Battery Budget Question

[lippysyd]

So we're really new to our boat (72 Catalina 27) and I know very little about batteries. Usually we just day sail or dock with shore power, so I haven't really worried about it much. But we're planning a trip this weekend and it looks like we may have to moor out. All I'm worried about is having enough juice to run some small fans for the night.

I've been reading around and here's what I think I know :
Small clamp fan uses .2 amps. I have 3. That's .6 amp hours. Run them for maybe 5 hours, that's 3 ah.
Am I right so far?

I have only one house battery and it's rated for 80 ah. Donno how old or weak it is.

What do you think? I just don't want to melt.

 

[nybor]

the question is how old or weak is your battery. Maybe take your car battery out of your auto and have that on board for backup?

 

[Stu Jackson]

Your math is right. Don't forget the lights, if you'll use them. Assure your battery is fully charged before you leave. Have a great cruise.

If you'd like to learn more, feel free to wander around here:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

 

[centerline]

you can use all the amps that the battery can possible supply, but thats not recommended at all.... about 50% of the available amps of the battery is the maximum you should draw it down. so with your understanding of how to count amp usage and knowing your battery should only be expected to give up 1/2 of its bounty, and that the battery may be a bit weak besides, you can go forth and have fun without any unexpected disappointments concerning dead batteries

 

[lippysyd]

Thanks Stu! I did read your posts which was really helpful and I'm going to have hubby read it as well. So far we've got along fine with just one house bat & one starter. But I think next year's big project will be to add another house battery and 1-2-B switch. Gotta educate ourselves first.

Good to know that we may get by if we have to this weekend.

 

[The Garbone]

A solar panel is nice also. We went on a 2 week trip this spring with 300ah of batteries and a 15watt solar panel mounted on the stern pulpit. Our outboard was not hooked up to charge the batteries and we still were good towards the end of the 2 weeks. Of course we used an oil lamp and all the bulbs on our boat are LEDs and we monitored a small handheld VHF and used the boats only to make calls. We never hook up our shore power, at $50 a month for shore power the panel and controller had already paid for itself by March.

I would worry about the actual draw of those fans being over what is advertised, you can check it with a amp meter.

 

[rgarrison@gmail.com]

good dialog!!

 

[SailingHarry]

the question is how old or weak is your battery. Maybe take your car battery out of your auto and have that on board for backup?

Can't agree more with this! The first season I had my boat (OK, I got it in July, so it was more like a half season) I had really bad batteries, but wanted to make a decent battery box before I bought new ones (the batteries I wanted to buy wouldn't fit in the existing space). So, I cruised that year, including a week cruise, with the "house" bank being the garbage batteries the boat came with. Then, my #2 battery was the one out of my Honda Civic. Barely as large as a lawn tractor battery. Started my 2 cylinder Volvo first time every time. I've got a much better battery system now, but that little car battery made the first season work, at no extra cost.

 

[jrowan]

We always keep a backup jump starter type battery for emergency power to start the engine, if we accidentally draw down our batteries overnight at anchor. Its the type that has its own jumper cable built in, & has saved me more then once. Just have to remember to charge it up before you leave! But it will hold a charge for months at a time.
I always follow the Boy Scout motto: Be Prepared.