Battery Question - What is best

[kevin carroll]

I have three batteries - two connected to an 1-2-all switch and one isolated (I used the third primarily to run a 15 inch flat screen and DVD) I charge it before I go - I have ran it well over 2 hours with the DVD and TV running. I am a little concerned that draining and recharging will shorten it's lifespan.

My question, can I simply run wires to the 2nd battery and treat it like a another ' bank' of batteries. Also will a simple pos & neg line to the 2nd battery allow my guest charger to charge the 3rd battery - as long as the battery selector switch is switched on 2nd battery?

What is the solution if I this will not work??

Kevin Carroll
Jump the Shark
01 26X
San Diego, CA

[Paul S]

Deep cycle batteries are made to discharge and recharge. The batteries we put on our boat (2 of the same - group 27) will, at worst, at 100% discharge, have 300 cycles...at best 900 cycles.

Just keep it charged and topped off with water, you should be set for many years of service.

Here is a link to any and all battery questions : http://www.rollsbattery.com/Bulletins/bulletins.htm

Paul

[mike]

My question, can I simply run wires to the 2nd battery and treat it like a another ' bank' of batteries. Also will a simple pos & neg line to the 2nd battery allow my guest charger to charge the 3rd battery - as long as the battery selector switch is switched on 2nd battery?

The general consensus seems to be that it's not a good idea to parallel 2 batteries as a single bank unless the batteries are identical (same brand, bought at same time, etc.).

--Mike

[Duane Dunn, Allegro]

The number of cycle you get out of deep cycle batteries is directly related to how deep the discharge is. While a deep cycle battery may last 300 - 100% discharges, the same battery could get 1000+ - 50% discharges. The relationship is not linear.

It's simple math. If you have two group 27, each with 85 amp hours you have a total capacity of 170 amp hours. If you pull 80 amp hours out of one battery alone you will be shortening it's life. If you hook both up in parallel, now you are only pull 50% out of the pair rather than 100% out of one. Both batteries will last longer doing this than if you alternate pulling each down 100%.

I'm not really clear on your question. You can connect the first battery to the second by using a heavy wire #4 to connect positive to positive and negative to negative. This is wiring them in parallel. You will not have two banks, you will have a single larger bank. You connect your charger output to one of the batteries and it will charge both. The same is true of your engine output. This is how I have my boat wired, a single large bank, no switches other than a main off/on. This combined with a good amphour meter to monitor the charge state works very well. I have a Link 10 meter.

Another beauty of this system in addition to it's simplicity, is it's expandability. With a single bank handling all loads it's really easy to just add another battery and increase the banks capacity. We are heading out this summer for a 4 week cruise and I want a bit more capacity. By just buying one more battery and two more #4 cables I can add 50% more capacity very simply. Now all my discharges are 1/3 less in depth and all the batteries will last even longer. 80 amp hours out of 170 amp hours equals a 47% discharge. 80 out of 255 amp hours equals a 31% discharge.

From your question I also think you may be considering splitting loads, running some to one battery and some to the other. The two batteries are not directly connected to each other. This is a more complicated setup and you'd have to have separate negative buss bars, etc. You'd also have to have a charger made to charge two separtate banks. These chargers have two separate isloated outputs. If you take the output from a single charger and connect it to two separate batteries you will have crated a link directly between the two batteries through a very light guage wire and this is a problem. The batteries will atemp to equalize their charge states through this wire as one draws down and the other isn't used. You could have a fire hazzard as a lot of current may flow through this small wire.

If you want to keep two separate banks you could go with the standard 1, 2, Both big red switch method or you can go with the 3 on/off switch method, one for each bank and an emergency parallel switch along with a charging combiner.

Here are some links with more info.

article #1

Article #2

[mgg4]

This is a more complicated setup and you'd have to have separate negative buss bars, etc.

You are right that it would be a more complicated set up, but your statement about the negative buss bars is inaccurate. ALL grounds on the boat should come to the same grounding buss. This includes all DC circuits, as well as the green (ground) wire from any AC installation.

This is very important for safety, as well as forming the basis for bonding your underwater metals to prevent galvanic corrosion. Everything must be grounded to the same buss, or there exist the potential for nasty (if not fatal) shocks, and/or the fast disintegration of your underwater metal fixtures (including your engine's lower unit).

