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Why a battery switch?

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seastream
Navigator

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USA
242 Posts

Initially Posted - 02/24/2005 : 20:59:45

I'll be installing two batteries on my '83 this season, where there was one. I'll simply wire them in parallel. I see no need for a battery switch. I could be wrong. Aren't battery switches usually employed to reserve one battery as spare to start larger engines in case you've run down the primary battery? Most of us have sub 10 HP engines, with emergency pull starts included. Thoughts?

Seastream

Edited by - on

atgep
Master Marine Consultant

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1009 Posts

Response Posted - 02/24/2005 : 21:54:46

The charging can go haywire if the batteries are charged in parallel. One of the batteries will have lower resistance and invariably suck up more of the juice. I put in a switch to allow a reliable disconnect of the boat's power. The mickey mouse way catalina wired it had an undersized master switch that would get hot when everything was turned on! Not good.

When I install a second battery selector for the charging circuit. It may be overkill on a 25footer, but my electrical system is now safe and works 100% of the time.

Higher dollar battery chargers will charge each battery individually. The only way I would wire batteries in parallel would be if they were both identical age, model etc.

Just a couple of thoughts, Tom.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/24/2005 : 22:19:36

If you need two batteries to carry the load you put on them between charging cycles then they should be paralleled permenently. If you are using more than 50% of capacity you need more batteries. Actually while thats true for big boats that are used a lot and have systems that require large battery banks it might be more efficient to replace our small battery banks (1 grp. 24 battery) more often and save the weight. Battery switches are a waste of time. They also add a bunch of connections to the circuit. Seastream, you are correct, leave them out. That said if you are going to service any part of the electrical system that requires disconnecting things you should remove the negative terminal connection from the battery(s).
Personally we get along fine on one group 24 battery for 6 to 8 weeks of cruising with minimal engine and no solar panels or wind generators.
I also have a fuse on the battery positive side. A 100 amp seems to handle starting loads (9.9 Yamaha) with no problem and offers a lot of protection from major wiring incidents.
The new boat that I am designing will have no battery switches. It will have a fused positive. Dave

Edited by - Dave Laux on 02/24/2005 22:37:09

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 02/24/2005 : 22:49:15

seastream,

Here are a few thoughts if reliable electric starting is not an issue.

There's not much reason to go with two smaller 12V batteries vs. one larger battery. One issue is weight, as in lifting the sucker in and out of the boat without injury. If that's a problem, consider two 6V golf cart batteries in series. If you do wire batteries in parallel, I agree that it would be best if they were identical twins - same model, purchased at the same time, treated identically.

Remember to install over current protection in series with each battery.

-- Leon Sisson

Edited by - on

seastream
Navigator

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USA
242 Posts

Response Posted - 02/25/2005 : 07:27:34

Tom, I'll be buying two new group 24 batteries, so they should be nearly identical electrically. Leon, I like electric start, but at least we CAN pull start our engines...not the case with inboards. I'm primarily adding the extra battery so I don't run short after a day (and perhaps an overnight) of running instruments, lights, etc. Yes, I'll fuse the positive lead. I'll also have to look at a solar panel as I'm on a mooring this season waiting on a slip. I doubt the 2-4 hours/day an engine is run will be long enough to fully charge the batteries.

Bob

Edited by - on

cvwall
1st Mate

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USA
56 Posts

Response Posted - 02/25/2005 : 08:40:19

I can recall having my brother hold down the cylinder compression relase on a small Yanmar while I spun up the flywheel. When I had it going as fast as I could, he re-engaged compression and the engine started. Sort of like crank starting a flivver. This was on an Islander 30 tring to get into Stonington against the tide, mirror calm and dead battery.

Edited by - on

JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 02/25/2005 : 11:32:25

I would wire the batteries in parallel, but don't neglect a master battery switch to turn off the entire electrical system before Catalina's minimal panel.

25 year old wires cracked where properly supported in the lazerette. The wires shorted at the crack. An electrical fire began while I was 10 miles out at sea and over 2 hours from home. My crew for the day turned off the master switch. No more problems. Motorsailed back in.

Later I discovered that over 6 feet of marine cable was burned to a crisp.

Do not hook anything directly to the battery, except an automatic bilge pump. Do not bypass the master switch. Do not forget to have properly sized fuses.

