Truck wouldn't start after work today(never when you are going to work,only home). any hoo got a jump and it was fine for the 40 mi.trip home, gauge right where it should be, but I thought my battery was going bad, so I swithced one in from another truck at home. When I hooked the neg cable I got a small arc, thought maybe the hood light so I disconnected it and tried it again-same thing happened. Then I left the pos hooked and put a volt meter from the neg post to the neg cable, got a full 12 volt reading???? Like something was on,but nothing was. this aint normal is it? how can I check the alt because I think this is what is draining the batt when parked.
03 s-cab v-6

 

What you observed is a normal observation.

Connect the cable. Measure battery voltage. Typical voltage should be between 12.4 and 12.8 volts, depending on the state of the battery's charge.

Start the engine and measure the battery voltage again. It should rise to between 13.8 and 14.6, again, depending on the state of charge of the battery and the capability of the alternator.

 

It's normal to get that little arc. If I'm not mistaken, your pretty much resetting everything so you will get a power draw

 

I am familar with the the arc, the part i wasn't sure about is with the pos cable connected and the neg not and everything turned off when I put the volt meter from the batt post to the disconnected cable I get a 12 volt reading.
thanks for the replies just wanted to check.

 

ima try to explain this as best as i can. i believe thats normal. cause when you put the one side of your meter lead to your "positive battery terminal" and the other meter lead to the "disconnected postive cable", you should read voltage because your reading thru other circuits that are also grounded (hooked up to the "negative" cable"). that make sense?

 

Yea I get that, but the neg was the one not connected. got reading from the Neg post to the Neg cable. Same theory?
thanks ANTZ

 

i would imagine so.
anytime..

 

Thanks again ANTZ I guess what I should have asked, because I'm getting a draw down on the batt when it's parked, is about amps not volts. The volts are always there but the amps is what shows me the current flow,which is what will drain the batt, right? sooo does anybody know what that should be for normal?
sorry to be such a PITA thanks for the patience.

 

well i wouldnt know about the amps. but i believe as long as you got 12.2-12.8 steady volts after your truck is off, it should be good..now keep in mind that it does take a few minutes for the pcm and everything to shutdown. so keep in mind that the voltage will drop a lil bit even when the truck is off, if ya didnt know. not sure if ya did.

 

i think you would want to watch the volts. for amps, you need what i think is called an ampprobe to measure amps. im positive you cant get that on the average multi-meter. if your voltage is droping steady when truck is off and parked, do troubleshooting if ya havent already. like leave the meter on there with the cables on the post and watch the rate of votage drop and then try it with the cables off the post... make sense?

 

Jgger - I'm getting into this late, but - if there is ANY current draw on the battery with the key off, you're probably going to read 12+ volts if you connect a voltmeter between the negative battery terminal and the negative cable. The voltmeter has VERY high resistance, so it effectively halts any current flow. In this configuration, with almost no current flowing, you're actually almost measuring the voltage drop from the positive to the negative battery terminal so the reading is totally meaningless.

You really want to read amperage, and this is much harder. First you have to let everything stabilize (about one hour after shutdown and after closing doors, turning everything off, etc.) The ammeter has to be providing a complete circuit from the negative cable to the negative terminal during this time too, because reconnecting that circuit will give a false reading.

After about an hour, if you're seeing more than about 0.05 Amps (50 mA), I'd say you have a problem. I have a constant 50 mA draw on my battery to power the keep alive memories in the radio, the PCM, the clock, anti-theft device, etc.

A dying battery COULD just be a sign of one that needs replacing though. Get your battery load tested.

- Jack

 

Thanks every one. When I was doing the volt meter thing I thought I'd check the amps with my analog multi meter, it has a 150mA scale, and it blew the fuse in the meter. That was by putting it from the neg post to the disconnected cable. Sorry about going on so much about this but I'm really a shipdit when it comes to electrical stuff.
Thanks again for everybody's help.

 

Put it back together and do the tests I recommended. Otherwise, quit dinking around with it...

 

projectSHO80
Idid those tests, both readings are at the upper end values. the problem is'nt with the charging it self, it charges fine. The problem is it is going dead when it's parked with nothing left on. Is there a way that a simple mind like me can check the alt to see if it's diodes or rectifier that is bad. It won't go dead every time it's parked, it's more like russian roulette. I think the alt has to be stopped at a certian point then it drains the battery.
thanks

 

150 mA is too small a scale. When you first put the ammeter into the circuit, if you've had the battery disconnected before that, you'll get a "surge" that easily exceeds 105 mA. You need to have the engine off, hood up, and doors closed for about an hour before you do any current draw test. Then you have to connect one ammeter lead to the negative cable and have the other touching the negative battery post as you disconnect the cable! This way, the circuit is not broken, but it is simply rerouted through the ammeter. It is NOT an easy thing to do. (When I do it, I connect to the cable, then slide the cable up the post and along the top to expose the post. Then I can touch the other ammeter probe to the post before removing the cable.)

I really doubt your problem's in the alternator too, but that's just a gut feel of mine. I think you can get your battery load tested for free at a place like Autozone - why not do it?

- Jack