Dumb battery charging question

[mstailey]

Here's the battery setup on my 43 DC: (4) 8D batteries. (2) for Start (2) for house. Combined amp-hour equals 820Ah.
Here's what I want to do: Install a Charles 5000 50 amp charger and a battery combiner. Charger has output lead to house batteries only and combiner connects start and house batteries.
Based on the rule of delivering a charging current equal to 25% of the amp-hour capacity of the batteries, won't I be short on charging current?
25% of 820Ah = 205 amps. Do I need multiple chargers?
Am I looking at this all wrong?

Thanks.

 

[Nonchalant1]

Mike,

The question is whether 8D the batteries are connected in series (-to +) or parallel (+ to + and - to -). If they're connected in series, you can't add the amp hours together because you're adding the voltage together. For example, my boat has four big 8 volt 250 amp hour batteries connected in series. Therefore I have a 32 volt, 250 amp hour battery bank. If I connected them in parallel, I'd have an 8 volt 1000 amp hour bank.

The starting bank won't need much charging at all if it's really a starting bank. The reason is that it just starts one engine and then the engine alternator charges it right back up because it's running after the engine has been started. The rest of the time, the starting bank just sits. I have four 8 volt, 195 AH batteries in series in my starting bank and they were always getting boiled by my battery charger because it only monitored the house bank, and then just supplied the same charge charge current to the starting bank whenever it was charging the house bank. I went through a lot of distilled water. I simply disconnected the charger and let the engines recharge the starting bank. It has worked perfectly ever since. The starting bank stays fully charged but I only had to add a little water once last year at the end of the season. For backup, I put a manual parallel switch on my parallel circuit so I can charge both banks from the charger, but I never have had to.

IMHO 50 amps should be plenty for your boat. Mine is 32V 30 amps and it rarely needs to crank out 30A.

Hope this helps,

Doug Shuman

 

[Genesis]

You're fine - that's exactly the setup I have on my boat except I used a 40A charger. No problems at all.

 

[REBrueckner]

Everyting depends on how you use you boat and systems. Assuming all the batteries are equal voltage and connected in parallel Charging at around 200 amps is ideal only to minimize genny run time. Let's say you use 150 amp hours daily. At 50 amps recharge, you'll have to run the genny three hours at least. Actually probably 20% more to overcome battery losses via heat and resistance losses.

If you charge at 200 amps, you can get the job done in under one hour. Huge difference in genny wear and tear!!! But if you run the genny for other reasons, like air conditioning, then you are in no rush. And ditto that fior shore side charging...who cares if it takes two or three hours from shorepower its there all the time anyway.

But if you don't use any batteries at anchor, except for say lights and TV, then you have a very low charge requirement.

See my post on dc system design for general ideas...I posted around November 2005.

 

[mstailey]

Okay guys, think I've got it. It boils down to the batteries being connected parallel , amp-hours used and time to recharge. At 40 or 50 amps charging current if I use little amp-hours not so long to re-charge. If I use a lot, a longer recharge time.

Plus, it's the same setup as on Karl's vessel. Good enough for me.

Well, I feel better. I started this question feeling dumb and I'm now a little smarter - maybe..

They should rename this forum to Hatters-Owners-U

Thanks guys.

 

[luckydave215]

On my boat I have two 32V banks of different size that the old (dumb ferroresonsant) charger was charging. When the small bank was charged, the charger turned off, never fully charging the large bank. When I ran the engines, the alternators charged the banks correctly.
NEWMAR!! Problem solved! And I almost NEVER have to add water.

 

[Freestyle]

My turn with a stupid question.

Same 43 DC setup. Port starter battery for port engine and genset with starboard bank for house and battery charger linking them both. There is a selector switch at either helm that has proved its worth by starting the starboard after the house use ran it down.

Above each engine is a battery selector switch with choices of off, 1, 2, and both. When I bought the boat they were set to "Both" and I have never changed them. Why isn't one battery on "1" and the other on "2"? By having them on both am I risking the house load on both? Or do the barrel switches have to be set on "Both" for the charger and/or parallel function to work?

It's kind of scary to me that I have cruised 1400 hours and not thought this through.

Thanks

Bruce

 

[Nonchalant1]

Bruce,

It depends on how it was originally wired up. In some cases "Both" means they're paralleled. However, if that were true, you wouldn't need the helm station parallel switch to start the starboard engine after the house bank ran down, so likely yours is set up where "Both" means both banks are on, but not paralleled. Also, if they were paralleled, they'd both run down together instead of just the house running down.

