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6V Battery Test; Voltage Check
Topic Started: Aug 27 2013, 05:29 PM (894 Views)
ehrawn
Member
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I've been having some intermittent starting problems. Every once in a while, I try to start and the starter will weakly turn the engine for a couple of seconds, and then die. After a few hours on the wall charger, everything is back to normal. I checked the voltage across the battery terminals, but I couldn't find good numbers for a 6 V battery. Dividing in half for a 12 V battery, I'm right on the edge. After a recharge, it was 6.28 V. Cranking, it dropped to 4.8 V. Running, it rose to 7.15 V. Can someone weigh in on the starting voltage? Is it lower than it should be?
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Rus Curtis
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It should not be below its rated voltage. The 7.15V while running makes me think your charging system is doing its job. I'd suspect the battery but it needs to be checked to verify. Do you not have an electrolite tester?

I would suspect a store that sells a 6V should be able to test it.

Rus Curtis
Alabama
'54 CJ-3B "Green Gruntt"
Bantam T3-C
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div4gold
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Really it sounds just like what you would expect from a battery reaching the end of it's life. How old is the battery?
Old retired fart living in Ione, WA. I have a 1964 CJ3B. Recently overhauled original motor, transmission and overdrive. 11" Bronco drum brakes on all 4. Needs a new coat of paint but that will have to wait till next summer, it's next summer and I'm working on that now :) UPS & FEDEX will continue to profit :)
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oldtime
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6.28 volts seems a bit too low for a fully charged 6 volt battery.
Yes 7.15 indictes a funtional generator.
Expect 5 years service life from the average battery.
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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elawson
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A fully charged 6V battery that was just removed from the charger will likely be around 6.5 to 6.6 volts. After it's been setting a few hours (but not used), it will settle down to the 6.4 or so volts.

The voltage dropping to 4.8 volts is a bit low but not horribly so.

The 7.15 volts when the engine is running sounds just right.

Before you go out and spend the money on a new battery, get some 400 grit emery paper, take apart and clean *EVERY* connection between the battery and the starter. Don't forget the ground side of things as well. Also, if one is not used, add a battery cable (with ends designed to be held with a bolt) between the starter "ear" that ties to the bracket on the side of the engine and the place where the battery ground cable connects to the frame.

You have to be 4 times as careful with a 6 volt system as compared to a 12V system. 6V devices take twice as much current to run compared to a 12V device. This makes a bad connection drop twice as many volts...and since you have half the voltage to start with, each volt is "twice as precious".

Do you have a starter solenoid or a link activated (like a CJ3A) starter switch? If so, is the solenoid bolted to the starter or mounted somewhere else? If you would like, I can describe how to test the connections with the volt meter...what kind of volt meter do you have...analog or digital..if it's digital, does it automatically select the right voltage range, or do you have to manually select the right range?

One other thought...you are using the thick cables..#2 gauge or better yet #1 or even #0 gauge wires??????

I have a FC-170 with a 6V electrical system. About once a year, I go through the ritual of cleaning and tightening all of the starting system electrical connections. When I go to the FC roundups, one can't tell that my 170 is a 6V system just by listening to how the starter spins the engine.

Eric
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jyotin
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Voltage should be just about 2.2 volts per cell.

A 6 volt battery has three cells..
It's just my luck that something good is going to happen to me today.
54 - 3B - down on the farm
67 - cj6 - former state of Alabama vehicle
?? - cj5 T98a - made from spare parts - Ford tractor blue
?? - cj5 T98a - made from spare parts - Jeep green
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jyotin
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even a dead battery will read 2.2 volts per cell as long as one is only measuring voltage with no load.

It is the load (current) draw that will draw the voltage down. That's why when a battery is tested they always put it under load to see if it will supply the rated amps and still hold the proper voltage.

It's just my luck that something good is going to happen to me today.
54 - 3B - down on the farm
67 - cj6 - former state of Alabama vehicle
?? - cj5 T98a - made from spare parts - Ford tractor blue
?? - cj5 T98a - made from spare parts - Jeep green
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ehrawn
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Thanks for your responses, guys. Most of the work on the Jeep was done in 2011., but the long trip from the PO to my garage might have been enough to shorten the life. The battery top is always wet (sulfuric acid), and it's not bulging, but i can hear pressure leaking from the case which made me suspect the battery to begin with.

