Share |
DragRaceResults.Com    Bracket Talk    Bracket Talk Forum  Hop To Forum Categories  Tech Talk - by Abruzzi    Master disconnect good or bad
Go
New
Find
Notify
Tools
Reply
  
Master disconnect good or bad
 Login/Join
 
DRR Trophy
posted
I've been having starting issues on my dragster, at first thought it was a bad battery, but after two new batteries and two new starters, I'm convinced it is something in the electrical system draining the battery. I've done a lot of checking so far and I found the voltage regulator in my one wire alternator was bad, so that was changed out. I still have a small voltage at the master disconnect when turned off, I see .2vdc, and am wondering if this is enough to cause a dead battery. After I charge the battery all is good, and the alternator keeps it charged thru the race event. Any ideas if the master disconnect is faulty, it is an old unit, seen many race seasons.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post
DRR Pro
posted Hide Post
Rusty, I would just change it out as a maint item regardless !! One way to see if it causing your problem is disconnect the battery cable from it and see if your battery still goes dead.
 
Posts: 524 | Location: On the the dark side now | Registered: April 30, 2010Reply With QuoteReport This Post
DRR Sportsman
Picture of Hammons Motorsports
posted Hide Post
Do you tun an alternator?

If you do, get it checked...

Have had 2 over the years that started "bleeding" down the battery.


Bill and Cindi Hammons
Hammons Motorsports

Old age and treachery, if we only knew then what we know today.....

95 Spitzer, 1.041 60 ft, 4.76 @ 142.85, 1740 lbs, 421" SBC

10/9/2016: 1.049 60 ft, 4.721@143.80 at 1780 lbs.

4/15/2017: 1.017 60 ft, pedaled 4.742@134 at 1780 lbs.
 
Posts: 1021 | Location: Georgetown, KY | Registered: May 29, 2001Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
Hammons Motorsports, yes I do run an alternator, and have done the diode check, it passed with the hot wire and VR disconnected, but failed when the VR was plugged back in. I had another VR on hand, so replaced it, and now the diode check passes, so I believe the alternator is good. I took the master disconnect off the car this morning, and found the brass post portion will move in relation to the housing, so it may be damaged internally, a new one will be ordered.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
You should do a voltage drop test across that disconnect switch while starting the engine. Nothing more than .02 volts
 
Posts: 19 | Location: chicago | Registered: July 28, 2013Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
I've been busy this week, installing a second battery, and replacing the master disconnect with a new high current unit. So the results, with the switch off and before connecting the cables, there is no continuity between the terminals. When I connect the hot side only, and switch off, no voltage is seen on the other terminal. When I connect up the other side with the cable that goes to the starter, I see the .2vdc again, same as before I changed the switch. My MSD and delay box are wired direct to this side of the switch, so they are hot as long as in the on position. I'm thinking now there are some capacitors in the MSD and possibly the delay box that are storing energy, and it shows up when I probe the switch........I don't know if I fixed anything. or not.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post
DRR Sportsman
posted Hide Post
quote:
Originally posted by topfuel:
I've been busy this week, installing a second battery, and replacing the master disconnect with a new high current unit. So the results, with the switch off and before connecting the cables, there is no continuity between the terminals. When I connect the hot side only, and switch off, no voltage is seen on the other terminal. When I connect up the other side with the cable that goes to the starter, I see the .2vdc again, same as before I changed the switch. My MSD and delay box are wired direct to this side of the switch, so they are hot as long as in the on position. I'm thinking now there are some capacitors in the MSD and possibly the delay box that are storing energy, and it shows up when I probe the switch........I don't know if I fixed anything. or not.


Try this.

With the disconnect OFF place a wire from the OFF side terminal to ground for several seconds then remove. After this meter the OFF side to ground and see if voltage still present.
 
Posts: 640 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
Thanks for the suggestion markmark I will try that. In the mean time, I fired the engine this afternoon, and checked the voltage output of the alternator at the battery, 14 volts and rising, so that part is working. After I shut the engine off, I rechecked the master cut off switch again and now the .2vdc is gone....humm. Like I said before I don't know if I fixed anything or not. I will let it sit in the trailer for a few days and see if the battery voltage stays up.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post
DRR Pro
posted Hide Post
quote:
Originally posted by topfuel:
Thanks for the suggestion markmark I will try that. In the mean time, I fired the engine this afternoon, and checked the voltage output of the alternator at the battery, 14 volts and rising, so that part is working. After I shut the engine off, I rechecked the master cut off switch again and now the .2vdc is gone....humm. Like I said before I don't know if I fixed anything or not. I will let it sit in the trailer for a few days and see if the battery voltage stays up.


