Is a 345A switch enough for my engine?

[wingssail]

Originally Posted by coopec43

I hope the "slow cranking speed" doesn't occur as a 200,000 oil tanker bares down on you!

Coopec43, I just want to add something in response to your comment (which I recognize was a joke, but still...)

If I am sailing, I will turn my boat, not turn on my motor. If I am sailing my speed will be about the same as my motoring speed, so what do I gain by trying to start my motor?

If I am motoring my motor will already be on, no issues.

I guess what I am saying is that I do not depend on my motor to get me out of trouble. I have a sailboat, a very good sailboat, and I usually try to sail out of trouble, or better yet, try not to get into trouble in the first place.

The last thing I do in a bad situation is reach for the key to start my motor.

[wingssail]

Originally Posted by Wotname

^^ 40+ years is a good field test. This is a case of don't fix it if it ain't broke

Unless you have some evidence of a failing switch like slow cranking speed or the switch getting warm, it will likely outlive you.

Wotname, the problem is this. I have a small switch and it is fine. Yet the big brains at CF say you must have a switch capable of 900 amps, or whatever and they tell the newbies that.

If my switch is fine, why should anybody listen to these guys who maintain we need to spend $300 or $500 for a fancy switch?

[coopec43]

Originally Posted by wingssail

Wotname, the problem is this. I have a small switch and it is fine. Yet the big brains at CF say you must have a switch capable of 900 amps, or whatever and they tell the newbies that.

If my switch is fine, why should anybody listen to these guys who maintain we need to spend $300 or $500 for a fancy switch?

I'm most certainly don't consider myself an expert but what would be wrong with a switch like this?

Or this? @ $30.39

[Wotname]

Originally Posted by coopec43

I'm most certainly don't consider myself an expert but what would be wrong with a switch like this?

Or this? @ $30.39

Nothing wrong with the red one, dunno about the other one as the specs aren't stated (and I woz too lazy to look 'em up )

[Jim Cate]

Originally Posted by coopec43

Why does the Perkins 4-108 manual say you need a 900A (intermittent) solenoid switch?

Perkins 4 108 diesel engines have quite a high compression ratios so I don't think "general advice" is relevant.

I agree with Wotname (comment above)

Compression ratios around 22:1 are standard for nearly all modern or semi-modern small diesels. The 4-108 is not in any way unique in this regard and its starter loads are similar to most engines of similar displacement. The "solenoid switch" must make and break high currents every start cycle. The battery switch normally just sits there conducting... a less stressful activity for a switch.

And FWIW, lots of us have used similar battery switches for decades, ones rated far below the peak current ratings of our starters, and they seem to last longer than most components of our engines... or us, for that matter!

Jim

[coopec43]

Originally Posted by Wotname

Nothing wrong with the red one, dunno about the other one as the specs aren't stated (and I woz too lazy to look 'em up )

I didn't look at the specs for the black one as I took their word for the switch.

SEAFLO ON/OFF Battery Kill Switch 900 AMP Isolator 2-Position 12v 24v 32v 48v

I'm wondering about the suitability of one of these?

[Pizzazz]

I experienced a stuck starter this summer. Cummins 450 hp, original starter (20 years old), relays must have been rebuilt a few times. It got stuck turning while the clutch was not engaging. You need to have a quick battery disconnect in this situation, separate for each engine. It could be a regular switch or a kill switch.

Everything on a boat is a trade-off. If the boat/engines older, then make sure you have the safeties on. If you are paranoid, oversize the switches. I would not have a problem with the smaller switch the OP is proposing as the starting current may be 900A for a few fractions of a second but then it drops to the power/voltage which is much less. But in general, you want to put your biggest switch on the starter, next biggest on the AC/heating circuits and everything else is too small to worry about.

[Wotname]

Originally Posted by coopec43

I didn't look at the specs for the black one as I took their word for the switch.

SEAFLO ON/OFF Battery Kill Switch 900 AMP Isolator 2-Position 12v 24v 32v 48v..........

My bad, I need new reading glasses
So yes, it appears to be OK.

