Hi all. Here is what I did to my 85 fullsize bronco: I installed a new alternator, new voltage regulator and replaced ground cable that ran from starter bolt to frame and then to battery, I also installed new ground cable from engine to firewall. I got a used battery (950 cca) that I charged and load tested(battery passed the load test not problem) 3 days ago. The battery was in my trunk for 3 days. After I got everything hooked up, I put a volt meter on the battery. It read 8.7 volts. I hooked up jumper cables from my van to bronco. With bronco off and van running, the voltage was about 14.7. I started the bronco then disconnected the jumper cables. The battery was reading about 15.5 volts and was slowly dropping. I checked the ameter in dash and it was just slightly to the right of the center mark. Reving the engine did not change the ameter reading. I left it run for about 5 minutes then shut the bronco off. The battery was now reading 14.1v.
To sumerize, battery voltages:
battery, engine not running- 8.7v
jumper cables connected with van running-14.7v
bronco running, jumper cables disconnected-15.5v, slowly droping
bronco shut off-14.1v
Do these battery voltage readings sound normal?
The 15.5v reading sounds high to me, since the battery started out at 8.7v.
I know I need to get a new battery but can't afford one right now. I just don't want to ruin a new alternator and regulator.
Any input would be greatly appreciated.
Thanks. Bill

 

are you having trouble starting the bronco or what made you start checking voltage.
8v at the battery sounds like one of the cells might have collapsed, or you have a power leak. Now 13-16v running is normal and reving the motor wont change anything if there is no load on the system, That is all controlled by the regulator. Your alt. Actually creates 3Ø Ac voltage and your regulator then converts it to Dc and adjusts the voltage as needed. Now as far as the 15V at shutoff how long was the engine running and how long does the voltage hold?

 

aciancio, The battery that I had died. I got a used one and charged it and load tested it(load tested good). It started the bronco once then had to jump start it. I took the alternator out to be tested, alternator shot. I installed a new alternator and external regulator. also installed new groung cables.
After everything was hooked up, engine and key off, the battery was at about 8.7 volts. I used my van to jump start the bronco. With the jumper cables disconnected, the first battery voltage I got at the battery was 15.5v. After running for about 1 minute, the voltage came down to about 14.6v. I shut the enging off. the voltage at the battery was 14.1v. So the 15.5v was only when I first started the engine, it came down after that.
After about 3 hours of sitting. I tried starting the bronco, no start. checked the voltage at the battery and it was down to 8.4v.
AT this time, I checked for a voltage drain by removing the negative batt cable at the battery an put a test light between the cable end and the post and the test light did not light. So I know that nothing is draining the battery. I think the problem is the battery. I will get a new one on monday and see what happens. With no drain, it almost has to be the battery since the alternator, regulator and ground cables are all new.
Thanks for your input and I will post monday night with the results of the new battery.
Thanks. Bill

 

Wrong.

Just because the test light doesn't show anything, that doesn't mean something is not draining the battery -- it just doesn't drain enough to lit up your light. Use an ammeter to measure drain -- most digital volt meter can measure current, too, and they are very accurate. Start with a 10A or 20A setting.

Alternatively, there's a simple test -- charge up the battery, run the engine for a few minutes, measure the voltage on it, shut down the engine, *disconnect* the battery cable, then measure the voltage on the battery once every hour for 3 hours. If it's down to 8.4V again in 23 hours, it's definitely a bad battery, but if it stays above 12.4V or so, it's probably good.

 

Who load tested the battery? Also aurgathor is right test lights don’t work on power drips the wires/light isn’t big enough to allow current to pass. An ammeter is built for that very thing. Also running the engine for only a few min. will never charge the battery, especially from a low voltage start. To properly test the system you need to fully charge the battery first. use a charger or take it to some place like AutoZone and have them charge it overnight.

 

Your partly right but the reg. only regs the dc output of the alternator, the rectifiers inside the alternator converts the ac to dc and then puts out.

 

Load testing a battery is not something I would very often to a battery. An impedance tester will tell you if there is a dead short in a battery far more surely than the load tester plus it doesn't hurt the battery.

 

This is true but an inpedance tester wont show a colapsed cell and we already know there is not a dead short because he has voltage with the engine off. also you cannot properly load test a battery thats is not fully charged.

 

Thanks to everyone who put input into my charging problem. My charging system is working as it should.
After replacing: alternator, regulator, ground cables from starter to motor mount-motormount to batt. ground and ground from engine to body and brand new battery, my charging system is now charging normal. 14.6 volts at idle.
Thanks again to all who replied.
Bill

 

The only way you could hurt a battery from load testing is 1 if the voltage is below 12.5 or 2 if there is something wrong with the battery and you didnt know it but testing will show the weaknesses. Witch I would rather have the battery take a crap on the bench during a load test than while I'm in the middle of nowere.

Now given 1 load test typically will show you the picture I'm sure that doing one after another will and can hurt it.