Wattage Usage on a 30' sailboat

[cards26]

I had a discussion with a guy that designs marine systems, and he hit me with a command that I still do not fully understand.

He goes, "you don't want all that DC going through your boat, USE YOUR GENERATOR!" Says it to me just like that.

I wished I probed more, because what he said is really nagging me at the back of my mind. I've seen plenty of threads here on adding service batteries, solar, and wind, but I've never seen a thread on 'too much' DC as a result. Also, how much is too much DC?

Can anyone figure out what he's talking about, or should I just forget it?

[newhaul]

Sounds like lots of hookum to me forget it. Heck all I have on my boat is DC. Never hook up to shore power .

[cards26]

Originally Posted by newhaul

Sounds like lots of hookum to me forget it. Heck all I have on my boat is DC. Never hook up to shore power .

He seemed to be suggesting that I wanted 'too many' service batteries. He said he would design it that way, but he doesn't recommend it; he wanted less batteries, and then use the generator more often to charge them. I really don't think I'm overdoing it.

[valhalla360]

Originally Posted by cards26

He seemed to be suggesting that I wanted 'too many' service batteries. He said he would design it that way, but he doesn't recommend it; he wanted less batteries, and then use the generator more often to charge them. I really don't think I'm overdoing it.

Define: guy who designs marine systems

There are a lot of guys who will install stuff without really knowing what they are doing. If they buyer doesn't know, they do what the guy tells them to do.

Unless he can come up with a clear cut reason, I would ignore it. Pretty much all boats have a DC system, so you will have DC running thru your boat and solar is cheap enough that it doesn't make sense to run a generator to charge the batteries. Unless you are trying to run the air/con or some other huge load, it makes no sense based on what you told us of the conversation (of course, there may be more info you haven't shared that might create a reason but unlikely).

[barnakiel]

Originally Posted by cards26

Also, how much is too much DC?

It depends.

If you can generate at any time (example: a fuel cell) then you simply generate what you need when you need. Anything else will then be 'too much'.

Now think of a more real case when there is a battery. You want to make some overhead to allow for charge/discharge losses. Then think about a 100% solar boat that does not produce juice by night and may be reduced in storage technology by day. Etc.

You will soon come to the vision that 'too much' starts where your charging/battery choices combination could generate say a regular excess of juice. Then you just buy a watermaker and run it on the excess day. Or else you can sell off the odd solar panel. Your choice.

In most cruising scenarios 'too much' is hardly ever a problem. Not enough is a far more common problem of consuming too much while generating too little.

b.

[barnakiel]

Lithium batteries are fine and I am sure over time will become a norm. Today the price may still be the limit for some.

I have also found some that cannot be used in series or parallel. Some require special chargers, etc. These are not limitations if you build from scratch but they are if you already run a lead-acid based system. Another challenge is finding a replacement in a remote location.

If we go lithium for our next trip, I will post my impressions somewhere on the forum.

b.

[jamhass]

I don't want to go into all the intracacies of power management, but just give you our experience.

We cruise Mexico west coast and the Sea of Cortez 8 months a year. For most of the time, our 250 watts of solar meet our needs, including underway under sail with our autopilot and refer on. We have ALL led lights, manage our computer use and run the 12v watermarked as needed.

We almost never run the engine just to recharge and find we run the engine "normally" enough to maintain our battery bank. Our normal overnight deficit (refer, tv,computer, lights ) comes to 50 to 80 ah.

We don't see much difference summer or winter. Summer the refer works harder, but the days are sunnier and longer so all evens out

[Paul54]

Years ago I used to spend a lot of time on solar power forums and news groups. The approach to system design was the same.

If you want a system to be cost efficient, meet your needs, and perform for a long time, you need to "do the math", learn about the science, and design based on real numbers.

If you don't want to learn the science, do the math, use the right terminology, you may end up with a system that works well enough. But did you buy too much? or too little? Are you over or under utilizing your batteries? How do you know? How long will it last?

[barnakiel]

That would imply being lazy.

Anybody who understands why and HOW to correct the course for set and drift will have zero problem understanding how to optimize a solar/battery setup.

Then again, why aim for an optimum system if sub-optimum systems work 'just as well'.

Many ways to skin a mono.

b.

[StuM]

Originally Posted by Pete7

Do you really think the OP has money for LifePO4? You criticised me for using amps instead of amp hours, and then post this in a thread when someone looking is looking for advice on solar for a 29ft yacht.

Thankfully barnakiel and I posted some real life experiences with solar set ups.

Peter

You seem to have completely misinterpreted my post.

No, I don't think that the OP will be installing LifePO4 - which is why I pointed out that mitiempo's quoted 22% was not realistic in the more likely case of the OP using LA.

And I fail to see the connection between this and your misuse of basic terms.

[kmacdonald]

He still doesn't get it. (It might as well be Calculus to him)