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Battery voltage at starter
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DRR Trophy
posted
Anyone measure voltage at starter while cranking engine with ignition off?

Have a little more then a 2v drop from battery to starter. Right around 9-9.2 at starter. Battery in nose of dragster. So almost 16-18 feet of cable. Single 12v optima. 0 gauge from battery to starter relay. 2 gauge from relay to starter.
 
Posts: 75 | Location: nitrousville | Registered: January 30, 2012Reply With QuoteReport This Post
DRR Pro
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Generally speaking, your number seem slightly low. A fully charged, fully soaked battery should show 12.4 static range. Then, as you describe with ignition off, engine spinning, I would expect to see around 10.1 - 10.2.

Some things to consider, double check all grounds and all connections. Consider changing the cable from relay to 0 gauge. All ground should be 0 gauge or short 2 gauge.

If your battery will not charge and show 12.4 or better after setting a day or two you may need a new battery.


Larry Woodfin



 
Posts: 1845 | Location: Kilgore TX | Registered: March 12, 2004Reply With QuoteReport This Post
DRR Pro
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Ideally you want 10.5v at starter when cranking. Do a voltage drop test across relay to see if the voltage loss is there. Do same across the disconnect switch and same from disconnect to positive battery terminal. If you suspect disconnect possibly bad, land both ends to disconnect on same terminal bypassing disconnect and try.

With 2 gauge cable in my door car it’s 10.5v+ when cranking at starter with 12.8v battery reading.
 
Posts: 2530 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Pro
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The above comments about the disconnect switch is valid and a potential trouble spot. And the voltage checking at each component is a good idea.

However, if your battery will not charge to and hold 12.4 or better, you need to begin there.


Larry Woodfin



 
Posts: 1845 | Location: Kilgore TX | Registered: March 12, 2004Reply With QuoteReport This Post
DRR Pro
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You’ll basically lose volt thru everything it goes thru….if you have some welding wire laying around just throw it outside along car an hook it straight you’ll be surprised
 
Posts: 1268 | Location: USA | Registered: December 04, 2008Reply With QuoteReport This Post
DRR Pro
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Also meziere has a good video about this on their page
 
Posts: 1268 | Location: USA | Registered: December 04, 2008Reply With QuoteReport This Post
DRR Pro
Picture of Goob
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Measure cranking voltage at the battery, and at the starter, there should be very minimal difference.
If there's a big difference, it's cable / connection deficient.

Healthy battery and connections, you need to maintain 10.2v minimum.

Under 9.6v is borderline for any ignition electronics to function properly.


"Despite the high cost of living, it remains popular."
Dave Cook
N375
 
Posts: 1719 | Location: Indy | Registered: November 21, 2008Reply With QuoteReport This Post



DRR S/Pro
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9 volts is low. I assume you checked the cranking voltage at the battery and that should be above 10 with a good battery. Two things, your battery cable is too small, change the cable from the battery to the starter with 1/0 welding cable. Welding cable is very flexible vs battery cable. Next, I'd bet your ground cable is a short one and mounts to a stud welded on the chassis up front. This is also bad. Steel's resistance is much higher than copper. Ideally, run the same 1/0 negative cable up to the motor, you can keep the #2 cable grounding the chassis. I did this years ago on my dragster, 632 CID motor and a small 12v battery in the nose, no starting issues! I don't remember the exact voltage I picked up at the starter but is was around 1 volt. Also you can check the cranking voltage before and after the master disconnect switch to make sure that's in good condition.
 
Posts: 2161 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR Elite
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quote:
Originally posted by Nitrous1:
Anyone measure voltage at starter while cranking engine with ignition off?

been there done that and the best I could do is raise the voltage .5

quote:
I’ve gone through the entire system, have the right cables, connections, ground, starter, etc. replaced the disconnect switch too and still have less than 9 volts at the starter and always have.

I added a 1 AWG that runs from the battery directly to the block resulting in No noticeable difference in cranking and it probably weighs 15 lbs.

I installed a new solenoid and rewired it, landing both battery cables on the same side and ran a 10ga. wire from the other side, directly to the starter solenoid. Gained .5 volts at the starter solenoid but still have less than 9 volts.





That said, I removed the additional 15 lbs. of cable and I swapped to one DS1600 16 volt battery for the start of the 2021 season and ain't ever looked back, no more slow cranking, no more low voltage and no kickbacks.