--Mark

[craiglaforce]

Just a few words for consideration:
Whatever wires go between batteries to parallel them should have a fuse to keep from overheating the wires in the event of a short or something.
There are 2 schools of thought on bonding underwater through-hulls. One is that through-hulls should be totally isolated electrically rather than bonded to the boat's electrical system. Avoids the possibility of completing a current circuit where the charger pumps amps through the though-hull thus disintigrating it in about a day of charging. I saw this happen to a larger sailboat and every bit of metal was GONE that touched the water, There were about 4 through-hulls, several zincs and a metal cored rudder all gone. The rudder broke and the relatively new owner had it put on the lift to remove the remains of the old rudder. I had to point out to him that his through-hulls were gone. The outer mushroom was gone. Just a little bit of sealant was holding the internal pipe in place. He went inside and tugged on a hose and the whole works came out in his hand. Along with the bonding wire of course.

I suspect that he added his own charger and that it did not have an isolated ground.


What is meant by the comment about lethal shock potential with 12 V?
I've never heard of anyone getting killed by a 12V shock.

[mgg4]

What is meant by the comment about lethal shock potential with 12 V?
I've never heard of anyone getting killed by a 12V shock.

I agree, it's highly unlikely that a 12V circuit could create a lethal shock. It is possible, just highly unlikely. If you were to happen to get across a high current circuit, with wet hands, and were stupid enough to grab the positive wire in one hand, and the negative in the other, it might ruin your day.

Actually, my comment was related to the grounding of the AC side of the house (boat). I am currently working on a project to rewire and relocate the DC power sources and controls, as well as adding shore power and an inverter. So, I'm reading up on all of the requirements.

Sorry if I created confusion with my post.

You are also right about the bonding question. Anyone considering bonding should be very careful, and read up on the subject. I can't remember the title, but there is a very good book (green cover, hardback) that does a very good job of covering all topics related to electrical systems onboard a boat. Good reading.

--Mark G

[Duane Dunn, Allegro]

Voltage won't kill you, high or low. It's the current, amps, that matters. That's why people often survive lightning strikes, mega volts but no real current. grab two 12v wires carrying high current and it can kill you just as easily as higher voltage.

I don't agree with the need for fuse links in the wires paralleling batteries. I have seen many many parallel battery installations in boats, UPS (Including some amazingly giant ones in co-location data centers) and even home applications installed by professional electrical engineers and these do not use links with fuses. Would it hurt to have them? certainly not, but this is not a requirement.

It is correct to have a single negative 12v bus bar in a dual battery setup. Sorry for the error. There is a good picture on page 613 of the recent west marine catalog showing there recommented 3 on off switch wiring. They now even have a good selection of prewired panels for this so you don't have to built it from parts.

I don't see the need to worry about a full bonding sysystem on these boats. We have no metal through hulls, the only thing in the water is the engine, and when it's up only it's galvanic plate on the transom mount is in the water. Why add this complexity. Stick with KISS. These a little trailerable sailboats, not ocean crossing mega yachts.

[Chip Hindes]

While a deep cycle battery may last 300 - 100% discharges, the same battery could get 1000+ - 50% discharges. The relationship is not linear.

Yes, but using this to justify additional batteries is faulty logic.

How many times a year do you intend to do this? Lets assume as you did 100% discharge every time you go out, (unrealisitic, but we'll concede it for the sake of discussion). Realistically, unless you are able to sail a lot more frequently than the rest of us, a warm weather sailor like you could expect to do this, what, roughly 30 times per year? For we in northern climes who can only sail perhaps 6-7 months per year, it might be half that. So our allotment of 300 discharge cycles will last you 10 years, me 20 years? I doubt it. With two batteries, will 1000 discharge cycles last you 33 years, me 66? I doubt it to the third power, and the point is moot because I'll be long dead.

Realistically, no battery is giong to survive more than six or seven years, no matter how frequently or infrequently you discharge it, so it's unlikely that you will ever use up all your 300 cycles, inceredibly unlikely that I will do so. So what's going to happen, really, is after six or seven years you'll be replacing two batteries instead of just one. Or in your case, three.

You can justify additional batteries because you need more capacity. You can't do it based on number of discharge cycles.

