Understanding your Boat's Electrical Capacity

[Hampton]

This started as a reply to a particular thread, but I thought it would be helpful to a number of people who were not interested in that thread. It's about running a bunch of AC appliances and possibly over-loading your circuits.

The microwave draws quite a bit. If we have it on at the same time as a couple of other items, the amperage goes over the 30 amp rating of the circuit, and it trips. You can see it on the meter on the A/C panel. High amp items include the micro, water heater, toaster, space heater, hair dryer, and curling iron. These are all obvious. Usually any two are fine, but the micro and water heater is a combo we avoid.

All of those are on one circuit. When out on the hook with the genny, you have another issue with which to contend - the other circuit. It holds the A/C and a 2-burner stove. Run one or two burners, the A/C, and a couple of items above such as a toaster and water heater, and you are pushing the limits of the generator. We are really careful with that because of obvious reasons (safety, damage), but also because it's a pain to have to crawl into the ER to reset the switch on the genny.

Watts are amps multiplied times volts. 5KW genny divided by 110 V AC leaves 45 amps, or only 75% of your shore power rating (2 X 30 amp circuits on our boat).

http://www.powerstream.com/Amps-Watts.htm

 

[carterchapman]

John,

You are right on - when we have our ceramic heater on in the cockpit, we can't add the microwave - totals 35 amps and trips the elec panel breaker after about 30 seconds. I've done this twice - once, the first time it happened, and the second time watching the panel and verifying what happened. Now the Admiral has to "inform" me (never has to ask "permission") when she is going to use the microwave. I'm like you - don't want to stress the circuits, but it sure proved the CB is working correctly!

 

[320Bob]

Unlike you 340 Starships my 320 has a single 30 amp service but a 5KW generator. So based upon your numbers I have more amps with the generator than shore power but am limited to 30 amps because of the breaker. So can I run the coffee maker(resistance heating device) and the A/C at the same time with or without the water heater?

 

[Hampton]

Unlike you 340 Starships my 320 has a single 30 amp service but a 5KW generator. So based upon your numbers I have more amps with the generator than shore power but am limited to 30 amps because of the breaker. So can I run the coffee maker(resistance heating device) and the A/C at the same time with or without the water heater?

You have a greater percentage of power available by the genny than we do. You have 100% of 30 amps - you are not limited by your genny. We have 75% of 60 amps - our limitation is the genny. You are limited to your single 30 amp circuit. You won't be able to run as many items as we can either at the dock or on the hook, but you don't have to change your habits when using your genny.

Just check the meter next time you turn on a high-load item, and make a mental note or a logbook entry of how much each item draws, then don't exceed 30 amps and you'll be fine.

 

[topgun1185]

SR makes all there newer boat so that all application can be running (water heater, air, microwave) can all be on and working. Certainly if you load any outlet with a large draw beyond the circuit breaker limit, the circuit breaker trips correctly. SR's can be run on shore power or genny with everthing on. They are designed that way. You don't have to be woried about what's on. Just rember the outlets have limits, as they do in your home. These limits are for safety factors which is part of wire size and its capacity to carry the load.

 

[hack4alivin]

SR makes all there newer boat so that all application can be running (water heater, air, microwave) can all be on and working. Certainly if you load any outlet with a large draw beyond the circuit breaker limit, the circuit breaker trips correctly. SR's can be run on shore power or genny with everthing on. They are designed that way. You don't have to be woried about what's on. Just rember the outlets have limits, as they do in your home. These limits are for safety factors which is part of wire size and its capacity to carry the load.

Correct and I agree, but I have on occasion tripped breakers on my boat. Especially in the morning with the stove on, or the microwave, heat or air, hot water heater, and so on and so on. But having a bit of electrical background I will just reset the breaker and turn the hot water heater off while I’m cooking breakfast. Drop the load and continue, no big deal.

 

[topgun1185]

Correct and I agree, but I have on occasion tripped breakers on my boat. Especially in the morning with the stove on, or the microwave, heat or air, hot water heater, and so on and so on. But having a bit of electrical background I will just reset the breaker and turn the hot water heater off while I’m cooking breakfast. Drop the load and continue, no big deal.

While I certainly belive you this is contrary to my experience unless I have to turn on more stuff. Also at the SR yatch expo in florida I posed this exact question to a SR engineer I he said run everything no problem. I really going to try an turn every thing on. No matter what all great info.

 

[katricol]

John..nice post. Now I know my 8kw genset supplies73 amps...more than my 2 30 amp shore cords !!!!thanks Ric

 

[tobnpr]

While I certainly belive you this is contrary to my experience unless I have to turn on more stuff. Also at the SR yatch expo in florida I posed this exact question to a SR engineer I he said run everything no problem. I really going to try an turn every thing on. No matter what all great info.

There are two separate issues here.
One being discussed is genset vs. shorepower to the main panel. So yes, my 8kw gen can provide every bit of the 60 amps available at the panel.

However, on mine and many other boats- this doesn't mean that you can "turn everything on". Even though I've got 60 amps available, it's split into two sub-panels that are each limited to 30 amps.
As an example... the hot water heater, microwave, and forward ac unit are on the same 30 amp circuit (and a few other things as well). The micro and the water heater are both 1500 watts- pushing the 30 amp limit. Kick in the air conditioner, and the breaker will trip.

 

[bluebelly]

SR makes all there newer boat so that all application can be running (water heater, air, microwave) can all be on and working. Certainly if you load any outlet with a large draw beyond the circuit breaker limit, the circuit breaker trips correctly. SR's can be run on shore power or genny with everthing on. They are designed that way. You don't have to be woried about what's on. Just rember the outlets have limits, as they do in your home. These limits are for safety factors which is part of wire size and its capacity to carry the load.