[Wotname]

Originally Posted by coopec43

........................
I'm wondering about the suitability of one of these?

I wouldn't touch one of those with a 10' barge pole on a cruising boat; might be OK on a motorcycle or a shopping trolley sized car or small outboard engine.

I would have zero trust in the materials and manufacturing quality control etc.

Plus you can't see at a glance whether it is ON or OFF.

Some of the ebay sellers didn't offer any specs while some had differing numbers for what looked like the same item.

Here are two descriptions I found -
1.

*Knob Type Car Auto Battery Terminal Power off Disconnect Switch Protective Switch
*Mainly used to solve the leakage and loss of electricity caused by the infrequent use of the battery of motorcycles and automobiles
*Suitable for all 6V, 12V and 24V batteries cars, vans, boat, motorcycles
*Easy to operate and practical to use
*Material: Zinc alloy copper plating
*Color: As Pictures Show
*Withstand current: 400A
*Aperture: 17mm (Approx.)
*Suitable for battery terminals: 16~17mm

2.

Car Battery Cut-off Switch Terminal Isolator Quick Disconnect Master Shut Kill

Description:
Battery disconnect switch
Directly meets the negative terminal
Simply loosen or remove the wheel to disconnect
Anti-theft anti-theft device or keep charges over time
Continuous 125A
Difference 500A
Suitable for 6V, 12V and 24V batteries

Specification:
Colour: Black / Brass
Placement on Vehicle: Battery
Classic Car Part: Yes
Product size:8.5*3*3cm


You might have a different risk/reward profile...

[Uncle Bob]

Originally Posted by Wotname

I wouldn't touch one of those with a 10' barge pole on a cruising boat; might be OK on a motorcycle or a shopping trolley sized car or small outboard engine.

I would have zero trust in the materials and manufacturing quality control etc.

Plus you can't see at a glance whether it is ON or OFF.

Some of the ebay sellers didn't offer any specs while some had differing numbers for what looked like the same item.

Here are two descriptions I found -
1.
2.

You might have a different risk/reward profile...

But But But it must be alright, it's on Ebay.

[Ballsnall]

Originally Posted by wingssail

Yes, and I also worry about an asteroid falling on me. So far my cranking speed has been sufficient.

Oh and ask Lodestar. They never will bear down on me, but if they do, it's my fault.

Sweet Jesus, I forgot about asteroid's, now I'm going to have to get helmets for the crew, and converting to air start just to be safe.

[coopec43]

Originally Posted by Uncle Bob

But But But it must be alright, it's on Ebay.

I'm not sure why you stated that? Maybe you should look at what is sold on eBay (you might be surprised)!

I buy just about all my requirements on eBay. Purchases have included:

Hitachi brands
Rule bilge pumps
Victron electronics
Renogy Solar Panels
Stainless Steel fasteners
Electrical shunts, circuit breakers, switches, meters, Electrical cable
Epoxy Resin
3000/6000 Inverter
Muir Winch.
AGM Batteries
Through hull fittings

https://www.ebay.com.au/sch/i.html?_...nogy&_osacat=0

[goboatingnow]

Eaton , has a good treatise on starters. Their tests show inrush is 10x plate rating

Hence say on my MD2030 the starter is 1.2kw at 12v nominal. Hence 100A current with an inrush current of 1000A possible



Hence that Guest 2111 would not be suitably rated.

[coopec43]

I think this would be the way to go but it is only rated at
250A Continuous
400A Intermittent
750A Instantaneous Current (??????)


But if I looked further I'm sure I'd find Heavy Duty versions

https://www.ebay.com.au/itm/17539465...Cclp%3A2047675

[goboatingnow]

Originally Posted by coopec43

I think this would be the way to go but it is only rated at
250A Continuous
400A Intermittent
750A Instantaneous Current (??????)


But if I looked further I'm sure I'd find Heavy Duty versions

https://www.ebay.com.au/itm/17539465...Cclp%3A2047675

Don’t use knife switches this isn’t the 1790s