What size Generator?
- Thread starter mcgann454
- Start date
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Simi 60
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Some of this ought to help with the numbers or it has for me as I still have difficulty with electrickery and loads.
WILL MY GENERATOR POWER MY AIR CONDITIONER and other devices?
https://rvdaily.com.au/will-generator-power-air-conditioner/
Power calculator
https://www.bundupower.co.za/calculator.php
WILL MY GENERATOR POWER MY AIR CONDITIONER and other devices?
https://rvdaily.com.au/will-generator-power-air-conditioner/
Power calculator
https://www.bundupower.co.za/calculator.php
Fletcher500
Guru
I haven’t added it up, but I think the loads and use on our boat will be similar to what you described, maybe a bit less because I am always load shedding when possible.
I originally asked the builder for an 11, but he said that was overkill and would take up more space.
We are getting the same Cummins onan model 9KW that you are calling out.
I know a lot of builders for new boats use Northstar, but I have heard nothing but good about the Cummins onan gen sets. Past boat had a 7.5 and it ran like a champ.
I originally asked the builder for an 11, but he said that was overkill and would take up more space.
We are getting the same Cummins onan model 9KW that you are calling out.
I know a lot of builders for new boats use Northstar, but I have heard nothing but good about the Cummins onan gen sets. Past boat had a 7.5 and it ran like a champ.
FF
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The size hassle comes mostly from starting the air cond unit.
When 2 AC attempt to start at the same time , the amps required get ugly!
At start the AC may require 3x the running load , there are simple solutions , mostly from the RV folks.
One is a timer not always built into the AC that re quires about 3 min between the time the unit shuts down and is allowed to restart. This gives time for the head pressure to bleed down.
Second is a device that only allows one AC unit to start at a time , waiting a couple of min before allowing a second unit to operate.
You might consider using the noisemaker cooling circuit to heat the boats HW heater, as the noisemaker maybe on more than the propulsion engine on a cruise.
Load shedding is almost invisible if done right.
The second air cond going on might turn off an electric water heater , which may not be noticed.
When 2 AC attempt to start at the same time , the amps required get ugly!
At start the AC may require 3x the running load , there are simple solutions , mostly from the RV folks.
One is a timer not always built into the AC that re quires about 3 min between the time the unit shuts down and is allowed to restart. This gives time for the head pressure to bleed down.
Second is a device that only allows one AC unit to start at a time , waiting a couple of min before allowing a second unit to operate.
You might consider using the noisemaker cooling circuit to heat the boats HW heater, as the noisemaker maybe on more than the propulsion engine on a cruise.
Load shedding is almost invisible if done right.
The second air cond going on might turn off an electric water heater , which may not be noticed.
Ski in NC
Technical Guru
AC startup amps will not be an issue with that Onan. That unit uses a heavy flywheel and rotor and a somewhat oversized stator for its output. Lots of stored energy in the rotating inertia. When the AC starts the load might exceed engine output briefly, the stored energy in the rotating masses will take care of it.
Some of the belt drive units use much smaller gen ends that don't have as much reserve capacity.
Also highly unlikely that both AC's will start at exactly the same time.
Some of the belt drive units use much smaller gen ends that don't have as much reserve capacity.
Also highly unlikely that both AC's will start at exactly the same time.
mcgann454
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I did some early research and ended up with a Victron Inverter/Charger that has their powerassist feature. If there is an overload detected, it will slow the battery charger down to lower the power needs and if it is a sudden surge like the AC starting, it will draw from the batteries to compensate and then charge the batteries back up to float.
obthomas
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You can take all of the engineering out of the generator sizing by simply deciding to mach your shore power. If you have one 30 amp 125 volt cable a 4 KW generator is right. If you have two 30 amp 125 volt shore cables, an 8 KW generator is right, If you have one 50 amp 125 volt cable a 6 KW generator is right If you have two 50 amp 125 cables or one 50 amp 250 volt shore cable a 12 KW generator is right.
dhays
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That makes way too much sense. I never thought of it that way. Must be why I have a 50A/125v service and a 6kW generator.
Wolfcreek01
Member
It is possible to install load limiting circuitry which disconnects specific loads when generator current gets high (load shedding) instead of you having to manage every detail yourself. You would need to decide what your highest priority loads are.