Well you added 45lbs to your car by adding a 2nd battery if you call that a fix, at least it should start when you pull out of the lanes onto the track
 
Posts: 524 | Location: On the the dark side now | Registered: April 30, 2010Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
Big Steve, well yes I added some weight, but I have two 25 pound ballest bars in the nose, so I plan to lose at least one of them. I'll take a few more pounds as long as the pig will start.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post



DRR Pro
posted Hide Post
Cant turn on the win light if the car wont start
 
Posts: 524 | Location: On the the dark side now | Registered: April 30, 2010Reply With QuoteReport This Post
DRR Sportsman
posted Hide Post
quote:
Originally posted by topfuel:
Thanks for the suggestion markmark I will try that. In the mean time, I fired the engine this afternoon, and checked the voltage output of the alternator at the battery, 14 volts and rising, so that part is working. After I shut the engine off, I rechecked the master cut off switch again and now the .2vdc is gone....humm. Like I said before I don't know if I fixed anything or not. I will let it sit in the trailer for a few days and see if the battery voltage stays up.


One last suggestion. If the 9v battery in your multimeter is over 2 years old replace it. Low meter battery voltage could possibly be a problem in actual readings.
 
Posts: 640 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Trophy
Picture of 1leg
posted Hide Post
Voltage drop test is easy. This video will help.

https://www.youtube.com/watch?v=rrDlXn-RYcM&t=110s
 
Posts: 22 | Location: Escondido | Registered: July 01, 2011Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
Well, the dragster has been sitting for 4 days now, measured the battery voltage tonight and see 13.0 vdc, and starts the engine without issue, and best of all no voltage loss at the master disconnect. Issue solved.
 
Posts: 148 | Location: Midlothian, Texas | Registered: October 19, 2000Reply With QuoteReport This Post
DRR Sportsman
posted Hide Post
Yeeee Haaaa
 
Posts: 193 | Location: Justin, TX | Registered: July 18, 2013Reply With QuoteReport This Post
DRR Pro
Picture of BarneyB
posted Hide Post
Your alternator wire is live from the battery to the the post of the alternator 24/7. Install a relay that is turned on and off by the ignition switch. Place it close to where it hooks to the battery or disconnect switch as possible. your car will be safer during transporting and eliminate your scenario.


Blaster Chemical Co.
www.abruzziracing.com
www.moserengineering.com
www.houseofpayneperformance.com
WiredTwoWin race car wiring
J & J Performance
Trick Flow Specialties



 
Posts: 2408 | Location: Wadsworth, Ohio | Registered: December 12, 2001Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
Have you done a voltage drop test across the disconnect switch and the battery cables? How many volts are at the battery when the car is running. And how many volts are at the back of the alternator at idle?
 
Posts: 19 | Location: chicago | Registered: July 28, 2013Reply With QuoteReport This Post
DRR Pro
Picture of Eman
posted Hide Post
quote:
Originally posted by topfuel:
I've been having starting issues on my dragster, at first thought it was a bad battery, but after two new batteries and two new starters, I'm convinced it is something in the electrical system draining the battery. I've done a lot of checking so far and I found the voltage regulator in my one wire alternator was bad, so that was changed out. I still have a small voltage at the master disconnect when turned off, I see .2vdc, and am wondering if this is enough to cause a dead battery. After I charge the battery all is good, and the alternator keeps it charged thru the race event. Any ideas if the master disconnect is faulty, it is an old unit, seen many race seasons.

You fixed your parasitic draw when you repaired/replaced your alternator. You should have installed a 4 terminal master disconnect or wired in a HD relay to shut the power off to the alternator.
I'd don't see how changing the master switch could cure any parasitic draw. Not bad that you changed to a higher amperage rated switch. This was a good test subject to practice voltage drop testing and amperage draw testing.
http://www.yellowbullet.com/fo...wthread.php?t=229395
Here's a link to voltage drop testing basics.
For parasitic draw the best is to have a bridge for the battery cable, one of those battery shutoffs with the green knob that connects at the battery, install on the negative cable. Keep the bridge closed so the car will start. Then hook up your amp meter so that when you open the bridge the current will flow through the meter, one lead at the battery one at the cable. When you open the bridge you will see if there is any current flow with the car shut off. If you have any electronics it might take a few minutes for everything to shut down once you shut the car off, especially on a street car with any control modules. 30 milliamps or less is generally acceptable but on a basic race car it should go to zero.
 
Posts: 575 | Location: E TN | Registered: February 13, 2009Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
.2 of a volt will not take down a battery.
 
Posts: 19 | Location: chicago | Registered: July 28, 2013Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
posted Hide Post
Just a friendly reminder that everyone should occasionally test their master cutoff switch by shutting it off while the car is running. In over 20 years of racing I have only seen ONE tech official do that as part of his inspection. And it was at what many would call a little "Podunk" track, (rural airstrip). As I pulled slowly forward to the tech station, he walked behind my car and killed the power. He said he had failed dozens of cars each year, that were not properly wired at the cutoff. If you think about the awful possible consequences, should a car hit the wall or roll over, driver trapped or unconscious, fuel pump running, with possibly a severed fuel line or battery cable shorted to frame/sheet metal... Just do it.


Dan "Jim" Moore
This year = "Transbrake Jim"
Much too young to feel this damn old!!
 
Posts: 426 | Location: Dallas, TX  | Registered: December 05, 2002Reply With QuoteReport This Post



  Powered by Social Strata  
 

DragRaceResults.Com    Bracket Talk    Bracket Talk Forum  Hop To Forum Categories  Tech Talk - by Abruzzi    Master disconnect good or bad

© DragRaceResults.com 2017