As far as your questions, Eric, I have an engine ground, but no additional cable run from the starter to the battery ground. Which "ear" did you tie to: the forward one or the rear? I don't have a link-activated starter. I'm pretty sure there's no solenoid on my starter- just the bendix drive (one less electrical part to fail). I have a digital volt meter. Any help you can offer about where to test would be appreciated. It might help to see if a starter ground is needed. The battery cables are thicker, but I can't get a good measurement under the cloth jacket. Here's a pic:

Posted Image
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Bruce W
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There should be a ground strap from the RH engine mount frame bracket to the engine front plate - basically going "around" the RF engine rubber mount. The cable mentioned by Eric would serve the same purpose - providing a ground path back to the battery, "around" the rubber mounts that insulate the drive train from the chassis. BW
Bruce Walker
Northeast Colorado
'53 CJ3B "Nellybelle", '48 CJ2A "Uncle Lyndon", '47 CJ2A "Teddy", '47 CJ2A "Rusty", '47 CJ2A "Zak", '43 GPW "Sarge", '88 XJ "Pluto"
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ehrawn
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Bruce W,Aug 31 2013
01:41 PM
There should be a ground strap from the RH engine mount frame bracket to the engine front plate - basically going "around" the RF engine rubber mount. The cable mentioned by Eric would serve the same purpose - providing a ground path back to the battery, "around" the rubber mounts that insulate the drive train from the chassis. BW

Yes, and it was covered in grease and paint. I took Eric's advice this morning and cleaned up all of the connections between the + and - side of the battery. The post on the starter was the most corroded. It runs better, but still has trouble starting. I'm taking a lunch break and then I'm going to check the voltages again. I especially want to see if there's a big drop between the starter and the negative post on the battery. I see how a direct connection from the starter mount to the negative terminal would bypass the block, mount, and frame.
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elawson
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It looks like you have the large cables, so that is good.

The digital meter makes life a lot easier. Disconnect the small wire between the coil and the distributor (or leave the key off it that will allow you to crank the engine without it starting). Measure the battery voltage at the terminals while you are cranking the engine. Next, put the positive lead of the meter onto the post on the starter that has the big wire and the negative terminal on one of the bolts holding the starter to the engine. When you crank the engine, read the voltage. The two voltage readings should be within 3/4 of a volt or less.


The starter ear I'm talking about is the one under the oil filter...between the starter ear and the bracket. You only need either the cable from the starter ear to the frame or the cable that jumps around the motor mount. If you go with the cable jumping around the motor mount, clean the surfaces between the starter flange and the bell housing and between the starter ear and the bracket, between the bracket and the engine block and the surfaces involved in the jumper around the motor mount These are important too and are often overlooked.


Two possibilities with the wet battery top. One is overcharging...not too likely with the 7.15V reading your seeing. Or the battery is overfull of water..easily checked. Or the battery is on it's "death bed". The battery condition *may* be able to be checked at a parts place..but don't bet on it.. It's hard enough finding a 6V battery charger...let alone an automatic tester that will deal with a 6V battery. :-)

Don't feel bad about doing all the work and possibly still needing to replace the battery. When everything is working correctly, the 6V system will start the engine just as nicely as a 12V system. Like I said earlier, a 6V system will work just as well as a 12V system..you just need to be 4 times as careful with everything.

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ehrawn
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6.154 V static, 4.6 V cranking on the battery, 1.45 V on the starter. Nobody has a 6 V battery tester but Napa has a replacement.
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spm1us
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FWIW, here is a link to the "patented" Dr Vern/Vernco Voltage Drop Test: http://www.vernco.com/Sparks/id606.htm . It has a lot of very good information on checking and verifying the condition of your Willy's electrical system. I hope this helps, Sam Michael Jr, Jax, FL
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ehrawn
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spm1us,Sep 3 2013
06:08 AM
FWIW, here is a link to the "patented" Dr Vern/Vernco Voltage Drop Test: http://www.vernco.com/Sparks/id606.htm . It has a lot of very good information on checking and verifying the condition of your Willy's electrical system. I hope this helps, Sam Michael Jr, Jax, FL

Great information. I wish I would have found that earlier.
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ehrawn
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Late Report: replaced the battery. Holy cow, it's a different Jeep. The starter spins like crazy and I get more than one chance before having to put it on the charger. Voltage under load is ~6.15 V. Thanks for you help, guys.
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