# Outboard circuit breaker sizing



## Red (Mar 11, 2021)

After a dead battery scare at a little mountain lake with the whole family last year, along with wanting to clean up the PO’s work, I’m about to rewire my 17’ Alweld with center console. 

The basics:
-Move the starting battery to the front with the trolling motor battery
-Add a Perko switch so I can crank with the trolling motor battery in a pinch and so I can charge either battery while running
-Add an accessory switch panel to the console

I’m in industrial maintenance, and don’t feel comfortable with a run of heavy wire under the aluminum sides of my boat where I can’t see them without circuit protection. My question, I can’t find the starter motor amperage for my early 90’s Evinrude 60hp 2 stroke. I know I can run up to the amperage rating of the wire, but will a 150 amp breaker be enough for the starter? I would think that would be plenty, but I’d like to verify. I’m planning on a run of around 35’ of #1 welding wire, which is rated to 240 amps.


----------



## InSaneFisherMan (Mar 11, 2021)

Not sure if this will help.

My DF9.9 starter is rated at 1.4kW, if my math is correct, the amperage at 12vdc would be 116a.

My 6 cylinder GMC has 100a fusible link at battery post.

Without the specifics on the starter, or a clamp on dc amp meter, it may be difficult to get a a good number.

The peak current happens around the first 5-15 seconds of starting (motor starts to spin) and this is when too small of a breaker would likely trip.


----------



## Red (Mar 12, 2021)

That’s a good data point anyway. The fusable link acts as a slow-blow fuse, this breaker appears to have similar functionality. I’m going to give it a shot, if it doesn’t work out I’ll get a larger one. 

This is the one I’m looking at:
 https://www.bluesea.com/products/7148/187-Series_Circuit_Breaker_-_Surface_Mount_150A


----------



## InSaneFisherMan (Mar 12, 2021)

One recommendation first, if there is a starter rebuilding shop in your area, call them and ask if they know amp ratings of your starter or similar.

It looks good, having circuit protection is smart.

You don’t want a lot of false trips when starting, so 150a breaker is probably a good choice.


----------



## DaleH (Mar 12, 2021)

I recall that V6 OB starters had peak amp draw of ~235 initial and dropping to ~175 or so under load. A smaller OB starter should be lower. A quick Google search showed a 115hp Honda with a running load around 125, but no info on the peak amps, that 1st SLAM that hits whence energized. 

I have the OMC 60hp Service Manual but is has nothing for peak amp draw from the starter, regretfully.


----------



## Red (Mar 12, 2021)

Great suggestion on the starter rebuild shop, I didn’t think of that. My local shop could only tell me about automotive starters though. The chart above shows the relay holding 900+ amps for 1 second and 300 amps for 10 seconds, so that should easily hold the inrush current for the numbers y’all provided. I appreciate the help, I’ll post back up after the project is finished.


----------



## DaleH (Mar 12, 2021)

I think your starter is going to draw > 45-amps running under load ...

FWIW if you really want to know, here's a 'clamp on' Amp Meter for $40 shipped:

https://www.ebay.com/itm/Extech-MA140-True-RMS-300A-AC-Clamp-Meter-We-Ship-Fast/402332706225?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D7138830e7703472ea28bc305d2169b55%26pid%3D101195%26rk%3D4%26rkt%3D12%26mehot%3Dpf%26sd%3D254693457888%26itm%3D402332706225%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseUnbiasedWeb%26brand%3DExtech&_trksid=p2047675.c101195.m1851


----------



## MrGiggles (Mar 12, 2021)

DaleH said:


> I think your starter is going to draw > 45-amps running under load ...
> 
> FWIW if you really want to know, here's a 'clamp on' Amp Meter for $40 shipped:
> 
> https://www.ebay.com/itm/Extech-MA140-True-RMS-300A-AC-Clamp-Meter-We-Ship-Fast/402332706225?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D7138830e7703472ea28bc305d2169b55%26pid%3D101195%26rk%3D4%26rkt%3D12%26mehot%3Dpf%26sd%3D254693457888%26itm%3D402332706225%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseUnbiasedWeb%26brand%3DExtech&_trksid=p2047675.c101195.m1851



That meter is AC current only, not many clamp meters will do DC current.

This one does though.

Edit: Apparently my link isn't working. Uni-T-B4Q094-UT210E is the model, $50 on Amazon.


----------



## DaleH (Mar 12, 2021)

MrGiggles said:


> That meter is AC current only, not many clamp meters will do DC current.


Well ... that was DUMB of me, I went by make & price, not voltage, sorry ...


----------



## MrGiggles (Mar 13, 2021)

DaleH said:


> MrGiggles said:
> 
> 
> > That meter is AC current only, not many clamp meters will do DC current.
> ...



No worries, you really have to look to find one that will read DC current, and the crappy search algorithms will not show them even if you search for that specifically.


----------

