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Old 08-16-2018, 02:00 PM   #61
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I spoke with Trojan battery tech and they say the short circuit rating for T-105 golf cart batteries is 2000 amps so if you have the Blue Seas battery terminal fuses, you are OK.

They have a 10000A interupt rating at 14V.



Well that's good news.
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Old 08-16-2018, 05:33 PM   #62
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Yes and theres already a lot of hand wringing over it..... hopefully it will become more clear as all the tech heavy guys debate it for awhile.
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Old 11-03-2018, 06:20 AM   #63
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Is there a reason to have a separate On/Off switch for each engine?

I have 3 diesel engines, 2 mains and a generator. The generator is 12v to run, and the two mains are 12v to start and shutdown but once started run fine without power. The current DC wiring does not reflect the good practices discussed in this thread, and I intend to correct that this winter, but there is a mechanical On/Off switch in the engine room for each engine between the battery bank and the starter. I'm wondering if there's a good reason to preserve the On/Off switches or if there's a general design practice I've missed that indicates the switches are a good idea.

Thanks for your help and insights.
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Old 11-03-2018, 08:44 AM   #64
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... but there is a mechanical On/Off switch in the engine room for each engine between the battery bank and the starter. I'm wondering if there's a good reason to preserve the On/Off switches or if there's a general design practice I've missed that indicates the switches are...
Starter solenoids have been known to stick ON. If that happens without an upstream switch, then describe what to do next.

I've only seen it once, but that was enuf to convince me.
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Old 11-03-2018, 09:31 AM   #65
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Is there a reason to have a separate On/Off switch for each engine?

I have 3 diesel engines, 2 mains and a generator. The generator is 12v to run, and the two mains are 12v to start and shutdown but once started run fine without power. The current DC wiring does not reflect the good practices discussed in this thread, and I intend to correct that this winter, but there is a mechanical On/Off switch in the engine room for each engine between the battery bank and the starter. I'm wondering if there's a good reason to preserve the On/Off switches or if there's a general design practice I've missed that indicates the switches are a good idea.

Thanks for your help and insights.
There are a few "small" exceptions which then must be fused, but having a shutoff switch between every battery and its load is absolutely the right thing to do.

Ken
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Old 11-03-2018, 10:01 AM   #66
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In response to post 63. Sure, the mechanical diesels will run w/o power. They won't shut down w/o power unless you can reach the fuel cutoff solenoid and manually operate it. The instruments and warning sounder won't operate w/o power. You cannot operate your engine/battery cutoff switch, or manually shut the engine down unless you're in the ER. You would have to deal with post 64's stuck solenoid scenario by flinging the furniture aside, opening the engine hatch and climbing down, or at least by getting there from the helm in some PDQ way.


I have finished my rewiring project by arranging battery/engine switches at the lower helm and fuses on the battery posts.
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Old 11-06-2018, 06:10 AM   #67
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"On/Off switch in the engine room for each engine between the battery bank and the starter. I'm wondering if there's a good reason to preserve the On/Off switches or if there's a general design practice I've missed that indicates the switches are a good idea."

KNOWING the engine electrics are disconnected is the safest way to service the engine.

The off- on switch should include a field disconnect , if you value the alternator.
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Old 11-06-2018, 11:05 AM   #68
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"The off- on switch should include a field disconnect , if you value the alternator."

...if your alternator charge cable is wired through the switch. If your charge cable runs directly from the alternator to the battery, this is not applicable.
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Old 11-06-2018, 08:42 PM   #69
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If by"charge cable " you mean the power to the alt. field ,, the diodes will depart if the charging alt is disconnected from the battery.


Perhaps a 1 wire auto unit will not blow the diodes, I have never tried.
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Old 11-06-2018, 10:53 PM   #70
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I have a large charging cable running directly from my alternators to their respective battery banks. These cables are not switched but they are properly fused.

Only my loads are switched at a point outside my ER door. If I turn both switches to off, it doesn't affect the charge circuits. It only cuts the load side of the system.

Both engines continue to run and both alternators continue to charge the battery banks.
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Old 03-15-2020, 02:59 PM   #71
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"The instruments and warning sounder won't operate w/o power. You cannot operate your engine/battery cutoff switch, or manually shut the engine down unless you're in the ER.

