Follow my wiring crazy - inverter and solar install thought

[k9medic]

Thanks Chris. What I was referring to is the fact that with a few exceptions, everything on my boat runs on AC power. If I want anything to work with the generator not running then I have to run it through an inverter.

I'm aware that there is some loss in the conversion but didn't realize that there was a such an amp difference when converting.

My optimas are new as of last year and I'd rather not replace batteries if I don't have to. I know this is asking for champagne on a beer budget.

John, thank you for the additional links for the electrical references. I'll look into the kill a watt too.

I'd hardly consider myself a "noob" when it comes to boating but I will admit that my electrical background is weak when it pertains to the conversions.

Sometimes all it takes is a simple phrase change.

For example, in my professional world, I asked a student of mine to explain the laws of conservation of angular momentum as they relate to a rotary planform. After a few moments of the "deer in the headlights look" I realized that he had no clue what I was asking about but then I said, "tell me about Coriolis effect" and he immediately described the laws of angular momentum.

 

[sunchaser]

There are some inverters that are more efficient than others, but there are no "free lunch" inverters. You will lose in that conversion. The only variable is How Much.
My own inverter steals from 5 to 8 amps just to sit there and be ready to convert DC to AC. While converting, the stealing of DC amps continues, but is harder to measure.

Good points Keith. One way to really save house bank amps when on the hook is to shut down the inverter once 110v loads no longer needed. This assumes of course your refrigeration is 110/12 V.

 

[ranger58sb]

Thanks Chris. What I was referring to is the fact that with a few exceptions, everything on my boat runs on AC power. If I want anything to work with the generator not running then I have to run it through an inverter.

I'm aware that there is some loss in the conversion but didn't realize that there was a such an amp difference when converting.

My optimas are new as of last year and I'd rather not replace batteries if I don't have to. I know this is asking for champagne on a beer budget.

Got it.

Be clear that the "amp difference when converting" is from two factors. One is just the electrical math. W/V = A. Dividing by 120 (AC voltage) versus dividing by 12 (DC voltage) is a difference factor of tenfold.

The other part is about loss during the inversion process. Probably varies a little depending on inverter, but the process is not perfectly efficient.

You could maybe flog the Optimas to partially fund new batteries... but in any case, increasing your initial capacity from 264 Ah to 400-440 Ah (or more) would be a good thing eventually, if you intend to run AC stuff via inverter from your batteries.

-Chris

 

[diver dave]

Right now 1kw is metered at $0.65 in the Bahamas. .

so, I'll point out that generation of your own power is $.41 per kWh using Lucaya diesel and just $.26 per kWh using FL diesel prices.

Now, there may be issues running genset at dockside, not sure about that one.

 

[Dougcole]

I'm really bad at electrical stuff, even David's simple explanation makes my head spin. I have spent a ton of time on my boat in the Bahamas though, so I can comment on that.

Save money on dockside power by turning off the stuff you aren't actively using; notably the Air conditioners and the water heater. Turn on the water heater for an hour or so before you shower, then turn it off. Only run the AC when you are on the boat. Or, if you have more than one AC only use one of them. During the day I close off the sleeping cabins and only run the Salon AC. It makes a surprising difference.

I agree though, you are limited by a boat that is set up for primarily AC power. My brother's Ocean is like that, he has to run his genset 24/7 if he isn't at the dock. It's not a good set up for cruising.

 

[DavidM]

Let me try to close out this very confusing thread for the OP.

He has an almost 100% AC powered boat and is paying a high price for shore power in the Bahamas so he runs his genset all of the time. His OP was based on the premise that he could use solar power through an inverter to power his AC loads but he was not aware that DC amps supplying an inverter are about 12 times the AC amps (including inverter losses).

He understands that now and of course that it would be impossible to power large AC loads with solar power through an inverter. It looked ok when he thought the amps were the same, but not so good at 12:1.

And as a side note- It probably costs him about as much to produce power from his genset as to pay the marina's high $.65/kw charge. Not too surprising because the marina is probably producing its own power with a diesel genset, albeit probably a more efficient one than his.

Bottom line- plug into the shore power, but reduce loads as much as possible to save money.

David

 

[diver dave]

And as a side note- It probably costs him about as much to produce power from his genset as to pay the marina's high $.65/kw charge. Not too surprising because the marina is probably producing its own power with a diesel genset, albeit probably a more efficient one than his.

Bottom line- plug into the shore power, but reduce loads as much as possible to save money.

David

GBPC utility charges close to $.22 per kW-h. The smaller islands are closer to $.32. These are going to be oil fired boilers at the gen site. The really small islands (cat cay), I've heard are close to $.95/kW-h. They are diesel, with not much efficiency improvements over your northernlights, etc.

So, if the Lucaya marina is at $.65, you can see a bit of a markup there at close to 3X.

 

[k9medic]

Let me try to close out this very confusing thread for the OP.

He has an almost 100% AC powered boat and is paying a high price for shore power in the Bahamas so he runs his genset all of the time. His OP was based on the premise that he could use solar power through an inverter to power his AC loads but he was not aware that DC amps supplying an inverter are about 12 times the AC amps (including inverter losses).

He understands that now and of course that it would be impossible to power large AC loads with solar power through an inverter. It looked ok when he thought the amps were the same, but not so good at 12:1.

And as a side note- It probably costs him about as much to produce power from his genset as to pay the marina's high $.65/kw charge. Not too surprising because the marina is probably producing its own power with a diesel genset, albeit probably a more efficient one than his.

Bottom line- plug into the shore power, but reduce loads as much as possible to save money.

David

Excellent summary David. Thank you.

 

[dhays]

Good points Keith. One way to really save house bank amps when on the hook is to shut down the inverter once 110v loads no longer needed. This assumes of course your refrigeration is 110/12 V.

I was rereading this thread (very helpful btw, I appreciate the OP asking the questions) and saw Keith's comment and your response. It was kind of an eye opener.

I know that inverters are pretty inefficient when converting AC to DC. However, I never really thought about the parasitic draw while they are just sitting there waiting for work to do. I leave my inverter on most of the time as there always seem to be AC work to do on the boat, anything from the sound system (120v unfortunately) to charging electronics to making coffee. However, when we are out for a while, I think I will start to make a habit of shutting down the inverter unless I really need to use it.

Thanks for the clarity guys.