Coyote Starter Current Draw?

[Alan_C]

Anyone have a good estimate for the current draw from the 2nd Gen Coyote starter when cranking? I have contacted Ford Performance, but like most of my questions to them, it has gone unanswered.

I am using 100A as a guestimate for my wiring planning, but I have seen numbers more like 120 to 140A suggested elsewhere. I am characterizing the IR drop from the battery to the starter based upon cable size. I also plan to use a Odyssey battery and would like to get some feedback from them on the voltage output drop from the battery at load. Looking for typical numbers at room temperature. I recognize that the current draw will change based upon temperature.

Does Factory Five still supply 4 AWG cable as part of the MK4 kit? That is what I received in 2011 when I got my MK4 kit. I had the battery in the trunk and I felt, as did others, that 4 AWG was marginal.

I am now doing a 70 Mach 1 restomod with the battery in the trunk. The length of the POS 12V cable run is just under 13 feet in my Mustang, far longer than that in the Cobra. I am planning to use 1 AWG at this point for the run.

Thanks

[Nigel Allen]

I used 50mm2 flex. From rear mounted battery, via isolator, to reduction starter on my Coyote. Basically just arc welder cable. Cost a few bucks per metre, but didn't need a lot. Cranking never an issue.

[Nigel Allen]

If in doubt, measure the cable size on a Coyote equipped late model Mustang. Maybe go up one size for a rear mounted battery. Use the same size cable for the ground/s.

[Alan_C]

Nigel: I have measured the length of the POS cable on a 2017 Mustang GT as I have the donor cables. Ford only used 4 AWG, however the cable is slightly less than 4 ft in length. The POS cable run in my Mustang restomod is about 13 ft. This is where my concern for the voltage drop comes from. With my run being 3x that in the donor GT, three times the voltage drop. I had a 4.6L DOHC in my MK4 and I felt the 4 AWG supplied with the kit was marginal with the trunk mounted battery and that run was likely less than 10 ft.

In my Cobra build, the stud on the starter was the source for 12V for the PCM and the rest of the car. In my restomod, I will not make that mistake as I will have a parallel run to the controls pack power distribution box directly from the fused battery source. So my Coyote PCM will see the voltage at the battery, not the lower voltage at the starter. This should be an improvement in itself and it is the same thing that Ford did on my 2017 GT donor. Ford also ran a parallel cable from the battery to their power distribution box.

[Nigel Allen]

G'day Alan, I calculated my 50mm2 cable and came out with 0AWG, give or take a few strands. Regardless of what the starter draws, it cranks fast. Any noticeable volt drop on my roadster is internal to the battery, which is not overly large. My go to as mentioned before is welding cable, high purity copper, super flexible and robust insulation.

Cheers,

Nigel

[JohnK]

I came across this handy wire size calculator a while back, and have found it very helpful whenever I'm adding circuits to my build:

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

If I make a few assumptions, the tool can help answer your question. If the stock POS wire on the Mustang GT is 4' long, the tool says that Ford sized it to be able to handle a 200A load. No doubt there's a safety margin in that. That's not likely what the starter is actually drawing. But if we keep that same 200A number and scale to 13', the tool says you'd need to go with a 0 AWG. wire.

[Alan_C]

Thanks for the link to the calculator. Easy to use and check various scenarios. Using published resistance per foot numbers, 1 AWG cable should be OK, but 0 AWG would be better. @200A, the 1 AWG cable will have a drop of 0.33V, more than 2%. However, I think 200A is excessive or a worst case number. I have seen others suggest numbers more like 120 to 130A and I would think no more than 150A.
I plan to purchase all my cable from BatteryCablesUSA. I will speak with their sales folks before making a decision. I wish I had a clamp on ammeter as I have a neighbor up the street with a 2017 GT. It would be great to have a real life number to work with.

[jiriza84641]

Thanks for the link to the calculator. Easy to use and check various scenarios. Using published resistance per foot numbers, 1 AWG cable should be OK, but 0 AWG would be better. @200A, the 1 AWG cable will have a drop of 0.33V, more than 2%. However, I think 200A is excessive or a worst case number. I have seen others suggest numbers more like 120 to 130A and I would think no more than 150A.
I plan to purchase all my cable from BatteryCablesUSA. I will speak with their sales folks before making a decision. I wish I had a clamp on ammeter as I have a neighbor up the street with a 2017 GT. It would be great to have a real life number to work with.

