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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Battery Switching Fact or Myth

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EAbrams
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USA
130 Posts

Initially Posted - 09/07/2007 : 09:54:33

I've read many postings stating it is not good practice to switch batteries while the engine is running. Something to do with damaging a diode inside the outboard's 12v charging system.

In the September 2007 issue of BoatUS magazine there is a question and answer section called "Ask Chuck" In it he answers a question and clearly states to start the engine on one battery then once the engine is running turn the switch to "both".

So I did a search and I found at least one of our forum members thinks it is ok to switch batteries while the engine is running. Of course I'm confused.

What say you all?

Ed & Michele
Spirit #5644
1987 Catalina 25 WK/SR
Peconic Bay, Long Island NY &
Oriental, NC

Edited by - on

Justin
Admiral

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502 Posts

Response Posted - 09/07/2007 : 10:09:09

I have read about this in the past as well. My Honda outboard owner's manual says not to and that it can damage the electrical system. A couple weeks ago I made the mistake of turning the switch to off while I was packing up and letting the outboard run while flushing the cooling system. The following weekend, I checked the battery voltage, turned the switch back to on, started up the outboard, and checked the voltage again. It showed a higher reading while the outboard was running, so the alternator is still charging the battery. Maybe since the outboard was idling when I turned the switch off, the current was low enough not to cause damage. Maybe at a higher throttle setting the amperage would be higher and cause damage. That's my guess. I'm just happy I didn't find any problems, but I'll still try to make sure I don't turn the switch while the engine is running.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/07/2007 : 10:34:24

I NEVER move my switch from BOTH.
IMHO
The only reason to is if you need to kill something while you work on it. There are no issues with starting your OB from both batteries or charging to both batteries. Sometimes I think a lot of marine protocols are just to give people something to do and get them to buy stuff. Battery isolators? For what? From what? Maybe inboards complicate the scenario but remember, OBs are designed for fishing boats and are simple and rugged.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/07/2007 : 10:53:54

Ed, I have deleted your identical multiple posts in the Catalina 25 forum, the general forum is the right place for this question and it confuses everyone to have a question posted in two locations and more than once.

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farrison
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USA
166 Posts

Response Posted - 09/07/2007 : 11:26:03

Ed;

I think there is some truth to this problem with battery switches frying the diodes in a charging system, but I think it is more of a problem with an engine with an external alternator like would be found on a desiel engine. An outboard has a magneto, diodes and a voltage regulator so this may not be an issue with outboards. Perko sells a battery switch model that has two additional terminals on the back to hook up a line from the alternator so if you switch it while the engine is running, it protects the diode pack. The instructions for installing the switch addresses which wires on the alternator should be hooked up to these terminals, but it doesn't address hookup to an outboard. I am no expert though, so the best thing to do would to ask the manufacturer of your outboard to be sure. Since the newer outboards are all electronic ignitions, frying diodes may mean that you have to replace the entire elecronic "pack" and that could be pricey.

Paul--Great Salt Lake

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OLarryR
Master Marine Consultant

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USA
3468 Posts

Response Posted - 09/07/2007 : 11:26:30

I do same as Frank - I leave my switch on "Both" all the time. For me, it minimizes risk of forgetting to either switch it on or switch it while the motor is on.

As far as battery isolators, I have not installed one but I read an article some time ago (forget where) that indicated if you have dual batteries and do not have a battery isolator a weaker battery will draw down a good battery if there is one battery weaker than other. The article indicated that a study of dual batteries in use indicated that they do not get twice the life or use. It is more like 30% more out of what one would get from one battery.

As it is right now, I just leave the battery switch in "Both" all the time. Solar panel hooked up to both batteries as is the motor. maybe I will look into an isoltor in the future but...lot of wiring back there...not sure if i want to mess with the electronics again. Working on other projects right now and giving the electronics a break.

Larry

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 09/07/2007 : 12:05:49

Ed.

It depends on the switch that you have. If the switch breaks cleanly between positions that switch has the potential to cause damage. If on the other hand the switch remains on while switching the problem doesn't exist. To test your switch, turn on a cabin light and leave it on while changing battery positions. If the light turns off momentarily while doing so your switch has the potential to harm diodes. If the light remains on while changing positions your switch won't harm diodes.

Having said that I still shut off the motor while turning on the battery switch. Old Dog New Tricks Syndrome, I guess.

Val on Calista, # 3936, Patchogue, N.Y.

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stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 09/07/2007 : 12:49:59

always on 'both'.

general rule with electricty relative to small systems, is not to monkey around with anything - if its on - don't make any changes until it's off. Minimalist wiring means there isn't anywhere for surges to go, except where you least want it to go.

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 09/07/2007 : 13:16:49

This is a good question, one that I've pondered for a while. We always do multiple variations of switching when on long night races. Battery on 1 while racing at night, midway through we'd switch over to the #2 to fire up the engine, then switch back to all to charge everything up. After about a half hour we'd shut her down and go back to 1. Other boats I've been on have a starting battery that they'd fire up the engine then switch to all once things were going.

I asked one of the owners about it once and he said that they've put things in place to handle those quick surges. I kind of took it for what it was worth and did what he wanted on his boat. I never really had the chance to inquire if it was the selector, the engine or the batteries that had things in place. Or if it was the owner or the manufacturer.

