Battery switches / isolator

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
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.
 
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.
 
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.
 
... 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. :eek:

I've only seen it once, but that was enuf to convince me.
 
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
 
Last edited:
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.
 
"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.
 
"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 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.
 
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.
 
"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.
 
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
 
"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.
 
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.
 
"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 “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.
 
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.
 
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. :eek:

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. :thumb:
 
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
 
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

I recommend parallel

https://www.google.com/search?sourc...AhURPK0KHey_ATgQjJkEegQIDxAB&biw=1304&bih=667
 
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.
 

Attachments

  • 20201027_184358.jpg
    20201027_184358.jpg
    94.5 KB · Views: 52
  • 20201027_184414.jpg
    20201027_184414.jpg
    119.4 KB · Views: 50
  • 20200920_122534.jpg
    20200920_122534.jpg
    127.8 KB · Views: 51
  • 20200920_122541.jpg
    20200920_122541.jpg
    113.7 KB · Views: 51
What happened to DHeckrotte?
 
What ever you do, the alternators must be connected to a battery (a load) at all time otherwise they get damaged.
 
I don't even understand what that means. Can anyone translate?

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...
 
A great battery diagram that makes sense ( to me ) thanks for sharing.

I see a lot of reference to " battery isolators - combiners etc " here. I would be skeptical of any diode based device as I think there would be a forward voltage drop. + / - 1 V maybe more, depending on the quality of the diodes, unless they are https://www.google.ca/aclk?sa=l&ai=...ahUKEwipg_G0n67TAhXL3YMKHd2vDPAQ0QwIIA&adurl=Schottky diodes which are quite expensive at alrge currents. Frank B.

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.
 
Hate to bother you folks again on this subject.

I've got twin Perkins with a group 31 deep cycle battery for each and the lower helm is equipped with battery switches (off, 1, both, 2) that purportedly will enable me to start either engine with either battery. Additionally, I have a house bank (currently 4 6v batteries) and the 12v house panel has a switch for two batteries (off, 1, both, 2).

Nothing seems obvious about how the boat is really wired; I cannot see how the two helm position switches are interconnected and it does not seem to make any difference to whether they start. It also does not seem to have hurt anything(!) by having both switches off; the alternators still work.

Since the boat was pulled last fall, the battery banks went totally flat and the 110v charger refused to charge anything. I've since found that one of the start batteries was probably faulty and was boiling. I disconnected it totally; the charger and the other two banks seem fine.

The Charles 20 amp, 2000SP, battery charger has separate outputs: Marine: 2000 SP Series Battery Chargers but apparently it cannot tolerate a failed battery. Yeah, it looks haywired: something to fix; pic.

It appears that the Perko diagram below is appropriate for the boat except that it does not show how to interconnect the start bats with the house bank which might be a nice thing to be able to do. I also do not have a stand-alone genset start batt.

I am reasonably certain that I do not have a battery isolator, thus it would seem that the charging circuit interconnections inherent in the engines' alternators would serve to flatten all batts. I presume that the Charles 110v charger isolates the batts.

It would seem that I need to figure out the wiring and interconnections and add a battery isolator. The Guest 2503 at $400 seems to be a reasonable, but expensive choice.

Comments? Enlightenment? Newby here; it should be obvious.
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
 

Latest posts

Back
Top Bottom