battery getting drained while driving
- Thread starter ckdezert
- Start date
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67Dart273
Well-Known Member
Few if any parts store bench testers can fully load test an alternator. That would likely come back "good" whether it can put out full output or not.
S' why I suggested "riggin" a voltmeter you can see up front, and turning on a bunch of accessories.
What are the pulley sizes, crank and alternator?
S' why I suggested "riggin" a voltmeter you can see up front, and turning on a bunch of accessories.
What are the pulley sizes, crank and alternator?
nm9stheham
Well-Known Member
All alternators put out less juice at idle speeds; it is not a matter of shutting off. So that behavior seems normal, and with a heavy 48 A fan load, it will no doubt be discharging the battery when at low idle.
You need to do the test as suggested with meter on the seat and watch what the voltage is with other loads, and then when driving to see if the belt tension is adequate. The alternator pulley can be slipping and not make any noise......How are you setting belt tension with the manual set idler? Keep in mind that you are pulling a full HP to run just those fans so the alternator pulley is very heavily loaded.
The other possible problem is that the alternator has 1 or 2 of the 3 diodes sets blown out. This would cause your problem but you could only measure 14.7 volts at fast idle if the heavy fan load is not on.
Are the fans on a relay with temperature control? If not, it would be a good idea the change the fans to run only when a thermostatic switch activates them. There is likely little need for them at cruise speed.
A poor ground will not cause the battery to undercharge or discharge per se (but then you likely would have serious starting problems even with a good battery charge). But an erratic ground could cause the alternator voltage to spike and damage the alternator. So check all grounds to be sure that they are to totally clean metal.
Have you checked your voltmeter for accuracy? Get a brand new 9V battery; it should measure 9.6 to 9.7 volts.
You need to do the test as suggested with meter on the seat and watch what the voltage is with other loads, and then when driving to see if the belt tension is adequate. The alternator pulley can be slipping and not make any noise......How are you setting belt tension with the manual set idler? Keep in mind that you are pulling a full HP to run just those fans so the alternator pulley is very heavily loaded.
The other possible problem is that the alternator has 1 or 2 of the 3 diodes sets blown out. This would cause your problem but you could only measure 14.7 volts at fast idle if the heavy fan load is not on.
Are the fans on a relay with temperature control? If not, it would be a good idea the change the fans to run only when a thermostatic switch activates them. There is likely little need for them at cruise speed.
A poor ground will not cause the battery to undercharge or discharge per se (but then you likely would have serious starting problems even with a good battery charge). But an erratic ground could cause the alternator voltage to spike and damage the alternator. So check all grounds to be sure that they are to totally clean metal.
Have you checked your voltmeter for accuracy? Get a brand new 9V battery; it should measure 9.6 to 9.7 volts.
younggun2.0
Well-Known Member
your alt. is not up to the task. you need to either down size the fans amp draw or up the alternator output. if you up the alt. output you need to adjust the wire sizing accordingly. i think your fans are EXCESSIVELY over drawing current. I have duel fans on my big block dart that only draw 18 amps combined.
OK,had a chance to check things out again.Batt was at 12.80 volts.started car on choke.1800 rpm batt droped to 12.08 and same at alt charge post.turned car off and removed the alternater charging wire.restarted car-1800 rpm.alt showed 1.39-1.40 volts.The new alternater is bad or built on reg in bad. called summit-they are going to warranty with a new one. when I first installed the alternater was getting 14.7 with both fans on.
UPDATE
Just got back from test drive with new alternator.As it turns out the new alternator was bad.Would charge intermittently.Would charge at high RPM-around 1400-1800 in the garage,but would stop charging or would slowly trickle charge driving around.Any way was not charging properly.Made it hard to diagnose with out an ampmeter in the car. Now its charging at 13.48 with both fans,fuel pump,MSD,head lights on around 1400 rpm.Also starts charging as soon as rpm pick up-where the old alt would trickle charge up.Not good.
Drove around and rechecked the voltage at the batt.Read 12.80 where it was before I started or drove the car.
Also to anwer your question-yes both fans and fuel pump are on there own relays.Fans come on at 185 degrees .
Thank you everyone for all the input.
Just got back from test drive with new alternator.As it turns out the new alternator was bad.Would charge intermittently.Would charge at high RPM-around 1400-1800 in the garage,but would stop charging or would slowly trickle charge driving around.Any way was not charging properly.Made it hard to diagnose with out an ampmeter in the car. Now its charging at 13.48 with both fans,fuel pump,MSD,head lights on around 1400 rpm.Also starts charging as soon as rpm pick up-where the old alt would trickle charge up.Not good.
Drove around and rechecked the voltage at the batt.Read 12.80 where it was before I started or drove the car.
Also to anwer your question-yes both fans and fuel pump are on there own relays.Fans come on at 185 degrees .
Thank you everyone for all the input.
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