SailNet Community banner

1 - 13 of 13 Posts

·
Registered
Joined
·
75 Posts
Discussion Starter · #1 ·
I'm about to re do the electric wiring, my boat is a Merit 25. I've already installed navigation lights, but everything else in the cabin will be redone.
I'm thinking to put together 2 24DC wet cell deep cycle batteries in parallel for the house. I don't need a starter battery 'cuse I have an outboard.
The tricky part is this: I will have aboard a gas gen (honda, I know about gas hazards, but I'm already carrying gas for the motor, not an issue) with the generator I plan to charge the batteries via a AC charger -20 amp. and use the DC current it delivers to hook it up to the 2nd slot of the battery switch, so I will have 12 volt current from the gen at the same time I charge the batteries, am I nuts to do this?
Thanks
 

·
Registered
Joined
·
198 Posts
Seems to me that you're introducing variables that will do nothing but complicate things. What's wrong with generator -> AC charger -> battery bank -> 12v house? That way, there is only one path to diagnose when it breaks.
 

·
Registered
Joined
·
75 Posts
Discussion Starter · #4 ·
Seems to me that you're introducing variables that will do nothing but complicate things. What's wrong with generator -> AC charger -> battery bank -> 12v house? That way, there is only one path to diagnose when it breaks.
There's nothing wrong with that, but I wan to use the generator only when needed. Also my thought is that if I don't use power from batteries it will charge faster and I'm still able to run lights and instruments from the 12 volt outlet of the generator
 

·
ancient mariner
Joined
·
439 Posts
alecs123------ since you are hooking up 2 24v batteries in parallel your output voltage is 24v. is everything in your boat set up for 24v , lights & all ? if you also have a 12 v setup everything gets more complicated. the only plus for 24v is half the current draw for lights , etc.
 

·
AEOLUS II
Joined
·
2,938 Posts
I reviewed your photos, looks great down there!!

There didn't seem to be any shortage of places to plug in a battery charger though.

What are you running on that non-marine generater on a 25ft boat??

Air conditioning??

Frozen Margharita machine??
 

·
Registered
Joined
·
219 Posts
I have the same question. Why 24V? Are you running 24V appliances? The normal setup is usually a couple of 12V deep cycle house batteries, a 12v starter battery, a genset running a 12V converter/charger to charge batteries and run 12V appliances when on genset or shore power, and shore power and the genset outputing 120VAC to run AC appliances.

Some people add an inverter to run a few AC appliances off their 12V system.

If you use 24V you are going to have to have a step down transformer or some other device to take off 12V.


Oh yeah, running a non marine genset on a boat is not only hazardous to your health it's hazardous to the boat. See http://newboatbuilders.com/docs/portable.pdf Portable Generators on Boats Pro and Con.
 

·
Registered
Joined
·
5,979 Posts
The only problem I see is the 12v outlet of the generator doesn't match the 24v of the rest of your system. Makes me scratch my bald spots.

Using the 24v to run lights while charging via a generator will extend charging time by the amps used, no free lunch to be had, installing a totally separate 12v system or set of lights would be even more.

I would not use the Honda to top off your batteries to 100% - a better usage is to get them to 80%, maybe 90% depending on your charger's 'smartness'.

You don't mention the ah capacity of the battery bank and I'm not sure your charger is 20 amp at 24v. Let's say it is. That implies at max output it's 26.4 (12v full charge wet cell is really 13.2) and 26.4 vdc at 20 amp = 528 watts.
It's all about the watts, or power.

The Honda 2000 puts out a max continuous wattage of 1650 so I think you have the room to run the 12v if you really want to, and maybe even do it in economy mode which is much quieter and sips gas a lot better.