Are you running the battery in the Trunk? or using the breeze front battery mount. The battery IMO doesn't draw that much amps to start the engine. If you look at EDWARD B's build you will see a great reference on cable used.

I followed his build and used 2 gueage from the front battery mount to the quick disconnect and a 4g to the start from the quick disconnect. I works great and no issues. I purchased about 6 feet of battery cable from Interstate battery and about 2 feet of ground with the battery terminals crimped on for about $35.

Hope this helps!

[Alan_C]

Early in this thread I noted that this effort is not for a FF Cobra, rather for a 70 Mach 1 restomod. Yes the battery is in the trunk, far corner on DS side behind the wheel well. So the length of the run of 13 feet is far longer in my Mustang than for the Cobra. So this is the rub, longer run yet needing to keep the IR drop to about 2% or less if possible. This is why I was looking for a real number on the starter current draw.

I was looking at battery disconnect switches on Summit. Most are in the 150 to 180 Amp continuous range with surge to 1000 Amps. This kind of supports that starter current is in this range or less.

One of the reasons I continue to participate here is that people here are builders and second more Coyote based build experience here than just about anywhere else.

[NAZ]

The current draw will be influenced by the load on the starter and that is variable. Plan for worst case not for what your neighbor's engine pulls on a warm summer day. Starters have the potential to pull significantly more amps than your 100A estimate so you might want to grab your multimeter and check the field resistance then calculate the stall current (I=V/R).

Also, I've used welding cable before but the insulation doesn't hold up well in that application. It's better to get automotive battery cable and if you can't find a local source, look at Summit Racing.

[JimLev]

If your looking for high temp and low wire resistance look at this wire.
It is very flexible, has a silicon jacket covered with a fiberglass coating.
I had some left over from a job. I made cables for a neighbors LS1 36 Chevy and another building an 818.
https://www.awcwire.com/part.aspx?partname=srml-2
Or
https://www.awcwire.com/part.aspx?partname=srml-4

[progmgr1]

Also, I've used welding cable before but the insulation doesn't hold up well in that application.

I've got welding cable in my Hot Rod. What was it that caused the insulation to degrade - heat, abrasion, oil / gas / other contamination? Does it help to add a plastic sheath, or do I just have to give up on that cable? Thanks, Keith HR #894

[NAZ]

I've got welding cable in my Hot Rod. What was it that caused the insulation to degrade - heat, abrasion, oil / gas / other contamination? Does it help to add a plastic sheath, or do I just have to give up on that cable? Thanks, Keith HR #894

Welding cable has to be very flexible in all weather so the insulation is usually made from neoprene or EPDM. Battery insulation is typically made from a PVC and is much stiffer than welding cable. The PVC holds up to abrasion, fuel, oil, acid, salt, and ozone much better than the rubber insulation on welding cable. The PVC material used in battery cables is somewhat flame retardant too where welding cable is not so much. So I suggest you just watch for signs of cracking of the welding cable insulation and at the first sign, switch to a automotive battery cable with the more robust insulation.

[Alan_C]

The comments about using welding cable have my thread off track. I never asked about what type of cable to use, I have that covered and it will not be welding cable as there is much better cabling available.

I have upped my estimate to somewhere between 120 and 150A. I just wish someone had a real number to work for reference.

I will work with the vendor for my cable to choose between 1 and 0 AWG.

[NAZ]

Alan, I believe you should be able to measure the resistance of the starter field windings and get a good approximation of the steady state max amp draw of the starter using ohms law.

As an example, a starter may have something like .05 ohms resistance and using ohms law we can solve for the current (I) by this formula: I=V/R. So, divide 12-volts by .05 resistance and that equals 240-amps (we measure current in amps). Don’t forget to include the starter solenoid windings which let's say is .8 ohms so do the math again, 12/.8=15-amps. So, in this example, we should size our starter electrical circuit to handle at least 255-amps (240+15=255).

