Battery concerns

[Johnandheather]

Hi
I’m new to having a boat with an inverter, I have a xantrex 2000 watt. My question has to do with battery capacity, I have a new norcold 7 cubic ft fridge and a 12 gallon water heater that a few years old. My boat has 6- 6 volt and 2 12 volt, we are heading out for our first weekend without shore power and was thinking should I turn off the hot water heater to save power ? Or would it take more power to heat it up from cold than to maintain a temp ? Or am I worrying about the wrong stuff.
Thanks john

 

[ScottC]

Yes. Shut the hot water heater off when not needed. It’s a real energy hog! Do you not have a heat exchanger to heat the water when your engine is running? I have a 22 liter electric heater and it heats up to scalding temp in about 15-20 mins. It stays hot for hours after I cut the electric to it. You might find that with the water heater on, your inverter won’t be able to handle anything else. Experiment and monitor closely as you learn.

 

[Shifty]

Yes, turn off the water heater. Are you sure it's on the inverter? Most water heaters require shore or generator power. And ditto to what ScottC said - most boats have a fresh water heat exchanger for the engine coolant which provides hot water under way. Also, in summer weather, the water in the hot water tank will stay warm for hours.

 

[DavidM]

Many inverters are installed cheaply and are hooked up to supply ALL power to the boat even though that might kill the batteries in an hour or so. The better way is to split the power between shore power/inverter sourced and shore power only sourced. This was discussed probably ad nauseam on a recent thread.

In my limited experience, newish trawlers rarely are delivered with the coolant system plumbed to the water heater. I guess most customers don't care. OTOH I have never seen a sailboat that wasn't plumbed.

It isn't difficult to plumb your engine to heat the hot water. It just takes some 3/4" heater hose and fittings. If you do a lot of weekend anchoring out or take long cruises and avoid marinas it is definitely worth doing.

David

 

[Swfla]

Something else to keep in mind with an inverter. If you drain your batteries down more than 50% multiple times, you affect the longevity of the batteries. Doing the math for what your items draw will give you an idea of capacity. A rule of thumb is 24 hours for 210 amps. If your batteries are healthy, 6-6v batteries will do nicely for a weekend if fully charged. The 2000 watt inverter is a reasonable size to handle most needs as well. But not a water heater without engine heat to be the main source.

 

[dhays]

Trying to heat water with your batteries will drain them quickly. Every boat I've owned has had a heat exchanger with the engine cooling system so that it heats the hot water tank. So, take showers in the evening before bed after you have been going to a location.



You didn't mention if you have any way of charging your batteries at anchor. Solar is great but doubtful that it would provide enough to heat water. Genset is great and if we haven't run the boat we use the genset AC to heat the water directly. In fact, in my boat the inverter won't heat the water. It would just kill the batteries.


If the only way to recharge at anchor is to run the engine, and your engine cooling system will heat the water, then you will accomplish both at the same time.


Anyway, a lot we don't know about your situation but the bottom line would be don't count on heating water via your inverter and battery bank.

 

[Bacchus]

I could hook up water heater to main eng but dont/wont bother. A short gen run will heat water and charge battys. Many folks afraid of running gen but more gens are hurt by not running or running with light loads (charger only) so heating water not practical or desirable from inverter and a good way to put some load on gen while charging battys.
A good batty monitor is a worthwhile
Investment IMO if you spend much time on the hook.

 

[dhays]

I could hook up water heater to main eng but dont/wont bother. A short gen run will heat water and charge battys. Many folks afraid of running gen but more gens are hurt by not running or running with light loads (charger only) so heating water not practical or desirable from inverter and a good way to put some load on gen while charging battys.
A good batty monitor is a worthwhile
Investment IMO if you spend much time on the hook.

Great point. As the demand from the battery charger drops, I flip on the hot water tank to increase the load on the generator. I also try to do it when we are normally using electric items such as the microwave or coffee maker.

 

[Comodave]

Welcome aboard. You have gotten good advice already so I won’t repeat it. Look at your water heater and see how many hoses go in and out of it. If there are only 2 hoses then you can’t heat water with your engine. If there are 4 hoses then you should be able to heat the water while your main engine is running. 2 hoses would be for the cold water inlet and the hot water outlet. The other 2 would be for hot water from the engine going into the water heater and through the heat exchanger in the water heater. The other hose would be to return the water to the engine. If you have a closed cooling system on your engine then engine coolant would be going to and from the water heater instead of water.

 

[DrissZougari]

First, welcome aboard.
Do your homework and find out how your batteries are configured first before you go out, and the batteries main switches are your best friend to manage your batteries.
Yes, definitely turn off the inverter (will shutoff the heater) and reduce the fridge temperature setting.
Enjoy your new boat

 

[Peter B]

Yes, indeed, welcome to TF, but to enhance exposure, I have moved your post & thread from Welcome Mat to the electrical area.

 

[ranger58sb]

Hi
I’m new to having a boat with an inverter, I have a xantrex 2000 watt. My question has to do with battery capacity, I have a new norcold 7 cubic ft fridge and a 12 gallon water heater that a few years old. My boat has 6- 6 volt and 2 12 volt, we are heading out for our first weekend without shore power and was thinking should I turn off the hot water heater to save power ? Or would it take more power to heat it up from cold than to maintain a temp ? Or am I worrying about the wrong stuff.

You should first determine exactly what appliances, outlets, etc. the inverter feeds. For example it may or may not power a microwave/convection oven, an electric cooktop, a water heater, TV, maybe fridges, etc. Map all that...

And then you'll know better what to turn off so you don't hose your batteries... and what you can actually use underway or at anchor, etc.

-Chris

 

[ScottC]

I had one other thought on this topic that may be of use...

I mentioned in my earlier post that it takes 15-20 minutes on electric for my heater to get to scalding hot. What I didn't mention is that it takes only 7-10 minutes to get to "usably hot".

Years ago, just after I bought my boat, I was regularly almost getting burned by the temperature of the water. I didn't want the water in the tank to be so hot for safety reasons. It was also wasting energy to make it this hot when I was running on a power source other than shore power.

I unscrewed the cover of the heating element in my water heater and found a tiny thermostat wheel on the heating element. I turned it all the way down to the lowest setting. This worked out well, as the water is still plenty hot and it uses significantly less energy. I have uploaded a picture below to illustrate. I'm sure your water heater looks much different than mine, but the element will most likely be similar -- and hopefully, it will have a thermostat on it. Click on the picture to enlarge it.


Good luck learning all there is to learn about your new boat!

 

[Johnandheather]

Thanks for all the info, I’m not sure if the water heater is wired through the inverter, I will need to check that out. So far I’ve found the inverter is powering the fridge , microwave, 2 halogen lights and a couple outlets.

 

[CharlieJ]

Here is the rule of thumb for 12VDC and 120VAC boats (in a perfect world): The inverter is a 10x machine; i.e., a 5AAC load will take 50ADC to run it.

 

[FF]

For folks that prefer to anchor out, next time you buy a generator purchase one that can have an alternator mounted on the front.

HW heaters are fairly cheap, so a second unit plumbed into the generator cooling circuit would be simple.

Heating the ocean with the genset circ. water doesn't make a load of sense.

 

[FoxtrotCharlie]

Welcome aboard and good luck. When we bought our boat it had a dead (shorted out) Xantrex 2000w inverter. Through it away and installed a 3000w pure sine wave inverter (stand alone) connected to three circuits only - refrig, ice maker and 110 outlets. Has remote control at lower helm. Works great - note, water heater is not on inverter.