That all newer boats are made this way is too much of a generalization. The 40 motoryacht and 40 sundancer and 44 sundancer CANNOT run all appliances at full output without tripping the circuit breakers. On the boats I mention and maybe a few others I have not had experience with, the operation of the water heater, stove, microwave, bow thruster charger, battery charger, and all three heat/ac units will draw more than 30 amps on one side of the dual 30 amp service. The stove and water heater alone draw 28 amps!!! The two battery chargers can draw a max of 13 amps combined. The three ac units pull about 30 amps in a/c mode and about 36 amps in heat mode. The three refrigerators pull about 2 amps. Oh, and the microwave, 10 amps for that. As you can see it is real easy to exceed the capacity and trip breakers in a dual 30 amp service.

 

[Daddubo]

This is a very important post, something that also needs to be stressed is checking the tightness of the connections at the breaker panels and at the outlets. More with salt water than fresh because salt will deteriorate copper, a loose connection will generate heat and start a fire, most of the fires on big ships are due to electrical failure at the panel, there is a lot of vibration on a boat to loosen things up.

In the office building I maintain we do a thermal scan every year (it takes an actual picture of the different temperatures and can pin point a hot spot) to look for any heat build up you can do basically the same thing with a laser thermometer under full load.

The more times a breaker trips the weaker it gets so if you had one tripping a lot or having trouble keeping one set it could mean it is worn out. If you have access to an amp probe you can amp each circuit and see what each appliance is drawing.

A lot of people do not know the difference between the ground and and a neutral, the neutral is part of the Circuit and the ground is not so you can get electrocuted from the natural if it is not connected properly and touch it. I have opened junction boxes and the wire nut would be burned off because it wasn't tight enough. The Ground gives the current some where to go besides through you.

It is also a good Idea to use GFI outlet's on your AC circuit's that will guarantee you won't get shocked, it reads Milli amps and will trip before you get zapped, Also at the dock your grounding is only as good as the Marinas

 

[boughtabouy]

Thanks for all the great info, guys. Does anyone happen to have an idea how much fuel a 7.5KW (gas) burns? I know it's a general question that depends on load, but is there a general range. I'm thinking about 1-2 GPH, based on our experience cooking thanksgiving dinner on the hook...

 

[CSR_Admin]

Thanks for all the great info, guys. Does anyone happen to have an idea how much fuel a 7.5KW (gas) burns? I know it's a general question that depends on load, but is there a general range. I'm thinking about 1-2 GPH, based on our experience cooking thanksgiving dinner on the hook...

Hampton was checking CSR from the cockpit of his Eagle over the Gulf :smt024and sent me this message to post here because he could not log in from the plane..... or his desk or whatever -

"gen will use about .5 - 1 gph as a wag depending on
load. He should try to run it loaded up to prevent fouling the plugs."

 

[Hampton]

I'm home, and back able to post.

340 Electrical:
Refrig's - Less than 1 Amp
Batt Chg - 1 Amp (trickle?)
Hair Dryer - 2 - 10 amps depending on setting
Space Heater - 4 - 10 amps depending on setting
Water Heater - 10 amps
A/C - 10 amps (heat mode)
Microwave - 14 amps

That's why the micro is our big issue. We generally turn off the water heater and/or the cockpit space heater prior to turning on the microwave.

WB 7.5 max fuel consumption 1.2 gph http://www.westerbeke.com/productBrochures/7_bcga.pdf

Diesel gensets
http://www.victronenergy.com/upload/documents/VE_Marine_generator_test_RVA_07-jan-2008.pdf

 

[boughtabouy]

Thanks, found this:

http://www.kohlerpower.com/onlinecatalog/pdf/g2098.pdf

Kohler 7.3 is .96 GPH at 100% load.

Kevin

 

[Hampton]

Hampton was checking CSR from the cockpit of his Eagle over the Gulf :smt024and sent me this message to post here because he could not log in from the plane..... or his desk or whatever -

"gen will use about .5 - 1 gph as a wag depending on
load. He should try to run it loaded up to prevent fouling the plugs."

Thanks, Jim!

 

[mawyatt]

Hampton was checking CSR from the cockpit of his Eagle over the Gulf :smt024and sent me this message to post here because he could not log in from the plane..... or his desk or whatever -

"gen will use about .5 - 1 gph as a wag depending on
load. He should try to run it loaded up to prevent fouling the plugs."

John, texting while flying an F16? Didn't think that was allowed :grin:

 

[Hampton]

John, texting while flying an F16? Didn't think that was allowed :grin:

Oh, that's right. I'm only supposed to do that when I'm flying passengers around : )

On a less technological note, my Father-iin-law called us from his car phone as he was traveling across the desert to Vegas in the late 80's - very impressive. Not to be out-done, I was in a T-38 flying North along the Eastern Seaboard when I called base operations on the UHF radio and asked for a phone patch to the operator at Castle, Merced. He then dialed the local number to my Father-in-law's house and we carried on a slightly delayed, slighly uncomfortable, but mostly cordial conversation for about the next 2 minutes. 1-upsmanship - not always a winning proposition.

 

[quality time]

I apologize if this is off topic, but it is close.

How many amps do you guys consider "loading" the generator? I've heard that you should run them at atleast 75% of output. If that's the case then I should be pulling 45 amps on my 7.6KW generator to load it properly. I struggle to keep a steady 30 amps total between the two legs during general use. Any thoughts or am I figuring something out wrong?:huh:

 

[Hampton]

75% would be tough. I make sure that I either have the A/C (and it's running) or the water heater, or the space heater, and all of the little stuff on. Some nights, the A/C goes on and off and only the little stuff is on. It has worked for 3 years that way. Just don't run it completely at idle for extended periods, and use it often.

Little stuff = battery charger, fridges, lights... Not the big heavy stuff.