truck battery keeps loosing charge replaced alternator and diode duse on 1997 ford f150 any other suggestions

 

your battery could have a bad cell,check wires to make sure there not exposed anywhere, and check the alternator nothing is perfect start the truck and pull the positive off the battery and it dies right away you got a bad alternator go return it

 

thanks i will try this but this is the second battery, but it is worth a try at this point anything is worth a try. somebody told me to check the voltage regulator but i am not sure if it is in the alternator on a ford or if it is on the firewall or the starter do you have a clue

 

NEVER unhook a battery while the engine is running, if you do the voltage can go over 120 VDC and fry anything in your truck. Also all trucks will die with out a battery, as there is no residual magnetic field in an alternator.

Yes the regulator is in the alternator in 1997.

 

Has never been my experiance, not on my F-150, either Toyota nor S dime. Only time the truck should shut off with the positive cable disconnected is if your alternator is bad. Never has anything fry from it either. I know the alt. is to charge the battery and also powers all things electrical when truck is running, if your above statement is true than wouldnt it start frying stuff when the battery is fully charged. Correct me if I am wrong, but isnt that the purpose of the regulator, hence the name, dosent it regulate the voltage that the alt. puts out?

 

The regulator in the alternator monitors the battery voltage to adjust the alternator output. If you disconnect the battery the voltage drops on the sense wire and the regulator goes all out and can peak at over 120 vdc.

If you have done this and got away with it with an internal regulator you were lucky.

Most manuals say that the engine should die in about 3 to 4 minutes when the alternator has lost battery power.

I know Franklin2 has also echoed this caution about disconnecting the battery.

 

Thanks for clarifying that. I did unhook the positive cable on my F-150 but not for 3 or 4 minutes, maybe just a minute, never left it unhooked that long on the other ones either, I feel an experiment coming on.

 

i just went out side and pulled the positive all 3 of my truck nothing got fried started right back up ...also ive done this countless times with out having a problem

 

Batteries can be bad, and lose charge because of that, but more often than not, there is something draining the battery.

Turn off *everything*, then remove the positive cable and quickly hook up a 10A range ammeter, and write down the current. If it's under 100 mA, switch to 100 mA range and note the current there. The computer, clock, and few other things may drain up to 50 mA or so (exact numbers will vary somewhat) but anything more than 50 mA is suspicious. A current over 500 mA (0.5 A) is definitely bad.

 

I'm a dummy (with a meter no less) so I'll ask the dumb question. Where do I connect the meter? The battery, the cable I just unplugged? Do I ground the black lead at the battery terminal also?

Sorry, I just want to be clear - I have a definate battery drain problem also on one of my vehicles. I'm on the third battery in a year, covered by dealer, but I'm getting tired of the truck being dead all the time. I purchased one of those jump-start battery deals (with air compressor and light) because of this. I also purchased a "priority start" that is supposed to keep the battery from going dead - I can hear the mechanical components in this thing running all the time when the truck is turned off and sitting in the driveway!

Thanks!

 

first test on the battery positive and negative then test on the wires after the battery terminal (positive and neg) to make sure you dont have a bum terminal

 

I'm assuming aurgathor means I should connect the meter to the cable I just disconnected - so I can determine the current draw from the vehicle - not the output from the battery. Is this correct?

If I connect to the battery with the positive cable disconnected, won't I just get a read for the battery output?

Sorry - Like I said, I'm not familiar in this area.

 

If there is nothing wrong, then yes, you most likely will not fry anything, though there is still a risk of a voltage surge when you do it, taking out some of the electronics.

Now if there is really something wrong, you can definitely fry things, I have personally done it. I had an old truck that was not charging correctly. I pulled the + cable off, and it ran for about 20 seconds more and then quit. It never would start again till I replaced the electronic ignition module. Come to find out, the regulator in that case was bad, the alt went to wide open and fried the module.

 

You need to measure the current (idle drain) between the battery post and the battery cable you just removed from that post. Use a probe with a sharp tip to pierce the oxide layer on the lead to get good connections.

This measures the current draw of the vehicle from the battery when everything is off (doors closed, key not in ignition, lights off, etc.)

"battery output" can mean several different things. When you look for shorts in the wiring you don't care much about voltage or maximum current the battery can supply, as long as the resting voltage of the battery with both cables connected is above 12V. Less indicate a bad/weak battery, and/or a major short, but you can still measure idle drain in the way described above as long as the battery is not completely dead.

Might be a good idea to ask someone for help.

 

This thread is getting very confusing. I think we have three topics going on all at once. I hope nobody gets lost in the shuffle.

An easy way to see if you have a drain is to hook up a testlight like shown below.