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  #21  
Old 08-26-2014
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Re: fuse popped, ARRRG

Quote:
Originally Posted by deniseO30 View Post
I'm going to borrow a DC clamp on amp meter! I want to see this "mega amp" draw my little starter is claimed to be drawing on startup!
Be sure to grab one that can capture DC in-rush, most can't...

Even my Fluke at a 100mS sampling rate (0.1 seconds) is a tad slower than I would like for starter motor in-rush capture. My Midtronics EXP-10000HD however is designed for this and is faster than my Fluke....

This test was a 375Ah bank, 1.2KW starter at 32F..


You can see the starter current is not steady, it blips and it blips fast, too fast for 98% of the DC clamp meters out there. This entire screen shot is 0.765 seconds because this motor fires right up, as they should.. In this case the 1.2kW starter drew 640A +/- peak...


This screen shows the voltage performance of the batteries during starting.


This screen shows the averages & start duration loaded to unloaded starter; Average voltage during starting = 12.04V, Average Amps = 286A (1.2kW starter), Starting Duration Loaded to Unloaded Starter = .765 Seconds, Starter Circuit Resistance..


Measuring starting current is not simple and most clamp meters do not have the resolution/speed to do this. If it was easy to measure everyone would make a clamp meter that could do it. The EXP-1000HD with accessories for measuring starting loads runs about 2.2k, not a toll even most marine electricians are willing to pony up for.............
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Last edited by Maine Sail; 08-27-2014 at 10:18 AM.
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  #22  
Old 08-27-2014
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Re: fuse popped, ARRRG

That is a pretty impressive meter MS All this just makes it pretty obvious that any fuse on a starter will suffer the effects. Do big circuit breakers handle it better?
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  #23  
Old 08-28-2014
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Re: fuse popped, ARRRG

Quote:
Originally Posted by deniseO30 View Post
That is a pretty impressive meter MS All this just makes it pretty obvious that any fuse on a starter will suffer the effects. Do big circuit breakers handle it better?
Denise,

Are you asking because you're considering changing to breakers (which will trip slower), or do you just want to fix the problem? If your interest is in fixing the problem, see my (edited) post above, which implies that you get almost 10 seconds for the inrush current to drop to nominal levels. i.e. FIX = SWAP FUSE TO HIGHEST ALLOWABLE RATING

From your HVAC background, you should be familiar with the fact that all motors require a lot of current to get them spinning. This is especially true of a starter motor, as we not only have to get the motor to spin, but also have a solenoid to engage, and push the cog wheel to engage with the flywheel. That is why Maine's second pic showing the amperage drawn, looks like a "mountain with two peaks", and it then drops into foot hills, as the motor gets up to speed. One could assume that the peaks of the foot hills are the cylinders coming to the top of the compression stroke, or a bad spot on the contacts of the starter motor. You can also see in the third pic, which is showing available voltage, the inverse of the picture of the mountain range. You can easily see that the peaks in pic 2 correspond to the valleys in pic 3.
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Last edited by eherlihy; 08-29-2014 at 10:55 AM.
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  #24  
Old 08-28-2014
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Re: fuse popped, ARRRG

I'm going to get 175 or 200 amp cubes E. Like I said, the 125 seemed to be "holding" for many starts until the terminal became loose again.

Yes I'm aware of the inrush with motors but many ac motors have capacitors to "kick" the start winding that drops out with a relay & start cap.

I'm really not wanting to change all the cables to #2 for such a small engine but I could eventually.
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Old 08-28-2014
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Re: fuse popped, ARRRG

Even 2 gauge is small for cabling to a starter. I use 1/0 or 2/0 for all starting cabling, as do others I know. Bonus is very fast starting and easy fuse selection without going over wire ampacity. I have never had an issue with nuisance blows.

My 8 hp diesel is wired with 1/0 and it is a very short run.
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  #26  
Old 08-28-2014
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Re: fuse popped, ARRRG

Quote:
Originally Posted by MarkSF View Post
I went with the 300A fuses for my Universal 5424. The cabling is 00, so according to the table my fuses are just about small enough to protect the cabling. 00 is rated for 280A continuous inside an engine space. I think I read you are allowed a certain rating over the continuous rating, when selecting fuses. Mainesail, do you know what that percentage is?

"the new terminal is all green on the cable". Does this mean the conductors are not tinned?

Genuinedealz.com will sell you nice cables, terminated, with tinned marine-grade wire. That's what I use, and the price was less than the bare cable at my local chandlery.
EDIT: Usually I read the entire thread before posting. This was a good reminder to always do so, because my question is answered in the thread. Thanks.

Mark, where did you find this information. I've always heard that you should "fuze for the size of the wire" but after much searching I could only find voltage drop tables for wire and never found the fuse ratings for wire.

MedSailor
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Last edited by MedSailor; 08-28-2014 at 12:16 PM.
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  #27  
Old 08-28-2014
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Re: fuse popped, ARRRG

One thing to consider if your cables keep getting loose is heating at the terminal. When the terminal heats up, it expands. If the fastening bolt does not expand as much as the terminal, the terminal gets crushed. When the cable and bolt cool, the cable is loose. Each cycle lossens the connection more. The loose connection causes more heat which causes more crushing and looseness...
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  #28  
Old 08-28-2014
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Re: fuse popped, ARRRG

I guess you did not read the whole post, but thank you just the same
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  #29  
Old 08-28-2014
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Re: fuse popped, ARRRG

Denise, you don't even want to ask how much a circuit breaker with that high an amp rating would cost.
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  #30  
Old 08-28-2014
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Re: fuse popped, ARRRG

Quote:
Originally Posted by hellosailor View Post
Denise, you don't even want to ask how much a circuit breaker with that high an amp rating would cost.
I did check LOL. the whole system on the boat really works great. I'll deal with the cable and cubes at some point, but not today The bat to start cable is quite short and easy to repalce with #2 The rest run through the ACR and the isolated switch so they hopfully aren't going to deal with the starter UNLESS the start bat goes dead completely.

AGAIN AGAIN AGAIN, THE whole terminal was about to fall off. I really think it was me that didn't make sure it was tight. Guessing I will have to use a stainless nyloc on the plated copper stud.
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