Battery switches / isolator
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GregBrannon
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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.
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.
diver dave
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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.
OP
OP
DHeckrotte
Guru
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.
I have finished my rewiring project by arranging battery/engine switches at the lower helm and fuses on the battery posts.
FF
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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.
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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"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.
...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.
FF
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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.
Perhaps a 1 wire auto unit will not blow the diodes, I have never tried.
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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.
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.
FF
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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.
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.
OldDan1943
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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
FF
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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.
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.
Island Cessna
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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.
FF
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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.
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.
Comodave
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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.
@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.
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.
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.
TWedd
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Lots of good info on this thread! I am starting a project to replace/upgrade my house bank. I have just about finished tracing out my existing wiring, and am trying to figure out the best way to wire/install my new house bank. Is there a single source for this info laid out in a easy to read format. I seem to remember Nigel Calders name mentioned, any suggestions?
Thanks
Tom
Thanks
Tom
SteveandZoila
Senior Member
Nigel Calder
My wife gave me the 4th edition a few years ago. I am still learning and still rereading. Want to be safe and improve. Planning to go LiFePo4 system. Have installed solar and redesigned the house bank system, charging, and monitoring. One trickle charger, 2 Inverter chargers, work still IP, needs grounds on units.
My wife gave me the 4th edition a few years ago. I am still learning and still rereading. Want to be safe and improve. Planning to go LiFePo4 system. Have installed solar and redesigned the house bank system, charging, and monitoring. One trickle charger, 2 Inverter chargers, work still IP, needs grounds on units.
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DrissZougari
Senior Member
What ever you do, the alternators must be connected to a battery (a load) at all time otherwise they get damaged.
It means that if your bank exceeds the CCA or Ah specification you'll need to default to the manufacturers "short circuit rating". Not too many even publish this rating. Odyssey does and each G-31 battery has 5000A of short circuit current. A 400Ah bank of four, in parallel, would be 20,000A..
If you can't find a short circuit rating, then you need to default to a Class-T fuse which is has a 20,000A interrupt at 125V. The Class-T AIC rating will be much higher at 14V. Class-T is the only fuse recommended for LiFePO4...
jgwinks
Guru
If your alt or external regulator has a sense wire, you can eliminate the diode voltage drop by connecting the sense to the down stream side of the diode. The alt will then put out 15v to get 14v. But running alt B+ direct to the house through a fuse with a combiner or ACR to charge the start is better and doesn't matter what kind of alt you have.
sealandsky
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You do need a battery isolator, or you can draw down your start batteries along with your house batteries. the problem is that isolators are inefficent. Chck in to the Blue Sea ACR. Blue Sea Systems ML-ACR Automatic Charging Relay with Manual Control
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