Lets do some math regarding that. 1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

With no other loads applied you could run all night long and not have to run your generator if you had around 800 amp hours of battery.

If you had a higher load or higher duty cycle you could use a State Of Charge meter and tie that to an auto start on your generator. Then when the batteries got low the generator would automatically start up, charge your batteries, then turn itself off.

You could even use a system like that to keep your batteries charged while you were anchor'd off and playing on shore all day, or stuck on a mooring bouy and off the boat for a few days exploring.

""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


Bob

You're not missing anything. The problem was with both terminology and math. What you wrote is correct

Richard

Actually my math is accurate. Terminology is of course open to interpretation.

1500 watts /12 volts = 125 amps. This would mean at a 100% duty cycle the drain would be 125 amp hours per hour, but I did not say 100% duty cycle I said 1/3 or 33% duty cycle.

so 125 amp hours /3 to account for the duty cycle is 41 amp hours per hour

So, as I indicated if you had an 800 amp hour bank you'd be entirely safe to run this load overnight. Thats all I said and that is accurate.

I did not want to enter into the discussion variables like how far down you should draw a battery bank, or inverter inefficiency, or other loads, or allot of other things. If that made things a bit confusing, my apologies.

The point was and is that it can be beneficial to run some heavier loads on your inverter as opposed to having to buy a second small generator. I was also trying to point out something not many boaters are aware of or have, that being automatic starting on their generator.

 

[BobH]

Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.

On our last boat, 1984 sailboat, the pump only ran when either A/C compressor came on. How much more 'old school' is there?

Bob

 

[psneeld]

Back into the 80s for sure...they could have been wired either way...

For boats with more than one compressor....it was easier and cheaper to just turn on the pump separately...no extra relay setup.

 

[Ski in NC]

My ac pump has a relay to start with either unit. I put an extra switch next to panel that bypasses the relay and starts the pump. Helpful for priming and for thawing a frosted unit. Can run the pump without compressors running too.

 

[kulas44]

My gen has a Magnum Energy AGS wired directly into the ME2000 inverters. It monitors batt. voltage and is set to come on at 12.4 volts. It also monitors interior temp and starts the gen at a preset temperature. The AC is set to come on at a slightly higher temp. It has a few other bells and whistles that I dont use.

 

[ksanders]

my gen has a magnum energy ags wired directly into the me2000 inverters. It monitors batt. Voltage and is set to come on at 12.4 volts. It also monitors interior temp and starts the gen at a preset temperature. The ac is set to come on at a slightly higher temp. It has a few other bells and whistles that i dont use.

very nice!!!!!

 

[ktdtx]

oh my!
so much to learn....I hope the lessons are relatively inexpensive.

 

[Britannia]

Actually my math is accurate. Terminology is of course open to interpretation.
...

Kevin,

BobH was actually quoting FF (post #19) and not you. It was his math and terminology that was off and not yours. It was a bit confusing since he didn't actually attribute the quote.

Richard

 

[stornoway7]

Show us your genny(s) !
Back to the dual genny thing.
We have two Onans,originally a 25kv and 12kv.
The small one was replaced at about 12000 hours with a 17 kv Onan.
The 24kv unit currently has about 6600 hours on it.
We usually only run the larger genny to cover high AC loads (8 units !) it's great peace of mind knowing you have a backup.Nothing wrecks the day like no power.

I love my new genny (don't tell my wife please,she already wonders why I spend so much time on board.)It so quiet that even though it's under the galley floor you can hardly tell it's running,I keep forgetting to turn it off.
We are a galley down boat, so the engine room is aft of the galley ,on the same level.The 25kv unit us under the cover below the electrical panel.

 

[FF]

"Lets do some math regarding that. 1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank."

Using a 1/3 duty cycle the discharge would be perhaps 1/3 of 9 hours or 3 hours. (ez math)

3 hours at 125A is 450 AH , so a 1000AH bank would be down at least 50%

Remember the very high discharge rate , flattens the bank faster than the 20 hour rate..

So at least 500ah would need to be returned , plus about 15% to "push it in".

How goes a typical noisemaker put almost 600AH in a battery bank during the day?

1/10 of 1000AH bank size (C-10 charge rate) would require 100 amps for at least 6 or 7 hours .

Fine if the AC is required all the time there is sunshine .

 

[Bay Pelican]

A few weeks ago I was anchored out and left my water heater (1200W) turned on while I was on my inverter. I had used up about 300Ah of battery by the next morning!

Richard

Electric panel can easily be wired so that the chargers/water heater and AC cannot be operated off of the inverter. In my case with AC/DC refrigeration I have also wired the panel so the refrigeration is not run off the inverter.

Basically the inverter feeds a breaker on the panel and the desired AC appliances are fed from that breaker - using their own breakers of course.

 

[Britannia]

Electric panel can easily be wired so that the chargers/water heater and AC cannot be operated off of the inverter. In my case with AC/DC refrigeration I have also wired the panel so the refrigeration is not run off the inverter.

Basically the inverter feeds a breaker on the panel and the desired AC appliances are fed from that breaker - using their own breakers of course.

Yes - there are some AC loads on the boat that aren't energized by the inverter. I found it amusing that the water heater was one of the loads that is.

 

[BobH]

I put in a separate breaker panel for just inverter loads. Powers the galley outlets, head outlets (hair driers), TV/entertainment outlets and outlet on the flybridge for keeping the tablet charged.


Bob

 

[psneeld]

I put in a separate breaker panel for just inverter loads. Powers the galley outlets, head outlets (hair driers), TV/entertainment outlets and outlet on the flybridge for keeping the tablet charged.


Bob

...bought new electrical panels this year...specified one separate 6 breaker panel just for outlets...which is all I really need or want on the inverter load....

easy to deal with...eventually if I decide to add an appliance or two..I can always add them in a circuit or double up outlets and replug-in....

 

[N4712]

That's how our boat is also setup, a 120V non inverter service and a 120V Inverter service panel. Along with the 240V Ships panel, and 240V HVAC panel. Only thing not on the inverter is the water maker. But it doesn't matter as the inverter is a pas through when the gennys on or on shore power.

 

[SCOTTEDAVIS]

"

How goes a typical noisemaker put almost 600AH in a battery bank during the day?

1/10 of 1000AH bank size (C-10 charge rate) would require 100 amps for at least 6 or 7 hours .

Fine if the AC is required all the time there is sunshine .

If you are going to run the main have a high amp alt putting out 75a for say 6.5 hours running (or twins with same putting out 40 or so amps each)

Most 3000watt inverters have 100amp chargers built in and already have large cables to provide the current with ease, an 8Kw gen-set should handle that with ease and still provide power for running limited system power (AC but not stove and hot water as an example).

Battery size would dictate battery heating and that would limit charge rate, I would want large Rolls L-16 deep cycles as found on electric fork lifts for a bank in this situation.

You are correct regarding the effect of high/fast rate or discharge being greater then a lower/longer depleting the battery at a greater rate then the math would suggest this is called the Peukert effect.

The scenario suggested would not be very satisfactory in the long term I would suspect.

 

[bayview]

How are two gen sets electrically isolated?

 

[Britannia]

How are two gen sets electrically isolated?

On Stillwater I have a big rotary switch to select the AC source. It has 4 settings, Shore 120V, Shore 240V, 8kW Gen, 20kW Gen. Each source also has its own main breaker on the panel.

Richard