I do know that on my old selector the all was in the middle with 1 and 2 on the ends. Off was at the bottom. You would have current flowing at all times when switching - I can't speak for all of the selectors though.

Thinking about this logically though, on a boat with an outboard where pull start capability exists I can't see any reason why you wouldn't keep the battery selector in the "all position" at all times while the engine is running.

dw

Edited by - Champipple on 09/07/2007 14:26:19

EAbrams
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USA
130 Posts

Response Posted - 09/07/2007 : 14:19:01

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Frank Hopper
 Ed, I have deleted your identical multiple posts in the Catalina 25 forum, the general forum is the right place for this question and it confuses everyone to have a question posted in two locations and more than once.
<hr height="1" noshade id="quote"></blockquote id="quote">

Sorry. I repeatedly got an error message every time I posted and thought my posts went into cyberspace. When I finally got frustrated I closed the 25 forum and opened the General forum, then retyped my message. I never knew of the multible posts. I would have deleted them myself.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/07/2007 : 14:49:52

No harm no foul. There was a time a few years ago when we were on a different hosting service when posts took so long to acknowledge that people were posting multiples all the time, thinking nothing had happened. When you read archives you will see those threads. This site is so much better than it used to be!

Edited by - on

EAbrams
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USA
130 Posts

Response Posted - 09/07/2007 : 14:51:21

How this applies to me is......

My #1 battery does not seem to have enough juice to start my (1987) Yamaha 4 stroke. ( Don't some smart guy tell me to switch battery positions

) So I start it with #2 (or both). Then I would like to be able to switch to #1 while motoring to attempt to charge it by itself. I'm figuring more juice dedicated to just one battery. Anyway it seems like the jury is still out on this one. Fear of damaging my electrical system will keep me from doing it.

Then maybe one day in the future I will cringe as I turn the switch and if nothing breaks I will go over to the other side.

Did anyone happen to read Ask Chuck in BoatUS?

Edited by - on

Stu Jackson C34
Admiral

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844 Posts

Response Posted - 09/07/2007 : 15:17:15

It all depends on how your boat is wired.

Most boats have the alternator wired to the switch, and then the wires go to the batteries. That means that the wires between the switch and the batteries do TWO things: feed current INTO the batteries, AND take them out to run the DC panel and its loads. This is also the reason people use BOTH, because if the charging source goes to the switch, the ONLY way to charge both batteries is to have the switch in the BOTH position.

Some people have wired their alternators (and chargers and solar panels) directly TO the batteries. The advantage is that the switch is no longer in the circuit to the alternator, which could fry the alternator diodes if the switch is NOT make-before-break or is old and the contacts fail. It's the easiest way to avoid the problem, and then the switch is ONLY being used to direct battery output, instead of serving the dual use.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/07/2007 : 15:35:33

If your batteries are not very close in performance toss them and get a matched pair of new ones. On my 89 I have the OB wired directly to one of the batteries, (on my '82 I had everything run to the back of the switch), but since the ground is common and the switch is always on both then electrically the OB has a path to both batteries. For me all of this OB charging talk is odd, I believe a boat should have an onboard charger which keeps everything up. I also question how many of us could run an OB, with it's small charging output, long enough to do much to a battery. Once again, remember these are designed for fishermen who run them all day. I really don't care that my Honda has an alternator, I just care about the starter having a good circuit!

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 09/07/2007 : 16:21:06

Since my outboard only runs around 10 minutes (more like 5 minutes) when coming and going from the marina, I've never bothered to hook up the alternator to the battery.

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EAbrams
Navigator

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USA
130 Posts

Response Posted - 09/07/2007 : 19:49:59

The post kinda evolved into a charging issue. I was really asking about the switch thingy.

Anyway already have been pricing two new group 24 batteries. $ 45.00 a piece at local Sam's Club.

Both of you have just stated what I really knew already. How much charge could our batteries be getting. First the small amp output and second the short time our engines are running.

No electric at my dock. Me thinks ( <--- look I kin talk like Popeye

) I should get a small solar panel and throw it on the cabin top

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/07/2007 : 21:09:24

Wont there be a lot of power soon from the wind turbines off of Martha's Vineyard?

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sweetcraft
Admiral

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USA
816 Posts

Response Posted - 09/09/2007 : 23:00:55

Ok, the discussion has been around for a long time as I have used two batteries, group 27, for 28 years (not the same batteries) with an isolator. We have cruised for up to 5 weeks and if the first battery goes down and can not start the outboard I switch to the other battery. The isolator continues to charge both to their own level and soon they are both up as full as possible. Yes there is a way to get the batteries up to the top charged level and it is more complex and higher cost. I have never had a problem with batteries too low to start and now the charging is done with a Honda. Switching is suppose to not be a problem with an isolator but I still only switch with the outboard off. Proving that the isolator won't burn out the diodes is not my interest. Tomorrow I go to the boat for the first time in a while as we finally will have a smoke free day with a breeze, 53,000 acres of the Moonlight fire is within 10 miles of the lake. Will see if the batteries are still up.

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 09/10/2007 : 19:12:39

The reason they tell you not to mess with the switch is so you don't turn it OFF. Switching between 1-ALL-2 can be done without problems.

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