Edited by - on

sweetcraft
Admiral

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USA
816 Posts

Response Posted - 02/25/2005 : 12:23:49

I chose to upgrade my system by using 2 group 27 btrys and then fused the positive wires with 50 amp breakers on the btrys inside the btry boxes. I use the 3 position btry switch to select btry for start and the other for utilities (lights, radio, etc)and when leaving the boat the switch can turn off everything except the bilge pump which is fused on it's own circuit. I connected the isolator at the switch so that each btry is charged independently with the outboard or charger. The panels are protected by a box with a plexiglass cover with just 2 screws for easy access. I added the second panel next to the first panel. The boat came with 2 btrys located on opposite sides and a lot of extra and exposed wires. Btrys are now together with less wires in plastic conduit and fused. Btrys are in boxes tied down for safety. We have stayed out at an anchorage for a week with problem with btrys. Good luch with the upgrade.

Edited by - on

John V.
Admiral

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USA
559 Posts

Response Posted - 02/25/2005 : 14:43:14

I use two deep cycle batteries on Nin Bimash, and have two three way battery switches. One controls which battery is sending juice to the panel and the other sends power to the off battery from the wind turbine. Since we do a lot of wilderness cruising we may see a marina only one day in five, power management is crucial. Each day we rotate batteries. A goes to charge while B runs the ship. The next day we switch again. Battery switching is very important in that you can isolate one battery or cut them all off in case you have an electrical fire. The bilge pump and the voltage converter are the only items that are directly connected to the battery.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/25/2005 : 18:49:18

The two Jims above are good examples of why all circuits incuding main battery connections should be fused. A fuse should have opened the circuit on Jim B long before a fire started. If you need two batteries to suport your load both of them should be working all the time. In other words the percent reduction in charge level of the battery(s) should be minimized. Jim S isolators have been implicated in many early battery failures ( from reduction in charge voltage) and fires ( from diode failure)and IMHO should not be in any boat. Dave

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 02/25/2005 : 19:09:08

WOW, Charles your tale of flywheel starting your diesel is exactly the way we started the old single cylinder Buda on Capt. Charlie Allis's dragger back in the early fourties. Lordy it had a flywheel the size of car tire right at the bottom of the companionway hatch. Just the mention of it and I can close my eyes and hear the THUMP THUMP THUM THUM MUM MUM MUM now. That dang thing is probably still going.

Val on the hard DAGNABIT

Edited by - on

sweetcraft
Admiral

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USA
816 Posts

Response Posted - 02/26/2005 : 02:01:08

Wow, I learn I have another item to check. A fire at sea can ruin your whole day. There have been other helps from the forum but I will be checking tomorrow about how I can upgrade/change the situation I have with the isolator. Making the boat safer is the bottom line. Thanks Dave.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 02/26/2005 : 08:12:21

I like'm cause they are orange and have a big knob!

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Dave Laux
Captain

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318 Posts

Response Posted - 02/26/2005 : 08:26:03

Val, about 10 years ago I had the pleasure of spending a few hours with Ron Ackerman on Record. She had a two cylinder 60 HP semi-diesel. Each cylinder was separate and about 20 inches in diameter with the head at eye height as I stood on floor plates that were at crankshaft level. It idled slowly enough the count the turns and ran about 500 to 600 RPM at full power. Swung a 40+ inch VP propellor. It was wonderful. Was supposed to weigh over 20,000 lbs. Exhaust note was just a gentle chuff-chuff sound. Air start. Neat
The boat itself was built in Norway and was 65 ft long and built as a coastal freighter. I was on it for the start of one of the single hand RTW races from Newport Harbour. Dave

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 02/26/2005 : 10:07:29

Dave, Sounds like it had a stroke near five or six feet x twenty inch bore x two... where's my calculator

I'm struggling to understand a "semi diesel"...WASSAT ?

Val on the hard DAGNABIT

Edited by - on

aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 02/26/2005 : 10:57:46

Frank,

I liked them for the dame reason. That wouldn't be considered a fetish would it? Now I'm all nervous.

Al
GALLIVANT #5801

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/26/2005 : 11:14:33

These are two stroke engines with direct injection and a hot bulb for ignition. Much like a model airplane. The bulb was a cartoon dog bone piece of iron that passed through an insulator into the combustion chamber. To start you first heat the bone with a blow torch, then admit HP air from a flask to roll the engine. The injector sprayed fuel onto the bone, it lights and away you go. I'm guessing but probably 12 to 14 inch bore, 30 to 36 inch stroke, all ball and roller bearing, crankcase scavenged.
There used to be a book on Fishing Vessels of the World from the UN in the fifties that had drawings and pictures of these engines. This was the only one I ever saw. Record was aquired by some group and overhauled but I don't know where it is now. The boat was in MAIB a while ago after the overhaul. Dave

Edited by - on

John V.
Admiral

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USA
559 Posts

Response Posted - 02/27/2005 : 11:56:37

Hey Al,

As Rogers and Hammerstein said "...There aint nothing like a dame.."

put another log on the fire, quit shivering at the old computer.

