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Ford 9N, 2N & 8N Discussion Forum

6v battery volts vs specific gravity

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09-06-2019 17:20:22

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My tractor spends more time cranking than running and the battery doesn't seem to get charged while running. The battery charger charges it and I will often leave the charger hooked up while starting the tractor. When I do have it running for close to an hour of use the battery doesn't seem to charge enough to crank crank crank to start again. (I'm working to reduce the crank crank crank...)

So I put the charger on and I am reading 6.45 volts. I bought hydrometer without any thermometer reading. Never used on before. All three cells had quite a bit of fluid and the liquid was clear. I tested each cell at about 75 degrees tonight. It was hard to read exactly, but the fluid line was right in the middle of 'fair' which looks like close to 1230. Give or take a line which looks like they are in units of 5. So I guess each cell was somewhere between 1225-1235. All the cells were very close to the same reading.

Does 6.45 volts with this specific gravity indicate a healthy battery or one with issues? Also, would this impact how the tractor runs? If the battery is fine then I will probably need to start looking into the charging system or does it just take a long time for the battery to charge during use?


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09-08-2019 14:38:04

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  
Quoting Removed, click Modern View to see

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09-07-2019 17:27:01

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  
I went out this morning and the charge had dropped to 6.35v. I started it up and ran it for about an hour maybe a little longer. Turned if off and read 6.25 volts. Waited a couple hours and it was still at 6.25 and was able to start it back up.

Appreciate all the comments. I'm going to keep tracking the readings and see what happens over time. I think I will probably start looking into a new battery and a float charger to go with it.


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09-07-2019 07:02:50

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  
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Hit the starter for 5 seconds to burn off the surface charge no need to wait a day... A good battery will recover fast after the event and should read full battery charge... With a voltmeter you will see the voltage start to clime if it does not the battery is undercharged are bad...

Lets not forget whats the voltage cranking under load... If it cranks the starter is your load tester and its FREE : )

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Tim PloughNman Daley

09-07-2019 04:55:35

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  

You have a bad battery. Itís not sustaining a charge under load and that is required for ignition and starting. 6.4 V static is not a full charge; itís only about 85% and that is while being charged. You need to check static.. As stated a fully charged 6V battery should read about 7.5V static. Take the battery to your local starter/alternator shop or auto parts store and they can bench test on the proper equipment under load. It takes a minute and is usually free of charge Ė pun intended. Is it a front mount or an angle mount distributor? A 9N/2N or an 8N? Only matters if your whole system is as OEM -6V/POS GRN and wired correctly. That means a 1 Wire/3 Brush generator and cutout if a 9N/2N after s/n 12500, and a 3 wire/3-Brush generator with a Voltage Regulator for early 8Nís, 2 Brush/3-Wire for late 8Nís. BTW, the 9N/2N uses a 1-wire starter motor with NO solenoid and the 8N uses a 3-wire starter motor with a solenoid. All things being equal, a correctly tuned distributor is vital to ignition/running. Everything must be wired correctly as well. Start with testing the battery. If bad, replace with a new GRP 1 6V AG type and donít get a bargain house model. Invest in a good brand like INTERSTATE, DEKA, EXIDE, or DURECELL. The other item well worth the in investment is a float charger, not a trickle charger. The Battery Tender brand is a good one. Simply charging a battery does not ensure you have a good battery. A float charger will maintain a full charge in the battery when connected at idle times so itís ready to go when needed. It will also prolong the life of the battery. The biggest reason battery life is reduced is the constant discharging and recharging. If you want at least 6 years or more on your battery, get a good battery and a float charger. Start there then go thru the wiring and components.

Tim *PloughNman* Daley(MI)

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Bruce (VA)

09-07-2019 05:32:01

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 Re: 6v battery volts vs specific gravity in reply to Tim PloughNman Daley, 09-07-2019 04:55:35  
7.4 volts is needed to fully charge a 6v battery. A fully charged 6v battery should read 6.32 volts.


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Bruce (VA)

09-07-2019 04:51:28

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  
As Bob said, 7.4 volts for charging.

100% charge should get you 1.265 per cell on the specific gravity.

At 1.225, you're at 75%.

Both your specific gravity and voltage readings are suspect however. You're seeing a surface charge. Take your readings 24 hours after you take it off the charger.

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09-06-2019 18:54:27

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 Re: 6v battery volts vs specific gravity in reply to ram74, 09-06-2019 17:20:22  
Check the charging system voltage with the tractor running above low idle, should be about 7.4 Volts.

When fully charged, "load test" the battery, that will tell what it's capable of.

More "real world" and a LOT less messy than fondling acid with a hydrometer, IMHO.

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