[Nigel Allen]

I agree with Naz, I wouldn't use rubber sheathed cable anywhere on a car. The welding cable I speak of is double sheathed PVC/PVC. The inner sheath provides the electrical insulation properties, whilst the outer provides mechanical protection. Without exaggeration, I have made and fitted hundreds of battery leads using this cable. None have failed.
No-one really uses rubber insulated cables in Australia anymore. Submersible bore pumps being one of the few exceptions, so I apologise for not being clear on this.

Al, I have a calibrated DC clamp meter and can log a typical Coyote crank cycle for you if you like. Just let me know.

I can recommend Cole Hersee battery isolators. I use them on 600hp diesel generator sets with non reduction starters. Nil issues.

Cheers, Nigel

[mike223]

The comments about using welding cable have my thread off track. I never asked about what type of cable to use, I have that covered and it will not be welding cable as there is much better cabling available.

I have upped my estimate to somewhere between 120 and 150A. I just wish someone had a real number to work for reference.

I will work with the vendor for my cable to choose between 1 and 0 AWG.


Industrial electrician here - 30 years experience.

Amperage ratings for cable are for sustained amperage flow, which your battery is never going to carry for long enough to cause a major problem.

The ratings are to keep you from burning the insulation off the wire when you are hooked to the grid.


It's difficult to get a good amperage draw reading on the starter because the proper meter is expensive and not handy to install, and the amperage varies so much from initial surge to when it is spinning the engine - and all that is very momentary (hard to get a good reading on).



Short answer is that you're likely pulling at least 300 amps (300-500) in the first instant, and less from there.

Video here: https://www.youtube.com/watch?v=k7ba7Jcb_qw


Notice the first time he cranks it you get a high reading of 332A on inrush - second crank inrush shows 232A max - this is due to the refresh time (delay) of the meter - challenging to get a solid reading in the time you have to read it.




OEMs rarely exceed #4 on battery cables, and I've never seen a passenger car use anything larger than #2.


When you start using multiple batteries (such as in diesel heavy trucks), you might see something bigger.


But a single passenger car battery is never going to move enough amperage for long enough to hurt #2 cable.

And a single passenger car battery is never going to move enough amperage for long enough to need anything larger than #2 cable.


Run as big a cable as you want - but it's never going to do anything for you (in a car) that #2 would not have done just as well.

[mike223]

Run as big a cable as you want - but it's never going to do anything for you (in a car) that #2 would not have done just as well.



Heh - make that "except get you up into cable connectors that are too big to connect to what you're trying to connect to"... :cool:


Just another afterthought.

[JimLev]

I’ve got high temp lugs for 2 and 4 gauge wire that have holes for 1/4” and 3/8” studs. You just need the correct BIG crimper to properly crimp these lugs.

[mike223]

I’ve got high temp lugs for 2 and 4 gauge wire that have holes for 1/4” and 3/8” studs. You just need the correct BIG crimper to properly crimp these lugs.

And as I said, nothing bigger than 2 gauge wire is necessary or desirable - but the OP is talking about 1 + 0 AWG.




I have upped my estimate to somewhere between 120 and 150A. I just wish someone had a real number to work for reference.

I will work with the vendor for my cable to choose between 1 and 0 AWG.


Here is an ampacity chart for the sorts of *extremely temporary* loads the OP is concerned with.

***WARNING*** this guidance is only relevant for use in wiring systems that are powered by a single passenger car battery!!!


http://4xspower.com/support/amp-chart/

[mike223]

Here is an ampacity chart for the sorts of *extremely temporary* loads the OP is concerned with.

***WARNING*** this guidance is only relevant for use in wiring systems that are powered by a single passenger car battery!!!


http://4xspower.com/support/amp-chart/


I went ahead and saved images of the linked charts - because I would never put this chart on the internet without the context I have provided.

Someone who does not understand the context of "powered by a single passenger car battery" could cause themselves major problems referencing these charts.

The different specs between the two types of wire probably relates to the number of individual strands in these two specific products.