[Dimitri-2000X-Tampa]

Realistically, no battery is giong to survive more than six or seven years

Wow, you get that long out of an average battery? Maybe it is this warm climate, but my [auto, marine] batteries only last 3-4 years before they start getting tired. My last boat had a couple of nice marine "diehard" batteries that lasted about 5 years, but thats a record for me and they probably cost twice as much as the average run of the mill battery that will last 3-4 years.

Btw, I run a group 24 and a group 27 battery. When I put my big red switch on "both" (something I do frequently while motoring or popping popcorn), these two dissimilar size batteries are in parallel. I've noticed that the group24 will charge right up from the group27, ie, it takes as much as it needs and then the group27 is the one that needs to be charged up from the battery charger. I believe its like having a big jar of water connected to a small jar with a hose. The small jar will always be full before the big jar.

[Chip Hindes]

Quote:
Realistically, no battery is giong to survive more than six or seven years

Wow, you get that long out of an average battery?

Nah. I get more like what you get. I was just giving Duane the benefit of the doubt in his calculations.

Back in the day when I kept my cars forever, every 3-4 three years just like clockwork I'd trot over to Sears and get the remainder of the 72 month warranty on my Diehard, toward the purchase of a new 72 month Diehard. 3-4 years later, repeat.

Now Walmart has a similar warranty on their store brand Everstart for quite a lot less than the Diehard.

[Billy]

every 3-4 three years just like clockwork I'd trot over to Sears and get the remainder of the 72 month warranty on my Diehard, toward the purchase of a new 72 month Diehard. 3-4 years later, repeat.

Chip, FWIW, this goes to prove there are no 72 month batteries for the public. It is a sales ploy. They sell you a 48-60 month battery with a 72 month warranty. When the battery fails, you go back to the seller to redeem the warranty. They then get to make another sale. They have you hooked for as long as you own batteries and you believe they're great because they are standing behind their warranty. (And it's built into the price.) Pretty smart, huh?

[Chip Hindes]

They have you hooked for as long as you own batteries and you believe they're great because they are standing behind their warranty. (And it's built into the price.) Pretty smart, huh?

Yeah, I know. If you work out the numbers it comes out pretty even between the higher priced battery with the longer warranty and the lower priced battery with shorter one, except that the Diehard also had a higher rating in both CCA and reserve capacity, always a help in our brutal winters, so it was worth it. Probably

It's interesting; on this matter I figured I was gonna hear from at least one or two who get ten years out of a battery. They would probably be the same guys who get 30mpg from their V8 pickups while towing the boat, 20mpg from their four stroke outboards, and can do 17mph under sail It's a joke, guys!

[Paul S]

They have you hooked for as long as you own batteries and you believe they're great because they are standing behind their warranty. (And it's built into the price.) Pretty smart, huh?

Yeah, I know. If you work out the numbers it comes out pretty even between the higher priced battery with the longer warranty and the lower priced battery with shorter one, except that the Diehard also had a higher rating in both CCA and reserve capacity, always a help in our brutal winters, so it was worth it. Probably

It's interesting; on this matter I figured I was gonna hear from at least one or two who get ten years out of a battery. They would probably be the same guys who get 30mpg from their V8 pickups while towing the boat, 20mpg from their four stroke outboards, and can do 17mph under sail It's a joke, guys!

FWIW...the battery in our old powerboat is going into it's 8th season - sears dual purpose starting/Deep Cycle battery. Still cranks over the V8 in it. Certainly on it's last leg, probably won't make the season for the new owner. I may give them my old (new) 26M no-name battery.

I have started buying my car batteries at Costco now. They seem to last longer than the diehards I used to get. They have 84 mo warranty/24 mo non-prorated. So far 6 years on our 94 Chevy truck that gets 30 MPG (kidding...16 or so mpg) and 5 years on our 92 Honda Accord costco battery.

Never got 10 years on any battery. Maybe the Costco battery will do it. We will see in 4-5 years

Paul

[Billy]

Actually, I do have a '95 Ford F250 (purchased '94) that has the original Motorcraft battery and is still strong. Never been so lucky with aftermarket batteries. I can't help but think the auto manufacturers must get better stuff--batteries, tires (excludes Firestones), etc.