I think that answers your question. The un-asked question is how long will it take to put a unknown about of amps back into your batteries. We can't help on that because we don't know how many amps you need to recharge. Keep in mind that if your bank has 200 ah capacity and you use 20 ah a day and charge every day that charging for 1 hour does not imply a full load, batteries and charging don't work that way.
Up until about 80% of fully charged a battery will take the full output of the charger (bulk loading), at about 80% it slows down just like stuffing a suitcase that last little bit and you only get about 10 ah the second hour; then at 90% of full charge it really slow down and it can take you another 5 hours to get the remaining 10 amp in. That's irrespective of the charger's rated output, it's more about the batteries chemistry and ability to absorb the charge being applied. Smart chargers help on that to a degree, but the curve described is roughly what it is, and how it is regardless.

Size your bank capacity to be good for a full day with the batteries between 50% and 80% and you have a golden system and short run times on the Honda, but don't forget to fully top off at the pier or via solar panel etc.. at least monthly, and mind the water level on those wet cells.
 

·
Registered
Joined
·
75 Posts
Discussion Starter · #9 ·
I reviewed your photos, looks great down there!!

There didn't seem to be any shortage of places to plug in a battery charger though.

What are you running on that non-marine generater on a 25ft boat??

Air conditioning??

Frozen Margharita machine??
It's a great lake and beleive or not, marinas down here don't have power to charge batteris, and I'm done taking them to my home just to charge'em.
There is another thing I would like to address, the batteries are 12V but the model is 24 DC (I never thought that would be mistaken with "direct current"), I have only 12 volts on my boat...
 

·
Registered
Joined
·
5,979 Posts
It's a great lake and beleive or not, marinas down here don't have power to charge batteris, and I'm done taking them to my home just to charge'em.
There is another thing I would like to address, the batteries are 12V but the model is 24 DC (I never thought that would be mistaken with "direct current"), I have only 12 volts on my boat...

The figures I gave above work for the 12v, simply half :)
 

·
Registered
Joined
·
75 Posts
Discussion Starter · #11 ·
I have the same question. Why 24V? Are you running 24V appliances? The normal setup is usually a couple of 12V deep cycle house batteries, a 12v starter battery, a genset running a 12V converter/charger to charge batteries and run 12V appliances when on genset or shore power, and shore power and the genset outputing 120VAC to run AC appliances.

Some people add an inverter to run a few AC appliances off their 12V system.

If you use 24V you are going to have to have a step down transformer or some other device to take off 12V.


Oh yeah, running a non marine genset on a boat is not only hazardous to your health it's hazardous to the boat. See http://newboatbuilders.com/docs/portable.pdf Portable Generators on Boats Pro and Con.
Thanks for your reply, my system is 12 volt (look previos post reply), anyway I misslead the whole forum, sorry for that...
 

·
Registered
Joined
·
219 Posts
I suspected as much. you have two 12V Group 24 batteries. Actually the Group number has nothing to do with capacity, it is a strictly related to the outside physical dimensions of the battery. The best way to state what batteries you have is voltage, amp hour rating or MCA or CCA rating.

CCA is Cold Cranking Amps, a measure of how many amps the battery can deliver for 30 seconds at 0 deg F without dropping below 12 V. The MCA rating (Marine Cranking Amps) is the same thing but at 32F. Usually these ratings are on the battery label.

Obviously the higher the ratings the longer the battery will last before it has to be recharge, and the longer it will take to charge it.
See Batteries New Boatbuilders Home Page - Basic Electricity DC Page 3 - Batteries
 

·
moderate?
Joined
·
1,000 Posts
And in answer to your question...don't hook the DC output of your Honda into the battery switch. Just use the AC charger and make sure the AC 20amp charger is a 3 stage charger for good results.
A single GROUP24 12V battey typically has 75 AMPHOUR rating so TWO will give you a 150AMPHOUR bank. You can use 75 amphours of that total before recharging so it will take around 4 hours of recharging to get to "full" again. A 30 amp charger would be better and save gas...but no more than 30 amps.
Hope this helps.
 
1 - 13 of 13 Posts
Top