Quick question on wiring

[xeitosaphil]

Just a quickie In the middle of a rewire, can I ask would this work or would the engine start current blow the 80A fuse!


Also could I use and existing 200mm 35mm2 cable in the middle of a 50mm2 engine start circuit without any detrimental effects?





Trying to use one feed from the battery post to two feeds of different fuse ratings and wondered if this would work.


To see diagram you may need to zoom in with your computer

 

[pvb]

Yes, that would work. The link bar would need to be substantial. You should install the link bar on top of the ends of the 2 MegaFuses, so that the MegaFuses themselves sit squarely on the fuse holders.

200mm of a slightly smaller cable won't have any detrimental effect.

 

[xeitosaphil]

Yes, that would work. The link bar would need to be substantial. You should install the link bar on top of the ends of the 2 MegaFuses, so that the MegaFuses themselves sit squarely on the fuse holders.

200mm of a slightly smaller cable won't have any detrimental effect.

Thanks PVB great news thanks for your help -Philip

 

[Talulah]

Personally I would not be using a Megafuse for the Windlass. I would fit one that can easily be reset. Potentially you will be tripping it several times a season.

 

[sarabande]

I'm a little bit concerned about the rating of the 250Amp fuse. Some engine starting cycles reach higher surge current loads for a short while. What's the 'blow' profile of the fuse ? What's the rating of the starter motor ?

http://bluesea.com/viewresource/114

 

[marklucas]

Your proposed circuit would work - the circuits are in parallel so don't know anything about each other - other than any voltage drop over the cable from the battery to the link bar.

Agree with earlier posts that certainly the anchor windlass should be on a circuit breaker not a fuse - if your anchor gets stuck the fuse will blow. That's the nature of the beast.

Also, again as posted earlier, 250A for a starter motor is not a lot - at 12V that's only 3kW to turn over the engine (and only if the battery holds at 12V -which it won't - so more like 2kW max). Plus a starter motor is by its nature an inductive load so will take way more current for a few tens of milliseconds until the motor starts turning.

 

[pvb]

A 250A MegaFuse will be fine for the starter circuit. MegaFuses have a slow-blow characteristic.

 

[VicS]

Your proposed circuit would work - the circuits are in parallel so don't know anything about each other - other than any voltage drop over the cable from the battery to the link bar.

Agree with earlier posts that certainly the anchor windlass should be on a circuit breaker not a fuse - if your anchor gets stuck the fuse will blow. That's the nature of the beast.

Also, again as posted earlier, 250A for a starter motor is not a lot - at 12V that's only 3kW to turn over the engine (and only if the battery holds at 12V -which it won't - so more like 2kW max). Plus a starter motor is by its nature an inductive load so will take way more current for a few tens of milliseconds until the motor starts turning.

Doesn't he have a circuit breaker in the windlass circuit any way that will take care of overloads due to the anchor getting stuck. The fuse is there to protect the wiring from faults

The necessary minimum fuse size in the starter circuit will depend upon the size of the engine. It's there to protect the wiring so should not be greater than its safe working current
Fairly small engine IIRC

 

[xeitosaphil]

Doesn't he have a circuit breaker in the windlass circuit any way that will take care of overloads due to the anchor getting stuck. The fuse is there to protect the wiring from faults

The necessary minimum fuse size in the starter circuit will depend upon the size of the engine. It's there to protect the wiring so should not be greater than its safe working current
Fairly small engine IIRC

Engine Yanmar 2GM20 , Starter Motor 1.2Kw, supply 50mm2 cable , windlass circuit breaker at chart table for windlass 80A trip ( no problems last summer cruising) - fuse there only to protect cable as suggested, 32mm2 cable feed,


slow blow fuses rated for 15sec @ 200% overload - 5 sec @ 350% overload