A stupid battery question

[davidpm]

This came up in one of my dockside conversations. I doubt if their is any merit to this idea it sounds way off. But just in case their is some grain of truth however hidden I thought I would ask.

Some guy was saying that in week or two cruising the alternator will not charge the batteries all the way up and you will start to have problems keeping the batteries at full charge.
The solution is to put a rectifier that powers a 110 volt shore power charger that then charges the batteries with just having to run the engine an hour or so and gets them to a better fuller charge.

Now I know that this makes no sense at all. My expert had his boat about 90 days and probably heard something that he got all mangled up.

So the question is what is it possible that he was talking about?
Is there some kind of extra charging system that can fast charge batteries that he thought was a rectifier?
How fast would a normal Catalina 309 simple two battery system be able to charge by running the engine?

I know I'm really fishing here but I suspect he head something and got it bollixed up.

[peikenberry]

Not stupid. Yes he got it bollixed up.

The conventional wisdom is that alternators "maintain" a battery, as opposed to fully charging it with a 3 step or four step charger. So the battery companies all recommend that you occasionally put a smart charger (a 3 or four step charger) on the batteries and bring them up to full potential. If you use a four step it will also equalize the cells so they are all putting out exactly the same voltage.

This "rectifier" he is talking about is not called a rectifier. It's called an inverter. An inverter changes 12V DC to 120 V AC. You can plug an AC charger into it and recharge your batteries. However, this seems a bit round about but it would work. But you are using the same 12V DC that is already charging your battery. It would work better if the batteries could somehow be disconnected from the circuit and charged. This would work with a diesel but not with a gas engine since a gas engine need s the battery to keep running.

However, since an alternator puts out AC, Which is then "rectified" to 12V DC, it seems rather an odd way to charge your batteries. A device on the alternator acts as a rectifier and voltage regulator so you get straight DC out and it is regulated between about 11 volts and 14 volts (depends on the regulator)

The problem is that generally speaking charging systems run off an engine are strictly bulk charging systems, that is they put out the same amount constantly. Batteries don't particularly like that. They prefer the bulk, absorption, float system that brings them up to peak. So your battery is never quite fully charged. But you can get around this by using a variety of other means, a genset, solar cells, a wind generator, or just waiting until you tie up and charging it from the shore power.

[camaraderie]

I have a different take on this. Factory engines typically come with internally regulated alternators which are not good for deep cycle banks. Converting from an internal regulator to an external 3 stage regulator can properly maintain the batteries assuming the alternator itself is large enough for the battery bank installed.
This involves an alternator shop converting the alternator OR buying a new alternator with high output which is useful if you have a large bank or AGM batteries...AND...buying an external three stage regulator.
Visit balmar.com for some examples.
I think your friend got REGULATOR and RECTIFIER confused.

[badsanta]

When you motor for several hours a day it will give a bulk charge till the batteries are about 80-90% full, then it will take many hours of running the engine to top off the battery for the last 10-20% and on a long cruse you may never compleatly charge the battery. So if you are not motoring all day, but just start it up at anchor to top off the batteries they never get fully charged. ex, you leave the dock at 100% sail all day and anchor. depending on your use, lets say you used 20% you are at 80% now run the engine for an hour you are now at 90% the next day you use 20% now you are at 70% charge for another hour you are back to 80% you use another 20% now at 60% I think you can figure out where this is going. On weekend sails you never worrie as when you get back, the shore line and charger brings everything back to normal. On longer trips your power use and lack of full charges will bring the system down. People who cruse alot either use a gen set, solar, wind charging or all.

[LoTech]

Since we're on the subject of stupid battery questions I have one too.

If I ran a Honda 2000 generator with a sustained output of 13 amps for two hours a day into a 40 amp charger, theoretically, how many amp hours would it put into my batteries? 26 amp/hrs?

I would be using the generator to run my laptop, and maybe some other small appliance too, at the same time. Not sure how that would effect the charging, if at all.

[Hartley18]

Originally Posted by LoTech

Since we're on the subject of stupid battery questions I have one too.

If I ran a Honda 2000 generator with a sustained output of 13 amps for two hours a day into a 40 amp charger, theoretically, how many amp hours would it put into my batteries? 26 amp/hrs?.

Approximately.. yes - but you'd have to hope the batteries were not too flat and that the generator's over-current protection system works, otherwise you might just wind up with a dead gen-set. You don't have a smaller charger you can use?

Originally Posted by LoTech

I would be using the generator to run my laptop, and maybe some other small appliance too, at the same time. Not sure how that would effect the charging, if at all.

It depends on how much current they draw and how the generator copes with the overload from the charger. Most gen-sets reduce the output voltage which may upset your laptop..

I'd suggest starting with the charger only and then add the laptop and whatever else only if the gen-set seems happy enough and after the batteries have had an initial top-up charge.

Cameron

[sailingdog]

First, I'd have to agree with Cam and BadSanta regarding their posts. Running an engine for a few hours a day is very unlikely to get the batteries much past the bulk charging phase or the 85% level charge level. The charge acceptance rate of batteries normally used on sailboats drops off quite steeply once it reaches about 85%, and the amount of current a smart charger or regulator will push through them drops off quite dramatically.

Originally Posted by LoTech

Since we're on the subject of stupid battery questions I have one too.

If I ran a Honda 2000 generator with a sustained output of 13 amps for two hours a day into a 40 amp charger, theoretically, how many amp hours would it put into my batteries? 26 amp/hrs?

I would be using the generator to run my laptop, and maybe some other small appliance too, at the same time. Not sure how that would effect the charging, if at all.

If you're talking about a Honda Generator, the 40-amp battery charger will only be drawing about 6-7 amps at 120 VAC... so the 40 Amp charger will be able to push 40 amps into the batteries if they're bulk charging, so theoretically, you could be getting 40 amp-hours per hour of running the generator, not counting losses due to charging and such.

Hartley's advice on leaving the laptop disconnected until the generator stabilizes is a very good one. Also, are you going to be using the laptop via its AC adaptor or via a DC adaptor? That makes a bit of a difference as well.

[davidpm]

Originally Posted by camaraderie

Converting from an internal regulator to an external 3 stage regulator can properly maintain the batteries assuming the alternator itself is large enough for the battery bank installed.

My captain likes to take about 3 months off during the summer and just sail the LIS.
Is this 3 stage regulator the answer. He just finished his three months and wants this fixed for next year. He made it but it wasn't comfortable. So I don't think his usage was bad he just doesn't plug in for 3 months.

Catalina 309 with factory setup. What should I give him? Not a lot of room.
I'm thinking two battery house bank agm (what size)?
Echo
3 stage regulator

[erps]

My captain likes to take about 3 months off during the summer and just sail the LIS.
Is this 3 stage regulator the answer.

Yes.

I'm thinking two battery house bank agm (what size)?

Most folks find 6 volt golf cart batteries a good compromise. 2 of them in series for your house bank gives you around 225 amps, so a little over 100 usable.

[sailingdog]

The major caveat to using golf cart batteries is that if you only have two batteries in the bank and one goes bad, you lose the entire bank... if your going to use golf cart batteries, you really should have a four-battery bank as a minimum, but that is a pretty big house bank for most people.

Originally Posted by erps

Most folks find 6 volt golf cart batteries a good compromise. 2 of them in series for your house bank gives you around 225 amps, so a little over 100 usable.