The Murphy Switch gauges are mechanical, and will automatically secure the engine if any pre- set number is reached.

The engine cut off is a T handle on a spring , when set a dry batt pulls a pin to allow the spring to shut the engine down.
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Old 03-15-2020, 07:18 PM   #72
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That manual/emergency T handle is not meant for everyday use. It is a brutal way to shut down the engine. So as the name implies.... manual/emergency only. I would not recommend even trying to stop the engine as a test. Check the linkage and make sure it does close off the air inlet but do use it unless it is an emergency
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Old 03-16-2020, 06:15 AM   #73
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"That manual/emergency T handle is not meant for everyday use."

There does not seem to be many engines made anymore with emergency shutter shut downs .

Only place I have seen them is on OTR trucks and buses with DD 71 series engines.

The Murphy shut down T handle pulls the normal stop control. One can switch to a manual stop if the engine only has an electric solenoid.
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Old 03-16-2020, 12:31 PM   #74
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That manual/emergency T handle is not meant for everyday use. It is a brutal way to shut down the engine. So as the name implies.... manual/emergency only. I would not recommend even trying to stop the engine as a test. Check the linkage and make sure it does close off the air inlet but do use it unless it is an emergency


You are right, only use in an emergency, but on 2 stroke Detroit’s with unit injectors periodically test the linkage with the engine off by pulling the handle,tripping the flap valve, and then resetting it.
Never disconnect it because you don’t use it. The “emergency” it was installed for is a stuck fuel rack, resulting in overspeed, and if you don’t pull the handle to cut off the air the engine will stop when it is done scattering rods, pistons, crankcase parts, and oil all over your engine room.
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Old 03-17-2020, 06:51 AM   #75
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"The “emergency” it was installed for is a stuck fuel rack, resulting in overspeed, and if you don’t pull the handle to cut off the air the engine will stop when it is done scattering rods, pistons, crankcase parts, and oil all over your engine room."


The other emergency flaps are installed for is the engine being worn enough that it starts to use its own lube oil as fuel.


High time indeed , but pumps and power plants , get dont get replaced often.
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Old 03-17-2020, 09:47 AM   #76
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"The “emergency” it was installed for is a stuck fuel rack, resulting in overspeed, and if you don’t pull the handle to cut off the air the engine will stop when it is done scattering rods, pistons, crankcase parts, and oil all over your engine room."


The other emergency flaps are installed for is the engine being worn enough that it starts to use its own lube oil as fuel.


High time indeed , but pumps and power plants , get dont get replaced often.
I'd like to know the stats on marine gas engine fires as compared to diesel engine fires. During my six decades of being on or around the water... have seen two diesel engines in a flame-out, scatter parts, lube oil fueled condition. Have not seen a gas engine on fire.
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Old 03-17-2020, 11:03 AM   #77
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I would not be scared of a gas engine fire but rather an explosion due to leaking gas. I saw a 40’ gas powered boat blow up when I was young, 4 dead, 4 blown out of the boat and 3 not hurt at all. Made a powerful impression on my young brain. I was always very careful when we had gas powered boats.
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Old 03-17-2020, 02:20 PM   #78
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@Art #26
An interesting sea story: I was the Chief Engineer on a WW II vintage diesel electric Navy salvage ship during Vietnam. The main propulsion plant was diesel electric with four Cooper-Bessemer GSB-8 prime movers.

The blowers had very large lube oil sumps and one fear was the loss of mechanical seal between the oil sump and the blower proper. In case of a runaway where the blower lube oil was fueling the engine irrespective of the throttle or fuel shutdown system, we had a bail of rags pre-positioned by each blower and the damage control tactic was, should this condition occur, the Engineer of the Watch was to pull off the intake screen and start throwing rags into the maw. Thankfully we never had to test this process out.
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Old 03-17-2020, 05:55 PM   #79
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I would not be scared of a gas engine fire but rather an explosion due to leaking gas. I saw a 40’ gas powered boat blow up when I was young, 4 dead, 4 blown out of the boat and 3 not hurt at all. Made a powerful impression on my young brain. I was always very careful when we had gas powered boats.
Verrry correct... be verrry careful with gasoline.

But, if you are careful, gas engines can in many ways be a great, easy to maintain marine power source, for boats that are not too big.
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