Microwave or Battery?

[Johnatkatys]

Went out for a picnic last week, and because of the cool weather we decided to bring soup. When we got tied up to a public mooring buoy, I shut down the engine and we attempted to warm the soup in the microwave. The microwave would run a few seconds (10) and then shut off. I started the engine and then it ran fine.
This is a 2017 R25SC, new to me, and batteries are AGM type, probably original, so 6 years old.
My question: Is this due to the funky sine wave, the microwave, or the batteries?

 

[Red Raven]

The microwave creates a huge amp draw via the inverter. Can be near 100amps from the battery. This level of current draw will draw down the voltage of even a relatively good battery. Not surprising a 6 year old battery cannot handle the draw without the engine running. We pretty much always run the engine when running the microwave off the inverter for this reason.

Probably time to replace your house batteries anyway or at least get them load tested.

Curt

 

[ALICE J]

I would suspect batteries. Microwaves draw a lot of power when used on battery only mode, but you may have had other other items connected to via the inverter which further sucked on the older batteries. Check all the batteries with a load tester to determine their capacities. If you are always hooked to shore power when your boat is in its slip, you probably never noticed the declining batteries. A good battery monitor installed properly will be a good investment to warn of creeping problems. In the future you may want to combine the thruster battery to the house battery to give you more amps for the microwave and other power users. On my previous Ranger I connected all the batteries into one power bank and watched the battery monitor like a hawk. :geek: My system worked well for over eight years and 2500 engine hours and 50,000 road miles. (Detractors my wax and wane eloquently on my battery set up, but proof of the pudding lies in its delicious fruits that gave lots of energy.)

 

[Johnatkatys]

I would suspect batteries. Microwaves draw a lot of power when used on battery only mode, but you may have had other other items connected to via the inverter which further sucked on the older batteries. Check all the batteries with a load tester to determine their capacities. If you are always hooked to shore power when your boat is in its slip, you probably never noticed the declining batteries. A good battery monitor installed properly will be a good investment to warn of creeping problems. In the future you may want to combine the thruster battery to the house battery to give you more amps for the microwave and other power users. On my previous Ranger I connected all the batteries into one power bank and watched the battery monitor like a hawk. :geek: My system worked well for over eight years and 2500 engine hours and 50,000 road miles. (Detractors my wax and wane eloquently on my battery set up, but proof of the pudding lies in its delicious fruits that gave lots of energy.)

Are you suggesting using the "Parallel" switch so all 6 batteries are available?
Red Raven notes the draw could be 100A! Yikes, I had not thought of that. Definitely need a good battery(s).

 

[glider4]

This is my opinion based on 9 years of cruising in FM boats.
First, I never use the microwave unless on shore power. On the hook or mooring buoy and using the inverter to power the microwave, even with the engine running, is a major draw on the house batteries. The microwave is such an high current draw that you are rapidly draining the house battery bank even with the engine running at idle.
My practice is that the Parallel switch is to be used to save your butt if the engine battery dies. And that’s it!
If you use the Parallel on a regular basis and drain the house bank with the Parallel on, then you have drained your engine battery as well. You might be able to jump the engine battery using the thruster battery to start the engine. Maybe. Otherwise you would need to get a tow boat out to give you a jump start. Either way, not a good practice in my book.
In our boat the Admiral says, “If it has a 110 volt plug, use it only when plugged in to shore power.” The microwave and coffee maker are both 110 volt.
I’d suggest new batteries. Many, many threads on this site regarding best batteries to buy to replace yours.
If you need more power add one or two more AGM batteries to the house bank. Heat the soup up using the stovetop’s propane burners. If you only have an electric/alcohol cooktop I get a camping butane cooktop for cooking when off shore power. The butane cooktops are inexpensive, small, efficient and easy to use.
If you haven’t watched this video from FM, I highly recommend doing so:
https://youtu.be/Uj_am-ecSt4?si=SJbFxeFSHG7EMdb4

 

[Martin610]

If we are talking about the Cuisinart convention/microwave that FM often uses that is definitely a large power draw. I can't run that off the inverter either.

Having a battery monitor on the boat really helps with power management.

My Cutwater 28 actually has two microwaves. The smaller Haier micro in the forward cabin draws about 1000 watts. I have a small coffee pot that takes about 700 watts. We added a NuWave portable induction burner that I can dial down to 900 watts. All doable with the inverter while on the hook. Solar panel helps too.

To check out small appliances without a battery monitor a device like the Kill A Watt meter https://www.amazon.com/P3-International ... 174&sr=8-6 is very helpful.

The FM video on power management is an excellent reference.

-martin610

 

[ALICE J]

I did not use the Parallel Switch, but directly connected all batteries to one battery switch to turn off all current. I should add that I had a Mase generator that had an entirely separate battery for starting the generator, (a Honda generator would also work) if all four "house" batteries went to sleep :cry: . The generator was connected to the charger/inverter. My four batteries had a gross Ampere of about 400A, usable maybe 200--250 amps. I had installed a Blue Seas Multi meter so could monitor power on my electrical system, giving me input and output, amps, volts, and watts.

If you are not familiar with 12 volt systems, have a qualified marine technician do the work.

 

[mlanger]

It sounds like a battery life issue. I replaced mine at about 3 1/2 years, about 1/2 year after I bought the boat used after having some issues with the engine battery. (Unrelated to your problem.)

I anchor out a lot and I use the microwave and some other AC current appliances, like a coffee maker, a few times a day. My new (now 1 year old) house batteries do fine. I'm currently at anchor and have been here for 3 nights. This morning the batteries were down to 11.5v so I ran the engine for an hour (no generator on board) and got them up to 12.2v.

Your house batteries and inverter SHOULD be able to handle the load of the microwave, as long as you don't run it or other high draw AC current devices a lot. Practice power conservation. If I know I'll be at anchor just one day, I use whatever I want as much as I want and do fine. But if I know I'll be at anchor for 2 or more days and there isn't a lot of sun in the forecast, I'm a lot more conservative on how I use power.