Battery Voltage Values ?'s
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Posting Guru
Joined: Sep 2002
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Battery Voltage Values ?'s
Hi guys. I bought a voltmeter today. I bought it to test the charging system in my 1990 Bronco.
1990 Bronco
351W
New Battery
75 amp alternator
All these voltage measurements are based off a .5 voltage scale.
Idle with all accessories off: 13.3 volts
Idle with all accessories on: 12.3 volts
1800-2000 r.p.m. with all accessories off: 13.3 volts
1800-2000 r.p.m. with all accessories on: 13.2 volts
Cranking voltage: 12.1
Battery: 13.1 volts
I just need to know if all these numbers are normal for my truck.
Also when I say all accessories on I mean, Headlights, radio, and A/C on full blast!! THanks for all the help.
1990 Bronco
351W
New Battery
75 amp alternator
All these voltage measurements are based off a .5 voltage scale.
Idle with all accessories off: 13.3 volts
Idle with all accessories on: 12.3 volts
1800-2000 r.p.m. with all accessories off: 13.3 volts
1800-2000 r.p.m. with all accessories on: 13.2 volts
Cranking voltage: 12.1
Battery: 13.1 volts
I just need to know if all these numbers are normal for my truck.
Also when I say all accessories on I mean, Headlights, radio, and A/C on full blast!! THanks for all the help.
Posting Guru
Joined: Aug 2002
Posts: 1,214
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From: Minneapolis, MN
Battery Voltage Values ?'s
IMHO, 13.3 volts charging, (high idle, no load) is just a little low. I usually like to see 13.8 to 14.2 volts, even a little higher with a sealed "Delco" type battery. Even though it is charging, it might be a sign of things to come. Keep an eye on it.
Thread Starter
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Posting Guru
Joined: Sep 2002
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Battery Voltage Values ?'s
Actually, it probable is around 13.8. That's because, like i stated in my first post, that is based off a .5 volt scale. Meaning the highest point I could go is .5!! For examply 13.5 is the highest I can go for 13!! THanks for the input though!!
Posting Guru
Joined: Aug 2002
Posts: 1,214
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From: Minneapolis, MN
Battery Voltage Values ?'s
Is your voltmeter autoranging or switchable? Can you change to a lower scale as in say 20 volts? Most digital voltmeters should be able to read to at least .05 resolution at that range, you just throw away the last digit as a 5 or 0 reading is more or less worthless. For example, at rest a 90% charged battery (with no surface charge) will read 12.6 to 12.7 volts while a 25% charged battery will read 12.2 to 12.3 volts. It's all in the details.
Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Battery Voltage Values ?'s
Take it back. Then spend half that at Wal-Mart, Home Depot, Sears, or Radio Shack.
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Posting Guru
Joined: Nov 2002
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From: Napa
Battery Voltage Values ?'s
Radio Shack digital auto ranging mutlimeter 22-802 (part number).
Usually $29.99 but goes on sale for $19.99 or less depending on the sale.
When I worked at the Shack it's the only meter I used. In fact, I have 3 at my house (I keep "losing" them only to "find" them after I bought a new one).
It has a max of 400volts ac/dc at 10 amps. It's compact and fairly sturdy as well
Usually $29.99 but goes on sale for $19.99 or less depending on the sale.
When I worked at the Shack it's the only meter I used. In fact, I have 3 at my house (I keep "losing" them only to "find" them after I bought a new one).
It has a max of 400volts ac/dc at 10 amps. It's compact and fairly sturdy as well
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Senior User
Joined: Dec 2002
Posts: 277
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From: San Rafael, NM
Battery Voltage Values ?'s
bronco351--
Just be sure you always have an analog meter also. But not a $50 one, something much cheaper. They are great for testing batteries while starting your engine. You can actually see the amount of voltage drop by the current drain during startup and use it to determine if the battery is good or not. (If you get more than a .4V drop, your battery is on the blink/high internal resistance)
Just be sure you always have an analog meter also. But not a $50 one, something much cheaper. They are great for testing batteries while starting your engine. You can actually see the amount of voltage drop by the current drain during startup and use it to determine if the battery is good or not. (If you get more than a .4V drop, your battery is on the blink/high internal resistance)
10V is an acceptable cranking voltage.
Senior User
Joined: Dec 2002
Posts: 277
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From: San Rafael, NM
Battery Voltage Values ?'s
10V, yikes. Must not have an electronic ignition. I don't think I have ever experienced this amount of drop even with a bad battery. An ideal battery would have close to a 0 ohm internal resistance so even a reletively low resistance load (i.e. high current load) should not drop nearly 10 V. The larger voltage would develop across the higher resistance. I'm not saying it can't happen, but I have never experienced it. How can the computer system continue to function on only 2V?
PS I think the most I have ever seen is a 3V drop.
PS I think the most I have ever seen is a 3V drop.
Senior User
Joined: Dec 2002
Posts: 277
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From: San Rafael, NM
Battery Voltage Values ?'s
steve83--
Now that I reread your posting it seams that I made a mistake. I thought you meant a 10V drop, but you really meant a 2V drop. Sorry. We still have slightly differing thoughts but at least we are on the same page.
I seem to remember my dad's caravan had a 2V startup drop once and the electrical system worked fine. The battery failed a couple of months after that though (may not have been related) . I think the electronic ignitions system is more forgiving of weaker batteries.
Now that I reread your posting it seams that I made a mistake. I thought you meant a 10V drop, but you really meant a 2V drop. Sorry. We still have slightly differing thoughts but at least we are on the same page.
I seem to remember my dad's caravan had a 2V startup drop once and the electrical system worked fine. The battery failed a couple of months after that though (may not have been related) . I think the electronic ignitions system is more forgiving of weaker batteries.