Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-19-2008, 10:21 AM   #1
Rivet Master
 
guy99's Avatar
 
1984 31' Airstream310
Dunsmuir , California
Join Date: May 2004
Posts: 1,334
Images: 16
Measuring specific gravity of battery electrolyte

Measuring specific gravity of battery electrolyte

Recently I purchased a hydrometer to check the cells in my batteries. My main interest was whether any cell or cells deviated substantially from the others.

I checked all 24 cells in my 4 batteries and found them to be very close and concluded that I didn't have any bad cells. BUT, the value of specific gravity I got suggested that the batteries were quite discharged. I charged the batteries again, let them 'settle' for 45 minutes and checked them all again. This time I got a slightly higher reading but still not 'in the green' on the scale. Beginning to suspect that my newly purchased hydrometer might be mis-calibrated I borrowed a friends hydrometer and checked all the cells. On his device all the cells read higher but still not 'in the green'.

I'm wondering if the low readings might be due to the temperature of the batteries (in the 50's)?

I also wonder if there is a way to check the accuracy of an hydrometer, maybe using distilled water?

Both hydrometers I used are like turkey basters with a float inside. I wondered if the other sort that seems to have a curl in it and claims to be temperature compensated are any better.

Last, I poked around looking for an electronic device to measure battery electrolyte specific gravity. I didn't find any. Is such a thing made? If so, how expensive are they?
__________________

__________________
If you want others to be happy, practice compassion.
If you want to be happy, practice compassion - The Dalai Lama

1984 310 Limited Motorhome
Courtesy Parking (W/S/E/Wi-Fi) on I-5 in Northern California, 70 miles from Oregon border
guy99 is offline   Reply With Quote
Old 01-19-2008, 11:21 AM   #2
3 Rivet Member
 
Kajtek1's Avatar
 
1965 22' Safari
Currently Looking...
Orinda , California
Join Date: Dec 2007
Posts: 217
Don't think electronic gravity checker exist.
As you experienced all gauges have margin for error. (I own 5 tire pressure gauges and none of them repeats reading of the other one).
I think you worry too much. Make sure the batteries are charged and go from there. Gravity checker is necessary only when you are checking potential cell failure. The battery in our SUV is turning 10 years in the matter of days. Have never touched it. In my motorhome I have automatic battery charger. With that advanced gizmo took me 3 seasons to notice electrolyte level drop big enough to add some distillate water. Other members using converters have to add water on monthly basis.
__________________

__________________
Kajtek1 is offline   Reply With Quote
Old 01-19-2008, 11:26 AM   #3
_
 
. , .
Join Date: Dec 2004
Posts: 8,812
hi guy...

yep i'd speculate it's the temperature, which can affect charging and stored potential...

take one battery inside and warm to 70 or so...

then re test it.

as i recall almost all battery references/specs are at established 70-75 degrees...

and the graphs show clearly the drops offs with progressively cooler or really hot temps....

the main value of the turkey baster is comparing cells and looking for a bad one in the mix.

cheers
2air'
__________________
all of the true things that i am about to tell you are shameless lies. l.b.j.

we are here on earth to fart around. don't let anybody tell you any different. k.v.
2airishuman is offline   Reply With Quote
Old 01-19-2008, 12:15 PM   #4
Well Preserved
 
overlander63's Avatar

 
1974 31' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 18,621
Wet storage batteries should have a fully charged specific gravity of about 1.265 at 80 degrees F.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
overlander63 is offline   Reply With Quote
Old 01-20-2008, 05:55 AM   #5
4 Rivet Member
 
SilverCottage's Avatar
 
2007 27' Safari FB SE
LONDON , ON
Join Date: Dec 2006
Posts: 256
My cold batteries read ok

FWIW, I store my 2 batteries in the garage during the winter and use a slow automatic trickle charger once per month to maintain them. The garage is about 40 and after a charge both batteries were in the green on my $5 hydrometer.

So, I don't think the temperature has as much effect as some would think on the hydrometer reading.
__________________
SilverCottage is offline   Reply With Quote
Old 01-20-2008, 07:28 AM   #6
Rivet Master
 
, Minnesota
Join Date: Aug 2003
Posts: 5,661
Images: 59
Quote:
Originally Posted by guy99
Last, I poked around looking for an electronic device to measure battery electrolyte specific gravity. I didn't find any. Is such a thing made? If so, how expensive are they?
Here's your electronic hydrometer. Look at the fifth item from the top. I don't know the price, but it probably costs as much as your four batteries.

You can check the calibration of your hydrometer if you have or can borrow an accurate graduated cylinder and gram scale. If you have a pharmacist in the family this would be easy. At 77F, a 100 ml sample of battery juice should weigh exactly the same as the reading on the hydrometer divided by 10. If the hydrometer reads 1220, the sample should weigh 122.0 grams.

A distilled water sample should read 1000 on your hydrometer, but they usually aren't marked that low.

Temperature compensation charts are available. If your battery is at 50F, the correction factor is -12 points, or -.012 if reading specific gravity directly.
__________________
markdoane is offline   Reply With Quote
Old 01-20-2008, 07:31 AM   #7
3 Rivet Member
 
Join Date: Mar 2002
Posts: 113
Images: 3
Temperature correction

Here is a formula for temperature compensation. The 0.03 pts per 10F uses 70F as a starting point.

Correction factor = (0.331 x T/F - 23) / 100 or 0.03 pts per 10 F
__________________

__________________
1985 25' Sovereign
Corner Bed

2003 3/4 ton Suburban
6.0, 3.73

Bellingham, WA
alan is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Measuring inverter output guy99 Electrical - Systems, Generators, Batteries & Solar 8 01-04-2007 07:24 PM
measuring propane pressure emanon25 LP Gas, Piping, Tanks & Regulators 2 09-27-2004 05:48 PM
Argosy-specific parts tandemfish General Motorhome Topics 1 09-24-2004 03:55 PM
propane, measuring pressure emanon25 LP Gas, Piping, Tanks & Regulators 4 09-20-2004 11:46 AM





All times are GMT -6. The time now is 09:24 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.
Modal Click