139313

139314

[Railroad]

I’ve got high temp lugs for 2 and 4 gauge wire that have holes for 1/4” and 3/8” studs. You just need the correct BIG crimper to properly crimp these lugs.
Try some of these. They are easy to use and make a great connection on wire end. I guess you could crimp after it cools, if you want.
I just drop the pellet into the connector cup, holding with some vice grips, heat with propane torch until the pellet liquifies, insert wire and let cool.

https://www.google.com/search?q=electric+solder+pellets&client=firefox-b-1-d&sxsrf=ALeKk00gMVly8ZJtMlgkhAPo-Jcm5wVGrw:1607959506315&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjlgr_5483tAhWLhK0KHTyBAHcQ_AUoAnoECAYQB A&biw=1280&bih=579&dpr=1.5

[edwardb]

I use #2 battery cable from West Marine for my builds. Has worked great. Not cheap, but sold by the foot so you only get what you need. The conductors are small (lots of them...) so it's relatively flexible. Tin coated to reduce corrosion. Plus a high quality jacket for marine. Recommended.

I tried and like solder slugs OK. For battery ends though I really like these: https://www.delcity.net/store/Straight-Barrel-Fusion-Battery-Terminals/p_804069.h_804070.

[Alan_C]

I use #2 battery cable from West Marine for my builds. Has worked great. Not cheap, but sold by the foot so you only get what you need. The conductors are small (lots of them...) so it's relatively flexible. Tin coated to reduce corrosion. Plus a high quality jacket for marine. Recommended.

I tried and like solder slugs OK. For battery ends though I really like these: https://www.delcity.net/store/Straight-Barrel-Fusion-Battery-Terminals/p_804069.h_804070.

Paul: Thanks for the response. Finally, a real world answer. Nigel from this site, will use a clamp Ammeter to measure the peak current after he returns from a vacation. I am guessing that the run from the trunk area to your starter is likely less than 10 ft. With my run closer to 13 ft., I was thinking a 1 AWG would be appropriate in my case. I submitted a question to BatteryCablesUSA and their recommendation is to use a 1/0 AWG cable. This appears to be over kill IMO, however it is another data point.
How big of a cable did you run to the power distribution box in your Cobra? Since the high current path is to the starter, I plan to run a parallel 6 AWG to the PDB. The parallel run limits the voltage drop seen by the PDB to that at the battery terminal, not the temporarily lower voltage you would see at the starter.

Thanks

[edwardb]

How big of a cable did you run to the power distribution box in your Cobra? Since the high current path is to the starter, I plan to run a parallel 6 AWG to the PDB. The parallel run limits the voltage drop seen by the PDB to that at the battery terminal, not the temporarily lower voltage you would see at the starter.

Thanks

Not sure if that was meant for me. But this is the power wiring I've used in both Coyote builds. It's been copied a bunch of times also successfully:

#2 cable from battery positive to master disconnect on firewall.

#4 cable from same terminal on the master disconnect (e.g. unswitched) to the 250 amp Ford provided fuse and then another short piece to the PDB.

#2 cable from the other side of the master disconnect (e.g. switched) to the large lug on the starter.

#8 cable from the same switched side to a bus bar where the Ron Francis power leads are attached.

This is with a Breeze front mount battery, so the main run is relatively short. For ground, I have a short #2 cable (approx 18") from the battery ground terminal to a fixed location on the chassis. Powder coat removed. Held in place with a tapped hole and bolt. Also under the bolt I home run the ground wire from the PDB. Probably not necessary. But Ford recommends it so I just go with it. There are other grounds. Two on the engine, the usual Ron Francis ones, etc.

Starting and operation through multiple seasons and a bunch of miles has been trouble free. Not sure how much of this fits your situation. But has worked well for me.

[Nigel Allen]

Okay, hooked up two fluke 289 series meters. One to capture overall DC current and the other to capture voltage drop along the positive lead between the battery positive clamp and positive terminal on starter.
- Engine is stock Gen 1 Coyote with TKO600. Clutch disengaged during tests.
- Reduction starter. The starter is just run of the mill, not high output.
- 50mm2 battery leads.
- Rear mounted battery.
- Tests done with cold engine.

Initial crank peak current: 260A
Initial crank volt drop: 0.699V

Current once starter motor up to speed: 159A
Volt drop once starter motor up to speed: 0.358V

starter current is 159 - 11(fuel pump and miscellaneous ) = 148A

Battery was dropping to 10.0VDC on crank, so starter power is 148 x 10.0 = 1.48kW

Hope this helps.

Cheers,

Nigel