circuit breaker amps?

If I find some time at work I'll stick a fluke meter on the zed for something to do and report back.

 

I would ignore the amps the starter motor drew, and concentrate on the amps the wire can safely handle, as I suspect anything more than 200amp would be overkill.

At 200amp, get a 6 gauge wire too long, and it will burn the protective cover off the positive wire, short against the body, and possibly set fire to your car before the fuse will blow.

At 200amp, a 4g wire will maybe run twice the distance to take the same power before running into the same problem.

Remember that the standard starter wire is around 1.5m long, 6g from the look of it, and has no fuse on it, so to start with I would ask how long does the wire need to be?

A reference for wire gauge
http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

In terms of testing a fuse, you would need to simulate the amount of real current going through the fuse, so the only real test would be on a test bench where you could control the delivery of the amps, rather than just strap your battery to the fuse and see what happens ...

 

I just had a quick look in the boot of a VE Commodore at the battery set up, i couldnt see any fuses without ripping all the trim out. does anyone know how they are set up? They have a huge 700cca battery.

 

Mate no offence but you have no idea, the current draw of the starter motor is the most important thing to look at when choosing a fuse as that's going to be the biggest current draw, and the fuse needs to be selected accordingly.

The voltage drop from a 5m length of the cable in a car would be negligible. I can even calculate it for you if you really want.

A short circuit against the body will draw full load current out of the battery and the fuse would blow instantly, probably 1500A or whatever the battery can supply depending on the resistance value of the short.

There is a reason I said to use at least 16mm squared cable, it is rated at 65A continuous load obviously not as high as the starter current ~150A but how long does the starter run for maybe 10sec max no way the cable is going to over heat. A cable taking 150A is something like 50mm squared and not practicable.

The stock cable is only just big enough really with extended cranking that thing gets hot.

 

Seems I was a bit hasty, I just checked out the hager website and you can use one of their main circuit breakers on DC up to 60V. So with 16mm squared cable use a 63A D-curve MCB and the cable is then protected also. Cost is f-all, your mate probably has one lying around op. I can't find a specific trip time graph but it looks like if it doesn't start within 10seconds it will trip going by 150A starting current.



"Can I use a hager MCB to protect a DC system?
Yes, maximum voltage is 60Vd.c. using 1 pole or 125Vd.c. using 2 poles. The breaking capacity of the MCB remains the same although the magnetic tripping point is increased by 50% (i.e. a C-curve characteristic is altered from 5 - 10 x In to 7.5 - 15 x In)"

 

Can anyone actually tell us what the factory specs from a 300ZX starter motor are, before this turns into another dyno readings repeat.
The closest figure I can find is 1.4KW or 117a at 12v, although another site lists this as an KWh figure, which then means this figure might not be right ...

 

I am am afraid I have to go with Tass, electric motors draw more amps on startup than on normal running, however with a starter motor on the Z as each piston comes to TDC of compression the starter will load up and draw amps as well. Most multimeters have an inbuilt dampner and unless they have a peak function will not measure spikes or lows accurately.

For another analogy go to any old under powered workshop and watch the lights as their bodgy old air compressor fires up. If they are like our old workshop the lights will dim down and come back as the motor gets going. Yes i know it probably has extra starting windings as well but that is beacuse the load on the motor is greater to get it going from a dead stop.

 

Do you guys read the whole thread? Rob said he was going to set is meter to peak hold. And the meter is not dampened it reads an RMS value of the fluctuating current.

 

sorry I was a bit vague on what I was agreeing with, my agreement is that the current draw would be highest on the initial engaging of the starter motor, as to the actual current draw figures I would not know and wont even guess at the values, but I was not trying to say the Rob had not used a peak hold (although yes I must have missed that post). I have been following this thread since the start and thought I had reread the whole thing before I posted above.

 

"Analogies are for sooks"......??? Is that so?

Jeezuss H Chroiooiiissstt M8.... are you ignorant, retarded, blind, blatantly stupid or a sad combination of all of them.
Selective comprehension is obviously your issue as well.

Just tell me, what part of;

And this:

(now, my simple test using a digital multimeter and a 12" fan... run current 7 amps, initial startup current..in excess of 20 amps.... gee..lookit that 4 x 7 = 28... seems my "sooks" theory is perhaps somewhere near what an experienced electrician is saying.......