If you have separate voltage meters for each bank, look at them and if the only way to have the house bank and the starting bank on and reading a voltage is "both" then yours is set to have that mean both are on, but not paralleled. If they're both on and the voltage is a little different between them, they're not paralleled because paraslleled banks equalize the voltage between them.

I think you're OK.

Doug




Doug

 

[REBrueckner]

Freestyle,
If you have two battery banks, port and starboard, and your engine switches are on "both" then almost certainly both banks ARE tied together and your house load is running off both. So you potentially risk losing all battery power...

An advantage of this set up is that if one alternator fails, you charge all batteries...but I'd use the "both" setup only if that happens. Another potebntial advantage is that you discharge both banks to a lesser degree than running off only one..extending battery life. But using and "1" and "2" instead of "both" enables you to exercise and test your start parallel switch...when working you'll find the engine turns over faster with both banks in parallel....another exercise/test which you should do periodically. If you don't use electrical contacts, they will almost certainly corrode and fail over time...just when you really need them.

Check your wiring diagram..find out which is "1" and which is "2". Or put the port on "1" and lift the port positive batt term off....see if the engine starter turns over...if not port is "1".

Finally, even if you decide to keep them in "both" position, you should rotate the switches several times at least once year to keep contacts clean. Whenever I check my batteries, twice annually, I flip those big switches.......that's the only sure way to know things are working....

 

[J's Dream]

My turn with a stupid question.

Same 43 DC setup. Port starter battery for port engine and genset with starboard bank for house and battery charger linking them both. There is a selector switch at either helm that has proved its worth by starting the starboard after the house use ran it down.

Above each engine is a battery selector switch with choices of off, 1, 2, and both. When I bought the boat they were set to "Both" and I have never changed them. Why isn't one battery on "1" and the other on "2"? By having them on both am I risking the house load on both? Or do the barrel switches have to be set on "Both" for the charger and/or parallel function to work?

Maybe I'm reading this wrong, but I seem to think that the switch over the port batts selects ONLY the port batteries. I am assuming you have port batteries with cables running from one positive to another and one negative to another, right? If this is the case, the switch would allow you to use both batteries to run (1) the starter, (2) the house power or (BOTH). It would NOT allow you to separate the two batteries tied together. On my 45C, the stbd bank is 2 8D in parallel, and port is the same. You are probably the same way. The port switch controls ONLY the port battery bank and determines what they power; stbd switch the same way. The switch should control what the batteries supply, whether that is the starter, house power, or both as you are selected now NOT which battery in the bank is used. The switch on the port has NO influence on the stbd bank, and vice versa. Maybe you're wired differently, but I don't think so.

 

[REBrueckner]

My 1972 yachtfish is NOT wired as described by J's Dream.
So the best course is to test your set up so YOU KNOW what arrangement is used. See my prior post.

 

[Freestyle]

Thanks for the brainstorming.

I flipped some switches to test the foregoing theories. Neither engine will start unless that engine's selector is on "Both". If either selector is on "Both" the parallel switch will allow me to start both engines.

With the starboard (House) battery on "Both", 1 or 2, the house stuff works. If starboard is on "Off", there is no setting on the port battery that powers the house.

So as crazy as it sounds, I think the selector switch for each engine is selecting battery 1, 2, or both on that side's battery bank.

 

[Nonchalant1]

Yeah, it's exactly as "J's Dream" described it. Each selector controls just the batteries in that engine room. They should be left on "both" unless there's a problem with one of the batteries, in which case you can just use the good one.

 

[Traveler 45C]

Mike, I think it would be better to combine the 8D’s into one house bank and install a set of starting batteries for the start bank. The more house capacity you have, the better. If you have the room, of course.

Based on the rule of delivering a charging current equal to 25% of the amp-hour capacity of the batteries, won't I be short on charging current?
25% of 820Ah = 205 amps. Do I need multiple chargers?

That’s a guideline and not usually practical. The 50A charger is fine. Using a smaller charger just means a longer recharge time. No big deal. No multiple chargers necessary.

 

[Jaxfishgyd]

Yup, battery switches have nothing to do with the port and starboard sides. I replaced my 4 8D's with group 24's last summer. Lot easier to replace due to our 43's battery location and better starting power.
Plus 3 group 24's fit exactly into an 8D box.