Edited by - on

ronrryan
Admiral

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USA
561 Posts

Response Posted - 02/27/2005 : 13:42:26

The legend about Bolander one-cylinder diesels in Norwegian fishing boats was that you could drop a potato down the intake and the hot spud would be fired up out the exhaust pipe the next revolution. Beats a microwave, ron in SW FL

Edited by - on

seastream
Navigator

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USA
242 Posts

Response Posted - 02/27/2005 : 19:11:07

How big should the primary fuse be? Worst case would be crank current for a 9.9 OB. 100 amp seems a bit excessive, yet anything less (>80A) in the WM catalog is like the auto 'ATC' blade type, and IMO their holders don't seem to give enough surface contact area. The ones that literally bolt into their holders with 4 AWG leads coming off them seem a better choice but they start at 100 amps. I don't want my wiring to burn up to save the fuse.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/28/2005 : 07:45:52

I used 100 amp due to availability and the fact that starters have high surge current. I then used 8 gauge wire to connect to the distribution panel. Since everything from there on is individually fused its only that 3 foot piece thats not properly protected and its not way out of range. Dave

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 02/28/2005 : 08:25:06

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by seastream
 How big should the primary fuse be? Worst case would be crank current for a 9.9 OB. 100 amp seems a bit excessive,...
<hr height="1" noshade id="quote"></blockquote id="quote">

An electrician friend of mine measured the current draw on his Yamaha T9.9: 95 amps inrush surge, 75 amps steady state cranking. That was quite a surprise, as I had not expected that such a small motor would have such a high current draw. Anyway, a 100 amp fuse might even be too SMALL for a starter motor circuit, based on my friend's discovery.

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ilnadi
Captain

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452 Posts

Response Posted - 02/28/2005 : 13:09:33

Another thought/question on the subject: The battery(s) at least have 3 connections: Main cabl, charger, bilge pump. The main goes to the battery selector but the other two do directly to the charger and fused to the pump. I would like another switch in between for catastrophic cases. I even thought about a Frankenstein switch (a.k.a blade switch: http://www.gizmos-gadgets.com/product_info.php/cPath/7_9/products_id/359?osCsid=8c0176d3536e7139c5c2e1736bfa09e2) in the battery compartment. Something that would disconnect the batteries from everything for manual use (I cannot imagine a breaker big enough for a starter would trip on a mangled charger drawing 10 amps into it; so might as well call it a switch).

Problem is I have not found any decent double pole switches to do this. Anybody have any ideas?

As far as the inrush, some EL motors have very low impedance when they are not turning. The inrush you see is probabaly tempered by the motor/engine starting to turn. If the engine seized you may see even a higher current.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/28/2005 : 18:49:46

Look people, the more stuff you have in the system, the lower the reliablity is. Thats why automobiles with some of the most complicated electrical systems ever built on a routine basis don't have a lot of extra bs in them. They do have a lot of fuses that are well thought out though. Dave

Edited by - on

gnorgan
Admiral

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USA
563 Posts

Response Posted - 03/01/2005 : 00:23:45

Okay, now that all you experts have chimed in I think it's time for some schematics. Looks like we need wiring diagrams, including proper wire size, fuse amperage, where to place the switch(s), for one/two batteries in parallel/series, 12 volt and 6 volt x 2 batteries, etc., etc. I've seen the ones in our manual but maybe there is a BEST system wiring diagram that is maximum protection against fire hazards and includes how to wire in accessories like VHF, stereo, auxiliary 12 volt plugs, your tiller pilot system, lights, etc. We're visual animals. We need pictures!!
Just my 4 cents worth.

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 03/01/2005 : 13:55:40

My '83 came with a fuse panel and a switch that could choose battery one, battery two, both or none. Seems to me it has what everyone is asking for. I can't say that I like the idea of having to dig into my battery storage area to disconnect the batteries. Which I might be wanting to do while underway. Doing so might bring me very close to the "midwest" by the time I tossed aside my starboard cushion, raised the battery storage hatch, untied the battery box covers, found a wrench and undid two connectors. Turning a switch works for me.

Val on the hard DAGNABIT

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