Starter/solenoid current draw (amps)
#2
Race Director
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Nope. But if you have an Ohm meter (VOM or DVM, etc.), it is an easy calculation to make on the solenoid.
Current (I) is equal to Voltage (V) divided by the Resistance (R).
Measure the Resistance of just the solenoid coil, and divide into 12 (for nominal voltage while pulling in the solenoid).
Example: If you see 6 ohms, divide 6 into 12 (for volts), equals 2 amps.
Note that the solenoid draw will be nowhere near the actual starter motor current draw. If I was to guess, I would say somewhere under 10 amps (judging from the wire gauge that supplies current to the solenoid).
As for how much the starter draws, I have "heard" up to 300 amps depending on a lot of factors (ambient temp, oil viscosity, size of engine, starter windings, etc.).
Plasticman
Current (I) is equal to Voltage (V) divided by the Resistance (R).
Measure the Resistance of just the solenoid coil, and divide into 12 (for nominal voltage while pulling in the solenoid).
Example: If you see 6 ohms, divide 6 into 12 (for volts), equals 2 amps.
Note that the solenoid draw will be nowhere near the actual starter motor current draw. If I was to guess, I would say somewhere under 10 amps (judging from the wire gauge that supplies current to the solenoid).
As for how much the starter draws, I have "heard" up to 300 amps depending on a lot of factors (ambient temp, oil viscosity, size of engine, starter windings, etc.).
Plasticman
Last edited by Plasticman; 07-03-2008 at 01:10 PM.
#3
Drifting
yep, 175 to 250, the lower the better. amp tested starters for years, about 200 is the norm...
EDIT: this is the amp draw through the bat cable with the starter motor cranking,just to be clear.
EDIT: this is the amp draw through the bat cable with the starter motor cranking,just to be clear.
Last edited by mechron; 07-03-2008 at 01:14 PM.
#4
Race Director
#5
Drifting
Quiz answer: Matt, i use snap on inductance ammeters. they have a U shaped channel on the back of the gauge, you just lay it over the outside of the cable and it reads the current running through the cable. it takes about 2 seconds...
#6
Drifting
Thread Starter
Thanks everyone. The problem I'm trying to solve is a hot start problem with the starter and/or solenoid (when hot no cranking).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
#7
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Thanks everyone. The problem I'm trying to solve is a hot start problem with the starter and/or solenoid (when hot no cranking).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
1st I would check the wiring to the solenoid for frayed strands (from the ignition switch), poor connections, etc.
2nd Would try a new solenoid, or the lighter solenoid spring that I have seen mentioned elsewhere.
3rd, I have had good success on another vehicle with just changing to heavier gauge wire to the solenoid (less voltage drop).
If the starter is turning over, but is just heat soaked (weak from heat), then a heat shield would be in order, or a stronger starter.
Plasticman
#8
Drifting
Thread Starter
Thank you for the good ideas.
Was considering the stronger starter. My understanding is a OEM start only has about ~180ft-lbs of torque. When normal temperature it turns the engine over slowly and fires after about 2 - 3 turns. But when hot (immediately it restarts but after 10 min it won't) the starter won't even engage.
Will recheck the solenoid and connections to ensure they are good.
Also, does a heat shield really work well? Seems so hot down there it is hard to believe it reflects that much radiant heat. This would be the best approach and turn me around as a skeptic.
Was considering the stronger starter. My understanding is a OEM start only has about ~180ft-lbs of torque. When normal temperature it turns the engine over slowly and fires after about 2 - 3 turns. But when hot (immediately it restarts but after 10 min it won't) the starter won't even engage.
Will recheck the solenoid and connections to ensure they are good.
Also, does a heat shield really work well? Seems so hot down there it is hard to believe it reflects that much radiant heat. This would be the best approach and turn me around as a skeptic.
#9
Drifting
Thanks everyone. The problem I'm trying to solve is a hot start problem with the starter and/or solenoid (when hot no cranking).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
Have about 0.4 - 0.5 ohm resistance so at 200amps so I think my problem is too large of a voltage drop to engage the solenoid. (Very embarrassing when I can't restart the car until it cools down).
#10
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If your starter is turning over slowly when cold, might want to try a new starter. It only gets worse when hot due to heat losses in the starter and solenoid windings. Or at least take it down and inspect it for worn brushes, etc.
Another thing I have done is to increase the size of the positive cable going to the starter/solenoid (from the battery). It made my starter turn over much faster. Also check your ground cable and connections as well.
Plasticman
#13
Race Director
just measure the v drop on the heavy starter wire cranking, then the v drop headlights on only.
then headlight amps(up to 20)
v drop is directly proportional (starter wire is the shunt) or use battery to ground as shunt
then headlight amps(up to 20)
v drop is directly proportional (starter wire is the shunt) or use battery to ground as shunt
Last edited by Matt Gruber; 07-04-2008 at 07:11 PM.
#14
Melting Slicks
Thanks, Mat, I get it!! Will explain for posterity.
The bat cable acts as the shunt, and you will be reading small voltages (actually they better be else cables are bad ).
Then using the amp function directly measure the lights (pull the fuse and use 20 amp scale or higher) and compare. I would calculate the shunt resistance value R=V/I and repeat the V drop test for cranking
The bat cable acts as the shunt, and you will be reading small voltages (actually they better be else cables are bad ).
Then using the amp function directly measure the lights (pull the fuse and use 20 amp scale or higher) and compare. I would calculate the shunt resistance value R=V/I and repeat the V drop test for cranking
#15
Race Director
good.
Not to knit pick, but there is no need to calculate R.
use a solve for x equation
ie if
20 amp = 0.2v,
a 2.0v drop is how many amps?
answer 200
that example is easy enough to do in your head.
Note: cranking amps may be lots lower than starting amps. IIRC starting was ~300 on my 61. This is due to my aggressive spark advance.
If anyone wants to chime in with their results it would show they can really do it.
Hint:turn on enough stuff to get 12-16 amps; $3 DVM meter on 10a scale will read that ok.
The poster should check all connections for v drop. Ground to frame often overlooked and corrodes
Not to knit pick, but there is no need to calculate R.
use a solve for x equation
ie if
20 amp = 0.2v,
a 2.0v drop is how many amps?
answer 200
that example is easy enough to do in your head.
Note: cranking amps may be lots lower than starting amps. IIRC starting was ~300 on my 61. This is due to my aggressive spark advance.
If anyone wants to chime in with their results it would show they can really do it.
Hint:turn on enough stuff to get 12-16 amps; $3 DVM meter on 10a scale will read that ok.
The poster should check all connections for v drop. Ground to frame often overlooked and corrodes
Last edited by Matt Gruber; 07-05-2008 at 08:41 AM.