what instrument to trust?

[Ralph Day]

Hi
A long time since I started a thread :o

I've found it difficult to charge my batteries (FLA) to the final full point of 1.265 SG reading on my "good"hydrometer...for a while now. Perhaps this is why...the hydrometer isn't so good?!

Today I purchased a refractometer at CarQuest of all places ($100+), and after zero-ing it the reading from my pilot cell was 1.270 while the hydrometer (bulb, float, tube etc) read 1.260. Sample from another cell also read .01 higher with the new optical refractometer. It only takes a drop of electrolyte to test so that's more fun than trying to read the graduated markings on a float inside a tube ....and so on.

So, trust the more expensive instrument? I'm inclined to, seeing as that last little SG number was so hard to get up to testing with the hydrometer.

Comments and suggestions? If you have experience with refractometers in an industrial or laboratory setting that would be great.

Thanks

Ralph

[Peter Klaassen]

I have felt the same about my $20 hygrometer from Can Tire. There must be better ways to get a reading for the acid density. The expert at Surrette said it is important to monitor and record this in case of a battery failure. It will make warranty claims much easier to assess. This machine is easy to use? It sounds like a more accurate device.
Pete Klaassen

[Ralph Day]

It's really easy to use the refractometer...you test and adjust with a null sample (distilled water at the same temp as the acid), then wipe down and use a drop of the acid.

I tried the acid at Picton's Can Tire (nice of Gord to let me) and even though the jug says 1.265 on it the reading was 1.285 or so. Perhaps the acid is stronger when raw and actually levels out to 1.265 when interacting with the lead in the battery. It was to check if the refractometer was reading my electrolyte properly.

The readings I'm getting now are probably correct, the absorb charge current when the SG is 1.265 is about 1/5% of the 20 hour charge rate of 820ahrs...or thereabouts. That's supposed to be when you are ''full".

The Carquest in Picton got the meter for me, just over $100, 2x the price of the best hydrometer I have.

Ralph