Electric drain
Thread Starter
|
New User
Joined: Mar 2006
Posts: 24
Likes: 0
Electric drain
I have a 1977 F-250 that is used as a salt truck. Twice the electrical has drained to a point where the truck dies & then needs jumped but the lights are bright & everything else works. I have replaced the regulator & checked the battery which was fine & the alternator which was putting 14 volts out. I even pulled the ground strap on the block & cleaned it up but this didn't help. I have salted several times this year but this has only happened the first time & about a week ago. Any help would be greatly appreciated.
Moderator
Joined: Jan 2001
Posts: 56,976
Likes: 2,733
From: Virginia
Hook up a testlight like the diagram below. It will glow bright if you have a drain. If it glows bright, start pulling fuses and unhooking stuff till thelight goes out. If it never goes out, unhook the atlernator wires. When you finally get the light to go out, then that's what is causing the drain. Make sure the domelight and any trouble lights are off when you are testing.
Elder User
Joined: Jan 2007
Posts: 612
Likes: 0
Originally Posted by Franklin2
Hook up a testlight like the diagram below. It will glow bright if you have a drain. If it glows bright, start pulling fuses and unhooking stuff till thelight goes out. If it never goes out, unhook the atlernator wires. When you finally get the light to go out, then that's what is causing the drain. Make sure the domelight and any trouble lights are off when you are testing.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
This is a 77. No EFI, no PCM. Only an ignition control box that would not be powered up unless the ignition switch was on..
There is about 99% chance the alternator has a bad doide stack.
The lights are bright because the regulator can't control the chargre rate.
The battery may have also been cooked by now.
You need to have the whole system checked because there may be more than one problem by now.
It will save you from ongoing problems to have the whole system gone over and certified as operating properly.
There is about 99% chance the alternator has a bad doide stack.
The lights are bright because the regulator can't control the chargre rate.
The battery may have also been cooked by now.
You need to have the whole system checked because there may be more than one problem by now.
It will save you from ongoing problems to have the whole system gone over and certified as operating properly.
Moderator
Joined: Jan 2001
Posts: 56,976
Likes: 2,733
From: Virginia
A test light works but a digital multimeter is preferable so you can see how much current you are actually drawing. If you use a DMM put it on the 1 amp range or 500 mA amp range and series it inline with the ground like the above picture suggests. If it reads over 200 mA with everything off, you are drawing too much current.
I never have tested how much it takes the testlight to glow bright, but it's probably pretty high. I would be curious if it would ignore 200 ma, or what brightness it would be at 200 ma.
Elder User
Joined: Jan 2007
Posts: 612
Likes: 0
Originally Posted by Franklin2
That's the problem with a multimeter reading current. There are so many different opinions to what is too much. I read somewhere that anything over 70ma is too much, and most vehicles with the normal amount of electrical stuff are around 12-35ma.
I never have tested how much it takes the testlight to glow bright, but it's probably pretty high. I would be curious if it would ignore 200 ma, or what brightness it would be at 200 ma.
I never have tested how much it takes the testlight to glow bright, but it's probably pretty high. I would be curious if it would ignore 200 ma, or what brightness it would be at 200 ma.
Well lets say you have a battery that has an amp hour rating of 100 hours. It can provide 1 amp for 100 hours. Well that means it can provide 200 mA for 500 hours. After that you probably wont be able to start your vehicle. Well considering that if you were to draw that much, you could still start the vehicle after two weeks, but the battery would be around 65% dead. That’s unacceptable.
Anyway at the tech school I went to I was taught 120 mA is the limit. I generaly say about 80 mA is the limit however in this case he would need a good 1,000 mA + of draw to have this problem after only a day. You could have 1,000 mA of draw and be fine if you started your vehicle twice a day. However that would be hard on the battery so its not a good idea.
Last edited by SPL Tech; Feb 2, 2007 at 10:55 PM.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Most late model cars and trucks will drain between 25 and 50 ma. at rest.
The amount depends on how many memories need to be kept alive per the vehichle.
Most will have the PCM KAM, Radio, clock, any other devices that need to continue operating from their last setting/running etc.
This truck has no memory unless an aftermarket radio was installed or an analog clock etc..
Using a lamp in series works fine as long as the right size is used.
An over nite drain is usually a good size to take a fully charged battery flat in about 8 hrs. Think currents like what would be drawn by such things as parking lamps left on etc. That's at least several amps +/-.
Also the alternator case could be warm to the touch if a diode stack is conducting battery cirrent to ground after the engine cools down. A good indication of whats wrong.
The amount depends on how many memories need to be kept alive per the vehichle.
Most will have the PCM KAM, Radio, clock, any other devices that need to continue operating from their last setting/running etc.
This truck has no memory unless an aftermarket radio was installed or an analog clock etc..
Using a lamp in series works fine as long as the right size is used.
An over nite drain is usually a good size to take a fully charged battery flat in about 8 hrs. Think currents like what would be drawn by such things as parking lamps left on etc. That's at least several amps +/-.
Also the alternator case could be warm to the touch if a diode stack is conducting battery cirrent to ground after the engine cools down. A good indication of whats wrong.