This message has been edited. Last edited by: 1320racer,
 
Posts: 13522 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
DRR Trophy
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Right at 11 at battery. Getting right at 1 volt drop(7 feet of 0 gauge wire) from battery to master power relay.

Combined .25 volts loss from power relay to starter relay including the couple small sections of cable. Another .75ish drop from starter relay to starter through about 15 feet of 2 gauge. This runs through the chassis. Don't think a 0 will fit through the tube.

For science I moved the battery closer to the center of the car with a 4 foot 2/0 cable and it picked up about .15-.2 volts.

Are you guying seeing similar results with these long runs of cable on dragsters with the battery in the nose?
 
Posts: 75 | Location: nitrousville | Registered: January 30, 2012Reply With QuoteReport This Post
DRR Elite
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Yep
 
Posts: 13522 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
DRR Sportsman
Picture of 329L
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And is the reason most go 16 volt in a dragster anymore


Jeremiah Hall
 
Posts: 721 | Location: Evansville, IN | Registered: February 24, 2010Reply With QuoteReport This Post
DRR S/Pro
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quote:
Originally posted by Nitrous1:
Right at 11 at battery. Getting right at 1 volt drop(7 feet of 0 gauge wire) from battery to master power relay.

Combined .25 volts loss from power relay to starter relay including the couple small sections of cable. Another .75ish drop from starter relay to starter through about 15 feet of 2 gauge. This runs through the chassis. Don't think a 0 will fit through the tube.

For science I moved the battery closer to the center of the car with a 4 foot 2/0 cable and it picked up about .15-.2 volts.

Are you guying seeing similar results with these long runs of cable on dragsters with the battery in the nose?


If you have 9v at the starter that means you are drawing about 350 amps. Based on that a 7 foot run of 0 gauge wire, your voltage drop should only be .78 volts. I'd have a look at your cable ends! Were they just cripped on? If so, over time resistance will build at these connections. That's 28% more voltage loss than you should have! Solder or Noalox will prevent corrosion from occurring in these connections.

What about the ground cable? It's a circuit so both sides count!
 
Posts: 2161 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR S/Pro
Picture of Eman
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The most misunderstood use of a DVOM is a voltage drop test.
 
Posts: 1496 | Location: E TN | Registered: February 13, 2009Reply With QuoteReport This Post



DRR Sportsman
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Longer the cable(s), the higher the resistance.
 
Posts: 556 | Location: somewhere between been and never was | Registered: November 03, 2002Reply With QuoteReport This Post
DRR S/Pro
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quote:
Originally posted by I Hate Dragsters:
Longer the cable(s), the higher the resistance.


Voltage drop is a function of the cable's resistance per foot, length, and the current it's carrying. This is just the bare cable, not connections, cripped on ends, switches etc.

What many don't know or understand is the lower the cranking voltage is, the higher the current is in that circuit which means more voltage drop! This is why a 16v battery helps a bunch, more voltage means less amps to create the same power. Less amps, less voltage drop for the same circuit.
 
Posts: 2161 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR Pro
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quote:
The most misunderstood use of a DVOM is a voltage drop test.


^^^^THIS X2
 
Posts: 2530 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Trophy
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With a 12 volt battery I like to see better then 10.5v at the starter. Battery cable will go bad overtime and poor quality cable goes bad even quicker. If you got a known good quality cable and it over 8 to 10 years old it may need replacing.

And

You don't want to measure just at the starter, you want to measure at each connection point all the way to the battery. This will tell you where you are losing the most voltage. I have seen old cut-off switches use a volt.


Meziere Tech.
Make sure your water pump is on whenever you check your coolant level.
 
Posts: 254 | Location: Escondido | Registered: July 01, 2011Reply With QuoteReport This Post
DRR Elite
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you can rip out every cable and wire from your battery to the starter, replace every product in between those two hoping to get better than 9 volts at the starter no mind north of 10.5 or you can just swap to XS Power's DS1600 and call it DONE!
 
Posts: 13522 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
DRR Trophy
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I'm starting to think I'm chasing a ghost here. Minimal drop between the 2 relays(master power and starter)

Was hoping for data from similar style setups. Seems like to ask for to only get 1 volt drop through 20+ feet of cable.
 
Posts: 75 | Location: nitrousville | Registered: January 30, 2012Reply With QuoteReport This Post
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