What more testing do you need when 2 obviously experienced and capable electricians backed each other up based on subjective testing with aboratory quality instruments and my own tests back this same result up...sadly im just a stupid truck driver to be a subject of scorn for you with all your experiences x 12,000 starter motor draw tests eh? and then you trot out the likes of:

And finally (Drum Rolls........) This little gem:

Ahhh yep, your a real smart guy M8.

E

 

"Analogies are for sooks"......??? Is that so?

Jeezuss H Chroiooiiissstt M8.... are you ignorant, retarded, blind, blatantly stupid or a sad combination of all of them.
Selective comprehension is obviously your issue as well.

Just tell me, what part of;

And this:

(now, my simple test using a digital multimeter and a 12" fan... run current 7 amps, initial startup current..in excess of 20 amps.... gee..lookit that 4 x 7 = 28... seems my "sooks" theory is perhaps somewhere near what an experienced electrician is saying.......

What more testing do you need when 2 obviously experienced and capable electricians backed each other up based on subjective testing with aboratory quality instruments and my own tests back this same result up...sadly im just a stupid truck driver to be a subject of scorn for you with all your experiences x 12,000 starter motor draw tests eh? and then you trot out the likes of:

And finally (Drum Rolls........) This little gem:

Ahhh yep, your a real smart guy M8.

E

 

im confused wtf r u guys argueing about

 

OFFS Mods, please lock this thread and end this inane rubbish. Better still delete the thread. This guys is rather weird.
This has decended to argument for arguments sake.
There are those who cannot see the wood for the trees and this individual is a shining example.

E

 

It looks like a Blue Sea 150A or 200A circuit breaker would do the job. The circuit breaker doubles as a battery on/off switch.

eBay Link


Panel Mount Circuit Breaker




Surface Mount Circuit Breaker







Blue Sea Mega fuse < $20



Mega Fuse Mounting Block 7721






Terminal Fuses (MRBF - Marine Rated Battery Fuse)



Terminal Fuse Mounting Block 5191

 

Nice find Andy, I didn't even think of gear for marine applications.

 

Ok lets all just go back to school for just a couple of minutes and calm down, forget who's done what and who knows what, this doesn't need to turn to a blood bath

There is that pretty basic little mathematical equation you all know:

V = IR

As per http://en.wikipedia.org/wiki/Ohm's_law and about fifty bazillion text books etc around the globe.

(for the novices V = Volts, I = amps/current, R = Resistance)


You should all also know that a DC electrical motor produces the highest torque when stalled and the torque and current reduce as the RPM picks up.

Peak torque and peak power consumption at at zero RPM, I wont go to details as people will try to argue but if you let a DC motor free spin then current draw drops to almost zero/very low compared to peak current draw when stalled. (it will only draw enough power to overcome its own internal resistance). But this is sort of off topic.

All you need to know to work out what the current draw will be at the instant you start the starter and the clutch engages is the resistance of the actual starter motor assembly and the cable supplying it + the earth back to the battery.

Now seeing as the bible says this:
http://300zx-twinturbo.com/cgi-bin/...0&cycle=off&slide=24&design=default&total=133

I can't quote the figure and I bet if I give a figure here people will argue they have tested otherwise so I will simply counter this with a simple suggestion.

If you doubt the current draw when the starter is first engaged will be significantly higher than what some here are posting as being the maximum - please measure the resistance from the positive terminal on the main power cable to the negative terminal (obviously with the battery disconnected!!) while bridging the solenoid on the starter.

A typical starter has an internal resistance of 0.006 ohms, - if you know what you are talking about you know this is a good starting point.

So we have a voltage of ........... it's not as easy as that as it starts at ~12.6V and drops in the instant you try to start the car, nominal voltage is 12v so lets just use that for the first instant before the battery drops away.....

V = IR so I = V/R therefore Amps = 12/0.006

therefore amps = 2000!!

Your starter motor WILL NOT take 2000 amps when you flick the key, your starter motor will take pretty much as much as the battery can deliver in the first instant - it's pretty much a dead short in that first instance.

The actual draw in each car will depend on the size and the quality/condition of the battery.

Even a quick google will resolve any doubt of this, as RPM increases current draw reduces, Circuit breakers and fuses etc wont trip immediately - someone already mentioned quick blow fuses etc.

A 200Amp CB or fuse should do the job BUT there is far more current draw potential in that first instance, most people are on the same page just some reading some lines as being more important than others.

Have a vodka and chill out :zlove:

Oh: http://www.ybw.com/forums/showthread.php?t=7962 even the silly yatchies can figure it out

 

Your on the money mungy. Not sure how the thread got out of control?