Voltage Charts / Hydrometer

[dmr]

Many thanks for that chart.

 

 

The two I have are as follows:

 

 

Chart 1 Chart 2

 

 

100% 12.70 / 12.60+

 

95% 12.64

 

90% 12.58 / 12.50

 

85% 12.52

 

80% 12.46 / 12.42

 

75% 12.40

 

70% 12.36 / 12.32

 

65% 12.32

 

60% 12.28 / 12.20

 

55% 12.24

 

50% 12.20 / 12.06

 

40% 12.12 / 11.90

 

30% 12.04 / 11.75

 

20% 11.98 / 11.58

 

10% 11.94 / 11.31

 

0% 10.50

 

As you can see, at 12.20 one reads this as 50% the other 60% SOC.

 

This morning, I completed the little test recommended by grahame r in an earlier thread ([1] fully charge [2] discharge to reasonable indicated SOC [3] note indicated amp use [4] read open circuit Voltage [5] back calculate to get true battery bank capacity) from this I calculate my actual capacity is about 525ah rather than the 660ah I had assumed (6 x 110 ah 4 week old batteries).

 

I have now programmed this into my Bat. Mon. and have begun a new discharge test.

 

I have a feeling this will solve the problem of the discrepancy between my indicated SOC and actual voltage readings, time will tell.

 

You have, however, raised another doubt in my mind, namely the accuracy of my voltage readings, I only let the bank rest for about 2 hours, I was actually amazed how much they recovered in that time from the reading I had taken with just the inverter on and nothing else.

 

With inverter on and drawing an indicated 1.9 a and an indicated SOC of 81% my voltage read 12.14, with everything off for 2 hours this increased to 12.28!

 

 

 

One question, is it normal for a labelled battery bank of 660ah (6 x 110 ah open wet cell batteries) to provide only 525ah or so?

 

 

Joshua

I did something very similar a couple of years ago and was surprised at how low the capacity of my brand new batteries was.

With the benefit of hindsight, and a couple of years of learning about these things, I suspect that I never got the new batteries fully charged (in fact Gibbo pretty much said this at the time).

If the new batteries have sat around in the shop or warehouse for a while then they will already be a bit sulphated when you get them and so it can be very hard indeed to get them fully charged. A sulphated battery gives the impression that its fully charged when its not and so many chargers go straight into float mode. I have now learned all about equalisation and this can really help.

 

............Dave

[pistnbroke]

you will know you have a quality hydrometer if it has a built in thermometer.

 

Hydrometer readings vary if you keep the bulb compressed as it pushes the float up and down like a piston ...you should relax your grip and not tilt the hydrometer . Read below the miniscus